Is there a cheapest/lightest/simplest wing structure other than aluminium tube and fabric?

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TFF

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With a homebuilt, you subsidize the labor. Free. You can choose materials; even used materials. If you have to wait and save to buy a component, you can.

If a factory builds it, cheap labor is too expensive. It costs that much because of tooling, engineering, materials, engine, radios, labor, facilities, and regulations. All have a dollar attached. Once you turn it into something that has to make money to survive, there is no benevolence.

Of course it’s a non starter, that’s why there are none on the market. The market is not 20,000 a year for the next 25 years. It’s 10 or 100 or 1000 total.
 

Blackburn Mark

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Rather ask, how many Unicorns do you regularly see. There's the Narwal, and the Heavy Duty Assault Unicorn ( Rhino ) , and the Triceratops, so they have, and Do exist, but don't seem to be common.
So you were passing off subjective speculations for expertise or knowledge.....?
Why else you would invoke "Darwin" and side with the negative riding on such thin evidence instead of asking for information or demonstrating your conclusions?
I genuinely thought you may have evidence of boom mounded propeller failures.


Is the "heavy lug" you remove needed to support a "conventional" belt drive PSRU?
You left it a little late to ask if it can be done or how it might be done... You already know it cant be :)
I, on the other hand, do NOT know if it can be done but I am aiming to find out despite those who get their kicks from conflating speculations with useful information.

I do have my doubts, many of them... I'm guessing a 50/50 chance of failure.
1) Weight
2) Weak weight saving aileron design on my part
3) prop-shaft flail vs fatigue conflict to solve
4) Tail boom resonance
5) Destructive crank propeller resonance (I think the prop shaft might blow before the crank snaps which would be nice)
6) Running out of steam
Then there are those problems that sneak up on us from the dark corners of our ignorance.
1, 5 and 6 are the big ones.

Being told "it cant be done" doesn't feature on my list :)
 

Lucky Dog

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Aug 4, 2021
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I probably missed it, but may I ask the reason for keeping it below 70 kg? I'm afraid it will be a futile exercise if you want a viable flying contraption, unless you just want to do it as a personal challenge. That's perfectly fine, as long as you are fully aware that the end result may not be practical at all.
I think this class of aircraft represent one of the last and perhaps most difficult design challenges left. It's a largely unexplored flight regime that I, for one am interested in. All of us 70KG and FAR 103 airplane builders should start looking for a contest sponsor who could underwrite a prize for the best conforming "microlight" over a specified 100km course that includes climbs to altitude, a GPS-point XC and graded maneuvers over the field. Maybe a World Championship every four years, with annual contests in participating countries?
 

proppastie

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contest sponsor
I could support that, maybe a large prize or prestige could add incentive.....but the challenge and joy of design and build should be enough to birth these aircraft....they do not weigh that much such that it should not be a large outlay in cost of material.....
 

Aesquire

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I genuinely thought you may have evidence of boom mounded propeller failures.
I didn't say that, I know of a few ( Moyes! lovely machine ) but an idea so elegant and clean would be the dominant form if it didn't have downsides that caused it not to be popular.

If your application is intended to be a minimum drag craft with a high boom/tube tail support, by all means design, build, and fly it!

I say that I do not recommend the hollow prop hub on boom, Or the use of long extension shafts. Not that they can't be done. ( P-39/P-63 for example. Very well designed! The "problem" the Airacobra had was timing and requirements. Not the shaft. I have a whole rant on that it you want it! ;) )
I think this class of aircraft represent one of the last and perhaps most difficult design challenges left.
Agree!

Don't mistake skepticism with condemnation, here. :)
 

Blackburn Mark

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Sep 17, 2020
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I didn't say that
My apologies, I may of somewhat misinterpreted.
Omitting the "exotic" drive requires more structure (weight) believe it or not.
I was drawn to the simplicity of tractor mounting the prop but I couldn't get it to look like it would work with the same level of redundancy (with its additional weight, other compromises would need to be made)
Every design iteration had its Pro's and Con's and I went through a good few of them (round and round in circles for months)
Currently, I am confident I can lose one weld anywhere on the airframe without a catastrophic failure of structure besides the nose tube which I am hoping will take a failsafe cable without too much effort.

The prop-shaft is only 300mm long and will be either bonded carbon fiber thin wall tube or aluminum thin wall tube... More to prevent the Thomas coupling going into flail mode than overall airframe weight saving.
The drive is my biggest unknown, I am fearful it could cause me a LOT of problems so its implementation is not taken lightly but between it failing and having additional airframe redundancy, it won by an easy vote :)
Its differing torsional flex may also cause a destructive resonant coupling between the crank and prop, my only optimism on this issue comes from the fact that snapped cranks on these particular motors was remedied by adding rubber gaskets under the prop which I have had to remove but the shaft, with backlash free couplings ought to give me some level of backlash free flex back (very unscientific)
Its a gamble but like I said, I prefer having doubts on the drive train than the airframe.

Minimal drag is NOT really a consideration for this kind of machine (besides its very low speed), its ALL about the weight AND attempting to maintain a strong confidence in the airframe.
 

oriol

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Dec 31, 2009
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Barcelona, Spain.
Hi!

