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Impact testing

Old 3rd Mar 2018, 20:30
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Impact testing

Advice please,

What/which formula is used for certification of aircraft structures impact forces in the following cases?

1. Birdstrike on windscreen
2. Ice impact from propellor shed ice?

FAA or EASA, not fussy, if you have a reference for same all the better.

Trying to establish impact on forces involved from external impact of something like an SLR or LiON battery pack.
darkbarly is offline  
Old 4th Mar 2018, 11:57
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If you want the design/test case for engines...

• Ingestion of hailstones up to 25 mm in diameter up to 35,000 ft, decreasing to diameters of 6 mm at 59,000 ft, at a density appropriate to the aircraft’s operating environment. The worst case hail density used is 10g/m^3 between surface and FL200, then the numbers tail off above that.
• Ingestion of rain, of a density appropriate to the operating environment of the aircraft. 20 g/m^3 between surface and FL200, then tailing off above that.
• Ingestion of a single large bird, normally impacting no slower than 200 knots(103 m/s, 337 fps) and into the most sensitive part of the intake.


Intake area / Minimum mass of bird
< 1.35 m^2 / 1.85 kg (4 lb)
1.35–3.9 m^2 / 2.75 kg (6 lb)
> 3.9 m^2 / 3.65 kg (8 lb)

All of this is in CS.25 and FAR-25, so far as I know the requirements are identical.


Clearly with a battery pack, you've both got a much harder physical object than a bird, and much more stored energy than either.

Standard disclaimer - always thaw out frozen poultry before either cooking it, or firing it at aeroplanes.

To find the exact references, just download the certification standard and search on standard keywords like "ice", "hail" and "bird". Should take you about 2 minutes.

I'm less clear on windscreen cases, but broadly speaking, I think that the engine design cases are just mapped over to windscreens, with the bird or hail treated as stationary, and the Vd case used for airspeed. Common sense is that you do that about the ceiling, where TAS is greatest and thus so is the closing speed of the impact object. I think that this is obvious enough standards don't actually need to say that.


G

Last edited by Genghis the Engineer; 4th Mar 2018 at 12:11.
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Old 4th Mar 2018, 14:13
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Join Date: Dec 2002
Location: UK
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I surmise from your examples that you are interested in drone collisions. The following may help:-

https://www.gov.uk/government/upload...sion-study.pdf

https://publicapps.caa.co.uk/docs/33...27_Jan2018.pdf

https://www.theverge.com/2016/10/18/...est-uk-dangers
safetypee is offline  
Old 4th Mar 2018, 17:54
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Thanks both. I am specifically interested in the formulae used for calculating 'an object meets the strike/ingest' standard, be it CS or FAR.

Looking around the net there are several means of calculating but wondered if any testing types on here had insight into which formulae, specifically, were used. Obviously these are tested physically to verifiy the results.

??
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