REFLECTOR: sparrow strainer (old post)

[Pat Shea]

Hmmm,

 If the strainer only works as a levered airfoil to
dampen pitch deviations, then I'm puzzled why it
wouldn't be rigged to have a neutral angle of attack
(relative to the line of flight) when the elevator is
in its typical cruise position. That would mean the
strainer would need to have neutral-to-positive
incidence relative to the elevator. With negative
relative incidence, the strainer will actually
increase stick/spring forces the faster you go
(essentially like a trim tab bent the wrong way). The
inverted airfoil shape only adds to this this effect.
Obviously the factory does it this way for a reason -
maybe they are looking to lighten trim loads at lower
speeds. BTW, my templates leave the strainer incidence
open to a little interpretation. I guess it's not
critical since builders' are running them from
positive 20 degrees to negative 20 degrees...
 Funny, but sometimes it seems people are
hypercritical about some pretty minor stuff, yet we
can't even get a consensus on proper control surface
balancing or sparrow strainer incidence. Maybe it's
just me...

Pat

--- SlvEgl99@aol.com wrote:
> I agree, the strainer has a negative angle of
> incidence as compared to the 
> elevator. I simply made the airfoil as the templates
> showed. My plane was 
> constructed at the Velocity Service Center, so am
> confident that it is correct.
> 
> The autopilot sometimes does a bit of "seeking" in
> altitude, and in 
> discussions some have recommended two sparrow
> strainers (one on each side) as a 
> possible cure. I have not done that yet, but make
> sure the plane is stablilzed and 
> trimmed before turning on altitude hold.
> 
> Bob Wood
> 658SE
> 



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