On Sat, 28 Feb 2015 16:54:40 -0700, BobW wrote:

On 2/28/2015 10:19 AM, Dan Marotta wrote:
I must admit that I didn't read the article thoroughly, but it seemed
to me by looking at the picture that the thing would enhance wingtip
vortices (the Windows spell checker did not like that word, BTW).
Anyway, I thought the idea was to reduce vortices since they're wasted
energy that could be used by the aircraft.

Aero engineers, please chime in.

I had the same off-the-cuff gut reaction when I first looked at it, too.
Upon further cogitation, I'm still uncertain eggzackly what-n-how the
designer was seeking to achieve what I think he was seeking to achieve.
I also noticed the article said he was an aeronautics teacher, so this
may be a case of: Those who can't do, teach!

In any event, I'm not investing my retirement in any company trying to
make and sell these babies...

Bob W.

I had good results with a form of Hoerner tip on my F1A competition
models (wings 2011mn span, 150mm parallel chord centre panels, short tips
tapering to 100mm chord by keeping the TE straight and sweeping the LE
back. The general tip design guidelines I used we

- sweep the LE at least 10 degrees to promotee spanwise flow on the top
surface

- rake the edge of the tip about 30 degrees with a smooth,
rounded join to the LE and a sharp, acute angle join to the TE

- the tip's outside edge should follow the lower surface of the airfoil
with the upper surface smoothly blended down to meet the lower surface
at an acute angle.

The idea was for the spanwise flow to help move the tip vortex out from
the tip while the pointed TE would help stability by localising the tip
vortex.

My wings had carbon D-boxes with open structure behind that. The tips
themselves were carved from block balsa, finish sanded and covered with a
doped-on layer of 25 gsm glass-cloth. It all worked pretty much as I
hoped. The design flew well enough to be competitive and was extremely
stable and well-behaved in all sorts of air. There was an unexpected
bonus too: the glass covered tips were very tough. I lost count of the
number of times those models got overturned after landing and blown down
blacktop runways upside down, but always with remarkably little damage to
the tip blocks.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
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