Flight Trimming

calgoddard
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Humidity

Postby calgoddard » Sun Apr 04, 2010 9:47 pm

StampingKid:

You have raised one of the most difficult issues with Wright Stuff. After years of coaching Wright Stuff I eventually realized a major problem but could not get an adequate answer, even from experts with 50 years of indoor rubber powered flying experience.

Here is the problem. You practice for weeks or months in your gym, much of it during the winter. The gym is empty and cold, e.g. 60 degrees F. You keep maticulous records on winds, torque, rubber size, max height, duration, etc. so you can do a no-touch flight at the compeition, i.e. one in which the plane will climb just short of the max ceiling height without ever hitting.

You go to the competition. You launch the plane with a rubber width, torque and winds that should take you just below the ceiling. Instead, the plane rockets to the ceiling and diasaster strikes. The plane crashes into the ceiling a couple of times and you don't get a lucky bouce. Your plane evenetually lands on a light fixture. What happend?

Well the gym is full of students and spectators, and all the lights are on. So the temperature is much higher, e.g. 15 to 20 degrees higher, than when you practiced. The humidity is often different, depending on weather conditions.

All other factors being equal, a Wright Stuff plane can fly as much as 20% longer with a 20 degree increase in the temperature at the flying site. It sounds counter-inutitive because the air is warmer and thinner.

The plane will also climb much more rapidly when the temperature is 20 degrees warmer.

Solution: Your first competition flight is a conservative flight, i.e. you launch your plane with low torque and low winds based on your flight logs. Depending on the max height achieved by your plane during the first lfight, extrapolate to determine the best torque and winds for your second "aggressive" flight that will get your plane close to the ceiling.

Practice flights in the gym where the compeition is held early in the morning on the day of the competition are of little value because the gym has not heated up yet.

I have also heard that high humidity can result in lots of broken motors. This happened at Nationals in D.C. a few years ago. It cost Wright Stuff Monster a medal and he was one of the very best builders and flyers at that competition.

Now as to storing your planes, don't worry about the humidity. If your planes have plastic film wing and stab covering variationa in humidity should not result in warps serious enough to ruin your trim. There may be a small weight gain but not enough to significantly impact your time, and certainly not enough to warrant storing your plane in a Turkey roaster bag and risking damge on removal.

I would be interested in Jeff Anderson's take on how to adjust your motor width, torque and/or winding for different humidity and temperature. When I have asked other experts, they seem unable to give clear guidance on how to effectively deal with this issue. I guess it is a non-issue if you are flying an F1D or Penny Plane airplane in a flying site with a 90 foot ceiling.

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GitItWright
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Re: Flight Trimming

Postby GitItWright » Sun Apr 04, 2010 10:16 pm

On the rubber/humidity issue, one of the greats in indoor flying, the late Pete Andrews felt the best plan on how the rubber will react on a humid/hot or cold/dry contest day was to subject sample motors with a wind to destruction test at the contest. He would then expect that max winds would be 20% less then the point of destruction. He would then wind another to those "new max" winds and record the torque figuring that would be the max torque to expect for that day. Of course, if new a record or a tight win was at hand, he would adjust or "'push the envelope" in both winds and torque.

In fact, the Vaparaiso HS team that won that Wright Stuff event at the 2008 Nationals in Washington D.C. followed this technique and no motors were broken except for the initial test sacrifice.

Good Luck!
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Re: Flight Trimming

Postby jander14indoor » Mon Apr 05, 2010 1:24 am

OK, here's where I get to prove I'm NOT some kind of be-all, know-all expert. I don't have enough experience to have a solid answer to your questions on rubber response to heat and humidity.

GitItWright has a very good approach that SEEMS logical to addressing the question. Certainly seems worth trying. PS, he's also a very experienced coach/flyer in his own right and worth listening to.

In addition to testing a motor in actual conditions, you also need LOTS of data on that flight log to use the info you learn that day from your destructive test. You should be able to find an equivalent thickness rubber from your cool weather testing to extrapolate airplane behavior as to height and torque. But you'll get more turns for that longer flight so MAY have to back off a little.

And to expand on GitItWright's idea of testing the day of the event. Why wait till then? You've got a shower and space heaters, right? Break some of those motors ahead of time. Collect the data ahead of time. Adjust ahead of time. Then the day of the contest, you'll be most of the way there as soon as you know the conditions.

And calgoddard's advice about a first conservative flight is VERY wise. Lock in that good time you know you can do, then go for first place. Many times that good time is enough to win on its own!

I will say, I strongly expect that temperature is the dominant factor on rubber, not humidity. I suspect humidity more strongly affects the wood stiffness of the plane.

And here's an idea. It seems to me there's a 'common' wisdom that you can get better flights at the end of the day than the beginning. But in many years of supervising, I've seen early flights win about as often as late. I've also seen teams fly their planes to destruction on the day of the contest making sure they've wrung every last second out of the site and have to fly on a severely repaired or backup plane, not a recipe for success. Test flying the day of the contest is important. But it should be only enough to understand the drift patterns of that site, tune torque to ceiling, and then go. My opinion anyway.

Just some ideas.

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Re: Flight Trimming

Postby eta150 » Tue Apr 06, 2010 7:44 pm

I was wondering, is it possible for a plane to gain .4g because of humidity? I'm really worried because I replaced my stab, and that coincided with that weight gain. This seems impossible, because the original one was fairly heavy (broken and repaired), and a stab is generally a .4g piece, so it couldn't result in that kind of weight gain.
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Re: Flight Trimming

Postby StampingKid » Wed Apr 07, 2010 1:21 am

Calgoddard, GititWright and Jander, Thanks for the advice. I am on spring break and really looking forward to getting back in the gym. Need to make up competition motors and extras to break.
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Re: Flight Trimming

Postby jcollier » Wed Apr 07, 2010 2:29 pm

eta150 wrote:I was wondering, is it possible for a plane to gain .4g because of humidity? I'm really worried because I replaced my stab, and that coincided with that weight gain. This seems impossible, because the original one was fairly heavy (broken and repaired), and a stab is generally a .4g piece, so it couldn't result in that kind of weight gain.


