Flying Wires vs Struts

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challenger_II

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Question, for those who have the experience:

On ultralight-type aircraft, which has the most drag- flying/landing wires, or struts.

I have seen opinions, both ways. Thought I would get some empirical data.

Thanks!
 

proppastie

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might have to do a little math.....how big is the strut how big is the wire?
 

Dana

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Round struts will be draggier than wires. Streamline struts, hard to say, they may be draggier but if not won't be much less drag than wires.

I know that for the Quiksilver, the wire braced version was much more rigid and a better flyer than the later strut braced version. The main advantage of the strut version was that it cleared low hangar doors that would be a problem with the kingpost on the wire braced version.
 

challenger_II

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Dana, some how, I figured you would chime in! :)
You are the second person that has related the rigidity/performance example. The other gent used the wired vs strutted Drifter as the example.

Hangar clearance isn't my issue. I'm trying to balance weight vs drag considerations on a new bird.

Thanks, to both responders.
 

Pops

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Friend of mine built 4 different MiniMax's. On one, he hotwired foam to a streamlined shape, epoxed on the struts and used fabric tape and white glue and wrapped the foam and went from 65mph to 75 mph cruise with the 1/2 VW engine.
 

challenger_II

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We had similar results with a Mini Max, except we used aluminum sheet formed into a teardrop, wrapped around the tubes.

Friend of mine built 4 different MiniMax's. On one, he hotwired foam to a streamlined shape, epoxed on the struts and used fabric tape and white glue and wrapped the foam and went from 65mph to 75 mph cruise with the 1/2 VW engine.
 

TFF

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You can see how bad a little wire is and there is an old video that has been posted many times with that in a lab. To me wire is cheap, but requires to be rigged if it comes apart and it can stretch when new and need an adjustment. Struts will cost more, but once fitted, should be sturdy, not a tangle if it you take it apart and easier to set up.
 

flitzerpilot

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The Flitzer Z-1 (and 21 series) has about 10' in total of 1" steel tubing in its main landing gear. Flying initially with this unfaired, it was at some stage (about 20 years ago) faired with foam and glass-cloth into a 3:1 ratio airfoil with the diameter of the tubes forming the curved leading edge. It did make a difference to the cruising speed but with changes of propeller and other factors this was not measured accurately. However there is another important modification that can be made to flying and landing wires, which are stranded galvanised round-section cables, not lenticular. That is to glue small-section trailing balsa fairings to the cables and wrap the whole length with adhesive backed foil tape. It needs to be applied with care to avoid it separating, especially if there is any tendency to wire 'buzz'. The fairings will stiffen the wires and ideally anti-vibration javelins should be used to stiffen the bracing cellule at mid-point.

The cabane tubes, although they are only 5/8" dia. project only slightly above the decking line, but would also benefit from fairing. Meanwhile I have used streamlined hollow wooden 'I' struts in the interplane locations which themselves provide the best streamline solution with no incidence bracing required. Win-win!
 

wsimpso1

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See this article by member and noted aerodynamacist Barnaby Wainfan


Any reasonably streamlined strut is lower drag than a round wire doing the same job. That is comparing one circular wire to one streamline strut. Then we look at rag and tube airplanes that needs one big strut and one small strut per side, while if it is wire braced, it needs four wires - twice as many wires as struts follows into monoplane wings with structural skins and even into biplanes. So round wires hit you twice on drag and are each more draggy than the wings themselves.

One big improvement is to split a thick wire into two smaller wires and put them in tandem. This reduces the drag coefficient of the set and reduces the frontal area too. Other tricks are to sweep them and/or put a trailing fairing on them.

Go to bladed wires, and the drag drops quite a bit. An improvement yes, but then you still have to have twice as many and they tend to be costly. Struts are nice...

Billski
 

cluttonfred

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It might be useful to compare two aircraft that are basically similar except for the flying wire/strut question. Quicksilver and Airdrome Airplanes have such models you can compare, and historically you could go back to look at an Aeronca C-3 vs. Aeronca K using the same E-113C 40 hp engine.

The Aeroncas clearly show that for low-powered, low-speed aircraft the wires are not a huge handicap in terms of performance and they do provide substantial weight savings. The C-3 has a 436 lb useful load while the K carries just 296 lb. I am not entirely confident in those numbers, and the K's greater weight is probably due to other "improvements" as well as the switch to struts, but I think the principle is sound.

IMHO, if you want to maximize load-carrying ability in a true Part 103 design without using exotic materials, wires are the way to go. Since drag increases with the square of the speed, the slower you go, the less it matters and the more the weight savings come into play.




