Single Struts

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DarylP

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Hi everyone,
I know this is a basic question for most of you and although I can research it online, I like getting info from you all too.

I was curious as to the design of a wing structure that allows a manufacturer to use a single strut as opposed to the dual V struts (and jury struts). I am sure that the single strut design has a lot less drag, but is it as strong as the dual? The wing itself has to be redesigned I would think, when doing a single strut, so that it would distribute the loads better.

Then there is the Wilga (and others) that use a cantilevered wing, which in my limited knowledge I figured would never work on such a plane that lands in rough terrain. It uses a larger spar that runs straight through to get it's strength...right?

I was looking at pictures of two of my favorite planes, the Bear Hawk Patrol and the Highlander. I had not noticed before that the Patrol uses a single strut while the Highlander uses the dual V struts. These are similar (just as the Wilga) aircraft in that they are all used as STOL aircraft, but yet three different wings (strut vs no-strut) designs.
If you were to design a STOL aircraft, which would you use, and why?

Thanks,

Daryl
 

Dana

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To use a single strut, the wing has to be able to handle all torsion (pitching moment) loads internally. With two struts, the wing doesn't need to be as stiff, and small adjustments in strut length can twist the wing for roll trim.

-Dana

Chaste: why virgins run.
 

orion

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Exactly, what Dana said. The dual strut wing will be the lightest since it needs only light spars and it takes care of the torsional loads by resolving them through the two spars directly into the struts and the fuselage attachments.

The single strut configuration allows the strut to handle only the bending load so torsional loads (moment due to airfoil shape, control deflection, flap deflection) must be sheared into the skin. For light loads this can be done with just a structural "D" section, but most designers like doing the whole wing of aluminum.

The cantilever wing will be the heaviest and it will also take up the most space on the inside of the cabin since it needs a full depth carry-through structure. The strut braced wings only need a structural attachment at the side of body, and a compression member going across, which can be a simple tube.

The strut braced wing has two drawbacks - one, the strut(s) are a source of drag but, in reality, the penalty is not really all that big. And two, when landing in the bush, the strut can get snagged on growth or damaged through mishap. That ends your flying until it can be repaired. The cantilever wing is not so easily damaged but it does have the penalty of more weight and the inner volume usage.

I've designed several bush planes and have used the cantilever wing and the single strut. Usually it's the customer's choice. Personally, I prefer the cantilevered configuration.
 

TFF

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Although the missions are different the Tailwind and the Buttercup is a good example of structure with one or two struts by the same designer. Similar but different. If you can pay the weight penalty no struts are always the best as nothing to snag in the bush and less drag. Strut wings are probably easer to design and easer to build, and for a design not engineered to the nth degree, stronger and lighter. There has to be a crossover point at some weight and HP where no struts becomes preferred and does not have as big of a weight penalty.
 

PTAirco

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I would venture to suggest that in some cases a single strut braced wing can be as light as a two spar-two strut wing. I went through this with my current single seater (UL3 - in the projects list and my avatar). I designed two wings, one with a single spar and D-box leading edge, partially fabric covered and a conventional two spar, two strut design. If you added up the weight of the extra spar, strut, fittings and the non-structural leading edge sheeting, it came to pretty much the same weight as the D-Box and slightly heavier spar. There really was little to choose between them and the single strut won out because of being simpler, with a much lower parts count and less drag. This is at the lowest end of the weight scale, heavier designs might show up a bigger difference.
 

Dan Thomas

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Several bush planes use cantilevered wings:

The Helio Courier
11589385UrmGyaQnkr_ph.jpg

The Found FB2 series:
2203373498_444933bc32.jpg

The Wilga:
pzl_wilga_1.jpg

The Cessna 210 is used by some bush operators:
pg008.jpg

And the wings don't fall off. The cantilevered structure is as strong as a strut-braced affair, just considerably heavier.

Dan
 

Jan Carlsson

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If it is a strut braced wing, isn't it a minimum to have two struts? one per side? :)

Jan :)
 

Jay Kempf

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If it is a strut braced wing, isn't it a minimum to have two struts? one per side? :)

Jan :)
Not at all. The two strut versions are attaching to both the main and rear spars individually meaning the fuselage has to have structure to grab on to that in more than one plane. In a cub they do that but the struts are v shaped and only attach to the fuselage at the gear. Others like the C1xx series normally just have a single strut.

It is all about how you deal with the reactions and moments generated. Which means the answer is one of those "it depends" sorta things.
 

autoreply

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Not at all. The two strut versions are attaching to both the main and rear spars individually meaning the fuselage has to have structure to grab on to that in more than one plane. In a cub they do that but the struts are v shaped and only attach to the fuselage at the gear. Others like the C1xx series normally just have a single strut.

It is all about how you deal with the reactions and moments generated. Which means the answer is one of those "it depends" sorta things.
The clue is in the "one per side"-comment ;-)

Even though the Catalina has only one (in total).
 

Jan Carlsson

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I thought the same about the Catalina, for a sec, then realise it realy have 4 struts and the pylon. I was just bored for a moment. Then I changed brake caliper on the car.
Jan
 

Dan Thomas

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Man oh man,
That FB2 (Bush Hawk) is the most handsome machine I've ever seen. Man oh man. Thanks for the view Dan.
Yer welcome. The Found is a Canadian design dating back to 1946 and they built airplanes until 1967 or so, then was resurrected in the '90s. A Found is available as a taildragger, a trike (yuck) and a floatplane. It costs less than a Cessna 206, carries as much weight, takes off and lands shorter, and is built with good bush stuff like a floor that is level with the doorsill (no lip to snag stuff being dragged in or out) and reinforced with strong flooring to take a pounding. No flimsy aluminum here.

Found Aircraft: Found Aircraft

Expedition (the trike is here): Home - Expedition Aircraft

Drool some more!
0066.jpg

Dan
 

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PTAirco

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The Found Bush Hawk looks like a very sensibly designed aircraft - pity it costs about half a million....
 

DarylP

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Wow...thanks everyone! I knew I would get the lowdown from you guys.
 

Dan Thomas

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The Found Bush Hawk looks like a very sensibly designed aircraft - pity it costs about half a million....

A new Cessna 206, nearest equivalent to the Found, starts at $533,400, base price.

The 206:
Takeoff roll 1860 ft
Landing 1395 ft
Rate of Climb 989 fpm
Max Cruise 151 kts (they don't specify power setting)
Useful load 1373 lb

The Found Bush Hawk XP:
Takeoff 900 ft
Landing roll not given
ROC 1120 fpm
Cruise @ 75% 145 kts
Useful load 1525 lb

The Found's takeoff distance, climb rate, and useful load are all better, at a lower price, and the thing is built stout. Sorta makes one wonder why there aren't more of them selling, unless the advertising isn't reaching the people who buy such airplanes for their operations.

Dan
 

DarylP

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So has anyone ever had a off field landing where the struts got in the way? Some of you pointed out the possibility of that, snagging something on a strut on a landing. That must be was the Polish were thinking of when they designed the Wilga without them.
 

orion

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I've had three Alaskan customers (or at least three pilots who operate in Alaska) - all indicated that at one time or another they hit something with or snagged and damaged the strut. Another part that apparently can snag is the lower brace on the horizontal tail. One snagged a bush between the elevator counter-weight and the stab, nearly ripping the tail off. In short, it does happen and it really changes the approach one takes to a bush plane design.
 
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