REFLECTOR: Elevator Trim Spring

Wed Feb 1 18:34:01 CST 2006

The stiffer the trim spring, the more stick force is required to overcome
the force of that spring in the case of an in-operative trim unit.

My opinion is that the criteria should not just be the ability to
control/land the plane if the trim unit fails in cruise position; but if the
trim unit fails in either extreme position; as would be the case with a
shorted wire or stuck/failed trim switch.  Unless you are VERY strong; the
standard, untrimmed spring may not allow you to meet this condition.  In
other words, the spring needs to be trimmed (narrowed) until you can
reasonably achieve full down elevator (trailing edge down) with the trim set
to full up (trailing edge up) elevator.

 If proper trimming ability is not achievable with such a spring, then
perhaps an alternative trim system should be considered.

I am reasonable strong, and found that I needed to trim the width of the
spring to 1 ¾” to meet the criteria.  I haven’t flown yet, so don’t know how
well the trim system will work.

FWIW,

Al

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Chuck Jensen
Sent: Wednesday, February 01, 2006 7:36 AM
To: Velocity Aircraft Owners and Builders list
Subject: RE: REFLECTOR: Elevator Trim Spring

Scott,

You wrote that "I think it would be hard enough trying to fly it with an

inoperative trim  system as it is, any stiffer and I'd be out of muscle

pretty fast."  If I understand the issue here (and that is not a given),

the installation of a stiffer trim spring would assist you, not create

additional resistance that you would have to overcome, in other words,

the stiffer spring would be a force-multiplier for you.

Then, instead of using your muscles to compensate for the trim spring,

you can use them for important things like tuning your Sirius radio.

Chuck Jensen

-----Original Message-----

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On

Behalf Of Scott Derrick

Sent: Wednesday, February 01, 2006 10:08 AM

To: Velocity Aircraft Owners and Builders list

Subject: Re: REFLECTOR: Elevator Trim Spring

I can see how he might need more travel.

As my trim is set up, I have just enough down trim to cruise at 65% 

power with just me in the front. If its bumpy I don't have enough, I 

have to constantly give it a shove forward  or use George. If have two 

in the front I don't have enough up trim for a hands off 90 knot 

approach, just me its fine.    If I fix it so I can fly a 90 knot 

approach hands off with two, I'd loose my  hands off cruise trim

setting.

So as Scott B. said, I could possibly stiffen up the spring, I don't 

like this option because    Or I could use a trim actuator with more 

travel. I had not considered that  and will have to think about it.

However I do like the design of the Strong Pitch Trim system and would 

welcome the added space behind the panel if I removed the fiberglass 

spring trim system.  Strong now has a PWM controller for his trim system

for fine pitch adjustments at fast speeds. A problem I partially solved 

on the original system with a electric brake.

Scott

Ron Brown wrote:

> John,

>

> I don't think you will need more travel if you use the unmodified 

> factory ? shaped spring installed per the manual

>

> You'll just need to adjust its location to get the amount of up and 

> down trim needed for your plane.

>

> Ronnie

>

>

>

> ----- Original Message ----- From: "John Dibble"

<aminetech at bluefrog.com>

> To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>

> Sent: Tuesday, January 31, 2006 6:56 PM

> Subject: Re: REFLECTOR: Elevator Trim Spring

>

>

>> Where can I get an actuator with more travel?

>>

>> John

>>

>> Scott Baker wrote:

>>

>>> While its interesting to think about the benefits of variable

geometric

>>> wings, canards, and winglets - lets remember the practical elements

of

>>> system design as it applies to weight, complexity of design and 

>>> maintenance,

>>> and of course cost.  The Beech Starship had a base list price of 

>>> $3.9M when

>>> it was introduced in 1989.  There are lots of cool things that would

>>> be fun

>>> to try - given relief from $$ constraints.  The subject of 

>>> pitch-trim has

>>> been discussed on the Reflector off and on in the past.  The basic 

>>> linear

>>> actuator/fiberglass spring system works well to my liking.  I happen

to

>>> think it is one of the finer flying attributes of the Velocity.  If

an

>>> aircraft does not have enough pitch trim (in cruise or in slow 

>>> flight) the

>>> answer in most instances is to re-mount (adjust the location) of the

>>> linear

>>> actuator so that it gives the needed travel.  Sometimes the

fiberglass

>>> spring needs stiffening - this can be done by adding a few plies of 

>>> glass -

>>> or replacing the spring with a new one from the factory.  A few 

>>> builders

>>> have installed linear actuators with an additional inch of travel 

>>> (in order

>>> to get enough up _and_ down trim).

>>> Scott Baker

>>>

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