Elevator trim indicator directions

Hi. It seems a silly question, and maybe it is, but I'm thinking on this for a week without an answer.

I just wired my Ray Allen elevator trim LED indicator. I fixed it so when I go down with my thumb on the hat swtich (A/C nose up), LED goes down. When I go up (A/C nose down), LED goes up.

When I was about to apply the self-sticking memo, I noticed that it has a trim up and down only writing. So, it seems that when I will trim the aircraft for a nose-up attitude, LED should go up and viceversa. This is the opposite of what I supposed to be right.

In such way, if you look at the LED indicator during flight and would like to centralize trim, you shall follow the "contrary rule": trim down if light is up and trim up in the opposite case.

Which is the standard/correct setting?
Thanks.

There is no CORRECT way to orient the buttons/indicators. Some people prefer the way you have yours installed with the top of the indicator labeled DOWN (me included) others like the indicators to be reversed. Ray Allen provides an ELEV 1 and ELEV 2 label for his trim systems, one has TRIM DOWN at the top and the other has TRIM UP at the top so you should be able to install and label the system however you prefer.

http://www.rayallencompany.com/products/indsens.html

As mentioned...............no correct way. It varies in production aircraft too.

I use a hat switch on my stick also, but the co-pilot/passenger side has the rocker type trim switch mounted right next to the trim indicator on a section below the main panel. In this case, pushing the top of the switch, pushes the nose down, same as stick movement, and the trim indicator follows the same direction.

Another builder who has his trim indicators far removed from the actual stick trims, prefers the indicator to show nose up trim as the bar moves to the top of the indicator.

In reality, I never look at the trim settings, except for the pre-takeoff checklist.

L.Adamson --- RV6A

I went through this while building and polled my Test Pilot buddies at work. Generally, when I drop a grenade question like this among the group, I get answers split between service lines - the AF guys like it one way, the Navy guys another (and the Army guys have trouble reading the quesitons....no - sorry, that was just a joke!). But in this case, I got no definitive answer at all - completely random preferences. My indicator LED goes UP with Nose Up, Down with Nose Down - and I only use it to set trimm for take-off. Lousie's RV-6 doesn't have indicators at all, and I really don't miss them.

Paul

As has been said before, there is no right or wrong way. It's whatever you are comfortable with. The important thing is the labeling. Approximately 1/2 of the airplanes that I inspect have the trim indicator labeled backwards. If the trim indicator says "up" the elevator tab should be down.

L.Adamson said:

As mentioned...............no correct way. It varies in production aircraft too.

L.Adamson --- RV6A

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That is a good point... Every time I fly(usually a 172 or Piper) I set the trim for takeoff and don't worry about it after. The 172's trim indicator goes UP with nose up trim and vice versa...however...a Cessna Citation X's indicator goes down with nose up trim, which is showing the position of the leading edge of the horizontal stabilizer. I would go with what you like seeing.

Trim Direction

Any transport category aircraft I have dealt with follows the pickle switch. Most have the indicator as part of the backup mechanical trim wheel on the pedestal. Pickle forward and the indicator goes forward or nose down. Trim back the opposite or nose up.

dhammer said:

Any transport category aircraft I have dealt with follows the pickle switch. Most have the indicator as part of the backup mechanical trim wheel on the pedestal. Pickle forward and the indicator goes forward or nose down. Trim back the opposite or nose up.

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Absolutely correct - the trouble comes when you have the indicator on the panel in front of you - it just doesn't seem to translate to the coolie hat. I learned I can argue for both cases....

Ironflight said:

Absolutely correct - the trouble comes when you have the indicator on the panel in front of you - it just doesn't seem to translate to the coolie hat. I learned I can argue for both cases....

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Not that it settles the argument, but on the few spam cans I have flown with autopilots such as the Century III have pitch wheels marked Pitch with DN on top and UP on the bottom. Roll the wheel up and the nose goes down. To me that would translate well with the coolie hat and a thumbs up or down motion. I've seen the panel mounted trim indicators on several turbine aircraft marked the same. Maybe someone else has seen the opposite. I'd be interested to know.

Here is the trim panel in a Piaggio Avanti. The switch panel pitch trim switches are backup to the hat switches on the sticks that do pitch and roll and to me seem like an industry standard if not a Part 25 requirement -

Thanks

Thanks to everyone for your input.
I think I will leave as it is, for now. I will have to decide which will be more comfortable to me.

The only "logical" reasoning that I can do is that the indicator, as the name says, should "indicate" an immediate solution, as, for example, the airplane attitude: light UP, nose UP, A/C is climbing. But this would involve a correct label: a TRIM - NOSE UP/NOSE DOWN label.

If I well recall, Spruce sells Ray Allen TRIM UP/DOWN labels. It is not so immediate to a pilot very busy in a cabin what TRIM UP would mean: trim tab going up? elevator going up? nose up?

I'm trying to build my airplane stupid-free. Even if I don't feel me (so) stupid, I may become stupid momentarily in iper-stress situations. So, I would like it to be safe even when iper-charged or iper-stressed.

Camillo said:

It is not so immediate to a pilot very busy in a cabin what TRIM UP would mean: trim tab going up? elevator going up? nose up?

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You should NEVER label a trim indicator or switch with relation to the "trim tab"! The label needs to relate to the direction the aircraft will go. i.e. "up" should mean "nose up".

Thanks.

Oh, so my label will be OK as it is...
Camillo

Camillo said:

Oh, so my label will be OK as it is...
Camillo

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I'm still a bit confused when reading the first post, because of the interpretation of up & down on the thumb switch, as compared to forward & back. I have the Ray Allen stick grips that have the four way thumb switch instead of the four separate buttons. This is Ray Allens newest version. Even though the grip is mostly vertical.....................imagine that it's horizontal in relation to the aircraft.

To trim nose down, I push forward on the thumb switch, just as I'd push forward on the stick. And of course up trim follows the stick direction of pulling back. Note: I'm using forward and back on the thumb switch instead of up and down, because that's where it get's a bit confusing. The point is having the thumb switch or separate buttons follow the stick movement. I've seen some that have been reversed.

Since I have a Ray Allen rocker switch low on the panel for the passenger side, and the fact that the trim indicator is right next to it, the trim indicator shows down when I push the top of the rocker switch (forward/down trim). The trim indicator follows the rocker switch. Again, imagine this "panel mounted" rocker switch and trim indicator as being horizontal with the airplane.

Yet, if I was to have the trim indicator somewhere high on the pilot's side of the panel, then it's perfectly acceptable, and probably better to have the indicator show "up" when the trim is up, which will cause the plane to climb. So it's really a case of where the indicator is placed on the panel.

I've often seen trim tabs wired in the reverse direction, so that no matter what the pilot thinks, it's all screwed up for the first flight! Happily, I built many radio control models before the real airplane, and knew what the tab is suppose to do, along with ailerons and elevators...

L.Adamson