#### Sparrow strainer stall conundrum

Jay Scheevel

Here is the basic problem and I am not sure if vg’s on the sparrow strainer can fully solve it:  The first picture below is the streamline flow-field around the LS1 airfoil, with the standard sparrow strainer position depicted with the red outline.

Zooming in on the sparrow strainer and flipping it over, you can see the relative wind (AOA) of the sparrow “Clark Y” airfoil to the streamlines is 27 degrees (the green angle). This is way beyond the stall angle of that airfoil, which is why is appears to be stalled at all airspeeds in my videos.

Maybe sparrow strainers can allow the Clark Y to reach that AOA before fully stalling, but I doubt it.  Another option to give the sparrow strainer the same aerodynamic effect, is to move it farther back from the trailing edge and lower its angle of attack, thereby giving it the same moment relative to the elevator pivot point, of course this would require longer arms. It needs to have a certain amount of lift, but it certainly is not producing a lot of lift when fully stalled. Maybe just lowering the angle to below the stall point would do the trick, because it would pick up more lift in the process.

I have modeled the combination of the two airfoils (LS1 and sparrow strainer) in a single flow field and here is that result.  You can see the result below and it shows the same flow that is demonstrated by the tufts in my video. Now I will scratch my head and see if the vg’s may do the trick.

_._,_._,_

Brian Larick

I’m on pins and needles for the magic solution.  Question would a longer arm with a better angle of attack have the same negative aerodynamics or would they improve on the negative airflow due to the longer angle?

Brian

On Feb 22, 2022, at 20:12, Jay Scheevel <jay@...> wrote:

﻿

Here is the basic problem and I am not sure if vg’s on the sparrow strainer can fully solve it:  The first picture below is the streamline flow-field around the LS1 airfoil, with the standard sparrow strainer position depicted with the red outline.

Zooming in on the sparrow strainer and flipping it over, you can see the relative wind (AOA) of the sparrow “Clark Y” airfoil to the streamlines is 27 degrees (the green angle). This is way beyond the stall angle of that airfoil, which is why is appears to be stalled at all airspeeds in my videos.

Maybe sparrow strainers can allow the Clark Y to reach that AOA before fully stalling, but I doubt it.  Another option to give the sparrow strainer the same aerodynamic effect, is to move it farther back from the trailing edge and lower its angle of attack, thereby giving it the same moment relative to the elevator pivot point, of course this would require longer arms. It needs to have a certain amount of lift, but it certainly is not producing a lot of lift when fully stalled. Maybe just lowering the angle to below the stall point would do the trick, because it would pick up more lift in the process.

I have modeled the combination of the two airfoils (LS1 and sparrow strainer) in a single flow field and here is that result.  You can see the result below and it shows the same flow that is demonstrated by the tufts in my video. Now I will scratch my head and see if the vg’s may do the trick.

Mike Dwyer

Nice work Jay.  Wouldn't moved down produce better results than moved back?  Moved down, less angle of attack, and likely smaller area because now the sparrow strainer will not be stalled.  I wonder how much drag they cause now?  Relatively easy to make this mod to a flying airplane too.  As is, people seem to want to step on the darn thing.  Moving back could be irresistible to them!  Oh, and the strainer, at least mine, is basically flat on the bottom.  Doesn't look like the air foil in your drawing.
Fly Safe,
Mike Dwyer

Q200 Website: http://goo.gl/V8IrJF

On Tue, Feb 22, 2022 at 8:12 PM Jay Scheevel <jay@...> wrote:

Here is the basic problem and I am not sure if vg’s on the sparrow strainer can fully solve it:  The first picture below is the streamline flow-field around the LS1 airfoil, with the standard sparrow strainer position depicted with the red outline.

Zooming in on the sparrow strainer and flipping it over, you can see the relative wind (AOA) of the sparrow “Clark Y” airfoil to the streamlines is 27 degrees (the green angle). This is way beyond the stall angle of that airfoil, which is why is appears to be stalled at all airspeeds in my videos.

Maybe sparrow strainers can allow the Clark Y to reach that AOA before fully stalling, but I doubt it.  Another option to give the sparrow strainer the same aerodynamic effect, is to move it farther back from the trailing edge and lower its angle of attack, thereby giving it the same moment relative to the elevator pivot point, of course this would require longer arms. It needs to have a certain amount of lift, but it certainly is not producing a lot of lift when fully stalled. Maybe just lowering the angle to below the stall point would do the trick, because it would pick up more lift in the process.

