Wright Stuff C

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xiangyu
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Re: Wright Stuff C

Postby xiangyu » November 13th, 2019, 7:33 am

Xiangyu,

Sounds good. If you send more flight details it will help analysis too. Besides measured CG location, wing incidence, rudder deflection, upper and lower wing washin; also send rubber weight and loop length (length before winding), max turns, max torque, backoff turns, launch torque, circle size and propeller pitch angle (probably measured at the 1” radius, both blades).

Brian T
Sounds good, thanks!
2020 Events: Wright Stuff, Gravity Vehicle. Machines, Circuit Lab, Boomilever, Ping-Pong Parachute, WIDI

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FranklinHung
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Re: Wright Stuff C

Postby FranklinHung » November 15th, 2019, 12:30 pm

Hey guys!

Does anyone have the problem where the rubber band randomly falls off in the middle of flight? The plane would be in the middle of a good flight when the rubber band come loose off the propellors shaft and cause the flight to come to a early end. This problem only occurs when im using o rings. If o rings are the issue, what kinds do you recommend to use?

Thanks!

Franklin Hung
Cypress Woods High School 22'

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CrayolaCrayon
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Re: Wright Stuff C

Postby CrayolaCrayon » November 15th, 2019, 1:29 pm

Hey guys!

Does anyone have the problem where the rubber band randomly falls off in the middle of flight? The plane would be in the middle of a good flight when the rubber band come loose off the propellors shaft and cause the flight to come to a early end. This problem only occurs when im using o rings. If o rings are the issue, what kinds do you recommend to use?

Thanks!

Franklin Hung
Your rubberband sounds like it isn't optimal; how secure is your prop hook? Which end is it falling off?

Edit: I'd go with what BJT mentioned below; at the most recent invitational I was at, there was a LOT of deadsticking up at the top.
Higher RPMs are definitely something to get used to this year. Get the turns in; it's important!
Last edited by CrayolaCrayon on November 15th, 2019, 6:24 pm, edited 2 times in total.
Wright Stuff National Runner-up 2019
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bjt4888
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Re: Wright Stuff C

Postby bjt4888 » November 15th, 2019, 4:37 pm

Franklin,

You might also consider that the motor is probably not optimal for the prop and airplane. If you are still in the air when the motor runs out of turns, possible changes would be: thinner motor, longer motor, more propeller pitch or different propeller design.

All of these changes will potentially increase flight duration. A typical number of turns to have remaining upon landing would be equal to backoff turns. For example, if backing off 200 turns to fly under your particular ceiling height, 200 turns would remain on the motor upon landing. Of course, this year’s rules create an airplane that is very non-typical, so test a lot of combinations of the above (and more) specifications and keep detailed data logs.

Good luck and have fun,

Brian T

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Re: Wright Stuff C

Postby lechassin » November 16th, 2019, 5:58 am



at the most recent invitational I was at...
WHAT WERE THE TIMES???!!! (Sorry for yelling ;) )

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Re: Wright Stuff C

Postby CrayolaCrayon » November 16th, 2019, 7:21 am



at the most recent invitational I was at...
WHAT WERE THE TIMES???!!! (Sorry for yelling ;) )


The room was drafty, and these planes were almost killed by drafts with that small stab. Times aren't really relevant at that point.
Wright Stuff National Runner-up 2019
USA F1D Team 2020

lechassin
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Re: Wright Stuff C

Postby lechassin » November 16th, 2019, 9:20 am

I hear you about the vents. We were concerned about that even before the HVAC was turned on so we tried to incorporate as much extra stability into the plane as we could.

See here at 1'27" into the flight: https://www.youtube.com/watch?v=rt8HQGQ ... e=youtu.be
The plane flies directly under a vent (2nd time in the flight) and gets blown down about 5 feet, but stays stable. I think the flight would have been over 1'50" without the HVAC.

We compensated for the small stabilizer with a very long tail moment (5x wing chord, 40cm), which I think is longer than the kits that are out this year. In order to avoid nose weight, we endure two compromises: The tail boom, tail feathers, and rudder trim mechanism are minimal and they need TLC in use and in storage. Also, the nose moment is very long. That does have the advantage of supporting a very long motor without risking it falling off mid-flight. The downsides are that the motor stick is whopping 18" long and we need to judiciously taper it to avoid going over the 8 gram minimum, plus the mid-point of the motor is not on the CG so we need to re-balance the plane with each change in motor weight.

I don't think it would be difficult to modify a kit accordingly. HVAC is an unavoidable inconvenience in many parts of the country, and I suspect the kits were designed in the late Summer when HVAC wasn't a problem.

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Re: Wright Stuff C

Postby FranklinHung » November 17th, 2019, 4:40 am

Hey guys!

I don't think you fully understood my problem. The rubber band isn't landing with out winds. Rather, in mid flight, the rubber band would slip off the front propeller assembly and then only leave the other side keeping it on the plane. This would cause the plane to lose a substantial amount of time.

Thanks!

Franklin
Cypress Woods High School 22'

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Re: Wright Stuff C

Postby CrayolaCrayon » November 17th, 2019, 5:44 am

Hey guys!

I don't think you fully understood my problem. The rubber band isn't landing with out winds. Rather, in mid flight, the rubber band would slip off the front propeller assembly and then only leave the other side keeping it on the plane. This would cause the plane to lose a substantial amount of time.

Thanks!

Franklin
What does your prop hook look like?
Wright Stuff National Runner-up 2019
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lechassin
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Re: Wright Stuff C

Postby lechassin » November 17th, 2019, 5:59 am

Most likely, the motor is too long or the motor stick is too short. As the motor unwinds, it doesn't maintain enough tension to stay on.

I read somewhere that this is a problem as the motor gets to be about twice as long as the motor stick. In support of that estimate, our motors are 33 inches long on an 18" motor stick and the motor will sometimes fall off just as the plane is landing.

The small props this year mandate long thin motors, it sounds like you've noticed that. A long motor stick that is rigid enough and not too heavy is one of the challenges we encountered. We make the motor stick after everything else and we make it as long as possible to end up just under 8.0 grams (minimal ballast). We moved the wing to adjust the CG.

We settled on a 18" piece of firm 1/4"x3/32" balsa that we taper to 1/8"x3/32" at the tips (there's less bending moment at the tips). To illustrate how close we cut it: when we carry a loaded plane, we have to hold it level or the weight of the tail plus the tension on the motor stick will cause the plane to bow sideways. Just moving up to a 1/4"x1/8" motor stick to prevent that put us over 8 grams.

I agree also be sure the hook itself isn't shallow or twisted, which can aggravate things.


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