Polini THOR 250 DUAL SPARK engine has many more advanced solutions,
including:
- The cylinder is die-cast in light alloy, it ensures a better thermal
stability.
- The piston, gravity cast at high silicon content light alloy, reduces
thermal expansion and the coupling slack. The design of the piston top is
specific to optimize the compression ratio.
- It is provided with a balancing countershaft; this feature cancels the
vibrations and guarantees such a driving comfort never felt during a
flight and a longer life for the engine itself. The counter-rotating
rollers decrease greatly the upsetting torque-steer for an extra comfort
in flight.
- The centrifugal clutch is in oil bath with helicoid mechanical
reduction.
- The electric starting is standard but to offer the maximum safety the
engine is also equipped with manual starter with easy system thanks to the
flash starter device that speeds up and simplifies the movements.
- It is equipped with the comfortable closed-circuit system for the
recovery of fuel during transportation and the 12 V output for any use.
Small and compact THOR 250 DUAL SPARK engine has an extraordinary power
to weight ratio.
Advanced technology and high performance of the new THOR 250 DUAL SPARK
allow a better feeling of driving performance, making the flight more
dynamic, responsive and sensitive, besides ensuring even greater
stability.
The new THOR 250 DUAL SPARK engine adapts to different types of
applications including one or two-seat trikes, powered hang gliders,
one-seat small three-axis ultralight aircraft, and ULM motor-gliders
Polini THOR 250 DUAL SPARK is a 100% Made in Italy product.
Power: 36 HP at 7500 R.P.M.
Fuel type: Lead free petrol with 2% synthetic oil minimum ; 50:1
typically used after break-in
Starting: (Electric starter optional) Pull start with self winding cable
FLASH STARTER
Engine weight 18 Kg (19kg with electric starter) without radiator: =43#
without radiator, ~54# complete installation
Propeller rotation: Clockwise.
Above: My modified Skymax PPG Lowboy Quad
with the Polini THOR 250 engine after many modifications as of August
11th, 2016.
In July of 2017 my rig's dry weight after modifications, ready for
flying is checked at 135# with no fuel in the tank. Mounting the Apco
Mayday Bi rescue parachute adds 9 pounds. Fully loaded with fuel and gear
ready to fly, it's at roughly 180 pounds. With me in the pilot's seat with
helmet and clothing, etc. my takeoff weight may be close to 355 pounds.
============================================================================================
TECH NOTE: The minimum recommended operating temperature for this
engine is at a water temp of 130 degrees F. While Polini now offers an
optional 60 degree C (140 degrees F) thermostat (Polini part # 928830009 )
which mounts inside the cylinder head water hose fitting, it was not
included with engines being shipped when I ordered my engine. With the
rather large radiator, many flyers were reporting covering up to 2/3 of
the radiator surface in order to get the operating water temperature to
stay above 130 F degrees while flying. Adding the thermostat makes a lot
of sense to me... flying with the engine below minimum temperature or
flying with duct tape covering part of my radiator in hopes that I've
covered the right amount of the radiator's cooling fin area doesn't work;
I'm seeing H2O temperatures in flight that are much too low. UPDATE: I've
now installed the thermostat- see details & photos below.
With the thermostat installed, once the water temperature is up & the
thermostat is working, the water temp reading is holding at ~156 degrees F
at full throttle on around test on a ~62 degree morning.
NOTE: wile disassembling the engine in late August of 2019, I found
that the frame of this thermostat had separated on one side where two
brass tabs are inserted through slots in the end plate and bent inwards. I
managed to squeeze it back into shape in a small bench vise, and then
re-bent all four brass tabs more thoroughly to the inside to keep it
together as intended- the photos below tell the story.
08-16 UPDATE: My THOR 250 setup uses a Powerfin two blade propeller set
with a 57-3/4" diameter. This is a ground-adjustable pitch propeller and
each blade is adjusted individually. Pitch is adjusted to limit the THOR
250 engine's top end RPM to a maximum of 7500 engine RPM; I'm presently
adjusted for ~7350 RPM max in flight. (UPDATE: Replaced with a two blade
56" GSC Tech Series prop with the Urethane leading edge inserts in 2019)
When previously using the 56" diameter 3 blade GSC prop which Leon had
supplied with this quad, I had to reduce the pitch on the three blade set
to 9.1 degrees of pitch at the 75% of blade radius point, in order to get
the engine top end RPM up to 7500. (I am using a digital
angle gauge purchased from Harbor Freight for $30. Blade pitch is
referenced to the center flat surface of the prop hub; that means that you
set the gauge to zero against the face of the prop hub, then measure the
angle of each blade at 25% in from the tip on the blade's back surface.)
This pitch setting allows the THOR 250 to run at 7500 RPM at full throttle
at 9940 ASL, but it was not really generating the thrust and speed that I
need at this setting.
I've now switched to a two blade propeller setup using two of these
blades in a different mid-part / hub; blade pitch setting will be steeper
on the two blade setup. I'm now flying it at 12.5 degrees pitch, which
does generate better thrust and airspeed. Presently for flying form
~10,000 feet ASL flying site: main jet is #118 (or #120 used later); Pilot
Jet is #35 ; Air Screw is set to 7/8 to 1 turn out from bottom; Jet needle
now has the clip in the second to the top slot of 5 for a leaner lower
mid-range run. I'm running a 50:1 gas-oil mix, using 91 octane gasoline
and 2 cycle synthetic mix oil.
TECH NOTE: GSC BLADE PITCH ADJUSTING: My technique for getting fine
changes in blade pitch while making the adjustments: with all bolts
loosened to no tension on the prop center hub and both pairs of prop blade
mounting bolts, I'll simultaneously rock each blade forward and back
within the prop hub while exerting the twisting force. A fine index mark
on the base of each blade where it enters the prop hub helps me to see the
slight changes in pitch angle while doing these adjustments. Once I have
both blades at the identical angle, I snug down the hub bolts lightly, and
push both blades fully FORWARD. The idea with this is to get the tracking
of both prop blade tips as close to identical as possible (- within
1/16"). I'll do some final tweaking until they match as closely as
possible. I use a measuring stick from the side cage frame tube to insure
that both blade tips are tracking the same distance from that frame tube
as I rotate the prop, recheck the pitch angle once more on all blades, and
then tighten all bolts to the 100 foot-pound torque recommended by GSC.
I accessed the engine control box's wiring harness connections for the
magneto ignition [pale blue wire in the photo below= hot & black =
ground], located back near the engine, to add in the wires for the kill
switch connections (coming from the Normally Open
contact section of the DPDT Momentary push button switch which I added
into the throttle's handle.)
To do the kill switch wiring for the secondary electronic ignition, it's
necessary to interrupt the 12 volt supply to that ignition. That 12 volt
supply comes into the ignition wiring unit on the violet wire
with the black stripe shown in this photo below. The
heavier pair of Red & Black wires runs inside the sleeving over the
throttle cable down to the second Normally Closed
set of contacts of the momentary push button switch in the end of the
throttle grip.
My Strobe Light can be quickly mounted just above the radiator, using
nylon tie wraps. It is now wired wired through an on/off switch into the
12V system. Operation with a strobe visible from 3 miles allows extended
flight operations 1/2 hour before sunrise and 1/2 hour after sunset. It
also makes this PPG more visible to low flying aircraft.
Above is one of the cage edge line support fixtures I made from tough and
flexible plastic.
Above and Below: I've mounted a 58" Powerfin Propeller for testing.
This is the earlier style hub
I set the initial pitch at 12.5 degrees (measured at 75% of prop
radius out from the center.) A test run here at 10,290 feet ASL in 59
degree dry air gives a peak RPM of 7400 to 7420 RPM- very close to the
ideal of 7500 RPM for max H.P. output.
This propeller is running smoothly and providing good thrust; it's a
good match for the THOR 250 engine flying at this altitude.
[It was later replaced with the 56" two blade GAS propeller.]
====================================================================
FURTHER MODIFICATIONS COMPLETED:
Adding An Extended Prop & Line Guard Hoop with 7"
Stand-Offs To The Prop Guard Cage
&
Above: since the THOR 250 engine has the centrifugal
clutch on the prop drive, when the engine is shut down the propeller
has a lot of inertia and easily continues to windmill. During a
landing, when laying the wing down after roll out & stopping the
quad, the lines could easily get wrapped around the engine's output
shaft- the prop cage did not extend far enough to protect the long
prop blades and keep the lines from dropping between. The solution:
Add an extension to the prop guard cage. Net added weight : only 3.1
pounds!
&
Above: after shaping the hoop using a 1/2" EMT conduit
bender and my homemade Hip Bender the six extra stand-offs were
fabricated and welded to the extension hoop. This is the result
after painting, ready for installation.
The extension guard hoop is mounted in place to the
original aluminum cage with 8 stainless steel worm drive clamps.
This photo shows that the 58" propeller is now protected within the
extended cage. It has good clearance.
&
Prop blade end clearance is over 1.6" minimum.
A rock kicked up by a wheel on the quad caused this
damage to one GSC maple blade's tip. I filled it with slow setting
epoxy, shaped it carefully, and re-varnished the blade before adding the
stainless steel tape to the leading edges of all blades.& I have
repaired other blade rock damage since this; when flying from the
irregular ground of South Park's short grass prairie, this is an ongoing
hazard. I have put in a lot of time smoothing ground and picking up
loose surface rocks to minimize the possibility of a rock getting kicked
up into the prop, but it does happen. Johnny Fetz showed me some good
techniques for prop repair; that info has come in handy on several
occasions.
I decided to remove the pull starter; I never use it, so that's
1.1 pounds that I don't need to carry. The internal pawls degrade from
vibration during normal flight, and require ongoing replacement to
continue to function properly.& The electric starter works well,
although I'v had to do maintenance work on it too periodically;& but
this engine starts very easily with it.
After completing these modifications, I have flown many flights
over South Park, starting from& one of two launch points: one at
~9680' MSL and another& at 9944 feet MSL, and eventually climbing up
to a maximum of & ~15,029 feet ASL according to my Garmin GPS.
Photos from this and subsequent flights are now being combined on the PHOTO GALLERY page- CLICK HERE to jump to that
page.
_______________________________________________________________________________
A SIMPLE CROSS-COUNTRY CRUISE CONTROL FOR THE AVID /
SKYCRUISER HAND THROTTLE
Flying longer cross-country flights with a PPG
leaves a pilot gripping the hand throttle fairly tightly for extended
periods of time- often with your hands held up in a high position while
also holding the control line handles. For me (& a lot of others I
suspect) this can lead to tired / aching hands, reduced circulation, and
colder hands during cool weather / extreme altitude flying.
