Scioly.org

coachchuckaahs wrote: ↑January 13th, 2020, 7:59 pm Thanks Airco! Been busy with grandchildren over Christmas (my 4 year old built a Delta Dart), racing r/c planes, and managing builds and travel plans for the F1D team. SO had been on slow burn this year!

I am also trying to remotely help some NM schools struggling to trim their planes.

Coach Chuck

izzanom wrote: ↑January 14th, 2020, 6:58 am Hi guys, I've been trying to make my plane fly right and am running into a problem. It rises fine but once it starts descending its nose dips and starts falling fairly quickly in a smaller circle (almost like spiraling down but not that extreme). I've tried a variety of things but can't seem to figure out what is causing this. Does anyone have a guess?

calgoddard wrote: ↑January 14th, 2020, 6:21 am This post analyzes the potential use of a gearbox in a WS 2020 airplane which has been discussed previously in this thread. The primary goal of using a gearbox would presumably be more efficient use of the energy stored in the rubber motor given the tiny propeller dictated by the WS 2020 rules.

Any mechanical system with moving parts has friction. This friction converts part of the energy input into heat that is dissipated into the surroundings environment. A basic gearbox consists of gears (simple or planetary), shafts and bearings. The efficiency of a gearbox depends mainly on the efficiency of the gear mesh and the bearings.

Gearboxes have been used in rubber powered airplanes but primarily in small scale models with short nose moments such as a Piper Cub. In such models the weight of the gearbox replaces the ballast otherwise needed to achieve an optimum CG. In a scale rubber powered model airplane, a speed increasing gearbox allows a wider and shorter rubber motor to be utilized to spin a smaller, and therefore more realistic propeller at a relatively high RPM.

Expect losses of at least 15-20% in overall efficiency when using a gearbox in a rubber powered airplane. One advantage of a smaller, faster spinning propeller is that it reduces the torque roll that would otherwise have to be counteracted with a larger propeller.

Use of a speed increasing gearbox in a WS 2020 airplane would enable a configuration with a shorter motor stick to be utilized. However, the motor stick would have to be stronger and therefore typically heavier (per inch of length) in order to resist motor stick bending due to the wider rubber motor used with a speed increasing gearbox. Very lightweight precision plastic gears and metal shafts would be needed and would have to be assembled in a lightweight precision frame or housing. If mounted at the front of an airplane, a lightweight gearbox would be prone to breakage from head-on crashes of the model into a beam, a light fixture, or a wall. Therefore, an indoor endurance rubber powered stick model airplane with a delicate gearbox would preferably have a pusher configuration. However, it is well established in the rubber powered free flight hobby that a tractor configuration (propeller in front) is more efficient than a pusher configuration (propeller in back).

Gym time available for flying indoor rubber powered airplanes is almost always very limited. Therefore, students should not waste it experimenting with concepts that are unlikely to yield beneficial results. Use of a propeller with more blade area than a cut-down Ikara propeller would be a more fruitful area for experimentation with a WS 2020 airplane than use of a gearbox.

Pay particular attention to the recommendations in the posts by Brian T, Coach Chuck, and Jeff Anderson. They contain very helpful advice from experts. I hope you find this post to be useful. Good luck to all you students at your competitions. PS - Use a check list when competing, as has been recommended.

scioly2345 wrote: Could somebody break this down for me into more general terms? I’m very new to WS lol (It’s from the Josh Finn kit):
“Please note: we now recommend adding all ballast required for the 8g minimum weight to the nose, then balancing the model at 50-55% of root chord by sliding the wing forward. Add stab incidence as required to achieve a slightly nose high cruise.”