Re: Preliminary analysis of aerodynamics of sparrow strainers (or not)
David J. Gall
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Nice analysis. I’m heartened to see that someone else has independently concluded what I’ve been saying for years: the Roncz R1145MS airfoil is a better choice than the LS-1. The Roncz airfoil also solves other issues such as eliminating sparrow strainers. I think Rutan broke off his involvement with QAC over this very issue.
I note that you’ve asserted that the elevator floating angle of the Roncz airfoil would require mounting the canard more nose down by one degree. I believe this is incorrect. The elevator floating angle you found is not intended to be achieved at “high speed cruise” as compared to your first illustration on the LS-1; rather, the elevator floating angle is intended to give a *low* speed cruise so that in the unlikely event of a total mechanical disconnection of the elevator from both the trim system and the control stick the airplane could still be flown to a destination or diversion airport (long-range cruise) yet that trimmed speed would also be slow enough that a semblance of a “high speed landing” without elevator control could be survived on arrival, using only throttle for climb/descent. See Rutan’s CP59; also see the fate of George Mead’s Piper “Pugmobile.”
So I would recommend mounting the Roncz canard at the same angle of incidence as the LS-1, not a reduced angle of incidence. In flight, the “down” trim spring should be able to hold the needed nose-down elevator bias to achieve hands-off trim at high speed cruise, and the “up” trim spring should be able to hold the needed nose-up elevator bias for slow flight (but not stall).
Besides having significantly lower drag than both the GU and LS-1 airfoils, the Roncz drag is lower still compared to the LS-1 airfoil because of not needing sparrow strainers and also because of not having that crazy negative lift zone in the spanwise lift distribution that is caused by the LS-1’s sparrow strainers.
Another benefit of the Roncz airfoil is that it is almost as thick as the GU airfoil (20.5% vs. 21% for the GU). Structurally that makes it almost a direct replacement for the GU canard, not needing the tubular carbon spar but able to be built using glass and a slightly modified GU canard layup schedule (think: Waddelow canard). For a Q1 Quickie or for a Q2 (max. gross weight 1000 lbs.) it could be a direct replacement; for a Q200 the added engine weight (MGW 1100 lbs.) would require additional structure. Of course, with some of these planes currently operating at 1300 lbs., all bets are on a structural redesign using carbon.
Finally, Mike’s point about the lower angle of incidence on the canard is actually countered by the elevator deflection stop limits; one would run out of elevator deflection before achieving stall if the canard incidence were set too nose-down. However, it would be prudent to check the maximum CL and the AOA at which that occurs when selecting the canard installation incidence angle. It might be necessary to shorten the canard chord slightly if the new airfoil is a significantly better performer than the one it replaces, in order to prevent a main wing stall. (Trimming the chord is preferable to trimming the span because the resulting surface has a higher aspect ratio that gives it a steeper slope of the lift curve, so it achieves CLmax at a lower AOA than a lower aspect ratio surface would.)
Keep up the good work,
David J. Gall
From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of Mike Dwyer
Sent: Sunday, February 27, 2022 4:15 PM
Subject: Re: [Q-List] Preliminary analysis of aerodynamics of sparrow strainers (or not)
With a lower angle of attack on the canard, wouldn't that reduce the margin of having the canard stall prior to the main wing?
On Sun, Feb 27, 2022 at 6:37 PM Jay Scheevel <jay@...> wrote: