What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

manual elevator trim position indicator

P

[email protected]

I'm New Here
Hello,

I am finishing my 9 left elevator and at the point to decide on electric or manual trim. I originally planned to go electric but have read many post stating manual is the way to go. I have flown many aircraft with both manual and electric and do like electric in some cases. But with a small light plane like the rv9 it seems simple might be better. The vernier cable would be very simple and reliable compare to the little ray allen servo that could be problems sooner or latter.

I do plan to install a good 2 axis autopilot.

With manual how and where is the trim position indicated for take off?

Any advise is appreciated.

Thank you!
 
Every model and even different aircraft will be different. And yes, even loading can affect trim settings. You will have to determine this by trial and error. That's what phase I is all about.

On my -6, I always use 13? flap for take off. My trim tab is set to 0?.
For a no-flap take off I set the tab about 1/4" above the elevator.

YMWV! (Your Mileage Will Vary)
 
[email protected] said:
Hello,

I am finishing my 9 left elevator and at the point to decide on electric or manual trim. I originally planned to go electric but have read many post stating manual is the way to go. I have flown many aircraft with both manual and electric and do like electric in some cases. But with a small light plane like the rv9 it seems simple might be better. The vernier cable would be very simple and reliable compare to the little ray allen servo that could be problems sooner or latter.

I do plan to install a good 2 axis autopilot.

With manual how and where is the trim position indicated for take off?

Any advise is appreciated.

Thank you!
Click to expand...

A rear view mirror works well. I even use it in my HR-II which has a trim indicator..... just to be sure.
 
Adjust the vernier knob so the tab is in a neutral or trailing position. On my 7, the knob would be about 1" out. You will be able to set the appropriate take-off setting by sight during pre-flight and confirm by knob position once in the plane.
 
There are different benefits with each system (manual vs electric)

The electric is actually lighter over all.

The manual isn't dependent on electrical power.

because of nearly 180 deg bend that has to be put in the knob end of the manual cable, there is a small amount of play in the trim tab that can sometimes cause the trim point to wander when near neutral tab position (if this occurs it can be resolved by adding a small preload spring to the trim tab

The manual is infinitely variable in change rate (depending on how fast you choose to turn the knob) and it is very easy to get a minute small amount of change (as in tweaking the trim at cruise speed).
The electric can be improved greatly with an adjustable PWM speed control (a necessity in my opinion), but then you are still stuck with one speed. You can make it even better by having a dual rate system by using a switch that changes the servo to full speed using a speed sensor of a switch on the flaps, but this adds more complexity and failure opportunity in the electric system.

I like things about both systems but lean towards favoring the manual trim (which is what I have on my current airplane). After a short amount of time getting acquainted with the airplane, it becomes very easy to set the trim just by feel by checking the gap between the knob and the base. Just being close is more than adequate because the pitch forces are very low at slow speed (right after take-off), and the actual precise setting needed will always be variable (differing fuel load, etc.) so you will generally make a small adjustment early in the climb regardless of what you set it at.

BTW, a lot of RV's are flying with mis-rigged pitch trim systems. It should be set up so that with the tab at neutral most of the system travel is in the nose up direction. For side by side models, about 3/4 of the travel should be nose up and 1/4 nose down. For tandems, about 2/3's of the travel nose up and the remaining 3rd nose down.
In most situations, very little nose down trim is ever needed.
 
rvbuilder2002 said:
There are different benefits with each system (manual vs electric)

The electric is actually lighter over all.

The manual isn't dependent on electrical power.

because of nearly 180 deg bend that has to be put in the knob end of the manual cable, there is a small amount of play in the trim tab that can sometimes cause the trim point to wander when near neutral tab position (if this occurs it can be resolved by adding a small preload spring to the trim tab

The manual is infinitely variable in change rate (depending on how fast you choose to turn the knob) and it is very easy to get a minute small amount of change (as in tweaking the trim at cruise speed).
The electric can be improved greatly with an adjustable PWM speed control (a necessity in my opinion), but then you are still stuck with one speed. You can make it even better by having a dual rate system by using a switch that changes the servo to full speed using a speed sensor of a switch on the flaps, but this adds more complexity and failure opportunity in the electric system.

I like things about both systems but lean towards favoring the manual trim (which is what I have on my current airplane). After a short amount of time getting acquainted with the airplane, it becomes very easy to set the trim just by feel by checking the gap between the knob and the base. Just being close is more than adequate because the pitch forces are very low at slow speed (right after take-off), and the actual precise setting needed will always be variable (differing fuel load, etc.) so you will generally make a small adjustment early in the climb regardless of what you set it at.

BTW, a lot of RV's are flying with mis-rigged pitch trim systems. It should be set up so that with the tab at neutral most of the system travel is in the nose up direction. For side by side models, about 3/4 of the travel should be nose up and 1/4 nose down. For tandems, about 2/3's of the travel nose up and the remaining 3rd nose down.
In most situations, very little nose down trim is ever needed.
Click to expand...

Don't forget that electric trim allows you to easily add autotrim when you have an autopilot. Also, flying formation is easier with the electric trim.
 
Takeoff setting

On mine I simply set neutral on the tab then counted how many turns in.
So now I wind full down (in) on the trim, then in my case 3 1/2 turns out for takeoff. Simple and works every time.

Peter
 
Mine has a ring engraved around the circumference of the shaft which lines up with the plastic bezel on the base of the trim knob when the tab is neutral. You can feel the ring with your fingernail if the trim is too far aft.

During run up checks I wind it out until I can feel the notch, then wind it in again 'till it all lines up. Simple.

- mark
 
I have manual trim in my -8 but think a lot about changing to electric so that a back-seat passenger could trim the plane and more safely and comfortably land if I was incapacitated. Especially for a non-flyer or low-time flyer trying to land with the trim set for cruise would reduce the odds of success.
 
If you are planning on a well developed AP then electric trim is a fantastic option.
Most now have speed control for minor trim at high speed and faster trims at lower speeds. As Vern mentioned most will now have autotrim in AP.
i.e. Garmin.
I sure like having the trim on the stick. Flying the plane, flaps and trim at the same time only takes two hands. Manual trim would take three.
 
Except for the little bit--about 1/4"--of play in the tab, which Van's told me was normal, I love my manual trim. Occasionally I check it before takeoff by looking back at the elevator, but the reality is is that I just do whatever is necessary to take the load off the stick. No indicator necessary. In flight I never use more than one full turn one way or the other, again, just adjusting as I FEEL the need.

Flaps, stick, throttle, trim all with two hands not a problem. And, having just had my first flight where I lost my alternator and landed with no electrical power, it was nice not having to rely on electrons to adjust the trim.

Just another $.02.
 
rvbuilder2002 said:
...

BTW, a lot of RV's are flying with mis-rigged pitch trim systems. It should be set up so that with the tab at neutral most of the system travel is in the nose up direction. For side by side models, about 3/4 of the travel should be nose up and 1/4 nose down. For tandems, about 2/3's of the travel nose up and the remaining 3rd nose down.
In most situations, very little nose down trim is ever needed.
Click to expand...
I have the manual trim and Scott is right on the money. Mine is rigged as he described and if you trim it for an excessive nose down setting then you will quickly find yourself heading to Vne in a quick hurry.

As for a position indicator, I use my index finger. I have learned what the knob to finger relationship is for my takeoff setting. Even if I don't set it for takeoff, it is easy enough to give it a few quick turns and set it properly. The trim on the -9 is very effective and the inflight adjustments are on the order of magnitude of an 1/8 to a 1/4 turn.
 
rvbuilder2002 said:
BTW, a lot of RV's are flying with mis-rigged pitch trim systems. It should be set up so that with the tab at neutral most of the system travel is in the nose up direction. For side by side models, about 3/4 of the travel should be nose up and 1/4 nose down. For tandems, about 2/3's of the travel nose up and the remaining 3rd nose down.
In most situations, very little nose down trim is ever needed.
Click to expand...

Scott, my RV7A Construction Manual specifies the trim tab angles up and down. In fact all control surface angles are specified. If builders comply with Van's specifications they should have the required trim capacity for both nose up and nose down.

What you seem to be saying is that many builders are not complying with Vans specifications.

