# Witold Kasper

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#### henryk

##### Well-Known Member
In order to attain the max. neg. drag at the bottom of the wing, the bottom surface has to be made rough.
The drag decreased by 30%.
The reverse wing warping is not needed.

=
the max. neg. drag at the bottom of the wing, the bottom surface has to be made rough.
The drag decreased by 30%.=

NEG.DRAG=THRUST?

"the bottom surface has to be made rough."

=I dont understand exactly=Yours explanation?

"The reverse wing warping"=???=not clear...

"
The spar-rib attachment detail is the most difficult design issue right now."

=
http://www.hanggliding.org/photos/displayimage.php?album=14&pos=14
http://www.vole.ch/cgraph/impactgalweb/source/flugel_von_innen.html

-moore...IMPACT

"I sent my modified Kasperwing drawings to Witold Kasper many years ago for his evaluation.
The design featured a higher aspect ratio, single spar, and wing warping for turns."

-can I see that drawings?

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#### danmoser

##### Well-Known Member
In order to attain the max. neg. drag at the bottom of the wing, the bottom surface has to be made rough.
The drag decreased by 30%.
The reverse wing warping is not needed.

=
the max. neg. drag at the bottom of the wing, the bottom surface has to be made rough.
The drag decreased by 30%.=

NEG.DRAG=THRUST?

"the bottom surface has to be made rough."

=I dont understand exactly=Yours explanation?

"The reverse wing warping"=???=not clear...
How I interpret Witold's words:
The bottom surface vortex formed at a low angle-of-attack creates an airflow on the bottom surface that is in the opposite direction to the free stream air velocity.
The skin friction from this reverse flow was thought to create a small thrust force, and that the bottom surface should be rough to take full advantage of it .
Witold claims this reverse flow friction on the rough bottom surface reduces the overall wing drag by 30%.
I am mildly skeptical of this claim, and have not seen any data that confirms it.

Reverse wing warping is a control technique used to sustain a small radius turn with slow flying, large wingspan aircraft.
In a turn, the inside wing is always at a much lower airspeed than the outside wing.
To balance the lift forces on the two wings, the inside wing must have a higher angle of attack... in other words, opposite aileron.
The most extreme example is with human-powered aircraft, which have to use this reverse wing warping to make even mildly banked turns.
I have personally noticed that when flying a sailplane in small thermals, a small amount of opposite aileron must be used to keep from over-banking while also using some positive rudder to sustain the turn rate.
Kasperwing tip rudders are canted such that they simultaneously provide both opposite aileron and positive rudder action, and they can perform small soaring turns extremely well !!

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#### Tom Nalevanko

##### Well-Known Member
What exactly are we looking at in the first picture? Thanks

#### danmoser

##### Well-Known Member
http://www.twitt.org/tufts-r.jpg
I thing,at bottom side vortex flow is equall...

Here is Witold's sketch & description.
I still think he is wrong about the drag reduction.
Kline-Fogelman airfoil tests always showed drag increase for trapped vortex features, but I don't think anyone has ever tested this phenomenon completely.
I am open-minded about the possibility that somehow friction against the reverse flow causes drag reduction.
But increased friction can only dissipate more energy, so I conclude that the overall drag of any airfoil configuration could only increase with more friction, no matter the flow direction.
Am I wrong?

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#### henryk

##### Well-Known Member
What exactly are we looking at in the first picture? Thanks
in the first picture? =spar or tufts?

znaczniki op

=right wing BKB1-A...

SUMMARY DRAG of this wing was LESS then left wing,WITHAUT TUFTS!!!

thanks Dans for Kaspers copy!

#### danmoser

##### Well-Known Member
To clarify, I think the trapped bottom surface vortex is actually a very clever idea overall.

It does have what amounts to automatic camber adjustment to a degree, and it prevents bottom surface laminar bubble formation & its problems.

My skepticism is that added roughness results in drag reduction, but I'd be happy to be proven wrong.

#### danmoser

##### Well-Known Member
http://bkb.koendu.pl/doc/Kasper art..pdf
-I think=You can understand moore than I can\english\...

from=

Bibliografia - Brochocki Kasprzyk Bodke

Henryk... thank you for the link to the very detailed bibliography. Very good collection.

The "Kasper art" document has some good information, but it also has Kasper's controversial claim that a very low minimum sink rate happens during the deep stall & reverse flow on the upper surface of the BKB due to the vortex flow.
The vortex flow is real, but nobody else who flew any of Kasper's wings ever verified the very low sink rate claim.
It would require a CL, Lift Coefficient of over 6 !! .. and with very low drag.
This has never been demonstrated on any aircraft or in any wind tunnel.
The vortex flow in a deep stall or "vertical mush" always results in a very high sink rate.

