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

[Laurence Coen]

Geoff,

With my plane, I had to hold forward stick solo when I passed 170 kts.  I solved the problem by reducing the down angle of attack of the sparrow strainer (about 3 deg.).  I think this is an easier way than adjusting the trim spring.  I no longer have up or down trim issues and still have good pitch stability.

Larry Coen
N136LC
SE/RG Franklin IVO


From: John Abraham 
Sent: Friday, September 14, 2012 9:42 AM
To: geoff.gerhardt at gmail.com ; 'Velocity Aircraft Owners and Builders list' 
Subject: Re: REFLECTOR: Sparrow strainer - I'm confused...


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

         

                  200 W. Airport Drive

                  Sebastian, FL 32958

            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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