Wright Stuff C

Airco2020
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Re: Wright Stuff C

Post by Airco2020 » January 13th, 2020, 10:24 am

I've been having Coach Chuck withdrawal! Glad you're still out there!

coachchuckaahs
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Re: Wright Stuff C

Post by coachchuckaahs » 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
Coach, Albuquerque Area Home Schoolers Flying Events
Nationals Results:
2016 C WS 8th place
2018 B WS 2nd place
2018 C Heli Champion
2019 B ELG 3rd place
2019 C WS Champion
AMA Results: 3 AAHS members qualify for US Jr Team in F1D, 4 new youth senior records

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Re: Wright Stuff C

Post by Airco2020 » January 13th, 2020, 8:52 pm

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
We appreciate all your help. Cheering your F1D team on from afar!

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Re: Wright Stuff C

Post by calgoddard » 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.

izzanom
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Re: Wright Stuff C

Post by izzanom » 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?

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Re: Wright Stuff C

Post by CrayolaCrayon » January 14th, 2020, 9:03 am

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?
Sounds like a CG + Trim problem. Maybe move ballast farther forward and increase incidence?
Wright Stuff 2nd 2019 Nationals
USA F1D Team 2020 Image
1391 Turns

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Re: Wright Stuff C

Post by coachchuckaahs » January 14th, 2020, 11:50 am

I agree in part with Andrew (Crayola). It appears that your trim is not optimal. However, it appears to me that the plane is likely nose-heavy (or insufficient decalage).

It is IMPORTANT to trim the plane for cruise and letdown, not for climb. Basic trim should be for a level or maybe slight nose-up attitude as rubber winds down. We fly with a low torque wind, usually about half the total expected winds, and observe the flight. We increase incidence or move the cg rearward until the plane begins to exhibit some stall, then adjust back just enough to remove the int of stall.

This condition can be reached in numerous combinations of decalage and CG. Basically, as you move CG forward, you need to add decalage (wing incidence or tail negative incidence). A further forward CG with more decalage has more stability (recovery form hits), but more drag. So there is an optimum that will be clear from your stopwatch. In this year's plane, I would be looking for wing incidence between 3 and 5 mm, with level stab.

Once cruise/letdown is good, do not further adjust the basic trim setup! Adjust your climb with rubber selection, prop selection, torque, and wing wash (and possibly rudder deflection). After each of these changes, be sure to verify the cruise/letdown performance.

In your case, try adding incidence or moving CG back until the late flight behaves. If this causes a power stall on climbing, adjust wing wash and rudder to compensate.

Coach Chuck
Coach, Albuquerque Area Home Schoolers Flying Events
Nationals Results:
2016 C WS 8th place
2018 B WS 2nd place
2018 C Heli Champion
2019 B ELG 3rd place
2019 C WS Champion
AMA Results: 3 AAHS members qualify for US Jr Team in F1D, 4 new youth senior records

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Re: Wright Stuff C

Post by Airco2020 » January 14th, 2020, 2:07 pm

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.
Thanks for the feedback. I appreciate all the help on the forum!

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Re: Wright Stuff C

Post by scioly2345 » January 15th, 2020, 6:07 am

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.”
2016-2019 Brother Joseph Fox Latin School
2020-2022 Kellenberg Memorial High School
2020 events - Boomilever, Disease Detectives, Write It Do It, Wright Stuff
God Bless and Rest In Peace Len Joeris (Balsa Man)
“for the betterment of science”

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Re: Wright Stuff C

Post by jander14indoor » January 15th, 2020, 8:23 am

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.”
When the plane is finished, weigh it (without rubber, but otherwise complete). It should be under the 8 gm rule minimum.
Add enough clay (ballast) to the very front of the plane to bring it up to 8 gm. If your plane is MORE than 8 gm, consider rebuilding. Add no ballast! Weight is EVIL in Wright Stuff. Well, if it is your first plane and under 10 gm, you can still use it to learn things while you build a lighter plane.
Move the wing so the plane balances level about half way between the front and rear edges of the wing at the motor stick. Maybe slightly further back. Typically we describe this position as a percentage of the distance between the front and rear edges of the wing (chord) at the fuselage (root) measured from the leading edge of the wing.
At this point wing should be level. Adjust stab incidence so the plane flies slightly nose high during the cruise portion of the flight. Cruise portion is the flattish portion of the rubber torque curve. Typically between say 20 and 80% of max breaking winds.

Jeff Anderson
Livonia, MI

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