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Cantilever wings and 4130 fuselage questions?

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FoamandTape

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hey all,

Currently thinking about crafting up another ultralight but have been thinking of making a smaller than "usual" (and lighter) craft. After building the last two (one of which was sorta successful- never mind the 2nd one haha we wont talk about it) I'm beginning to think about copying less of other "fat" ultralight designs and build something proportional to myself and utilize smaller powersystems etc. I did get an aerolite 103 to learn more from it but am itching to try another airplane with a hybrid of three different methods- chromemolly for the fuselage, traditional fabric covered wings/tail sections. possibly even a hybrid wing, foam/fiberglass "D" section of the airfoil and standard ribs for the middle/trailing edge portion (covered in oratex UL 600)

Still brainstorming about constraints but itll be gas powered for now, swapping the motor out for electric is planned as well once battery tech catches up. I'm really going to try to shoot for 125-155 AUW, 20ft WS 14ft length etc... I want to make it small and simple, will probably use a modified clark Y airfoil with a much thicker height to get more material into the spar. Monoplane design for less parts count and low wing to keep material for the fuselage down. Drawings will follow soon


Its all just spit balling for now till I figure out how to piece it all together, I'm mainly wanting to seek advice/plans on successful cantilever UL designs and if anyone has plans for an air bike/legal eagle! would love to just look and study these!

Also thinking about using a para motor engine such as this http://www.eos-engine.com/index.php?lang=1&hID=29 The AUW of the entire engine with accessories is about 21lbs!
 

lr27

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Well, the Sky Pup has been a successful cantilever wing ultralight. It has an 18 percent thick (more or less) airfoil, as I recall. The original was supposed to come out at 195 lbs, but I guess most of them come out considerably heavier. Still legal weight, though, I think. Spar has Styrofoam shear web, with ply near the joiners. Somewhere I saw some tests indicating that foam and wood ultralight ribs are a bit lighter and stronger than conventional, but that probably depends on a bunch of things. The SP has thin plywood sheeting on the first part of the wing. Might be worth buying the plans. According to them, an SP shouldn't have more horsepower than the engine you're considering, but I seem to recall reading that the engine can be up to 60 lbs, so you might need to extend the nose a bit. So just using a light paramotor engine might meet your weight goals without changing the design. (other than stretching the nose) The wing is a lot longer than what you have in mind, but that means less power is needed. I imagine, if you're lighter than the 170 lbs max pilot weight of the SP, and relatively small, you could probably shrink it somewhat. Not to 20 feet, though. If you want to go electric eventually, you'll be able to do it sooner if you pick something that's got a long wing and is relatively clean. If you really want to keep the span down, and you think you might go electric eventually, you probably should consider a bipe. One with a big gap and not a lot of struts and wires. But there's only so much span that will save you.

Something to keep in mind is that fat ultralights may not meet the stall speed requirement either, even if you get the weight down. Some require fairly implausible lift coefficients to do so. The original Legal Eagle is one. With a 170 lb pilot and 5 gallons of gas, to stall at the legal limit I get a Cl of 2.1 for the entire wing, which means it has to be higher in some places. You'd need some kind of fancy flaps to get that, or a very unusual airfoil, perhaps. I think the XL with vortex generators might get there, though. The Sky Pup, with that 170 lb pilot and the recommended 2 gallons of fuel, requires a CL 1.5, which I think its plausible. Not a lot of extra, but plausible.
 

pictsidhe

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I have a spreadsheet that generates Riblett type airfoils. It can use multiple camber lines. It can probably spit something out that works better than a thickened Y. Or use a NACA 4 digit. Don't be afraid of going thick. I'm working on a Hurricane 103 and don't see a need to thin it's 19% root, depsite that being a drag issue with the full sized ones. Thin airfoils are not needed or even beneficial on 103s. 15% is about max lift for unflapped. If you have split flaps, you'll get a higher CLmax/Cdmin going much thicker, maybe up to 25-30%. A Cl of well over 2 and pushing 3 is possible like that.
You don't want to prune your span too much, or the induced drag will get silly.

