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Oct 16, 2020, 10:46 PM
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Horten IV and Horten Wings High Speed Characteristics


Id like to inquire in this Group Nurflugel as to suitability of the Horten Wings as high speed ships. Specifically the wing section of the IV wing of the Sailplane. Considering use for Dynamic Soaring and considering what modification may be used such as reduced span or thinned chord to provide for high speeds. What theoretical speeds are achieve able? If the IV is not particularly suitable what wing is that would also be suitable for unpowered flight?
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Oct 19, 2020, 02:56 PM
You know nothing....
Stuart A's Avatar
Have a look at Tail Saw. He’s the high speed Horten guy,I seem to recall him flying DS with one of his wings.
https://www.rcgroups.com/forums/show...&highlight=Uwe
Oct 20, 2020, 08:20 AM
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EdSoars's Avatar
I'm no expert on plank design, but I've sure crashed a lot of my own designs... after a lot of enjoyable fast flying... but not in DS.

DS flight produces very high flight loads, which create torsional loads on swept wings, which in turn requires some exotic structural design (like thick airfoils) and lots of carbon fiber.

Planks can't achieve the high lift coefficients of conventional airframes, so they don't set DS records. The Horten wings used bell-shaped lift distributions, which are another breed of cat from planks with tailfins or swept wings with tiplets.

Unlike most US designers, Uwe Heuer (tailsaw) uses 4 or 6 servos to give his planks a wider lift coefficient/speed range. Not easy to set up!

Also check out Peter Wick's Amokka, designed for pylon racing, so it should work for DS.

Tailsaw videos:

http://https://www.rcgroups.com/foru...io-Plank/page9

http://https://www.rcgroups.com/foru...io-Plank/page5

http://https://www.rcgroups.com/foru...io-Plank/page8
Oct 21, 2020, 02:53 AM
You know nothing....
Stuart A's Avatar
Quote:
Originally Posted by EdSoars
I'm no expert on plank design, but I've sure crashed a lot of my own designs... after a lot of enjoyable fast flying... but not in DS.

DS flight produces very high flight loads, which create torsional loads on swept wings, which in turn requires some exotic structural design (like thick airfoils) and lots of carbon fiber.

Planks can't achieve the high lift coefficients of conventional airframes, so they don't set DS records. The Horten wings used bell-shaped lift distributions, which are another breed of cat from planks with tailfins or swept wings with tiplets.

Unlike most US designers, Uwe Heuer (tailsaw) uses 4 or 6 servos to give his planks a wider lift coefficient/speed range. Not easy to set up!

Also check out Peter Wick's Amokka, designed for pylon racing, so it should work for DS.

Tailsaw videos:

http://https://www.rcgroups.com/foru...io-Plank/page9

http://https://www.rcgroups.com/foru...io-Plank/page5

http://https://www.rcgroups.com/foru...io-Plank/page8
Hi Ed,those links are coming up with an error code
Oct 21, 2020, 10:23 AM
Registered User
Flying wings are DS record worthy??? well look at number 1 in this list: http://www.rcspeeds.com/aircraft?t=60

BUT Horten wings would not make a good DS model in my opinion. The major problem is directional stability at low cl´s, which is just not good enough for flying wings without any vertical stabilizer.
Another difficulty is to provide proverse yaw in all flying situations with enough authority in critical flight situation, where fast reaction is needed.
and then there might be some critical issues in terms of structural stiffness under the stress that occurs in DS.

so all in all: If you go for DS records.....Horten flying wings are not a good idea.
Oct 22, 2020, 12:39 PM
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EdSoars's Avatar
Peter, you're absolutely right! I must update my understanding of plank performance. The video of the Stormchaser on page 8 of the High Aspect Ratio Planks thread shows what kind of speed a heavy (66gm/dm2, or 22oz/ft2) plank is capable of. Too fast for my old reflexes.

