Design Tips

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TSOlympian
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Design Tips

Post by TSOlympian » December 17th, 2015, 12:59 am

How does one come up with original plane designs? My team has a "no kit" policy for our building events, and so far we've been using other people's plans published online, like Chuck Markos's Tips Packet. However, I've been wanting to move away from using other people's designs and start coming up with my own original plans. So far I thought of just maxing out the possible wing/stab dimensions and somehow adding a polyhedral and tapered tips, but I feel like my design isn't working or that efficient.

Is there a general process for drawing original plans from scratch? Are there certain guidelines/considerations/physics principles I should follow or observe when I'm drawing plans? Any advice is appreciated esp. from people who have been doing own plans or adaptations on others'.

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Re: Design Tips

Post by jander14indoor » December 17th, 2015, 12:24 pm

Have you seen the following website?
https://www.soinc.org/sites/default/fil ... iad5.0.pdf

First principle, make it light.
Second principle, MAKE IT LIGHT!
Third, maximize wing and tail area.
Fourth, see above document to get balance point & wing stab spacing. Typically your center of gravity on these things will be around the rear wing spar.
Fifth, for now, stick with conventional trimming, again see above document.
Sixth, match prop to rubber.
Seventh, build accurately and minimize drag.
Don't go crazy on wing camber (part of minimizing drag). A little is good, none is OK, a lot is draggy.
IF you use wing fences, make sure they are parallel to line of flight (drag).

Generic comment, if you aren't already flying a 2-3 minute plane, your time is probably better spent building an existing design (or minor variation) and flying LOTS. If you are flying a 2 and definitely if you are flying a 3 minute plan, design alternatives are probably worth exploring.

Hope that helps some.

Jeff Anderson
Livonia, MI

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Re: Design Tips

Post by TSOlympian » December 22nd, 2015, 9:02 pm

I did see that document! It's been incredibly helpful! So far I've just been adapting the design described there for this year's restrictions (like the new chord length) and also other things I've read about, like polyhedral and tapered tips but the resulting plane has not really been flying that well. It generally turns but refuses to climb upwards. I'll consult that doc for more info since I think it does address this problem but I was wondering what other additions I could make.

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Re: Design Tips

Post by bjt4888 » December 23rd, 2015, 9:39 am

TSOlympiad,

Jeff Anderson has given you very good guidance regarding design and strategy to improve your results. If you haven't already done so, read the entire Wright Stuff wiki from last year. While it may appear from the number of pages in last year's wiki that this might be a daunting task, it actually will only take you a little over an hour and the knowledge gleaned will advance you rapidly from basic understanding of the problem to advanced understanding. You will find that many pages on the wiki have simple comments that can be skimmed over till you find the detailed recommendations posted by those of us that have flown indoor model airplanes for many years (50 years, in my case). In the wiki you will find pictures and videos, rubber motor winding instructions, details regarding important parameters like aerodynamic center, decalage angle, and many details on setup.

Although I applaud your creativity and desire to design your own airplane, this method is not typical when performing "best practices" research or performing a systems approach to problem solving. If you are a novice at any endeavor and are charged with improving your knowledge and outcome, a typical first phase of investigation is to find out who has the best solution to the problem and copy what they do. Once you have a better understanding of the problem by copying the best, it is then that you will benefit from trying creative, personal solutions. Jeff Anderson has given you a good methodology for pursuing this project in his post above.

Tapered wing tips benefit airplane design mostly by reducing induced drag. However, they also reduce wing area and for a span limited rule set like Wright Stuff, reduced wing area will potentially reduce performance more that a tapered tip will help. Since the wing loading (grams per square inch of wing, or wing and stab area) is very high for this year's rule set, it would not be a good idea to pursue this design element. If you want a slight reduction in induced drag, you could consider a slight rounding of the leading edge at the wingtip and stabilizer tip. Also, polyhedral wing configuration may improve performance only a very tiny amount (and maybe not at all). Focus on the design and strategy ideas in Jeff's posting.

If you would like specific assistance via this wiki, please include all specifications, including: airplane weight, wing incidence, stab incidence, stab tilt angle, tailboom offset angle, airplane component part dimensions and wood densities (and weights), propeller shaft offset angle, rubber motor length weight and thickness, rubber motor winding style (number of turns, lubricated with?, maximum torque, backoff turns, launch torque, wing panel washin or washout, propeller pitch, type and blade style (flaring or symmetrical, sanded or not, etc.), flight characteristics (rate of climb in feet per circle, circle size, stalling or not, banking or not, etc.), and anything else you can think of.

If some of this terminology is not familiar to you, you will find details and descriptions in last year's wiki to help understanding.

Good luck and good science,

Brian T.
AMA member since 1972 (off and on)

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Re: Design Tips

Post by bjt4888 » December 23rd, 2015, 9:40 am

One more spec to include: Center of Gravity location.

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Re: Design Tips

Post by calgoddard » December 24th, 2015, 5:31 am

Jeff Anderson and Brian T. have given you about the best general advice you can get.

Brian T's request for specific information to help you with your model airplane is also appropriate.

I suggest that you post a video of your airplane in flight on Youtube and then provide the link. We need to see a full flight even if it is short.

Last year the WS team I coached built an airplane that embodied a very sophisticated custom design incorporating many concepts I had learned coaching the WS event over a ten year span and in competing in many Penny Plane and A-6 contests. This WS airplane flew extremely well at the State finals but was beaten by a 2015 FFM kit airplane at that competition.

World record holders like Bill Gowen and Kang Lee benefit from custom designs for lightweight indoor duration rubber powered airplanes. Other folks - not so much.

I applaud your effort and dedication. That is the ticket to success in the Wright Stuff event. Oh by the way, one final piece of advice is in order, namely, practice, practice, practice!

Keep us posted and good luck.

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