Re: Need a Sparrow Strainer alternative


Allan Farr
 

I wonder why they're not needed on the GU canard. 


--- In Q-LIST@..., <q-list@...> wrote:

You're right Charlie.  When my TriQ goes faster the sparrow strainers pull down more and I have to push the stick forward to hold it level.  With the set up that Pat show us you could trim for all speeds perhaps.  That would be a plus for Sammy when he is at 208 mph I would think.
Bruce

---------- Original Message ----------
From: Charlie Johnson <oneskydog@...>
To: "Q-LIST@..." <Q-LIST@...>
Subject: Re: [Q-LIST] Need a Sparrow Strainer alternative
Date: Thu, 19 Sep 2013 17:40:29 -0600

 

Jim,

Sparrow strainers are also proportional to the speed so the right correction is applied at all air speeds automatically.

Regards,

Charlie Johnson



On Sep 19, 2013, at 10:55 AM, Jim Ham <jimham@...> wrote:

> 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 :-).
>
> Jim
>
> 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.
>>
>> http://issuu.com/contact.magazine/docs/dragonfly_newsletter_97
>>
>> And if I uploaded it properly, it should download to a printable PDF.
>>
>> Pat
>>
>>
>> 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
>> flutter.
>> 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:
>>
>> __
>>
>> Guys,
>> 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
>> __
>> Sammy,
>> 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
>> <Q-LIST@...
>> <mailto:Q-LIST@...>>__Subject: [Q-LIST] Need a
>> Sparrow Strainer alternative__Date: Wed, 18 Sep 2013 16:14:44
>> -0500____
>> 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.
>> Sam
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