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Mechanical Trim Indicator

U

USCANAM

Well Known Member
The biggest problem I've had with the 9A is setting elevator trim before take-off, which I guess is no big problem, just annoying.
When landing, and on roll out, I give the trim handle a few small twists, and hope 2 things...1;, I hope I'm close on the next take-off, and 2; I remember to look at the trim tab and see if it's close to the right position before I get in the plane
It's no big deal to make the correction after rotation, but I hate the guessing.
I read a while ago about making colored grooves on the inner shaft of the trim rod so you can see where you are, but I've found that the trim is so sensitive, that is not good enough. I've found that there is less than 1 1/2 turns of motion of the knob to cover the whole flight envelope.
Has anyone come up with a form of a mechanical indicator that is neat and accurate.
The closest thing I can think of is some sort of a spring loaded arm that rests up against the trim knob, which moves in and out as you're making adjustments.

Thanks
Jack
RV9A
52 hours
Just painted !!
 
Eyeball it!

I simply look over my left shoulder at the tab before closing the canopy. For rough setting after landing, I screw it in to "2 finger widths" between the knob and the mounting nut.
On my -6, best take off position is with the tab about 1/4" above the elevator. YMMV.
 
USCANAM said:
The biggest problem I've had with the 9A is setting elevator trim before take-off, which I guess is no big problem, just annoying.
When landing, and on roll out, I give the trim handle a few small twists, and hope 2 things...1;, I hope I'm close on the next take-off, and 2; I remember to look at the trim tab and see if it's close to the right position before I get in the plane
It's no big deal to make the correction after rotation, but I hate the guessing.
I read a while ago about making colored grooves on the inner shaft of the trim rod so you can see where you are, but I've found that the trim is so sensitive, that is not good enough. I've found that there is less than 1 1/2 turns of motion of the knob to cover the whole flight envelope.
Has anyone come up with a form of a mechanical indicator that is neat and accurate.
The closest thing I can think of is some sort of a spring loaded arm that rests up against the trim knob, which moves in and out as you're making adjustments.

Thanks
Jack
RV9A
52 hours
Just painted !!
Click to expand...

Jack,

After you get a few more hours on the plane, this will become a non-issue. You will instinctively set the trim as part of your pre-takeoff routine because you will have learned how much you need to twist the knob to be set for take-off.

And....if you forget, you can easily fly the plane a little out of trim 'til you set it back to the way you would have if you hadn't forgotten. :)

No need to complicate matters with an indicator.
 
Just a thought from my model airplane days.
On the trim tab, I believe there are two holes that the cable can be connected to. The one closest to the trim tab will provide a higher throw than the hole further away from the trim tab.
On my electric trim installation, I, I used then inner hole and cut away the extra.
 
Sam
You might have the easiest method.
Don't touch the trim upon landing, then by trial and error, adjust the trim before take-off.
Of course, the best thing to do is look at the tab before getting in.

As mentioned, it's no big deal to adjust on takeoff, but with 180hp, sea level airport and 3 blade MT prop, it gets your attention fast.

As a little side story
My wife who had done a lot of flying with me when we had the Mooney, stated after her first flight in the 9A..."you sure don't use a lot of runway on take-off!!"

Jack
 
I have a small 2x1" mirror mounted on the canopy bow on the left side with Velcro. Pre take off, I pull back on the stick, then adjust the trim to neutral by looking in the mirror.

It also doubles as a control check indicator for elevator and rudder, and is useful in formation.

Vern
 
USCANAM said:
Sam
You might have the easiest method.
Don't touch the trim upon landing, then by trial and error, adjust the trim before take-off.
Of course, the best thing to do is look at the tab before getting in.
Jack
Click to expand...

Actually, it's simpler than that. Giving the knob a couple of twists as I lean the mixture for idle while taxiing off the runway is standard procedure. The position of the knob is looked at during run-up, but it is usually in the correct position. ;)

The security of the tab and its cable are often a part of preflight, but can't recall ever checking its position.

This whole deal may be less of an issue in my taildragger than in your -9A. I will know immediately as the tail is raised during early take-off run whether or not the plane is in trim. In your case, trim might not be very noticeable until rotation.

