Flight Times

Flight Times

Postby SMS SO Rules on Sun Jan 10, 2010 1:43 pm

Based on this year's rules what are your best flight times.Our very best time was 2:52 minutes in a small middle school gym. It kept hitting and bouncing off the walls. Scared me and my partner whenever it got close to something. :o
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Re: Flight Times

Postby jander14indoor on Sun Jan 10, 2010 3:02 pm

That's a good time in a small gym. Nationals last year was in a small gym and the winning time was just over three minutes. This years times should be a little longer with the larger tails, but not much. In tall sites (like the field house where this years nationals will most likely be held) 4 minutes should be doable.

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Re: Flight Times

Postby blue cobra on Mon Jan 11, 2010 5:36 pm

I was getting about 2 minutes in a fairly small gym.
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Re: Flight Times

Postby calgoddard on Mon Jan 11, 2010 9:51 pm

Jeff:

The winning time at Nationals in 2005 Division C was reportedly around 7 minutes but with a two gram max motor.

The plane could have 50 x 10 cm main wing but had an 8 gram minium weight as I recall. Bi - planes were allowed, but the experts told our team not to bother with a bi - plane that year, for many reasons. They were right.

Under the 2010 Division B rules, and by extrapolation, I would not be suprised to see someone break five minutes at the 2010 Wright Stuff event at Nationals given the 98 foot ceiling there. Someone will almost assuredly break four minutes.
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Re: Flight Times

Postby calgoddard on Tue Jan 12, 2010 12:43 pm

I forgot to mention that the 2005 Wright Stuff Nationals were held at the University of Illinois, the same place where they will be held in 2010.
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Re: Flight Times

Postby Draylon Fogg on Thu Jan 21, 2010 12:24 am

ok so i am haveing lots of trouble... our current plane is only doing about 1:23 at its best and im really starting to worry... any ideas?
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Re: Flight Times

Postby jander14indoor on Thu Jan 21, 2010 9:18 am

Draylon Fogg wrote:ok so i am haveing lots of trouble... our current plane is only doing about 1:23 at its best and im really starting to worry... any ideas?


Lots of ideas, check the other threads on this bulletin board and last years archive.

But if you can tell us more about your plane and how its flying we can be a lot more specific. Without that, all we can do is repeat advice given in the past on this forum.

Info needed. Design features of the plane, weight, wing size, tail size, prop size and pitch, length between wing and tail, cg location, trim settings. How its flying, what size (width) rubber motor, winds, torque (if you measure it), flight profile (climb, cruise, descent, turn radius (increasing or decreasing through flight)) roll, dutch roll or stalls (different things) height achieved, etc.

Note, 1:23 means the plan is actually flying, so you are well on the way to success. That would win or place at many invitationals. Not all, but many.

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Re: Flight Times

Postby eta150 on Thu Jan 21, 2010 12:49 pm

That would have won our regional last year, and would probably be a top 15 plane anywhere but the "elite" competitions (a couple states and invitationals, and nationals.)
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Re: Flight Times

Postby Draylon Fogg on Thu Jan 21, 2010 10:52 pm

OK so as far as the plane, we have it working but on all of our attempts to get more built I've built them without problem but when it comes to flying they just don't seem to work, i mean when we glide test them they do great but when the rubber band goes on they fly for about two seconds and then nose dive.... Design features of the plane is the basic design of the one you buy on pitsco, weight is approx. 11g, wing size, tail size, prop size,are all the max sizes of the rules and the length between wing and tail is 5 1/2 inches... i know that's pretty vague but I'm at home and the plane is at school.
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Re: Flight Times

Postby jander14indoor on Fri Jan 22, 2010 7:44 am

OK, with that I can help.

First, 11 grams is WAY to heavy, build lighter. Minimum weight is 7 grams and you need to be close to that (within a couple of tenths of a gram) to fly three minutes. Heck, 1:23 with a 11 gram plane is actually pretty good.

Second, BUILD LIGHTER!

OK, first plane flying, but rest not. Same design? Check for trim differences. Are the wing and tail and the same relative angles? Is the center of gravity the same? Are the control settings the same? Are the wing and tail warps the same? Sometimes subtle differences in building can make the 'same' plane fly very different and you have to sort that out during the initial trim sessions.

Flight pattern. Very short flight then dive. Several possible problems.
Are you glide testing with the prop and rubber band? If not, the center of gravity may be shifting when you add the rubber band.
Check the plane before and after installing the wound motor. Does the motor stick bend significantly pulling the tail down? If so you need a stiffer motor stick.
Does the plane first nose up as if trying to climb hard, then fall off and dive? If so you have a power stall, need some down thrust in your prop mount.


Plane design:
There is no such thing as a max SIZE wing, only a max span. The rules limit span to 40 cm, but no limit on chord. You need to be flying on a 10 to 12 cm chord wing for max times. Note there is a bonus for narrow wings, but only for states or nationals, you have to get there first so go for a BIG chord at regionals. And only experimental data will tell if the narrow wings are worth there bonus.

Same story for tail, no chord limit. New rule this year, but there is some advantage to be gained with a wide chord tail, just not much data yet on how much.

