[JoeF]

Backstory on aft-keel device?

TcraftkilleenClipFalcon3device.png (37.75 KiB) Viewed 3769 times

[wingspan33]

Joe,

That's a Wills Wing tail fin. I believe it was designed to reduce/minimize PIO. I think you could get it as an option on at least some (many?) of their gliders. Not sure if that's still how things work.

[Bill Cummings]

The k2 should never have been released for sale without a vertical stabilizer. I installed one on mine and it then was good as an intermediate glider. (but not before)

[JoeF]

Some related:

Tcraftkilleen answered my question at the video comment space:

I was a new HG pilot and used the fin mostly for aerotow. I got used to the fin and decided to use it all the time.

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Then we also have:
https://www.willswing.com/accessories/wills-wing-vertical-stabilizer/ "Vertical Stabilizer" or just "Stabilizer" (in context).

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Then BillC noted something about k2 ... Do you mean Airwave K2 ? http://www.delta-club-82.com/bible/33-hang-glider-k2.htm
See archived 2009 note by BillC below.

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As I tend to do, I offer for experimental HG design:
VSWW : Vertical stabilizer When Wanted.
YD : yaw damping
The fin is set in stowed position; the fin is pulled from furled position to the amount wanted from slight unfurled to full semicircle fin.
Upon release of unfurling pull, the fin rolls back into its stored position. The finning thus could be graded from small to large
during a flight or from one flight to the next.
I have found vertical fins to be stark yaw-oscillation dampners. Stowed fin could be rolled or accordion fan. Device could be an add-on or embedded in a mod keel. Be careful when experimenting.

Similarly, one may explore: HSWW :: Horizontal Stabilizer When Wanted.
And consider furling to the degree wanted at a moment or during a sector of time, say partial flight or full flight. Open the HSWW to the amount wanted. Take this exploring in tiny steps.

VSWW and HSWW are now set into public domain relative to this input. Explore and report.
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Posted: Mon Apr 06, 2009
Noman3,
I started towing January 1978 and along the way I found some gliders that didn’t handle well when towing. An old Magic III that I towed with had such a pitch positive pressure that made holding on speed very tiring. A pro tow with a glider of this handling characteristic would leave a pilot exhausted when it was time to get off the line. I did find ways around the problem such as using a keel release about 20 inches a head of the kingpost. Other pilots used “Pitchies,” or similar CG altering contraptions.

Another problem that I ran into when the K-2’s came along was the ease with which these gliders could get out of hand towing at high speed. This was due to anhedral in its design which allowed it to roll easier. The bump technique was the only way to keep this glider tracking correctly behind the aero-tug. This glider towed best from a platform with the tow line hooked to the pilot. The second best way to tow this glider was with a Skyting bridle. The third (and I hesitate to use the word best here.) was aero towing with a K-2. It can be towed but for someone that doesn’t know that regular piloting control input while aero-towing will absolutely not work and would have them PIO-ing all over the sky.

Because of the anhedral design, to be fair, I would have to say not all of the wing walking was P.I.O. Some of it should be called D.I.O. D = Design. I drilled holes in the tail end of my K-2 keel and borrowed the vertical stabilizer from my Wills Wing Ultra-Sport. It made the K-2 handle like a trainer. I never flew the K-2 again without the vertical stabilizer. (I had over a hundred hours on the K-2 before the fin.)
Before I put on the stabilizer I did a test. In ridge lift I climbed into the control frame and stood on the control bar, locked my neck and shoulders into the top of the control frame so that I would be motionless while the glider was flying fast. IT WING WALKED ALL OVER THE SKY! IT WAS NOT -REPEAT- NOT P.I.O. It was D.I.O.

To a lesser degree newer double surface gliders while flying fast will exhibit some of this (what I call) D.I.O. and it can be exacerbated with some basic control input and sometimes called P.I.O.

Since different double surface gliders yield their own unique handling characteristics one type of tow bridle may work good on one glider while not proving as good on the next glider.

I know I’m very much alone with this thinking but I feel that if a glider will wing walk on a pilot at any speed below the gliders vne then the vertical stabilizer should go on and stay on. General aviation has been using them for years and years.

I know pilots that have been seriously injured due to P.I.O.,D.I.O. while not even towing.

So I said all that to say this: When you transition to a double surface glider and then onto an even higher performance glider, while towing, I would really have to recommend starting out with a vertical stabilizer and then progressing to a half size stabilizer. Next try without the stabilizer in good conditions. This way you can ease up to flying a glider fast under tow and not P.I.O.-ing, D.I.O.-ing it all the way to the scene of the accident. (Like low on tow just off of the dolly.)

Good luck noman3

https://en.wikipedia.org/wiki/Vertical_stabilizer Vertical stabilizer
https://en.wikipedia.org/wiki/Tailplane Tailplane or horizontal stabilizer
https://en.wikipedia.org/wiki/Empennage Empennage
Notice the realms of fixed surfaces, trimming surfaces, and adjustable area (VSWW, HSWW), ruddering, pitch trimming, ...
In foot-launch hang gliding, one aims for design basics that allow performance wanted. Modifications away from manufacturers' specifications is a serious matter, as alteration of dynamics of the system may bring unexpected results ... sometimes good and sometimes bad.

My personal explorations are going into "High Hats" instead of conventional empennage. Very little and mostly obscure has been "high-hat" explorations for pitch stabilization/control; high hats in the center of the wing space have high moment for pitch and could have little moment for yaw damping. Wing tip space has been a place for some yaw control. Various yaw-roll devices on wings form a huge space of exploration.

Otto Lilienthal explored horizontal stabilizer that would upon parachutals waft up so as not to pitch over the main wing. My HSWW put away upon parachutal landing would serve similarly perhaps.

[Frank Colver]

Similarly, one may explore: HSWW :: Horizontal Stabilizer When Wanted.

You mean like the John Lake "Sailfeather"? It sure made my Eipper FlexiFloater a lot more docile in pitch, including easier launch run pitch control.

FC

[JoeF]

Yes, in that arena. Frank, did you set it firm always? Did you consider adjustable furling of the Lake Sailfeather?

[Frank Colver]

I adjusted the furling when setting up, to set the degree of upward pitch force. It was never completely tight as I found that to be too much "up elevator". My keel also had some upward bend so there was already some reflex in the wing.

BTW - I just corrected my spelling to Sailfeather, the name John used for his device.

I was too cheap to pay him the price of $5 so I made my own copy. Now, I wish I had an original from John to put on the glider when it is on display at the vintage meets.

Paul MacCready once told me he thought it was the most important improvement in the "standard" ever made.

Frank

[JoeF]

ARP (our Tony Prentice) is opening some boyhood drawings to be in wingsuit topics soon. One of the drawings shows a vertical stabilizer fin at aft region of the wingsuit.
The pilot's "hang" was super-short coupled to the wing. The fin would give some yaw stability.
Here is that particular drawing:

BoyhoodDrawingFinOnWingsuitTonyPrentice.JPG (29.15 KiB) Viewed 3736 times