I can adjust the trimmers on my MACPARA Muse3 wing for close to
hands-off flying as far as the control lines are concerned; when let
go, they're easily in reach right against the pulleys, but when I'm
cruising cross-country, I can have my hands off the control lines for
extended periods of time. This allows me to work with my cameras and
GPS controls while flying. But up to now, that throttle control has
always been tightly in my grip... so I decided to design a simple
device to use as a 'Cruise Control' - to keep the throttle cable
pulled in the desired amount for extended periods of time, whether at
full-power climb when heading for the higher altitudes, or at an
intermediate setting to maintain a given altitude in 'cruise' mode.
The photos below show what I came up with.
The device is a type of variable-effect stepped shim which,
in use, is slid into the throttle housing straddling the cable to keep
the throttle lever from being able to be pulled back up by the return
spring within the carburetor. The material I had on hand was a piece of
Basswood 1/4" x 1/2" x ~1.5" long. I cut a slot up the center from one
end for about 3/4"; the slot is wide enough to straddle the throttle
cable without hanging up on it. A hole was drilled in the opposite end
where a ~6" long section of spectra 200# fishing line is tied; the other
end is tied to the heavy wiring running from my throttle's kill switch.
This line simply keeps the cruise control device from being dropped /
lost.
When the device is slid all the way into the throttle housing, the
throttle lever is held at close to full throttle position.
When the device is slid part way back out, a 'level cruise' RPM /
throttle opening can be selected with a simple bit of trial and error of
sliding the shim device either in or out.
When not in use, the device slips snugly inside the throttle grip,
available for it's next use.
Being Prepared For An Engine Outage Over Heavily Timbered Terrain
When planning cross-country flights over the terrain we have here
in the central Colorado Rockies, It's always good to give some thought
to how to deal with unanticipated situations. One of those unlikely but
possible situations which a PPG pilot might someday have to deal with is
that of having an engine or wing malfunction while flying over timbered
terrain.
As pilots, we do our ongoing maintenance and pre-flight checks to
assure ourselves that our equipment is in serviceable condition, ready
to perform reliably and continuously. But it also doesn't hurt to be
prepared for a possible landing in less than favorable terrain. Being
hung in a tree in your gear is a remote possibility; being able to get
yourself down safely if you ever are is close to priceless!
Above is a "Self-Belaying Kit" which I will carry when on longer
flights over the heavily timbered terrain. It consists of :
[1] A light weight climber's seat harness and Chest harness and 1
locking carribiener; I built this one from 4000# + 1" tubular
climber's webbing and the heavy bonded polyester thread which I use to
sew the low hang loops for my Quad. (The adjustable waist belt with
the cam buckle to which the main leg loops are sewn just helps keep
the leg slings in place; the main leg sling loops carry all of the
load when in use. )
[2] A "Figure Eight" descending / rappelling device
[3] A 100 foot long length of 6mm quality climber's accessory cord
[4] A good pair of gloves for rope handling with leather palms
[5] A 4 foot section of 1" climber's webbing (Or a good quality Cam
Buckle strap) & another carribeiner for use in fashioning an
anchor point.
[6] 30' of strong 4mm utility cord
To use this gear if hung in a tree, etc., a stranded pilot
(transformed then into being a climber) would first carefully get out
a shorter section of rope and tie them self and their gear off to the
tree- no need for a sudden unscheduled early decent! Next is to put on
the climbing seat harness and rig the carribieners and figure eight as
shown; the loose end of the rope in the above photo would be the one
tied to or looped around a solid branch or part of the tree trunk, or
tied to the webbing anchor point. Using the rope run through the
figure eight more than once increases friction, and running this 6mm
rope through doubled is fairly standard self-belay procedure; the
center of the rope is looped over an anchor point attached to the tree
so that, once on the ground, the rope can be retrieved from the anchor
point for further use. [Mammut's 6mm cord has a breaking strength
rateing of 1700 pounds. Sterling Rope's 6mm cord is rated at 1978#]
[A book or website on climbing ropes, rigging, and use and a bit of
hands-on practice should further help in an understanding procedures
for rappelling using a descender. Professional ski patrol personnel
carry a similar kit for self-evacuation from a chair lift if the lift
is shut down while they are on it; fire fighters carry similar gear
with high temperature-resistant rope. A practice self-belay decent
from a very modest height might not be a bad idea for those unfamiliar
with rope & self-belay techniques. A Gym with a climbing wall and
instructor might be a good place to familiarize yourself with the
equipment and techniques; that info is beyond the scope of this web
page.]
Above: REI gear. (I changed out to the buckle for my PG kiting use.)
The figure eight chest harness helps keep you upright while doing a
descent if your technique is less than perfect, and you may like the
solider feel of rigging that way. REI sells both- I bought the set from
them many years ago. I have used this climber's seat harness a lot for
kiting my PG wing. The gear I'm carrying is lighter and more compact.
(Above & Below): My self rescue / rappelling kit as shown in
the previous photo weighs 46 ounces, packed in this light weight mesh
bag, ready for use. I have a converted day pack which is mounted to the
forward lower frame of my Quad, where I carry this gear in easy reach. I
can carry this kit, a GMRS radio, my cell phone, and a survival kit in
the mounted pack and still have room for my wing's empty carrying bag
and other items.
(Above): This is a photo of most of the main items included in my survival
kit (28.75 ounces) which includes 2 Orion "Skyblaster II Alert signal
flare launchers, a lightweight emergency bivy sack (3.4 ounces) and two
mylar space blankets, two 30' lengths of 200# Spectra line, a LOUD
signaling whistle, plus a small first aid kit including a roll of tough
nylon tape, a chemical hand warmer, a fire starting kit, a mini 47 lumen
LED flashlight & extra AAA battery, 3 protein bars, a light warm poly
stocking cap, paper towels & TP, and a few other useful items. (An 8
oz. water bottle is not shown in this photo, but can be carried in the
pack.)
I fly with the reserve parachute mounted and with these emergency
survival and self-rescue kits always along because I'm inclined to fly
over high rugged remote areas most days - that's where I live &
fly- and I figure it's worth having along this 4.5 pounds of emergency
gear. That's my personal approach - a part of prudent PPG flying in
this beautiful and rugged part of Colorado's high country!
I carry a Midland GTX1000 GMRS radio which has up to 36 miles of
line-of-sight range, while leaving a matching radio with someone back
on the ground, and I leave my flight plan with them. If I do have to
put down somewhere other than at my launch point, I'm fairly well
prepared.
For photos taken during my flights, please CLICK HERE to visit the PHOTO GALLERY.
2017
Updates and Modifications
This update section was last
updated on October 27th, 2017
Late in 2016, I had Andy McAvin
ship me a new MacPara Charger 31 wing. This is a Reflex wing with a
higher cruising speed when the trimmers are let out into the full reflex
mode. In the thinner air here at altitude, with the ~380# total ready to
fly wing loading of the quad and me, I'm cruising at an average
speed of 37 MPH. With trimmers pulled in fully for better climb angle,
the speed is at 33 MPH. [In comparison, the 31m Muse 3
would cruise at 32 MPH when the trimmers were let out fully.]
Really like the way that
this wing launches and flies, and I find the wing tip steering very nice
to work with. However, for use on my quad with it's riser guide rings on
the upper frame, I had to do some modifications.
With the long travel trimmer
adjustment range and the added wing tip steering, the Charger's risers
are more complex and far bulkier than those on a simpler wing like the
Muse 3 which I had previously been flying. The 2" I.D. riser guide rings
provided with the Skymax quad (mounted on the quad's upper frame members
to control the hang attitude)& were too tight a fit- the wing tip
steering lines were regularly fouled / hung up and unusable, and other
parts of the stock risers would also hang up in the guide rings, leading
to problems and aborted takeoffs.
First, I fabricated a new set of
low hang point loops that positioned the trimmer clamps where they were
workable below the riser guide rings. Next, I fabricated a new set of
larger 2-9/16" I.D. riser guide rings which offered more adequate
clearance for the Charger's risers. I use the 2" guide rings to route
the reserve parachute's risers separately, inside the upper frame
members, and then down to the main carabiners on the low hang loops,
keeping them clear of the wing's risers.
These modifications helped, but
all of the extra D-rings and shock cord form the original rigging and
routing of the Charger's wing tip steering lines running up through the
middle of the riser bundle through the riser guide ring still left the
wing tip steering toggles & lines fouled and unusable a large
percentage of the time... so I decided next to try to remedy this
aggravation.(This situation might not necessarily be an issue for a
trike or quad rigged with a high hook-in setup, or for foot launch
pilots.)
(The photo below shows the
stock Charger risers through the 2 inch I.D. riser guide ring, with the
stock wing tip steering line run up through the midst of the bundle.)
The
photo below shows the original stock wing tip steering line rigging
run through 6 D-rings with a lot of ~1/8" shock cord run back and
forth everywhere.... when these risers are used through riser guide
rings on a quad or trike setup using low hang point rigging, all the
extra D-rings & shock cord result in wing tip steering line
fouling and hangups far too often.
My
solution: The risers come with two brake line pulleys sewn in place on
the risers. On my quad with it's low hang point rigging, I need to use
the upper pulley for the brake line. I use the upper brake toggle
retaining magnet (the right one in the photo below) to park the brake
/ control line toggle while in flight. ( I use the wing tip steering
all of the time while cruising; I only use the brake control lines
during takeoffs and landings.)
This
leaves the lower brake line pulleys unused, and so available to be
re-positioned and re-purposed in a cleaner wing tip steering line
setup. The idea is to end up with the wing tip steering line routed to
bypass the riser guide ring completely, eliminating any
of the fouling and hangups.
The
photo above shows the 2nd lower brake pulley sewn in it's original
position, down low and close to the trimmer clamp. I carefully pulled
the stitching to remove it with it's webbing loop. Next, as shown in
the photo below, I sewed it to the existing upper brake pulley's
webbing loop with heavy duty bonded polyester thread; it's solidly in
place. I then proceeded to remove all of the 6 un-needed D-rings and
shock cord, and the old low eyelet through which the wing tip steering
line had once been routed leaving nothing left for lines to hang up
on. (I later found that the extra low position brake toggle parking
magnet was hanging up in the riser guide ring, so I pulled it's
stitching and removed it, too.)