#### Tom Nalevanko

##### Well-Known Member
Let's say Kasper's claims are true. How do you land a craft at such a high angle of attack still descending at 150 fpm? Granted it is not that much but most of us would rather land at 0 fpm and avoid the crunch/bounce. Will one have enough airspeed to flare? Or does the flare concept even hold in this case?

Blue skies,

Tom

#### danmoser

##### Well-Known Member
Let's say Kasper's claims are true. How do you land a craft at such a high angle of attack still descending at 150 fpm? Granted it is not that much but most of us would rather land at 0 fpm and avoid the crunch/bounce. Will one have enough airspeed to flare? Or does the flare concept even hold in this case?
150fpm = 2.5 feet per second = 1.7 mph, which would be a bit of a bounce, but not that bad. And flaring probably wouldn't be possible.
Of course, the problem is: the actual vertical speed of the BKB-1a sailplane wasn't anything close to 150 fpm in the vertical mush as Witold claimed.
The Kasperwing ultralight with much lighter wing loading had a vertical mush descent rate of approx. 1,000 fpm.. ~ 7 times faster.
I've heard stories of people landing in that mode.. crunched landing gear & undercarriage, but pilot basically unhurt.
One such story was an engine out over a forest, and only a very small clearing ringed by 200 ft. tall Douglas Firs was available for landing.. which was done successfully.
I don't think the mush is a terribly useful mode of flight except for the rare emergency such as this.

#### henryk

##### Well-Known Member
The Kasperwing ultralight with much lighter wing loading had a vertical mush descent rate of approx. 1,000 fpm.. ~ 7 times faster.

=in the case of KASPERWING we have Vhor=0!
and Vver=circa 5m/sec...

MUSH MODE=
New Page 2

except for the rare emergency such as this.
-but at BKB1-A Vhor=10 m/sec and Vver=0,5 m/sec === L/D=20 -not BAD!

#### Tom Nalevanko

##### Well-Known Member
The pilot clearly noses over in this video and uses his altitude to pick up forward speed to flare. Impressive...

#### henryk

##### Well-Known Member
The pilot clearly

"noses over"

=I dont unerstand?

in this video .
=I dont unerstand?

#### danmoser

##### Well-Known Member
"nose over"
=I dont unerstand?
in this video, the pilot shifts his weight forward and gets out of the deep stall vertical mush just before landing with the normal flare.
American pilots use the slang term "nose over" for when you let the aircraft nose rotate down to get out of a stall.

The Kasperwing stall doesn't have a sharp break to it, like many other aircraft do.
And even a deep stall can be maintained with full control, which is a very unique flying ability.

#### henryk

##### Well-Known Member
in this video, the pilot shifts his weight forward and gets out of the deep stall vertical mush just before landing with the normal flare.
American pilots use the slang term "nose over" for when you let the aircraft nose rotate down to get out of a stall.

The Kasperwing stall doesn't have a sharp break to it, like many other aircraft do.
And even a deep stall can be maintained with full control, which is a very unique flying ability.
-thankyou!

=do You have moore materials\data\ from Witold Kasper?

=KASPERWING can made the ZERO speed landings,like a hanggliders...

http://kasperwing.com/Bird Landing.WMV

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#### danmoser

##### Well-Known Member
-thankyou!

=do You have moore materials\data\ from Witold Kasper?
I received two letters from Witold, but not with any technical data.
He also sent me some old photocopied data on the FX05-H-126 airfoil, which is F.X. Wortmann's modification of the NACA 8H12.

It's an interesting book.. about 70 pages.. but all rights are reserved, so I think it would be illegal to copy & distribute.

You can buy the book for \$15.. email meheen@gmail.com or call (303) 337-4040

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#### henryk

##### Well-Known Member
Thanks,we have this book too\see Bibliografia\...

We have the set of BKB/BEKAS drawings and orginal BEKAS in restoration process\to examine the dynamic soaring\.

#### danmoser

##### Well-Known Member
Thanks,we have this book too\see Bibliografia\...

We have the set of BKB/BEKAS drawings and orginal BEKAS in restoration process\to examine the dynamic soaring\.
Best of luck on restoring and flying the BEKAS-N.
Kasper's claims that he dynamic soared it... but others dispute that and claim the BEKAS was so flexible that it was dangerous.
It would be nice to know the facts.
I'd love to see a modern stiff composite version of it built & flown.