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Old 11-14-2017, 07:45 AM
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grubbat grubbat is offline
 
Join Date: May 2012
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Default Kitplanes: Build it Better - Margins Margins Margins

I enjoyed reading the Kitplanes "Build it Better" article by Mr. Dye. When building my -9 several years ago, I would ponder different ways to build in extra margin here and there. Never once did I entertain the desire to exceed VNE true airspeed. I'm a firm believer that the designer owns the design and VNE was one area that I just didn't want to play with.

HOWEVER, building in some margin south of VNE has always been lurking not far from my thoughts. The 50ft/sec gust in the yellow zone at full gross is like a reoccurring nightmare, and it should be. That's why its a yellow zone. One wonders what will fail first when one finds themselves in they yellow zone in a deteriorating situation. They are not supposed to happen, but in reality, everyone will find themselves in a less than desirable situation at one point in their flying days and margin or lack of it will define whether you live to write about it or if the task is left up for the NTSB to do.

Data suggests oftentimes the tail will fail first when overstressed, and then the wing spar shortly thereafter. So, whats a builder to do to add in a little bit of margin for the tail? Well the answer is not so cut and dry, so to speak.

Airplane are a bunch of compromises. Designing a stronger tail usually means thicker skins, less overlaps using one piece skins, and more ribs which translate to more weight exactly where you don't want it, unless of course you are nose heavy anyway. Then you got to deal with the diminishing useful load due to the new and improved (and heavy)tail. A feller can't win.

Needless to say, the more I learn about these things, the more my appreciation grows for the engineers who spend countless hours designing and ensuring that the margins are acceptable given all the compromises. I've only been fixing planes for over three decades and not a day goes by that I learn something new from one of these designers.

To all you Engineers, designers, and smart folks, my hat is off to you. Thanks for all that you do. Mr Dye, thanks for another great article.
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Old 11-14-2017, 10:37 AM
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Ironflight Ironflight is offline
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Glad that you found that (or anything I have written) useful Craig.

The "Build it Better" series was something I did in Kitplanes back before I became the editor. It grew out of a presentation I did (and still do) called "Lessons from Mission Control" - things that transfer organically throughout aviation and aerospace that can help builders and pilots of experimental as they progress through this avocation.




A year or two ago, Belvoir, the owner and publisher of Kitplanes wanted to put together a premium for new subscribers, and we diced to pull together the entire series of articles into a booklet. It has all of the photos and original illustrations by cartoonist Robrucha that were used in the original magazine, and you don't have to page through your old back issues, or search the archives.

The only catch is that the booklet isn't for sale - it is only available as a premium for new subscribers. However - and this is the good news for current subscribers - it is available as a pdf download if you already have an active subscription! That way, you can download it to your computer or tablet and have it to read any time you want. Makes it harder to put it on the wall of the shop and use it as a dartboard though.....

You can find it here if you'd like to read it.

People have told me for years that I need to write a book (and the truth is, I am....very slowly....). Well here's a sort of book for those interested.

Paul
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Old 11-14-2017, 12:10 PM
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rv7boy rv7boy is offline
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Thanks, Paul. After downloading it and quickly reviewing it, I believe it to be a valuable resource for anyone involved in building an airplane.

Another good reason to subscribe to KITPLANES(r).
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