DO-160 Helicopter Vibration Query

[SlipperyPete]

I have a query related to the DO-160 Helicopter Vibration test procedure. A sine sweep has been conducted on a piece of equipment that has identified several closely spaced resonances within the 1st sinusoidal test band. The test house is conducting 4 separate sine dwells at the 4 highest resonances. My opinion is that this is over-testing the unit and that only the most severe resonance in each of the 4-off forcing frequency bands should be tested.
DO-160 seems to be open to interpretation on this point, so I would be interested to hear the opinion of other members.

Peter

 

[IRstuff]

how would the helicopter know which is the most severe frequency?

I would propose doing all 4, but with proportionally allocated amplitudes, since it's unlikely that all 4 would get the same, maximal, energy input.

TTFN
faq731-376

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[SlipperyPete]

The procedure states "..select the most severe frequencies (maximum of 4). Perform sinusoidal dwells at each of these frequencies for 30 minutes".
The most severe are those with the highest responses, and the reason I would suggest that it says 'maximum of 4' is that there are 4 sinusoidal bands.

 

[boyze]

Wouldn't it depend on what is causing the specific response and it's fragility to that response and even other components to that response? Component A might be less durable to a lower response than component B to a higher response.

Have Fun!

James A. Pike

http://www.xl4sim.com

http://www.erieztechnologies.com

 

[SlipperyPete]

Many thanks for the replies, and I appreciate that in any complex system there will be many resonances on the many separate components.
However, this is a Qualification test and not a development test, so I am trying to understand what the specific requirements of DO-160 are. My belif is that the 'worst-case'(ie.highest Q-factor) resonance in each sinusoidal excitation band should be chosen. The procedure states 'maximum of 4' which implies 1 resonance per band.

Regards,

Peter

 

[lbell]

Pete,
I believe the test house is correct. If there is more than one resonance in a frequency band (+/-10) then there is more than one thing in the system causing that resonance. The qualification testing is suppose to expose any feature that may cause failures therefore was designed to dwell at that frequency. I would say I'm surprised that you would see four resonances that are the most severe in magnitude within one band, but then I've been surprised many times by what happens on a vibration table.
Regards,
Louis