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Elevator / stab adjustment


Austintatious

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7 hours ago, EricJ said:

What "trim" piece are you talking about?   There really isn't a trim piece, just the elevator.   The methodology from the service manual for both the rudder and the elevator is to bend the edge of the elevator.   The same on the rudder.  Since aluminum work hardens every time it is bent, I think this is why some express concern here.   I wouldn't fault folks for trying to help, on the internet that takes many forms and points of view.   Most can be learned from, either if they're a bit off the mark.

 

It’s not a trim tab in the traditional sense, it’s an extension of the elevator trailing edge.

Clarence

DB829139-CB7E-49BD-B8AD-D51838474920.jpeg

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@Austintatious,

have a look at the drawing Clarence has posted...

Somewhere along the way... Mooney added an extension to the elevator...

Which may Be an opportunity for replacement, inversion, or flattening... something to consider...

The Long Body also got the extension...

PP thoughts as usual...

Best regards,

-a-

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Remove the rear fuselage inspection hatch and look for play in the Elevator  bell-crank linkage that takes the single push/pull tube to a double output.  I personally would not attempt to "bend" aluminum to find a sweet spot.  Something else is wrong.  I recently replaced a worn out bell-crank which included a new bushing.  The plane has NEVER held pitch so well since the change........  

Rick

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47 minutes ago, carusoam said:

Somewhere along the way... Mooney added an extension to the elevator...

Anthony, this started on the K. The extension increases elevator area and its fixed deflection creates an aerodynamic ANU force to balance the variable down spring which creates an AND force. This was a change from the trim bungees used on previous models that create an elevator up or down force depending on trim setting and was presumably the easiest fix to compensate for nose heaviness of the K. 

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12 minutes ago, Releew said:

Remove the rear fuselage inspection hatch and look for play in the Elevator  bell-crank linkage that takes the single push/pull tube to a double output.  I personally would not attempt to "bend" aluminum to find a sweet spot.  Something else is wrong.  I recently replaced a worn out bell-crank which included a new bushing.  The plane has NEVER held pitch so well since the change........  

Rick

The original issue had to do with concern over elevator position when trimmed for cruise, which was probably normal. 

However, your point is well taken. The Mooney control system has a lot of bearings and rod ends and if these are not kept well lubricated they can add friction (which increases breakout forces) and wear (which causes lost motion and a dead zone around the trim point). The aileron push-pull tubes pass through guide blocks which should also be kept lubricated to reduce friction. 

Lubricate the rod ends with Tri-Flow which dries to form a dry teflon coating that does not attract dirt; oil attracts and retains dirt which will cause excessive wear. 
 

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1 hour ago, PT20J said:

Anthony, this started on the K. The extension increases elevator area and its fixed deflection creates an aerodynamic ANU force to balance the variable down spring which creates an AND force. This was a change from the trim bungees used on previous models that create an elevator up or down force depending on trim setting and was presumably the easiest fix to compensate for nose heaviness of the K. 

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Have to admit I don't think I've ever noticed that.  I was trying to figure out what this mentioned tab was and thinking the idea was to bend the trailing edge like for rudder "trim".    Next time I'm around a K or up I need to take a look at one of these.

Edited by EricJ
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FWIW, I flew the aircraft yesterday... With a CG at the Foremost limit I don't quite need full up trim to be trimmed for hands off fully configured for landing and 70 KNIAS.  That seems to be a reasonable place for it to be. I want to measure it, but It is just not straight enough to be able to get a good measurement.  I would have to take 5 measurement off it and then try to average them somehow... Does not seem worth it.  Perhaps next time I am down I will order new pieces that are not so wavy and have them installed and be done with it.

Edited by Austintatious
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As has been mentioned, all y'all are way over analyzing this.

Trim drag is affect by several parameters … none of which the pilot in flight or the mechanic on the ground can control on a Mooney.  In other words, you already have the least drag that can be accomplished.  Al did a great job.  Here's a few points to consider.

  • At the same speed, trim drag will be higher at higher gross weight because the wing needs to be flown at a greater angle of attack.  Trim drag will decrease as the airplane gets lighter (lower angle of attack).  The pilot can't change that.
  • Trim drag will be lower the further aft (and lighter) within the weight and balance envelope as less tail power is required.  Although loading the same weight further aft will lower trim drag (within the envelope), the pilot can't change that once airborne.  Yes, if a passenger moves from the front seat to the back, the trim drag will go down.

Now let's look at the amazing Mooney tail.

  • Trim drag is the lowest possible because the entire tail pivots to change the angle of incidence of the horizontal stabilizer.  It is also the lowest possible because there is no gap between the stabilizer and the fuselage (worst place to have a gap and why other airplanes that have a moveable stabilizer have a wiper to reduce airflow through that gap).  Great job, Al.  The pilot can't change that.
  • Trimming (via the empennage pivoting) sets an airspeed.  Adding or subtracting thrust (to a point) will only change the rate of climb/descent and not the airspeed (or stabilizer position or elevator position).
  • The elevator will float to where the hinge moments about the elevator hinge line are zero.  This includes: where the stabilizer is set (trim position), the shape of the elevator (has it been hangar-rashed, etc.), the weights and balances of the elevator pushrods, and whether your model has a down-spring (for low speed stability) and how strong it is (and what position the trim is at as stabilizer position changes the down-spring force).
  • So, bending the TE of the elevator (whether a separate tab or not) may slightly change the float angle.  It will only be perfectly aligned at one airspeed, weight and CG.

Bottom Line: Make sure the TE is in spec.  Leave it alone :)

PS.  You should always have enough trim to fly hands off at 1.3Vs.  Maximum gross weight at forward CG will be the worst case. 

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