The
important thing to keep in mind if someone else decides to clean up
their wing tip steering line routing for a quad /trike with riser
guide rings and low hang point rigging is to only cut the
thread carefully- do NOT damage
the risers themselves! A seamstress's 'stitch puller' tool is
very handy for this type of careful work.)
The
photo below shows the finished result- the wing tip steering line
toggle still parked on it's magnet and snap fastener, the line
run freely on the outside of the riser bundle up through it's own
pulley. It performs flawlessly in flight now.
While flying my early flights
with the Charger wing, I found that the torque from the Polini THOR
250's gear drive resulted in a left turn tendency when both trimmers
were set to neutral. Since I wanted to be able to fly the full trimmer
range during normal flying, I was looking for a way to compensate for
this left turn tendency... after all, for long cross country cruising
flights, it's really pleasant to have the rig set up for hands-off
straight line flight for extended periods of time.
I noted in watching the wing
that it only takes about 3" of inward deflection on the wing tip via a
modest pressure on the wing tip steering line to compensate for that
left turn tendency. On the Charger Riser control line setup, there is a
short line which I have come to refer to this 495mm long " stC1 line" as
a 'snubber' line connected between the C riser quick link / mallion and
the wing tip steering line; by shortening it the right amount, it can
also function as a 'torque compensator' device.
I first made up an adjustable
parallel line with a 3/4" wide strap and cam buckle- similar to the
regular trimmer cam buckle and strap setup. Once in flight, I pulled in
the adjustable line until I had a hands-off straight line cruise. After
the flight I determined that I needed a 'stC1' line that was 100mm
shorter to keep that right wing tip pulled in the required ~3" to result
in a straight ahead hands-off cruise.
So I made up a 395mm long line
from 220 pound test Spectra line and installed it in place of the
original 495mm green line. It's been performing as intended for many
long cross country flights since then. You can see the short grey line
in the photo below.
====================================================================================================
ELECTRIC STARTER ISSUES AND SOLUTIONS
[Updated 06-20-2018] I like the electric starter on my
POLINI THOR 250 engine... but it does have it's own maintenance
requirements. James Weibe, in his BELITE blog, wrote of having to repair
a broken internal brush wire; nice to know.& I have had to do the
same myself.. I ended up having to solder both brush wires to their
terminals; it seems that the spot welding of the fine strand copper
braid to the terminals results in a heat-induced fatigue of the copper.
Since I did the initial soldering of the brush wires, I'v had to go back
in and re-solder them on several occasions over the course of the first
80 hours of flying time. I've emailed Polini directly about this issue,
requesting to obtain a replacement set of brushes, brush holders, and
the attached pass-through terminal. This is an ongoing maintenance
requirement on the THOR 250's electric starter which can be done if the
parts are made available. I'll add info to let you know how Polini
responds on this issue.
The second starter issue deals with the starter's output shaft... the
splined section is a separate piece of metal which is inserted into the
starter armature's shaft, and crimped in place. It can work loose in
service.... not an ideal design! The photo below shows the splined short
shaft sitting inside the engine housing, visible when the starter was
removed. The only good news is that it can't escape this area to get
deeper inside the engine to cause more extensive damage. The bad news is
that once it happens, you get to fix it.
The photo below shows the recess in the end of the
starter's armature shaft, and the insert shaft's smooth end laying along
side just below to the right.
My solution was to first thoroughly clean both parts with
spray 'Brake and Electrical & Parts Cleaner", to remove any oil ,
etc. I then put some thin CyA glue (super glue) into the armature shaft
recess, inserted the smooth end of the splined shaft, and seated it to
bottom solidly. Once the glue cured well, the starter has been back in
service reliably for many long flights. The photo below shows the
reassembled shaft. [06-2018 Update: Shaft staying in place since being
glued last year.)
The photo below also shows the brass pass-through terminal
for the starter's red positive wire from the starter solenoid; I have
had two of these terminals break off at the sharp bend where it comes
out the top of the pass-through plastic insulator. To repair this
failure, I cut away about .1" of plastic so that a good quality wire
could be soldered directly to the remaining brass terminal.
UPDATE JULY 21, 2018:: The starter motor's brushes have
developed breaks in the brush wires several times during the first 100
hours of flying. I've solder them to get them back in service several
times. (James Weibe first wrote of this issue in his BELITE blog several
years ago onw; it seems to be a very common failure mode for this
electric starter. Recently, when a brush wire broke away at the top of
one of the brushes, I could not solder it to repair it. My email to
Polini requesting either a set of replacement brushes, or alternatively
information as to a source for suitable replacement brushes remained
unanswered for over a month. Leon to poliniparts.com also had nothing to
offer, saying that I would have to source them myself.
After extensive searching across the web, I eventually sent
an inquiry to ricksmotorsportselectronics.com; they replied promptly,
asking for photos in addition to the dimensions (= 6mm wide, 9mm high,
~12mm long with the wire coming out of the top 6mm wide surface near the
outer end) which I had sent. After sending photos, I again received a
quick response, saying that their part # 70-109 might work. (19.95 list
for a pair.) I found an Ebay vendor offering Rick's 70-109 with free
shipping... they arrived this morning. I checked and found the brush
size very close to ideal- correct width & length with terminals. The
brush height was 9.5mm instead of the stock 9mm height. A bit of careful
sanding on some 220 grit silicone carbide sandpaper resulted in an ideal
fit. (These brushes sand easily- use light pressure, keep it even, and
check for fit in the brush holder often.
These brushes are used in the starter motor for a Yamaha
225 Moto 4, late 1980's vintage; they are now primarily available from
RICK'S, & distributed through many dealers across the country, and
offered by several merchants on Ebay.
A replacement for the case pass-through terminal can be
scavenged from an inexpensive starter motor for the Chinese made GY6
scooter; these starters are sold on Ebay for ~$16.00 with free shipping.
While the starter housing looks similar, the 9 spline output shaft is a
larger diameter- not a match for the THOR250's needs. The internal brush
assembly is also different... but the output terminal is an exact match
to the THOR250's terminal, and screws in place. You'll just need to
solder one brush wire end / terminal to the inside end of the
pass-through terminal.
With the Polini -sourced replacement starter motor costing
over $200 & taking quite a while to get delivered, if you have the
skills, maintaining your original electric starter is a reasonable
option; with parts on hand, you can have the starter back in service
very quickly- less than an hour in my experience.
The Polini manual starters are one of the more aggravating
features of an otherwise fine performing engine; they really need to
improve the design. It's made partially of plastic parts which
self-destruct from vibration while the engine is running normally. While
the 'pawl set' is relatively inexpensive, it's generally a too-frequent
maintenance requirement if you are using only the manual starter. I had
started my engine with the pull starter only 2 or 3 times, and left it
mounted as a 'backup'.... but when I tested it, it would not engage. So
I removed all of the pull starter components, and then glued a
protective cover over the magneto flywheel opening where the manual
starter had been mounted. This keeps debris from being able to get into
the engine's magneto area.
UPDATE: There is a direct replacement starter, designed for
the APRILLA RS125 scooter with it's Rotax engine, which mounts directly
to the THOR engine case at the two threaded mount holes with the same
bolts which were used to mount the Polini starter. The splined shaft
matches when installed, engaging the starter spur gear to the same
degree as the polini. It's a cleaner mount, not using the polini's
bolt-on mounting brackets. The cost on Ebay as of July 2021 is around
$30, including shipping from outside the U.S.
I prefer to solder on a wire and do some form of
anti-vibration strain relief; I installed one of these to try in the
summer of 2020. I had one stop working after about ~45 hours of flying
time... but that's about the same life expectancy of the starter brush
braided wires inside the stock Polini starter... The failure was due to
an open in the armature windings that is un-repairable - the same fault
which also killed one of my Polini starters. At roughly 1/6 the cost or
less, having a spare starter on hand is very reasonable; the swap-out
can be completed in about ten minutes.
STARTER BRUSH WIRE
BREAKAGE & THE WAY TO FIX IT
The above photo shows
the interior of the starter end housing which holds the brushes; the
interior of the Polini stock starter is similar, dealing with carbon
brushes which are held against the armature's commutator by springs
which are trapped in the brush holders beneath the brushes. The
problem with both the Polini stock starter and the APRILLA 125
replacement starter shown in the photo above is that the brush wires
are spot-welded to the terminal. This spot welding weakens the brush
wire right at the spot weld; after about 40 hours of flying time, the
internal vibration causes the wire to break at that spot. Again, this
hap[pens in BOTH of these starters.
The FIX: open up the
starter and solder the end of the brush wire back to the terminal.
This requires a ~40 watt soldering iron, solder, and a bit of liquid
soldering flux. My best technique is to apply flux to the ed of the
brush wire, then flow some solder onto that wire's end. I then add a
bit of flux, and then flow a small puddle of solder ont the terminal
just above where the wire had beel spot welded. I then complete the
solder joint by re-heating the two solder areas together - it takes a
very brief application of heat, and results in a reliable solder
joint. (Don't let the wire move while the solder is re-solidifying.)
THE TRICKY PART:
Getting the springs into the brush holders, sliding in the brushes
over them in their positions, and then having them STAY IN PLACE while
you get the end housing over the end of the armature. I know of no
other way than to tie back each brush's wire to the outside with
strong thread while the spring and brush are held in place with a
finger. This is at least a three-handed job, so having a friend do the
ttieing of the thread is very helpful. In the photo below, you
can see that the top brush 's wire is tied back to the outside with
thread already; the lower brush is being held back in place, ready for
the thread to be tied tightly.
In the photo below, you can see
that added pieces of scrap have been inserted to further tension
these threads, to givre full clearance for the armature's commutator
to slide into the housing without hanging up against the brushes.
You will want to have the
arrmatureout of the can housing with it's magnet before trying to
reassemble the starter. It's a good idea to lightly burnish the
commutator's copper segments before reassembly; remove any grit. I
also add a slight bit of grease to the bearing surfaces of the
armature shaft before reassembly. The photo below shows the
armature slid in past the brushes, fully forward in the end
housing; once in place, the threads are cut and removed.
The last trick is to hold firmly
to the splined shaft's splines as you slide the rear can housing
with it's magnets over the armature; you don't want the magnets to
pull the armature out of it's place in the end housing . Then
install the screws that hold the starter together.
====================================================================================
Below: The battery rides in a
nice Velcro mounted nylon carrier, isolated from any frame vibration.
On my Skymax, the wires would vibrate enough to eventually loosen the
screw on one of the battery terminals... not so good a thing to have
happen. So I added long cable ties around the battery and it's wires
close to each terminal, so that the wires can not move. (I like to use
lots of cable ties!)
