Design

jander14indoor
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Re: Design

Post by jander14indoor » November 25th, 2014, 3:14 pm

If you just changed the prop from the small plastic one to the Ikara, you committed one of the sins of testing, changing several important parameters at the same time without plan.
The Ikara prop and hanger that comes with it are MUCH lighter than the red ones. That changes the total weight (less, good if not under 8 gm) and center of gravity (in a bad direction, tail heavy, will want to stall) unless you added ballast to bring it back to original.
The Ikara are larger and higher pitch. Requires a very different rubber band to develop ideal power matched to the plane.
The Ikara will probably require a different optimum torque affecting trim for turn.

Jeff Anderson
Livonia, MI

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Re: Design

Post by bjt4888 » November 26th, 2014, 3:39 pm

I have the greatest respect for Jeff Anderson and if students read all of his forum comments carefully, they will have an excellent framework for success with this event and for a fulfilling science experience. I do however have a slightly different perspective on use of kits like the one available from Freedom Flight. I am an experienced indoor flyer and an occasional competitor and have coached several high school science olympiad teams in elastic launch glider for the last few cycles. As the time required to construct a high-quality Wright Stuff airplane is a pretty fair commitment for the students, and as I have found that a number of students involved in SO are also involved in other activities, limiting SO time to a certain extent, I like the idea of using the Freedom Flight kit in order to get construction done as efficiently as possible and allow more of the student's time for testing, data recording, modifications and learning a systems approach to problem solving.

Six of the students that I am coaching completed three of the Freedom Flight kits in a one-day, nine-hour session a couple of Saturdays ago. The kits fly great! In their first day of testing their best flight was 3:02 at about 22' altitude. This flight used a motor that had already been wound hard five times and an unmodified stock propeller, so the potential to do longer duration is a definite. Better yet, the students took extensive notes and pictures to learn procedures and filled a page and a half of a flight log with data and additional notes. There were tons of questions, lots of discussions and a great science experience overall.

I agree with Jeff that for the same money as a Freedom Flight kit package (which constructs two airplanes) you can build about five airplanes from scratch. One other item to be aware of when scratch building though is the rule 3.a. "Airplanes may be constructed from published plan(s), commercial kits and/or a student's design." Constructing a kit takes care of any possible issue documenting that a scratch build that is not a published plan is a "student design" and not a coach design.

Brian Turnbull
AMA since 1972 (off and on)
NFFS also for a long time (off and on)

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Re: Covering adhesive?

Post by 28builder » December 5th, 2014, 8:32 am

mylar doesnt seem to stay glued to balsa aftwr a few test flights. i tried 2 methods. small paintbrush applied 1/2 water 1/2 glue and also tried glue stick. should i ise ca glue or will that burn right through the lightweight mylar? and btw we crinkled it up before we applied and each time pressed it down and let it cure before flying

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Re: Design

Post by retired1 » December 5th, 2014, 11:07 am

I do not think that you will find anything better than 3M super 77 spray.
You do have to be careful to not use too much.
I would practice with some scrap balsa and the thin grocery sacks before using it on the mylar and your wing. You are fairly well stuck with where ever it first touches.
Available at most big box stores.
You will have enough for next year's planes and then some.
It is like a paint can in that you need to turn it upside down and spray for a couple seconds to clear the nozzle.

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Re: Design

Post by jander14indoor » December 5th, 2014, 7:20 pm

Almost any good spray adhesive will work, just not too much.

While I strongly recommend light grocery bags there can be one problem. To keep them from sticking to each other and to help open them some seem to be coated with a very light powder or release agent. When I detect it, but don't do anything about it, I also have trouble getting it to stick. I have found if I wash the bags well with some good grease cutting dish detergent, Dawn or similar, and let it dry good the problem goes away.

Comment on designs. Where does it say you can't do a coach design? Coach built, clearly not, but coach design? How is that different from the Freedom Flight design, some design posted on the web (there are a number) or a published design in a book?

You may want ask a clarification on the official site, but I'm not aware (doesn't mean it hasn't happened) of any students ever being DQ'ed because of the source of their design.

You may also wonder why I take that position. Well, because the authors of the WS rules (of which I'm only one) feel that the best design (which none of us are convinced really exists) will not succeed without the student building it and testing the heck out of it to get that ideal prop/rubber/trim/winding combo for the site of the competition. The difference between the 'best' design and any number of pretty good ones is only a couple of percent, if that. Well within the noise of the experiment. The difference between a well trimmed and wound plane and a poorly trimmed and wound plane is a much, much larger amount.

As to tricks, I've only seen one effective one and it been discussed widely in the past so no secret or trick any longer, torque burners (do some research on this site at least before you ask me what that is). And it is only a killer advantage in a low site. And even that takes so much work to execute that any one who can, deserves the win. Heck, they'd probably win without the burner. They would have had to become so expert at WS, just by a smaller margin. The last guy I saw do it, Brett Sanborn, is now a regular member of the US F1D team and in contention for the World Title one of these years.

Oh sure there are things like students not taking advantage of a bi-plane in the years we don't specify a monoplane, or underestimating the advantage a bonus might (or might not) provide, but those things aren't really secrets either. Easy to test and determine for yourself.

