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Rigging

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GrummanDude

Joined: 15 Jan 2006
Posts: 926
Location: Auburn, CA

Posted: Mon Mar 12, 2007 10:46 am Post subject: Rigging

I'll post this on TeamGrumman-list for you.  TeamGrumman-list is not 

the same as TeamGrumman(at)aol.com



Many years ago, 23 years I think it was, I removed all of the trim tabs 

 from my Cheetah.  You know, the trim tab on one aileron, the redundent 

one on the other aileron, and the rudder trim tab.  Then, I spent 2 

weeks (I had a 40 hr/wk job at the time) playing with the rigging to 

see if I could get the plane to fly straight and level without any trim 

tabs.  That was when I discovered it's the flaps that control roll, not 

the ailerons.  I also tried reflexing the ailerons up until the plane 

got mushy, and then down until they acted like partially deployed 

flaps.  Then I tried doing the same with the flaps.  I did find that 

under certain loadings and winds (lots of wind on the desert) reflexing 

the ailerons about 1 to 2 degrees (any more than that and there is no 

gain.  At 5 degrees, the plane is really mushy.) would let me get about 

1 to 2 knots more airspeed.  I fooled with this for about 5 years.  As 

for the flaps, I tried everything from flaps reflexed 7 to 8 degrees 

(that is about the limit of adjustment) to about 5 degrees down.  What 

I found was, really, for all practical purposes, the factory settings 

are about as close as you can get for a mixutre of loading and wind 

conditions.  Without a very accurate map of the lift/drag curve for the 

wing and fuselage and horizontal (and an inclinometer to watch in the 

plane), it's impossible to gauge the best settings for the ailerons and 

flaps for each condition.  At most, there is 1 or 2 knots hidden in the 

adjustments.  What I will say is, one of the tirm tabs on the aileron 

is redundent.  And, the rudder can be trimmed with tension on the cable 

to achieve the desired rudder trim.



As for the holes, I'd put the backing plate back (that backs up the 

tab) and flush rivet it in place.



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_________________
Gary
AuCountry Aviation
Home of Team Grumman

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Posted: Mon Mar 12, 2007 1:34 pm Post subject: Rigging

I asked the question "why two aileron trim tabs" of  the AYA back in 94. Dave Fletcher replied and you can see the full text if you  are a AYA member on their web site. Download the General Section of the  Maintenance Compendium page 15.

  

 Part of Dave's reply was, "The preferred setting for the trim tabs is to  reduce lift on one aileron, rather than increase it on the other. How you trim  depends on which wing is heavy." and "Remember: bend the tab in the direction  you want that wing to go, and remember that bending one tab  down, which decreases that wing's lift and drag, is  preferable to bending the other tab up, which increases lift  and drag for that wing." So may be that last quote is the reason for two, if I  read that correctly, ideally one should always be neutral and the other  down depending on which wing is heavy.

  

 Ian

  

  

  

  

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GrummanDude

Joined: 15 Jan 2006
Posts: 926
Location: Auburn, CA

Posted: Mon Mar 12, 2007 9:26 pm Post subject: Rigging

I see a lot of plane that require one tab significantly up with the 

other significantly down.  This tells me that instead of making the 

plane fly right with proper rigging, people are compensating with trim 

tabs.



ALSO, how do you know when tab is neutral?  I think that was in the 

original post.



If a tab is a tweaked up, it affects that wing.  To correct that wing, 

the other is tweaked up also.



Removing one tab makes the correction to one aileron.



Now, it there less drag with one aileron up slightly to correct a light 

wing? or is there less drag with two tabs making the ailerons fight 

each other?



For me, I have one trim tab that is nearly neutral.  And, now I need to 

see if it's up or down . . . . . . . . . . . . .

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Gary
AuCountry Aviation
Home of Team Grumman

pitts_pilot(at)bellsouth.
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Posted: Fri Mar 23, 2007 7:18 pm Post subject: Rigging

I didn't read Davids reply, but I believe the reason for two trim tabs stems from the fact that the only difference between the left and right aileron is the location of the drain holes.  Both ailerons are made the same up to the point of the drain hole 'installation'.  I found a lot of interesting construction 'constraints' in the Grummans that reduced the manufacturing parts count.  A lot of parts are interchangeable and some with minor mods.  The rudder and elevator are interchangeable on the -1s and that part is modified with the trim tab for the other elevator.  The vertical fin and the horizontal stabs are interchangeable.  The wing is designed to use two sheets of 4'X8' aluminum for skins so no custom aluminum sheet is needed.  There may be more 'similarities' that I've missed.

 Linn

 

 Ian Matterface wrote:

 [quote]            I asked the question "why two aileron trim tabs" of the AYA back in 94. Dave Fletcher replied and you can see the full text if you are a AYA member on their web site. Download the General Section of the Maintenance Compendium page 15.

    

   Part of Dave's reply was, "The preferred setting for the trim tabs is to reduce lift on one aileron, rather than increase it on the other. How you trim depends on which wing is heavy." and "Remember: bend the tab in the direction you want that wing to go, and remember that bending one tab down, which decreases that wing's lift and drag, is preferable to bending the other tab up, which increases lift and drag for that wing." So may be that last quote is the reason for two, if I read that correctly, ideally one should always be neutral and the other down depending on which wing is heavy.

    

   Ian

    

 [b]

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GrummanDude

Joined: 15 Jan 2006
Posts: 926
Location: Auburn, CA

Posted: Mon Mar 26, 2007 11:48 pm Post subject: Rigging

I looked at my plane and my tab makes my aileron very slighly down.  If 

I thought there was a knot in it, I'd change it.  Right now, everything 

is pretty close to flat when straight and level.



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_________________
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AuCountry Aviation
Home of Team Grumman

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