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Custom Aileron Trim Tab

GAHco

GAHco

Well Known Member
Even though I did this a while ago I just took pictures of it last week.

I just could not put piece of hinge :confused: for an entire trim tab assembly, on my aileron and have it truly look like a total afterthought.

If you want to see what I thought would look better, go to

www.gen-aircraft-hardware.com/toms/plane_proj.asp

It gives more text and details. or just look below and let the pictures talk.

Wait a while for all the pictures to load, and then go toward the last few entries.


TabSide1.jpg


tabarm2.jpg



Have fun!
 
Last edited:
Nice Job.

The aileron trim tab is nice and very creative. Since I have never needed more than the spring loaded aileron trim that Van's sells I was wondering why you put a tab on? Judging by the pictures your building skills are good so I am going to bet you won't need it much after you start flying. It looks like you are building a clean and straight airplane. Keep up the good work.
 
A question for those aero engineers out there.

I have the Vans under the seat spring trim system. I have been thinking about doing what GAHco has done to replace it.

Why. I was thinking that the current system seems to be correct only at one speed. If you change speed you need to change the trim again.

Now would the trim on the aileron be consistently set for any given speed?
Also would there be any difference in drag between the two system once they were trimmed?

Kent
 
kentb said:
.....I was thinking that the current system seems to be correct only at one speed. If you change speed you need to change the trim again..... Kent
Click to expand...

:confused: Isn't that exactly what adjustable trim is for???? So you can change the trim as speed/conditions warrant? Otherwise, you'd only need a fixed tab. Or am I missing something? (Entirely possible, BTW.) FWIW, I'd like to have cockpit-adjustable trim on all 3 axes! But probably not worth the weight/$$/build time, etc.
 
Yes, no, maybe....

PCHunt said:
:confused: Isn't that exactly what adjustable trim is for???? So you can change the trim as speed/conditions warrant? Otherwise, you'd only need a fixed tab. Or am I missing something? (Entirely possible, BTW.) FWIW, I'd like to have cockpit-adjustable trim on all 3 axes! But probably not worth the weight/$$/build time, etc.
Click to expand...

The spring on the stick will have differing effect at different speeds. If you are trimmed for climb and then level off and build speed the spring will need to be adjusted to hold the same aileron position.
My thinking was that the aileron trim tab would not have this problem in that it just adjusted the angle to the airstream, no matter what the speed was. I was hoping that some of the aero engineers would confirm my thoughts.

Kent
 
It is airspeed sensitive

kentb said:
The spring on the stick will have differing effect at different speeds. If you are trimmed for climb and then level off and build speed the spring will need to be adjusted to hold the same aileron position.
My thinking was that the aileron trim tab would not have this problem in that it just adjusted the angle to the airstream, no matter what the speed was. I was hoping that some of the aero engineers would confirm my thoughts.

Kent
Click to expand...

Sorry, but the tab is airspeed sensitive just like the spring. Do you use the same control deflection at all airspeeds? The trim will be more effective as the speed goes up. On the same subject, I haven't moved the aileron trim on my '8' for some time. No need, if the fuel is somewhat balanced (10-15 gallons) it goes straight.

John Clark
RV8 N18U "Sunshine"
KSBA
 
Trim tab

Hinge moments are directly proportional to dynamic pressure (q) and the spring constant is just that--constant. As you change speeds, the aileron deflection due to the spring system will decrease, but the trim tab should maintain a nearly constant deflection. With that said, the rolling moment you are trying to overcome will be both aerodynamic and due to weights. The weight based rolling moment (eg. I'm in the left seat and the right seat is empty, or I'm burning the left tank, etc.) does not change with q, but the aerodynamic rolling moment does. So.... in my opinion, both trim systems will require adjustment during flight.