I have modeled the combination of the two airfoils (LS1 and sparrow strainer) in a single flow field and here is that result.  You can see the result below and it shows the same flow that is demonstrated by the tufts in my video. Now I will scratch my head and see if the vg’s may do the trick.

Bruce Crain

My sparrow strainer is already a couple of inches below the trailing edge of the elevator and midpoint on the elevator.  When i pushed forward as in unloading when doing an aileron roll it stalled out before I put the 5 or 6 vortex generator on the bottom side of the strainer.
Apparently mounted in board in the blast from the prop the strainer doesn't stall out over the whole surface of the strainer.
Bruce Crain

From: "Jay Scheevel" <jay@...>
To: <main@Q-List.groups.io>
Subject: [Q-List] Sparrow strainer stall conundrum
Date: Tue, 22 Feb 2022 18:12:22 -0700

Frankenbird Vern

27 degrees AOA is a lot. One would think lowering the AOA of the Strainer Clark Y, thereby taking it out of a
stall condition, would increase the effective "inverted lift".  Is everyone using the same degree of AOA Strainers?
Gonna presume so since the Strainer templates in the newsletters were never revised that I remember.

I think what you ment Jay is "VG's" on the Strainers. What Bruce experienced is the laminar "sticks" to the Strainer by
using the VG's which is of course what they do on other lift surfaces (up to a point of course). Any lift surface with the
power sources we have available will stall at an extreme enough AOA.

So..if Bruces VG's provided laminar flow to stay attached even at that AOA, it must be working for his aircraft. But this
all begs to ask.. was there any real testing for the AOA of the Strainers other than simply patching the lift loss problem?
I think not. The obvious plan was get these darn airplanes where they don't scare anyone to fly near (or in) rain anymore.

I do remember seeing the adjustable Strainers, Jay. You are correct they were aluminum if memory serves. It would
be nice if there was some record of tuft testing them to see where the least AOA resulted in the resolution. No
cameras like we have now back then. I bet they were effective at 18 or maybe even 16 degrees AOA and the drag
would have been reduced.

What if the Strainers are made larger..lets say 12"? Same dimension aft of the trailing edge, but less AOA yet
physically greater surface area?  Peter had this issue..remember his Strainers were at first too large and he reduced
the surface area by cupping out the Strainer T.E.?

We get this pinned down guys and it looks like a simple revision that will offer large gains for small cash outlay.

From: main@Q-List.groups.io <main@Q-List.groups.io> on behalf of Jay Scheevel <jay@...>
Sent: Tuesday, February 22, 2022 7:12 PM
To: main@Q-List.groups.io <main@Q-List.groups.io>
Subject: [Q-List] Sparrow strainer stall conundrum

Here is the basic problem and I am not sure if vg’s on the sparrow strainer can fully solve it:  The first picture below is the streamline flow-field around the LS1 airfoil, with the standard sparrow strainer position depicted with the red outline.

Zooming in on the sparrow strainer and flipping it over, you can see the relative wind (AOA) of the sparrow “Clark Y” airfoil to the streamlines is 27 degrees (the green angle). This is way beyond the stall angle of that airfoil, which is why is appears to be stalled at all airspeeds in my videos.

Maybe sparrow strainers can allow the Clark Y to reach that AOA before fully stalling, but I doubt it.  Another option to give the sparrow strainer the same aerodynamic effect, is to move it farther back from the trailing edge and lower its angle of attack, thereby giving it the same moment relative to the elevator pivot point, of course this would require longer arms. It needs to have a certain amount of lift, but it certainly is not producing a lot of lift when fully stalled. Maybe just lowering the angle to below the stall point would do the trick, because it would pick up more lift in the process.

I have modeled the combination of the two airfoils (LS1 and sparrow strainer) in a single flow field and here is that result.  You can see the result below and it shows the same flow that is demonstrated by the tufts in my video. Now I will scratch my head and see if the vg’s may do the trick.

Frankenbird Vern

Ah!  Yes, so the prop blast is assisting the prevention of totally Stalled. Several aircraft use that same principal for additional lift
at lower airspeeds but at higher airspeeds I would think that effect would be diminished, Bruce. Yes? No? Need to see what is
happening on the fastest in the known fleet.

Wow..my brain is hurting!! This is harder than learning DELMIA! Grrr.

