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ElectricFlight J


ohn Krouse has coined the term TCFF (Throttle Controlled Free Flight) to describe his use of a radio to control the electric motor on a freeflight with fixed control surfaces. When flying in a gym it’s nice to be able to cut the motor before the model hits the rafters and possibly hangs up. It is also quite useful to adjust the throttle to limit excessive power and unstable flight. We have found that if the model is trimmed for a turn with side thrust adjustment, the size of the circle be- comes a function of throttle setting. In the extreme case it can be made to turn one way under power, the opposite direction in glide, thus achieving a pseudo directional control.


Outdoors, we take the TCFF concept one step further by hooking up a dethermalizer servo to the receiver. It’s still freeflight since no trim changes are made. You want a re- ceiver with a fifth channel output for this. The gear switch on the transmitter is ideal for this DT control. The Flying Aces Club frowns on this for competition, but it’s great for trimming as detailed below. And that DT is a real safety factor if you hook a thermal while trimming or sport flying. To make the model legal for FAC Power Scale or Oldtime Gas Replica simply replace the receiver with a timer with speed and DT control. Now a few words about trimming an elec- tric freeflight model. An electric scale freeflight model requires less power than the same plane flown as an R/C model. Too much power results in an unrealistic flight pat- tern; indeed, given enough power, any model or full scale aircraft will go unstable. I be- lieve a scale freeflight model should have a gentle climb that replicates the performance of the full scale airplane, not the rocket-like ascent of a contest model like an E-36. R/C


by stew meyers You can reach Stew Meyers at 8304 Whitman Drive, Bethesda, Maryland 20817, or via e-mail at stew.meyers@verizon.net


PHOTOGRAPHY: STEW MEYERS


Yes, there really was a radial engine Cub, the J-3P equipped with a Lenape Papoose 3-cylinder radial engine. Brian Allen flew this fine example at one of the local events. It was not bothered by the wind.


models can handle more power as they can be throttled back, and the excess power can be momentarily applied when required to ex- tricate the model from hairy situations. That being said, the ParkZone J-3 or P-51 motor is suitable for a larger freeflight mod- el than the R/C model it was salvaged from. Furthermore the wing loading of the freeflight model should be less resulting in lower kinetic energy to cope with when it arrives back to earth without a pilot to flair for landing. This again argues for a larger model.


A scale freeflight model, regardless of the power system, is first trimmed for the glide condition.


With rubber power, further


flights are made increasing the number of turns put in the motor and therefore the power available, while adjusting the thrust alignment, mostly down thrust to avoid power stalls. Not so easy to do for a freeflight electric power model unless your timer has a throttle function. A modern electric power system with Li- Pos demands a timer. Without one, the mo- tor will run until your model is well out of


A BMJR Mini DakotaTCFF model (above left) with a J-3 motor and Emberprop. This was originally designed around a Mirco-4 and Ni-Cds which weighed 24 grams. The new J-3 motor, receiver, and Li-Po system weighs 8.5 grams. Here


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(above right) you see the receiver and battery. Stew had planned to stick the battery in the open hatch, but the c.g. forced him to mount it under the nose with a rubber band. One drawback of a light motor.


JULY 2013


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