Ultralight struts/cantilever/additional weight

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lr27

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rotax:
What you're telling us is that a poorly designed wing may fail in flight. That's true with any style of wing. The CH 701 is considerably heavier and faster than an ultralight, so it's not particularly relevant. It's been shown that a 1/32" plywood d-tube can provide enough torsional stiffness for a cantilever ultralight wing. And that's with 0-90 grain orientation. +/-45 would be a lot stiffer.
It would be nice to know how much typical strut arrangements weigh, though.

Matthew,
An enclosed d-tube ought to add considerable torsional stiffness, though with those diagonal ribs you might not need it. If the skin is a uniform thickness, the additional torsional stiffness should be proportional to the area enclosed. At least if the skin is supported well enough not to buckle.

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Any of these issues require more than TLAR engineering, though I suppose carefully conducted tests might replace SOME of that.
 

wsimpso1

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You have already been told that for US Part 103, decreasing drag has little to zero point, while lowest weight with high drag works fine.

All these questions skip the real crux of the matter. If you want to investigate what wings made each of these ways weighs, go ahead and do the design calculations each way for something that you could build and fly. Then you will know where things stand for your conditions.

Billski
 

lr27

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I already know that for a conventional ultralight, used conventionally, with an oversized engine and no concern for aesthetics, fuel cost, sink rate, or L/D, there's no point in drag reduction. OTOH, if you're doing an electric, a motorglider, a replica, or if you just want your aircraft to look cool, a cantilever wing and drag reduction may be just what you need.

No amount of engineering will reveal what the struts on existing ultralights weigh.
 

lr27

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Ok, I don't know if it's typical, but I have the Texas Parasol plans. Unless I screwed up the calculations, the four strut tubes together weigh on the order of 9.5 lbs. And yes, that's for the ultralight version. That figure doesn't include the jury struts, end plugs, fittings and hardware. So it seems to me there's some weight available for a cantilever wing.
 

rotax618

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In our country an ultralight is an up to 2 seat aircraft with a TOW of less than 544kg (about 1200lbs).
The greatest percentage of your part 103 ultralights are either strut or cable braced, mostly because speed and weight are limited.
Without having a masters degree in aeronautical engineering and building from unobtanium, the safest legal ultralight the average Joe can design and build would be have either a cable or strut braced wing, there is no advantage for a cantilever wing, only disadvantages - (More critical to design, have to add drag producing features to keep within speed limits, would have to be one piece to keep within the weight therefore more difficult to store and transport)
I rest my case!
 

pictsidhe

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My wing load test at 5g. Conventional Wagner beam main spar, truss diagonal ribs for torsion and drag. Tube rear spar.
Leading edge somewhat like the Ercoupe but with light formers instead of full upper skin like Ercoupe.
View attachment 92237
I love the weights!

Chris Heinz CH701 has a fairly substantial D box leading edge and stressed metal skin yet he chose to use 2 struts for safety. I note that BBersons wing is not loaded to test torsion. Aeroelasticity in torsion is a killer, in normal flight regimes it lowers control effectiveness, but an airframe vibration caused by an out of balance prop or engine missfire can cause catastrophic flutter.
Having the shear centre too far back can result in tip stalls at high g. The Fw190 being a good example. It stalled in a docile way at low g, but was vicious at high g. For that reason, I'm planning a triangular truss. spar caps, web, one rear tube at aileron mounting chord with a truss joining everything. It'll likely still have the shear centre somewhere aft of 25%, but less than with a 'proper' rear spar. Flutter doesn't need strong excitation. That dam Peking butterfly is plenty!
 
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lr27

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rotax:
In post 43, I gave some reasons one might want a cantilever wing. Let's call them advantages. Are you saying those are somehow wrong? Remember that this thread started,with part 103 ultralights as examples. I'm fully aware that the word ultralight can mean something else in other countries.