From: main@Q-List.groups.io <main@Q-List.groups.io> on behalf of Bruce Crain <jcrain2@...>
Sent: Tuesday, February 22, 2022 10:10 PM
To: main@Q-List.groups.io <main@Q-List.groups.io>
Subject: Re: [Q-List] Sparrow strainer stall conundrum

My sparrow strainer is already a couple of inches below the trailing edge of the elevator and midpoint on the elevator.  When i pushed forward as in unloading when doing an aileron roll it stalled out before I put the 5 or 6 vortex generator on the bottom side of the strainer.
Apparently mounted in board in the blast from the prop the strainer doesn't stall out over the whole surface of the strainer.
Bruce Crain

From: "Jay Scheevel" <jay@...>
To: <main@Q-List.groups.io>
Subject: [Q-List] Sparrow strainer stall conundrum
Date: Tue, 22 Feb 2022 18:12:22 -0700

Frankenbird Vern

What I was thinking also, Brian. Either larger area as in Peter's Sparrow Strainers on his aircraft which he trimmed by flight testing until best effect..or in cleaner air below the canard. Further aft would provide more arm also.  All of these are valid investigations which the camara available allow, not as in the past.  There is a "sweet spot" on this.. and at Boeing the same general pondering happend on the blended tip designs. Still evolving if you look on 777X and probably on the 787-10X (soon to become 797 because of the massive structural boo-boo's I hear rumors of, the Fed has them by the short hairs as they should!).

The truth is even using wind tunnels and Aerodynamic modelling there were always surprises when it comes down to actual flight test.

Vern

From: main@Q-List.groups.io <main@Q-List.groups.io> on behalf of Brian Larick <blarick@...>
Sent: Tuesday, February 22, 2022 7:35 PM
To: main@q-list.groups.io <main@q-list.groups.io>
Subject: Re: [Q-List] Sparrow strainer stall conundrum

I’m on pins and needles for the magic solution.  Question would a longer arm with a better angle of attack have the same negative aerodynamics or would they improve on the negative airflow due to the longer angle?

Brian

On Feb 22, 2022, at 20:12, Jay Scheevel <jay@...> wrote:

﻿

Here is the basic problem and I am not sure if vg’s on the sparrow strainer can fully solve it:  The first picture below is the streamline flow-field around the LS1 airfoil, with the standard sparrow strainer position depicted with the red outline.

Zooming in on the sparrow strainer and flipping it over, you can see the relative wind (AOA) of the sparrow “Clark Y” airfoil to the streamlines is 27 degrees (the green angle). This is way beyond the stall angle of that airfoil, which is why is appears to be stalled at all airspeeds in my videos.

Maybe sparrow strainers can allow the Clark Y to reach that AOA before fully stalling, but I doubt it.  Another option to give the sparrow strainer the same aerodynamic effect, is to move it farther back from the trailing edge and lower its angle of attack, thereby giving it the same moment relative to the elevator pivot point, of course this would require longer arms. It needs to have a certain amount of lift, but it certainly is not producing a lot of lift when fully stalled. Maybe just lowering the angle to below the stall point would do the trick, because it would pick up more lift in the process.

I have modeled the combination of the two airfoils (LS1 and sparrow strainer) in a single flow field and here is that result.  You can see the result below and it shows the same flow that is demonstrated by the tufts in my video. Now I will scratch my head and see if the vg’s may do the trick.

Michael Dunning

Jay, that RAF CP 59 that Dave listed makes some interesting points. Burt recommended fixed tabs riveted on (and 10" long, to boot) to unload the elevator trim springs; different idea but something to think about.

Note that the attached pdf is one I found before he posted his repository link. Might be poor quality.

--
-MD
#2827 (still thinking about planning on visualizing how to finish building)

Jay Scheevel

Thanks Michael,

I did read this after David pointed me in that direction. The problem with this approach is that the net moment arm is smaller because it is closer to the trailing edge, and the problem that the sparrow strainer is trying to solve is much larger than trying to balance trim spring loads. The basis of the problem is the shape of the elevator, which causes it to have a lot of upward deflection in the absence of the sparrow strainer. The issue that Burt was addressing was more of a tweak for builders that did not get everything perfectly set up while building.

Cheers,

Jay

From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of Michael Dunning
Sent: Wednesday, February 23, 2022 8:12 AM
To: main@Q-List.groups.io
Subject: Re: [Q-List] Sparrow strainer stall conundrum

Jay, that RAF CP 59 that Dave listed makes some interesting points. Burt recommended fixed tabs riveted on (and 10" long, to boot) to unload the elevator trim springs; different idea but something to think about.

