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This thread is privately moderated by VicT, who may elect to delete unwanted replies.
Mar 14, 2019, 01:38 AM
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Turbo Timber motor glider: initial testing successful

As an experiment I want to see how the TT would perform as a motorglider but still retain the sportplane qualities. I removed the stock landing gear and installed the Valiant 1.2 gear which saves about .7 oz but is about half the area drag. I installed the Aerostar 60 amp ESC and activated the prop brake. With 10/6 folding blades on a 55 mm B+B aluminum spinner and 2200 4S she pulls 33 amps and 470 watts. She pulls very strongly.

The flight test was successful and I am pleased with the performance of the folding prop and Valiant landing gear. There is enough thrust on the smaller prop to maintain full up elevator (in SAFE Self Level) and climb at a near vertical pitch angle. At 200-400 ft with the motor stopped and flaps retracted she has a much better L/D glide ratio. Driftdown times are increased so that with 2:42 minutes of power used there was a 9:21 flight. There was 45 percent remaining on the 3200 4S 40C Kinexsis lipo pack so total flight time can be extended. However the style of flying is different than most flyers in my club.

The motor glider uses the motor to climb and glide. The glide can be slow or fast depending upon thermal and lift activity. On my test flight it was around sunset so wind and lift was scarce. However on sunny days between 10-2 lift is usually enough to maintain altitude and depending upon wing loading increase or climb. Iíll be comparing her to more dedicated foamy motor gliders like my Conscendo, Calypso, Radian Pro, Radian, Heron, Cularis, and Funter motor gliders.

Foamy motor gliders can pick up speed in a shallow dive but they donít carry that speed much when pulling out from a dive. An exception would be the V900 foamy 125 mph pylon style foamy. This is also a function of wing loading and drag. A composite fiberglass and ply wood covered foam wing motor glider is capable of diving at 125 mph and keeping much of that speed through at least one large loop. Iíll be further testing Timber to see if that can be done. Iím happy that I can put Timber in a full down (SAFE On) dive and pull up elevator at about 10 ft and wings donít flex. The speed is much more than the stock configuration and although I was expecting some whistling sounds but Timber is pretty quiet. Iíll have to have some clubmembers radar her but I estimate max dive speed is about 60-70. No wing oscillation was noticed so no need to put a V900 receiver in with itís 125 mph gyro gain programming.

Valiant gear is retained with balsa sides and fore/aft hard wood blocks. A swivel lever can be moved 90 degrees out of the way so the gear can be removed for flight or for storage/transportation. I made some rough landings and higher speed landings to test the strength of the gear mounting and no problems were seen. I may use screws or bolts for a stronger attachment but until then I will continue to use this plug in no bolt landing gear design. There is definitely half the frontal area of the Valiant gear compared to the stock Timber gear. This definitely helps in glide and dive performance.

Initially I was going to put the largest prop on that would pull just under 50-60 amps. However Iím happy with this low power set up with a 4S pack drawing 33 amps. Maybe in the future I willl experiment with larger prop but for now I will continue to use the 10/6 blades on the 55mm O.D. Aluminum spinner. I donít think the turbo style intake will be needed and will experiment with a bullit style spinner next. Unfortunately I have not found a folding spinner with a long ďturboĒ style nose. Maybe the stock black spinner can be modified to mount on the middle part yoke and collet style prop shaft adapter.

Ground clearance with the Valiant gear and 10Ē blades is 2.5 inches and is enough for grass take offs. With half flaps she lifted off in about 10 ft wing zero headwind. High speed touchdowns were tested for nose over risk and no pitching was noticed. The lower center of gravity helps in reducing nose over landings. The prop blades being parked flush with the turbo cowl do not pose any risk in prop strikes or prop drag in grass that can cause nose overs and inverted full stop landings like the stock gear causes. Iíll be next testing hand launch and belly landings with the gear removed. Clear 3M tape will protect the belly from scratching.

Weight with a 3200 4S 40C Kinexsis lipo pack (302 grams) is 1,717 grams or 60.5 ounces. With 527.3 inches of wing area this figures out to a wing loading of 16.5 ounces/square foot. The Heron foamy motor glider has a wing loading of 12.9 ounces per square foot. I have not seen much of a difference in Timber flaps. With a tight turning plane in a thermal flaps will help but for minimal sink I will have to do more testing. Our club has a 20 second climb and glide informal contest. This will be used to record flaps up and down driftdown times.
Last edited by VicT; Mar 14, 2019 at 11:32 PM. Reason: Flight test report
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Mar 17, 2019, 10:34 AM
Registered User
Looks really good with the Valiant landing gear, I'm not a wheel pants fan but they compliment the overall look and I'm sure are functional when gliding. Nice clean work!
Yesterday, 01:28 PM
weniger, aber besser
austntexan's Avatar
I really do not like the battery bay on my Turbo Timber. What do you figure is the design reason for situating it in such a cumbersome location with very little space to affect the CG with a larger than 2200 4S LiPo. I much prefer your mod on the hatch. That is exactly how the UMX Timber is designed and the Multiplex FunCub. You simply remove the hatch to place the battery inside. No fuss at all. If one doesn't have a cradle handing, changing the battery on any of the Timbers is an irritating process at times. Do you have any pics of your process of cutting the cabin LiPo latch in?

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