Rocket Conversion of a 48" span R/C Slope Combat Glider

This is a project originally started by Kevin McKiou, when he was doing VectorAero. The Zagi Flying wing, by Trick R/C, was becoming pretty popular at the time as a slope soaring glider. Kevin got pretty far along with it, including covering the wing, but lost stem on the project. Kevin asked me if I'd like to take it over, and shipped it to me.

I did not create a web page on the Zagi at the time, only had tacked a single photo to the Robart UFO Twin glider page. To save some time in creating this page, I will use most of the text of a reply I sent to Doug Holverson who asked a few questions in May, 1999. Fortunately I saved the text of that message.

Doug Holverson wrote:

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I loved the modified Zagi. Gotta make one of those one of these days! What's the thrust line through there? (Is there a rule of thumb or formula for thrust lines through RGs?) Are Zagis stabilized by washout or reflex?
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For the engine mount, basically I hollowed out an opening into the top aft part of the foam to allow the bottom of the BT-55 engine mount to be about 3/8" above the bottom of the foam. When I got the wing from Kevin, it was already glued together, and even covered, so the engine mount was added retroactively. To avoid the engine mass adding weight to the back, I moved it pretty far forward, though it is still a little aft of the CG. The rear of the engine is about 1.5" ahead of the rear of the wing. To avoid damage, I allowed an extended lip of the engine tube to run back to the TE and applied adhesive aluminum tape to it. The F13/G12 reload exhaust is mild enough not to roast or mess up the aluminum tape.

Now, is the Zagi stabilized by washout or reflex? Answer is: YES.

BOTH. The fixed part of the wing itself is not washed out that I noticed. But the elevons are weird. They are 1" chord at the root but 2" chord at the tip. So even though they are reflexed, they also produce a lot of washout too with the reflex. Now, I found the original 1/8" elevons to be too flimsy. I was concerned about the elevons twisting from aerodynamic loads at high speeds. I have had RBG's that used fiberglass or graphite tailbooms become destroyed when the booms were too flexible for the size and speed of the model, the boom bending down so that full up elevator still could not pull the model up, making them crash under thrust. I imagined that with the Zagi too, if the long thin elevons flexed in twist.

So, for one, I made the elevons 3/16" thick. For the other, to get more strength, I made the elevons 2" chord all across, instead of 1" at the root, as it is near the root where the control horns are attached. Now, it did affect the control characteristics of course, not as much effective washout. But since the tips of the wings are a narrower chord than the root, there still is "some" washout created by the elevon reflex, just not as much. But it glided OK.

You can see a little bit of the mount, the Rx, Battery, noseweight, and servo installation. For maximum density of noseweight I hollowed out a compartment full-depth (down to fiberglass cloth on the bottom), used lead sinkers and filled it about half-depth with epoxy. Good thing I didn't add all the lead I expected it needed, since I later found it could glide with the CG more aft than the plan.

One thing that was a big turn-off though it how much noseweight the model needed. About 4.5 ounces! And that's not including the weight of a 225 mAh battery pack. It would have been even more weight to hit the indicated glide CG in the plan, but I found that the glide CG of the plan was too far forward, by about 3/4". Now, this is the Zagi LE (EPP leading edge), the much lighter Zagi THL would not have that problem and would of course boost a lot higher and glide better due to the significantly lower weight (but it would sacrifice some robustness, this thing is so hard to throw that I've crashed it at least 8 times, 4 of which would have severely damaged any other kind of model).

Launching it is not hard, at least if you have a C-rail. I glued "H" cross-section Plastruct to the bottom and use the same C-rail that I flew the SkyDart off of. Sure, I have the adjustable glider tower but one thing the glider tower assumes is there's a fuselage, somewhere, to keep yaw alignment and no such thing here.

I launched it at an angle of around 45 to 60 degrees. However, it does teeter-totter when on the rail. So, to keep the wings level, a couple of dowels were laid under the outer wings, to keep them level (added eraser tips to the dowel tips so the dowels would not slide off the wing bottoms easily). The dowels only have to hold the wings level for ignition, once it starts to move the model keep the wings level as it leaves the rail.

Basically I feel like this about the Zagi. A simpler, easier, and cheaper alternative to having a "Phoenix". Same span range, mass range, and different look. Does aerobatics. Not exactly the same Aerobatics that Phoenix is capable of, but then there's some things this could do better than Phoenix (for semi-obvious reasons, Zagi can pull tighter radius pitch maneuvers). I'm not really an aerobatics flier myself, but I like to play around with it at times. And never have flown aerobatics with a Phoenix, got to test-pilot a Phoenix 3-4 flights and that's all.

- George Gassaway

Model Status as of 2008: Mothballed, waiting for a good opportunity to fly it a few more times.