# Electric elevator trim servo

Discussion in 'Instruments / Avionics / Electrical System' started by Pops, Dec 17, 2018.

### Help Support HomeBuiltAirplanes Forum by donating:

1. Dec 17, 2018

### Pops

#### Well-Known Member

Joined:
Jan 1, 2013
Messages:
6,906
5,822
Location:
USA.
I have been using this 12 V electric servo with limit switches built in and using a DPDT rocker switch for many years. First on the SSSC and I have one installed in the JMR Special. They are so small I welded a tab on the rear of the elevator front tube and mounted the servo in the elevator with an aluminum inspection cover on the JMR. I don't have an electrical system but do use a 12 Volt , 7 amp model airplane starting battery to power the handheld radio and GPS and the electric elevator trim servo. Used an L-16S, 12 volt, 50 mm stroke, 150 to 1 gearing, 40 lbs of force, weight 3 ounces, for the elevator trim tab. Just the right speed to set the trim with the rocker switch. Price $70 +$10 for the rocker switch.

https://www.actuonix.com/category-s/1823.htm

Corrected -- At first I had the specs for the P-16S instead of the L-16S that I have been using.

Last edited: Dec 17, 2018
2. Dec 17, 2018

### Pops

#### Well-Known Member

Joined:
Jan 1, 2013
Messages:
6,906
5,822
Location:
USA.
On the simple high drag of the SSSC, I mounted the elevator trim servo on an aluminum plate on the outside , under the elevator. Added the trim tab on the elevator made from 1/4" alum honeycomb from the B-1 bomber surplus store. Red on the trim tab and red on the rudder and N numbers is stickly back model airplane trim Monocote.
Tail wires are Piper J-3 Cub drag and anti-drag wires. Painted with a 4" roller.

#### Attached Files:

File size:
33.7 KB
Views:
30
File size:
45 KB
Views:
26
• ###### DSCF0012.jpg
File size:
52.8 KB
Views:
27
blane.c likes this.
3. Dec 17, 2018

### lr27

#### Well-Known Member

Joined:
Nov 3, 2007
Messages:
3,216
463
Can you overpower the trim by hand if the wires to the servo break or the switch fails?

4. Dec 17, 2018

### Pops

#### Well-Known Member

Joined:
Jan 1, 2013
Messages:
6,906
5,822
Location:
USA.
That depends on how large you make the trim tab. Yes, the trim tab is sized to be effective enough but still easy to overpower. On the SSSC I installed a homemade autopilot for a couple of years and easy to overpower the pitch and roll with the stick but responsive enough to fly the airplane . Took the autopilot out after a couple of years. The SSSC is a fun little airplane to fly, with very light control forces, not a large, heavy high speed cross county cruiser. The autopilot was having all the fun

Picture of the SSSC with the autopilot trim tabs, notice that the pitch tab is smaller than what is used as a elevator trim tab. The autopilot trim tab needs to be a little smaller because of the higher cruise speed where the autopilot is used, the elevator trim only tab needs to be effective down to the slower approach speeds. With the autopilot off , I still could use the servos as electric trim but need full up trim with the autopilot size tab. The size of the tab is a compromise on having enough pitch trim on approach speeds and pressure on overriding the autopilot servo in cruise.

#### Attached Files:

• ###### picture 7.jpg
File size:
73.3 KB
Views:
13
Last edited: Dec 17, 2018
blane.c likes this.
5. Jun 15, 2019

Joined:
May 3, 2015
Messages:
89