Re: Sparrow strainer stall

Jay Scheevel
 

Thanks for the standard practice guidance, David. Always appreciated.

 

Cheers,

Jay

 

From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of David J. Gall
Sent: Tuesday, March 24, 2020 4:09 PM
To: main@q-list.groups.io
Subject: Re: [Q-List] Sparrow strainer stall

 

Jay,

 

Javafoil, of course! Try to design so that the elevator’s natural float angle is correct for the best rate-of-climb airspeed. This is the desired condition in case of trim failure and/or total loss of elevator control linkage. It’s slow, but allows completion of almost any long overwater flight before fuel exhaustion, and slow enough to do a reasonable job of landing using only power to “flare.” (Or reflex if you have one. 😉)

 

Springs as a primary pitch trim system are always a bad idea. If you use springs, try to use them as “down” springs only, meaning that the spring pushes the elevator in the same direction that forward control stick pressure would push it. The spring should work against the elevator’s natural aerodynamic desire to bring the nose up, except at very slow air speeds (slower than Vy) it’s OK to have a spring helping to bias the nose up, but limit that spring so that you can’t “trim into a stall” at least not at normal or forward CG. 

 

Matthew Curcio could probably chime in here with some industry-standard advice....

 

 

David J. Gall



On Mar 24, 2020, at 2:54 PM, Jay Scheevel <jay@...> wrote:



Thanks David,

 

I will keep at it. Maybe I will add a little reflex to the trailing edge. It is possible to design the elevator so pressure loads are essentially zero when it is not deflected. I can load the GU to see what it does, because it did not require sparrow strainers. It may have required some spring assisted trim, I don’t recall.

 

I am using Javafoil. It is Martin Hepperle’s freeware.  I like it because it is simple and I am simple.

 

Cheers,

Jay

 

From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of David J. Gall
Sent: Tuesday, March 24, 2020 3:36 PM
To: main@q-list.groups.io
Subject: Re: [Q-List] Sparrow strainer stall

 

Jay,

 

Nice work. Your modified LS1 elevator would go a long way toward reducing the workload required of the sparrow strainers, but you’d still need something like sparrow strainers to push the TE down for normal ops. The Roncz airfoil’s elevator is intentionally designed with a slight “reflex” on the trailing edge just so that it won’t need sparrow strainers or trim tabs. I suppose that with a little more work you could achieve the same with your modified LS1 elevator. 

 

Keep at it!

 

(BTW, what software is that?)

 

 

David J. Gall




On Mar 24, 2020, at 8:38 AM, Jay Scheevel <jay@...> wrote:



Hi Bruce,

 

A few years ago, I tried modeling the existing LS1 and only changing the shape of the elevator to try to eliminate the strong asymmetric pressure on the trailing edge (which is the reason you need the sparrow strainer). The reasoning was, that maybe someday, I would build a new set of elevators with the revised shape and leave the sparrow strainer off because it would not be needed. Here is a comparison of the pressure distribution on the the original LS1 for 0,3,and 6 degrees AOA (first graph) and for the same airfoil with the revised elevator (second graph), which would fit in the same slot. Note the difference in pressure on the top/bottom near the trailing edge. The modified version provides slightly lower lift than the original.

<image002.png>

<image001.png>

<image005.png>

<image006.png>

 

 

 

From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of Bruce Crain
Sent: Monday, March 23, 2020 9:04 PM
To: main@Q-List.groups.io
Subject: Re: [Q-List] Sparrow strainer stall

 

I see no Sparrow Strainer!  We've been "punked"!  Shoulda, Coulda Woulda!

B

Please note: message attached

From: "Jay Scheevel" <jay@...>
To: <main@Q-List.groups.io>
Subject: Re: [Q-List] Sparrow strainer stall
Date: Mon, 23 Mar 2020 18:13:28 -0600

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