Aeronca C-3 Duplex (1936)*Aeronca K (1937)**
Span36' 0"36' 0"
Length20' 0"20' 0"
Height7' 10"6' 3"
Empty Weight569 lb744 lb
Gross Weight1005 lb1040 lb
Cruising Speed85 mph80 mph***
Maximum Speed93 mph93 mph
Maximum Rate of Climb450 fpm450 fpm
Service Ceiling12,000 ft12,000

*Specs from Skytamer attributed to Jane's All the World's Aircraft 1937
**Specs from from Wikipedia attributed to Airlife's World Aircraft by Rod Simpson
***Cruise speed from EAA Museum as Wikipedia did not quote this figure, but since the EAA site also quoted a 90 mph top speed I suspect printed specs for both models are optimistic and 80-90 mph is more realistic for both little planes.
 
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Kyle Boatright

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Now that someone introduced Aeroncas into the discussion, I have a question. Following the C-series of Aeroncas, didn't the FAA ban that system of wire braced wings from certified aircraft? Can someone (anyone...Bueller?) explain why that was regulated out of the certified world, and why it isn't (or hasn't) been an issue in the UL/Experimental world?

Thank you,
 

TFF

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They are not going to issue a design FAR for homebuilts and you don’t want them too. The safety police would kill anything original because that’s how they would do it. Homebuilt Cessna 172 spec planes only.
I would imagine the original was probably quality or passing on maintenance not replacing wires. Ones that survive today sat outside their first forty years. I bet plenty of rusted wires and bad crimps made the CAA say enough.
 

cluttonfred

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There's a nice history of Aeronca and Jean Roché in an EAA chapter newsletter here: A Brief History of the People Who Created the Light Aircraft Industry in the U.S. – Part 5 | Lincoln EAA Chapter 1541

My understanding is that wings braced entirely with wires, wooden box main spars for wings, and single-ignition engines were three (of many?) elements prohibited for certified aircraft but not for amateur-built aircraft. I don't know the exact details of the CAA decision, but I bet Ron Wanttaja does! Until Ron weighs in, here are a couple of his relevant Fly Baby articles:

 

Kyle Boatright

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They are not going to issue a design FAR for homebuilts and you don’t want them too.
My question was more around the engineering. I don't understand why wire bracing using a pylon system would be banned on the certified world. Is there some fundamental flaw that I'm not aware of? My reference to HB and UL's was that whatever the problem with the Aeroncas is/was, I don't think it has manifested itself in more recent implementations of the same (or a similar) bracing scheme.
 

bmcj

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What kind of plane? If you are trying to go fast, go with struts. If you are a slow Part 103, wires can ba lighter and provide more rigidity for a lightweight frame. When flying something like a Quicksilver, I value the slow speed flight, so wires are fine. When it comes to easy disassembly though, struts can be a better choice. Depending on cockpit access design, struts might provide easier access for ingress and egress.
 

oldguyflier

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Mike Sandlin built (and documented) his GOAT gliders in both strutted and wire-braced versions. Google "basic ultralight glider". Has a lot of interesting info on those pages.
John Collins
 

Dana

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I could be wrong, but I doubt wire bracing was ever banned, except by the laws of aerodynamics. Certified wire braced biplanes are still being made today (though with solid streamline wires, more properly called "tie rods"), but most people want faster airplanes, and that means no wire bracing.

Ditto for wood structures. There may well be a ban on uninspectable closed box spars, but public sentiment after the 1931 Knute Rockne crash (caused, at least in part, by water damaged wood spars failing) meant no airline could make money selling passenger flights on anything but an all metal plane.

There was a mention of inspecting crimps... back then, they would have woven splices wrapped in soft wire and soldered, nicopress didn't exist yet. But yeah, tough to inspect.
 

Kyle Boatright

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I could be wrong, but I doubt wire bracing was ever banned, except by the laws of aerodynamics. Certified wire braced biplanes are still being made today (though with solid streamline wires, more properly called "tie rods"), but most people want faster airplanes, and that means no wire bracing.
I wasn't gonna do a deep dive, but Wiki says:

Production of the C-3 was halted in 1937 when the aircraft no longer met new U.S. government standards for airworthiness. Many of the C-3's peculiarities—a strictly external wire-braced wing with no wing struts directly connecting the wing panels with the fuselage, extensive fabric construction, single-ignition engine, and lack of an airspeed indicator—were no longer permitted. Fortunately for the legion of Aeronca owners, a “grandfather” clause in the federal regulations allowed their airplanes to continue flying, although they could no longer be manufactured.

I realize anything on Wikipedia is suspect (note the comment about fabric), but I've seen the wire bracing issue referenced in the Aeronca forums more than once.
 
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