Re: Need a Sparrow Strainer alternative

Jim Ham <jimham@...>

I just thought of another plus for the sparrow strainer. It is placed below and behind the trailing edge of the elevator. This does two things: It puts it in relatively undisturbed air and it increased the lever arm on the elevator. Greater lever arm means lower down force needed and lower induced drag for the same torque on the elevator.

But wait - doesn't an anti-servo tab and a sparrow strainer do the same thing? Namely, produce an aerodynamic down force on the elevator. Remember that the sparrow strainers are constructed with an airfoil. Airfoils have very little parasitic drag compaired to other shapes. Why would you think that a servo tab as less parasitic drag than a sparrow strainer?

Spoken by a novice - let the experts come in on this :-).

Patrick Panzera wrote:

BTW, when I was the Dragonfly newsletter editor, Terry O'Neill submitted
an excellent article on how he did away with his sparrow strainers by
installing anti-servo tabs that are also used as an aerodynamic pitch
trim system. He also talks about balancing the elevators to avoid flutter.

I just uploaded the entire issue.

And if I uploaded it properly, it should download to a printable PDF.


On Thu, Sep 19, 2013 at 9:10 AM, Patrick Panzera
<editor@... <mailto:editor@...>> wrote:

Adding weight aft of the center of rotation is a sure recipe for
Even at low speeds, a little bump could start it.

Look how stable a car's antenna is under normal conditions.
Now imaging a weight at the tip... or note what happens to it when
weight is added from ice.

On Thu, Sep 19, 2013 at 8:15 AM, Jason Nemake <fg13fg@...
<mailto:fg13fg@...>> wrote:


Are the elevator control surfaces statically balanced on the LS
airfoil, like they are on the GU airfoil? If so, then I would
guess that if you unbalanced the control surface and started
increasing the cg of the control surface aft, to try and cancel
the lifting effect caused by the LS cuspt then heavy springs or
sparrow strainers might not be needed. One could possibly go as
far as weighting the trailing edge. The result would be a
drooped elevator on the ground until reaching flying speeds, and
a positive effect on the stick at low speeds. Maybe even a
combination of springs and aft weight. There of coarse would be
G effects to this idea. Some things to ponder..
Jason Nemake

*From:* "jcrain2@... <mailto:jcrain2@...>"
<jcrain2@... <mailto:jcrain2@...>>
*To:* Q-LIST@... <mailto:Q-LIST@...>
*Sent:* Wednesday, September 18, 2013 8:55 PM
*Subject:* Re: [Q-LIST] Need a Sparrow Strainer alternative
Didn't Tom Moore and Bob Malecek have an adjustable flat piece
of aluminum or stainless in place of the upside down airfoil? I
think it had a slight up kicker at the back though. Call them
to see what their ideas were. It might be a bit less drag
perhaps X 2.
Bruce ____---------- Original Message ----------__From: Sam
Hoskins <sam.hoskins@...
<mailto:sam.hoskins@...>>__To: Quickie List
<mailto:Q-LIST@...>>__Subject: [Q-LIST] Need a
Sparrow Strainer alternative__Date: Wed, 18 Sep 2013 16:14:44
The Sparrow Strainers are draggy and slow our planes down.
There must be an alternative. Every time a speed specialist
looks at the the sparrow strainers they go "WTF"?
So, let's start at the beginning. Why are there in the first place?
As I understand it, they are an aerodynamic trim designed to
counteract the high pressure on the bottom of the canard
elevator. Air wants to push the TE of the elevator up, causing
the plane to dive, so the sparrow strainers help by pushing it
back down.
Is this logic correct?
So, what would be a drag-free alternative? Well, I suppose one
could increase the spring tension already used for the control
stick. Why didn't QAC do something like that? Maybe it would
increase the stick forces. Just guessing but when they first
flew flew the new LS-1 airfoil, they probably found they needed
an extraordinary amount of nose up trim. Followed by going with
the cheapest fix - add sparrow strainers.
Another issue with using internal trim, is you are applying a
constant torque to the joint there the elevator bellcrank slips
into the elevator torque tube. Maybe it's not a big deal, bit
it's there.
This is all supposition. Is anyone privy to the real story?
So, all of you aerodynamic tinkerers, what could be a viable way
to eliminate the sparrow strainers?
Thanks for reading.
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