Facetmobile (oz16554)

 

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I spent a couple of weeks building one of these last autumn [main pic, 005] . I had seen someone achieving reasonable flights on Facebook so I assumed I would at least be rewarded by some sort of performance as it’s certainly light enough . Considering it is a delta one could have expected a modicum of stability but it was hopeless and worse unpredictable. There is no doubt that the designer, a Grumman employee, was talented but it cannot be claimed that the full size has caught on . This could be because one has to climb in from underneath (the opening of any top glazing in flight would cause a catastrophic loss of lift, and as like Concord the promised low speed approach has to be achieved by adopting a steep angle of attack the contraption has to be landed by peering through the floor!
I look forward to being corrected but only by successful builders please.
Richard Falconer - 04/02/2026
Hi Richard
I think I saw Chris Strachan flying one successfully a few years ago. I had never heard of it but it was going well, without any drama.
bill dennis - 06/02/2026
I do have some experience with this model, not all that good. I was selected to test fly one built by a friend, a bigger version of this model but still small and electric powered. It wallered (that's a technical term) side to side most of the flight and never seemed to be much under control, elevons in the back. We tried a bunch of adjustments, never quite made it fly in a reasonable manner. We considered it pretty much a failure.
doug smith - 06/02/2026
I think the term ‘wallered’ is a perfect technical description.
Richard Falconer - 06/02/2026
Full marks to Chris Strachan then!
bill dennis - 07/02/2026
I'm very curious as to the flight test card used by anyone who finds this model unstable.
It's a common complaint about this model, but not about larger RC versions, which in Youtube videos, fly well, just like the full size airplane:
https://youtu.be/44kDq_PXvro
the full size FMX-4 was stable about all axes in slow flight, although there was a certain amount of drumming on the skin at very high alpha as the vortex spilled over the LE.
I'm wondering what is happening here. Is the vortex lift phenomenon, so forceful at full scale, just as forceful here, but with a different effect because the airframe at small scale is somehow different ?
My first guess is scale effects. Re ? but how ? I doubt the answer is found in the Re, because the amount of lift seems to be the same: the airplane flies slowly at small scale without stalling.
What other scale effects could be causing this model to fly so poorly ?
Perhaps the wing loading and weight distribution combined with very low speed means the wingtips have so little mass that once there is any difference at all in the vortex lift on the left vs. the right side, you have uncommanded roll which is then damped by the planform's inherent stability. Then the process starts all over again on the opposite side.
I wonder if the solution is Adding wing tip weights , and then something on the nose to regain the proper CG. Or dividing up the nose weight given on the plan so, e.g., 10% on each wing tip, and 80% on the nose. That way the required lift doesn't change.
Wainfan's explanation of the flight characteristics and performance (If I follow him ) tells me that this airframe is capable of carrying a much larger percent of empty weight as cargo than the usual 'tube with wings' layout. So maybe higher wing loading , distributed correctly, will fix the problem.
[ scratches head ]
Bruce H McCaskey - 06/05/2026
hmmm... and have you actually built the model, Bruce?
SteveWMD - 06/05/2026
Here's video of a Peanut scale Facetmobile that flies very well. The builder rigged right thrust and left rudder, and explains in detail his mods.
https://youtu.be/wWaBCViGU5A
Bruce H McCaskey - 07/05/2026
Hi again Bruce. A while back, I was asking if you'd actually built this model. You never answered.
SteveWMD - 19/05/2026
Thinking about the failure we had with our Facetmobile, oscillating in roll no matter what we tried, maybe it has to do with the ultra short wingspan, typical of such designs. I think back to the Flying Flag I built years ago, which certainly qualifies as short, 5 feet long but 3 feet wide. It had the same fault, unsteady in roll, more so when slowed down for landing. It also was extremely tail heavy, even when balanced exactly as per the plans. I had to add 3 POUNDS of lead to the nose to make it fly. But it had no nose, so the best place for lead was on the wingtip landing gear. Much better, but the flopping from side to side was not helped, maybe even a bit worse. I decided to just let it be, with the tail heaviness cured it flew OK most of the time. It usually landed on one wingtip wheel, then the other, in the middle of a flop. My ultra reliable K&B 61 never let me down. I blamed it all on the short wingspan.
doug smith - 20/05/2026
More likely, the builder of the failed model didn't exactly duplicate the exact angles and shapes of the real thing. Barnaby Wainfan designed the real thing exactly the way it needed to be. Any alterations would send the model off into aerodynamic no-man's-land.
DB - 20/05/2026
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