====================================================================================
SKYMAX
QUAD AIRFRAME MAINTENANCE
FLYING
IN THE CHALLENGING ENVIRONMENT OF THE HIGH COUNTRY OF COLORADO
In this ~70% density air, with my loading on this 31
square meter wing, the GARMIN GPS's recorded track data shows that
I need to get rolling up to 28 to 29 MPH to lift off and fly. landing
approaches are also typically at about 28 MPH, until I begin to flare
for landing, when the glide speed reduces below that approach speed.
This 29 MPH required speed for liftoff results in a need for a fair
amount of usable ground to get up to liftoff speed- especially when
taking off from soft ground.
A 380 pound rig rolling across natural short grass prairie
at 28+ MPH puts a lot of stress on the quad's structural members.
So the fiberglass axles and their steel mounting tubes on
the quad's frame undergo a lot of stress when being used in these
conditions, which necessitates some ongoing monitoring / inspection and
maintenance. Even trailering the Skymax quad on poorly paved and gravel
roads takes it's own toll, stressing fiberglass axles and the 1" ID
tubes which carry these axles. Below I offer information on the items
which I've had to rebuild, repair, weld, and reinforce on my quad due to
these structural stresses.
***********************
Upon returning home from the Lost Stirrup Fly-In in mid
July this year, I found that welds had failed on both of the main
upright frame member mounting points, as shown in the photos below. This
attachment is formed by welding a larger I.D. sleeve tube to the underside
of the main lower frame's lengthwise tubes on each side to support the
entire upper frame members, engine installation, and prop guard cage. A
major amount of weight is carried by these two MIG welds which are
holding everything above up in place... The load is
from above, but these welds are trying to hold it all up by being welded
to the underside of the lower main frame. These welds both failed after
less than 50 hours of flying time, and some trailering to and from
flying sites within a few miles of home.
An added consideration is that the location of these welds
is not easily visible during a pre-flight or post-flight visual
inspection; I was unaware of the developing problem until they broke
loose completely. The resulting downward movement of the entire upper
structure also caused damage to the prop guard cage structure; luckily
the prop was not damaged.
Instead of tearing the entire rig totally apart and
packing in in a box to ship back to Skycruiser, I decided to repair and
reinforce these weld failures myself. Yes, it required totally removing
the engine and control system so that I could work on it properly; but I
had the equipment here to do it effectively and quickly.
My approach was to first trim down the remaining excess
lengths of the inner lower ends of the upright frame tube members.
Relocate them to a position ON TOP of the lower lengthwise frame tube
members required removing the motor mount cross members. Once
re-positioned, I added sections of steel angle iron to the underside of
the damaged lower frame tubes bridging over where the metal had broken
away.
The next step (once the pieces were clamped in their new
positions) was to drill and bolt through the new attachment points with
high strength 3/8" bolts and nylon insert lock nuts. The result is shown
in the photo below. The resulting structure is very solid, and the
downward-bearing loads are now carried on top of the reinforced lower
lengthwise frame members. I feel a lot better about flying this quad
after this modification / repair. It's now also easy to check these
through-bolt attachments during my pre-flight and post-flight
inspections.
========================================================================
I noticed damage to the rear fiberglass axles at the
point where they enter the rear axle carrier tube; the fiberglass was
showing fiber breaks at the point where the end of the steel tube made
contact with the fiberglass on the top surface. The original retainer
pin hole had been drilled vertically with only 3/8" separation between
the pin hole through the fiberglass axle and the contact point with the
end of the tube where I could see the fiberglass was failing.
On closer inspection, I also discovered that both ends of
the axle carrying tube had developed vibration fatigue cracks on the top
surface along the edge of the mig weld which connects the
axle carrier tube to the quad's framework above. The next three photos
below show what to watch for during your inspections.
The position of these cracks indicate that they may be the result of
vibrational down-load stress forces during flight; the axles with their
wheels on the outer end must vibrate constantly during flight. Arc welding
does induce stress into metals do to the heating being concentrated in a
very small area; that's why steel tube built light aircraft frames are
built using gas welding techniques, and heat stress relieving is done on
welded areas during the build after each weld is completed. Arc welded
joints need ongoing inspection and monitoring for the possible development
of these stress cracks.
After doing an overlay weld with my wire feed welder
as shown in the photo above, I smoothed down the welds and repainted the
area. I drilled new horizontally oriented holes for the axle locating
bolts well away from the fiberglass axle load stress point at the end of
the axle tube. I then chamfered the inner ends of the steel tube to
minimize fiberglass surface fiber stress in those areas before
installing new black 1" OD fiberglass axles.
NOTE: I am now buying black 1" diameter round solid
fiberglass sections for replacement axles from
Max Gain Systems
(The black color may be more resistant to long term U.V. damage of the
outer surface resins than light colored axles. I've had fibers raising
from the surface of the original off-white axles in the past. I like the
looks of the black axles.)
======================================================================
FRONT AXLE REINFORCEMENT
Below: While inspecting the quad, I noticed some deformation on the
right end of the front axle carrier tube where it was welded to the
upright piece. (This is rather rough ground I fly from, and the takeoff
runs are much longer than when flying in denser air at lower
elevations. I'm likely close to 380 pounds ready-to-fly weight
when I'm rolling at 28+ MPH across the terrain to get up to flying
speed. So for my purposes, I want tough axles under my rig. Being light
weight is a lesser consideration, versus a need for structural strength
and longer-term durability. )
After straightening, I welded on a close to full length piece of
reinforcing steel angle iron (3/4" x 3/4" x 1/8" thick.) Added weight is
modest, but the added strength is very welcome! I expect long service
after this modification.
In July of 2021, I cut away the 1" ID axle carrier metal
tubes which had been repair-welded on several occasions, and replaced
the old axle setup with 1-1/4" fiberglass axles carried in 1-3/8" O.D.
Chome Moly Steel tubing. Old welds were cut away with a rotary cutting
disc tool, and the new tubes MIG welded in place. Below is a photo of
the old front axle assembly; below that are photos of the new larger
axle carrier tubes being welded in place.
BELOW: The new front axle is a continuous 34" long section of 1-1/4" solid
fiberglass; it is kept centered with a single 1/4" stainless steel bolt.
Plastic flange bushings on the front assembly pivot bolt were replaced
with brass flange bushings, as the original plastic bushings were
disintegrating. The new 1-1/4" axle installation is the same weight
(within one ounce) as the reinforced 1" front axle assembly which it
replaced.
BELOW is the new 1-1/4" ID rear axle carrier tube being welded in place
after the original 1" ID carrier tube's welds had been cut and ground
away. Further welding was completed after this photo was taken. The new
rear 1-1/4" OD solid fiberglass rear axles extend about 6" into each end;
they can optionally be slid in another 6". Optionally, a single piece full
length rear fiberglass axle could be slid through this Chrome Moly steel
tube. Holes for bolting the axles into place are located well away from
the ends of the steel tubes to minimize stress in the fiberglass axles
where the holes are drilled; these drill hole ares are the places where
splits and damage has occurred in the past on the 1" fiberglass axles.
NOTE: A broken right front 1" axle occurred when hitting a hole dug by
a badger during a high speed takeoff run; the result? The axle carrier
steel tube dug into the ground, flipping the quad on it's side, with the
earlier lighter build prop guard cage collapsing into the prop (which
was turning at full RPM at that moment) destroying both the prop guard
cage and the propeller. Shock transferred into the engine likely
resulted in the internal damage to the engine, the disintegration of the
piston skirt, and the damage to the lower cylinder skirt, necessitating
the extensive rebuilding of the THOR 250 engine.(Photo of damaged prop
guard cage below). With the SKYMAX's solid upper frame, I came through
this incident uninjured.
These 1-1/4" fiberglass axles may be roughly 60% stronger than the
previous 1" fiberglass axles, and do not have holes drilled through them
close to the ends o the steel carrier tube, where maximum stress
develops; the 1" axle break from hitting the badger hole might very
likely have NOT occurred if heavier 1-1/4" axles had been in place,
installed as shown above.
======================================================================================
The photo below shows my Skymax quad after fabrication
& installation of the new 65" I.D. prop guard cage; it is installed
with SIX support struts. The spreader pieces between the double hoops
extend the rear hoop well past the prop's arc.
The photo below shows how I have my rescue parachute mounted with
3/4" cam buckle straps (from www.strapworks.com
). The blue pack which rides between my knees carries assorted tools and
gear. I now use my Garmin GPSmap64s tethered to the pack's outer pocket
zipper pull ring where it's easily readable while flying- it's positioned
similar to using a knee board.
The PPGmeter I had installed malfunctioned after about 38
hours of service, going into a constant error message flashing mode
which could not be reset; this made it unusable. So I removed it. I
installed a TinyTach to go with my separate H2O temp gauge. I now have
mounted a different EGT gauge. This water cooled engine runs very
consistently and reliably, so if the H2O temp is within it's typical
operating range of 157 to 161 degrees F, then all is OK.
========================================================================================
Below is the DTC T100 Digital EGT Meter which I am now
using; it's displaying 50 degrees F on a cool early November Colorado
morning. I will only keep this gauge mounted when needed to check a
change in carburetor jetting when I fly at lower elevations. It has a
quick disconnect wiring connector. This meter has internal calibration
and function selection programming capabilities via three internal
switches; it's set up for 12V power supply now, and for reading a Type K
thermocouple. I'm using the same type K thermocouple probe which I
installed from the now defunct PPGmeter.
Here's a link to the meter only (with a blue LED display) for only $15.99
.You can also find a Type K thermocouple EGT probe on Ebay for under
$15.00
Inexpensive
DTC T100 EGT Gauge
SUMMER & FALL 2018 & ONWARD MAINTENANCE & UPDATES
While first flying in Arizona's Senora Desert last February, I
dealt with a couple of issues. The first was re-jetting the carburetor
for flying from a site at about 1100 feet ASL. (Unfortunately, my EGT
gauge was malfunctioning when I first arrived there, so I read all of
the meager info offered online, and found info which said that a #126
main jet was appropriate for flying at sea level & a ways
above. Unfortunately, I had by then done several extended flights at
what I realized were excessive EGT temperatures. The H2O temperature
gauge gives no indication that the fuel mixture was lean enough to
elevate the exhaust gas temperature- with the coolant system with it's
thermostat functioning as desired, the higher internal temperatures
were not indicated. It requires a working EGT gauge to have this
information.
