Plane does not use all turns in the rubber motor

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sidda
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Plane does not use all turns in the rubber motor

Post by sidda »

We have a plane built out of a model kit and it reaches 20 ft height and goes around in a circle. When it comes touches down, it still has many turns (over 200) left in the band. The flight time was about a minute. We want to extend the flight time. The plane weighs around 8.3 gms and the rubber band is about 1.7 gms for now. Any thoughts on how to make it stay in the air longer are appreciated. We are using the 15 cms Ikara propeller.

Thanks in advance.

Sidda
jander14indoor
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Re: Plane does not use all turns in the rubber motor

Post by jander14indoor »

I hope you realize that airplane doesn't meet this years rules, you should fix that first if you want representative data and to avoid being tiered at a competition..
Max rubber is 1.5 gm, you are over.
Max prop size is 14.0 cm, you are over.
If those dimensions are wrong I'm a little concerned about the rest of the plane.

Rules say the plane must weight 7.5 gm minimum, OK so far. BUT, physics says your plane is over weight by 10%, that will ultimately cost you almost 20% in max time. A one minute flight is not the max you are capable of with good planes doing more than two minutes. 20% off that says you should be capable of 1:40, so it is not a limit yet. But it will become an important limit eventually.

General comment, in low ceilings (and 20 feet is lowish, and I'm assuming you are near the ceiling with your flights) you almost always land with turns left, even with everything optimized. One goal (but not the prime one) is to minimize them, but don't obsess, you don't have much energy in those first (winding, last unwinding) very low torque winds.

Now, for some constructive suggestions.
Sounds like you basically now have your plane flying. Once you have that, your goal is to optimize trim. Are you flying close to, but not stalling on descent? Are you climbing like a rocket, or slow? You want a slowish climb to the ceiling, a couple of turns near max altitude and a slow descent.

After that, its all about matching prop to rubber to plane. You have to either vary the motor width (which will of course change its length at 1.5 gm max) to match the prop, or vary the prop to match the motor.

Oh, how hard are you winding? What is the width of your current motor.

Thanks,

Jeff Anderson
Livonia, MI
sidda
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Re: Plane does not use all turns in the rubber motor

Post by sidda »

Thank you Jeff.

This is the first plane we got to work correctly. Now we are working on trimming weight of the plane, size of the propeller, and of the motor. Thanks for details on the loss of flight time due to weight. That number was very educational. Our plane climbs slowly to the top and then comes down gradually.

>>Oh, how hard are you winding? What is the width of your current motor.

We wound it to 1500 turns for 0.062" band.We will start lubricating the rubber band as well.

We are going to try out a new plane this week that meets specifications. Thanks for your guidance.

Cheers
jander14indoor
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Re: Plane does not use all turns in the rubber motor

Post by jander14indoor »

With that flight pattern, sounds like you are well trimmed.
I suspect 1500 turns on a 1.5 gm 0.062 motor is not maxed out, you should be able to wind harder. Especially if you have been winding that hard without lube.
If you are reaching the ceiling with that motor and not maxed out, I'd try a SLIGHTLY thinner motor (long enough to stay at 1.5 gm) and wind it harder. to at least the same, or slightly higher launch torque.

Jeff Anderson
Livonia, MI
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