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ACRO E-mail Archive Thread: Pitts S1S Roll Rate

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ACRO E-mail Archive Thread: Pitts S1S Roll Rate


Thread: Pitts S1S Roll Rate

Message: Re: Re[2]: Pitts S1S Roll Rate

Follow-Up To: ACRO Email list (for List Members only)


Date: Tue, 11 Mar 1997 16:52:46 UTC


  Extension of ailerons to the tips is less effective than extension inboard
due to turbulent flow in the tip region.  End plates on the ailerons probably
helps this.  Lee Manelski did this modification , many, many years ago.  He
thought it helped.  I believe that Bob and Jacquie Herendeen later owned that
aircraft and Jacquie might remember its characteristics.  There have been
some who believe that extending ailerons all the way to the fuselage creates
turbulent flow over the tail which creates a built in tendency to "barrel" on
vertical up lines as speed slows.

Blunt trailing edges on the ailerons produce a centering effect which
increases the break-out force.  This, however, requires an offset force for
full deflection by increasing the volume of the spades.  It's a good trade
off.  Alan Geringer did this sort of modification to Fed Abramson's Pitts S
1-S.  It made a significant difference.  I critiqued Fred before and after
modification.  It looked to me like it helped the vertical rolls. Dennis Yugo
now owns that aircraft.  

The tapered trailing edges on my S 1-T with heavy spade volume require
constant handling when flying cross-country.  The Dr 107 and DR 109 are very
neutral in center and fly hands off upright and inverted. The roll rate is
greater than the T due to increased relative volume and efficiency of the
ailerons.  It is nice to have an aircraft which doesn't flip over every time
you unfold a map when going cross country, yet still has a very competitive
roll rate when you get to the contest!

Beware of double taper or chisel point trailing edges on ailerons.  They
reduce the centering effect and can give you a "hard-over" deflection beyond
your strength to control.   

When you start fooling with ailerons you are in an area that should be
experimented with incrementally to avoid catastrophy.  Aeronautical
enigneering in ailerons is a mixed bag.  What seems to have been fully field
tested is increasing ailerons to the tip or one bay in-board is
aerodyamically safe.  Blunt trailing edges are safe.  Stress analysis changes
due to hinge numbers and positions must be accounted for.  Hinge  forces will
change.  You may require a third hinge.   Aileron push/pull rod forces
change, spade requirements change and aileron wells need to be rebuilt.
 Begins to sound like a lot of work to me.

Think I'll go fly my model T.

Dick Rihn

I am an M.D. not an aeronautical engineer.  I'm good at taking care of sick
people,  doing surgery and delivering babies etc. etc.  I make no claims for
expertise in the field of aeronautical engineering.

Experiment at your own peril.  Try to keep it safe and within proven


© Dr. Günther Eichhorn
Email Guenther Eichhorn