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ACRO E-mail Archive Thread: Pitts S1S roll rate/Falcon ailerons

Thread: Pitts S1S roll rate/Falcon ailerons

Message: Pitts S1S roll rate/Falcon ailerons

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From: Allan Franko <allanf at cancerboard.ab.ca>

Date: Fri, 14 Mar 1997 21:58:57 UTC

Message:

  The issue of aileron flutter certainly deserves serious consideration.  I'm 
reasonably sure that it isn't a problem with the Falcon ailerons on my S-1S.  First 
on theoretical grounds, it is my understanding that a prominent aeronautical 
engineer and aerobatic aircraft designer has stated that a Pitts is inherently 
resistant to aileron flutter.  (I hope he'll add his opinion to this discussion.)  
Second, I haven't been able to detect any hint of a tendency to flutter in my system. 
 I have done what I understand to be the standard test at 5 mph increments up to 
210 mph:  hand off stick, knock the stick sideways abruptly.  Since the highest 
speed I use is 180, this seems to be an adequate margin.  I should add that I 
covered one bay (the one encompassing the I-strut) with plywood, on the insistence 
of the Transport Canada inspector.  The leading edges are  plywood as well, so the 
wings are considerably stiffer than standard.  Also, as part of my preflight, I check 
each hinge for looseness caused by shrinkage of the wood.  It's necessary to have 
inspection holes to let you reach every bolt and nut, because eventually all of them 
will require tightening.

Two points I forgot to include in my original post.  My ailerons are 1/4 inch thicker 
that the adjacent wing, which might contribute to the relatively low aileron forces.  
This apparently is supposed to keep the airflow attached over, for example, the 
curved top surface of a aileron deflected downward, which should maximize the 
top-to-bottom pressure differential ahead of the hinge, where it assists the 
deflection.  Second, a really nice feature of these ailerons is that the arms to which 
the slave struts attach do not project beyond the surface of the coves at full 
deflection, so there is no need to cut holes in the upper surface of the top wing or 
the bottom surface of the bottom wing.  The absence of a holes completely through 
the wings must increase the efficiency of the wings somewhat.

Allan Franko