Wing Structure/Stress question. 1

[proppastie]

I am attempting to convert the Carbon Dragon Ultra-lite Sailplane to aluminum structure. There is a spec. in Basic Glider Criteria (FAA) for a 150# limit load at the tip. Depending on the assumptions made with the wing structure the axial loads on the rear spar are from 3000# to 1500#. The latter is calculating a Phantom beam at the Leading edge, and the former is for no inclusion of the Leading edge in the calculation. How do experienced aircraft designers stress a D box leading edge structure,... fabric aft of the rear spar. Do you position a phantom beam at the centroid or some other place for the calculation of the stress????

 

[rb1957]

i'd assume pinned fttgs, particularly if the wings are pinned to the fuselage (ie wings off for transport).

ok, so the Dnose has a solid rib and a pin into the fuselage, so it sounds as though it's at least somewhat effective.

your sketches confuse me ...
3) why the kink on the fwd edge ? is that showing the centroid of the Dnose (your "phantom" beam) kinking fwd to the Dnose fuselage attachment (which should be on the centroid) ?
4) and 5) have the narrower chord fwd cell ... Dnose centroid ? but looks less than 3) ??
2) and 6) look alike, just with different ribbing schemes ??

Quando Omni Flunkus Moritati

 

[rb1957]

meant to ask ... why only one loadcase ?

Quando Omni Flunkus Moritati

 

[proppastie]

" 3.)...kinking fwd to the Dnose fuselage attachment (which should be on the centroid)

Yes a little bit of fudging. case 3 is the LE centroid kinking forward to the LE fitting. case 4 and 5 did not give good results as the end of that load path was not at the LE fitting.

"(which should be on the centroid) "

For some reason I thought the fitting should be at the LE. Reacts to CLm torque better there (more moment arm).


"4) and 5) have the narrower chord fwd cell ... Dnose centroid ? but looks less than "

case 4 and 5 did not give good results as the end of that load path was not at the LE fitting.

"2) and 6) look alike, just with different ribbing schemes ?? "

2 and 6 are a load path at the nose, LE, it gave the lowest numbers but was not at the centroid. The different ribs are the solid ribs per CD drawing, and all the ribs per CD drawing.


"meant to ask ... why only one loadcase ?"

Well I need to do them one at a time (I believe) before I can combine them. I would think it would be better to have separate threads for each load case and then combine them as another separate case thread. It would probably get confusing all in this thread. I understand there are other loadings...later on those.
Assuming you do not get tired of me asking all these basic questions.

 

[rb1957]

i think the LE attach point shoud be at the shear center of the Dnose, i'd buy some point between 1/2 and 2/3 of the Dnose chord aft of the LE. sure you can attach at the LE but the Dnose won't like it; and it probably won't be as effective (the Dnose will have to do a lot of shearing to get the reaction there). sure your load will be lower ('cause you have a wider base) but that really isn't the point ... what will happen in real life is the point.

react the load as you want to (you really should be able to draw a FBD) and test it later. it's very hard for us to validate your assumptions 'cause we don't see the whole puzzle.

i'd've thought that you wanted just about the minimum number of wing/fuse attachments (due to transport ?); which would be close to 4 or 6 (two at each spar) possibly 4 (two at the middle spar, one at the frone and rear). How does your base design attach ?

Quando Omni Flunkus Moritati

 

[proppastie]

"i think the LE attach point should be at the shear center of the Dnose, i'd buy some point between 1/2 and 2/3 of the Dnose chord aft of the LE."

Thank you very much.

"i'd've thought that you wanted just about the minimum number of wing/fuse attachments (due to transport ?); which would be close to 4 or 6 (two at each spar) possibly 4 (two at the middle spar, one at the frone and rear). How does your base design attach ? "

For the Semi span One pin (bolt) at the main spar other two to be determined. Probably AN4 attached to a steel tube fuselage, I can put the fittings where I want and design the fuselage to accommodate. 5 total for the wing (not including flapperon)

One of my initial conditions is for the aircraft to live outside assembled, That is why I wanted it out of aluminum.

 

[rb1957]

why'd you start with this loadcase (which really shouldn't be That critical) ?

I'd design the wing for max/min bending and then look into these "funny" cases.

Quando Omni Flunkus Moritati

 

[proppastie]

why'd you start with this loadcase (which really shouldn't be That critical) ?
I'd design the wing for max/min bending and then look into these "funny" cases.

I have the spar bending/shear designed (maybe,... perhaps or needs work) see "Built up Spar Question" this forum also attachment. The Hombuilt site will not check calculations, I assumed the same here. I can mount all my assumptions and results.

This is the next most severe case, the wing drag being calculated at a around 107# which is distributed along the semi span of the wing. that is a fairly simple calculation I can mount should you wish to see it.

On your forum I found a fantastic explanation to Buckling which referred me to Bruhn C7.16 and C7.17 and I was able to calculated the rear spar buckling 3 different ways. assuming the axial loads are reasonable.

I only have "black Box" verification of Clm torque form the Wilford design spread sheets, and I need to better understand that before I am satisfied.

 

[berkshire]

Proppastie

Since you are obviously interested in building an ultralight sailplane , you may be interested in attending the Experimental Sailplane Associations, Western workshop At Mountain Valley Airport (L94)
Tehachapi, CA
This will be held over the Labor day weekend (Friday 20th August to Monday Sept 1st) There will be speakers, exhibitors and workshops and lectures.
Feel free to attend.
B.E.

You are judged not by what you know, but by what you can do.