[JoeF]

Some early glider and powered aircraft utilized high-hat (HH) technology in their wing sets. Intended: a second auxiliary wing high above a main wing. Recognizing that canard secondary wings may be cousins to HH, we leave canard matters to a different discussion-study thread.
In our forum for almost a decade I've placed some notes and images regarding HH matters; some of those notes are in Safe-Splat and some in Wing5 matters. Using the search tool of the forum with "high hat" brings up some of the scattered notes.

In some hang gliding scenes, HH might resolve tail challenges (non-flying tails at some launch sites, tail complexity, tail weight, ...). Actually, Otto Lilienthal's double-decker gave some seed for HH pitch stability even though he also had a rear tailing empennage on the apparatus. Großer Doppeldecker. The Burgess-Dunne flying wings of double decks hint at the HH matter. Lovejoy's High-Tailer Image High-Tailer.

At 10:15 ... on [url=https://www.youtube.com/watch?v=SNtA1cbIUSA[/url], see a powered HH example from Paris, France. The HH is contollable: the two parts of the HH may be opened and closed.

PoweredHighHatExample.PNG (160.28 KiB) Viewed 2438 times

But stark small very-high hats for pitch stability and control may be an arena deserving of more attention than I've found in the literature.

This discussion thread is open to careful study of HH in the hang glider space. Resultants in yaw and roll may be important issues in HH.

Some tease with a video that claimed "New" without proof; the HH technology was known before the video's 2016 date.
Video title: New method of positive pitch stability

HighHatExample.PNG (160.19 KiB) Viewed 2442 times

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Filler, no-HH:

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Early HH, though with other tail

#916quinquies Belbin cycleplane (UK, 1912)
Image Challenge * *
A pedal-powered monoplane built by Handsworth blacksmith H. W. G. Belbin, using an old bicycle frame and wings made of bamboo and oiled canvas. It was driven on the ground by the rear wheel, which also drove the tractor propeller. The machine was "constructed under difficulties, and in spare time, the family kitchen having been utilized as a workshop", and it bore "unmistakable evidence of the trade of its builder in the form of many fancy bits of smithing"

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Not sure:

Not sure:

[Craig Muhonen]

Sailboat Reflection.png (128.55 KiB) Viewed 2410 times

Just for fun, Is this a "high hat" glider, or a reflection?
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[Frank Colver]

I think it is a "jib sail" configured pitch stabilizer.

Frank

[Bob Kuczewski]

I think it is a "jib sail" configured pitch stabilizer.

Ding, Ding, Ding!!

I think Frank wins the prize!!

[Craig Muhonen]

That's not 'Fair' Frank, you live overlooking one of the greatest harbors in the world, and see sailboats quite often. I 'captured' this picture watching SAIL GP, which is the most exciting racing, and commentary I see. It takes me back to my old Hobie Cat daze, in the 60's.
Thanks Joe for these incredible pictures of "High Hat" gliders.

Sheet the main and, Trim, Trim, Trim.




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[KaiMartin]

Some tease with a video that claimed "New" without proof; the HH technology was known before the video's 2016 date.
Video title: New method of positive pitch stability

HighHatExample.PNG

The drag of the "high hat" varies very little with pitch angle. The opposite is true for the main wing. Slight changes of pitch result in substantial change of drag for the main wing. Since both are mechanically coupled, this results in a stable pitch angle at which both drag forces are in equilibrium.

Suppose, for some reason the pitch deviates toward smaller angles than equilibrium. This will reduce the aerodynamic drag of the main wing, while the drag of the high hat stays basically the same. This inequality results in a torque that lifts the nose of the glider. The constant drag of the high hat pulls the wing back into equilibrium. Something similar happens if the pitch deviates toward larger angles. In this case the increased drag of the main wing will turn the wing back to the equilibrium pitch.

I have never seen a high mounted pure drag device used for pitch stability before. So I am inclined to accept the "new" claim in this case. All the other "high hats" presented in this forum were some kind of lift producing shapes. These will change their drag similar to the main wing. I don't see how these lift producing high hats would induce pitch stability. Maybe, I am just blind. If so, can you enlighten me?

Unfortunately, substantial drag as a necessary part to provide pitch stability comes at a substantial price: It reduces the lift/drag ratio. The resulting glider may be stable. But it will not glide very far. Penetration would be abysmal. This is acceptable for a walk-along glider. But for a full sized hang glider I'd be inclined to consider this a no-go.

---<)kaimartin(>---
PS: Thank you for the impressive video. It makes me want to play with walk-along gliders again. Had tried paper versions years ago but was only marginally successful. Flying them involved lots of running. The trick of the gliders in the video seems to be paper thin styrofoam.

