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In a message dated 5/20/2006 6:09:37 A.M. Central Standard Time,
domcrain@tpg.com.au writes:
Hmmm.
I think I have a comment worth posting on
the tail size.Now, here in OZ I have a
“large tail” 320.
Yet, it seems that there were two ways of
determining the “large tail” design when the local authority demanded
it.One was to create a new 25% larger
horizontal stab with the elevator full width, and the elevator horns wrapped
around the ends.The other was to extend the
horizontal stab the 25% while retaining the same elevator width. ( Thus, my
request to Grayhawk for a measure of the length of his tail – er, elevator -
ahem!)
Now, at approach
speeds, I find I run out of pitch trim at about the point of stabilized
approach with landing flap (30) on final.This means that the there is always an
ever so slight tendency for pitch down at that speed.Which in turn means
stability.Now, Airbus, in its wisdom, and for those
who have flown or still fly ‘em know, decided Lancair had a great idea with this nose down pitch stability
on approach.‘Cos at 100’ on final, the elevator computer takes a snapshot
of the pitch angle, and retains that in memory.Then at 50’ the elevator computer
commences a positive nose down pitch which demands the pilot commences a flare
into the landing.Bloody marvelous
mates.
Also I had the privilege of flying Bill
and Sue’s 320 at Fredericksburg last year, although I suggest Bill would
suggest the term, “fly”, is a gross exaggeration in my case, and confess I
couldn’t tell the difference between my tail and theirs.What I found a mystery was the
over-control I exhibited in both pitch and roll axes. Mine is very stable in
both areas.
Dom,
Egads, I forgot to do the measuring of my almost "built as designed" small
tail. Nothing was increased in size (except the pilot girth) - not the
motor (320), the mount or the tail. The "almost" is that the empennage
flying surfaces are thinner than most, improperly placing more faith in the
molded skins than the rib plans. Oh, and a shorter bellcrank.
Lancair 300 series characteristics - Hmmmm, I am able to trim to almost
neutral thru all normal speeds and flap deployments (full 45 degrees). I don't
like to totally trim out pitch forces on final as I prefer to feel some
small force against my hand (uh, fingers). I have landed with the
only fuel being 4 gals in the header (forward CG) and have found full elevator
authority to do so.
I do run out of nose down trim at race speeds. However, I will not
further adjust for the more needed nose down trim at race speeds as I
prefer to be holding the necessary wee bit of nose down force. Should I
start to daydream, I will climb rather than descend into the landscape beneath
me.
BUT, there are different trim mechanisms, each with its own pros and
cons:
1. I am using the shortened elevator bellcrank (3" instead of 4"), thus
shortening the stick throw by 25% and increasing the stick forces in
pitch. I also use the Dick Reichel geared walnut trim wheel (almost
matching the teak grips) with stiffer than normal springs. The
drawback of a spring bias trim system is the control surface same direction
movement dead band force. That is, if the springs are holding
"up" elevator, it takes little force to start to move the elevator further
up and more than normal force to move it down against the more compressed
positioning spring.
2. Trim tabs are frequently used and require little deflection at
cruise speed for effectiveness. They sometimes lose effectiveness at slow
speeds where the elevator may become sensitive to small forces in any
direction. This may be the case that some have indicated where excessive
elevator movement (even apparent control reversal) seems necessary and
might lead to pilot induced oscillations. Some of this problem may lie in
the size of the trim tab. Standard certificated airplanes seem to have
rather large tabs in proportion to the elevator size.
Scott Krueger
AKA Grayhawk
Lancair N92EX IO320 SB 89/96
Aurora, IL
(KARR)
Abnegate Exigencies!
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