Spruce for wing struts?

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challenger_II

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Somewhere, in my collection, I have a set of cabane, and interplane, struts for a Standard J-1. Cute steel strut end fittings, with balls on the outer ends. Those old birds were literally held together with wire! :)
 

Victor Bravo

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In regards to the OP question, the best example is that several boats were built using concrete as the construction method. "Concrete Canoes" and several others I believe, which demonstrated that yes you can actually build a floating boat out of concrete. You may not see an America's Cup yacht, or an aircraft carrier, or a Hobie Cat, or a cruise ship made this way, because they found a concrete boat is not the best use of material for a given task.

And so it is with wooden lift struts on an airplane.

 

challenger_II

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Ah! But concrete boats do have their place! Many of the units in the Mulberry floating docks, used at the Normandy Invasion, were concrete constructions! :)



In regards to the OP question, the best example is that several boats were built using concrete as the construction method. "Concrete Canoes" and several others I believe, which demonstrated that yes you can actually build a floating boat out of concrete. You may not see an America's Cup yacht, or an aircraft carrier, or a Hobie Cat, or a cruise ship made this way, because they found a concrete boat is not the best use of material for a given task.

And so it is with wooden lift struts on an airplane.

 

BBerson

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A 1/2" x 1/2" wood strut* is lighter than a common 1/2" X 1/2" steel strut. Because the steel needs to be very thin to equal the wood weight and they can't make it easily.
At some size the steel strut is lighter but maybe not if the wood is hollow also. I don't use wood because the connections are difficult.
*strut is any vertical or diagonal member in a truss.
 

challenger_II

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Considering the aircraft RTFM is working up, I would wager 1 1/2"x.058" round 6061T6 would be most adequate. To build a straight, tight-grain spruce strut, not allowing for the steel fittings on each end, of the structural strength needed, would weigh considerably more.
 

rtfm

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Hi guys,
Gosh - I seem to have kicked over the beehive. My intention in showing the Croses struts/wing masts was because a picture is worth a thousand words. No intention to say "Billski says..., but here is one" kinda thing. I have too much respect for Billski (plus our acquaintance goes back for many years) to do such a thing. OK - let's move past this, and on to some thoughts regarding a wooden mast/strut.

To the best of my understanding (from studying various photos of the Croses Flea), the "masts" (they have been variously called "masts" and "struts" in the Croses Flea context) attach at or near the wing hinge. From measurements in my drawings, attaching the masts to the wing hinge point, would make them 1731mm long, at an angle of 46 degrees from the vertical.

My plan would be to machine the airfoil like so, leaving a nice straight end piece to facilitate bonding onto the internal fuse structure. Pictured here is a NACA16021 airfoil (30% thickness at 50% chord) because it has a lot of "meat". I could cut this from either Spruce or Ply. My preference would be ply. I'd machine in a slot at the top end to accept a 3mm steel fitting to attach to the wing pivot. This airfoil would need to be cut in halves, and bonded after. A central channel could be cut to allow for a "safety wire" - a strip of steel running the length of the mast. This solid ply mast may be too chunky, but it would be a simple procedure to hollow it out 50% to lighten it. I'm exploring unknown territory here, so go gentle on me... Ha ha.

1623104203026.png

Question: I see a lot of planes (including the Croses) with struts which attach to about the 50% span position. Is this optimal? Bringing the masts/struts inboard to, say, the quarter-span position would shorten them to 1393mm, provide far more area inside the fuselage for attaching the masts, but it would leave a greater portion of the wing as cantilever.

1623108694782.png

Duncan
 

WonderousMountain

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If it starts to get too bulky, I would move to a Dense strong wood.
Softwood fittings are harder to.keep from fiber crushing. 3 ply is
An idea, for hollowing the centre, but then were off to the races...

~CK LuPii
 

challenger_II

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Fisher County, Tx. USA
Hi guys,
Gosh - I seem to have kicked over the beehive. My intention in showing the Croses struts/wing masts was because a picture is worth a thousand words. No intention to say "Billski says..., but here is one" kinda thing. I have too much respect for Billski (plus our acquaintance goes back for many years) to do such a thing. OK - let's move past this, and on to some thoughts regarding a wooden mast/strut.

To the best of my understanding (from studying various photos of the Croses Flea), the "masts" (they have been variously called "masts" and "struts" in the Croses Flea context) attach at or near the wing hinge. From measurements in my drawings, attaching the masts to the wing hinge point, would make them 1731mm long, at an angle of 46 degrees from the vertical.

My plan would be to machine the airfoil like so, leaving a nice straight end piece to facilitate bonding onto the internal fuse structure. Pictured here is a NACA16021 airfoil (30% thickness at 50% chord) because it has a lot of "meat". I could cut this from either Spruce or Ply. My preference would be ply. I'd machine in a slot at the top end to accept a 3mm steel fitting to attach to the wing pivot. This airfoil would need to be cut in halves, and bonded after. A central channel could be cut to allow for a "safety wire" - a strip of steel running the length of the mast. This solid ply mast may be too chunky, but it would be a simple procedure to hollow it out 50% to lighten it. I'm exploring unknown territory here, so go gentle on me... Ha ha.

View attachment 111447


Duncan, be aware that when you bring the lift struts inboard, the wing will want to wobble fore and aft. The outboard strut placement gives better stability to the wing.



Question: I see a lot of planes (including the Croses) with struts which attach to about the 50% span position. Is this optimal? Bringing the masts/struts inboard to, say, the quarter-span position would shorten them to 1393mm, provide far more area inside the fuselage for attaching the masts, but it would leave a greater portion of the wing as cantilever.

View attachment 111448

Duncan
 
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