margins of wing downthrust

[danyra]

Hi all

what are the dimensions ( direction ) of the downwash produced by the main wing ?

the question is - in what height can i put the horizontal stabilizer lower than
the main wing , and stil keep it clear from the downwash ?

the model is sloper wich flies on 15mph wind , so its speed may be about 20mph

[Sparky Paul]

The proper term is "downwash". Downthrust is applied to motor offsets.
As for placing the horizontal out of the downwash, it's usually installed above the line from the wing chord to the tail.
For a sloper it might be something not that important; turning ability is the main performance factor.

[Ollie]

http://www.grc.nasa.gov/WWW/K-12/airplane/downwash.html
http://www.av8n.com/how/htm/airfoils.html#sec-flow-intro

[BMatthews]

You can't avoid it without the stabilizer being mounted a crazy distance off center from the wing. The downwash off a wing affects the air a good chord length above and below the wing to a fair degree and tapers out to no effect over probably a two chord distance above and below.

Just ignore it and follow the typical wing and stabilizer incidences for your type of design.

[HELModels]

You know what? I'm going to plug these books. My late father wrote both of them in an era before the internet and they still apply. As I see questions posed on this forum, I see answers in both books. The first book probably wont get you the layout for a hotliner, but it will get you a stable sailplane, which still sell quite well. The second book will help you eliminate drag, and will show you a 10 step procedure for determing how you should build your spars so that you dont snap your wing like a toothpick. Procedure is the key, because it is a step-by-step procedure for designing a spar.

Here are the books, private message if you want further info on purchasing:

[Ollie]

Eric Lister!!! His books helped me a lot. I used his books in the 1970's and 1980's. His methods are ageless.

ElectroStorch is the son of Eric Lister. Good!

[danyra]

Thanks to you all

I probably will put horzontal stab. and main wing in different angle

[BMatthews]

You know what? I'm going to plug these books. My late father.......

I've got the Sailplane book as well. Lots of great stuff in there that really helped a lot.

[lockheed martin]

Thanks to you all

I probably will put horzontal stab. and main wing in different angle
Alternitivly you can add a V-tail to replace the vertical stab.

The V-tail will minimise the amount of downwash that it incounters and you should almost solve your problem.

Also you won't have to mount it higher than the centre line, it can be level with it which is good for low drag.

Nick

ElectroStorch - I PM'ed You on your DAD's books.

[danyra]

Thanks lockheed martin

Had V tail in mind but not for that sloper , may be will try it.