Re: Sparrow strainer stall
David J. Gall
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The LS-1 airfoil has been a poor choice since day one, precisely because of the elevator shape that causes it to float trailing-edge up requiring sparrow strainers to counteract. And QAC knew it; it was never “working well.” In fact, it resulted in Burt coming over from RAF and trying to get them to go a different direction, resulting in the “breakup” of RAF and QAC. A MUCH better airfoil was already under development at RAF, now known as the Roncz 1145MS “new” canard airfoil for the Long-EZ.
What you’re dealing with is uncharted territory since you’ve placed your sparrow strainers in a different location from “the plans,” but I would argue that even “the plans” had a less than thoroughly worked out specification for them. Nowhere has QAC ever addressed the stick-force and stick-position gradients or neutral point and CG range, or the corrections needed for airplanes that end up out of trim as a result of construction variances. These issues were thoroughly discussed in Rutan’s “Canard Pusher” newsletter but were never echoed in any QAC guidance.
All QAC ever addressed was ground handling, and they did it by various aerodynamic band-aids that contribute to bizarre and outright aberrant flight control positions in flight — and yet, there have been (to my knowledge) no resulting loss of control incidents. That’s NOT a testament to great aerodynamic design work, but to the cautious and judicious approach to flight testing and operations of the various builders, and this community of builders working together to corral the Mavericks before somebody hurts themselves.
You’ve identified a regime in which your control forces change in an unexpected and undesirable manner. A stalled sparrow strainer is a potentially dangerous condition since the sparrow strainers are so intimately tied to the tactile and visceral kinesthetic sense we humans use to operate machinery “intuitively” when our higher brain functions are engaged in more pressing matters. In other words, in a clutch, the damn plane can unpredictably depart from expected behavior just when you really need it to be predictable. I hope you figure out how to fix this. But don’t expect that QAC ever really had it dialed in, either.
David J. Gall
On Mar 19, 2020, at 7:33 PM, Bruce Crain <jcrain2@...> wrote: