This required cutting away excess plastic, then building in a balsa wood motor mount 'saddle' in the front of the plastic overlay as shown in the photo. 1/16" foam tape lines the saddle, and also lines the retainer strap, which is made from a section of plastic strapping about 1/2 inch wide. In the event of really hard nose-in impacts, the motor can simply slide back through this saddle, but has enough friction from the foam tape so it doesn't move during normal flight operations.
This "GIZA" , in the tractor configuration rather than the pusher configuration, may actually have certain handling stability advantages in high / gusty wind conditions, reducing pitch / attitude sensitivity as it 'pulls itself' through maneuvers.... I know it flies very well!!
Above is a photo of the 2001 rework of my modified ZAGI. The motor, a Mabuchi 390, is mounted in an extended nose configuration . The nose block was formed from the extra block of spare EPP foam included in the ZAGI 400 kit, cut and shaped to mount the motor with a 0-0 thrust line setup in relation to the wing incidence. The Gunther 7x6 prop runs at about 7600 RPM on an 8 cell pack, producing good thrust and airspeed. The sound is quite pleasant at this lower motor / prop speed.
Moving the motor in front of the wing on the chord line cleaned up the profile, likely dropping the drag substantially. The non-folding prop is now the major drag factor. A folding prop would be a nice feature, but I haven't come up with one yet. This present setup may still not be the perfect configuration by a ways, as possibly a longer nose with a motor & folding prop combination would still be desirable. But the nice thing about EPP foam building is that tape can be peeled away again, a new block of foam can be carved to shape, and a new configuration can be taped in place and flying in a relatively short amount of time.
The [GIZA] shown above is an electric powered, aerobatic flying wing, 48" span, flying at about 21 ounces on 8 600AE cells. It does nice outside loops, has a fairly good roll rate, flies inverted - anything you can do with elevons. Landings are very stable, right down to a full mush stall at touchdown, without any problems. If it'll handle this way at 10,000 feet and above here in South Park where I do most of my flying, it'll do fine about anywhere you care to toss it into the air, I'd guess, and double as a respectable slope soarer, too!
With the noticably thinner air here in the mountains of Colorado (close to or above 10,000 feet where I normally fly), I'm still inclined to work for minimizing wing loadings in all but high wind slope soaring applications, so have stayed with the 500-600 maH battery packs. I have a nine cell 1000mAH NiMH pack from Radical RC that I'll test soon- it's offered for motor/prop combinations drawing up to 12 amps, so the 9 amp draw of the 390 motor & 7x6 prop should work well on that pack.
The Zagi "Electric 400" version has a light weight white foam wing with EPP foam leading edge, designed to be covered with a nice grade of 2.2mm thick colored tape.
I also added a small lite plywood 'keel' just forward of the balance point on the underside, just large enough to allow for predictable launches. While I've seen the launching technique reconmmended in the instructions used effectively by another experienced slope flyer, my background with hand launch sailplanes goes back to about 1983; I like good attitude control on launch of any hand launch plane, and so I made this minor addition to this aircraft. (With the motor on the front, this was necessary.) I've broken the lite ply keel a couple of times on rocky landing sites, so I'd consider epoxying a piece of coroplast in it's place for this purpose the next time.
A radio with ELEVON mixing is needed, as with any flying wing configuration; the HITEC Focus 3 single stick radio is working nicely, and is available with a pair of mini servos for about $90 mail-order. Every extra fraction of an ounce adds up to reducing performance in the aerobatics category, so beyond distributing all components to eliminate the need for adding lead to balance the aircraft, using 1/2 ounce servos or lighter is one place where you can trim weight.
I put in some 1/3 ounce servos - Cirrus CS-21BB's - and they're more than capable of doing the job nicely! I'm told the CS-20's are also being used by many, doing fine.