Do whatever works best for you. :)
 
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I have a white dot on the knob for set take off trim. But I have a 0320 fp, and the landing trim is close to the take off trim. But try this... Find the take off trim that you like and measure the distance from the trim knob back, to the mount base. Cut a spacer (gauge) out of some scrap alum. and use it during your take off check list.

I was thinking of mounting it on a piece of hinge (3 tabs) and mount it under the trim knob. Then all you have to do is flip it up with your finger and twist the knob in till it stops at the spacer.........
 
Trim indicator

My 6a has a small score around the diameter of the shaft of the vernier I quickly set by eye avery time. Fool proof for me....
 
I echo the sentiment of looking over your shoulder to see the trim tab position as part of preflight. (Right before/after you check fuel tank selection.) This doesn't work when luggage compartment is stacked to the top (OSH!) though.

Maybe you could rig up a trim position sensor using the Ray Allen gadgets?

Matthew

USCANAM said:
The biggest problem I've had with the 9A is setting elevator trim before take-off, which I guess is no big problem, just annoying.
When landing, and on roll out, I give the trim handle a few small twists, and hope 2 things...1;, I hope I'm close on the next take-off, and 2; I remember to look at the trim tab and see if it's close to the right position before I get in the plane
It's no big deal to make the correction after rotation, but I hate the guessing.
I read a while ago about making colored grooves on the inner shaft of the trim rod so you can see where you are, but I've found that the trim is so sensitive, that is not good enough. I've found that there is less than 1 1/2 turns of motion of the knob to cover the whole flight envelope.
Has anyone come up with a form of a mechanical indicator that is neat and accurate.
The closest thing I can think of is some sort of a spring loaded arm that rests up against the trim knob, which moves in and out as you're making adjustments.

Thanks
Jack
RV9A
52 hours
Just painted !!
Click to expand...
 
Another approach

All good suggestions above.

I installed a marked cap which I bought from Bill Repucci (any cap or mark will do) so that I know where the knob is on this 360. The cap covers the hole where I removed the release button - a good safety measure. Between full turns there is a significant difference in the gap between the knob and the other end of the exposed shaft. For me, that gap should just fit the width of my thumb. So if the gap is OK and the mark is straight up then the tab is in the neutral position. And yes, I often look at it anyhow as a quick part of the preflight or anytime before closing the canopy. I don't think I could see a mark on the shaft even if it were there, given where it is below and forward of the panel lower lip.

For landing, just use the trim to accomplish the feel you want. I like to make the stick neutral at about 75 or 80 kias so that if I let go of it nothing bad will happen. But that's just my personal preference - you can easily land the airplane with cruise/nose down trim.
 
Vern
I like your idea of the mirror, but I have a tip-up, and no bow to attach it.
Gasman
I think the next time I fly, I'm going to bring a bottle of white-out, and on climb-out when I've trimmed where I like it, will put a dab of white marker on top of the knob. Piece of tape will also work initially.
That mark will also allow me to measure and create a feeler tab that I'll attach somewhere around the trim handle with some nice string or safety wire.
Maybe I'll find that the mark alone will suffice.
As stated before, it's no big deal, or maybe it's a "just being in control" thing.
Thanks for the ideas guys
Jack
 
Jack

Try placing your pointer finger under the knob. There should be some gap there. Get a feel for that gap and you'll hit take off trim every time. This method works great for go arounds and such because you never have to look at the trim knob to set it.
 
Back In Control!!

Using some ideas from previous post this is what we came up with. It works perfectly and is simple.


What you see is a black paint mark on the inner shaft. This we did with one of those small bottles of auto touch up paint that has it's own brush.
We found the proper position for the trim on a test flight take-off, and used tape to index it.
When on the ground, we positioned the trim in the proper position, then put that black mark on the shaft, and right up against the lock nut. What you see there is the trim screwed out one turn.
Then a piece of yellow tape to fine tune the position.
If the trim shaft was in too far, the black mark would disappear, if out too far, you would see the space as in the photo.
So, on take-off, the black mark is up against the lock nut, and the yellow pointer is straight up.
Simple!!!
Jack
 
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