Anway manual trim for me too. I've flown lots of aircraft with both electric and manual trim and I find manual trim MUCH easier and more reliable. The manual trim on my RV7A is just a dream to operate.
 
Captain Avgas said:
What you seem to be saying is that many builders are not complying with Vans specifications.
Click to expand...

People seem to get in the mind set that neutral should be in the middle of the range.
If this is done, there will always be a shortage of nose up trim and a surplus of nose down that will never be used.
 
MarkW said:
I sure like having the trim on the stick. Flying the plane, flaps and trim at the same time only takes two hands. Manual trim would take three.
Click to expand...

Makes me wonder how any of us ever flew Pipers and Cessnas with manual trim (often down low on the floor between the seats) with only two hands? :rolleyes:

Seriously, the control forces are low enough on RV's that if someone needs to trim at the same time they are moving flaps, they are probably way too fast.

The great thing about RV's is we can build it how we want, and for certain missions manual trim is a good choice.
 
Choose your mission. VFR vs IFR

My friend who built an RV-7 with electric trim + safety trim unit says he much prefers my manual trim. His you can only trim for 2 seconds so checking the trim operation and setting for takeoff can be a pain. Plus getting the trim set in cruise is much easier with the manual trim.
I'm in both camps as my new RV-10 has electric trim which works with the autopilot. But I wouldn't change the manual trim on my -7 as it's strictly VFR.
So choose your mission I guess.

Peter
 
Thanks for all the replies

Thanks to all for commenting on my elevator trim questions. I have decided to go manual on the elevator trim. VAF and it's users are a awesome.
 
Marking my manual trim position

On my -6A, I marked my manual trim, in the neutral position (with the elevator) by filing a (small) notch on the shaft at the twelve o'clock position where it comes out of the sheath, and filling with white paint. For the takeoff position (just a full turn nose up) a small notch is filled with red paint.

For most local flights, I can take off with the white notch and not touch the trim until I enter the pattern and lower flaps. Obviously, when I set the "go-fast" mode, a little twist to the nose-down works great.

I really prefer the manual trim after having electric on the -8A and 10.
 
RONSIM said:
On my -6A, I marked my manual trim, in the neutral position (with the elevator) by filing a (small) notch on the shaft at the twelve o'clock position where it comes out of the sheath, and filling with white paint. For the takeoff position (just a full turn nose up) a small notch is filled with red paint.

For most local flights, I can take off with the white notch and not touch the trim until I enter the pattern and lower flaps. Obviously, when I set the "go-fast" mode, a little twist to the nose-down works great.

I really prefer the manual trim after having electric on the -8A and 10.
Click to expand...

this post comes a bit late. I did something similar for the trim marking in neutral position. the manual trim is very beefy in that area, so it shouldn't be a problem:
 

Attachments

  • 20200827_182048.jpg
    20200827_182048.jpg
    697.7 KB · Views: 445
Last edited:
MarkW said:
If you are planning on a well developed AP then electric trim is a fantastic option.
Most now have speed control for minor trim at high speed and faster trims at lower speeds. As Vern mentioned most will now have autotrim in AP.
i.e. Garmin.
Click to expand...

The variable speed option is extremely useful with electric trim. Extremely.

Here's another point nobody has brought up yet: If you have a two axis autopilot that cannot control the trim (like manual trim), then autopilot disconnect could result in an out of trim airplane, possibly with enough lurch to upset the passenger. Or if the autopilot pitch servo decides that it takes too much force for whatever you're doing, the autopilot could disconnect on its own and that would not be pleasant.

So: if you have an autopilot, make sure that it can control the electric trim. An if you have electric trim, make sure that it is variable speed. (The Garmin G3X Touch does all this nicely, don't know about others). Some autopilot will indicate if they need trim, so that's a help.

And having read this thread, I may need to readjust my elevator trim. On final, full flaps and 60 knots, I'm out of nose up elevator trim. But before I do that, and after I do that, I'll want to experiment with full power go around and see how much nose down force is required. I might decide that I want to limit nose up trim so as to limit nose down force required on a go around -- I think there's a good possibility of that.
 
Last edited:
You must log in or register to reply here.
Back
Top