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Cantilever wings and 4130 fuselage questions?

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Victor Bravo

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heh, the difficulties of welding aluminum are why I bailed on the idea early on! Still kicking around the idea of this next project. Flying wings (specifically planks) but am nervous about airfoil selection as I don't have any exp with reflexed surfaces and how does one cover a concave wing?
The covering is not a problem at all. There is very little "concave" on the wing, and the "mechanical attachment" of the fabric to the ribs takes care of it completely. Mechanical attachment can be rib stitching, pop rivets, sheet metal screws, and even glue on some systems. It is a lot less of a big deal than it seems. Just think model airplane Solartex or Oratex, with one or two steps added.

You don't need experience with reflexed wings, and in the case of the Pelican you don't even have to even think about the airfoil, it's already been figured out safely. Fauvel came up with the basic airfoils long ago that were used with perfect safety on the AV-36 glider, and then just a thicker version used on the Pelican. (the Pelican is just a short wing powerplane derivative of the AV-36 glider)

The super-thick Fauvel airfoil on the Pelican provides very very high strength at low weight, with only a small price to pay in drag. For an airplane traveling at 60 mph or less, the drag is very small, you would not even notice it. Only when you get above 60 mph and up into the 80-100 mph range would the airfoil drag become anything to consider.

The important thing about the Pelican for your purposes is that the wing is big enough and thick enough that you will have the ability to fly it with a gasoline engine or carry the extra weight of an electric system. You could mount the battery pack on a rail or slide system where you simply move the battery pack forward or aft to balance the aircraft, and put four bolts in to keep it from moving in the event of a hard landing. THIS would allow you to use a light electric motor at the rear of the aircraft and not have the balance isues that you might have had with trying to use a 25 or 35 horsepower gas engine.
 
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FoamandTape

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good info! I'll try scaling one of the airfoils into the next revision of this, Still playing around with size and proportion although changing to a "plank" style plane may make it so I just build this plane as one single piece for maximum strength!
 

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FoamandTape

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also one other thing! How the heck is linkage done for elevon mixing with a stick??? I'm totally confused on how to set this up!
 

lr27

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Horten style mixer might work. The bits shown here still need a bellcrank out at the elevon, I think.
https://vimeo.com/236303749

I think if you messed around with the geometry, you might be able to dispense with the bellcranks and run the pushrods directly to the elevon horns. Depending on just how high the wing is mounted, you might put a pivot in the middle of the stick, with the two pushrods shown attaching below the pivot. This would let you use control horns that were above the elevon hinge points. If you don't mind bellcranks, of course, you can get it to come out however you like. Keep in mind that differential will be useless with elevons, because it would cause a pitch change, which you'd have to correct with forward stick, putting you right back where you were.

Seems like the configuration you show would be quite easy to build, and light.
 

FoamandTape

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awesome! that answers alot! Yes, the basis of what i've been tinkering with this design is to get something super simple, strong and light! I like the idea of direct push rods to the horns, it'll keep parts count to a minimum and less points of failure. Still trying to build the entire thing in my head, most likely will be building a few small scale test models to point anything out then a large 50% model, then the actual thing!
 

Victor Bravo

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An elevon mixer can be pretty simple. One bellcrank for operating the ailerons. The elevator pushrod slides the entire aileron bellcrank back and forth a couple of inches on rails.

Same mechanical principle as the old-old-old-school model airplane mixers from 40 years ago. The elevator servo is attached to the mounting tray for the aileron servo. The elevator servo moves the aileron servo tray, which moves both aileron pushrods at the same time, without preventing the aileron servo from moving the pushrods differentially.

But, all this is absolutely not necessary for the Fauvel (and Marske) flying wings like the Pelican. The Pelican 3-view clearly shows separate ailerons on the outer wing panels, and an elevator in the center section. Same with the Marske wings. No mixer, no problem, no hassle :)

If you insist on using a Backstrom or Horten flying wing configuration then you have to get involved with the elevon mixer. But both Backstrom and Horten layouts have significant disadvantages, and I believe that for your use (light weight simple ultralight with the least amount of hassle) you would have a much higher level of success with less wasted time using the Fauvel (Pelican) layout.

