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

[steve korney]

Jon....

Your sparrow strainer is inverted and the airfoil is inverted.... But, the angle of attack between the sparrow strainer and the elevator is positive by 20 degrees which in turn pushes the elevator up to give you a total down trim effect... A moveable trim tab would probably do the same thing if it was the right size and adjustable......


Steve 

> From: jonathan.bachman at mtsi-va.com
> To: reflector at tvbf.org
> Date: Fri, 14 Sep 2012 14:09:39 -0500
> Subject: Re: REFLECTOR: Sparrow strainer - I'm confused...
> 
> I'm not sure which way "up" is, concerning the airfoil on the strainer - but on my STD RG the airfoil on the strainer is inverted, as compared to the canard airfoil.  IAW the flatter side is on the top and the curved side underneath.  It does not produce negative stability.  As the aircraft speeds up the strainer airfoil makes more lift, which since the airfoil is inverted, causes the trailing edge of the elevator to move down.  With the elevator deflected trailing edge down, the canard makes more lift and the aircraft climbs.  The climb bleeds of airspeed until the reduced force on the trailing edge of the strainer returns the elevator to its previous position.  So at a constant altitude, while speeding up, nose down trim is required - or forward stick pressure. 
> 
> Jon Bachman
> 
> 575 430-9724
> 
>    
> 
> jonathan.bachman at mtsi-va.com
> 
> -----Original Message-----
> From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of John Dibble
> Sent: Friday, September 14, 2012 12:16 PM
> To: Velocity Aircraft Owners and Builders list
> Subject: Re: REFLECTOR: Sparrow strainer - I'm confused...
> 
> Scott,
> 
> Great explanation.
> 
> John
> 
> On 9/14/2012 12:37 PM, Scott Derrick wrote:
> >
> >>
> >>   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.
> >
> > Anybody who's actually flown A Velocity with the sparrow strainer 
> > installed both upside down, not installed and downside down, knows 
> > that the above statement is completely and utterly false.  The plane
> > will in no way act in the above manner.   What is described above is 
> > negative pitch stability, which the strainer is way way way to small 
> > to induce. In fact it's too small to induce neutral stability when 
> > installed upside down.
> >
> > Speaking from experience, upside or downside down installation changes 
> > the pitch stability in a slight way, in fact its hard to tell the 
> > difference in pitch stability, but it does make a slight positive 
> > change in pitch trim in cruise.
> >
> > Scott
> >
> >
> >
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