Message-Id: <3.0.3.32.19981104134329.00713630@olsusa.com>
Date: Wed, 04 Nov 1998 13:43:29 -0500
To: lancair.list@olsusa.com
From: Peter Field <pfield@mdc.com> (by way of Marvin Kaye <marvkaye@olsusa.com>)
Subject: lancair ES stall speed
Mime-Version: 1.0

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Mark:

      I gather from your remarks that lengthening the runway you have built is
not an option; however, if it is I'd look at that as a first fix alternative.
What do the runway approaches look like?  Do you have to make steep approach
angles to get over obstacles or can you use a 2.5 to 3 degree approach path
angle?  These factors will determine your touch down dispersion and how much
runway is left in which to stop.  

     Now to answer your questions:  All speed brakes will do for you is add
drag during the approach and require you to carry a slightly higher power
setting.  Speed brake effect on roll out will be negligible if it can be
measured at all (depends on the size of the speed brakes, so you'd have to
have
 some whoppers to shorten your roll out).  Approach path angle will not be
affected by speed brakes.  Vortex generators could help reduce approach
speed. 
I'm considering them for my Lancair 360.  If there is separated flow on the
upper surface of the flaps when they are fully deployed, vortex generators
placed at or just ahead of the wing/flap juncture could improve total wing
lift
by improving the wing's overall "circulation" (keeping the upper surface flow
attached), thus lowering your approach speed.  Where exactly to place vortex
generators is a combination of science and art, but tufting the upper flap
surface to determine if there is any upper surface flow separation would be
the
best place to start.

      You also need to consider safe flight testing practices (particularly as
a low time pilot).  You won't be able to make minimum distance roll outs until
you have built some familiarity with your new airplane.  I plan to use a 7,500
foot runway for my first flight and probably for a goodly number of the first
series of flights.  My criteria is to be able to get airborne and still have
enough runway to put it back down and get stopped on if, for example, the
engine sounds funny in the first few seconds after lift off.

     Other things I would do are to consider an Angle of Attack (AoA) system.
AoA is the best way to indicate how close to stall you are operating the
airplane.  Normally, a speed like 1.3 X Vs is chosen for approach speed
depending on the nature of the stall if you are using airspeed indication
alone.  If the stall is abrupt and exhibits a wing roll off with little
warning, then you have to add more excess airspeed.  On the other hand, if the
stall is benign and gives you plenty of warning you can operate a lot
closer to 
stall.  Rig up a set of VASI boards to show you a 3 degree glide slope so you
can get some idea of where you are going to touch down.  Runway distance
remaining markers could tell you if you can still get stopped after a long
touch down.  If there's not enough room left, take it around for another try
and "land on the first brick," as they say.  Hope this helps, stay in touch
(directly if you like) and let me know how it's going.

Cheers, 
Pete