Electric Elevator Trim on Ultralight Aircraft

First a friendly reminder:  This blog has many, many posts on many different topics.  Please explore the various posts -- I've written on all kinds things -- some serious, some contemplative, some informative.  Have a look around!  Now, on today's topic:  Electric Elevator Trim Tabs on Ultralight Aircraft.

Another item on our price list which is kind of unique is our electric elevator trim.  I thought I'd show a few pictures as to how we do it.

One of the joys of flying in an ultralight aircraft (such as our FAR Part 103 Belite Aircraft) is taking photographs.  In order to do this, I like to fly 'hands free', without the plane diving or climbing.  And I like to do it at various throttle settings, which means that I need a flight variable trim system.  There's a variety of ways to do this, but here is a system which meets all of the flight trim objectives AND provides an additional redundancy of elevator control, in the event of an elevator control system failure.  Just like a real airplane...  Jumping to what it looks like when it's all done, here's the electric elevator trim and manual rudder trim, as installed on our Belite Black Dragon Superlite (YES, the paint job is spectacular...):

The rudder trim is permanently set, and when properly set eliminates any left or right rudder tendencies.  (The big engine requires a lot of right foot, without rudder trimming, so I LIKE the rudder trim.)  The elevator trim uses an electric servo (designed by Belite) and a custom designed controller circuit board (which we'll get to in a few moments.) 

Now let's back up and look at these two trim tabs in the paint shop:

Well, that's kind of a boring picture.  But it does show the general clutter around the workshop fabrication bench, as well as our big battery charger.  So let's move on to some closeups.  Here's a pic of the rudder trim, prior to placement on the rudder:

And here's a shot of the elevator trim tab, complete with hinge, servo, linkage and control horn.  (Some of which is covered by painted masking tape):

This trim tab weighs about 9 ounces, as pictured.  With cable up to the cockpit, and controller board, the entire weight is about a pound.  The big holes which are drilled on the attachment tabs are used to tie wrap this to our elevator.  Let's mount this trim tab on the elevator:

You can clearly see the black tie wraps, along with the electric cable which has been snaked around the back of the elevator.  The wires have not yet been hooked up, but the linkage is clearly visible from the servo to the control horn.

Now let's move up to the cockpit, and look at the panel:

The big red push button switch is for the electric starter relay, the two red toggle switches are magneto kill switches (left and right) for our big Hirth F23 50HP engine, the white switch is the master avionics switch, and the black toggle switch is our electric trim switch.  It is shown in the central (neutral) position.  Moving it up causes the elevator trim servo to move one direction, while moving it down causes the trim to move in the other direction.  VOILA!  Easy elevator trim.

Now let's take a sneak look behind the panel, and see what's attached to that black toggle switch:

You can see a module which is 'shrink wrapped' and attached to the toggle switch.  It contains a small circuit board which regulates power and controls power polarity from the toggle switch to the trim servo.  This entire design is a product of Belite and is available on our assembled aircraft for $200.  This includes the servo, the electric trim tab, the controller board, the wiring, all installed.

You can see the Black Dragon Superlite, complete with electric trim and several other surprises, at 2010 Oshkosh.  Please come by our booth in the North display, and we also have a booth in the south Ultralight area.