I had also read about & ordered some BLUE MAX 100:1 ratio mix oil
from RPE. I taled with another ultralight engine tech about using the
leaner oil mixture; he advised that, with the Polini THOR 250 running to
it's power output optimum at 7500 RPM, that it would be appropriate th
mix the Blue Max oil at 80:1, or in other words to use 9 ounces of oil
per 5 gallons of gasoline.
When I finally got an EGT gauge functioning on my THOR 250 engine
again, I found that the readings at wide open throttle were well in
excess of the 1150 degrees F maximum... on climb out, I saw the EGT run
up to & over 1200 degrees F before I dropped to a lower throttle
setting and landed. Unfortunately, I'd done some flying at
I progressively tested a #128, and a #130 main jet in the PWK 28
carburetor, and was still seeing excessive EGT readings at full throttle
until I obtained and installed a #132 main Jet.
But once I arrived at the optimum jetting, I was noticing that the
engine was not running as strongly. I also checked the gearbox oil
level, and found that it was not only now low, but was also very dirty /
contaminated. I started checking & changing the gearbox oil much
more frequently, and continued to find it getting very dirty in a short
amount of flying time.
Later, when flying in the Sedona AZ area (re-jetted for that ~7000
feet ASL altitude) I continued to experience less power than should be
expected from this engine & the gearbox oil continued to get dirty /
contaminated quickly. I also was watching a leak on the gearbox output
shaft seal throughout all of this progression & topping off the oil
regularly; the shaft seal had evidently been damaged in the past when
canopy lines were caught in the propeller and were wrapped tightly in
the space between the propeller and the gearbox; the shaft seal was
damaged in the process.
After returning to our home in South Park, Colorado, I found that the
adjustable pitch prop had to be set to a lower pitch for the engine to
run at full throttle in the 7400 to 7500 RPM range for optimum power and
thrust production, compared to the prop pitch setting which I had been
using the previous fall. This was further indication of a loss of power.
This factor, combined with the rapid contamination of the gearbox oil
led me to suspect that the compression rings on the piston were possibly
sticking in the ring grooves, resulting in loss of compression &
power, and producing exhaust blow-by past the rings back into the engine
case & out through the shaft seal into the gearbox. Since the
gearbox's top filler plug is vented ,as well as having a damaged /
leaking gearbox output shaft seal, the exhaust gas blow-by was what was
contaminating the gearbox oil so quickly. (The elevated EGT temperatures
along with running the leaner Blue Max oil mixture likely were the
factors which accelerated the buildup of carbon on the piston rings.
And yes, that's exactly what I found when I pulled the Cylinder
& head to check the piston & rings.
My Understanding: Sticking piston rings are the most likely
cause of contaminated gearbox oil.
Excerpt from my reply to an email on this subject: "I've
experienced this after running too lean / hot in AZ last winter Internal
engine pressure / gasses from ring blow-by allows some combustion products
/ carbon to be pushed past the inner shaft seal into the gearbox; this is
how the oil becomes dirty / black. (The gear box has a venting check ball
on the top aluminum cap.)
Depending on the mix oil & mixture you use, and especially when the
engine has run at EGT readings above 1150 degrees F, the piston rings can
begin to stick in their grooves from carbon build-up. That results in
blow-by and results in that blow-by going the only place it can- into the
the gearbox, with the oil getting dirty.
After draining the coolant, You can unbolt & lift the cylinder
& head (kept together in one unit) off the engine block & off the
piston without disturbing the head gasket; the cylinder base gasket may be
reusable- mine was.
Remove one wrist pin retainer & slide out the wrist pin from the
piston
Carefully remove the top ring first without spreading it any more
than absolutely necessary to work one end out of the groove &
progressively completely out off the top of the piston. Note which side is
UP and note the locator pin which is in the ring groove. Remove the lower
ring next.
You can then clean the piston, rings, & especially the ring
grooves so that the rings once more slide in their grooves to full depth
all the way around without dragging or hanging up. I used an Exacto razor
knife to clean the ring grooves very carefully- just remove any dark
deposits without removing any metal! It just takes a bit of time &
patience. Clean the piston face completely too. A green Scotch-brite pad
is helpful and some spray "Brake & Electrical Parts Cleaner".
[Solvents alone don't remove the carbon deposits.]
Your other alternative is to order a new piston / ring / wrist pin
kit from Polini & install the new parts. With about 100 running hours
on my engine, investing the time to clean up my parts was my choice at the
time. I had the entire job done & the engine reassembled & ready
to run in less than 4 hours. I thought that process was better than
waiting three weeks for parts to get here from Italy!
(The cylinder head's interior may be fine if left alone- just clean
& lightly oil it before reassembly. It's the ring & ring groove
cleaning which is important.)
Oil & re-install the rings in their same position as when you
removed, bottom ring first - same side up with the locator pins in the
ring grooves observed carefully.
Clean & oil the wrist pin & it's piston bore & install
it and it's retainer clip. Re-coat the piston & rings with your 2
cycle mix oil before lowering the cylinder back down over the piston
slowly, while insuring that each ring's gap is matching it's locating pin
position. As each ring enters the cylinder you can gently press each ring
into it's groove carefully with a non-marring tool so that it slides
nicely into the descending cylinder
Running good mix oil at 50:1 mix & insuring that the
carburetor's main jet is not too lean will minimize future carbon
deposits; an EGT gauge helps verify the correct jetting / mixture.
In AZ, flying at 1200 feet ASL at my landing zone, I went to a #132 main
jet to get the engine / EGT running cool enough; Here in CO at 10,000 feet
& above, I'm presently running a #120 main jet; my EGT at wide open
throttle stays below 1115 degrees F, and runs below that a lot of the
time.
Hope this information helps; I've been working on my own engines for a lot
of years, so I consider this job fairly straight-forward. If you don't
have the experience & skills and decide to have someone else do the
work, at least you now sorta know what's involved in doing this work, or
having this work done.
UPDATE NOTE ON MY FUEL & MIX OIL SELECTIONS
I run fine on 91 octane with 10% ethanol: Shell V-Power or
EXXON .***NOTE *** {I'm NO LONGER running Blue Max
Oil at 80:1 mix. I had the carbon deposit buildup in the ring grooves
problem develop while running that 80:1 mix on that 'supposedly' 100:1
mix oil. )
Since 2019, I'm running a 50:1 ( 2% ) mix of AMSOIL
DOMINATOR mix oil; The rings & grooves may stay cleaner longer
while running the AMSOIL mix oil at the 50:1 mix - it's well recommended
for doing that!
I've also run with some of Lucas Oil's Octane Booster added when
flying up here at 10,000 ASL & above. 1 Oz added per 5 gallons.
10-22-2018
================================================================================
JET NEEDLE E-CLIP SHOULD BE REPLACED PERIODICALLY!
During a flight on 10-20-2018, the engine suddenly quit running. I
could restart the engine at idle but as soon ads I tried to open the
throttle, the engine would quit running. After gliding in to a landing
& getting the rig back home, I found that the jet needle had dropped
through the E-clip to block fuel passage through the main jet
completely. The E-clip was still in place inside the carburetor slide,
but had worn & deformed so that it no longer was in the center slot
of the jet needle. So I re-shaped the E-clip to once more clip into the
jet needle slot well & re-assembled the carburetor. I also ordered
some spare jet needle E-clips so that I can replace this worn part. I've
since flown a 56 minute flight without any issues... but I plan to
replace the original worn E-clip as soon as the new ones arrive.
Inspecting & replacing this E-clip after every 50 hours of flight
time might be a good plan.
6-2021 UPDATE: I've realized that, due to the design of the
PWK28 carburetor, the jet needle and the Jet needle holder develop a
lot of wear due to vibration. This results in increasing clearances
between the jet needle & the passage through the holder, which
therefore results in the engine running richer and richer over time.
Changing to a smaller (lower number) main jet counteracts this to a
certain extent, but the wear changes the mid-range mixture too. The
bottom line is that the jet needle and jet needle holder need to be
periodically replaced in the PWK28 carburetor for predictable
performance. Adding the jet needle hold-down plate, as written about
later on this web page, should help to minimize future wear of these
parts, especially of the jet needle, due to vibration; see the June
2020 Update below.
================================================================================
THOR 250 KEIHN / Polini PWK28 updated main jet selection &
setting notes
Last Updated 07-15-2021 by BKS
I'm flying the THOR250 with the PWK28 carburetor, in service since 2014,
from a site just above 9900 ft. ASL. I'm currently running a 2 blade GSC
maple blade Tech Series Prop with the urethane leading edge Inserts,
56"diameter, with the pitch set at +10.4 degrees. (I measure this at the
75% radius point with the digital pitch gauge placed on the middle of
the ~flat back side of the blade’s airfoil. My peak RPM after warm-up is
7400 to 7500 RPM. I run 91 octane auto gas with AMSOIL Dominator 2 cycle
mix oil 50:1
On a recent flight, once the prop uploaded a bit in flight, I noted the
peak RPM at up to 7600 briefly early in the flight; once up at 14,200 to
14,600' ASL for cruising over the mosquito range's several high peaks,
RPM peak was down to ~7370 to 7400 due to the reduced air density &
resulting reduced power. Air temp at higher altitude likely was
somewhere between 40 and 45 degrees F. [My average airspeed for
this recent 57 mile flight was 35 MPH under my MacPara Charger 31 wing;
My liftoff & landing glide approach airspeed with this wing & at
this altitude is 27 to 28 MPH]
My newer EGT meter, at full throttle, reads up into the higher 400's C
in flight [+/- 455 C peak?] with the probe mounted in the welded nut on
the newer "two piece exhaust system", ± 6" from the cylinder head.) Prop
pitch was set at 11.2 to 11.4 degrees for flying in Arizona in
late April.
As noted above, main jet selection is affected by wear in the jet
needle and jet needle holder, and has progressed towards smaller main
jets over the years I've been running this PWK28 carburetor on this THOR
250 engine. I'll likely replace the Needle Jet, Needle Jet Holder,
and some other parts at something like a 100 flying hour interval in the
future.
(Update: The previous jet needle had worn a lot before I added the
hold-down brass plate; the jet needle holder was .001" larger ID than a
new replacement jet needle holder. I'm still finding that my engine,
prop, & carburetor combination (1/2014 engine &
carb) now run best at this altitude (10,300 feet ASL) with a
smaller main jet; I'm down to a #114 main jet to run at full-throttle at
7600 RPM, with EGT in the low 400 C range... this is a substantially
smaller main jet than is expected, but the engine is running strong
& the EGT reading is good, with no drop-off in full throttle RPM
while running. A different carburetor may act differently.
