comfortcat

comfortcat

Well Known Member
Friend
Greetings!

I almost NEVER go off-plans for anything. I'm a systems analyst, not an engineer. BUT after looking at the VAF postings about rudder pedals, I thought I would have a look.

First, spending $50 on four bolts to solve a problem that may not be a problem at all seemed pretty excessive to me.

I saw guys buying steel, aluminum and brass rod, taping it, and bolting it into place as an alternative to bolts but I also saw that as a little excessive.

So, I bought a bit of 3/16" brass rod, cut to size and drilled it for a cotter key. Here is the result.

Can anyone think of ANY reason why the shaft would need to have a nut? (by th way, i used s 5/64 drill to do the hole)

Thanx!

142bxhu.jpg


2n0uclk.jpg
 
My opinion---------looks like it should work fine, it achieves the same effect of using a long bolt, that being getting the pivot axis in line.

My only concern is in a hard braking situation, you are going to put a lot of sheering force on a piece of brass instead of steel.
 
David,
Off topic observation....all parts get filed or sanded smooth, with rounded edges. It is a metal fatigue issue as well as pride of craftsmanship thing.
 
Mike S said:
My opinion---------looks like it should work fine, it achieves the same effect of using a long bolt, that being getting the pivot axis in line.

My only concern is in a hard braking situation, you are going to put a lot of sheering force on a piece of brass instead of steel.
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The shear force is way higher than 500 lbs. so should not be a problem...:)

Wear from the brass rotating inside the steel tab might be a problem though.
 
Corrosion

I seem to recall that brass and aluminum don't get along well, but I could certainly have it wrong. Engineers, what say you?
 
Sorry guys

But I used a length of all thread, appropriately sized, from Home depot aviation stores, stop nutted appropriately.

Maybe not the most craftsman like, but effective, simple and cheap.

PS - I think the brass is fine.
 
;559292 said:
But I used a length of all thread, Maybe not the most craftsman like, but effective, simple and cheap.

PS - I think the brass is fine.
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Read post three.................
 
Good looking work Dave!

What you have done appears to have been done carefully and with skill. They look great! I can not condone or condemn your efforts from a structural basis. That would be up to a materials engineer to run the numbers and perform physical fatigue tests.

My son is starting his 3 year at Cal Poly San Luis Obispo, and guess what his Major is? Mmmm Materials engineer and and considered a senior already because of all the grades and credits that he has.

He had a great time analyzing the grain structure of some of the bolts from our business.

He wont be back in school until September and unless you are ready to fly that would timely enough to get some results, just for fun.

Just let us know if that interests you. Of course I must ask him first.
 
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Since this is on the rudder support, it is steel and brass. No aluminum here.

Thanx for the feedback! I love this site!

szicree said:
I seem to recall that brass and aluminum don't get along well, but I could certainly have it wrong. Engineers, what say you?
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Brass and aluminum

Brass and aluminum are far apart on the electrochemical series. Any moisture between the brass rod and the aluminum angle will cause a corrosion problem with the aluminum. Brass and steel work well together, in fact many steel shaft bearings or bushings are brass or bronze.

The workmanship or the rod is fine although personally I would rather see a threaded nut with a cotter pin on each end. As previously mentioned, the brake cylinder side plates don't look like the edges were filed/polished.

So you can keep the rod as is but make sure the pivot is lubricated and inspect it during your annual. Or you could get a piece of thin wall steel tubing to put around the brass rod and go between each angle on the brake pedal. Or you could get the AN steel bolts which are cad plated. You could get some steel drill rod, but then you would have to paint it or plate it to keep it from rusting.
 
Nuts? You know there are about a hunnerd zillion cessnas out there with a hollow aluminum rod & 2 cotter pins in each pedal. Never seen one come loose and with proper neglect, they seem to last about 50 years.
 
and you could

obsess over this for the next month or so, run around looking for the perfect solution, do some engineering analysis and fly sometime in 2028.

Or you could knock it out in an hour or so with a reasonably good solution that will standup well in this relatively low stress application and get flying before your 2nd class medical is a distant memory.