ZAGI Electric 400 kit info is available at TRICK RC's web site: http://www.zagi.com/
Glen Magree at Action Hobbies (on Carr Street just south of West Colfax in Lakewood, CO) carries the various ZAGI Kits- there may be 100 or more flying in the Denver area now (May 2000). He sells the 'complete Kit' in the 7 cell version for 109.99 [list is $135] and $114.99 in the 8 cell battery version- same motor- and has several colors of covering tape, and the fiber reinforced tape used in assembly. The kit at this price includes the motor, Aveox 14 amp speed control, and a very tough flexible nylon prop, as well as one roll of covering tape. $5.00 per roll gets another color for contrast, top vs. bottom - - HIGHLY recommended!
For possible sage brush landings, the foam core ZAGI won't even notice... which may be one of the EPP aircraft's finest characteristics!
Lexan Hinges & Cold Weather Flying
I may have been a bit premature in the statement above about the micro CS-21BB servos doing nicely -they were doing well during the warmer summer months here in the high country, but last evening, at 22 degrees, a new issue surfaced.
It appears that those wonderful Lexan tape hinges (that were supplied with kits at one time) stiffen considerably in colder conditions... stiffen to the point where the light torque micro servos I used can not move to full travel as they did in warm weather... they stall at about 2/3 of their full expected travel.
The current drain is likely fairly high at higher elevon deflections with any servios you might use, due to the stiffness in cold weather. This means greater battery drain on any aircraft using the Lexan hinge tape when the temperature drops... While some might just throw in larger servos to overcome this unforseen characteristic of the Lexan hinge tape, I just removed it completely, and now use SCOTCH 3/4" wide Crystal Clear tape for hinging. They flex well in cold weather, and hold up very well to the demands of slope flying!
My first motor controller would unexpectedly cut out early in the flight, briefly but repeatedly. It did it on several different battery packs. Control surfaces would sometimes deflect briefly and radically at the same time that the motor would cut out. After some unusual handling, I took the controller out & called Trick R/C. they said, 'send it back- we'll send another'. And they did so promptly - thanks!
In the mean time, I'd installed an FMA20 controller, and found it performed fairly well well.
In October of 2000, I finally got around to connecting the new ZAGI 14 / Aveox controller to another motor that i was designing into another original design slow flyer. When set up & run on the test bench, I was alarmed to have even worse glitching while the motor was running, watching the servos repeatedly going to full deflection at each motor cutout. I started wondering, "What's going on with this motor controller?"
I next connercted the new controller to a new ZAGi 400 motor, laoded with a Robbe 6x3.5 folding prop, and ran it up. The glitching & servo deflection were not as bad... but they were there again.
The ZAGI 400 motors are assembled with two noise supression capacitors, barely visible in good light, inside the case, with one lead comimg out to each brush holder terminal (a small silver colored wire.) Many E-flight motor installation directions demand the use of three motor noise supression capacitors, not two: one from each motor brush holder lead to the motor case, and a third one connected between the two brush holder terminals. The ZAGI instructions do not mention adding any additional noise suprtession capacitors... but on a hunch, I added a .01uF monolithic ceramic capacitor between the two brush holder terminals, with small pieces of insulating tubing over the exposed wire.
NO MORE GLITCHES!!
Next, I replaced the FMA controller in my ZAGI / GIZA with this new controller, and before the extra capacitor was added, I again saw the glitching that had haunted my early flights. AH HAH! After another capacitor was soldered in place, this installation now no longer experiences any motor cutout glitches, and no resulting control surface erratic deflections.
Would every ZAGI 400 motor installation benefit from this simple addition? I'm not in touch with enough other ZAGI Electric 400 flyers to be able to answer this, but I do know that both of the motors I have on hand needed the additional capacitor when run on the ZAGI 14 / Aveox controller. This has now also helped a couple of other flyers in our local flying club.
