engineer help wanted

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stanislavz

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Looking for help with three piece wing spar(8' center section) design using pultruded carbon rods. Will gladly pay any reasonable fee.

Thanks,
That kind of help do you want to get ? I would not take any numbers with destructive testing..
 

Hephaestus

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Sonja's pricing seemed very reasonable to me, may want to talk to her.
 

stanislavz

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A tall order isn't it. Can't you just test to a an acceptable load and stop there before damaging anything?
I do not know. For one off - making an extra half wing is cheaper than funeral.

Ok - on my scale, designing longeron from pultrusion is kind of easy task - take Jim book, design it by max deflection and you will have it good till 12g.

Same done for wing ribs.

All easy if covered with fabric. Or by cf/fiberglass fabric, non load bearing 0/90 orientation. But give it an skin from cf - it will can/buckle under such high deformations + torque

On the other hand - adding one million ribs as per cri-cri will hold even thin one skin again buckling.. Where Sonja example used stiffeners in lower count.

But - if i look into lak16m wing, it. Is a wing made from shells only with cosmetic only spar web and ribs.. all loads go to three layered skins.

For me - composite magic is in tailoring layers and oridntation to get best possible result.
 

Map

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Sonja's pricing seemed very reasonable to me, may want to talk to her.

That does not sound too complicated. I would have to run some numbers to get the loads and need the dimensions of the wing, weights and speeds.
Sonja
 

Hot Wings

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Can't you just test to a an acceptable load and stop there before damaging anything?
In some situations - maybe.
The problem is that you have a hard time telling if there was damage due to minor yielding that has compromised the structure. There have been several discussions here on HBA about this paradox.
QAC load tested all of the Q-2 carbon spars for QC purposes. The running joke back then was that they were all 'pre-failed'. If you have a proven structure that is designed to say 9G U/6 G L then you might get away with testing to 4.4G and measuring deflection without fear of damaging the structure to verify quality.
 

stanislavz

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If you have a proven structure that is designed to say 9G U/6 G L then you might get away with testing to 4.4G and measuring deflection without fear of damaging the structure to verify quality.
But not your number. Plus some parts like skin will mess all your numbers.. just too high deflection
 

stanislavz

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That does not sound too complicated. I would have to run some numbers to get the loads and need the dimensions of the wing, weights and speeds.
Sonja
I think i will apply to this too with my billion ribs single skin wing..
 

stanislavz

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Yup, lots of variables. The BD-5 wing is a good example of the skin problem. The wing is strong enough but the skin permanently wrinkles before the spar starts to yield.
For single skin i always remeber construction of Cri-cri. And you cant beat mrs. Colomban on weight effiency.. Yes, it is on part of black aluminium, but still.. 1.8" ribs spacing but only single thin aluminium skin. Revatched all videos with cri-cri acrobatic, no cannig found.
 

raymondbird

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That does not sound too complicated. I would have to run some numbers to get the loads and need the dimensions of the wing, weights and speeds.
Sonja
So happy to hear from you! Have watched all your videos and am a very great fan. Should I PM you with more details?

It is something like a KR2 three piece wing that I have in mind(8' center section) but with overlapping pultruded rod spars instead of wing attach fittings. I have a one piece pultruded rod main spar already designed by Jim Marske but don't have the large hangar space anymore to work in.

I have tried to contact Jim but I know he's still recovering from a very bad case of Covid.

Salute,
Ray
 

Map

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Hi Ray,
Send me an email with your contact information, mine is on my web site, which you should know since you have seen my videos.
 

proppastie

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Yup, lots of variables. The BD-5 wing is a good example of the skin problem. The wing is strong enough but the skin permanently wrinkles before the spar starts to yield.
What loading does that happen
Is it past limit?
Link?
 

Hot Wings

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Don't have a link. Juan's site has been down for years. Maybe WayBack?
It was/is a well known 'problem' in the BD-5 world. There is/was a spar insert that was designed to eliminate the problem after doubling the number of ribs and/or shin thickness didn't fix the 'problem'.
I do not remember at what load the 'problem' manifested. Could have been past limit but I don't remember a "G" load being given by those that experienced the problem. Could have been past the tested limit load given that some of the BD-5s were likely flown rather aggressively?
 

stanislavz

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Don't have a link. Juan's site has been down for years. Maybe WayBack?
It was/is a well known 'problem' in the BD-5 world. There is/was a spar insert that was designed to eliminate the problem after doubling the number of ribs and/or shin thickness didn't fix the 'problem'.
I do not remember at what load the 'problem' manifested. Could have been past limit but I don't remember a "G" load being given by those that experienced the problem. Could have been past the tested limit load given that some of the BD-5s were likely flown rather aggressively?
I was able to get only limited data on bd4 wing 24" ribs spacing two or three layers of 7 oz fiberglass, and too many leaks. And yes, adding some stiffneres to make ribs spacing 12" was necessary..

On the other hand you can add even more stiffeners using that pe stripe technology.. and have you big wing from two small molds.

Just find a way how to replace or not that bif tube spar.
 

Lendo

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raymondbird, Perhaps get a copy of Jim Marske's manual, it covers most things. Additionally I would include using the Beam Bucking formula to calculate for any additional WEB Wrap numbers and watch for Too Much or Too Little - Flex or Stiffness.
Finish off with a Wing Load Test.
George
 
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