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Author Topic: Airfoil question / thoughts / ramblings  (Read 496 times)
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Kev
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« on: July 21, 2009, 11:22:06 AM »

Okay - so I have been coerced into this building lark again and am about to start writing an article for a digest in Australia on catapult gliders. I'm planning on it being about a competition model and one for fun (maybe something like The Worcraft Wonder which I love and with a hook on, flies like a homesick angel!). That way I cover both ends of the spectrum. Grin

However, here's a thought from this full size glider pilot. If you look at a lot of the early hlgs with polyhedral, they have also, swept back wings. No problem there. However, the airfoil is all wrong - isn't it?

When you next sand a wing - you will create a point where there is a high point and that's great. As long as there is no interference, then the usual rule applies about 70% of the lift from a wing is from the top and 30 from the bottom.The flow of air goes out from where it joins the fuz and the smooth wing shape means the laminar flow is steady all the way to the tip. Perfect.

Now take that wing and sweep it back. The airfoil presented to the air is different from that as it would have been "un swept".

In order for the wing to be efficient, shouldn't we be changing the shape to take into consideration this flow of air over the airfoil and help it produce more lift? Huh

There's some thoughts for pondering over dinner this evening.
Have a good one.

Kev
Who waxes the wings of the PW5 to a high gloss, removes every bug and then polishes even more. Then climbs in and heads away in to distant thermals.
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probligo
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« Reply #1 on: August 28, 2009, 04:48:12 PM »

Kev,

I enjoy mucking around with nurflugel (no fin, no tail; flying wings have a fin) gliders, and because these are nearly always swept wings the same question arises.

My first F1A sized nurflugel glider was made exactly to plan, sections and all. It went well, except that the d/t was highspeed and vertical... :'(

The second followed the idea behind your question. It doesn't work a darn. It is a real pig. Angry

Inquiries among some of the more senior members at club brought the answer you need. Despite the wingsweep, and as long as the sweep is less than about 20*, the airflow and hence the airfoil is at right-angles to the leading edge. Above 20* sweep, other rules come into play and the wing is much less likely to work.

Apparently, and I agree this is totally counter-intuitive, that is how it works. Oh, and apparently the airflow tries to exit over the t/e at right-angle as well.

Hmmmmm....
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