.4g seems like a lot for humidity, but I suppose it is possible. If you think it is because of the stabilizer, the CG would also be shifted back a good bit, I'd think. The humidity can not only make the plane heavier, but also softer, especially the motor stick. Caused our team some problems last year. Both of my Wright Stuff guys are making new motor sticks to try and stay just a smidge over 7g. for total plane weight, and be stiff enough to let them wind up the motor without causing disaster.

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Re: Flight Trimming

Postby Draylon Fogg » Wed Apr 07, 2010 10:13 pm

eta150 wrote:I was wondering, is it possible for a plane to gain .4g because of humidity? I'm really worried because I replaced my stab, and that coincided with that weight gain. This seems impossible, because the original one was fairly heavy (broken and repaired), and a stab is generally a .4g piece, so it couldn't result in that kind of weight gain.

Also, (and this is going to sound weird) but even though pieces way weigh the same when put together I've noticed that they can sometimes weigh up to .5g difference. (again going to sound weird) It is all in how your pieces interact with each other.
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Re: Flight Trimming

Postby jander14indoor » Thu Apr 08, 2010 1:29 am

I'm sorry, but unless you are converting significant energy (and 0.5 gm of matter is a LOT of energy, we’re talking 10Kt nuclear bomb amounts of energy) to matter (Einstein physics), that just can't happen. At these scales and for these materials Newton applies well enough, conservation of matter is the law not an opinion,.

I can think of two explanations for what you think you observed.
First, you didn't account for glue. If you aren't careful, you can add this much glue to a wing or tail without hardly trying. See other threads for discussion of how to control this.
Second, you are using scales of unknown bias, insufficient accuracy, or insufficient precision. The rounding errors are consistent enough to miss, or the bias is enough to cause significant error on the small parts, but insignificant error on the assembly. Example, your scale weighs parts under size by 0.04 gm. A pretty small error. Ten parts, final assembly calculated to be 1 gram. Actual assembly will measure 1.36 gm on your scale, but weight 1.40!

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Re: Flight Trimming

Postby bd123 » Sat Apr 10, 2010 1:08 am

Does anyone know how to make my plane climb slower in the beggining?

bd123 wrote:My plane initally climbs really fast (while stalling), at a very high angle untill it gets close to the ceiling about 18ft. It then levels out and then decends. Is this normal? I feel that if the ascent is slower it would be better.

My plane is 7.0grams. Around .102 ish rubber, 45(15) winds, 1.4-1.5g. Fairly large wind chord. An ok number of winds left. The front of the wing is 1/8" higher than the back. Center of gravity is around the middle of the wing.

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Re: Flight Trimming

Postby blue cobra » Sat Apr 10, 2010 1:17 am

As rubber unwinds, it starts out with high torque, then it levels out a bit, then it drops again. If you dewind your rubber a few times before you launch, it will decrease torque, and so your plane should climb more slowly. If you do this on a torque meter, I at least have seen that just one dewind can significantly decrease torque. However, do some tests to see if climbing quickly (high launch torque) or climbing slowly (low launch torque) is actually better.
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Re: Flight Trimming

Postby YadoMestor » Sat Apr 10, 2010 3:36 am

If you're looking for a slower ascent without backing off winds and losing flight time, you can try using a "flared" broad style Ikara. The broad blades are soft and will bend or flex back to a higher pitch during the beginning of the flight when the torque is extremely high. The higher pitch will cause a slower ascent and use up winds much slower. Later in the flight, the blades will flex back to the original lower pitch.

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Re: Flight Trimming

Postby jander14indoor » Sat Apr 10, 2010 6:47 pm

Another thing to try is thinner rubber. Modify pitch, probably higher. The other suggestions are good too.

PS, this all assumes you have your plane at ideal trim. If not, you can play with that a little to get it right first then the other suggestions.

Jeff Anderson
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Re: Flight Trimming

Postby Amatuer » Fri Apr 16, 2010 2:12 am

I have a question on my plane. We are flying relatively well, but it seems to be turning in quite a tight circle (about 10 foot diameter). This has been causing quite a bit of problems for us. We are using Ziegler's plane design, thus the tailboom is in a fixed position, making this quite difficult to fix. Do you guys happen to have a solution without adding too much weight?

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Re: Flight Trimming

Postby Littleboy » Fri Apr 16, 2010 10:47 am

I would crack the tailboom and bend it out a little and reglue it.

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Re: Flight Trimming

Postby jcollier » Fri Apr 16, 2010 10:54 am

Amatuer wrote:I have a question on my plane. We are flying relatively well, but it seems to be turning in quite a tight circle (about 10 foot diameter). This has been causing quite a bit of problems for us. We are using Ziegler's plane design, thus the tailboom is in a fixed position, making this quite difficult to fix. Do you guys happen to have a solution without adding too much weight?


You should not need to add weight for that problem. You could carefully twist the tail boom to reduce the stabilizer's lean to the right (from the back of the plane) to see if this helps. If it does, moistening the tail boom piece near the motor stick, adding some twist, and pinning it to let it dry that way could help open the circle. BUT, don't try to make too much of a change until you see the results. Otherwise, I'd suggest carefully cutting off the stab and reglue at a lesser angle. The stab, being so far from the cg, has a big influence on how your plane flies. One reason we like to put both stabs and wings on with posts/paper rolls for adjustment.


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