The Murphy Builders Site

WIth all this talk about the rudder pedals and brakes, I went out to look at
mine, (already assembled by the guy I bought the airplane from).

Depending on how much pedal is required to move the rudder to it's max, I can
see where there might be a conflict with the back of the firewall on full
rudder deflection and full brake. I will have to measure the distance from
center and also the possible max brake deflection to see if I am ok, or out of
line.





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I came up with about 1.5" of cable travel from nuetral to the stop. Doesn't
seem like much to me but I haven't terminated the cables to put my feet on
the pedals yet.
Mike
----- Original Message -----
From: <pequeajim@dcsol.com>
To: <rebel-builders@dcsol.com>
Sent: Tuesday, January 03, 2006 8:28 PM
Subject: Rebel: rudder pedals

WIth all this talk about the rudder pedals and brakes, I went out to look
at
mine, (already assembled by the guy I bought the airplane from).

Depending on how much pedal is required to move the rudder to it's max, I
can
see where there might be a conflict with the back of the firewall on full
rudder deflection and full brake. I will have to measure the distance
from
center and also the possible max brake deflection to see if I am ok, or
out of
line.





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Hi Mike, here's something you might need to consider if you're making
changes to the flanges for your elevator cables. In a pull-pull cable
system like this, the distance between the holes you mount your cables to
must be the same on both the control stick, and the control surface.
Otherwise the cable length is not constant. If the distance is greater on
the control stick like you're considering, then when you move the stick in
one direction, the pulling cable will stay tight, but the other cable will
go slack, and possibly jump out of pulleys and guides. If the control
surface end has the holes farther apart, then when you move the stick, the
cables will get stretched because the length of the non-pulling cable gets
longer the farther you move the stick.

So, if you want to change the tabs on the control stick, then you'll also
need to change them on the elevator so that they are symmetrical.

Mike

----- Original Message -----
From: "Mike Betti" <mbetti@up.net>
To: <rebel-builders@dcsol.com>
Sent: Tuesday, January 03, 2006 6:35 PM
Subject: Re: Rebel: rudder pedals

I came up with about 1.5" of cable travel from nuetral to the stop. Doesn't
seem like much to me but I haven't terminated the cables to put my feet on
the pedals yet.
Mike

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I don't think I agree. (thinking cap on...)
Seems to me that as long as the up and down tabs on the control stick
are the same length and they are perpendicular it will be fine. By
perpendicular I mean that looking sideways (down the center of the
tube), with the stick centered, a radial line from the tube axis to the
hole in the horn is right angles to the control cable.

Same rule for the elevator bellcrank horns but they can be a different
length than the control tube horn tabs to achieve mechanical gearing.

I actually moved my upper control column tab rearward a tad (wanted to
move it sideways anyway) to achieve that geometry and the cables seem to
stay pretty consistantly tensioned. There was a slight improvement in
geometry by doing that when using a pair of pulleys behind the control
column instead of just fairleads several feet back..

Ken

Mike Davis wrote:

Hi Mike, here's something you might need to consider if you're making
changes to the flanges for your elevator cables. In a pull-pull cable
system like this, the distance between the holes you mount your cables to
must be the same on both the control stick, and the control surface.
Otherwise the cable length is not constant. If the distance is greater on
the control stick like you're considering, then when you move the stick in
one direction, the pulling cable will stay tight, but the other cable will
go slack, and possibly jump out of pulleys and guides. If the control
surface end has the holes farther apart, then when you move the stick, the
cables will get stretched because the length of the non-pulling cable gets
longer the farther you move the stick.

So, if you want to change the tabs on the control stick, then you'll also
need to change them on the elevator so that they are symmetrical.

Mike

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I may have to concede this point Ken... I've never actually tried it, but as
a pull-pull cable system is common in larger R/C aircraft I've installed
several of them. I've read several articles regarding this type of
installation in R/C aircraft, and they always stress the importance of this
symmetry... but as I said, I've simply made sure my installations were
symmetrical, and have never actually tried one that wasn't. So I might be
completely off the mark. It wouldn't be the first time I thought I knew
something that I didn't. ;-)

Mike

----- Original Message -----
From: "Ken" <klehman@albedo.net>
To: <rebel-builders@dcsol.com>
Sent: Wednesday, January 04, 2006 6:05 AM
Subject: Re: Rebel: rudder pedals

I don't think I agree. (thinking cap on...)
Seems to me that as long as the up and down tabs on the control stick
are the same length and they are perpendicular it will be fine. By
perpendicular I mean that looking sideways (down the center of the
tube), with the stick centered, a radial line from the tube axis to the
hole in the horn is right angles to the control cable.

Same rule for the elevator bellcrank horns but they can be a different
length than the control tube horn tabs to achieve mechanical gearing.

