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billderou(at)yahoo.com
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 Posted: Tue May 13, 2008 8:02 am Post subject: Low Tech Rudder Trim |
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All-
Just thinking overnight about the major issue of breaking force. Intuitively it seems very solvable.
I have already installed a small trim tab on my rudder set to cruise. As all those flying know with the weight shifting around, differential elevator trim trying to roll the plane when the tab trailing edges are at different height, nose wheel not centered - these create differences that only a variable trim can solve. But once a fixed trim tab is set to cruise then the forces necessary to center the ball are fairly light compared to a leg on the pedal. In my experience the force necessary to move the ball 75% of the ball diameter would be sufficient.
It would seem that replacing the big screw with an over the center lever retracting a rod with an adjustable spring that pulls the blocks together would do the trick. It needs some experimenting to get the pull distance and spring style correct. The downside is we give up the gust lock feature.
Jason may be able to add to the implementation with his single point concept which reduces my approach to one lever.
Given no better ideas at this point, this is the direction I will pursue for Revision B.
Others are welcome to purchase a block of nylon and give it a go!
Bill DeRouchey
N939SB, flying
"Mike Doble (Home Office)" <mikedoble(at)wi.rr.com> wrote:
[quote] Interesting idea. Just a note, the Cessna 400 (former Columbia 400) has a “rudder hold” switch next to the flap lever. I flew the 400 twice last week for a total of about an hour and the “rudder hold seems to work nice. How did they do it? Anyone know?<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />
Mike
Do not archive
Mike Doble
Builder 40691
Working on my tail.....STILL
Waukesha, Wisconsin
From: owner-rv10-list-server(at)matronics.com [mailto:owner-rv10-list-server(at)matronics.com] On Behalf Of Bill DeRouchey
Sent: Monday, May 12, 2008 1:22 PM
To: rv10-list(at)matronics.com
Subject: Low Tech Rudder Trim
After showing Deems this setup at a great RV-10 NW dinner and flying a while to prove its worth I am ready to go public. I thought of several complex designs using spring bias and scrapped them all due to various reasons.
Lets start with two statements. First, the proper engineering solution is cutting into the rudder and installing a servo and a small trailing tab. This approach has a built-in failsafe in that the rudder pedals can always override the rudder trim. Secondly, I expect my idea to be rejected many in the list because it will be judged as crude, however, a simple design can be elegant in its simplicity.
I chose to not cut into my beautifully painted rudder and opt for a less proper engineering solution. What I have devised is to modify the rudder cable nylon fairleads just in front of the fuel switch valve to also pinch the cable when a screw clamp is tightened. I set the rudder trim with my feet then pinch one or both cables. See attachments for a visual. There are some tricks to get this very simple design to work properly.
The big negative (in my mind) with this approach is I did not want to get caught with the rudder locked when I needed it. The imagined solution was to handle it with procedures kicking the rudder before takeoff and when beginning decent. As I began to fly, this issue became moot since my feet instantly sensed the lock when they are applied to the pedals and my mind learned how to react immediately. My feet feel they are pushing against a brick wall and the release knobs are within inches of my hand. Typically, only one of the knobs are tightened.
Two additional good features were observed. When parked it becomes a great gust lock for the rudder. Also, on my way to the NW RV-10 dinner the yaw ball was centered, my feet were on the floor, and the cable locks were loose when I encountered turbulence as the terrain rose north of Redding CA. We yawed around a bit then I locked both clamps (one per cable). The yawing diminshed about 80% and reduced my piloting effort. In the future, I do not know if I will lock the rudder during turbulence or use my feet. Need more experimentation in this situation.
The original design is pictured in the attachment and I got it about right. After these pics were taken I replaced the Nylox nut with a AN3 anchor nut (AN366F style probably best) to adjust the clamp loose cable tension without removing the tunnel cover. Also, I reduced the outboard nylon block thickness to 3/8" to route the cable around the fuel selector switch. Probably should have been 5/16". The knob is a Reid Supply Co p/n KA-1. Clamp the two nylon blocks together and drill an 1/8" hole through the mating surface. Then mill the thick block with the half hole surface down .015 to .020. This will create a rocking motion with the cable as its fulcrum to create the pinching force.
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billderou(at)yahoo.com
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| Posted: Tue May 13, 2008 12:07 pm Post subject: Low Tech Rudder Trim |
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All-
Just thinking overnight about the major issue of breaking force. Intuitively it seems very solvable.
I have already installed a small trim tab on my rudder set to cruise. As all those flying know with the weight shifting around, differential elevator trim trying to roll the plane when the tab trailing edges are at different height, nose wheel not centered - these create differences that only a variable trim can solve. But once a fixed trim tab is set to cruise then the forces necessary to center the ball are fairly light compared to a leg on the pedal. In my experience the force necessary to move the ball 75% of the ball diameter would be sufficient.
It would seem that replacing the big screw with an over the center lever retracting a rod with an adjustable spring that pulls the blocks together would do the trick. It needs some experimenting to get the pull distance and spring style correct. The downside is we give up the gust lock feature.
Jason may be able to add to the implementation with his single point concept which reduces my approach to one lever.
Given no better ideas at this point, this is the direction I will pursue for Revision B.
Others are welcome to purchase a block of nylon and give it a go!
Bill DeRouchey
N939SB, flying
[quote][b]
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Kelly McMullen
Joined: 16 Apr 2008
Posts: 1188
Location: Sun Lakes AZ
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| Posted: Wed May 14, 2008 2:48 am Post subject: Low Tech Rudder Trim |
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Bill, you might consider a material that has a bit less grip than
nylon, such as Delrin. Another idea would be to have one side of the
block covered with leather, that would reduce the grip, but provide
sufficient friction.
On Tue, May 13, 2008 at 1:05 PM, Bill DeRouchey <billderou(at)yahoo.com> wrote:
| Quote: |
All-
Just thinking overnight about the major issue of breaking force. Intuitively
it seems very solvable.
I have already installed a small trim tab on my rudder set to cruise. As all
those flying know with the weight shifting around, differential elevator
trim trying to roll the plane when the tab trailing edges are at different
height, nose wheel not centered - these create differences that only a
variable trim can solve. But once a fixed trim tab is set to cruise then the
forces necessary to center the ball are fairly light compared to a leg on
the pedal. In my experience the force necessary to move the ball 75% of the
ball diameter would be sufficient.
It would seem that replacing the big screw with an over the center lever
retracting a rod with an adjustable spring that pulls the blocks together
would do the trick. It needs some experimenting to get the pull distance and
spring style correct. The downside is we give up the gust lock feature.
Jason may be able to add to the implementation with his single point concept
which reduces my approach to one lever.
Given no better ideas at this point, this is the direction I will pursue for
Revision B.
Others are welcome to purchase a block of nylon and give it a go!
Bill DeRouchey
N939SB, flying
|
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http://www.matronics.com/Navigator?RV10-List |
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_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor
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