For a planar wing with an elliptical lift distribution, induced drag can be calculated as follows:

induceddrag.png

where

L is the lift,
rho is the air density,
V is the true airspeed, and
b is the wingspan.
From this equation it is clear that the induced drag decreases with flight speed and with wingspan. Deviation from the non-planar wing with elliptical lift distribution are taken into account by dividing the induced drag by the span efficiency factor {\displaystyle e} e.

If you aren't going to do your own structural analysis, then please, steal someone elses design!

If you haven't played with XFLR5, you should.
 

pictsidhe

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Another point, tapered wings have a struvctural advantage if you are going cantilever. The major down side is that you only make a rib twice, then make a new jig...
 

lr27

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You could cut out a big, fat foam core, glue on all the cap ribs, spar caps, sheeting, etc., and then cut away all the unnecessary foam. Wasteful of foam but might be faster to build.
 

pictsidhe

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Here's an idea.
Set up XPS rib blanks spaces as they will be in the wing. Then hot wire them like you'd cut a solid foam core with a template on each end (unless you are one of those flashy CNC dudes). Glue some thin ply caps on and Bob's your uncle.
 

Toobuilder

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The Goldwing was cantelever. Might look to that one for structural ideas.
 

ScaleBirdsScott

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So off the dome, two successful UL cantilever wings I can think of are the Hummel Ultracruiser and the Titan Tornado. Larger than UL and a lot start to open up. Unreleased, but the Murphy JDM-8 was ostensibly a UL with a fabric-covered cantilever wing.

The downside to cantilever wing is you really gotta be sure of the spar structure and mounting and there's not a lot of room to just go with it. I tend to think using some kind of struts would do a lot in simplifying these types of projects and structure, even if there's more parts by simple count, the strength assurance of those struts is a big deal. You could pretty-much go with some established sizes and layouts and know your wing will hold. But if you're talking low-wing monoplane it's not as cut-and-dry; strut supported still works but there are less examples. You're basically just making a 30's era monoplane so what's the fun in that? (Well I think it'd be a lot of fun, but in terms of interesting content I don't know how that fares)

That all said, been working on something similar minus the 4130. Riveted alum tube structure, cantilever wing, fabric covered, UL or near-UL weight, simple to build. Legal Eagle, Hummel Ultracruiser, Simplex Zing, Airbike and all that being touch points. Additionally been looking at that JDM-8 I mentioned, the Thatcher CX-4, the BD-5, Graham Lee Nieuports, and many more to get inspiration.
 

TFF

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Definitely get the numbers right if going cantilevered. The wing has to be be ridged in every direction instead of getting triangulation with struts or wire bracing. If you want to get lighter, you are going to have to shed the fiberglass covered foam. I like the execution but better for a plane that can carry the weight. Foam ribs and fabric. Depending on structure you might be able to use it for the leading edge. You can always rout ply ribs. Dacron is just line monokote is reality. I don't have plans but I helped build a LE and it is probably one of the strongest ULs on the market. Its like any other 4130 fuselage so you can study most any of them except the wing attach. If you find you have to add struts, low wing uses the struts in their weakest way. Really think it out or the wings will fold and not talking hangar storage. A hummel wing attached to a LE fuselage might be interesting.
 

ScaleBirdsScott

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Another option for struts would be Minimax or Fisher Avenger style, aka up from the landing gear. Pretty straightforward and helps quite a bit. But again extra drag, so if you're going for that 20-30hp range it's tough.
 

Victor Bravo

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Look into the Backyard Flyer ultralight. It has a cantilever wing that rotates 90 degrees parallel to the fuselage for storage. Do not just copy that design without running it by an engineer, because there have been some questions about that design. But it has NOT been definitely proven out that the Backyard Flyer is or is not safe, or has enough safety margin. Study it, see if it meets your needs, see what you can learn form it, and then just make sure you have the numbers figured out before you base a whole airplane on it.

There was also another Part 103 ultralight called the Hummel H-5 or H5. It had a cantilever wing built in sheet metal.

Something we have been discussing on this forum is the Debreyer JCD 02 and JCD 03 "Pelican". A google search for "debreyer pelican" will turn up a bunch of photos. The interesting thing about this airplane is that it probably meets Part 103 or could be made to meet it, it's a full cantilever flying wing layout, and was specifically designed to fly on minimum engine power. Now if you build a version of that airplane, scaled down to fit your size and weight, you might create something that has really good performance on a very small economical engine. Debreyer flew his on 9 horsepwoer, then went to 12 or 13.

