Re: Sparrow strainer stall conundrum

David J. Gall

Hi Jay,


I’m glad you asked; I was concerned about the aft shape of your airfoil approaching the trailing edge. It appears that the last ~15% of your shape is convex. That’s a big no-no aft of a hinge line. What you want in this area is a straight-flat or, better, slightly concave shape on both top and bottom. John Roncz made his Long-EZ elevator straight-flat on the lower surface (partly for ease of manufacturing – smart guy!) and made the upper surface straight-flat almost all the way to the trailing edge followed by just a slight concave “reflex” at the very end to establish the needed aerodynamics for the appropriate elevator floating angle.

Also, don’t put a radius on the extreme trailing edge, either. Hold the sanding block vertical and establish two sharp ~88° angles to make a “squared off” trailing edge that will shed the top and bottom boundary layers cleanly at the sharp corners.


Pay close attention to the handwritten notes in the image below.



David J. Gall






From: <> On Behalf Of Jay Scheevel
Sent: Wednesday, March 2, 2022 9:52 AM
Subject: Re: [Q-List] Sparrow strainer stall conundrum


Hi David,


Glad to hear you have your ears on the Q-list again. My redesigned LS1 elevator behaves nicely in the simple modeling software that I use (meaning it will remain in neutral trail at a minimum cruise speed and still produce necessary lift for a control free emergency).


Had a question for you: Since  I have designed it to have essentially no delta-pressure top and bottom, will this make it more prone to flutter?  Should I shoot for positive balanced pressure top and bottom in order to stabilize it?


You can answer me offline if this is getting too far in the weeds for the rest of the group.





From: <> On Behalf Of David J. Gall
Sent: Wednesday, March 2, 2022 10:34 AM
Subject: Re: [Q-List] Sparrow strainer stall conundrum


Just playing catch up on the last two weeks of frantic Q-LIST activity….

OMG, Michael, the “Mad Rocket Scientist” (Drew) is a nice enough guy but he’s wrong fully ninety percent of the time when it comes to his discussions of aircraft stability and control. Even the animated graphic you point to is wrong.

<Rocket Scientist> != <Aeronautical Engineer>


Caveat Emptor.



David J. Gall


PS: When encountering any prototype aircraft bearing the moniker “Raptor,” run away! Run away!! LOL




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From: <> On Behalf Of Michael Dunning
Sent: Wednesday, February 23, 2022 1:57 PM
Subject: Re: [Q-List] Sparrow strainer stall conundrum


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

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