I'm always fond of having that initial burst of power that a freshly peaked battery gives you for the first few seconds of the climb out; always want the most 'juice' in my battery. So while I was doing my testing on the bench, I checked out the current draw when the battery was connected, but the motor wasn't running. Without the rexciever connected, there was a 45mA current drain anytime the ZAGI 14 controller was connected to the battery. With the reciever connected, but no servos connected, the current draw went to 60mA.
The FMA controller has a On/Off switch; when turned on (with the same receiver connected), (no servos) the current drain was 45 mA, about 15mA less than the AVEOX / ZAGI 14. When it was switched off, there was no battery drain, as expected.
UPDATE: 01-21-2001: My observation about one possible 'shortcoming' of this particular FMA20 ESC, however, is that it seems to cut out early, even before any audible drop in RPM can be detected. This is especially unsuitable (according to today's testing) when trying to fly on 5 cells, or with a 6 cell 380 pack in the "WATTS INNIT?".
This is not an issue with the AVEOX controller provided with the ZAGI 400 kits- it will run a motor on five cells better than the FMA20, without the same 'early cutoff' actions.
With the ZAGI 14 controller in my ZAGI / GIZA again now, I've just installed a power On/Off switch in one of the battery wires (on the controller side of the connector, of course!)
Another ZAGI flier commented on his ESC glitching , especially early in the flight, and inquired. I sent the following reply on 2-27-2001:
The glitching seems to be definitely related to motor brush noise; I was doing some testing of different motors & props a while back, and hooked this ZAGI-14 controller to a different motor that had not been run in yet- (brushes not well seated). With a larger prop & heavy load, (higher amps draw) this setup was exceptionally noisy, causing severe glitching of the ZAGI 14 controller.
Earlier in your flights, with a 'fresh' battery, you'll see higher currents & consequently more arcing at the motor brushes; later in the run, the current drops off, and motor brush arcing may be minimized.
Seating the brushes by running the motor under water works well- it sounds strange when you first hear of it, but I've used it on the Mabuchi 390 motors recently, with excellent results. The technique was detailed in an aircraft construction article in M.A.N. a couple of issues back..... 400 RPM increase (driven prop speed) from motor after the water run seating of the brushes was the result I saw.
The third cap across the motor connections definitely helps !
Interestingly: I recently ordered an AVEOX A-15 ESC / motor combo, as recently advertised for $39.95 in the magazines. The motor supplied was one with a "ZAGI 400" label, and included in the bag was a set of three capacitors, .047 uF ... seems AVEOX isn't relying on the internally installed terminal- to- case capacitors, either, offering a full set of three to use.
The boards appear identical, except that the A-15 has an on/off switch installed; on the ZAGI-14 controller, there's a 0 ohm chip resistor bridging the contact pads where the switch wires connect on the A-15 (just below the center of the printed "AVEOX" label on the board.) This is said to disconnect power to the BEC and uP portions of the controller when switched off.
Another note I'll add here for now: I mentioned the FMA 20 ESC not being as prone to motor brush noise glitching . While this is true, I have since looked at the motor drive waveform on the oscilloscope, and see something I'm not fond of at partial throttle settings- a 'half-on' condition during part of the drive pulse, where only maybe 50% of the battery voltage is being applied to the motor during that portion of the pulse. There appears to be a significant amount of power that is likely being dissipated as heat in the controller at these throttle settings. This is most apparant at from 20% to 60% of full throttle settings. I haven't contacted FMA on this matter yet, so don't know if this is a situation with all FMA 20 ESC's, or not...
I had noticed a similar waveform while prototyping an ESC I built (working from earlier circuitry designs inspired by Joe Utasi) - thanks Joe!) and found that at higher frequencies, this "partial on" condition is eliminated. I went to a Pulse Rate (frequency) of between 17KHz and 19KHz to get to a really nice looking motor drive waveform throughout the entire throttle setting range from off to full on.
I haven't had a chance to test the AVEOX A-15, but it does look to be the identical board as the ZAGI-14.