Electric Trim Installation

[akarmy]

As a few have asked for pictures, ok, really just 1 of you.

I thought I would post some pictures of the progress on installing the electric trim system on my series 7 that used to have trim tabs on the elevator. It's not that hard to do, but takes a surprising amount of work and time to accomplish. The only easy part was buying the kit from John!

[Dave Holl]

Andy
What are the benifits of changing from the trim tab setup?
Dave

[akarmy]

Well, for me the main thing was the loss of elevator effectiveness at slow speed with the trim tabs. With full flaps, on a short strip I loose up elevator at about 60mph with the tabs. If you look at them they tip down when the elevator goes up and they account for about 1/3 of the area of the elevator. Not the best design.

I'm sure the part I will miss is the ease in trimming for cruise flight with the manual lever. I'll have a good comparison when the project is done and can report back the up's and down's of it.

[Dave Holl]

Andy
Thanks for the update.
I have not finished my tailplane and elevator so have a while to decide!
Will wait for your findings
Dave

[HighWing]

You say not the best design. I think I can agree for practical reasons. I opted for the Speedster trim tab on my first Model IV. It was on one side only and worked fine. I rarely used flaps as the lighter Kitfox models had a fairly low stall speed clean. Then when thinking of a way to add a trim tab to conventional elevator, I was at the Desert Fox fly-in several years ago and saw one of the locals with a home brew trim tab. As I recall it had about a four inch chord and was right at a foot wide - or maybe a little more, but definitaly not the full width tab that you see on the prebuilt ones. (am I remembering correctly?) Two giant tabs - one either side? Way overkill, it seems and not surprising the loss of effectiveness.

One question, do you know how much weight the project will add to the tail of the airplane. Consider that the arm is close to eleven feet. I think about this because I put in ribs and gap seals on both vertical and horizontal surfaces and even though I used urethane foam and very light weight glass cloth plus two RAC servos, I figure I added about six pounds - 66 ft. lbs. aft of the datum. Fun stuff, though.

[akarmy]

Alas I fail at being scientific... I have not weighed all the components that I removed and that I installed, but I can tell you this, The tabs & linkages were surprisingly heavy. The servo is about 2 feet forward from the elevator so I suspect it will be a wash in terms of CG and after removing the manual cable etc who knows maybe a win? Like I said, without weighing all the parts, I can feel good with my guesses! I'll put it on the scales when it's all done and confirm things there.

[Dorsal]

Having done the same conversion I am fairly confident the electric system weighs less (also not very scientific). Will be interested to see what Andy's scales say.

[akarmy]

Time for the next update. Covered the elevator and I am now ready to start spraying the polybrush, polyspray, and polytone!

Cut some fabric to size


Glue it down


Add some finishing tapes


All done. FYI "wool" on my 1950's iron is 250deg...

[akarmy]

Continuing my elevator covering process very slowly. It's amazing how long it takes to cover and paint just a small section of fabric when you don't have the time to get it all done back to back. I figure at this rate it will take another couple of months! As the weather has turned cold and rainy here I had to build a paint booth to continue the fun. At I'm about to spray the final silver coat, then on to paint!

[rogerh12]

"Well, for me the main thing was the loss of elevator effectiveness at slow speed with the trim tabs. With full flaps, on a short strip I loose up elevator at about 60mph with the tabs. If you look at them they tip down when the elevator goes up and they account for about 1/3 of the area of the elevator. Not the best design."

Andy; I saw others installing the Trim tab in the existing elevator , and figured I could have a trim tab and still keep all my elevator effectiveness if I hung the trim tab off the back of the elevator.
It was actually easy to add extra metal to mount the trim tab via piano hinge and my MAC servo sits on a metal shelf I installed (see picture below). The super thin but strong C-channel I used is called Piper Channel, and is sold by aircraft spruce. It makes a great receiver for sheet metal screws that will hold the trim tab hinge on, and the aerodynamic cover over the MAC servo.



Hope this helps \

Roger