Length between tail and wing. Seems a little short. Will be harder to trim. Very small changes between wing and tail angle make much bigger differences. Tend to be less forgiving when disturbed (ie you hit the ceiling). It also won't take as much advantage of that large tail if you use it. Note, none of the designs I saw on the Pitsco site are particularly good ones for SO.

That's the hints and tips I can see from what you've provided so far. Info on prop and rubber combo would be useful too.

Thanks,

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Re: Flight Times

Postby Draylon Fogg on Fri Jan 22, 2010 4:57 pm

ok so i guess i didn't clarify this right but im asking about my second plane, the 1:23 time is a different plane that is our main one im asking about my other two so here are the actual demensions of the second plane, wing length is 39.8cm, cord is 10.6cm, tail length is 25.scm, cord is 7.2, tail distance from wing is 37.1cm,fuelsilage length is 37.5 cm, prop span is 19.8cm. by what you are saying im doing really bad but even when i make one that is cm by cm to a plane that is 7.2 grams i still end up at 11g.
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Re: Flight Times

Postby jander14indoor on Fri Jan 22, 2010 7:06 pm

First I'm not saying you are doing anything bad. But it does look like there's some confusion between us. Sorry.

OK, lets see if I understand this. Last years (or your primary) plane weighed 7.2 gms and flew. New planes to same dimension weighs 11 grams? Is that the issue?

I'll stop there till I really understand, sorry.

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Re: Flight Times

Postby Draylon Fogg on Fri Jan 22, 2010 7:20 pm

I know you not but Im just getting really frustrated. Ok so we have plans for a plane that is 7.2 grams and our current one that looks exactly like it is 11.
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Re: Flight Times

Postby jander14indoor on Sun Jan 24, 2010 11:02 pm

OK, so you are asking why you aren't hitting target weight.

Do you weigh wood or parts as you build? Do you have a bill of materials showing what each part should weigh? If not, you need to start doing that.

Balsa, as you probably already know, is a hugely variable material. Density varies from below 3 lb/ft3 (rare) to 12 lb/ft3 (common) 20+ lb/ft3 (somewhat common). So two parts of exactly the same size can vary in weight by almost 700%! If you don't select your wood carefully, the same 'looking plane can go from 7 gm to 15 gm in a heartbeat. For Wright Stuff, the bulk of the wood will be in the range of 5-9 lb/ft3 for a 7 gm plane, but even that will leave a huge weight range if you don't stay aware of it.

OK, so how do you manage it.

Many (most?) SO plans are only half complete for this purpose. They describe all the parts and their dimensions, but at best give recommended density wood to cut pieces from. Unfortunately, even if you buy the right density wood, when you cut strips the density varies across the sheet, and two seemingly identical pieces can easily vary by two or three to one. Again, leaping from that 7 gm plane to a 14 gm plane in a heartbeat. Now selecting your wood by average density will get you closer, it still leaves a lot of variability.

To minimize variability you make a bill of materials and figure out target weights for the parts. (BTW, I'm an engineer at Ford Motor Company, and a BIG part of my job is just this! Fuel economy means weight is critical in cars, and if I can't tell my bosses what the engine or transmission we're designing weighs before its ever built I get my head handed to me. And it BETTER be right when built!)
- Your bill of materials should list each piece of the plane, from wood to prop wire to prop to covering to glue, everything. Each part should have a target weight. They must sum to slightly less than you desired weight.
- You get the target weights by using the dimensions to figure volume, multiply by recommended density (for steel parts just look up steel density) to get a target weight.
- For some parts, like the prop, simply weight it.
- For covering look up a area density or weigh a sample piece and calculate it. Multiply by the covering area.
- For glue, make an estimate. A very conservative starting point is 1.0 gm. Good builders will use less than about .3 gm. Use your judgement.
- If final weight doesn't equal 6.5 to 7.0 gm, increase or decrease density or piece sizes till your bill of materials total is in that range. When you have a choice, find a lighter covering first to lose weight. Strengthen the motor stick, wing posts or wing spars if you are underweight (you'll get there). Lighten the tail boom, tail spars, and ribs to lose weight.

Now, when you start building, make sure you have a good scale next to you. Weigh the parts you select for each use. Too heavy (heavy plane) or too light (weak plane) put it back and select another.

If you do this rigorously you can build a plane to within .1 to .2 gm of target every time! If you use at least PART of this info, you should be able to stay within a gram or so of your target.

Let me know if I'm starting to get at what you need?

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Re: Flight Times

Postby blue cobra on Mon Jan 25, 2010 3:52 pm

What jander said is completely true, but I think that if you are significantly over weight, you are using way too much of something. I personally don't find the densities of my pieces (though I know I should) and my most recent plane, including bass for the wing posts and a few other components, came out to 6.93 grams (but do NOT use bass until you can build light, then you probably still don't want to). I think that if you use "regular" sizes of balsa; about 1/8x1/4 for MS, 1/8x1/8 for boom, and 1/16x1/16 for your wing and stabs, and don't go crazy on the glue, your plane should come out under 7 grams. I'm not trying to disregard what jander said, I just feel that it is very easy to build to 7g and making a bill of materials might be better when you are a bit more experienced and can start worrying about consistency.
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