As Erkki and Bmcj pointed out a sub 70kg airplane/primary glider would not be something very performing. However from the design perspective it represents a very exciting challenge; to be able to do more with less.

Buidling a rectangular covered with fabric, without dope, and 3d printed widgets, like those used by addicted to climbing, seems the most straighforward wing for a three axis airplane. I really like the first version of the Swift flying wing which was tube and fabric.

If considering a parafan engine for a light aircraft design. A tractor engine would make a light aircraft nose heavy for a parafan or weight shift. In my particular case that makes very hard to add an engine in my recumbents. However, I was thinking to take off with a trike fuselage and a paraglider without engine like in the video below.


I do not know if with your experience with parafans Blackburn Mark this would easy? I know the engine helps inflate the wing which makes it more easy to take off. I bet that in the right place with the right wind this would possible.

A possible alternative to use an engine to help taking off with a paraglider, without adding prohibitive weight to the nose, would be to use an big electric RC/drone engine, and place the batteries on the back. Given the high cost of batteries for sustained powered flight, I would probably use some standard drone batteries. this would allow me to take off and perhaps stay below the sub 70Kg limit both using a paraglider, delta wing or even a rigid three axis tube and fabric wing.


Henryk, I know very well from my personal experience, and I bet that all in here agree with that, that being able to carry on with a build is very hard because life goes on. I hope you can work more on your projects!

Given said, that I agree with Aesquire that trying to design an engine/transmission for a homebuilt tends to overcomplicate it a lot. It is much better to adapt your design to an engine that is available on the market rather than the opposite. That being said we are lucky to live in a free world, at the end its our own choice what matters.

OTOH, I too agree with Aesquire that perhaps the theroetical Cl of a Kasperwing is very high but probably in reality is more or less standard.

Sorry I do not remember who mentioned, but I think the Whoopy was never commercially available after a pilot lost his life testing it. I think the accident was due to the wing collapsing in flight.

Thanks a lot everyone for your comments!

Oriol
 

Blackburn Mark

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I do not know if with your experience with parafans Blackburn Mark this would easy? I know the engine helps inflate the wing which makes it more easy to take off. I bet that in the right place with the right wind this would possible.
Thousand's of hours free-flight, much less with a motor.
Free-flight foot launching and landing is very easy once you have some practice.
Paramotor foot launching is reasonably easy but the weight makes it very physically taxing.
Paramotor trike is a bit of a *****, setup has to be quite precise, misaligned launches are difficult/slower to correct, A-line pulls are painful because of the uncomfortably upright body position, you need a reasonably flat and reasonably sized field.... The upside is, they are not physically taxing even in nil winds and high speed landings are possible.

I don't know why you would fly a powerless trike, all those disadvantages and none of the advantages.
Trikes are very clumsy but they are an option for tired old legs.


I would probably use some standard drone batteries. this would allow me to take off and perhaps stay below the sub 70Kg limit both using a paraglider, delta wing or even a rigid three axis tube and fabric wing.
I guess you are still in the wild speculative conceptual stage of design, its fun but concluding on specific goal takes some doing :)


Whoopy was never commercially available after a pilot lost his life testing it.
I think you may be mistaken, I couldn't find any info on such an incident, thank god :)
 

oriol

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Dec 31, 2009
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834
Location
Barcelona, Spain.
Hi Blackburn Mike, thanks for sharing your thoughts!

The idea of flying in a powerless trike is that the trike can be one of my recumbents, like the picure I posted before in the thread.

The thing is that, I like getting lost in the woods on a bicycle. It would be cool to tour the country, and be able to glide from paragliding spots. Having a bike that glides like a draggy primary glider would be worth and almost maintenance free wihout an engine.

The hardest part is to find a nice slope to perform a gravitational take off. The advantage of a paraglider versus any convetional aircraft is that the rotational speed of the wing at take off, helps to reach v take off sooner and without the need of a long run. That is the key point, If I could be in the air without the need of an engine.

Perhaps I am not being clear. The midpoint between using a parafan engine or going powerless would be performing an assisted take off and then shut down the engines. That is where the idea of using electric big size RC motors for assisting in the take off. The combination of electric motors with batteries allos for a reduced weight.

The videos above is a clear example of being able to take off with a lot of dead weight. In my case the dead weight would be my bike.

Another option would be designing an aircraft from scratch but it is costwise to recycle one of my recumbents. I am open to all options. Right now I am just considering the pros and cons of all of them, while I read aero books, before getting started and cut tubes etc.

I agree TFF with those specs this might qualify as a not useable aircraft. But that is the spirit of deregulated sub 70kgs aircrafts, paragliders, primary gliders or pafans, just fun!

Thanks again for your inputs!

Oriol
 

Gregory Perkins

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May 25, 2019
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175
Location
Atlanta
If I was aiming at a 70 KG build, I cannot think of a smaller better performing and better engineered plane than the Birdman TL-1A marketed by two companies in the mid 70s.
The first plane weighed 100 pounds, was two axis and had fragile thin wing skins with a square box aft fuselage with conventional tail. The 2nd company put a bigger motor on it, increased the wing skin thickness, converted aft fuselage to round cone and added spoilerons bringing it up to empty weight of 122 pounds or 56 kilograms leaving 14 kilograms for avionics etc.
 

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