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Old October 31st 08, 01:04 AM posted to rec.aviation.homebuilt
Steve Hix
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Posts: 340
Default Lancair Legacy Design Flaw?

In article ,
"Gregory Hall" wrote:

France? I don't live in France. I built and used to fly a Rotec Rally 2B
many years ago. It was a tail dragger with a high wing and the motor was
mounted atop the win[g] with a pusher prop.

When I got it trimmed out correctly at cruise speeds I could lean forward in
the seat to nose it down and lean back in the seat to nose it up.


Sort of like a Taylorcraft or Cessna 140 or similar small aircraft.

Even as
well-balanced as it was at about half throttle, when the engine quit it
would pitch up immediately and drastically because the high engine placement


.... Placed the thrust line enough above the center of drag that adding
power caused a downward pitch moment, and reducing power resulted in a
upward pitch.

and pusher prop had enough leverage so that the proper trim at the tail
counteracted the nose down force of the engine and prop.


Which is what the horizontal stab/stabilator is for.

If you didn't
immediately push the stick way forward when the engine quit it was a matter
of seconds before it would nose up fast and stall and then you would have no
control at all from the stick until it fell for a while and the nose dropped
(thank god for that) so you could gain speed provided you had enough
altitude to get control of it again. But it didn't glide too well being a
single surface wing with wire bracing. Perhaps 2:1 glide ratio. But it was
easy to land with no power but you had to come in hot and steep and at the
last second pull back on the stick and flare it.

It looks to me like the Legacy would act pretty much the same if the engine
quit.


Except for the Legacy not incorporating those design elements that
result in the pitch/power response of the Rotec Rally. The Rally needs a
lot of upward pitch dialed in for level cruise (which ought to be
contributing a lot of drag as an added bonus), giving you some nasty
response to losing power.

In particular, both thrust and drag components in the Legacy are much
closer in alignment, resulting in much less pitch change when power
changes.

The two aircraft behave very differently in many aspects, and the Legacy
not much at all as you've asserted.