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Old May 12, 2010, 09:36 PM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
New Product
The Horten Tailless Flying Wing Ė Letís Build One Together!

I am going to start a thread here on RCGroups that will cover the research, design, model development, prototyping and beta building a number of Horten tailless flying wings. These Horten wings will be offered by Mike Smock of Aerosente Glider Workshop.

Our plan is to develop two production models plus a prototype for design validation. I will be utilizing numerous tools to make this a fun project with as many visuals as I can offer. Many of you know that I love to work with Rhino to develop the 3D models of my subjects. Iíll be doing the same with the Horten wings also so will periodically present 3D models as eye candy!

Additionally, Iíll be utilizing a number of tools that make the design process for a Horten wing a little less cumbersome mathematically. Designing a Horten wing is VERY different than designing a standard sailplane so these tools will come in handy!

I have been digging deep into the history and technical aspects of Horten wing design and have gathered a lot of technical data related to specific Horten wing versions as well as the fundamental design aspects of such a tailless flying wing.

Additionally, there are a number of old pictures available that show what these wings were like in their heyday. Unfortunately, much of the data that is available tends to leave quite a bit to the readers imagination. The Horten brothers were not especially keen on developing good sets of plans and therefore, top quality plans are difficult to come by. Ee do however, have a number of resources we can pull from to create and good representation of a scale Horten wing.

Of special importance are the technical papers that were recorded by the Horten brothers as well as those developed from interviews. These are especially important to understand the design concepts that create flight stability in such a swept back, flying wing configuration. Iíll be going over the primary aspects of these concepts as I progress with the thread.

For now, I will leave it here. If you are interested, please follow along. I will try to post fairly frequently and I guarantee I will be requesting your input on quite a few topics. Iím looking for honest feedback so donít hold back!!

Tony Elliott
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Old May 12, 2010, 09:58 PM
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so. cal.
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Tony, I have most if not all the books about the Hortens, plus an priginal Horten 4 is hanging at the Chino Air museum (the one that they did all the research on back in the 50's), and I owned and flew the Horten 4 that Edies Modellbau Paradies sells at his Nurnburg Hobby shop Rick and I visited may moons ago, strange things happened on the muitlple flights I had with it, we need to talk. This sounds like a great project, would love to see the model built right an successfully flown. Dennis
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Old May 13, 2010, 06:19 AM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
Dennis, I would definately appreciate any information you have that I could reference. While I am confident about the requirements for the design of a Horten wing, you can never get enough information.

Would you mind sharing the "strange things" that occured with the Horten 4 on this forum? It would be good for others to hear what you experienced. Maybe I can use these items and determine root cause so that we don't repeat them.

Have fun at Visalia this weekend - I hear the weather is going to be perfect - wish I was there!!

Tony
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Old May 13, 2010, 06:43 AM
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I would be very interested to hear what "strange things" happened in flight as well. I build several Horten flying wing 15 years ago. It was a 1.5 meter span molded skin over foam core. The flying characteristics were very impressive both from winch/high start launch and at the slope.
The funny thing happening was that you could put the wing in a "flip over mode" around its Y axis and it will go all the way down to the ground in this mode... Never damaged anything but once you entered it, no way to get out.
I tried different designs variations and played a lot with the CoG. If the CoG was not right it will be a bitch to fly, sometime right impossible. When the proper washout and profile evolution with the proper planform were used a dream to fly, except for the flip over flight mode... To enter it you just had to face the wind and pull on the elevator stick slowly to enter a stall. 3 times out of 5 you would get in the flip over mode and the wing would go down to the ground like a leave form the tree in the fall! You could enter it as well with entering a sort of dynamic stall in a sharp turn.
I tried different wing loadings, the lighter the easier to set up and fly. But with a higher wing loading the performances (penetration and L/D) could be quite spectacular.
The final model was with very funky colors and it was a good hit at the local slope with a few pilots buying it for the fun aspect, the simplicity and ruggedness.
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Old May 13, 2010, 07:03 AM
Deniable plausibility
Shedofdread's Avatar
Derbyshire, UK
Joined Aug 2008
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Tony,
Very best of luck to you - you'll need it! Seriously though, this is something that [with another RCG member], I've looked into and there are some significant issues to deal with. In no particular order, some of them are-
1, A lot of Horten 'theory' was invented AFTER the fact. This alone should tell you something... 'Bell shaped lift distribution' was apparently invented as a concept in the 1950s by the brother who went to Argentina who was feeling a little 'left behind' by the career of the other one (in the post-war Luftwaffe).
2, How good were they really? The 'mists of time' come into play here.
3, At model scale, the 'theory' doesn't always translate. Also, the practicalities of servo installation etc can pose problems with those thin, narrow wings.

