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

[John Abraham]

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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