Lu said:
(Nick)What you said about properly serviced oleo struts preventing ground resonance is not always true. ......... Any externally applied load will cause the helicopter to rock/roll on the struts and even though the wheels are up to pressure there is a rolling motion reacted by the tires. .......Because of this we could not keep the helicopter tied down and the only thing keeping it in place were the chocks on the three wheels...
Nick sez:
Few things are ALWAYS true (except gravity.) But the belief that oleos cause ground resonance is ALWAYS incorrect, and also the belief that your scenario has something to do with oleos is mistaken.
The aircraft as a system relies on all the ways it receives forces externally to quell its dynamic response. We have had this go-around before, Lu about dynamic (oscillatory) behavior, so I will only write this once, regardless of how many ways you work it around in the interminable posts to come on this subject.
Your shipboard example proves my point, because you had the aircraft tied down. The tiedowns change the oscillatory response of the whole system, and make ground resonance more likely. All Navy folks know this, we even stencil it on the side of the aircraft next to the tie down rings!
The oleos PREVENT ground resonance, virtually ALL the time, that's why they are used. They are really shock absorbers, just like a car's (which prevent the car from bouncing uncontrollably when a bump is hit). Of course if the oleo is broken or impropoerly serviced it won't do its job - if you are improperly serviced, you won't do your job either.
IF THE AIRCRAFT IS TIED DOWN, ground resonance might occur. This has NOTHING to do with oleos, Lu, it has to do with a crew preventing the oleos from doing their job.
Gosh, I wish you could stay on topic, and not use unserviced parts or tied down scenarios to confuse the group. Of course, I wish I'd win the lottery so I could buy my own S-76, but that's a pipe dream, too.
