Design

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Toms_42
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Re: Design

Post by Toms_42 » December 11th, 2014, 3:51 pm

jander14indoor wrote:Sorry, not clear, 1200 is a single loop of 0.093 or so rubber. A double loop would never take that many turns and would overpower the plane if wound close to max. Just to make sure when I talk single loop that means there is one loop of rubber resulting in two individual strands running front to back. There is a way to have a single strand front to back, but not particularly useful for WS. Double loop means four strands front to back.

Hook length vs rubber length, just not important as long as you don't get TOO short. Loose hanging rubber is the norm for an unwound motor. Those first few wind (or last few unwind) turns will not provide any meaningful torque however you set the hook to hook length. And by few I mean 50 to 100 or so. Just use 12-14 inches hook to hook on these things and don't sweat it. I've flown some classes where the rules required about a 6-8 inch hook to hook for a 20 inch loop of rubber. Biggest problem with hanging rubber is it falling off or changing the CG unexpectedly.

Suggestion to understand torque vs turns, make up some short test motors and wind them with a torque meter taking data every few turns. Wind the first motor to breaking. Plot it. Wind the next identical motor to just short of breaking and then unwind continuing to take data. Plot it. You'll see why I'm saying the first turns are useless in powering the plane and why you MUST wind to near breaking. Reason and more details discussed previously, dig in the WS archives.

And yes you'll need some sort of lube to hit the turns you need to be competitive. But nothing hard to get.
- I use Armor All (or Son of a Gun) vinyl protectant, the original general purpose stuff, last time I looked there are a lot of specialized formulations. Works fine, I'm on my second bottle after 15 years. And the only reason I bought a new bottle was the old one was just NASTY smelling after 10 years in my flight box. One good spritz and that motor is good for many winds.
- Some folks use the silicone oil from RC car shocks. Also stays on.
- Haven't checked availability lately but there was a free flight supplier who sold a variety of amusingly named rubber lubes, things like Snake Snot, Mongoose Mucus, etc that was basically silicone oil.
- Old school was a mix of glycerin, soap and what not. Works, but not as good as silicone oil and must be reapplied.
- Whatever you do, DON'T use anything petroleum based, will ruin your motor like NOW.

Besides lubricant, you'll need to stretch wind to get those turns. Do some digging through the WS archives for more info on that.

Regards,
Jeff Anderson
Livonia, MI
Is armor all still viable? I read some amazon reviews and it seems they have changed their formula to make it more viscous.

Also, my plane doesn't climb as high as it should, and while it stays level, it kind of drops quickly. I'm using max sized surfaces for everything, and I'm barely over 8g. Should I change the cg, adjust lift, change rubber, or change the prop? (I'm using an ikarus flaring prop at the moment, 2.4g)

Is there a specific order in which you adjust things? i.e. if it dives, should I move cg back first or change the lift first? Likewise if it stalls, should I add downthrust, reduce lift, or move the cg forward? Is there a way to know which type of trimming is necessary?
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artysophia
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Re: Design

Post by artysophia » December 11th, 2014, 5:38 pm

Okay, thanks! I was reading up in the old forums and I noticed a discussion about it whether it is better to wind off or on the plane? Which do you suggest? Also, are "O-rings" recommended or do they add necessary mass?

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Re: Design

Post by Chris_L » December 12th, 2014, 12:32 am

Hi,
I was wondering about where to order/buy the correct wood for wright stuff? And also as to the O-rings, they are very helpful when winding and attaching to the rear hook. And they don't add too significant a mass to the motor.
"A wise man can learn more from a foolish question than a fool can learn from a wise answer." -Bruce Lee

When asked what his IQ was, Stephen Hawking said "I have no idea. People who boast about their IQ are losers"

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Re: Design

Post by Toms_42 » December 12th, 2014, 8:11 am

artysophia wrote:Okay, thanks! I was reading up in the old forums and I noticed a discussion about it whether it is better to wind off or on the plane? Which do you suggest? Also, are "O-rings" recommended or do they add necessary mass?
Definitely off the plane, as if you wind on it you could risk breaking it.
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Re: Design

Post by Toms_42 » December 12th, 2014, 8:15 am

artysophia wrote:Okay, thanks! I was reading up in the old forums and I noticed a discussion about it whether it is better to wind off or on the plane? Which do you suggest? Also, are "O-rings" recommended or do they add necessary mass?
Definitely off the plane, as if you wind on it you could risk breaking it, especially of you use a high ratio winder. This is where small o-rings help, as it's super hard to transfer rubber without them. They add very little mass anyways.
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Re: Design

Post by jander14indoor » December 12th, 2014, 6:34 pm

On or off plane will work, but Toms_42 is right, there is less risk to the plane when you break a motor (and you will if you are doing things right).

