Wright Stuff C

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coachchuckaahs
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Re: Wright Stuff C

Post by coachchuckaahs »

xiangyu wrote: February 27th, 2020, 7:18 pm
coachchuckaahs wrote: February 27th, 2020, 6:26 pm Remember, the regular Ikara. Is cut down, so the pitch would be higher to match larger diameter. Probably want to re pitch to around 2.0 P/D, then vary from there. Probably between that and 1.5, but we are not using those props, so you need to test.

We are generally between 30 and 40 degrees at 1"radius, but the pitch is definitely specific to the prop planform. I've seen some much higher, some much lower, depends on prop.

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Huh, I didn't realize that :lol:. Well, it's been working so I never really thought about it.

Thanks for the new insight.

In terms of increasing flight times, what should I try next? My propeller I have rn is pretty much matched up to the rubber and I can fly consistent 1:35-1:40 or 1:50 probably if I "risk wind". Also, I am currently using a 39 inch rubber loop and ending up with very little winds when the plane lands. If I keep increasing the length of the loop (which would pack more winds), what might happen, would it keep increasing my flight time until the extra weight of the long rubber outweighs the power from the extra winds? (I'll be testing by experiment this weekend, but just curious atm)

Xiangyu
Pretty much what you do! Optimize. Adjust in one direction until the result tend reverses. But remember, it is multi variable optimization. Rubber width, rubber length (or mass), prop pitch, prop planform, etc.

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Re: Wright Stuff C

Post by scioly2345 »

Hi,

So I have rubber right now that’s 1.5 x the length of my hook to hook distance (josh Finn kit so the hook to hook distance is smaller than freedom flight hook to hook) and it won’t go more than 1500 turns without breaking the rubber, so should I elongate the rubber a few inches or should I go up or down in rubber size? I don’t know the rubber size in decimal but in fraction it’s 1/16 by 3/32 and right now about 20 inches which is a little more than 1.5x my hook to hook distance. My center of gravity is good but I only get around 30 second flights because the turns run out. I don’t know what to do since I think the length of my rubber is appropriate yet it runs out of winds and I can’t seem to put in anymore.

Thanks,
2345
Last edited by scioly2345 on February 28th, 2020, 7:45 am, edited 1 time in total.
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Re: Wright Stuff C

Post by vehicleguy »

Yesterday I began flying with a torque meter, and I noticed something odd happening. I would wind up my plane, note the torque, and when I launched, it would run out of winds by the time it came down. I kept on repeating this process with that same rubber band and I was able to improve my times. Then, I switched to a longer rubber band (same thickness as the last one, both .65) and put a lot of winds into it (around 200). I winded back to the torque of the previous launches with the old rubberband, and it actually didn't go up nearly as high, but it still stayed aloft for the same amount of time (also had plenty of winds left). I kept on raising my torque and the plane would not climb for the life of me. I'm not sure if I have to just raise the wing post or if there is other action I have to take. Any suggestions?
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Re: Wright Stuff C

Post by jsegal »

So in this case I would either increase the pitch of the propeller or use thicker rubber .072 inch because it seems that your plane is producing too much drag for you use longer .065 rubber.
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Re: Wright Stuff C

Post by CookiePie1 »

If I had a 12 in long motor and a 24 in long motor with the same width and density and everything, would they break at the same torque? Like, is it possible to measure the breaking torque of a certain motor by using a shorter piece of the same rubber?
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Re: Wright Stuff C

Post by coachchuckaahs »

CookiePie1 wrote: February 28th, 2020, 8:45 am If I had a 12 in long motor and a 24 in long motor with the same width and density and everything, would they break at the same torque? Like, is it possible to measure the breaking torque of a certain motor by using a shorter piece of the same rubber?
Yes. Torque does not depend on length. It should take twice as many winds to get to breaking on rubber that is twice as long, but torque should be the same.

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Re: Wright Stuff C

Post by CookiePie1 »

coachchuckaahs wrote: February 28th, 2020, 8:56 am
CookiePie1 wrote: February 28th, 2020, 8:45 am If I had a 12 in long motor and a 24 in long motor with the same width and density and everything, would they break at the same torque? Like, is it possible to measure the breaking torque of a certain motor by using a shorter piece of the same rubber?
Yes. Torque does not depend on length. It should take twice as many winds to get to breaking on rubber that is twice as long, but torque should be the same.

