Flutter Testing


Andrew Anunson
 

I have flutter testing coming up.

How do we recognize flutter in these EZ’s?
Is it felt in the stick?
Is it a slight buzzing like the canopy lip buzzing?

Thanks,
Andrew Anunson
Cozy MKIV #1273
Pound, VA


Marc J. Zeitlin
 

Andrew Anunson wrote:

I have flutter testing coming up.

How do we recognize flutter in these EZ’s? 
Is it felt in the stick?
Is it a slight buzzing like the canopy lip buzzing?

So what you're looking for is not flutter (because by then, it may very well be too late). What you're looking for, in the speed buildups, is incipient flutter, or increasing vibration with lower damping at higher speeds.

So, yeah - you start at some low speed (130 KIAS, let's say) and whack the stick. What SHOULD happen is a very short oscillation that damps out in 1 or 2 cycles at the most. You then move to the next speed, and exactly the same thing should happen until you get to the 213 KIAS top speed. If, instead, you move from speed "X" to speed "X + 3" kias, and instead of damping out the oscillation in 1 - 2 cycles at the most, you feel 3 - 5 cycles, it's time to stop - you're getting closer to incipient flutter, and you don't want to push it.

The feeling you may get is just a buzz, or it may be more pronounced, and it will be in the stick, rudder pedals, or even the airframe as a whole.

--
Marc J. Zeitlin                      marc_zeitlin@...
                                            http://www.cozybuilders.org/
Copyright © 2022                     Burnside Aerospace


skovbjerg
 

One important add-on:
Be sure that you are decelerating through the target airspeed before you whack the stick. That way you are already on the way out of an eventual flutter build up
:-)
Jay

On May 17, 2022, at 16:15, Marc J. Zeitlin <marc.j.zeitlin@...> wrote:


Andrew Anunson wrote:

I have flutter testing coming up.

How do we recognize flutter in these EZ’s? 
Is it felt in the stick?
Is it a slight buzzing like the canopy lip buzzing?

So what you're looking for is not flutter (because by then, it may very well be too late). What you're looking for, in the speed buildups, is incipient flutter, or increasing vibration with lower damping at higher speeds.

So, yeah - you start at some low speed (130 KIAS, let's say) and whack the stick. What SHOULD happen is a very short oscillation that damps out in 1 or 2 cycles at the most. You then move to the next speed, and exactly the same thing should happen until you get to the 213 KIAS top speed. If, instead, you move from speed "X" to speed "X + 3" kias, and instead of damping out the oscillation in 1 - 2 cycles at the most, you feel 3 - 5 cycles, it's time to stop - you're getting closer to incipient flutter, and you don't want to push it.

The feeling you may get is just a buzz, or it may be more pronounced, and it will be in the stick, rudder pedals, or even the airframe as a whole.

--
Marc J. Zeitlin                      marc_zeitlin@...
                                            http://www.cozybuilders.org/
Copyright © 2022                     Burnside Aerospace