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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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