On my previous original exhaust system (which developed repeated cracks
due to the older hard-mount system) I had mounted the EGT probe only
1.25" from the cylinder head; I was seeing peak EGT readings in the low
1100's F up to ~1125 F on a previous different meter. I had come across
a recommendation of a peak full-throttle EGT of between 1075 and 1150
degrees F for peak power output and fuel efficiency.... but I'm
suspecting that trying to run the Blue Max "oil at 80:1 mix along with
the higher EGT readings contributed to carbon buildup in the piston ring
grooves. After cleaning the rings & ring grooves carefully &
re-assembling the same parts, I've been using the AMSOIL Dominator mix
oil at 50:1 since 2019, and am running with lower peak EGTs; this
THOR250 continues to perform well for me.
The dual ignition engine uses an electronic ignition module on the
secondary ignition which is, in my experience, unreliable. My first
module malfunctioned / failed in under 40 hours of operating time. A
second replacement electronic ignition module also failed in under 40
hours. I'm presently flying with only the magneto ignition.
Some PWK28 carburetor adjusting issues:
<1> The original jet needle clip in my Polini PWK28 carburetor
appeared to be a chrome plated brass- not spring steel. Last year, while
in-flight, the clip apparently had fatigued while in service, so that
the needle was allowed to DROP DOWN through the clip, totally blocking
the main jet and abruptly shutting down the engine. The engine would
restart at idle speed, but any attempt to open the throttle resulted in
the engine killing again. I glided to a safe landing, but it could have
happened over much less friendly terrain. So my recommendation is to
replace that carb jet needle clip at 60 to 100 hour flight time
intervals.
Replacing the jet needle and jet needle holder should
also be done if wear is apparent.
<2> On my 2014 Polini PWK28 carburetor, there was a air port on
the top of the carb body’s inlet throat which likely had some form of
threaded plug in it. At some point, it had vibrated out, leaving an air
intake leak which leaned out the top-end mixture dramatically, to the
extent that I had changed the carb main jet up to a #136 to get the top
end full throttle EGT to stay below the 1150 degree F limit. Once I
discovered the open threaded port, I bought a 5mm threaded screw and
installed it to block that air leak. I’m back to flying the #122
main jet in the Sonora Desert of AZ, and NOW flying with a #114 main jet
here in Colorado’s high country.
<3> HOW TO TELL IF YOUR MAIN JET IS TOO LEAN (TOO SMALL)
Start your engine and let it warm up so the coolant temperature is up to
~130 degrees F. Then progressively go to 100% full open throttle, noting
the peak reading for full throttle RPM. Hold it at full throttle for at
least 30 to 60 seconds, watching the RPM readout; if it stays on your
peak reading without dropping off at all, you’re not too lean. If it
begins to drop off gradually in RPM, 10 RPM at a time, and continues to
creep down as you hold full throttle, it’s a prime indication that your
main jet is leaner /smaller that it should be, and you should increase
the main jet one step at a time until it will hold peak Full throttle
RPM with no progressive sag or downward creep for 30 to 60 seconds of
full-throttle running. Coolant temperature won’t tell you this; spark
plug color won’t tell you this (since you likely never fly an entire
flight at 100% open throttle.) Only this test will give you this vital
information.
If your main jet is to rich / too large, your peak EGT will indicate
that by not climbing to or above 1000 degrees F after an extended
full-throttle test run. You can change jets one step at a time to get to
that reading. 1050 degrees F might be a good target EGT readout on the
extended 100% throttle test run- that operating range results in good
power output combined with good fuel efficiency.
IDLE AIR SCREW ADJUSTMENT
Base setting for the idle air mixture screw setting is 1.5 turns open
from fully closed; the normal range for operation is between 1 and 2
turns open. If your adjustment ends up being outside of this range, it
indicates that you may need to change the size of the idle / pilot jet.
Once the engine is running & warmed up to operating temperature, If
the idle air mixture screw is closed too much after prolonged running at
idle, the engine will be slow to accelerate to full RPM when the
throttle is quickly opened (= idle mixture too rich = need to open
the air screw adjustment a bit) . If it drops off in RPM when the
throttle is quickly opened and is slow to respond, the idle air mixture
may bee too lean (= need to close the air screw adjustment a bit.)
JET NEEDLE CLIP POSITION ADJUSTMENT
Once you have the full throttle fuel mixture optimized, and your idle
air screw adjustment correct, you are in a position to evaluate the jet
needle clip setting. The stock setting is with the clip in the center of
5 slots. This setting primarily affects the mid-range fuel mixture; you
may not need to change it. BUT - If, after gettng the full throttle fuel
mixture (main jet selection) optimized, you climb out under full power ,
then drop back to an intermediate cruise speed throttle setting and find
that the engine does not seem to be running as smoothly, it’s time to
consider whether changing the mid range mixture will improve how the
engine runs. This is where the EGT meter again is the only thing which
can give you this information. If, after dropping the throttle opening
after a full power climb, when you reduce the throttle opening and the
EGT temperature drops a lot, your mid-range mixture may be too rich,
burning too cool/ burning incompletely. It might sound like it’s running
a bit rougher due to the too-rich mid-range mixture. You can optimize
this by moving the jet needle clip UP one notch to drop the jet needle a
bit deeper into the jet during mid-range throttle operation.)
IF, after doing a full-power climb, you decrease the throttle opening,
and the EGT reading CLIMBS significantly, this would be an indication
that your mid-range mixture is TOO LEAN, and you need to move the jet
needle clip one notch lower, so that the jet needle is farther up out of
the main jet, enriching the fuel mixture, and thereby cooling the fuel
burn.
http://www.keihincarbs.com/tips/gate.html
===============================================================================
JUNE 2020 UPDATE
Remedying One Polini PWK 28 Carburetor Design Flaw
While flying my PPG quad with it's THOR250 engine recently,
I had the engine shut down while I was in the air over rough
terrain. It was running fine, gauges showing nominal readouts...
then, it simply quit running abruptly.
I immediately turned towards the best landing terrain within
gliding distance and glided in to land on rough ground; one rear
axle broke on landing, but otherwise I & the rig came out OK.
This was not my first abrupt shutdown of this engine without
warning; I had experienced the same thing during another flight a
couple of years before. That time, I was over better terrain, and
glided in to land without any problem.
After landing & packing the wing - (I always fly with the
wing packing bag in my gear pack on the quad) - I turned the
ignition switch back on & hit the starter button... the
engine fired & ran at idle, but would cut out as soon as the
throttle was opened at all.
Yes, same thing as the previous time, and after I had done what I
thought I should.
After finally getting a rescue ride back to pick up mky vehicle
& trailer, returning to where I had left the rig, replacing the
broken fiberglass axle and then loading the quad back on the
trailer, I drove back home to start work on this problem.
Below is a look inside the intake throat of the carburetor once I
removed the air filter / silencer box. I have opened the throttle
all the way, so you see that the slide is all the way up / open; you
also can clearly see the main jet needle sitting bottomed in the jet
tube- no circlip to keep it in the air slide. Second time this has
happened to me- I've written before on this page about periodically
replacing the E-clip to hopefully prevent this from occurring. I had
last replaced that E-clip and installed a new jet needle about 5 or
6 months before... new jet needle & new E-clip. This shouldn't
be happening -I've never seen this happen on any other air slide
carburetor in the last 45 years, but it's now hapened TWICE in this
Polini PWK28 carburetor within maybe three years, even after
installing new parts recently..
Below is the original stock jet needle which I removed from this
carburetor when installing the new jet needle and E-clip. On the left
end are 5 slots for the installing the E-clip, where much of the metal
of the jet needle is worn away. the wear extends down the needle shaft
for nearly 40% of the jet needle's length from the top. Upon inspection,
I find a great degree of wear in the air slide's jet needle hole- the
newer jet needle ins now a very sloppy loose fit.
In the parts diagram below, the jet needle is part #11; the E-clip is
part # 12.
In Mikuni carbs, there's a flat washer which sits just between part
31 - a plastic piece which sits over the lower end of the Part #19 air
slide / throttle return spring- an sits firmly on top of the jet
needle's e-clip so that the jet needle is held stationary in the air
slide. In this Polini PWK28 carburetor, there is no such hold-down
device to keep the jet needle held exactly in place. As designed &
sold, the jet needle floats freely, able to slide up and down a
significant distance through the hole in the air slide, and free to
vibrate within the through-hole in the air slide.. The plastic piece
which fits over the bottom of the spring has a large cavity on it.s
lower side; it pins the throttle cable in place to keep it from
disconnecting, but does nothing to keep the jet needle form vibrating
all over the place, resulting in dangerous wear on the jet needle, the
air slide jet needle mount hole, and resulting in extensive
stress, fatigue and wear on the e-clip. After a period of operation, the
e-clip fatigues enough to allow the jet needle to simply drop right
through, blocking the main jet fuel flow completely--- the engine can
not run.
Below i an available kit of replacement parts for PWK carburetors
which includes the air slide, the jet needle and two e-clips, as well as
the other parts show,; the link into the Ebay listing where I ordered
mine is below.
I ordered a bag of 10 e-clips from another supplier on Ebay, and
installed TWO new ones on my jet needle. I'm waiting for the parts kit
above to arrive, so I can replace the air slide (with the very oversize
worn hole where the old jet needle had been vibrating around for too
long) withj a new one.
But without fabricating a jet needle hold-down device, the same
dangerous problem could rapidly develop again.
So I hunted through my collection of materials and came up with a
flat brass washer , 1/2" in diameter and just under 1/16" thick which
had a very small center hole. I used a #38 .106" diameter drill to drill
it out where it just fits over the top end of the jet needle, where it
can rest against the e-clip to hold the jet needle firmly in place when
everything is assembled. The notch is cut in this hold-down plate to
allow for passage of the throttle cable, which extends into it's
pocket in the lower area of the body of the air slide.
Below is a closer look at the brass hold-down plate.
Below is a view of the reassembled air slide with the brass hold-down
plate just under the plastic shoe on the lower end of the air slide /
throttle return spring; the jet needle with it's e-clips is now firmly
held in place where it can not vibrate and wear as badly as it did
previously..
UPDATE NOTE*** When replacing the jet needle, part # 35 on the carb
exploded view should also be replaced, as it too suffers from wear and
becomes oversize, enriching the mixture progressively; )
Unfortunately, this "Needle Jet Holder" is not included in any of the
carburetor repair parts kits which I've seen. It can be ordered
separately from:
Once both the jet needle and the jet needle holder are replaced, you
may need to readjust the size of your main jet .