Please don't think me negative but when you get under the 'legend', lots of questions are raised.

On a positive note, they are undoubtedly elegant and when one cracks a difficult challenge, the sense of acheivement is all the greater.

I'll be following this thread with great interest.
S
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Old May 13, 2010, 07:27 AM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
Gentlemen, your comments are actually very welcomed and I do not view them as negative in any way.

It is without doubt that I know this will take time to develop correctly and that it is not a simple task. One of the primary drivers behind the development of these models IS the difficult and chalenging nature of it.

As many of you probably already know, I like a good challenge and this is certainly going to be one. I have a very good grasp of the concepts of Horten wing design and later you'll see me present them. Be aware hoever, that I will be asking for your input. My next post is an example of gaining your input. Stay tuned.

Tony
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Old May 13, 2010, 07:38 AM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
What a great lead in fnev! This leads me to my first "question". This will be a little verbose because I need to set the stage a little. I'll try to keep future posts shorter.

After some quite extensive research across multiple versions of Horten wings, I must say that I do like the lines of the Horten IV and the Horten XVc. In my eyes, both of these Hortens simply have great lines. The Horten XVc had a number of names because this wing was actually built in Argentina after the war. It was known there as the I.Ae. 34 Clen Antķ or Sun Ray.

This post will focus on the larger scale Horten that will be designed and offered. The smaller Horten will not generally face the challenges noted here. This is also a call for your input.

The Ho-IV is a 20m ship and at 1:3 scale would be 6.666m or 21.9 feet - a large sailplane! The XVc is only an 18 meter ship so at 1:3 scale would be 6m or 19.7 feet - still large. The center section of the Horten IV at 1:3 scale is a rib that is about 29 inches long while the Ho-XVc is 43" long!

Estimating weight is a little difficult without significant material property analysis which I just haven't had the time to do yet. However, we have some data from existing models that may lead us to a close guess. I have noticed that the larger models of Horten wings with power assisted launching capabilities are in the order of 40 to 55 grams per dm^2. At 1:3 scale, the Horten IV is 218dm^2 which relates to about 8.7 to 12kg (19 to 26lbs). The XVc is even larger because of lower aspect ratio at 304dm^2 – now we are really getting heavy at between 12 and 17kg (27 to 37 lbs). I believe these weights are on the high side and really apply to the powered versions with batteries, motors and props. It is obvious that we need to keep the weight of these wings down and for more than just the launching requirements!

We'll get back to the reason for the dimensions in a few moments because this discussion is about methods of launching and the effect that size has on launch possibilities. There are generally four ways to launch a sailplane - aerotow, bungee/winch or bungee/winch assisted power, ROG and slope. Two of these methods imply some form of propulsion be available and therefore, just like many of the Horten wings being developed in Europe, we might need to consider a “not so scale” center section that houses a motor and prop as well as, perhaps, a second center section that is scale for display or non-powered launching techniques.

Let’s start with the non-powered launch methods – slope and aerotow.

Launching a flying wing from a slope shouldn't really pose too many issues assuming a reasonable wind exists so I don’t think the following discussion applies to this method of launching unless you can think of reasons why it would!

Aerotowing however, seems to be very different with a Horten wing. At a high level, the Horten wing relies on both aerodynamic, and if required, geometric wing twist to provide pitch stable flight. The angle of attack of the wing and the consequent lift distribution play a critical role in this requirement. Placing a Horten wing behind a tow plane that generates prop and down wash and significant turbulence has the potential of drastically changing the airflow characteristics over the Horten wing leading to changes in its pitch stability. I viewed a video of such an attempt to aerotow a Horten wing and was quite surprised when it simply "fell" out of the tow only to tumble to the ground - very similar to the behaviour described by fnev!. I wish I could actually find the video again but for some reason I didn’t bookmark it and I can’t seem to find it now otherwise I’d show you.

Now let’s go to the power assisted launching.

The bungee/winch or bungee/winch assisted power launch (electric motor and folding prop) appears to be a great way to launch these wings. However, this obviously becomes more difficult to do the larger and heavier the model becomes. Having watched the videos of our German friends who regularly use this method for their Hortens, I believe you can see the reason they are not building much larger than 4 or 5m!

The ROG solution requires alternative thought - retracting or drop-off wheels for example. As long as the power solution is a pusher type, I am of the belief that this type of system would be plausible - what do you think? One has to consider prop clearance, prop size needed to achieve the launch etc.

So, back to the comments on size, weight and wingspan. As we consider developing a 1:3 scale 6 to 6.7m Horten wing, we are faced with the question of how best to design the aircraft to provide the broadest range of launch capabilities. Certain capabilities may add cost to the kit so need to be considered carefully.

Here's my question to you. What do YOU think we should be designing it for? What would be the preferred method of launch considering the size AND the weight of such a wing.?

Please, feel free to add any comments you want in this area - we are open to all possibilities!

Tony
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Old May 13, 2010, 08:21 AM
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Tony, my old Horten 4 is still available at www.modellbauparadies.de It was 1/3.7 scale at 5.5 meters. Aerotowing was actually the most unremarkable aspect of flying it, although the initial takeoff was unusual in that it tended to hug the ground on takeoff, you had to give it a little extra up elevator to break ground, but once on tow if reacted like any other scale glider on tow, no surprises. I should say that the controls were basically like a big Zagi, just 2 large ailerons plus spoilers in each wing, with about a 2 to 1 aileron differential. I experimented with C.G. a bit, with the first flight at a somewhat forward C.G. (at least what I thought was forward) Off tow, with a hint of forward C.G., the model flew similar to an arrow, very straight, fast, not reacting to lift, controls were responsive in roll and pitch, but the model was coming down quickly, close to the ground there was lots of ground effect, very floaty. The second flight I moved the C.G. about an 1/8 inch back, tow was the same but off tow things changed, it had much slower flight, so slow that it had minimal directional stability, any little bump of air would make the model change direction, I let the model float along pretty much letting it determine its flight path, seemed somewhat responsive to lift, I tried forcing it to circle which it would do ok, but it seemed to want its own path, landing was once again no problem, spoilers worked fine to kill lift. One or two more flights with small adjustments in servo throw gave similar results, I felt the model had a pretty poor L.D., not what I was hoping for.

After some comments from you all, I will explain the next time flying it which is best described as unusual and almost disturbing.
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Old May 13, 2010, 08:43 AM
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Tony, I can still vividly remember the last time a Horton Flying Wing was towed at JR in 2008. It was quite a spectacle, the tow started off reasonably well but as the Horton gained altitude "unusual and disturbing" things began to happen. To me it seemed safer in ground effect and then become quite out of control at altitude.

As the instability grew worse on tow, the pilot released and seemed to regain control on a very fast final approach down the runway to land, almost took off Paul Naton's head as it barreled past him and into the corn arresting barrier. Photos of the carnage attached.