O-rings, definitely valuable winding off or on. Yes they add a little weight (not much if you use the right ones, back to that in a moment), but they save turns transferring the motor to the hooks on the plane.

O-rings, we aren't talking plumbing o-rings of any size here. You make your O-rings by cutting slices off semi soft plastic tubing. Tubing can come from ball point pens you've run the ink out of. Bic pens provided perfectly good tubing. Or you can use the suction tubing from a spray bottle. I use tubes about 1/8 to 3/16 diameter, wall thickness in range of 1/32, Cut slices off 1/32 to 1/16 inch long depending on the size of the motor I'm using. Total weight on the order of a couple of a hundredths of a gram. These rings are stiff and don't wind up or collapse when the motor is wound. You put two on a motor. Hook just the ring (not ring and motor or you defeat the purpose) over you winder's hook and the other end on a hook anchored to a heavy table, bleaches, whatever won't move as you stretch wind. Preferably your anchor is a torque meter.

You can't use plumbing o-rings as they are heavy, and soft rubber that just winds up like the motor still trapping the motor on the hook.

Hope that helps,

Jeff Anderson
Livonia, MI

science8
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Re: Design

Post by science8 » December 17th, 2014, 9:11 am

Hi guys,
I am still starting out and am building the freedom flight kit. I am towards the end of construction am confused. When attaching the wing to the wing mount I am confused how to do it. The middle wing riblet goes all the way to the back of the wing.

Essentially the leading edge is no problem when attaching because the riblet is not in the way, but the back part of the rib goes all the way to the trailing edge. Do I glue it on top of the rib or to the left or right side??

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Re: Design

Post by bjt4888 » December 17th, 2014, 6:10 pm

Science8,
My students have constructed seven of these Freedom Flight airplanes so far and I will tell you how we are mounting the wingposts to the wing. You can offset the wingposts slightly to the right of the center rib (maybe against the edge of the rib location if it continued through the LE and actually against the side of the rib at the TE). This will make the left wing panel slightly longer than the right wing panel. As you know, the design already has the left wing 1/2" longer than the right and another 1/16" due to offsetting the wingposts won't matter.

Another design change we have made is to notch the LE and TE about 1/16" deep to accept the wingposts and increase the distance between the wingposts slightly so that they fit into the notches. I also had the students reinforce the wingpost LE and TE joints with a very small triangular gusset (about 1/4" on each edge, right triangle). The notching and fitting of the wingpost doesn't weaken the LE and TE as they are quite wide pieces of wood. The wingpost to LE and TE joint is aligned using a jig and is one of the few joints on the airplane that we bonded with CYA (super glue). All other joints are double glued with thin duco cement.

Good luck, these airplanes fly great!

Brian T.
AMA since 1972 (off and on)
NFFS for a very long time too (off and on)

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Re: Design

Post by artysophia » December 18th, 2014, 5:16 pm

So I noticed that there isn't a limitation in length...what length do you recommend for a plane with a wingspan of 50cm? The model I am currently building has a length of 50cm, but the pictures of other planes I have seen online seem a great deal longer/larger... Also, is a dihedral or wing tips more effective?
I am still a little confused as how to wind the rubber off the plane and transfer/hook it (using O-rings?)

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Re: Design

Post by bjt4888 » December 18th, 2014, 6:59 pm

artysophia,

50 cm airplane length is quite short for a typical design of this wingspan and weight. Not that it wouldn't be possible to build a successful design of this length, but a longer tail moment (wing TE to stabilizer LE distance) allows a more rearward center of gravity and lower decalage angle resulting in lower drag and longer flights. A typical conservative design would be in the neighborhood of a 12" motor stick and a 12" tail boom (or about 61 cm total) with a 1.5" to 2' nose moment arm and about an 16.5" tail moment arm. Some designs are longer than this, like the Freedom Flight kit has a 16" motor stick and an 11.5" tailboom.

Here's a link to a video of an international level competitor winding his rubber motor off of the airplane. His rubber motor is attached to a torque meter. He is taking quite a bit of time to wind as in AMA competitions there is not the 8 minute Science Olympiad flight window. You will want to wind and load the motor to your airplane quicker than this.

https://www.youtube.com/watch?v=xyXeTJno0sI

BJT4888

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