-rob
 
I understand, I think...

rvermeland said:
Hinge moments are directly proportional to dynamic pressure (q) and the spring constant is just that--constant. As you change speeds, the aileron deflection due to the spring system will decrease, but the trim tab should maintain a nearly constant deflection. With that said, the rolling moment you are trying to overcome will be both aerodynamic and due to weights. The weight based rolling moment (eg. I'm in the left seat and the right seat is empty, or I'm burning the left tank, etc.) does not change with q, but the aerodynamic rolling moment does. So.... in my opinion, both trim systems will require adjustment during flight.

-rob
Click to expand...

As the weight changes (fuel burn) the left right trim will need to be adjusted (either type). As the speed changes the spring trim will need to be adjusted, but the trim tab will be selfadjusting (so to speak).

Kent
 
Trim tab

The elevator trim needs to be adjusted with speed because the angle of attack decreases with speed to maintain level flight. Pitching moment is a function of angle of attack. Rolling moment is a function of sideslip angle due to wing dihedral and does not vary with angle of attack.

As I mentioned in a previous post, the aileron trim will need to be adjusted for any rolling moments due to CG movement in the spanwise direction. Trimmed out rolling moments due to an asymmetric aircraft will not require a trim tab change with change in speed, but would require a spring tension change.

My $0.02 as an aerodynamicist.

-rob
 
Aileron Trim

Where did you run the electrical wiring through the wing to the aileron servo?

thanks,
 
Painting Today

n38139 said:
Where did you run the electrical wiring through the wing to the aileron servo?

thanks,
Click to expand...

I am painting that wing almost as I write (I am on break between mist coats)

I will look that up as soon as I can and let you know.
 
control load

I have an aileron trim tab that extends beyond the trailing edge. This no doubt changes the hinge moment and aileron aero cg. Regardless, it definitely makes the ailerons feel heavier at higher speed, and compared to my first RV6that had no aileron trim. I would think that GAHco's design is better.
 
WV4i Good point. Any tab that adds area AFT of the existing aileron TE will increase hinge moment, thus making the ailerons feel heavier. The tab shown in this thread will not change hinge moment as a function of planform shape.

And... the aerodynamic tab will not require re-trimming with airspeed changes, contrary to earlier assertions. IMHO its the best way to go.
 
Aileron Trim Handle Motion

I am a non-builder RV6A owner. When I adjust my aileron trim (handle between seats), soon afterwards, the handle has gone back to where it was. What is used to keep the trim handle from moving? Is there a friction knob somewhere?
 
n38139 said:
Where did you run the electrical wiring through the wing to the aileron servo?

thanks,
Click to expand...

On my RV-4, below (close to center of spar) and slightly inboard of the hole for the aileron push rod hole. Center of the 3/8" hole about 3/16" inboard of the 3/4" angle that's below the push rod hole.

When you move the aileron up and down, the cable has to clear the steel bracket and also the flap brace. I put a piece of "edge protection" U-channel on the flap brace.

Finn
 
GAHco said:
Even though I did this a while ago I just took pictures of it last week.

I just could not put piece of hinge :confused: for an entire trim tab assembly, on my aileron and have it truly look like a total afterthought.

If you want to see what I thought would look better, go to

www.gen-aircraft-hardware.com/toms/plane_proj.asp

It gives more text and details. or just look below and let the pictures talk.

Wait a while for all the pictures to load, and then go toward the last few entries.


TabSide1.jpg


tabarm2.jpg



Have fun!
Click to expand...

On your build site, what and where did you get the Underwood ribs? What's the benefits of them over the original?
 
I made a similar one for my -4

I also made a custom tab on my -4, installed at the outboard end of the L/H aileron. I ran my wires out the wing with the NAV light bundle and brought them through the wingtip straight into the end of the aileron.
 

Attachments

  • LH aileron servo.jpg
    LH aileron servo.jpg
    105.1 KB · Views: 154
  • Trim tab LH.jpg
    Trim tab LH.jpg
    131.5 KB · Views: 169
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