If you are lighter than Debreyer, you might be able to shrink that design down to an even smaller size and still meet all of the legal requirements for an ultralight. The Pelican even looks a lot more interesting and sleeker than most ultralights. Definitely not a slab sided box hohmely looking thing.

The original one was built out of wood, but the second one was foam and composite. It also has the potential to be far stronger and more robust than many other ultralights because it is very compact and uses a very thick wing (17%).

pelican_3d.jpg
 

BBerson

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A custom small size ultralight for a small person is a good idea. But it will need custom design. Doesn't need to follow the rules exactly. Plenty don't, as long as one seat.
The wing construction design of the Lazair could work. It is mostly cantilever with short struts. Using only the cantilever outboard section for a ten foot cantilever wing would work. It also uses clear 2mil Mylar which is twice as thick as Monokote.
The Lazair wing is a metal D-Cell with metal capped foam aft ribs.

A fabric cover cantilever wing can also be made with diagonal ribs, look at an Ercoupe wing.
 

cluttonfred

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image.jpg 1950355_orig.jpg

Something along the lines of the Barry MB02 Souricette micrlight might be a good way to go using shorter span, longer-chord, full-cantilever, wood-and-foam-and fabric wing like a Sky Pup and a very light two-stroke engine. Our own Ed Fisher might have something to say about very light welded 4130 steel tube fuselages since his own Skylite Part 103 ultralight has one.
 

PiperCruisin

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Maybe a carry-through spar structure would be simpler (Mooney or Robin type). Makes it harder to store/transport so maybe combine with folding outer wings where there is a lot less bending moment to deal with.
 

WBNH

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Plans are still be available for the Howland H3 Pegasus. Welded Aluminum frame, and cantilever low wing. No foam though, as far as I recall. Theoretically could make UL...but practically? https://en.wikipedia.org/wiki/Howland_H-3_Pegasus Perhaps an idea how they did cantilever however. https://www.aircraftspruce.com/catalog/kitspages/h3pegasus.php

It may be hard to dig up info on a defunct design, but the AmeriCana Eureka could be close to your thinking. Miminalist plane. They used aluminum skins over foam, not sure about the spar, but didn't opt for cantilever. https://en.wikipedia.org/wiki/Ameri-Cana_Eureka
http://eureka.mynucleus.ca/home.htm
Might be an interesting fusion of foam and aluminum? And looks like your sketches. I contacted them once many years ago, still never got photos showing internal construction and they weren't interested in selling plans, only wanted to produce finished aircraft.

Lots of attempts are out there for welded 4130 and ultralights. Legal Eagle may be closest. Kitfox Light, Sky Raiders, Avid Champion, Ridge Runners, TEAM AirBike, N3 Pup/J3 Kitten (same weldment) etc. Most if not all are heavy.

To hear of 4130 and cantilever, low wing according to your sketches, sounds something akin to trying an oversized wing on a Sonerai fuselage to make an UL. I'm no expert on space frames, but to get Ultralight weights for a welded steel structure, you'd likely have to optimize every single length of tube. Using a variety of diameters and wall thicknesses.
 
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BBerson

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Thanks for the replies all! I'll get back to them later and will check the aforementioned airplanes out. I ended up screwing around in cad last night and roughed something out for a small plane. This is with a 20' span.
Looks good!
I like low wing.
Should be fine if you keep it light.
 

cptcliffhanger

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never mind the 2nd one haha we wont talk about it
All joking aside, unless I missed a youtube video that explains the death of SN 2, it wouldnt hurt to discuss what went wrong if you want help making sure SN 3 is a great success! there may be some lessons learned there that would help move the conversation forward.

S
 

ScaleBirdsScott

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The design seems a rather narrow fuselage: but you did say you're building bespoke to your dimensions so I'll leave you to it on that.

Also aesthetically I wish it had a bit longer gear legs but, obviously other things are more important drivers.
 

Topaz

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... From this equation it is clear that the induced drag decreases with flight speed and with wingspan. ...
Induced drag is decreased by increasing airspeed, and increased span. That's why both of those terms are in the denominator of the equation.
 
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