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-   -   RV-8 rudder pedal mods (https://vansairforce.net/community/showthread.php?t=38815)

billdianne 01-23-2009 08:22 AM

RV-8 rudder pedal mods
 
I know of two mods for the problem of applying a little brake when wanting only rudder deflection.

One is to replace the the pedal attachment bolts with one long bolt across the face of the pedal.

The other is to add small extensions to the bottom of the pedals.

For people who have done one or the other, how has this worked out? And would you prefer one method over the other?

KirkGrovesRV8 01-23-2009 12:32 PM

Hi Bill,
I might get corrected on this but in my very very humble opinion, I would leave the pedals stock. I have never had a issue with inadvertent braking but I have had a time or too when I needed brakes NOW, and I personally like being able to quickly give a tap or two of brakes in a strong crosswind. I have overheard conversations where ground loops have happened and the pilots have quietly wondered if they had had better access to the brakes the ground loops might have been avoided???
Its all personal choice All the Best

Mike S 01-23-2009 01:23 PM

Quote:

Originally Posted by billdianne (Post 292359)
I know of two mods for the problem of applying a little brake when wanting only rudder deflection.

One is to replace the the pedal attachment bolts with one long bolt across the face of the pedal.

Actually, the long bolt is a fix for the brakes sticking. The long bolt forces the pivot holes to all align up on a single axis----and the two bolt set up can have the axises at a slightly different position, causing binding in the pedal motion.

The master cylinder return spring is pretty weak, and a little binding can prevent total return of the piston, which is needed to un-port the pressure relief.

cdmiller 01-23-2009 11:00 PM

Leave them stock
 
I agree with Kirk Groves. I have over 500 hours on my RV-8 with stock rudder peddles and I have had no problems applying brake when I just want rudder. I think that stock peddles work very well. I wouldn't change a thing about them.

Dan Miller

Ironflight 01-24-2009 08:17 AM

Quote:

Originally Posted by Mike S (Post 292442)
Actually, the long bolt is a fix for the brakes sticking. The long bolt forces the pivot holes to all align up on a single axis----and the two bolt set up can have the axises at a slightly different position, causing binding in the pedal motion.

While this is a true benefit of the single bolt mod, most people that do the mod (as I understand it) are trying to prevent the inadvertent braking that can come from pressing on the pedals with the factory geometry.

I have pedal extensions which I installed before I flew an -8 (based on Randy Lervold's design). I have also flown -8's with stock pedals. I like my pedal extensions because they fit the geometry of my ankles and feet - I fly with my heels on the floor, and the tips of my toes on the extensions. I have no problems with sliding my feet up to tap the brakes when I need them - but again, this is very, very dependent on your personal foot geometry.

Fortunately, the rudder pedals can removed with about an hour's work through the forward baggage compartment, so you aren't stuck with how you do them if you decide to change later on. Experiment until you get them right!

Paul

Mike S 01-24-2009 09:44 AM

Quote:

Originally Posted by Ironflight (Post 292636)
While this is a true benefit of the single bolt mod, most people that do the mod (as I understand it) are trying to prevent the inadvertent braking that can come from pressing on the pedals with the factory geometry.

Paul

Paul, the geometry does not change when going to a long bolt. Same pivot point, same throw, ETC.

Just corrects any misalignment that may have crept in due to two bolts being used.

chrispratt 01-24-2009 10:07 AM

Bill:

My 2 cents is the issue is the master cylinders not the pedals. Some (like me) have had master cylinders that tend not to fully release and thus drag the brakes. Most posters seem to agree that it is due to weak return springs on the Matco cylinders. No matter how I positioned my feet on the pedals including tips of my toes only on the lowest point of the rudder bar, I still had the problem. I changed to the Grove replacement cylinders and haven't even thought about it since.

Chris

Mike S 01-24-2009 10:18 AM

O.K., perhaps I spoke too soon---------should know better than to disagree with Paul:rolleyes:

I was looking around in the archives for photos of the long bolt fix. (scroll down to post 3). And I ran across another thread that shows a -8 setup.

It appears that the 8 is not like the units posted in the above link.

Is the pivot bolt/bolts in front of the pedal in the 8, or is this just a weird angle that makes it look like it is in front???

http://img147.echo.cx/img147/8898/rv...armockup2t.jpg

BuckWynd 01-24-2009 11:22 AM

Quote:

Originally Posted by Mike S (Post 292658)
It appears that the 8 is not like the units posted in the above link.

Is the pivot bolt/bolts in front of the pedal in the 8, or is this just a weird angle that makes it look like it is in front???

You're correct. In the RV-8, the pivot bolts are on the front side of the pedals. A long bolt doesn't change the pivot point, and doesn't significantly change the way your foot sits on the pedal. According to some people, it may help prevent "stickiness" of the pedal.

This a completely separate issue from the "inadvertent braking" / geometry issue.

Mike S 01-24-2009 11:38 AM

Thanks Buck.
 
Quote:

Originally Posted by BuckWynd (Post 292665)
You're correct. In the RV-8, the pivot bolts are on the front side of the pedals. A long bolt doesn't change the pivot point, and doesn't significantly change the way your foot sits on the pedal.

Thanks, learned something here.