[Bob Kuczewski]

The drag of the "high hat" varies very little with pitch angle. The opposite is true for the main wing. Slight changes of pitch result in substantial change of drag for the main wing. Since both are mechanically coupled, this results in a stable pitch angle at which both drag forces are in equilibrium.

This is an excellent explanation of the basic mechanism. Thanks!

However, my intuition is still nagging at me. It's interesting to consider the case where the high hat is raked forward such that the relationship between angle of attack and drag on the high hat are reversed. In that case, a more downward angle would decrease the profile drag on the high hat resulting in even more pitch down. Is that known to happen? Of course, it's not normally flying at that angle of attack.

I am wondering if the relative motion of the high hat also helps to regulate its drag and lends stability as either a primary or secondary effect. A small pitch down will increase the airspeed - and thus the drag - of the high hat (drag rises with the square of the airspeed). A small pitch up will similarly slow the high hat's airspeed and decrease its drag. Could that be an important contributor to stability?

As with many real world phenomena, there can be more going on than we can easily describe.

Either way, thanks for helping me exercise some long-dormant parts of my brain!!

[KaiMartin]

However, my intuition is still nagging at me. It's interesting to consider the case where the high hat is raked forward such that the relationship between angle of attack and drag on the high hat are reversed. In that case, a more downward angle would decrease the profile drag on the high hat resulting in even more pitch down. Is that known to happen? Of course, it's not normally flying at that angle of attack.

Well, that would be an angle of attack where the nose of the main wing points at least 45° down (relative to the apparent wind). This is not a very healthy condition for a conventional hang glider, either.

I am wondering if the relative motion of the high hat also helps to regulate its drag and lends stability as either a primary or secondary effect. A small pitch down will increase the airspeed - and thus the drag - of the high hat (drag rises with the square of the airspeed). A small pitch up will similarly slow the high hat's airspeed and decrease its drag. Could that be an important contributor to stability?

Very valid point!
IMHO, this effect dampens sudden changes of the pitch. It should be beneficial in that it helps to avoid PIO that drives the nose up and down with increasing amplitude.

---<)kaimartin(>---

[Bob Kuczewski]

Very valid point!
IMHO, this effect dampens sudden changes of the pitch. It should be beneficial in that it helps to avoid PIO that drives the nose up and down with increasing amplitude.

Thanks. Without numbers, it's hard to know if that effect is important or trivial, but at least we agree that it helps rather than hurts.

However, my intuition is still nagging at me. It's interesting to consider the case where the high hat is raked forward such that the relationship between angle of attack and drag on the high hat are reversed. In that case, a more downward angle would decrease the profile drag on the high hat resulting in even more pitch down. Is that known to happen? Of course, it's not normally flying at that angle of attack.

Well, that would be an angle of attack where the nose of the main wing points at least 45° down (relative to the apparent wind). This is not a very healthy condition for a conventional hang glider, either.

I think you are right that the wing would have to be at a negative angle of attack to see this effect, but I don't know if it would have to be 45 degrees down. It would just have to be in a configuration where more pitch down increases the drag on the wing and decreases the drag on the high hat. For a symmetric wing and a vertical (90 degree) high hat, that would be any angle of attack less than zero. But for a cambered airfoil, it wouldn't enter that configuration until the angle of attack were negative enough to offset the effect of the camber.. But either way, once the angle of attack were negative (negative enough to increase drag with further pitch down), then the wing's drag would begin to grow with more pitch down while the high hat's drag would be decreasing with more pitch down. That would be a divergent situation if relative static drag were the predominant effect, so I thought that divergence would prove that it's the static drag differences that create the stability over any other effects (such as my "dynamic" drag proposal). But in a practical situation, I agree that would be a difficult situation to create ... and not much fun to experience if it were divergent!!

Either way, thanks again for this exploration. It's good mental exercise.

[Frank Colver]

I agree with Bob, here.

One could assume that the very negative angle required to enter divergent conditions would never be reached in flight but I'll bet some Owens Valley pilots would disagree with that

I personally would not want to fly any craft that had any chance for divergent pitch or roll under some flight condition unless i could avoid that condition. The WW Condor 330 had exhibited a tendency for roll divergence when rolled beyond a certain angle, according to Wills Wing. That's one of the reasons that it should not be flown above "training hill" conditions.

I've flown RC gliders that exhibited both pitch and roll divergence, but because I had ample control surface deflection control I could force them back to stability equilibrium.

Frank