Brake lines

[Battson]

I have personally seen plastic/nylon lines fail twice (once on Patrol & once on an RV) when used in the high pressure areas. Theoretically they should handle the pressure fine. But I have seen them fail twice. Mark

You've told me before, but I forget - did the actual plastic tube fail in some way, or was it the end fittings which let go?

[Mark Goldberg]

In one incident heavy braking melted the plastic line going to the caliper (RV). And the other incident was a Patrol where the line rubbed and developed a BIG leak. Luckily, it was at my ranch and I had the fittings and line so the owner could make a provisional repair to get home. Mark

[whee]

I snapped a pic of my pedals with some of the Aeroquip hoses and one reservoir installed. I completely agree with making the airplane easy to maintain. I don't have any trouble reaching theses master cylinder mounted reservoirs. I don't have any real experience flying a airplane equipt with hydraulic brakes so I don't know how often the fluid should be checked but I can say that when I've flown with others they didn't check the brake fluid level.

[James]

Yeah Whee - you've answered a question I tried to ask elsewhere - you've connected your brakes L-L, R-R with a crossed line in the middle - did this setup work ok for you mate? That way, you've got the RH and LH flex lines to the wheels already on the outboard side of the outer pedals. :-)

James

[whee]

Zero issues with it so far.

[Battson]

I don't have any real experience flying a airplane equipt with hydraulic brakes so I don't know how often the fluid should be checked but I can say that when I've flown with others they didn't check the brake fluid level.

I have clear lines from my reservoir to my cylinders like Mark does. I check the fluid level EVERY time before I land by looking between my feet, its part of my GUMP / BUMP check. If I see pink in the tubes, I know I have a green-light for braking during landing.
If one of the brakes has leaked down, I want to know before I cause a ground loop. I know a lot of people who've written off planes when one brake failed. I figure this check it could save my plane one day. It also mitigates the risks of the plastic tube failing - at least I can see the failure.

[nichzimmerman]

I have clear lines from my reservoir to my cylinders like Mark does. I check the fluid level EVERY time before I land by looking between my feet, its part of my GUMP / BUMP check.

I had master cylinders with built-in reservoirs on my Pacer and never thought about checking brakes other than observing their operation on taxi. One day I do a wheel landing and as the aircraft slows down I try using a little right brake to help with keeping her straight. The pedal goes all the way down with no resistance and I end up ground looping. Post flight reveals very low fluid in the cylinder and I was able to "pump up" the brakes to work again, which I believe means air was in the lines. Amazingly, the only damage was to the drooped wing tip but it could have been a lot worse. I had not realized the safety implications of Battson's setup but now that I do I will copy him.

[whee]

I check the fluid level EVERY time before I land by looking between my feet, its part of my GUMP / BUMP check. If I see pink in the tubes, I know I have a green-light for braking during landing.

That's a great idea. I'm surprised that you can see the lines while flying though. We are similar height and the only what I'd be able to see my feet is if I slid my seat back. But those plastic lines do provide the opportunity to check fluid level during preflight.

[JimParker256]

A guy I know did significant damage to his Grumman Traveler (not once, but twice!) because he did not / could not check his brake fluid level. That airplane has castering nose gear (like an RV) and relies on differential braking for directional control on the ground. The first time, he wound up running the plane into the side of a hangar, damaging the left wing only. The second incident was much worse, as he ran the prop and right wing into a parked Mooney – absolutely totaled that airplane, and did $40K worth of damage to his own plane (worth about $50K at the time).

I think I'm going to follow Mark's example the brake fluid reservoir attached to the engine side of the firewall, plastic tubing to the "reservoir" side of the master cylinders. Then Aeroquip lines to the parking brake valve, hard lines from the valve to just inside the gear leg attach point, Aeroquip lines for that "flex" connection. The gear legs will have hard lines inside the "faired" area of the gear, and Aeroquip to the brakes themselves. I'm going to use a clear brake fluid reservoir (ACS) so that I can easily check the fluid level on every pre-flight, and I like Battson's idea of visually checking the line between the firewall and brake cylinders for visible brake fluid before applying the brakes. I'll have to add that to my checklist, and figure out a way to rig a mirror or something to avoid contorting...

Man, I love these forums!

[Battson]

I'm surprised that you can see the lines while flying though. We are similar height and the only what I'd be able to see my feet is if I slid my seat back.