Note that the attached pdf is one I found before he posted his repository link. Might be poor quality.

--
-MD
#2827 (still thinking about planning on visualizing how to finish building)

Brian Larick

My non engineer question.  Is there an efficient solution with a change to the shape of the elevator?  Would seem that if there was that it would have been developed a long time ago.

Brian

On Feb 23, 2022, at 10:48, Jay Scheevel <jay@...> wrote:

﻿

Thanks Michael,

I did read this after David pointed me in that direction. The problem with this approach is that the net moment arm is smaller because it is closer to the trailing edge, and the problem that the sparrow strainer is trying to solve is much larger than trying to balance trim spring loads. The basis of the problem is the shape of the elevator, which causes it to have a lot of upward deflection in the absence of the sparrow strainer. The issue that Burt was addressing was more of a tweak for builders that did not get everything perfectly set up while building.

Cheers,

Jay

From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of Michael Dunning
Sent: Wednesday, February 23, 2022 8:12 AM
To: main@Q-List.groups.io
Subject: Re: [Q-List] Sparrow strainer stall conundrum

Jay, that RAF CP 59 that Dave listed makes some interesting points. Burt recommended fixed tabs riveted on (and 10" long, to boot) to unload the elevator trim springs; different idea but something to think about.

Note that the attached pdf is one I found before he posted his repository link. Might be poor quality.

--
-MD
#2827 (still thinking about planning on visualizing how to finish building)

Frankenbird Vern

We think so..but remember that aerodynamics since 1980 has itself changed quite a bit, Brian.  Aerodynamics is still an evolving study. Actually Manufacturing and Structures Design is also. Internal Powerplant design is also improving.  AeroGeeks have learned a great deal since the days of Disco due to new tools like micro cameras that can be attached to birds.

No one knew back then how Peregrin Falcons could descend in an attack tuck at such incredible speeds. Impressive for a bird that is actually light weight compared to others like them. We understand more now. Still learning too.

Vern

From: main@Q-List.groups.io <main@Q-List.groups.io> on behalf of Brian Larick <blarick@...>
Sent: Wednesday, February 23, 2022 10:17 AM
To: main@q-list.groups.io <main@q-list.groups.io>
Subject: Re: [Q-List] Sparrow strainer stall conundrum

My non engineer question.  Is there an efficient solution with a change to the shape of the elevator?  Would seem that if there was that it would have been developed a long time ago.

Brian

On Feb 23, 2022, at 10:48, Jay Scheevel <jay@...> wrote:

﻿

Thanks Michael,

I did read this after David pointed me in that direction. The problem with this approach is that the net moment arm is smaller because it is closer to the trailing edge, and the problem that the sparrow strainer is trying to solve is much larger than trying to balance trim spring loads. The basis of the problem is the shape of the elevator, which causes it to have a lot of upward deflection in the absence of the sparrow strainer. The issue that Burt was addressing was more of a tweak for builders that did not get everything perfectly set up while building.

Cheers,

Jay

From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of Michael Dunning
Sent: Wednesday, February 23, 2022 8:12 AM
To: main@Q-List.groups.io
Subject: Re: [Q-List] Sparrow strainer stall conundrum

Jay, that RAF CP 59 that Dave listed makes some interesting points. Burt recommended fixed tabs riveted on (and 10" long, to boot) to unload the elevator trim springs; different idea but something to think about.

Note that the attached pdf is one I found before he posted his repository link. Might be poor quality.

--
-MD
#2827 (still thinking about planning on visualizing how to finish building)

Jay Scheevel

Hi Brian,

So here is the non-engineering answer:

The solution was developed a long time ago. John Roncz solved most problems for the Long EZ canard by introducing the new airfoil (Roncz MS1145). The quickie GU shortcomings were solved with the installation of the VG’s and the GU did not require the sparrow strainer anyway (this VG solution was not discovered until after QAC had gone entirely to selling the LS1).

Most people who built with the LS1 did not question the use of the sparrow strainers because they work as intended, are called for in the plans, albeit the additional drag issue was never discussed by QAC.

What we are talking about here is optimizing the solution, either by improving the sparrow strainer design or by eliminating the need for them with a modified elevator design.

Below is my working model for a redesigned elevator solution, where the sparrow strainer is likely not needed.  This is not a tested design, so PLEASE DON’T USE THIS.

Cheers,

Jay

From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of Brian Larick
Sent: Wednesday, February 23, 2022 9:17 AM
To: main@q-list.groups.io
Subject: Re: [Q-List] Sparrow strainer stall conundrum

My non engineer question.  Is there an efficient solution with a change to the shape of the elevator?  Would seem that if there was that it would have been developed a long time ago.

