Wing mounts on spar

[Flyguyeddy]

What is the lowest you can install the wing mounts on the spar?   Is right above the spar cap an ok place?   Im looking for as much vertical height as i can get. 

[CHARLES DEBOER]

Contact Leonard.  He has safe modifications that you can make for more head room.

[Flyguyeddy]

I would prefer not to bother the man if someone else can answer this question

[CHARLES DEBOER]

Leonard does read posts on this web site and has in the past requested others to contact him about this same issue.

[PropMan]

What is the lowest you can install the wing mounts on the spar?   Is right above the spar cap an ok place?   Im looking for as much vertical height as i can get.

If you are building the LEXL stick to plans, if it's the LEUL, use the XL position

[ParQld]

I recall in one of  Les Homan's Video's he mentioned he raised his somehow for extra head room, maybe he might chime in on this and tell you what he did.

cheers Paul

[Flyguyeddy]

If you use the airbike as an example, they are drilling right above the spar cap for theirs, and we essentially have the same wing minus some span (maybe an outer bay)

[CHARLES DEBOER]

I don't know if this photo will come through.  If not I have a post on page 3 of LE XL A67 of my mount.  View at your own risk.  I have about 2" higher.

[Vince Carucci]

The first attached image shows the standard LE wing mounting bracket configuration. It sits very high on the spar.

The second image might help understand the forces at the attachment point (A). The lift on the wing puts the strut in tension at an angle between the wing and the lower frame. The angle can be broken down into a vertical and horizontal component. The horizontal component has the spar in compression between A and C.

That being the case, I don't believe the wing would be compromised by lowering the mounting bracket to the bottom of the spar, assuming you moved enough of the solid wood filler to the bottom of the spar to support the bracket.

I welcome others to validate my conclusion or to point out flaws in my reasoning.

Vince

[leshoman]

This is how i mounted mine. basically just inverted attachment on wing root and moved from top to bottom.

[Flyguyeddy]

This is how i mounted mine. basically just inverted attachment on wing root and moved from top to bottom.

do your plans show the wing fittings to be top mounted?  mine do not.  they show basically the same as you have drawn.

[Flyguyeddy]

to add a little bit to this, my wing building video is supposedly for a legal eagle, and it shows the wing attach fittings angled down like the double eagle has.

[wojtekseta]

The first attached image shows the standard LE wing mounting bracket configuration. It sits very high on the spar.

The second image might help understand the forces at the attachment point (A). The lift on the wing puts the strut in tension at an angle between the wing and the lower frame. The angle can be broken down into a vertical and horizontal component. The horizontal component has the spar in compression between A and C.

That being the case, I don't believe the wing would be compromised by lowering the mounting bracket to the bottom of the spar, assuming you moved enough of the solid wood filler to the bottom of the spar to support the bracket.

I welcome others to validate my conclusion or to point out flaws in my reasoning.

Vince

Vertical force in the spar mounting bracket is close to zero (the struts are mounted in the midle of the wing). Force in spar from bending is small. As you write most important force is compression from the struts. The front spar is compressed with force of about 750 kG (1670lbf). Calculation data - MTOW 575lbf, 29 degree angle beetween wing and strut, 4G, safety factor 1.5 . I think the force acts along the longitudinal axis of the spar.
Few months ago I made model of the spar root. The model is made from pine (slightly weaker than sitka spruce), 1.5mm birch plywood and epoxy glue - in a 1:1 scale. In place of the heavy, solid piece of wood I glued diagonal member (weight savings are about 2 pounds total in four spars). I slightly lowered line of the spar bracket to achive more headroom space. I tested it on the hydraulic press in three cases of the load - along the top, middle and the bottom of the spar. Soonner I "calibrated" the press - the error should be less than 10%.
The worst case is force along the top cap. The mockup resisted in this case 880 kG (almost 2000 lbf) without destruction, but with light crackles. Along the middle axis the model resisted 1200 kG (2700 lbf) without crackles. The only deformation apeared in holes of the mounting brackets.
Films (sorry for the language):



Please treat above as a test of an option, not a proposal to modify the project.

[scottiniowa]

 The front spar is compressed with force of about 750 kG (1670lbf). Calculation data - MTOW 575lbf, 29 degree angle beetween wing and strut, 4G, safety factor 1.5 . I think the force acts along the longitudinal axis of the spar.

Few months ago I made model of the spar root. The model is made from pine (slightly weaker than sitka spruce), 1.5mm birch plywood and epoxy glue - in a 1:1 scale. In place of the heavy, solid piece of wood I glued diagonal member (weight savings are about 2 pounds total in four spars). I slightly lowered line of the spar bracket to achive more headroom space. I tested it on the hydraulic press in three cases of the load - along the top, middle and the bottom of the spar. Soonner I "calibrated" the press - the error should be less than 10%.
The worst case is force along the top cap. The mockup resisted in this case 880 kG (almost 2000 lbf) without destruction, but with light crackles. Along the middle axis the model resisted 1200 kG (2700 lbf) without crackles. The only deformation apeared in holes of the mounting brackets.
 

Are you relying on reading of .125" movement of the needle to present you with reliable  strength information? Rather than a standard bag weight test?  just curious

[wojtekseta]

The front spar is compressed with force of about 750 kG (1670lbf). Calculation data - MTOW 575lbf, 29 degree angle beetween wing and strut, 4G, safety factor 1.5 . I think the force acts along the longitudinal axis of the spar.

Few months ago I made model of the spar root. The model is made from pine (slightly weaker than sitka spruce), 1.5mm birch plywood and epoxy glue - in a 1:1 scale. In place of the heavy, solid piece of wood I glued diagonal member (weight savings are about 2 pounds total in four spars). I slightly lowered line of the spar bracket to achive more headroom space. I tested it on the hydraulic press in three cases of the load - along the top, middle and the bottom of the spar. Soonner I "calibrated" the press - the error should be less than 10%.
The worst case is force along the top cap. The mockup resisted in this case 880 kG (almost 2000 lbf) without destruction, but with light crackles. Along the middle axis the model resisted 1200 kG (2700 lbf) without crackles. The only deformation apeared in holes of the mounting brackets.
 

Are you relying on reading of .125" movement of the needle to present you with reliable  strength information? Rather than a standard bag weight test?  just curious

First I "calibrated" the press with the dynamometer. Next I loaded 4G with at least 1.8 safety factor. I did my best and I'm pretty shure of the results. Margin is big even if the error is bigger than 10%.
Each method has its weaknesses.