REFLECTOR: PITCH & ROLL TRIM

[Stephen Vaughen]

Dave,

I broke a series of stock pitch trim springs 
before waking up in the middle of the night with 
the answer.  As with so many problems I've ever 
faced, the answer was relatively simple, and was 
staring me right in the face.

The answer was to create a pitch trim spring 
which was a series of 2 bid layers instead of one 
solid fiberglass spring.

In other words, imagine the stock pitch trim 
spring shape and size, but made up of 10 
independent layers at 2 bid each.

What happens is that the layers slide against one 
another and no individual layer gets over 
stressed to the point of breaking.  Realize that 
2 bid of fiberglass can flex a lot farther 
without breaking than can a 10 bid layer.  A 
series of 2 bid layers can achieve the stiffness 
you want by just adding more 2 bid layers.

I recall that I found the sweet spot at about 10 
layers, 2 bid each.  No more broken pitch trim 
springs and I have full override movement with 
adequate stiffness.  You want more or less 
stiffness, add or remove 2 bid layers.

I mentioned to Scott Swing that I had conquered 
this problem on my plane, so I hope that the word 
gets around.  Scott asked me how I made it, and I 
told him that I started with the stock pitch trim 
spring, duct taped one side, laid up 2 bid, 
covered it with plastic, another 2 bid, another 
sheet of plastic, etc., etc.

Come to think of it, it may have been 8 2 bid 
layers.  I'll count the layers later this week.

I hope this works for you.  Regards

Steve





>I agree that the factory pitch trim system 
>leaves alot to be desired.  Last winter I worked 
>with Alexis Strong (of Cozy fame) to engineer a 
>system for my Velocity STD-RG based on his well 
>proven design that's flying in dozens and dozens 
>of EZEs out there.  I've been (slowly... very 
>slowly) putting together an article to describe 
>my results.  In net, working with Alex, we 
>modified the design for my Velocity and I'm 
>very, very pleased with the results.  I'll try 
>to post more in the next couple of days if 
>anyone's interested.
>
>Dave
>
>----- Original Message -----
>From: <mailto:tmartino at troubleshooter.com>Tom Martino
>To: <mailto:reflector at www.tvbf.org>Velocity Email List (E-mail)
>Sent: Wednesday, October 13, 2004 9:51 AM
>Subject: REFLECTOR: PITCH & ROLL TRIM
>
>I like most everything about the Velocity design 
>except for the pitch and roll trim.  So I am 
>finally doing something about it.  I am 
>installing tiny trim servos in the elevator and 
>one aileron and outfitting them with piano 
>hinged trim tabs.  The wires will be run inside 
>the torque tubes.  I am happy to be eliminating 
>that clunky linear activator and the cumbersome 
>fiberglass trim spring on the canard and the 
>string & spring roll trim.
>
>Anyone else ever do this?
>
>BTW – I have forgotten to post the paint designs 
>I promised 
 but it’s been difficult to get my 
>graphic artist to send me the digitals.  All I 
>have now are large print-outs.  They should be 
>coming soon.  
>
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