Brian

On Feb 23, 2022, at 10:48, Jay Scheevel <jay@...> wrote:

﻿

Thanks Michael,

I did read this after David pointed me in that direction. The problem with this approach is that the net moment arm is smaller because it is closer to the trailing edge, and the problem that the sparrow strainer is trying to solve is much larger than trying to balance trim spring loads. The basis of the problem is the shape of the elevator, which causes it to have a lot of upward deflection in the absence of the sparrow strainer. The issue that Burt was addressing was more of a tweak for builders that did not get everything perfectly set up while building.

Cheers,

Jay

From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of Michael Dunning
Sent: Wednesday, February 23, 2022 8:12 AM
To: main@Q-List.groups.io
Subject: Re: [Q-List] Sparrow strainer stall conundrum

Jay, that RAF CP 59 that Dave listed makes some interesting points. Burt recommended fixed tabs riveted on (and 10" long, to boot) to unload the elevator trim springs; different idea but something to think about.

Note that the attached pdf is one I found before he posted his repository link. Might be poor quality.

--
-MD
#2827 (still thinking about planning on visualizing how to finish building)

Anthony P

Jay, this is all very interesting.

Do your (model) numbers for the above profile include the effect of the pocket that the elevator partially occupies and the gaps to the trailing edges of the pocket?

I can't wait for you or someone else to try this.  Sparrow strainers are a P.I.A.
No lift, or net lift at the elevator pivot point would be great.

I'm willing to partially fund the investigation.

--
Q2 N86KL

Jay Scheevel

Not sure what you mean by “pocket”??

From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of Anthony P
Sent: Wednesday, February 23, 2022 11:17 AM
To: main@Q-List.groups.io
Subject: Re: [Q-List] Sparrow strainer stall conundrum

Jay, this is all very interesting.

Do your (model) numbers for the above profile include the effect of the pocket that the elevator partially occupies and the gaps to the trailing edges of the pocket?

I can't wait for you or someone else to try this.  Sparrow strainers are a P.I.A.
No lift, or net lift at the elevator pivot point would be great.

I'm willing to partially fund the investigation.

--
Q2 N86KL

Anthony P

Jay Scheevel

There I virtually no aerodynamic impact of the transition from the fixed elevator slot core to the elevator, so if that is what you mean, then no there is no effect.

Cheers,

Jay

From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of Anthony P
Sent: Wednesday, February 23, 2022 12:45 PM
To: main@Q-List.groups.io
Subject: Re: [Q-List] Sparrow strainer stall conundrum

"Elevator Slot" = "pocket"

(pic taken from http://samhoskins.blogspot.com/search?updated-max=2014-06-18T04:55:00-07:00&max-results=20&start=27&by-date=false)

--
Q2 N86KL

Anthony P

Ok, thank you.

Very hard to believe that an airfoil in free stream would behave similarly to the same airfoil tucked closely behind another body.
I'm obviously missing something.  I'll go back and re-read your posts on the development of your elevator profile.

--
Q2 N86KL

Jay Scheevel

I think you are misunderstanding a concept. The airfoil only changes the direction of the flow, it does not occlude the flow. It doesn’t matter how closely you “tuck in behind” another body. The relative wind (streamlines) you encounter is that of the flow behind the body. The exception to this rule is when the body in front is stalled and creating a bubble of turbulence behind. This does not happen when the stall conditions have not been exceeded.

From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of Anthony P
Sent: Wednesday, February 23, 2022 1:32 PM
To: main@Q-List.groups.io
Subject: Re: [Q-List] Sparrow strainer stall conundrum

Ok, thank you.

Very hard to believe that an airfoil in free stream would behave similarly to the same airfoil tucked closely behind another body.
I'm obviously missing something.  I'll go back and re-read your posts on the development of your elevator profile.

--
Q2 N86KL

Ben Wilson

Jay - Keep going!
This is great fun.
With yarn video and your flow analysis it's clear there is a problem.
What about an articulating tab, up only when it's needed?
Ben Wilson

Michael Dunning

Anthony, I believe what you are talking about is an elevator slot, similar to a slotted flap? Jay's proposed elevator design is plain-flap style, unlike the R1145MS which does make use of an elevator slot for improved performance (see animation about halfway down this page).
--
-MD
#2827 (still thinking about planning on visualizing how to finish building)

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