Curtiss Jenny Restoration

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Location: Peachtree City, Georgia, United States

Tuesday, January 07, 2014

Trim Tab

"Do ya think it's a little nose heavy?"


"Ah! Look.  A trim tab you operate inside the cockpit."

-a conversation between Ezra Stiles and Waldo Pepper while looking over the new Skiles Skystreak.

I saw The Great Waldo Pepper in the theater when I was nine years old.  I still remember it.  I've seen it hundreds of times since.  But I never knew the true meaning of this scene.  What was the big deal about a moveable trim tab inside the cockpit?  Every airplane I flew had one. I thought it was movie fluff.

Now I understand.

During our test flights, we had to hold a lot of back pressure on the control stick. Sure, with the Hisso and the larger radiator, I figured we would be a little nose heavy.  The plane flew fine.  It just got annoying holding the stick back all the time.

We added some weight to the tail.  That helped a little.  There was talk of changing the tail incidence.  Nope.  Can't do that.  If you move the back of the stabilizer up or down, it messes up the alignment of the lower rudder hinge.  How about moving the entire wing forward? No, the cabane struts are cut with a certain angle.  Moving the wing would require cutting new angles in the struts, not to mention making a bunch of new wires.

I didn't like any of these solutions very much.  Then I thought about a trim tab?  Hey, I know it was not original but every time you change the CG (add a passenger or  change the fuel) you will have to hold pressure one way or another.

I remembered reading about another Jenny owner having a similar problem.
 

Skeeter Carlson had to use two hands on the stick to keep his Jenny level.  He tried all the above mentioned solutions and said the trim tab was the only thing that cured the problem. I'm glad I saved every magazine article I could find about the Jenny for the last 20 years!

So, we decided to add a trim tab.  Just imagine flying a Cessna without a trim tab.  It wouldn't be much fun either.

Now I understand The Great Waldo Pepper movie.  Those early pilots probably were tired of holding stick pressure so the thought of a moveable trim tab was a big deal!

My Bucker Jungmann has a simple and effective trim tab system so I decided to copy it. I welded some straps to small tubes about the size of the trailing edge material.


The other hinge had the arm welded to it.  It is moved by wire inside a Bowden Cable.


We made the trim tab 1 1/2 inches wide.  The hinges bolted to the wooden structure on the elevators.


 We may end up changing the tab size.  I won't know until we try it.  I want to keep the tabs small enough to be inconspicuous but large enough to do the job.  Nothing is finished yet!  We are still building.  I have not made the cockpit lever yet.


Of course, routing the Bowden Cable required access to inside the elevators!  These holes are on the bottom and will be patched later.

Stay tuned for more progress postings soon.

In the mean time, I stumbled across this interview with Bo Svenson who portrayed Axel Olssen in The Great Waldo Pepper. He tells about the time he went wing walking while they were filming the movie.



If you love the movie as much as I do, you will find the interview fascinating.

Enjoy

Brian

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