REFLECTOR: Sticking rudder pedals

Brian Michalk michalk at awpi.com
Tue Nov 15 19:26:55 CST 2011


I have just completed the rigging of my Velocity, and studied the brake 
system in the process.  I didn't like the system the first time around, 
but this time around, I like it a little more.  This is not a story 
about toe brakes.

I bought some dune buggy master cylinders, and am using those.  They are 
also 5/8 bore, but the plunger may be a different length.  The square 
rod in the square tube arrangement that allows for rudder travel before 
brake actuation is an interesting design.

First to the sticky brakes.  Make sure the bolts that go through the 
square tube are not tight.  If they are tight, they will crush the tube 
and cause binding.  If it still binds, take it out, and maybe mark it up 
with a marker and reinstall it, then look at where it's rubbing.  File 
it down until it doesn't bind.  I wouldn't add lubricant to something 
like this, it'll just attract dirt.

I went about calibrating my system differently this time.  I also 
changed the arrangement of the square rod on the plunger, with the 
square rod threaded on closest to the brake end, then some number of 
washers, then a nut to lock it all into position.  The more washers you 
add, the less rudder throw you will get before braking.  I cut my square 
rods down a little shorter with the end result that I have more rudder 
travel before I get into the brakes.  I was going to adjust the braking 
so that the pedals would almost be against the canard bulkhead, but 
there is no way to push them that far.  I added a turnbuckle at the 
pedal assembly to adjust the amount of slack, so with a person at the 
rudder, I shortened the turnbuckle until the rudder began moving.  This 
allows for a taut cable that should be quite sensitive.

I used to think that under max braking, you would be stretching the 
rudder cables.  This is not true.  There is still available deflection 
to be had, and if you want it, remove some of those washers.  I'm 
getting the 1.5" of rudder deflection before braking, which is what I 
think the manual calls for.


On 11/14/2011 10:32 PM, John Tvedte wrote:
>
> Geoff,
>
> The pedals should run free and smooth -- and the toe brake system 
> should not require any additional return springs.
>
> You should not use the external springs on the Matco cylinders either 
> -- they can cause scratches in the cylinder shaft which can damage the 
> o-rings.
>
> Some comments from Scott @ Velocity...re. external springs on brake shaft.
>
> " There are return springs built in but these were added
> as helpers to make that better.  Actually they were to
> help a person keep from pushing on them when they didn't
> want to.  It just didn't work all the way around.  Bad
> idea.
>
> I would take those springs off the cylinders as I do not
> use them anymore.  They are not needed and do not do what
> they were supposed to do.  Scott"
>
> I used Lubriplate spray lithium grease to lubricate the pedals.
>
> http://www.lubriplate.com/products/spray-lubricants/spray-lube-a.html
>
> John
>
> *From:*reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] 
> *On Behalf Of *Geoff Gerhardt
> *Sent:* Sunday, November 13, 2011 6:14 PM
> *To:* Velocity Aircraft Owners and Builders list
> *Subject:* REFLECTOR: Sticking rudder pedals
>
> I have the toe break rudder pedal setup.  I just setup my rudders 
> yesterday and found that the co-pilot left rudder pedal doesn't work. 
>  Without the rudders attached both pedals, all the pedals work smooth, 
> but as soon as I connected the rudder cables to the pedal system, the 
> pilot pedals work nice and smooth and can exercise the rudders thru 
> their entire range, and the co-pilot right rudder pedal works just 
> fine, but when I try to depress the co-pilot left pedal, it just 
> binds.  It will only depress down if I either pull on the right rudder 
> pedal (either P or CP), or pull on the left rudder cable.  The only 
> thing I can think is that the tube-in-a-tube rudder actuation 
> mechanism is binding as the co-pilot pedal is pushed.  As I mention, 
> it works fine as the pedal is not depressing against a load (i.e. with 
> the rudder cable disconnected), so I'm guessing there's some torquing 
> of the mechanism going on that is causing it to bind under load.  I 
> don't see an easy way to get lubrication in between the tubes that 
> might help relieve some of this binding.  Is this a problem others 
> have experienced?
>
> Thanks.
>
> Geoff
>
>
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