I actually moved my upper control column tab rearward a tad (wanted to
move it sideways anyway) to achieve that geometry and the cables seem to
stay pretty consistantly tensioned. There was a slight improvement in
geometry by doing that when using a pair of pulleys behind the control
column instead of just fairleads several feet back..

Ken

Mike Davis wrote:

Hi Mike, here's something you might need to consider if you're making
changes to the flanges for your elevator cables. In a pull-pull cable
system like this, the distance between the holes you mount your cables to
must be the same on both the control stick, and the control surface.
Otherwise the cable length is not constant. If the distance is greater on
the control stick like you're considering, then when you move the stick in
one direction, the pulling cable will stay tight, but the other cable will
go slack, and possibly jump out of pulleys and guides. If the control
surface end has the holes farther apart, then when you move the stick, the
cables will get stretched because the length of the non-pulling cable gets
longer the farther you move the stick.

So, if you want to change the tabs on the control stick, then you'll also
need to change them on the elevator so that they are symmetrical.

Mike

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I'm not sure what to think here. But if I remember, the tabs on the control column are welded on at an angle that may not be in line with the axis. I was thinking maybe there is some thought there that as the stick is moved to the extremes that maybe the amount of throw changes and make up for any differences Mike Davis mentioned. ??? I need to take some measurements when I get home tonight.
Mike Betti

On Wed, 04 Jan 2006 10:05:11 -0500, rebel-builders@dcsol.com said:

I don't think I agree. (thinking cap on...)
Seems to me that as long as the up and down tabs on the control stick
are the same length and they are perpendicular it will be fine. By
perpendicular I mean that looking sideways (down the center of the
tube), with the stick centered, a radial line from the tube axis to the
hole in the horn is right angles to the control cable.

Same rule for the elevator bellcrank horns but they can be a different
length than the control tube horn tabs to achieve mechanical gearing.

I actually moved my upper control column tab rearward a tad (wanted to
move it sideways anyway) to achieve that geometry and the cables seem to
stay pretty consistantly tensioned. There was a slight improvement in
geometry by doing that when using a pair of pulleys behind the control
column instead of just fairleads several feet back..

Ken

Mike Davis wrote:

Hi Mike, here's something you might need to consider if you're making
changes to the flanges for your elevator cables. In a pull-pull cable
system like this, the distance between the holes you mount your cables to
must be the same on both the control stick, and the control surface.
Otherwise the cable length is not constant. If the distance is greater on
the control stick like you're considering, then when you move the stick in
one direction, the pulling cable will stay tight, but the other cable will
go slack, and possibly jump out of pulleys and guides. If the control
surface end has the holes farther apart, then when you move the stick, the
cables will get stretched because the length of the non-pulling cable gets
longer the farther you move the stick.

So, if you want to change the tabs on the control stick, then you'll also
need to change them on the elevator so that they are symmetrical.

Mike

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There's nothing critical here. If the top and bottom tabs are the same
length I'm sure you will be fine.
If you are going to move the tabs anyway, then try to also position them
(foreward and aft) to make the cables come off reasonably perpendicular
as mentioned below. The angle of the tabs doesn't matter, only the final
position of the hole is important.

If the cable tensioning is changing on you then also check that the
cables are coming off the elevator bellcrank perpendicular. Where you
position the pulleys at each end affects this. Not sure about an Elite
but on a Rebel if the cables are not perpendicular in one or both
places, you should actually be able to make some adjustment for how much
the tension changes by adjusting the neutral positon of the bellcrank.
You'd do that by making one cable longer and the other shorter. That is
assuming you have adjustment space in the elevator pushrod linkage.

Ken

mbetti@up.net wrote:

I'm not sure what to think here. But if I remember, the tabs on the control column are welded on at an angle that may not be in line with the axis. I was thinking maybe there is some thought there that as the stick is moved to the extremes that maybe the amount of throw changes and make up for any differences Mike Davis mentioned. ??? I need to take some measurements when I get home tonight.
Mike Betti

On Wed, 04 Jan 2006 10:05:11 -0500, rebel-builders@dcsol.com said:

I don't think I agree. (thinking cap on...)
Seems to me that as long as the up and down tabs on the control stick
are the same length and they are perpendicular it will be fine. By
perpendicular I mean that looking sideways (down the center of the
tube), with the stick centered, a radial line from the tube axis to the
hole in the horn is right angles to the control cable.

Same rule for the elevator bellcrank horns but they can be a different
length than the control tube horn tabs to achieve mechanical gearing.

I actually moved my upper control column tab rearward a tad (wanted to
move it sideways anyway) to achieve that geometry and the cables seem to
stay pretty consistantly tensioned. There was a slight improvement in
geometry by doing that when using a pair of pulleys behind the control
column instead of just fairleads several feet back..

Ken

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