One opinion anyway,

Jeff Anderson
Livonia, MI

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Re: Design

Post by bernard » December 5th, 2014, 9:20 pm

If you're wondering what a torque burner is, here is a simple description:
Torque Burner wrote:A torque burner is a mechanism which effectively divides a rubber motor into segments so that each section unwinds in series with the others, causing multiple climbs and descents, so kinda like what you saw with Harlan's VP prop, only doing so (potentially) more than once.
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Re: Design

Post by Toms_42 » December 6th, 2014, 7:35 pm

I'm still kind of new to this, so excuse me if there are obvious answers to these questions.

First, why is the wing lifted up above the motor stick? I was guessing it was to keep it out of the wind from the prop, but how high should I lift it? Also, quite a few designs have the horizontal stab mounted below the motor stick, why is that? Another area that seemed to change a lot was whether the vertical stab was mounted above or below the motor stick, does that matter?

Second, what is a good motor width for the ikara props? I have one of each prop (1.8g, a larger 2.2g, and the flaring 2.8g) Freedom flight offers .081”, .087”, and .094” as "for airplanes," and I was planning on ordering some of each, cut to the max length I can to keep it under the 2g max. Is there an ideal length to stretch these to? As in how should I calculate the distance between the front and the rear hooks. Again, I am totally inexperienced with most of this stuff but I'm interested in learning.
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Re: Design

Post by jander14indoor » December 6th, 2014, 9:17 pm

Wing high is more about balance/stability in roll. Center of gravity is below center of lift so less likely to roll upside down.

Low tail is partly to get stab out of wing wash and partly to lower center of gravity. But frankly a rear stab on the same level as the prop will work fine.

Vertical stab up or down doesn't really impact flight much, either works fine. One could argue that a down stab reduces flight time because it will likely hit the ground sooner than the prop if it hangs low enough. But the difference will be so small as to be relatively unimportant over a lot of other factors. If we were flying Rise of Ground it might be important to wing attitude on launch.

Rubber width will depend VERY much on prop AND ceiling height. Matching the rubber to the prop is the real 'secret' to this event and while we can provide suggestions, you really need to test for yourself. Any of those will probably work to get started. In my experience (not the final word at ALL, I'm not the best flyer out there by a long shot) skinny low pitch props need slightly thinner rubber than flaring props. That that's not an absolute.

Front to rear hook distance is not really very important. Anything around 10 to 12 inches will be fine.

Regards,
Jeff Anderson
Livonia, MI

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Re: Design

Post by someusername » December 6th, 2014, 9:57 pm

Sorry if this is in a bad section, but I had a question/problem that may be a bit hard to answer (again sorry if it is)

I built a wright stuff plane that does pretty well so far, but the facility I have has so much air conditioning currents that during testing, my plane can never get accurate results. For instance, my best flight during testing is about 1:03 because at about 55 seconds it went under one of the vents and was completely thrown off balance. Another time it was hit from the front by some air current and caused a massive stall and dive. Then when I went to a competition, I was easily able to break two minutes with relatively low winds. The gym that I am forced to use has about 16 different vents spaced maybe 10m more or less away from each other and are constantly on. The question is, does anyone have any form of solution that would maybe help or a design change that could fight heavy air currents better so I can improve my design and time in an effective manner?

sorry for the lengthy description. Any possible feedback would be greatly appreciated.
simplicity is key...sometimes

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Bad (rough or turbulent) air

Post by jander14indoor » December 7th, 2014, 6:40 am

someusername wrote:Sorry if this is in a bad section, but I had a question/problem that may be a bit hard to answer (again sorry if it is)

I built a wright stuff plane that does pretty well so far, but the facility I have has so much air conditioning currents that during testing, my plane can never get accurate results. For instance, my best flight during testing is about 1:03 because at about 55 seconds it went under one of the vents and was completely thrown off balance. Another time it was hit from the front by some air current and caused a massive stall and dive. Then when I went to a competition, I was easily able to break two minutes with relatively low winds. The gym that I am forced to use has about 16 different vents spaced maybe 10m more or less away from each other and are constantly on. The question is, does anyone have any form of solution that would maybe help or a design change that could fight heavy air currents better so I can improve my design and time in an effective manner?

sorry for the lengthy description. Any possible feedback would be greatly appreciated.
No problem about where you put it, changed subject for my response to help folks find this issue.

Rough air is hard to deal with effectively. That's why you can get shouted at for opening the doors during a competition flight. That's why competitors (and event supervisors) make such a stink about the ventilation system. But, due to site limitations sometimes its just part of the game out of the organizers control.

Can you get the school to turn the air off at scheduled times? Find another site to practice in. Might be worth giving up some ceiling height or floor space to get better air to dial in the trim.

If you can't control the air, you need to increase the stability. Move the CG forward more and retrim. Small amounts. Your flight times won't be quite as long in a calm site, but you'll recover from stalls faster. A smaller stab may also help stability at the expense of flight time. Longer distance between wing and stab may help.

Also, and this is true in any site, you need to be aware of where the hazards are. LOOK at the ceiling. Where are things hanging low, where are the vents, outlets and returns, external vents, windows (sunlight can create mini-thermals). Learn how to read a room. Adjust your launch site, direction and turn size to minimize the risk. Try to make sure your trim results in consistent turn radius. Be aware how your turn radius changes through the flight and adjust the flight plan accordingly.

Hope that helps some,
Jeff Anderson
Livonia, MI

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