Stuart, I get the same results from those links. I followed the instructions, so I can't offer any help, BUT! just pull up the High Aspect Ratio Planks thread here in Nurflugel and go to the posts by Tailsaw on pp. 5, 8 and 9. Lots of good info in that thread.
Oct 22, 2020, 05:11 PM
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turbonut's Avatar
I wouldnt say the Stormchaser is much of a Horten design..Looks cool ...
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Oct 23, 2020, 07:40 AM
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EdSoars's Avatar
Right, the Stormchaser isn't a Horten wing. Finless airframes are great for full-sized aircraft and birds, and the Horten designs were brilliant and elegant, but for a model constrained by complexity and budget, it might be best to answer the question in the first post about what modification to make to a Horten wing by, "Add a fin." But then it wouldn't be a Horten wing.

One of the reasons the Northrop YB-49 tailless bomber didn't serve in WWII was its slight "hunting" in yaw, which wasn't a problem for the pilot, but it was a nightmare for the bombardier looking through a telescopic sight that magnified the visual effect. It wasn't until computer stabilization was developed that the B-2 was possible.

Fins are cheaper than computer stabilizers, even cheaper than multiple flaps and servos. But then, it wouldn't be a Horten wing.

My apologies for going a bit off-topic, but Peter, where can we find the specs for the Stormchaser? Or are they confidential? And what is it about the design that makes it a record-breaking plank?

ed
Oct 26, 2020, 03:43 AM
Registered User
Dear Ed

I do not know the precise specs of the Stormchaser. The Stromchaser used a PW51 or a sligthly modified one.
A good way to go is to reduce thickness and camber of the PW51 to 8% and 1.2% at the root and 8,5% and 1.2%at the tip. That makes the plane more safe to tip stall. Another important thing is to use a long leverarm for the tail, good tail airfoils (fx from Thierry Platon) and a planform that reacts good in the sheer layers. A good tail is very important for DS also for a flying plank (sorry to say that :-))
The wing planform is not so important as long as you have enough reserves in lift at the tip (so not too much taper!).

If you want to go even faster, you have to use thinner airfoils with even lesser camber, like the Gizmo does.

Yours Peter
Oct 26, 2020, 09:06 AM
Registered User
EdSoars's Avatar
Thanks Peter. Actually, I've been using your 2019 3 meter plank airfoils, the root and tip, for my very simple planforms that taper from 8" root to 5" tip, with a straight-line leading edge. It seems to be adaptable to spans from 48 to 72", and performs well over a wide range of wing loadings.

I've been setting the tailfin leading edge 8" or one wing root chord, behind the wing trailing edge. But I will try a symmetrical airfoil as you suggest.

I'll try the thinned PW51 sections too. I like the PW 51's agility!
Last edited by EdSoars; Oct 26, 2020 at 09:30 AM.
Oct 27, 2020, 09:12 AM
Registered User
The PW2019 (root) airfoil is a much more "modern" airfoil then the PW51. It is a kind of replacement. I needs more building accuracy - but will offer more performance. It is a good choice for DS as well, but I think I would also reduce the camber to 1.2% / but not thickness and then I think I would not use the strak and tip airfoil - just the 2019 - as Reynolds Numbers are high enough at DS speeds - so no strak.
Oct 27, 2020, 02:55 PM
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EdSoars's Avatar
Peter, yes, the 2019 root airfoil needs accurate hotwire templates for sure. I don't fly DS, preferring to stay on the upwind side, where I crash enough as it is. So I may retain the 2019 3m Tip airfoil for the FAR below subsonic speeds I fly... and land at.

I reduced the root airfoil to 1.2% camber, and was surprised to see that the lift profile at positive alpha was not changed, but the negative alpha curve was much improved.

Google doesn't know how to translate "strak". Does it mean "intermediate" position in the wing's planform?
Oct 29, 2020, 04:34 AM
Registered User
Strak means that you blend one airfoil into another one..
Oct 29, 2020, 06:18 PM
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EdSoars's Avatar
Thank you! I'll tell Google what it means.
Oct 31, 2020, 08:25 PM
Ken Stuhr
Ed-

"It wasn't until computer stabilization was developed that the B-2 was possible. "

That is incorrect. Basic, simple yaw dampers (actuated rudder) were used on early jetliners to preclude Dutch Roll. Same problem as in the B-35/49s. Which means same could have been developed much earlier had there been a military need. It is possible that such may have been anyway, but I can't swear to it. The DR issue was a problem with most if not all swept wing jets of the period, so there was a motive.


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