Just caught this in the "Horten Ho-2 Flying Wing Test Flight 1935" YouTube video (screenshot below). I had NO idea their wingtips were so twisted into what almost seems like conical camber, as used in F-106, Concorde, F-22, et al.

The Hortens used zero camber symmetrical airfoil sections at the tips of all of their flying wings and large washout angles. The large washout is what you're seeing, not conical camber.

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Sorry but what is "conical camber"?

The F102 and F106 used fairly flat airfoils that had a sizable degree of fixed in place leading edge camber or droop. Apparently this came about early in the design testing to aid in achieving higher angles of attack and to aid in forming the proper high angle vortex flow off the leading edge. And while it was aimed at helping during higher angles of attack it apparently didn't greatly hurt the high speed aspect so they were built in as fixed shapes.

I'm not sure I would describe this as "conical camber" though. Or did you find the term used to describe that style of airfoil in some literature?

Originally Posted by BMatthews

Sorry but what is "conical camber"?

Basically it is more camber at the tip than the root. As usually used on deltas it is a leading edge modification where the nose camber traces the surface of a cone with its apex on the root leading edge and its bass at the tip. If you cut a foam core with an NACA OO12 at the root and an NACA 23012 at the tip you would have a conically cambered wing. No reason it wouldn't work with the Horten parameters, just not a feature they used. However the NACA 5 digit airfoil sections (and I suspect most other sections with extreme forward camber) have an abrupt stall with a lot of hysteresis so it might introduce a tendency to spin and be slow to recover.

Here's a paragraph from the history of Ames Research Center:

Originally Posted by nmasters

[…]No reason it wouldn't work with the Horten parameters, just not a feature they used. […]

Positively cambered airfoils are—in my experience—not suited for Hortens. Neither at the root nor at the tips. The negative pitching moment results in a too low design lift coefficient, which people tend to counteract with more twist, aft c.g. and trimming elevons up. None of these is really great. The small lever arm provided by the sweepback is simply not enough to level the pitching moment of cambered airfoils. I'm not pleading for symmetric airfoils everywhere, but camber should more or less follow the distribution of lift coefficient. Other choices increase drag either because some control deployment is needed, or because the airfoil section is forced to work at a suboptimal angle of attack. The best choice is using airfoils of slightly negative pitching moment and let the camber follow the distribution of lift coefficient. This supplies enough reserves for slow flight, keeps profile drag low and results in a good design lift coefficient of CL = 0.2–0.3.

Hortens are sensible creatures…

Cheers,
Andrés

yes, but ....

Originally Posted by Pile It

yes, but ....

You can't take ideas from tailed [supersonic] designs and expect them to work the same on tailless [Mach 0.1] designs

Originally Posted by andrecillo76

The best choice is using airfoils of slightly negative pitching moment and let the camber follow the distribution of lift coefficient.

Good point, Andrés, but the NACA 230 mean line of the airfoil I used in the example above only has 1.5% camber and a fairly low pitching moment. Cm0 can be reduced to zero by going to the NACA 231 mean line.

Originally Posted by nmasters

You can't take ideas from tailed [supersonic] designs and expect them to work the same on tailless [Mach 0.1] designs

really?

Rogallo wings typically have washout angles in the high 20s and are not very efficient. Nobody said you can't use a cambered airfoil section for the tip profile but doing so will increase the required washout or some other, more undesirable, compromise as Andrés listed in post #6.

Originally Posted by nmasters

Rogallo wings typically have washout angles in the high 20s and are not very efficient. Nobody said you can't use a cambered airfoil section for the tip profile but doing so will increase the required washout or some other, more undesirable, compromise as Andrés listed in post #6.

Maybe they flattened and shifted the cone so as to obscure it, or maybe it "just happened" .... but the difference between the spanwise curvature of the leading and trailing edges out at the tips by the elevons seems kind of "cone-like" to me.

Originally Posted by Pile It

Maybe they flattened and shifted the cone so as to obscure it

Probably not. The people involved in the Prandtl-D project have said it's basically a scaled down Horten H Xc.

the difference between the spanwise curvature of the leading and trailing edges out at the tips by the elevons seems kind of "cone-like" to me.

That's the result of the nonlinear washout, not airfoil blending. You can see a more exaggerated picture of nonlinear washout here.

Well, you all may be right that those Hortens didn't use actual conical camber. However, since this thread is about "conical camber-effect", I respectfully suggest that having raised elevons that do not extend to the wing tips has an effect equivalent to having a symmetrical airfoil at the elevon and a lifting, cambered airfoil at the tip. Many conventional full size and model planes use this instead of or to increase the effect of washout.

Of course, without today's carbon fiber, etc, their wooden aircraft needed somewhat self-stabilizing wing sections. To my understanding the bell-shaped lift distribution curves of Prandtl were also part of especially later Hortens.

And even if the Hortens didn't quite go so far as Prandtl-d in this regard, there is no major reason not to consider this effect in RC models. For a variety of reasons models fly differently than their full size counterparts, and a fine example can be seen in the Youtube videos of the nice Dutch RC Ho-229 bouncing off the runway when landing (they finally had to make the nose-wheel fold a bit to stop the bouncing). As far as I am aware that is a fairly precise scale model, but like most models has to fly at a higher angle of attack, or fly faster than linear scale speed in cruise and landing or both to make up for loss of efficiency of the model in the reduced size.

What the builders of the large twin turbine RC Ho-229 model builders should have done was to increase the washout twist even more than that of the real plane and especially for landing purposes when the model was forced to fly too fast and thus at too low a body angle. That meant that the nose wheel hit first and bounced the plane. If they had increased the twist beyond scale the model with a more efficient greater-twisted model wing would have been able to land slower before stall and keep the nose wheel up as in a normal trike-gear landing.

It would have been easier scale-wise to get away with using modified airfoil sections than simply twisting the wings more. Twisting wings, Prandl-d's results, winglets, "nonlinear washout" and even conical camber are all closely related to spanwise flow and its causes. In effect.

scale effect showing up in steeper glide-path and landing, resulting in bouncing .... even when nose-gear was re-designed and allowed to "shorten" on model's nose-down UN-scale touchdown as shown here

Horten Ho229 powered by 2 MW44 turbine engines (6 min 1 sec)