The "average Joe" cannot design or build a safe ultralight. Someone who can't design a safe cantilever wing probably can't design a safe strutted wing except maybe by TLAR (that looks about right) engineering and careful testing. TLAR engineering will create heavier airframe.
I admit that there ARE reasons for struts on ultralights:
-convincing the FAA that it's an ultralight
-adding enough drag to comply with the FAA's speed limit without having to make a gadget to throttle back automatically
-having a convenient place to hang a pitot tube or wet clothes
-having convenient tiedown points
-for a twin, you could install the engines at the intersections of the lift struts and jury struts
-you could build something that looked like a Hurel Dubois design without using carbon fiber.
......
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Matthew:
An enclosed d-tube might move the shear center to help with the issue pictsidhe raised in a prior post.

It's kind of mind boggling to me that the people at Focke Wolfe made this error. Maybe they were in a hurry.
 

rotax618

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We have a similar category to your part 103, it is an exemption from the ANO called 95.10, it is a little more generous than part 103, the limitations being that the aircraft must be less than 300kg, have a wing loading of less than 30kg/sqmetre at MToW and must be designed by the builder or built from approved plans or kit.
Hundreds of amateurs (Joe averages) have successfully designed and built their own aircraft. The Winton Opal, David Rowe’s UFO and hundreds of other conventional and unusual and advanced aircraft have been designed by Joe Averages - Scott Winton and his father Col had no formal training, David Rowe works on agricultural aircraft as a mechanic, professional engineers have little interest in the part 103 and 95.10 end of sport aviation.
Do you think only grownups have the right to dream.
 

pictsidhe

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Average Joes do not build or design their own aircaft. It takes a special nut to do that. They do need some knowledge to do a decent job, but there is no obligation for that to be formally obtained.

FWIW. This nut is going cantilever not for low drag or yadda, yadda, yadda, but because it looks cool!
 

Hephaestus

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If there's something I can trip over... Assuredly I will.

Cantilever for the win! :popcorn:
 

lr27

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I think wing struts are the kind of thing that you run into or hit your head on rather than trip over. ;-)
 

Hephaestus

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I think wing struts are the kind of thing that you run into or hit your head on rather than trip over. ;-)
Never underestimate the Sasquatches ability to trip over anything at less than 4' tall :dead:
 

pictsidhe

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I'm working on a low drag cantilever design. The appendix says I can have a calculated max power of around 15hp. But that will give really lousy climb. The appendix says that it is also fine to limit engine power to keep speed down to 55kts. I'm reading that as infinite power is legal below 55kts, the calculated power is legal above 55kts. I shall be using a speed sensitive power governor.
 

BBerson

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I don't know anyone that complies with AC 103-7 today.
That standard was only enforced at Oshkosh for about one year in the early 80’S.
The FAA is only checking compliance now for one seat and 5 gallons fuel maximum, according to EAA.
Full compliance with the outdated AC would require a technical committee inspection. There is no technical committee now. Partial compliance with the AC has dubious value.
 

pictsidhe

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I don't know anyone that complies with AC 103-7 today.
That standard was only enforced at Oshkosh for about one year in the early 80’S.
The FAA is only checking compliance now for one seat and 5 gallons fuel maximum, according to EAA.
Full compliance with the outdated AC would require a technical committee inspection. There is no technical committee now. Partial compliance with the AC has dubious value.
I have heard enough tales of grounded not-really-103s to want to stick to the rules that are current. It can be extremely difficult to make them legal if they are intially built to flout the rules. You can easily end up with an expensive pile of low value parts.
 

stanislavz

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Did everyone forget the Hummel Ultracruiser? A very successful all aluminum Part 103 ultralight with cantilever wings.

I would think that the answer to too little drag would be to limit the engine size. IIRC, the regulations limit the speed at max power in level flight, don't they?
And "funny" story - it was designed after author crash in mini-max.
 

rotax618

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Some of the early Maxair and Quicksilver types used a high lift airfoil with a large pitching moment counteracted by a large decalage angle, they also used Ultra Props, which had no twist, to keep the speed down while maintaining an acceptable climb rate.
 
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