REFLECTOR: Elevator Trim Spring
Ron Brown
romott at adelphia.net
Thu Feb 2 09:26:27 CST 2006
Al,
When you start flying (soon, right???), I think you will find that you will need the original spring installed per the plans. If it is any softer than stock, then you will find that you either don't have enough trim up trim for take off or enough down trim for cruise and descent or both. The factory set up is working very well in my 173. And, by the way, I left the sparrow strainer off after painting - I'm not sure I can tell much difference.
You DO need to install a trim power cut off in case of runaway. I have a pull-off breaker. The trim motor runs slowly enough (it is actually a 24vdc actuator so that runs more slowly), that you should be able to react and pull the power before it runs to either end. Well, maybe not. If the trim motor ran to the down limit, you would indeed have to pull hard for the landing. I think pulling the breaker if it runs to the up limit wouldn't be a problem. Then you can slow down and hold that until landing.
In summary, you will need just about all of the trim motor travel along with the stock spring: Take off and landing with two people up front pretty much requires full up trim at 70-80 knot rotation speed or approach to final speed. Single pilot cruise and descent will pretty much require full down trim - 170 knots.
By the way, where are you Dave Black???? Flying yet??????
Ronnie Brown
----- Original Message -----
From: Al Gietzen
To: 'Velocity Aircraft Owners and Builders list'
Sent: Wednesday, February 01, 2006 7:34 PM
Subject: RE: REFLECTOR: Elevator Trim Spring
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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>>
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>
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