View Full Version : Undersling and 2/rev
Stu Fields
March 21st 10, 11:44 PM
If an over weight pilot exceeds the recommended seat weight of his 
helicopter, will this affect undersling enough to cause an  increase in the 
2/rev vibration???  Does increasing G forces cause an increase in 2/rev??
Stu
Steve R.[_2_]
March 23rd 10, 04:39 AM
"Stu Fields" > wrote in message 
 ...
> If an over weight pilot exceeds the recommended seat weight of his 
> helicopter, will this affect undersling enough to cause an  increase in 
> the 2/rev vibration???  Does increasing G forces cause an increase in 
> 2/rev??
> Stu
>
On the first question, if you're talking about flying the bird outside the 
recommended CG range, I'd think it's a possibility, especially the farther 
out you go.  Taken to extremes, wouldn't flying an under slung system far 
enough out of the CG range risk mast bumping during certain maneuvers?
Don't know about the second question.  Is the 2/rev vibration really 
increasing or are the pilot and passengers just feeling it more because of 
the G loading?  Either way, I'd think it would "encourage" those involved to 
try to improve the situation!
Fly Safe,
Steve R.
Stu Fields
March 24th 10, 04:26 PM
"Steve R." > wrote in message 
 ...
> "Stu Fields" > wrote in message 
>  ...
>> If an over weight pilot exceeds the recommended seat weight of his 
>> helicopter, will this affect undersling enough to cause an  increase in 
>> the 2/rev vibration???  Does increasing G forces cause an increase in 
>> 2/rev??
>> Stu
>>
>
>
> On the first question, if you're talking about flying the bird outside the 
> recommended CG range, I'd think it's a possibility, especially the farther 
> out you go.  Taken to extremes, wouldn't flying an under slung system far 
> enough out of the CG range risk mast bumping during certain maneuvers?
>
> Don't know about the second question.  Is the 2/rev vibration really 
> increasing or are the pilot and passengers just feeling it more because of 
> the G loading?  Either way, I'd think it would "encourage" those involved 
> to try to improve the situation!
>
> Fly Safe,
> Steve R.
What I was thinking of was just a heavy pilot within the c.g range.  Since 
the coning angle and subsequently the proper undersling depend on the gross 
weight.  Since an extra heavy pilot would exceed the design maximum gross 
weight, the existing coning angle and undersling would not be optimum. 
Could we expect an increase in 2/rev and if so why?  I have found a case of 
a Mosquito pilot who stands closer to the lunch line than he should, 
complaining of 2/rev after he had taken pains to track and balance thinking 
that the vibration might be 1/rev.
It seems that if the heavy pilot could cause increase 2/rev, you should feel 
it also in an accelerated turn.  I'm not just talking about pilot 
sensations, we can measure the amplitude of the 2/rev vibrations both 
vertical and lateral by fooling the electronic balancer with two reflective 
tapes on the blade position sensor.  I have not done a measurement in an 
accelerated maneuver and my ship is down now so I ain't got a vehicle for 
the test.  I am hoping to stumbel accross some individual that has already 
experienced and measured the 2/rev vibration in say a 2G turn and straight 
and level...
As an engineer, I have to have a problem to look at or my mind goes numb.  I 
love helicopters.  There is no end of problems to look at.  Especially 
vibrations.
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