REFLECTOR: Sparrow strainer - I'm confused...

Sat Sep 22 20:43:46 CDT 2012

We installed the factory trim system with no modifications and installed the
sparrow strainer per the plans (airfoil down) and have never noticed running
out of trim or had to make adjustments.

We have an XL-FG with 750 hours

John Schoorl

  _____  

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Scott Derrick
Sent: Friday, September 14, 2012 8:19 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Sparrow strainer - I'm confused...

While agree with John in theory.....

The elevator trim system is like the nose wheel shimmy damper, its barely
adequate, though the factory will never admit it is anything but fine. Yeah,
normally if you keep the nose wheel tension within a reasonable range, which
makes taxiing a bitch, it works.  but let it get a bit out of that range or
have some other mysterious contributing factor and it will bite you and can
bite really hard! You will now notice the factory is selling a nose trim
system designed and initially built by one of our members here on the
reflector.  It's priced in the range of a certified airplane shimmy damper,
but it appears to solve the nose gear destroying inadequacy of the standard
shimmy damper.  

The standard elevator trim system is the same,  get it shimmed up and it
works OK(barely adequate for some, POS for others).  You can get it(shim) to
trim hands off in a max trim up condition(approach speed, max forward cg)
but then you aren't even close to  max trim down condition(aft cg, max
cruise speed), or you can go the other way.  And thats  with the sparrow
strainer installed in a standard configuration.  Most shim it somewhere in
the middle, not really good enough for either max up or max down condition.

I've never heard of any "builder" getting the trim to work properly without
installing the SS upside down, or increasing the stiffness of the spring.
The problem with increasing the stiffness is having a trim malfunction.
With a stiffer spring I question any body's ability except maybe a weight
lifter, of having the strength to over come a full down trim position, fly
to a near airport and land the plane.  Somebody on the reflector had to do
that with a standard spring and as I recall, he said he wasn't sure his arm
strength was going to last long enough  to get it on the ground and I
believe the trim malfunction happened in the pattern!

Just try it sometime.  In flight simulate a trim malfunction. Trim full down
and then fly the pattern and attempt a landing!  Do this at altitude!!!

I'd be glad to hear from any builder that has solved the elevator trim
problem with the sparrow strained in the normal position and not by
increasing the spring stiffness?

Scott

-------- Original Message --------
Subject: Re: REFLECTOR: Sparrow strainer - I'm confused...
From: John Abraham  <mailto:john at velocityaircraft.com>
<john at velocityaircraft.com>
To: geoff.gerhardt at gmail.com, 'Velocity Aircraft Owners and Builders list'
<mailto:reflector at tvbf.org> <reflector at tvbf.org>
Date: 09/14/2012 08:42 AM

Geoff,

Just the opposite.  The sparrow strainer is there to aid your trim system.
Since a trim system is to maintain airspeed you have to trim down as you
accelerate or the plane will climb.  Installing it upside down will work to
make the elevator "trim" itself, but will prevent your trim system from
being stable.  Your pitch should be 1.5 oscillations with a 10kts
disturbance, which is pretty good compared to other aircraft.  If you run
out of trim nose down you need to space out your trim spring down on the V
bracket on the concentric torque tube.  Nose up trim would be at the trim
motor and spring bracket.  

Other things to consider are the stiffness of your trim spring, if it was
ever weakened or cut down it won't hold trim very well at high or low speeds
due to air loads.  You can replace it with a stiffer spring if you want to
which will also help out.  I have seen some builders narrow their spring due
to clearance issues but you looks some stiffness as a result.  Also, look at
the top of the trim spring for stress cracks.  Always try to be close to
neutral trim when doing your run up and box check so you don't over stress
the spring.

Safe flying,

                      John Abraham

Chief Pilot, Executive V.P. Sales and Marketing

         Description: 4103

                  200 W. Airport Drive

                  Sebastian, FL 32958

             <http://www.velocityaircraft.com/> www.velocityaircraft.com

                  (P): 772-589-1860

                  (F): 772-589-1893

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Geoff Gerhardt
Sent: Friday, September 14, 2012 10:02 AM
To: Velocity Aircraft Owners and Builders list
Subject: REFLECTOR: Sparrow strainer - I'm confused...

Guys,

As I'm flying more, I'm getting a better feel for the plane and discovering
little issues.  I noticed yesterday that when I really dangle (i.e.
>160kts), I run out of down trim.  I guess I wasn't paying attention before,
but as I speed up, I need to keep adding down trim - I thought that's what
the sparrow strainer was for.  As speed increases, the canard is generating
more lift, so the sparrow strainer trims the nose down so that less trimming
is needed for speed changes.  But then, I was looking at the way the sparrow
strainer is mounted and it looks like it would do just the opposite.  As
speed increases, the sparrow strainer will be pushed down, adding trim up!
I have my aerodynamic trim installed as per factory instructions.  I've
heard of some who install it upside down, which to me sounds like how it
should be installed.  I have a feeling that if I remove it I'd have to trim
less with speed changes.  Unfortunately, I used some pretty aggressive
silicone glue to put it on and I'm afraid I'll make a mess of it taking it
off.

Any thoughts on the effectiveness/correct installation of aerodynamic trim?

Here's now I have mine installed:

http://thegerhardts.com/velocity/?p=491

Geoff

  _____  

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