Aluminum Dragon

[proppastie]

Load test failure....check out the link below

Wing Load Test Failure Aluminum Dragon

Better to fail on the ground than in the air.....and why we test. It looks like classic Euler buckling of the top cap strip......So after my last test where there was buckling of the skin and adding stiffeners I mounted the wing properly upside down and at 15 deg. .... I made shelves so the...

www.homebuiltairplanes.com

 

[proppastie]

turning over another look at the failure looking at the top .....kind of ugly....
bent part is cut out,,,, angle and new center cap and splice added to 1/2 between the rib 1 and 2....all that is left is to re-rivet a new z
stiffener.....then I can turn it over and do the bottom cap the same. ...

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[proppastie]

so ready to put back on the tractor for another try at the load test...The long angles are (I hope) permanently bolted so being able to remove or attach one wing at a time required the split and bar at the center in order to maintain the large moment of inertia in the fore and aft direction required. This is really stiff compared to my former poor design .

 

[proppastie]

So the wing has been back on the load fixture/tractor for a while.....I re-did the distribution to elliptical and added 10% for tail down load....the loading went from aprox. 700 to 800 lb. I decided I wanted to keep track of the deflections given all the problems I have been having....using the 7" deflection from an old FEA as a conservative estimate...it is not really accurate because it does not have the carry through fix, the stiffeners fix, but it also does not have the tail download additional weight. .......I am getting lazy in my old age. I decided the mount was very weak in the fore and aft direction ( the setup was talking to me and I listened this time) and so I added aluminum reinforcements as shown to the other side of the tractor......I also blocked up the tractor to get it off the rubber.....the mount was still moving in the vertical direction and I added the laser from the center of the wing to a reference out at the tip. I got to 50% load and was getting wrinkles from where the stiffeners ended to where they started on the other side of the rib, the deflections were too high also.......more bad design. I was very discouraged and what made it worse was my calculations to figure out what was going on did not find the problem....However I discovered I was off in my input of E (1.05x10^8 and not 1.05x10^7 makes a big difference) and now I am happy on the road to another fix and learning lots of stuff...... good things: I did not permanently bend anything....loading in 10% increments worked this time .....and even though the mount slipped.....when I un-loaded the wing the zero point movement along with the deflections measured gave me a net deflection very close to my estimate.

 

[proppastie]

did a bunch of calculations .....its not that I had not checked these locations.....I had just checked it wrong......the good thing about a failure at a known stress is now one can hopefully come up with the correct method to stress analysis a section.....with all my mistakes I am getting good at hind-sight-stress-analysis.....anyway here is the reinforcements which will bridge the z stiffeners across the ribs.....We will find out in a week or two if I did it right.

 

[proppastie]

Well failure again ....computer crashed too so pictures later. Not quite 60% or less than 3.2 Gs.....wing compression cap failed just outboard the drag spar.....I think there was not enough spar stiffeners so the web buckled and it stopped acting like a beam. Until I get my computer working I can not do any calculations. Wing is scrap....but it was a poor design and too heavy. I get to design a better one this winter (I hope ).

 

[proppastie]

I got my computer almost where I like it after Ransomware attempt.....so here is the pictures of the failed wing.......I plan to have a discussion thread about this soon I will add a link here.

Load Test Failure Main Wing Aluminum Dragon

https://www.homebuiltairplanes.com/forums/threads/aluminum-dragon.24732/post-615015 In the interest of education and completeness as regard the Aluminum Dragon I offer up this discussion of my most recent load test failure. This is the last load test of this design as the wing is too heavy...

www.homebuiltairplanes.com

 

[proppastie]

Somwhat hard to get back into it. .....but yes moving forward but only a little bit each day. Actually doing some detail design on this concept.

Cantilever Internal Braced Fabric Covered Wing

Do we have examples of aircraft with Cantilever Internal Braced Fabric Covered wings......I see lots of internal braced fabric wings with struts and twin spars like the Piet. I am looking for examples of double drag wire system for torsional stiffness.....I think it is the a set of drag and...

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[proppastie]

Some more help. .....moving along

Tube Calculations

While working on my new wing design I have discovered some interesting and new to me characteristics of tube strength. Basically where as the Ftu psi ultimate failure of 2024-T3 in tension is 64000 psi..... when doing the bending calculations of that same short tube and using test data the...

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[proppastie]

added more pictures to post 227

 

[proppastie]

On my new design there is no D-nose....Decided I should re-visit my nose ribs.....my calculations said the .016 nose rib should work......I had the 1/2 nose ribs for the other wing.... they will have to change for the new design so I decided to re-distribute the loads in such a way as to test if the max moment at the spar would fail the rib......The load at the far end is 39# of steel in the horse feed bucket.....the other 4 places are aprox 2 lb of sand each....The loading and re-distribution is somewhat involved and convoluted so I will skip that here.....the Idea was to match the max moment at the spar attach for the most severe loading (high angle of attack) at the highest loaded rib (root)......Rib shown after the test.

 

[proppastie]

Drawings done for inboard 3 ft. load test root of spar........material delivered.....the plan is to build it and test to limit portions of the spar and if it passes to continue on to finish the spar....I have to match the existing center section ....so cutting it off the failed wing is necessary.......not an easy job and I did use the Dremel with a cutoff wheel where I could.....

 

[proppastie]

Progress on test of spar root. Had to order "Quick Change Tool Post" and Tool Holders and Boring Bar for the end fittings...

 

[proppastie]

one fitting almost finished .....need to drill and ream the wing attach bolt hole at assembly with the center carry-through.

 

[proppastie]

Another view of the fittings.

I bought some clamps at Horror Freight but they did not hold well and pull down the sheet uprights to the tubes so ended up with band clamps which worked well....I returned most of the quick clamps......Shown in the assembly fixture. ( blocks screwed to table over a full size drawing) (checked with machinist square that all parts lined up with the drawing.

Clecoed prior to rivets.....Cherry Max rivets

Riveted assembly less cross members......

Cleared corners of bottom fitting so hopefully I will be able to load/unload the bottom wing fitting and swing the wing up to pin the top fitting......If I follow through on this I might be able to have this version live in a box like a real glider because it will be easier to remove the wings.

 

[proppastie]

Cross members installed.

 

[proppastie]

I borrowed an aircraft scale and set up my little jack with my homemade hydraulic scale to see if I could get stable readings and to calibrate the hydraulic scale at 900 lb. which is the load I will be using for my stub spar limit test.....sorry forgot to get a picture of the setup lifting my truck......so the jack could do the load, and the homemade hydraulic scale was right on the numbers as to the theoretical pressure for 900 lb.....400=900 lb....which even though the math predicted it I was surprised to the result as regard friction, exact cylinder dia. (or piston diameter) leakage...etc.