Doing the Pelican as an electric is cool/important/clever/relevant enough IMHO. Having a compact, sporty, attractive, and high performing electric ultralight that gets more flight time and truly useful performance/range is huge. The Pelican design (thick wing, light structure, able to carry enough battery to have a "Real" airplane) would allow you to focus on accomplishing that improtant goal in the shortest time.
 

lr27

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Well, if you want to make the controls REALLY simple, put the motor pretty far up front so you can sit in the back with your hands on the elevons, your feet on the rudder bar, and the throttle in your mouth like a PPG pilot. Add a rear (front) view mirror and you can turn around and put your feet on the rudder horns. ;-)
 

lr27

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Drawback of Backstrom type vs. Pelican type? That Horten style mixer looks awfully simple. If using a separate elevator, it would make sense to make the chord wider where the elevator is. This improves the lift distribution at different trim settings. At least if you've got a good match between the c.g. and the amount you extend the elevator.
planP2D.gif
A Backstrom Plank would benefit from increased chord at the elevons. Moving the entire trailing edge, as per FoamandTape's sketch, gets around this lift distribution problem.

Wondering what kind of vibration and noise result from having the prop so close to the elevator on the Pelican?
 

Victor Bravo

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Disadvantage of Backstrom is that the elevator is proportionately closer to the CG on a constant chord plank than on a tapered or semi-tapered wing, and that elevator deflection has a little more of a tendency to alter the lift of the entire aircraft the wrong way (control reversal of sorts) than it would have on a tapered flying wing. On a Backstrom wing there is a possibility that trying to flare on landing by pulling the stick back raises then ose as intended, but also reduces the lift of the entire wing so the sink rate increases, resulting in the exact opposite of what the pilot is try ing to do... and the airplane sinks into the ground hard with the nose up.

Marske got around this by using more taper to put the elevator as far way form the CG as possible, and increasing the chord of the elevator while decreasing the span of the elevator (compared to the overall wing). So there is a smaller percentage of the wing span that loses lift when you pull the stick back.

Another disadvantage of the Marske design is that the quarter-chord and spars are swept forward slightly, and there are more different rib sizes. Not as fast or simple to build.

Disadvantage of the Horten is the far more complex structure and swept planform, highly swept spars, and all there are hundreds of thousands of millions of different size ribs.

Fauvel also limited the span of the elevator, and the semi-taper planform puts the elevator slightly further away from the CG, requiring less elevator deflection than a straight constant chord plank.

So my advice to Peter was to keep it as simple as possible while still avoiding the problems of the Backstrom design. I believe the Pelican is the "sweet spot" here, with only three or four different size ribs, yet improved handling, increased "tail moment" for the elevator, and a much much more compact size/shape. The Pelican has straight spars and the entire wing can possibly be built in one piece in his shop (judging from his videos).
 

cluttonfred

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I attended the SHA flying wing workshop back in the 90s that included Marske, Backstrom, Nickel, even Macready. One take away for me was that the plain plank is by far the simplest flying wing type structurally and aerodynamically. Yes, it is less efficient in terms of induced drag and yes the CG range is limited. The stall behavior is often better because pulling back on the stick means the elevons wash out the tips unlike elevators at the roots.

The solution proposed by Backstrom to the reduced lift in landing configuration was to keep it the span of the elevons short and increase their chord so they actually stick out beyond the trailing edge. The elevons would be near the tips so outboard only. Full-span elevons exacerbate the problem but I could see them working with reverse taper like the Raceair Skylite.
 
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pictsidhe

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If you are really interested in a flying wing, Nickels 'Tailless aircraft' is worth buying. I have a link to a seller of the $45 British printing.
I think Koens (Mr Nest of Dragons) was negotiating to buy the pelican design at one point, so he's someone to talk to.
 

cptcliffhanger

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Les King did cool stuff along these lines. his mixer had the same DNA as the horton posted earlier. I wish there were drawings out there but all I have are pics i took with my moms minolta 35mm camera back in the '90s it's hard to imagine a layout with lower parts count and simpler build.. plus it looked cool.. he called it the primmer as I recall.
01.jpg08.jpg06.jpg07.jpg11.jpg
 

jedi

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IMG_0577.jpg

From Nickles "Tailless Aircraft". For what it is worth. If anyone is interested.

I had forgotten this was for single control eleveron. The above mixer discussion was, in part at least, for separate elevator and aileron control surfaces.
 
