REFLECTOR: Not enough Trim authority

Al Gietzen ALVentures at cox.net
Tue Nov 17 10:02:43 CST 2009


Scott;

 

I had similar issue – not enough down trim at high speed; more than enough
up trim for approach and landing.

 

I have the sparrow strainer installed per plans.  Its purpose is basically
to preload the control in either direction (resist the deflection) to
provide better pitch stability. I also have the WingCo canard (slightly more
camber, 8” wider span); and the standard factory trim spring.

 

During initial install I kept the trim spring as long as possible (just so
it clears the top of the fuselage) to give it more range; and trimmed its
width to allow full, or nearly full, elevator deflection opposite the trim
motor run to full extension to insure controllability in the event of a trim
motor malfunction.

 

Initially; in addition to insufficient down trim at speed; I had more than
enough up trim for landing, and a fairly high canard stall speed.  Taken
together meant too high an incidence on the canard.  That’s when I learned
that with the Shaw canard, the standard incidence gauge needed to be shimmed
to make the leading edge about 1/8” lower (less incidence). So I reduce
canard incidence.  That helped down trim and stall speed.

 

Later I added a wedge shaped shim block where the trim spring fastens to the
torque tube bracket to improve down trim a bit more.

 

I am now very pleased with the control and the trim.  An interesting thing
is that at cruise (~165-170 KTAS) the elevator trailing edge up (about ½ -
¾”), and up trim for landing, is very much the same with pilot only or pilot
plus front seat passenger.  But then trim requirements are determined by CG
as well, and when I carry a passenger I remove the nose ballast, so the CG
flying alone is at about 120”, and with a 200# co-pilot it is about 118”.

 

Your situation is different in many respects; but maybe there is something
here that gives a clue.  If you have more than enough up trim for landing,
perhaps a canard incidence adjustment is in order.

 

Al

 

 

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Scott Derrick
Sent: Monday, November 16, 2009 3:30 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Not enough Trim authority

 

John,

 

Musta been somebody else.  I've flown sans strainer and standard

install. Its on now with the flat side up, which I believe is the

standard way?    That would apply more up force which is exactly my

problem! 

 

I'll take it off and try it.  Then install upside down and see how all

three methods come out.

 

thanks,

 

Scott

 

 

aminetech at bluefrog.com wrote:

> Scott,

>

> Before I reversed the sparrow strainer, my pitch trim ran out at 155-160
kias.  I recall that you tried reversing it and didn't have enough trim up
for approach.  Perhaps no strainer at all would be a happy medium that would
work for you.

>

> John

>

> --- scott at tnstaafl.net wrote:

>

>

>

> I do have a problem with the trim.  I just don't have enough down trim

> for cruise speeds.  If my indicated is 150kias or below its fine. I am

> using the Strong System because I was under the impression it had a

> wider range of trim than the factory design. Now I wonder.  I have

> plenty of up trim on approach with single pilot but I haven't loaded up

> the front yet(forward cg).  Still waiting for the new Catto prop before

> I add any more ballast to the front seat.  I have the system installed

> so its got about 60% down trim travel, and 40% up trim, so I'm already 

> over  compensated  for down trim.  The instructions call for 50/50.  

> I'm sending Alex an email to see what he recommends.

>

> In the mean time I'm thinking about plan B, which is to reinstall the

> factory trim, but stiffen up the spring somewhat to provide more trim

> authority.  I'msomewhat reluctant because of the problem of runway trim

> with a stronger spring.

>

> What are the fast V's doing?  I had marginal trim before with the

> factory spring, not quite enough down, just barely enough up with the

> io360.  Thats why I changed to the Strong system. 

>

> Anybody else have this problem?  Solutions?

>

> Scott

>

>

>

>  

>

>

>

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