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There's an article in the EAA Experimenter about Paul Lipp's
235. Among other mods he describes spring-loading the aileron trim but
using a trim tab for pitch.
The way I picture it is that a trim tab maintains its
relative effect with change in airspeed whereas spring loading will change. (The
spring would compress due to the additional load on the surface, allowing
the surface to deflect).
I don't know enough about the subject to say one way or the other.
My question is- do those with the spring-loaded pitch trim have to adjust trim
very often as their speed changes?
My reason for asking is that my IV-P elevators are going
to need more lead than I can pack into them. I've been thinking about a
spring-loaded system for trim so I can lose the weight of the trim tab and MAC
servo. What I have in mind would be a fiberglass leaf spring that would act
in both directions. Although I'd like to use a mechanical control I may end up
using a linear actuator (Velocity builders might recognize that setup).
Looking for comments- Bill Wade
----- Original Message -----
Sent: Tuesday, March 02, 2010 1:07
PM
Subject: [LML] Re: Reichel Trim Wheel
With reference to Marv's explanation:
There is more to it than benefits from reduced weight and drag.
Many, if not most, LNC2 builder/pilots reduced the arm of the elevator bell
crank from 4 inches to 3. This modification resulted in reducing the
stick throw by 25% and also increasing stick forces by 25% - a really good
result because of the pitch "sensitivity" of these aircraft. Of
course when one changes a part of a system, the whole system is
affected. Finer pilot control of stick movement was required (famous
two-finger grip) and a stronger trim spring was needed to manage the
higher trim forces. A consequence of using the stiffer spring was the
need for more friction to hold the crucifix trim lever position
and more difficulty in fine tuning pitch trim. The Reichel trim wheel
resolves the spring/friction issues while still allowing the pilot to overcome
any trim setting with stick movement (that is, causing the trim wheel to
unwind). Benefits abound from this system including no possible
electric trim runaway in the all important pitch axis.
Another benefit of the Reichel Wheel is the window with its
precise trim position indicator. Mine is marked with the neutral
elevator position and the elevator is set to that position before each takeoff
- a known control surface position with pitch control totally in my
hands.
Since my experience is with my own small tail 320 (and others with small
tails), we will have to await the comments of others on its efficacy with
either a Mk II tail 300 series Lancair or a Legacy.
Scott Krueger
In a message dated 3/2/2010 10:12:48 A.M. Central Standard Time,
marv@lancair.net writes:
Posted for "Bay Elliott"
<bay@farwellgroup.com>:
Hi Marv,
I am a
relatively new Legacy builder (last 6 months) and I am not familiar
with
the Reichel Trim Wheel. What are the advantages of this system
over
others and is it applicable to the Legacy?
Warm
Regards,
Bay Elliott
Executive Vice President, The
Farwell Group, Inc.
Executive Recruiting
Consultants
(305) 529
4811 bay@farwellgroup.com
[I
thought I would move this out onto the LML to invite further discussion and
get some assistance from folks who know more about the intricacies of trim
systems than I do.
The earlier LNC2 was designed with a trim
system that used a spring bias applied to the elevator pushrod to control
the overall elevator position. It was controlled by a small cruciform
trim lever that moved the biasing springs forward and aft. Dick
Reichel invented his trim wheel to replace the lever, allow finer and more
precise trim adjustments, and to provide folks with the same sort of trim
wheel that they had flown with in any number of certified aircraft.
Trimming the location of the entire control surface is probably
aerodynamically preferable (less drag) to moving a trim tab to use the
airflow to move the control surface, and the removal of the trim tab
eliminates its weight and complexity, as well as those of the servo motor
and linkages... ie, less counterweight required for balance. There are
probably other aero issues, but I leave those things to folks more
knowledgable than I in these matters.
Whether or not a a
spring biased trim system would be applicable to the Legacy, I can't see why
not, at least for those folks who are still building and can opt to
incorporate it into their control system... I don't know how the trim tab is
built on the Legacy elevator, but if it's cut from the elevator similarly to
the method used on the LNC2, that part of the process could be bypassed and
the work, weight and complexity of the trim tab mechanism could all be left
out. To my knowledge no one has incorporated this into a Legacy, but
that doesn't mean that it couldn't be done.
The only
disadvantage with the spring bias system at this point is that it is totally
manual. Once I finish with the basic trim wheel system I'm going to
look into motorizing it while still allowing manual
adjustments.
<Marv>
]
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