Re: Sparrow strainer stall


Jay Scheevel
 

Comparison of shape of Roncz, and LS-1 airfoils. (from Q-talk 97)

 

From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of Bruce Crain
Sent: Friday, March 20, 2020 4:30 PM
To: main@Q-List.groups.io
Subject: Re: [Q-List] Sparrow strainer stall

 

Copy that David.

I wonder if the Roncz canard has the elevator top air moving in board at cruise or was it designed out?

I think Mark Shuck was working on a Roncz canard to the Quickie.  I don't know what he was planning to do with the calcs.  Would be interesting to see what he came up with and if it would work on the Quickie.  Need for speed!!

Bruce

 


---------- Original Message ----------
From: "David J. Gall" <David@...>
To: main@q-list.groups.io
Subject: Re: [Q-List] Sparrow strainer stall
Date: Fri, 20 Mar 2020 09:06:05 -0700

Bruce,

 

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:

Say Jay I

think the tufts on the elevator were moving the same direction in normal cruise (from outboard to inboard) regardless of the sparrow strainer stalling or not stalling.  It could be exacerbating where the air flow goes due to the strainers moving up and being blanked by the elevator perhaps.  I except when I pull the stick and lower the strainer back to cruise pitch or lower it still takes stalling the canard to alleviate the sparrow strainer stall.  Maybe my outboard strainer is the difference between my Q and others but then I believe DFly's have outboard maybe.  Charlie can you back me up on that?  Or maybe no one else has actually pulled up and unloaded their Quickie to the extent that I have.

 

It has bothered me for a few years that the airflow on the elevator move inboard like it does.  To an aerodynamisist it means a big loss in speed doesn't it?  I am sure when the LS1 airfoil came out they had it working well.  Maybe it's just me.

Bruce Crain  

Please note: message attached

From: "Jay Scheevel" <jay@...>
To: <main@Q-List.groups.io>
Subject: Re: [Q-List] Sparrow strainer stall
Date: Thu, 19 Mar 2020 09:39:12 -0600

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