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Victor Bravo

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I also saw the Les King "Primmer" about the same time as cptcliffhanger did. Les used many innovative and counter-intuitive ideas on this aircraft because it was created as much for cost reduction and construction shortcuts as it was to be a flyable basic trainer. The aircraft was built as a proof of concept, with little or no effort put into longevity or service life. Lots of plain styrofoam, no UV protection, kept in an enclosed hangar, etc. It was a nearly disposable one-off to see if his ideas would work, and he always had it in his head that there would be a version 2 and version 3, with more durable construction.

One of the things Les was experimenting with was vacu-formed plastic wing ribs in a Pratt or Warren truss shape. He made molds and vacuformed several different rib sections using the least expensive ABS plastic, to see if these parts could meet the structural requirements of a rib without having to glue sticks together into a truss. This led him to experiment with vacuform-able thermoplastic laminates that had fibers laminated between layers of plastic, and a lot of other innovative "outside the box" stuff.

The concept was to have something that cost a few hundred dollars in non-aircraft materials to build, that a couple of teenagers or a school science class could build and successfully fly.

Because of the nature and purpose of the Primmer, I doubt that much of it still exists. It was definitely more on the disposable side, like the Depron and tape electric R/C models that people can build in a day.

If anyone is interested in this aircraft, by far the best person to contact is Dan Armstrong who is a director of the ESA (Experimental Soaring association). Dan was the President of the organization during that period, and was a close friend and associate of Les King. Dan was also the test pilot of the Carbon Dragon foot launch sailplane, and I believe he is one of very few people to have successfully foot launched it.
 

cptcliffhanger

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that's right VB! he also had a very clever wing design that gave you washout that could be built on a flat table. aside from the very tip, the D box was constant from root to tip, and the trailing edge was also constant from root to tip.. the only thing that changed was the chord length and therefor the length of the parallel lines that connected the D-box to the trailing edge. this results in a flat section of wing that you can build on a table but aerodynamically it behaves like washout.

Quick sketch here shoes about what he had come up with.. you can see the relative AOA difference between the root and the tip (washout) even tho the wing is flat sided..
Untitled.jpg
 

pictsidhe

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Re flat wings with washout. If you look at a Hurricane wing, it is flat on the bottom. It has one degree of washout, though. This happens at the root airfoil is thicker than the tip, canting it's camber line up slightly.
With suitable selection of airfoils, you can build washout on a flat table.
 

Highflight

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awesome! that answers alot! Yes, the basis of what i've been tinkering with this design is to get something super simple, strong and light! I like the idea of direct push rods to the horns, it'll keep parts count to a minimum and less points of failure. Still trying to build the entire thing in my head, most likely will be building a few small scale test models to point anything out then a large 50% model, then the actual thing!

Peter,

My two cents is to build a constant chord wing with sweep like the Kaspwerwing, or a tapered trailing edge wing like the Monarch. A plank wing is enticing in it's ease of build, it is difficult however to prevent from being overly pitch sensitive and prone to tumbling.

This is a control diagram by Witold Kasper for his wing.
 

Victor Bravo

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I have read the flight test report article on the Backstrom Powered Plank WPB-1. No mention of over-sensitivity or tumbling, and remember Al Backstrom himself was an engineer or safety inspector for the FAA.

I have not read anything indicating that the Fauvel-based Pelican is prone to tumbling. Debreyer's articles have no mention of it. The JCD 02 Pelican flew safely and predictably enough that when he built the JCD 03 the aerodynamic design remained exactly the same. NO significant change in airfoils, reflex, CG, size of control surfaces, etc. If the Pelican was prone to tumbling then the guy would have changed the design when he built the second one. The JCD 03 was only changed to make it a little more heavy duty and with slightly more power, built in composite instead of wood.

A US Air Force qualified pilot (and 4 star General, Mike Hostage) has built, flown, and tested the Marske Pioneer 2 glider. No reports of tumbling or over-sensitivity. He found it to handle well enough that he went on to build a Pioneer 3, and he is likely involved in flight testing of the Pioneer 4. Not something a 4 star General needs to be doing if the aircraft is unsafe.

If I'm remembering right, the only "prone to tumble" I have ever heard about in a flying wing was the tumbling that Kasperwing pilots were able to do during aerobatic routines, on purpose. Before you believe any of the BS you hear on the internet, do a Google search for "kasperwing tumble" and see what you come up with. Then do the same search on "marske pioneer tumble", backstrom plank tumble" and debreyer pelican tumble".

I am not steering you in the wrong direction with the Pelican, and you would not be going in the wrong direction with the Marske configuration either.
 
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