Re: Sparrow strainer stall

Jay Scheevel
 

Hi Bruce,

 

If the airflow were to not detach from the elevator (in a perfect world), the airflow would follow the black streamlines shown in the computation below. These “ideal” streamlines suggest that the sparrow strainer would actually see a low angle of incidence, even when the canard is at a high attack angle (10 degrees) and the elevator is deflected 10 degrees down. Since my computation method is incapable of modeling the separation bubble and turbulent counterflow around the trailing edge of the elevator, the streamlines in that region of my model are not representative of real life. In the real world, I suspect what you are seeing from your sparrow strainer tufts is not related to the sparrow strainer stalling per se, but instead the sparrow strainer just happens to be caught up in the larger flow field of air flowing up and around the trailing edge of the elevator within the larger separation bubble. In other words, there is reverse airflow over the sparrow strainer because the elevator is stalled, not because the sparrow strainer is stalled. Not much you can do to get the sparrow strainer to fly when the airflow over it is backwards. My 2 cents.

 

Cheers,

Jay

 

From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of Bruce Crain
Sent: Wednesday, March 18, 2020 9:18 PM
To: main@Q-List.groups.io
Subject: Re: [Q-List] Sparrow strainer stall

 

On the bottom as the stall was happening on the underneath side of the strainer.  The tufts on the aft of the strainers were disappearing underneath the strainers.

Bruce 

---------- Original Message ----------
From: "Jay Scheevel" <jay@...>
To: main@Q-List.groups.io
Subject: Re: [Q-List] Sparrow strainer stall
Date: Wed, 18 Mar 2020 19:44:54 -0600

Bruce,

which side of the strainer did you put the zigzag tape on? Top or bottom?

Jay

 

 

Sent from my Verizon Wireless 4G LTE DROID



Bruce Crain <jcrain2@...> wrote:

Jon, 

I tried the zig zag tape and did get the stall to go away right up the last test where I finally had all of the zig zag cleaned off.  With the zig zag the stall would not happen on the strainer but it created drag and dragged the strainer up and thus the elevator also.  The elevator would ride up a half inch or so and stay and I would reflex the ailerons up to compensate.

 

I am going to test actual vortex generators next.  Trying to make them small enough so that they don't  create drag and pull the elevator up.  So the zig zag did work but with less than great results for the trim I am used to seeing.

 

Before the next tests I am pulling a cylinder to check for a leak around a cylinder base stud or cylinder base o ring perhaps.

 

Bruce Crain



---------- Original Message ----------
From: "Jon Finley" <jd@...>
To: main@Q-List.groups.io
Subject: Re: [Q-List] Sparrow strainer stall
Date: Wed, 18 Mar 2020 11:41:07 -0700

Howdy Jay,

I recently heard a woman admit that there are "degrees of yes" - I was stunned. Of course, I was very familiar with this phenomena but had never heard the other gender actually admit to it. Now you are talking about "degrees of stalled" - please confirm your gender!! 

:-)

Seriously, I know you are correct. I also saw this in my GU canard tuft testing (moving up/forward on the airfoil). 

Bruce; I don't know what to say on your strainers. I struggled to know how to set them (and eventually gave up on them on my GU, since they weren't needed/per-plans (instead, springs take up the load, as I recall)).  I imagine you have already tried reducing their angle of attack - and noted some change in stick force?? 

Jon  

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