Even with 60+ trips around the sun, still learning.

rickrv8 01-24-2009 12:19 PM

I think it may depend on which style of pedal you're using. I had this discussion with Danny King a couple of years ago and it seems to me that this problem of inadvertent brake application is more pronounced on the ground adjustable pedals. I have the ground adjustable (floor mounted) pedals on my -8 and they exhibit the exact same problem I had with my very early -6 which had floor mounted pedals. The geometry between the pivot point of the pedal and the base pivot point of the master cylinder allows for inadvertent brake when you apply rudder. The brake pedal is forced by the master cylinder to articulate back towards your foot. The more rudder input the further the brake pedal articulates back. Your foot is not able to bend back enough to avert applying brake pressure.

I installed Randy's extensions and like Paul I keep my heels on the floor. I can push the extensions with the balls of my feet and not apply any brake. However, it is quite easy to roll my toes forward and apply brake pressure if necessary. I agree with Paul, if you don't like the extensions they're very easy to remove.

jferraro17 01-24-2009 02:36 PM

Quote:

Originally Posted by Mike S (Post 292668)

Even with 60+ trips around the sun...



NO WAY! Never would have guessed that. Hope I look as "young" in 20 years!
:cool:


Joe


PS. Good topic, I've been researching this in the last week or two.

KirkGrovesRV8 01-24-2009 03:32 PM

Hey Rick!!! Laura saw your post and wanted to tell you hello from Bahama Mama:D



Quote:

Originally Posted by rickrv8 (Post 292676)
I think it may depend on which style of pedal you're using. I had this discussion with Danny King a couple of years ago and it seems to me that this problem of inadvertent brake application is more pronounced on the ground adjustable pedals. I have the ground adjustable (floor mounted) pedals on my -8 and they exhibit the exact same problem I had with my very early -6 which had floor mounted pedals. The geometry between the pivot point of the pedal and the base pivot point of the master cylinder allows for inadvertent brake when you apply rudder. The brake pedal is forced by the master cylinder to articulate back towards your foot. The more rudder input the further the brake pedal articulates back. Your foot is not able to bend back enough to avert applying brake pressure.

I installed Randy's extensions and like Paul I keep my heels on the floor. I can push the extensions with the balls of my feet and not apply any brake. However, it is quite easy to roll my toes forward and apply brake pressure if necessary. I agree with Paul, if you don't like the extensions they're very easy to remove.


rickrv8 01-24-2009 04:43 PM

Off topic....sorry
 
Quote:

Originally Posted by KirkGrovesRV8 (Post 292711)
Hey Rick!!! Laura saw your post and wanted to tell you hello from Bahama Mama:D

Hi to Laura. You need to get that airplane of yours painted so we can head South. Winter's getting cold. Plus, I want to see you kiss your spinner again after flying over all that open water.


mannanj 01-24-2009 05:58 PM

Mods
 
Quote:

Originally Posted by Ironflight (Post 292636)

I have pedal extensions which I installed before I flew an -8 (based on Randy Lervold's design). I have also flown -8's with stock pedals. I like my pedal extensions because they fit the geometry of my ankles and feet - I fly with my heels on the floor, and the tips of my toes on the extensions. I have no problems with sliding my feet up to tap the brakes when I need them - but again, this is very, very dependent on your personal foot geometry.

Fortunately, the rudder pedals can removed with about an hour's work through the forward baggage compartment, so you aren't stuck with how you do them if you decide to change later on. Experiment until you get them right!

Paul

Ditto on Paul's thoughts on Randy Lervold's mod. I installed the extensions on my -8 before I first flew it.

You never accidentally get on the brakes. If you need 'em; they're right there. If you don't like them take them off.

I think you will like them tho.

Danny King 01-25-2009 08:28 PM

Unintended consequences
 
If you put lower brake pedal extensions on your RV-8 pedals, you will not be able to stick your feet through the holes below the pedals, and stretch out your legs on those long flights. Before you do this mod, sit in your plane and put your feet through the pedals and rest your heals on the tubes.
I have flown three RV-8s with extensions including Iron's. I vote to not modify Van's design.

JAT 01-25-2009 10:04 PM

Bill,

Six years ago during the test period I noticed that the aircraft would almost come to a complete stop when I attempted to do a 180 on the runway. During subsequent flights I noticed that the aircraft accelerated when I took my foot completely off the opposite pedal during the turn. My big feet were causing the brakes to drag. I put a 1X1X1/8" aluminum angle on the bottom of the pedal with two bolts, so the arch of my foot would push on the horizontal portion of the angle. This meant that the force was applied below the fulcrum of the pedal and the brake rod was pulled up, not down. I believe the different opinions are the result of the fact that the standard geomerty works for some and some not. The angle works great for me. If interested email me at jpthornton@fone.net and I'll send you a picture.

Jim

mtnflyer 01-26-2009 07:12 AM

to all
many years ago I installed spacers (two inch nylon rod,drilled,split, then clamped to the rudder pedals) with much success,, when building my 7 I went with a set of the Cleveland pedals,,, I like them but they have two drawbacks, one, they are heavy, second and the worst, one can get a toe stuck in part of the pedal just when you need to get on the brake . don't ask.... but that was one ugly landing at 52f... thanks Rod I'm glad you a CFI


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