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

[Scott Baker]

Geoff,

The majority of builders using the Strong pitch trim system report 
issues with the system not having enough strength to trim 'hands off' 
though out the normal speed range of the Velocity.  More than likely, 
your fix is going to require a stronger pitch trim spring.

Regarding the Sparrow Strainer - yours is installed correctly.  In 
addition to acting as a 'buffer' to even out major pitch changes, the 
Sparrow Strainer (theoretically) helps trim the airspeed to somewhere 
near 140-Knots (Va) should the pitch trim system were to break (i.e. 
become disconnected).  If the Sparrow Strainer were inverted to provide 
nose down force as airspeed increases - this contributes to negative 
stability.  Which is to say, as the aircraft speeds up, the nose will 
want to pitch down ... which helps the aircraft speed up, which helps 
the nose pitch down further ... which helps the aircraft speed up - you 
get the idea. Imagine this situation if disoriented in IMC.

Best,
Scott B.



On 9/14/2012 10:01 AM, Geoff Gerhardt wrote:
> 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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