The vast spectrum of builder standards exhibited on these pages never ceases to amaze me. They are all good in their own way as long as you build it the way you want it and build it safe!

YMMV, IMHO, etc etc. Fly on!!

PS- disimilar metal corrosion should only be a problem in the presence of an electrolyte - assuming you are not taking your RV swiming on a regular basis, it is of little practical concern here.
 
gereed75 said:
obsess over this for the next month or so, run around looking for the perfect solution, do some engineering analysis and fly sometime in 2028.

Or you could knock it out in an hour or so with a reasonably good solution that will standup well in this relatively low stress application and get flying before your 2nd class medical is a distant memory.

The vast spectrum of builder standards exhibited on these pages never ceases to amaze me. They are all good in their own way as long as you build it the way you want it and build it safe!
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I agree....and along that line, it's also suprising that if you just go build it to the plans it ends up working fine as well! Often one will find that in the time it takes to discuss a solution looking for a problem you can just go build the the part acceptably and be done with it!

My 2 agreeable cents as usual!

Cheers,
Stein
 
I did the exact same thing on mine, except I threaded both ends and used castellated nuts and cotter pins (what a pain that was:rolleyes:). I've stepped on the brakes pretty hard and in 2 years of flying it still looks 100% and the brakes easily back off when released, which is the purpose of using the single rod vs. two bolts. My experience supports your approach.
 
Wear of the brass rod

I'd be worried about wear of the rod over time from repeated movement of the pedal pivot flange, brass isn't very good at resisting wear as in your application, if you can make up some sort of bussing to go over the brass rod that will help, make sure you retain the bush so it doesn't migrate away from it's intended location, seams like a lot of work to re-invent the wheel, personally I'd stick with bolts, strong, proven..

My 2 cents worth as well..
 
SteinAir said:
I agree....and along that line, it's also suprising that if you just go build it to the plans it ends up working fine as well! Often one will find that in the time it takes to discuss a solution looking for a problem you can just go build the the part acceptably and be done with it!

My 2 agreeable cents as usual!

Cheers,
Stein
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+1 Mine is done as per the plans and I've not seen a problem yet. I haven't looked, but I'm not sure why this modification even needs to be considered.
 
Sonny,

There have been a number of instances where the brakes did not fully release after applying them, and quickly wearing out the brake pads and/or causing overheating of the brakes while taxiing. The cylinders must fully expand after being compressed to allow the fluid to flow back thru and release the pads. The design of using two short bolts is more apt to stick and not fully extend the cylinders, preventing the fluid from flowing back to the master cylinder from the brake cylinders. An associated fix was to put springs on the brake cylinders to help them fully extend. The single bolt or rod thru the pedals prevents the axle from "cocking" slightly and binding in the nearly released position. You think the brakes are off, but they rub slightly at this point. I'm sure as much as you read the posts you've seen some of these, but probably forgotten :D
 
Spring mod as well...

I am doing the spring mod as well. There is a real issue about fixing problems that do not really exist, and brake drag might not occur in this plane. BUT addressing these issues now is easier, low risk and low cost compared to later if they pop up. SteinAir sells VERY EXPENSIVE electronic circuit breakers/power management systems because of the possibility of

"overall electrical system failure"

because a fuse or manual breaker might fail.

Since we are the builders, we get to look at literally thousands of builders who have gone before us and decide where we want "version 2.0"

Dkb



trib said:
Sonny,

There have been a number of instances where the brakes did not fully release after applying them, and quickly wearing out the brake pads and/or causing overheating of the brakes while taxiing. The cylinders must fully expand after being compressed to allow the fluid to flow back thru and release the pads. The design of using two short bolts is more apt to stick and not fully extend the cylinders, preventing the fluid from flowing back to the master cylinder from the brake cylinders. An associated fix was to put springs on the brake cylinders to help them fully extend. The single bolt or rod thru the pedals prevents the axle from "cocking" slightly and binding in the nearly released position. You think the brakes are off, but they rub slightly at this point. I'm sure as much as you read the posts you've seen some of these, but probably forgotten :D
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