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  #1  
Old 06-11-2009, 08:19 AM
Camillo Camillo is offline
 
Join Date: Sep 2006
Location: Roma, Italy
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Default 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.
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  #2  
Old 06-11-2009, 08:49 AM
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647jc 647jc is offline
 
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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
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  #3  
Old 06-11-2009, 09:03 AM
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L.Adamson L.Adamson is offline
 
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Default

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
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  #4  
Old 06-11-2009, 09:43 AM
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Ironflight Ironflight is offline
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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
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  #5  
Old 06-11-2009, 10:38 AM
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Mel Mel is offline
 
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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.
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  #6  
Old 06-11-2009, 06:20 PM
blandess blandess is offline
 
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Quote:
Originally Posted by L.Adamson View Post
As mentioned...............no correct way. It varies in production aircraft too.

L.Adamson --- RV6A
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.
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  #7  
Old 06-11-2009, 06:29 PM
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dhammer dhammer is offline
 
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Default 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.
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  #8  
Old 06-11-2009, 07:56 PM
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Ironflight Ironflight is offline
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Quote:
Originally Posted by dhammer View Post
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.
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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  #9  
Old 06-12-2009, 09:33 AM
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dhammer dhammer is offline
 
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Quote:
Originally Posted by Ironflight View Post
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....

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 -

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  #10  
Old 06-13-2009, 08:10 AM
Camillo Camillo is offline
 
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Default 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.
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