Wing Spar Design

[Andy Boylett]

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[Andy Boylett]

Reply from Rob Buckley...

Andy,

As your calcs give a max stress in the spar of 77.9MPa, this looks to be smack in the range of the bending strength of the Cyparis. Wouldn't the simplified spar fail at this load, most likely in buckling of the top element at the fuselage joint?

I'm assuming the spar is basically modeled as a rigidly supported beam at the fuselage edge, with the load uniformly distributed?

The strength you quote of 6500 - 12100MPa seems very high. 300M extra high strength steel that we make the Airbus landing gears out of has a UTS of 1970MPa & a 0.2% yield of 1655MPa. Good though Cyparis is, I'm pretty sure 300M is stronger!

http://www.thewoodexplorer.com gives the properties of cyparis as 82MPa bending strength and 40.6MPa compressive strength, which would seem to match real world wood spar performance.

Happy new year!

Rob

[Andy Boylett]

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[Nick Reeves 3055]

just out of curiousity, how are would you be able to pull more than about 10G?? i dont know the details or technical terms but i'm sure the wing would stall before being able to pull more than 10G due to the lift coefficient falling away or something with that in mind i'm off to read some aerodynamics books

[Andy Boylett]

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[Bob Thompson1894]

Hi Nick,
I did the sums on 5g but showed examples of how it could easily handle higher loads. I have seen deisgns for the extreme aerobatics planes at 10g. From what I have read the highest wing loads for us could rather perversly be not due to flying but due to landing. It is very easy when landing to bump the floor a little and cause an impact loading which resuts in very high g flex of the wings downwards.....obviously impossible to calc as it all depends on the flexibility of the UC and fus.

The highest g turn I have seen pulled in flight was by one of our club instructors who was training a young lad (with my trainer plane ). The trainee dived for the ground at very high speed and so the instructor decided to take back control of the plane. However, before releasing the trainer switch he had already applied full throttle and full up elevator. The result was a completely snapped wing!

Then he has learned a valuable lesson! When training, always have the throttle at high idle, and keep hands off the controls apart from the trainer switch...... This is one of the reasons why 40 powered trainers are better than the Greenly type for raw beginners, the stresses involved in training are just too much for wild manoeuvres!

[Andy Boylett]

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[Dave Berry 2911]

Is the stress you are quoting for the Cyparis the ultimate tensile stress or the elastic modulus - very few steels have a UTS above 1000MPa.

[Andy Boylett]

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[Dave Berry 2911]

Something a bit odd here Andy,coz 6500MPa UTS equates to about 470 Tons/sq. inch in old money.
The strongest usable engineering steel if i remember correctly has a UTS of about 120Tons/sq.inch, normal HTS bolts are about 50 Tons/sq. inch.
Even the new carbon nano tubes descended from "buckyballs" don't appear to be as strong as Cyparis!
Cheers
Dave B.

[Andy Boylett]

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[Andy Boylett]

Dave,
sorry, it was correct. I just looked up the figures for Oak that I use in building regs calcs and it has a modulus of 11GPa or 11,000MPa, so Cyparis at 6600MPa sounds about right. In my old Corus Steel tables structural steel is 200 GPa.

As for the LMA data, I think somthing is wrong as 1psi is 6894 Pa, so from my Cyparis figures of 6.6GPa this would be 957354psi.
Andy

[Andy Boylett]

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[Dave Berry 2911]

Hi Andy,
Yes, my earlier post was quoting Ultimate Tensile Strength, whereas you are quoting Shear Modulus.
However in your calcs you have identified the maximum stress, so to find the load factor you should surely compare that with the published ultimate stress, not the modulus.