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From: mmallory@netcom.com (Mark Mallory)
Subject: Re: g forces and trim (again)
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Date: Sun, 10 Jan 1999 01:39:20 GMT
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highflyer (highflyer@alt.net) wrote:
: Dave Mould wrote:
: > 
: > I posted a couple of weeks back about finding that a hands-off
: > recovery from a dive at twice the trim speed resulted in only
: > 2.5g.  At that time I had done the entire exercise with cruise
: > power set.  My aircraft is now back in the air after its check,
: > so yesterday I tried the same thing at idle power.
: > 
: > 1) HASEL check.  Throttle to idle, trim to 80KIS, let go of
: > stick to ensure the aircraft is stable.  Without power, I needed
: > to set the trimwheel almost fully back, and this is very close
: > to the stall speed of the aircraft, which was getting a bit
: > "mushy".
: > 
: > 2) Without changing the trim, dive to 160KIS.  Due to the
: > enormous drag from the big prop, this required a dive angle of
: > around 70 degrees.  Hold it for +/- 5 seconds to ensure the
: > speed is stable.  (Lost about 2000 feet in the dive).  Zero the
: > "g" meter.
: > 
: > 3) Let go of the stick.
: > 
: > Result:
: > The aircraft pitched up to an angle that was rapidly approaching
: > the vertical.  It would have most certainly gone passed the
: > vertical, and I was not happy with allowing this to continue
: > with the speed rapidly bleeding off as it was, so I rescued it
: > with a 0g pushover.  I suspect that if left alone, the aircraft
: > would have completed a very egg-shaped loop, or maybe stalled
: > off the top, but I was too chicken to wait and see.  The "g"
: > meter recorded a maximum of exactly 4g.
: > 
: > So the theory seems to work after all, but only if the initial
: > trim speed is set without power being applied.  I would think
: > that in most cases the trim would be set with cruise power
: > applied, and so the resulting "g" will be less than was
: > indicated in the original thread that prompted these
: > experiments.  So I guess its a case where everyone was both
: > right and wrong :-)
: > 
: > Dave Mould

: Boy Dave.  It is a good thing you have a tough airplane.  I really
: like to see these thought experiments turned into REAL ones though.
: It sure cuts through the bull!

It would be interesting to perform this experiment using a T-tailed 
aircraft like the Piper PA-38, which presumably would have lower trim 
sensitivity to power changes due to the horizontal tail being out of the 
prop slipstream.

Now who do you suppose we could find to do some flight experiments in a 
G-meter equipped Tomahawk?  Hmm...

YO, HILTON!

