Airfoils, Ordinates, Fat Wings, Harry Riblett and other musings…

[Franky139]

N3UW

Your statement would be true if i already had a set of Patrol ribs, that is not the case.

Until my engineer come up with his evaluation, i see only good points in using my spars: 1) i have thems,
2) single piece extrusion spar (no splices)
3) time and money saving, no need to build new spars, no materiel needed
4) outboard of the gas tanks, no need to make any noses ribs, it will be single piece ribs
all the way to the rear spar ( because my spars are less taller than the Patrol ones)
5) As my spars were designed for a fabric wing, they are stronger than the Patrol ones
designed for an aluminum skin wing, definitely can't take the Patrol spars and put thems in
fabric wing as they are.

[David Swartzendruber]

It is interesting how different people can have such different perspectives. I'm in the camp that your extruded spars are not desirable for building a Bearhawk style wing and you would be better off not using them if you want an all metal wing with an optimum design. In the all metal Bearhawk wing, the spars, ribs and skin all work together to provide the required structure. In a cub style wing with extruded spars and fabric "skin", the fabric plays no role in the primary structure and as a result, that wing design has no need for a direct connection between the skin and the spars. You can put metal skin on a cub wing, but the skin can't contribute to the structure in the same way it does in a Bearhawk style wing. As Jared mentioned, a cub style wing uses drag/anti-drag wires hidden inside to help make it structurally sound. The cub style wing also uses two wing struts per side instead of one in order to be structurally sound. If you try to insert a cub style extruded spar into the Bearhawk style wing, how are you going to attach the skin to the spar? The Bearhawk spar has a flange top and bottom that the skin is riveted to along the entire length of the spar.

Those are my thoughts, which I'll be the first to agree aren't worth much seeing as they are posted online from someone you don't know.

[kestrel]

N3UW

Your statement would be true if i already had a set of Patrol ribs, that is not the case.
[...]

The main thing that is missing is a design for a "Bearhawk style wing" with that set of spars. If you had proven plans for that, I'd say go for it. Perhaps it is, build a "metalized Cub wing with a Bearhawk airfoil"? I that comes close to being straightforward, but is also likely to be heavy. To build a lighter set of wings with that spar set and a metal skinned Bearhawk airfoil will be FAR more work than either building the wing the spars were designed for or building a Bearhawk wing with a Bearhawk spar. You're not saving or gaining much by using a spar that you already have in a manner that there is no design for.

Myself and others have offered the advice you requested. We assume that if you had all the needed knowledge and experience, you wouldn't ask. What we each offer is our opinions and advice. The choice is yours. ...and some here will know that I don't always accept the advice offered here.

If you said that you wanted to do it because you don't mind the extra effort it will cost you, it is the end result that matters, I would understand your position better.

...but you keep leading with "I have these spars and I believe it will save me time/effort/money to use them". On that one point, I advise that you are likely mistaken unless you put them in the wing that they were designed for.

For full disclosure, I have intent to color outside the lines in a few places. I do it knowing it will cost me time, effort and money. ...but it is the end result that I want.

[Franky139]

Thank's for the advices, that's the beauty of a forum, i did not expect any favorable support on using my spar, in aviation, the best advice is to stick with the initial design,
no doubt about that but, as i 've said before, i have an aeronautical engineer who will go over my plan, i will wait to see what he will come up with, he is the son of my best friend, who
is just finishing to build a Smith cub, it will not cost me the price that i would normally pay for that and the design you are talking about will be there, if he come with a negative answer, that
plan will end up in the garbage bin.

The point that the aluminium skin is not attached directly to the spar is a very good point, but maybe that can be done by a simple modification, again, let's wait for the engineer answer.