=======================================================================
REPLACEMENT PWK28 CARBURETOR August 12th, 2021
A few weeks ago I had ordered a PWK28 Clone replacement carburetor
from Tuning Parts Master, a seller on Ebay; the cost for the entire new
carburetor was well under $30.00 !
This new carburetor uses all of the readily available jets and
rebuild parts as all PWK 28 Carburetors. All I had to do was to remove
the Velocity stack- type intake throat from my old Polini PWK28
carburetor (three 3mm grub screws) move the O-ring, and then mount it
onto the intake of the new carb- a perfect match. New pink TYGON vent /
drain lines are included with this carb from this seller.
I moved in my jet needle brass hold-down plate into the air slide before
mounting the carb. I checked and found that this carb had come with a
#120 main jet installed- which just happens to be close to perfect for
flying up here at 10,000 feet and above. After testing I am fying with a
#118 main jet here again.
For flying at lower elevations, a slightly larger main jet may need to
be used; when I head back down into Arizona's low desert country next
winter, I'll likely go up to about a #122 main jet for my first test
run.
After setting the idle speed screw, I did some experimenting, and
ended up with the idle mixture air screw set at 1-3/8 turn open from
fully closed.
=======================================================================
GEARBOX OUTPUT SHAFT SEAL REPLACEMENT : LINK
Replacing
the propeller shaft seal without disassembly
Metric
Oil Shaft Seal 26 x 36 x 7mm -THOR250 Shaft Oil Seal - For Propeller
Shaft
Polini
Thor Flash starter problems and fixes
====================================================================================
EGT Meter Project 11-2018
Monitoring the exhaust gas temperature is the only way to really know
that your engine is running within the optimum range as far as power,
efficiency, and longevity. Its not necessary to fly with an EGT gauge
active all of the time. You could optionally temporarily mount an EGT
gauge to establish that you're running with your exhaust gas temperature
safely within the "optimum efficiency range: (580 degrees C to 620
degrees C / 1075 degrees F to 1150 degrees F for the Polini THOR
engines.)
Ounce you have your jetting optimized for a giving flying environment
(elevation) you could then remove the EGT gauge until you want to change
your tuning for another elevation / environment.
The devices shown below are relatively inexpensive to put together if
you have tools & are somewhat handy with tools. (It's not something
that a novice might do alone.) The EGT thermocouple probe installation
approach is fairly simple, requiring you to simply drill one 1/4" hole
in the appropriate area of the exhaust expansion chamber close to the
exhaust port, and clamp the probe in place with a hose clamp. The
display unit can be self-powered with a standard 9 volt battery -
(you'll only need a battery snap connector, available from many
sources.)
I've built mine into a housing containing the battery and an on/off
switch; for really temporary service, protecting the back of the display
module with some tape and mounting it with cable ties or velcro may be
all you need to do for your application.
I'll be working with the type K thermocouple probe with the 2 meter long
, braided metal guarded wires (shown in one of the photos &
available as one of the links at the end of this short article.) [If
you're able to get by with the 50 cm long wires on the probe which comes
with the display module, you won't need to get the longer wired probe; I
fabricated a ~5 foot long set of extension wires to optionally use with
that probe while still mounting the display farther forward, in front
with the other instruments.]
If you later dismount the meter & probe, you can simply clamp a 6mm
screw in the EGT probe hole to seal off the exhaust using the same
stainless steel clamp; reinstalling the meter later should be short
work. With this mounting approach, there is no need to dismount the
exhaust system from the engine to do what you need to do.
If you want to have a 6mm x 1mm pitch metric nut welded to the exhaust
expansion chamber over the 1/4" hole so that this type of probe can be
threaded directly into that nut, it's another optional approach. I may
do that myself in the future when I next have the exhaust system
dismounted from the engine.
Above: temperature display module bought on Ebay which included a type K
thermocouple probe with .5 meter length wire leads.
Below: open back of the meter module; I installed mine in a plastic box
along with a push-on, push-off switch and a 9 volt battery. It does not
come with any back cover.
Above is a photo of a different type K thermocouple probe with 2 meter
long armored wire leads; I've ordered one of these also, as the 2M length
is about right for the installation on my PPG Quad.
Above: Display Module, switch, battery, and extension lead for the
thermocouple probe assembled inside the ABS plastic housing- snug fit.
NOTE- I do not recommend battery power for permanently installed EGT
meters; wire it into the rig's 12 volt power system.
Above: the green display color seems to be more visible in bright daylight
than either the blue or the red options; this module displays to .1 degree
C resolution below 100 degrees, and then to single digit resolution above
that.
Above: Clamp-on type mount for the short wire length EGT Probe which came
with the display module; a 1/4" hole was drilled in a #28 stainless steel
hose clamp, and a 6mm x 1mm thread pitch nut & a washer were used to
mount the probe trough the clamp. Enameled copper wire was rigged to hold
the probe tip extended in through the threaded stud. All that's required
for installation into the exhaust expansion chamber is to drill a 1/4"
hole where the probe tip can extend into the inside; I chose a location
within about 2" of the cylinder head where the stainless steel clamp could
be tightened in place. (I'll switch to the other 2 meter wire length probe
later, mounting it with a similar stainless steel clamp.)
UPDATE 08-29-2021: I have replaced the EGT type K probe once since
installing this EGT Gauge; the gauge continues to work well. It does
consume enough power to use up 9 volt batteries fairly quickly, so this
one is hard-wired into the rig's 12 volt system.
Sources for these parts:
LED
DC12V Thermocouple K type -30~800℃ High Temperature Digital Thermometer
| eBay
2M
K Type Thermocouple Sensor Probe for Temperature Controller Xylnu
608641591781 | eBay
3.3"
X 2.1" X 1.4" PROJECT BOX | All Electronics Corp
2019 Updates
After an incident which occurred by trying to 'save' a bad takeoff on
rough ground on the short grass prairie, and hitting a badger hole ,
where the right front fiberglass axle broke, resulting in having the
quad flip and the propeller contact the prop guard cage, I built up a
new prop guard cage. The new prop guard cage has two hoops with an
inside diameter of 65", using 6 main support strut tubes. It's assembled
from 3/4" OD aluminum tubing using aluminum Tee connectors, with two pop
rivets in each connection point. The cage webbing is made with tough
weed-eater line routed through drilled holes.
_____________________________________________________________________
UPDATED - THE REST OF THE STORY!
On April 1st of 2021, I had the
original (1-2014) magneto fail in-flight over rough AZ desert back
country terrain.
Here are the photos of the
progression of the incident, the 'recovery,and the reflections and
upgrades that followed this incident.
Above is a view looking to the north
up into the canyon of the Santa Maria River, where it passes through
the Arrastra Mountains. I had taken off from the PPG site near
Wayside, thinking of possibly flying over to Hwy. 93 below Bagdad. I
had flown to the right side of the Santa Maria River, towards the old
inactive Anderson Mine site, when I began to hit turbulent air. I had
just decided to turn back and fly elsewhere for the morning, and was
starting a gradual turn to the right through sinking air, when the
engine abruptly stopped running. Knowing that I had just crossed one
of the back country ATV / UTV trails, I tightened the turn to get back
over a bit better terrain. I had little time to circle, flair, and
drop nicely into a narrow brushy desert wash; the photo below shows
the quad exactly as it sits where I landed. A later check of the
GPS track shows that when the engine cut out and I started the turning
decent, I was only 126 feet above the spot where I set it down...
things happened quickly, & it was a good time to focus on doing
that 'pilot stuff'!
Abo0ve & below are two more
views of the desert wash where I set down the PPG quad, laying the
wing out to my right as I stopped. It took a while to get the
Macpara Charger wing's lines untangled form the vegetation, but
there was no damage to any of the gear. I always fly with the wing
bag stowed in the compact backpack that is mounted to the quad's
frame between my knees, so I first packed the wing into that bag.
I had actually landed within a
hundred yards of the ATV trail, so I grabbed the quad's front axle
and drug / rolled it up the wash to park it just along the side of
that trail. I then cut the cable ties that attach the pack to the
quad frame, and prepared to start walking out to where I could get a
cell phone signal, so I could call some good friends to have them
come in on their UTV's to execute a 'recovery' . It's common for
ATV's & UTVs to have mechanical problems while traveling the
rough trails of the"Arizona Outback", and they routinely go in
and pull out a vehicle from wherever it happens to stop running.
Below is a view looking back down
towards the Santa Maria river bottoms into the rough country where I
landed and left the PPG Quad; From this viewpoint, I've traveled
about a mile, climbing several hundred feet of elevation, following an
old mining track which the recreational riders occasionally explore
these days. I'm still climbing uphill, working to get enough elevation
to get a cell phone signal from the tower that's located above Alamo
Lake State Park many miles to the west. The temperature is climbing,
in the mid to upper 80's at this time, heading into the 90's before
long.
I have my pack, which includes one
16 ounce water bottle, my cell phone, my Garmin GPSMAP64s, and my
survival gear set. The primary objective at this point is to get
high enough to get in cell phone contact with my friends to start
the 'recovery' crew heading my way. I'm probably 20-some miles
from my landing site by back country trails at this point, and I'm
not really looking forward to doing any more walking in the dry
desert heat of this day than I need to. About every half hour, I'll
take a modest sip of water, but I'm conserving it... ( I'm thinking
that, in the future I'll maybe carry more than one bottle of water
when flying this Sonora Desert back country!)
In this next photo below, I've
climbed to about 800 feet elevation above where I left the PPG quad;
I'm high enough to see the Wayside area as a faint yellowish
line on the ground in the far distance, and I now have a cell phone
signal, and have been able to call a friend who was to arrange the
rescue / recovery. I gave her precise GPS co-ordinates for where I
was on the back country trail, and the GAIA GPS app on her I-phone
showed one of her recent tracks as traveling that specific trail, so
she knew not only where I was, but more importantly, how to travel
the roads & trails to get there. One of my friends would drive
my 2002 Chevy Tracker with the PPG trialer behind it on in,
following two UTVs. I would get beyond the rougher terrain on the
trail I was walking, to a place where the Tracker with it's trailer
could be parked while all of us then went down into the rougher
country to recover the PPG quad.
Below: after getting to an area
where my Tracker with it's trailer could be turned around and
parked, I found the best patch of shade available under the edge of
this Palo Verde tree;
temperatures were into the low
90's by this time, and it was time to stay as cool as I could while
my friends covered the many miles of country between.
