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Apr 27, 2016, 12:56 PM
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50 cm super simple Horten wing


I am new here, so hello everyone!

I want to present my design of a simple Horten style flying wing. It is made out of a single sheet of xps foam. The "airfoil" is created by bending the sheet in one place. This bend also stiffens the wing and creates necessary twist (evident when looking from the back).

The design was done mainly by trial and error, with many prototypes made of foam and paper in various scales. I think that in current form, dihedral might be a bit excessive. Neverthelesss, the plane is rock-stable and achieves a glide ratio of around 15. With speed of about 3m/s and tip chord of 2cm, the Reynolds number is extremely low.

I will be thankfull for any opinions, criticism or suggestions for improvement. I have some experience with XFLR5, is it applicable to such small RE range?

Kind regards,
David Ziemkiewicz
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Apr 27, 2016, 01:48 PM
Everything's A Composite
Knoll53's Avatar
You accomplish wing twist and cambered to symmetrical airfoil with a single crease........Pretty clever.
Apr 28, 2016, 02:42 PM
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Thanks!

Here's a quick simulation of the wing in XFLR5. The lift distribution indeed resembles a bell, but the span efficiency seems poor and Cl/Cd is significantly underestimated The root airfoil is not derotated, so alpha of -3 deg refers to the tip.
Apr 30, 2016, 01:02 PM
B for Bruce
BMatthews's Avatar
Quote:
I have some experience with XFLR5, is it applicable to such small RE range?
Some of the calculations will be valid and others not so much.

In particular the airfoil performance estimates at the Reynolds numbers below around 60K become more a guess and trend than anything you want to trust. That's shown by the typically highly ragged curves produced by the calculations at these lower values.
Apr 30, 2016, 08:21 PM
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*many* have built and sucessfully flown Hortens (albeiit at moderate to low speeds :-) using Flat sheet wings.
Which work fine , with No twist and clearly No aero to speak of.. beyond what a bit of reflex on the full span ailerons gives.
Speed is the critical parameter.
Damn near anything including witches, stop signs, lawnmowers and even ersatz Dr Who Tardis's ...fly quite well ..at Low speeds.
That said:
Crispy's thrust vectored Batman and Drone flying wings.. fly Really well at speed, despite flat sheet wings sans even small lip service to Mr Reynolds .
Some things require simple 'doing' rather than obsessing over the aero of.
May 01, 2016, 01:19 PM
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Thread OP
Thanks for input!

Indeed, I'm very skeptical about XFLR results for RE < 20K. I prefer to test things by trial and error. Some observations so far:

-using any more camber than in posted plan results in flow separation and poor performance

-likewise, more dihedral is bad. I'm planning to make a zero dihedral model, maybe the effect of sweep is sufficient.

-finally, using more sweep also dramatically cuts performance, while a bit less is ok. Not sure why it is so.

I have made a 200% scale model, 1m span, only slightly less sweep. Still single sheet of foam, due to ludicrous wing loading glide speed is about 3m/s, no flutter and no spar needed Performance is pretty comparable to the smaller plane.
May 04, 2016, 11:14 AM
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More documentation?


The simplicity of your design is definitely intriguing. Well done!
-Cheers CryogenicMiner
Last edited by CryogenicMiner; May 04, 2016 at 11:15 AM. Reason: I missed the plans :P
Jun 02, 2016, 12:28 PM
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Powering it up


I have mada a powered version. The engine is a PowerUp 2.0 paper airplane kit. From videos I have found on YouTube it seemed a bit anemic, but actually it is overpowered for this airframe. The wing is identical as in plans, except the increased span - 70cm and no covering. At half charge the plane climbs for about 15 seconds, then glides 40-50 seconds. Glide ratio with dead engine is about 8-10 (tested indoors). On full charge, it makes loops, I need to adjust the thrust line

Heres video, sorry for quality
Flying wing test (1 min 40 sec)
Jun 02, 2016, 10:40 PM
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EdSoars's Avatar
Finally, the answer to all my aero questions:

I.D.M.

It just don't matter. And isn't it nice how the simplest Horten wing is still beautiful?

But I don't think I'll be able to kick the RC habit.

ed
Jun 03, 2016, 05:43 AM
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Quote:
Originally Posted by Bare
*many* have built and sucessfully flown Hortens (albeiit at moderate to low speeds :-) using Flat sheet wings.
Which work fine , with No twist and clearly No aero to speak of.. beyond what a bit of reflex on the full span ailerons gives.
Speed is the critical parameter.
Damn near anything including witches, stop signs, lawnmowers and even ersatz Dr Who Tardis's ...fly quite well ..at Low speeds.
That said:
Crispy's thrust vectored Batman and Drone flying wings.. fly Really well at speed, despite flat sheet wings sans even small lip service to Mr Reynolds .
Some things require simple 'doing' rather than obsessing over the aero of.
Amazing what will fly.
A friend of mine likes to make novelty planes and I think the best he has made is the flying elephant.

John

Radio controlled model flying elephant (1 min 49 sec)
Jun 03, 2016, 09:48 AM
Everything's A Composite
Knoll53's Avatar
Quote:
Originally Posted by John Wright
Amazing what will fly.
A friend of mine likes to make novelty planes and I think the best he has made is the flying elephant.
Good one John. You get the award for the most off topic post on this forum. Not only does it have nothing to do with David's Horten, it's not even a nurflügel.
Jun 03, 2016, 09:54 AM
Everything's A Composite
Knoll53's Avatar
Quote:
Originally Posted by Davidz90
I have mada a powered version.
The photo in this post shows the simplicity of the creased wing. My first thought is how to "improve" the design with a non-linear twist scheme, for example by building the wing from 2 sheets of foam, laminated together with epoxy and placed on a jig to create the twist.

THEN I realized, that such an effort might not improve performance at all. Is that part of your program David? That is to see just how simple a Horten can be?

Kent
Jun 03, 2016, 10:17 AM
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Thread OP
Yes, indeed, I want to keep it minimalistic. With single sheet wing, all I have to take care of is the angle of a single crease. Both leading and trailing edges are straight. I have tried gradual bend, there seems to be some performance improvement, but not dramatic one.

I have tried building few wings out of two sheets, but since I'm generally operating in very low RE regime, thick wing is just bad. Also, the wing without covering seems to fly a bit better, probably due to the sharp leading edge (or maybe just lower wing loading). What is not visible in the photo is the fact that while making the crease, I have managed to crack the upper surface a bit, making sort of turbulator in the place where separation might occur.
Jun 03, 2016, 10:52 AM
Herk
HerkS's Avatar
Quote:
Originally Posted by Knoll53
The photo in this post shows the simplicity of the creased wing. My first thought is how to "improve" the design with a non-linear twist scheme, Kent
Looks to me as if a non linear twist can be done in two steps. First is fold the wing just as David has. Then make some chordwise slits in the area aft of the fold. Shaping the slits a bit would allow that section of the wing panel to be twisted progressively. position the desired twist of each segment and glue the slits.

Way more complicated but possible. I think though that the first fold should start near the trailing edge at the root and toward the leading edge as it progresses twisting upward as it moves outboard. That would seem to be more Hortenish (is that a word?) than Dave's setup seen in the photo of the powered version. Either way of course achieves the goal.
Last edited by HerkS; Jun 03, 2016 at 10:59 AM.
Jun 03, 2016, 11:10 AM
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Thread OP

Calculating the twist


Okay, I have gone math heavy. As is, the twist IS nonlinear. I have derived the equation for it (attached pdf). Of course, the "airfoil" is not constant - towards the tip, the maximum camber point goes aft, so I really have no idea what optimum twist should look like .


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