I wish you much better luck with yours!

Steve
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Old May 13, 2010, 09:23 AM
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I'm sure you've seen this thread......if not here it is: Horten Wing
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Old May 13, 2010, 10:21 AM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
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Yep, that and a few others from Lothar. Lothar has one on this forum also under electric/flying wings. http://www.rcgroups.com/forums/showt...1131450&page=2

It is nice to see that while there is a fair level of doubt about the feasibility of such designs, Lothar's work goes to show that with the right dedication and tools, scale Horten wings are very feasible. He does great work.

Tony
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Old May 13, 2010, 10:22 AM
SoarScale
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Steve, can you describe the nature of the instability you witnessed on tow?
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Old May 13, 2010, 12:46 PM
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The previous flights were up at the Victorville flying site in the desert we used to have, the next were from aerotow at Costa Mesa. I had Larry Jolly with me for these flights, in fact I handed the transmitter to him for some flight time. What we both experienced was what I guess is called aeroelasticity, the strangest thing I have ever seen, at some points in these flights, when the model would be banked up in a turn, it acted like it had massive amounts of adverse yaw, it actually was close to a reverse roll control at certain airspeeds, but what was really scary was the wing was visibly like a wet noodle, you could see it making these strange oscillations, all the control surfaces were very tight, no slop. This model had been reported to fly just fine on the slope in Germany in stock form, my theory is it needed the triple trailing edge controls where the inboard surface are mostly elevator and where the outboard should be more biased to aileron only as on the original, also I think it really needs the tip spoilers for rudder control, on the B-2 Stealth you always see those tip drag rudders depolyed in flight to some degree. The model is currently in the hands of Gary Fogel in San Diego, as far as I know he hasn't attempted any flight with it, and since I sold to the previous owner he never attempted flight either.
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Old May 13, 2010, 02:47 PM
Deniable plausibility
Shedofdread's Avatar
Derbyshire, UK
Joined Aug 2008
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Hi S2000,

What you say re the tip rudders is apparently a common thing. I have the plans for a D/F Ho iX and the designer makes much of the need for them. He also makes the point that flying with them 1/2 deployed improves yaw stability. Well, it would but it's hardly the point.

You also mention the multiple surfaces per side. If the believers in BLSD (bell shaped lift distribution), think that's so important, maybe they could explain to us all how it's thus affected because, to me, it seems that all those carefull calculations are thrown out of the window every time you give a control input.

I'm really not trying to knock Hortens because I'm fascinated by them but equally, I think some mystique has grown up around them which maybe needs to be exposed. Maybe this is the place to do it.

At some point, I'm going to have to have to 'put my foam where my mouth is' and build one, aren't I?

S
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Old May 13, 2010, 03:35 PM
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Well,

nice thread, nice Ideas.

What I can promise You, for a good designed Horten, You do not really need those drag-rudders at the wing tip. I built them into my HXIV, because I wanted to test them. They can help a little bit to fly a "better styled curve", but that's all. At my HXV-shaped glider I used them too, but they didn't make me happy. They can "help" to make great tailspins. Looks like a windmill, when it comes down and feels really exciting.

By the way there are excisting different designs of the XV. The a-version (Clen-Antu) has a smaller sweepback than the c-version (Urubu).

Mine (a-version shape) has a wingspan of 5.15 m (scale 1:3,5) The weight is about 9.5 kg. I don't like flying it, because it's to much work to assemble and start this beast.

Uuuhhh, and before I forget, I am sure, You will need some lead im the nose. Those motors and batterys in our Hortens are well needed for a proper CG. And especially for research and development flights, a motor with a folding prop can help. The target we are working for is to make good aerodynamics. The scale centersections will follow afterwards for the slope.

Did You ever read the book NrflŁgel by Reimar Horten and Peter F. Selinger? It's a bible for Horten planes.

Regards

Lothar
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