Hi Graham
"very careful attention to the leading
> edge profile (digital airfoil section as Don designed) make an enormous
> difference to the character of the stall. 3 times and 3 airplanes now
> many hours spent on the LE have given very good low speed handling. It's
> the first 3 inches of the leading edge that make all the difference."
Don Dykins talks of Europa airfoil in his book and essentially what he
does is puts an amount of NASA Lead Edge Droop that keeps stall very
acceptable but not so much as to increase high speed drag too much.
He accomplished this by using computer at work and plotting many points.
On Classic it is a lot harder to keep airfoil to his specification
compared to XS I am sure!
On my 80 oz 3/4 hp 48" flying wing I put articulatable NASA Lead Edge
droop on the outboard 1" of wing that has range between -5 and +30
degrees.
Without any droop the plane is stink fast, but I will crash 1 in 4
landings! Will snap upside down, almost unrecoverable from 1000 feet,
make a hole from 100 feet guaranteed.
Dial in ~ 10 degrees and the plane turns into a pussycat as far as stalls
go! Anything more and stall is fine just begins to drag up at higher
speeds.
As a note if I go to -5 degrees the plane is even faster than with 0
degrees, you do not want to get anywhere near stall, plane snaps upside
down sooooo fast.
I fooled with 5 degrees droop on much lighter loaded planes that had poor
stall manors (35oz and 20oz) and it cured the problem instantly.
Anyway looking at my XS short wing, the first about 3 inches on the bottom
looks just about right to my "eyechrometer" to be a great compromise to
allow benign stalling and not drag up at higher speeds.
I can see on a Classic if shape on bottom of wing gets changed not even
too much, plane will fly fine, but stalls can become interesting.
In Dons book he speaks of how nasty stalling on some yesteryear aircraft
was dealt with by adding in the field NASA Lead Edge Droop (Brits have
another name for NASA Lead Edge Droop). Idea is to keep taking some away
till stall got nasty then add a little more back, then attach permanent.
I mentioned a while back if I have a plane that drops a wing, instead of
stalling the better wing at a faster airspeed by installing stall strips,
I think I would rather fix the worst wing to fly slower.
Even on a plane where AOA on one wing and flap is off, NASA Lead Edge
droop added will help out, if not a complete fix, then at least in part
with stall strips if really whacked. I know that Bud thinks not much or
changing angle of a wing for a poor flying plane.
NASA Lead Edge Droop changes the AOA of the wing, by adding to the bottom
of the lead edge of the wing it decreases AOA of that wing.
I fully agree with Graham that starting with the lead edge lower part of
europa wing to be what Don had in mind ("Dons Droop") is a great idea.
Graham would you be willing to make up some profile templates so mere
mortals could check their plane? I for one will order.
Having too much droop will only cause high speed drag, too little can make
stall a lot more violent.
Flying a heavily loaded plane will probably bring out the worst in a
Europa with not enough of "Dons Droop". Since plane was designed for 1370
AUW, flying at 1450, 1500 or 1525 even if it is only a few times in the
life of your europa it would be wise to make sure you have at least what
Don had in mind.
Ron Parigoris
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