Coach Chuck
thanks!
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Re: Wright Stuff C

Post by coachchuckaahs »

scioly2345 wrote: February 28th, 2020, 5:55 am Hi,

So I have rubber right now that’s 1.5 x the length of my hook to hook distance (josh Finn kit so the hook to hook distance is smaller than freedom flight hook to hook) and it won’t go more than 1500 turns without breaking the rubber, so should I elongate the rubber a few inches or should I go up or down in rubber size? I don’t know the rubber size in decimal but in fraction it’s 1/16 by 3/32 and right now about 20 inches which is a little more than 1.5x my hook to hook distance. My center of gravity is good but I only get around 30 second flights because the turns run out. I don’t know what to do since I think the length of my rubber is appropriate yet it runs out of winds and I can’t seem to put in anymore.

Thanks,
2345
If your rubber is running out, then your rubber is too wide for your prop. In most past planes, and generally indoor flying, a "balanced" flight has as many turns remaining at the end of your flight as you backed off when winding. I am not certain this holds for the tiny props. We competed at State with the rubber just running out as the plane touched down. However, since we had to back off quite a bit at the launch, I suspect that this was not optimum. We were on a new prop and had not yet optimized the rubber to the prop.

Rather than trying to determine the rubber "width", it is best to speak in terms of grams/inch (linear density). This is proportional to rubber cross sectional area (assuming constant volumetric density), and is a better representation of the power and energy available in the wound rubber. Better meaning more consistent. Probably the simplest way to characterize your loop is the mass of the tied loop, and the length of the relaxed loop BEFORE any winding has occurred (it will relax longer the more it is used). We find this more consistent than g/in. For example, in LPP, we are using 1.5g loops (to make it compatible with F1M as well), and we have loops anywhere form 35 to 40 cm for low ceilings. Half cm changes in loop size have notable impacts on the stopwatch! You will find more variation than this in a package of, say, 0.065" wide rubber.

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Re: Wright Stuff C

Post by coachchuckaahs »

vehicleguy wrote: February 28th, 2020, 7:23 am Yesterday I began flying with a torque meter, and I noticed something odd happening. I would wind up my plane, note the torque, and when I launched, it would run out of winds by the time it came down. I kept on repeating this process with that same rubber band and I was able to improve my times. Then, I switched to a longer rubber band (same thickness as the last one, both .65) and put a lot of winds into it (around 200). I winded back to the torque of the previous launches with the old rubberband, and it actually didn't go up nearly as high, but it still stayed aloft for the same amount of time (also had plenty of winds left). I kept on raising my torque and the plane would not climb for the life of me. I'm not sure if I have to just raise the wing post or if there is other action I have to take. Any suggestions?
On your first comment, two things. If it is running out before it comes down, you need thinner rubber or more load on your prop. You got better times each flight as the rubber further broke in, allowing more winds and dispensing these winds at slightly lower torque (acting like slightly thinner rubber). So you need to match your rubber and prop so that you do not run out of winds. That is the key optimization of any indoor rubber duration event.

It is likely that the new rubber, not as broken in, has higher initial torque. And I mean the whole initial burn, not just the moment of launch. Then, as you noted, you increased the torque and the plane did not climb higher. Two possible causes. First, if you have a "flaring" style prop, it may twist to an inefficient state at higher torque. Our findings so far is that flaring props are not working this year, because at this small size the centripetal acceleration overcomes aero loading, and the props are actually going to less pitch at high torque. If you can actually get more pitch at higher torque, then you need to tune the stiffness of the flare because over-flaring will overly limit the climb. But in our testing, we have not yet seen a positive flare.

The second possibility is that your plane is not trimmed for high torque. You do not mention the type of plane, CG, wash in, decalage, etc, nor the character of the climb. Because of the small stab and the very limited stability, many planes will roll in excessively at high torque, racing in a circle rather than climbing. This gets worse with higher torque, and the plane never climbs, or even goes downward. This can be addressed with wash-in on the inboard wing(s). Too much wash and the plane will power stall. A little goes a long way. It can also be addressed with wing offset.

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Re: Wright Stuff C

Post by sidnb »

Wouldn't the shim prevent nosediving as well as a reduction in the circle radius? For example for a left (clockwise) turn the shim should be positioned such that the right side of the wing has a higher angle of attack, which prevents spiraling inwards.
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