I updated my GPS
co-ordinates with my friends, cleared some pokey ground litter, and
got in under what shade I could.
A couple of hours later, Rosie,
Bradley, and James got to my 'shade' spot. With the tracker parked,
we rode down into the rough country below which I had walked out of
earlier in the two UTVs . The only reasonable way to get rigged up
for pulling my PPG quad out was to use my cam buckle straps to
attsch it to the ball hitch on a receiver hitch extension to the
back of Bradley's Can-Am, as seen below. The wing in it's bag is
stowed in the back of Rosie's Polaris.
Above & Below; the trial out
is rough, rocky, and steep in places with washouts, desert
vegetation- just what these UTVs are built for!
Once out of the lower canyons
& washes & back tpo where my Tracker with it's trailer was
parked, I loaded the PPG quad onto it's trailer, and we headed on
out. We were all looking forward to cold beverages and some food
back at the Wayside Oasis Bar & Grill. However, a ouple of miles
down the trail, we had to stop to change out the drive belt on
Bradley's Can-Am. He had planned on doing it soon and had the
replacement belt along, and always carried tools, but the time to do
it had simply come upon us- there was no traveling further without
doing the job. It took a while, but we all were eventually back on
our way and covered the miles back to Wayside. It's great to have
Friends- THANKS AGAIN!!
The following morning, I pulled
the magneto cover on the THOR 250 , and this is what I found: the
magneto magnet housing with the starter ring gear was riveted to
the crankshaft mount inner section with six rivets on this early
2014 engine. Evidently, starting forces / kickback from the
starter operation over the years had been enough to SHEAR all six
rivets! This resulted in the loss of magneto generated ignition
spark.
The 6 rivets which held the outer
flywheel with it's ring gear and magnets to the inner shaft-mount part
SHEARED OFF in flight! As a temporary fix, I cleaned up and matched
the parts back together and used a friend's wire feed welder to
solidly put the magneto back together; the following morning , I was
back in the air, flying with the repaired one.
The new replacement magneto assembly
for the THOR 250 which I ordered is now machined from one solid piece
of steel- no funky rivets!. I'm not sure when the change-over on the
design of this part was made, but if you own an older THOR engine and
you use the electric start system, you may want to inspect your
magneto assembly carefully, and consider replacing it with the newer
part. Photo below.
Below is a photo of the front axle
assembly from thre Skycruiser Skymax Lowboy Quad; it's vertical pivot
bolt passes down through the narrow piece of strap steel through a
large hole which has only a modest amount of metal left on each side
of the hole. You can see the breaks in the metal, and cracks at the
end welds. I got everything back together in working position and
welded everything thoroughly, building up more weld metel where the
breaks had occurred.
Now, I have to admit that dragging
this PPG quad out of rough back country by strapping this front axle
to the extended hitch of a UTV may be a bit beyond the normal
conceived service required of a PPG Quad front axle assembly... but
how else was this back country recovery to be executed? It was our
only option available at that remote place at that time, and it
worked nicely.
Above: repaired front axle assembly,
welded, painted, ready to fly.
Later in 2021, the 1" fiberglass
front & rear axles, which have had to be replaced numerous times
due to lengthwise stress cracks and breaks, were upgraded to 1-1/4"
fiberglass axles in new chrome-moly carrier tubes; the front axle is
now a one piece pass-through axle with only a single locator bolt in
the center of the pass-through carrier tube.
===========================================================
2022 Modifications & Updates
I replaced the MOTOBAT MBTX4U 70
CCA 4.7 AH Battery with this POWER SPORT YTL5X-BS 12V 125 CCA 5 AH
Battery. The new battery has the same length and width and close to
the same weight, so it fits in the carrier nicely. The higher CCA
rating results in better motor starting energy - the starter spins the
motor faster for better electric starts. Price on the new battery was
under $30, with free shipping included.
The upper motor mount bracket
failed after 7 years in service, as shown in this photo. I fabricated
a replacement from plate steel.
Flying from rough natural terrain results in a lot of stresses on the
fiberglass axles. One of the places these stresses first show up is in
fiberglass cracks running lengthwise from the axle inner end locating
pins / bolts holes. After seeing some stress cracking in the 1-1/4"
fiberglass axle at the right side of the rear axle carrier tube, I
decided to install a one-piece pass-through rear axle. There is now only
one locating bolt at the center of the rear axle carrier tube.
I replaced some failing pop rivets in
the prop guard cage, and completely re-strung the entire net structure
with new .065 weed eater line. Here is the quad in the trailer, with the
engine doing a warm-up run. the 145 cm diameter ground adjustable
pitch E-prop out-performs any previous propeller I've used - it
generates better thrust, giving shorter takeoff ground runs before
achieving lift-off speed.
I recently received my new NIVIUK R-BUS
34 square meter wing. I wanted a wing which would allow me to take off
at lower air speeds; the difference is substantial. My GPS data shows
that I'm now lifting off at 4 to 4.5 MPH lower airspeed than I was with
the Macpara Charger 31.
This R-Bus was available in the bright red, Black, and yellow "Rocket"
color layout pattern, offering high visibility - something I really
wanted in consideration of all of the military aircraft which share the
airspace over Colorado's Central Rockies. It's not unusual to see C-130s
and F15s flying over South Park- sometimes barely 400 feet AGL.
The "3D" multiple line tip steering rigging is very effective and
efficient, providing nimble handling to this large wing with very
moderate control line pressures.
Above & Below:
The stock Riser set routes the tip steering lines up through the middle
of the riser bundle, through a plastic thimble. When setting up to
fly this wing on a PPQ quad set up with low hand point loops and upper
riser guide rings on the Quad's upper frame, this routing of the tip
steering lines does not work. So I ordered a pair of high quality line
pulleys from Bluesky PPG, and mounted them just below the
brake pulley rigging on the upper area of the brake riser- (Shown in the
photo above.) I then fabricated new larger tip steering toggle /
handles with extension line loops, which will bring the tip steering
toggles down lower to the bottom of the risers. New added sets of N52
magnetic keepers will keep the tip steering lines in a comfortable
position, easily accessible- I am waiting for delivery of the magnets
now. (Note: The small loop on the stock tip steering toggle would fit
only a single gloved finger... I wanted comfortable room for two gloved
fingers; and my aging shoulders are fond of working with the lower
keeper location & longer tip steering line lengths.
Below: The new tip steering toggles
with their Magnetic keepers installed in the lower position, ready to
fly. A pair of N52 30mm x 20mm x 5mm were built into the new toggles,
and sewn into the new keeper assemblies which are then sewn in place,
wrapped around the lower A riser as shown and hand-stitched in place.
========================================================
LINKS TO FURTHER INFO & SOURCES OF PARTS
SKYCRUISER MANUFACTURING:
Polini Parts – Your one stop for
Polini parts here in the USA
Links To On-Line Documentation And Related Info
Groupe
public Polini Thor 250 Owners | Facebook
paramotorclub.org
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VFRMAP
- Digital Aeronautical Charts
FOOTFLYER.COM
Matching
Prop To PPG
POWERED
PARAGLIDING, VIDEOS, PARAMOTOR EQUIPMENT
CARB TUNING TIPS & PARTS SOURCES
http://www.keihincarbs.com/tips/gate.html
http://www.carbparts.com/keihin/needles_tuning/jetting_your_carb.htm
Scooter
Parts International : KEIHIN PWK JETS
Keihin
Pilot Jet Series 21 35 38 40 42 50 52 55 | eBay
CARB JETS : KEIHN PWK28 uses 6mm HEX main jets: 126 was stock ; [118
through #132 possibly useful on THOR 250]
https://www.treatland.tv/category-s/96.htm?searching=Y&sort=5&cat=96&show=50&page=1&f-keihin=495
10
piece pilot jet assortment kit - only $9.99 for all, free shipping
from CA
Motorcycle
Carburetor Repair Kit 28mm For PWK KEIHIN OKO Carburetor Spare Sets
6708699912300 | eBay
Amazon.com:
Lucas Oil 10115 Semi-Synthetic 2-Cycle Oil - 1 Gallon Jug: Automotive
Lucas
Oil Octane Booster | eBay
1pc
NGK 4684 Standard BR10ES SOLID Snowmobile Spark Plug Tune Up Kit Set
ls | eBay
Rick's
Motorsport Electrics Starter Motor Brushes 70_109 : Use For
Poluini THOR250
Digital
Red LED Temperature Meter for K Type Thermocouple EGT Sensors (12V/℃)
881314407798
2M
EGT Thermocouple K Type Temperature Probe Sensors Exhaust Gas Screw
Threads
LED
Digital Exhaust Gas Temp Gauge Car EGT EXT Turbo Diesel Petrol With
Sensor
MAC PARA Technology -
Charger
UFLY2.com
Andy McAvin : Mac Para U.S. Distributor
Mac Para Gliders | TX
Flysports
SAIL
REPAIR TAPE - WHITE RIPSTOP NYLON - 2" x 25' ( #251400 ) | eBay
Ripstop
repair tape, Kite repair tape | FunWithWind Kites
BlueWater
1" Climb-Spec Tubular Webbing - Package of 30 ft. - REI.com
MAX-GAIN
SYSTEMS, INC. : 1" Fiberglass Axles for Quad (Now using 1-1/4" axles)
BlueSkyPPG : Bulk & Finished PPG
Replacement Lines, Strobe, Assorted Parts
Airport Windsock with Reflective stripes
MotoBatt
MBTX4U Battery | Quadflex AGM $36.76
Premium
Quality OEM Tygon Fuel Line 1/4" ID X 3/8" OD Clear Yellow - 10 Feet |
eBay
https://www.ebay.com/itm/UNIVERSAL-2-WIRE-12-VOLT-STARTER-SOLENOID-RELAY-FOR-HONDA-ATV-MOTORCYCLE-BIKE/302716222028
Orion
Skyblazer II Aerial Signal Flare Kit | Bass Pro Shops: The Best
Hunting, Fishing, Camping & Outdoor Gear
3M
3361 Silver High Temperature Stainless Steel/Acrylic Adhesive Foil Tape,
1" | eBay
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Stenulson's Main Page. Photo Gallery Pages are linked from there
For photos taken of and from my PPG while flying during
2016, please CLICK HERE to visit the 2016
PHOTO GALLERY.
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www.stenulson.net/ CLICK HERE
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Bruce Stenulson, Fairplay, Colorado. (c) 2022; All Rights Reserved.