You do have to lean over sideways a few inches, but it's not too hard to see under there. But that said, I do have relatively long legs and a short torso!

[whee]

You do have to lean over sideways a few inches, but it's not too hard to see under there. But that said, I do have relatively long legs and a short torso!

Thats the difference; I have short legs and long torso. Another thing is I like sitting really far forward.

[Bcone1381]

I have always set up my planes the same - and of course think this is the best way. Plastic lines from the fluid reservoir on the firewall to the master cylinders (no pressure), then the Aeroquip made up lines from the master cyls to the fuselage/gear leg intersection, then hard aluminum lines down to the brake caliper. Has worked well for me all these years. I have never had to replace anything. N303AP has over 1,100 hours.

..... Mark

Digging up an old..ish post......

When hard aluminum tubing is from the top of the landing gear leg, all the way down to the caliper, verify for me what type of aluminum tubing is typically used...... I am looking at Aircraft Spruce, specifically, I don't want to assume, but are we talking about 5052-0, 1/4 inch, .035" tubing?

Maybe 1/4" 3003-0 soft flexible Versa Tube?

[Mark Goldberg]

Either would be OK. But I would use 5052 here. And the line does not straight to the fitting on the brake caliper. You make a little curve so the line can flex some. Mine is kind of a half loop right up to the caliper fitting.

[N942VT]

5052 - 7 years no problems but you've got to have a stress loop in it like Mark describes. Otherwise a short flex line.

[S Lathrop]

I will pass on my experience with brake lines from 40 years of building race cars. Now the line pressures in race cars are way higher than an airplane. Vibration frequencies are much higher but no where as long as in an airplane.

What I found was I had more issued with connections. So I worked to minimize the number of connections between the master cylinders and the calipers. I ran -3 braided lines from the master cylinder to each front caliper and at the rear I ran the same lines to a tee, then to each rear caliper.

Now it is common for the front suspension to run a line from the master cylinder, through a tube built into the front lower a-arms and then to the caliper. I have been thinking about doing this on my 4 place brake system. The tube would be in the gear leg so replacing a worn line would be quite simple. I have not cut metal on this idea. Frequently the lines in the a-arms are -2 size.

Just throwing out the idea for input.

[AKKen07]

I hear several people in different threads as well saying that 5052 is preferred over the versa tube. Is there any reason the versa stuff would not be fine for the gear legs? I don't have a tubing bender yet so I figured I'd use versa here... Thx

[Collin Campbell]

I have used the 3003-0 versa tube in the gear leg with no problems. I think 3/16" is adequate...more flexible than 1/4" . The loop at the bottom is important for the calipers to move. I like to exit the brake line on the bottom of the gear leg and loop it around the back side and up to the brake fitting.

[jim.mclaughlin924]

Agree with Collin here, 3/16 tube and -3 hose. I have used earl's speed seal hose and fittings several times with no problems;

[AKKen07]

Thank you Gents!

[Battson]

I need to add to this post - a caution:

Following maintenance of our plane, I had new calipers installed and needed to brake continuously and heavily for many minutes to wear the calipers in.
During the maintenance, I tightened all the brass end fittings on the PLASTIC brake lines around the pedals (only place I have plastic hose is around the pedals). But there was one fitting I couldn't reach.

During the ground braking work, I pressed especially hard and blew the plastic hose out of the brass end fitting. This caused an instant loss of brake control on one side, and a bit of a mess to clean up.

I have say, even at taxi speeds blowing a brake hose makes the plane hard to control. During a landing roll, there would be a high risk of ground-looping if you had an instant loss of brake pressure.

[James]

Hi Guys,

my plane's progressing along nicely, the brakes are installed, and I've routed the flex lines between the LH and RH brakes. Now I need a bit of guidance:

1) Every builder I've seen on this forum has pilot's and copilot's brakes set up as a pair, "in series" - e.g. the bottom of the pilot's LH master goes to the top of the copilots LH master, and the bottom of his RH goes to the top of the copilot's RH master. In my set up, the two inboard pedals supply the two outboard pedals via crossed tubes, and then the flex lines to each MLG assy run straight from the outboard pedals. Mathematically, it gives the same outcome, and it saves two extra brake lines crossing the cab, but is there a reason this setup should be avoided?

2) Can someone (or many of you!) supply me a good photo of how the flex lines run from the pedals to the MLG assy? I haven't built the tunnel or floor sections yet, and I'm not sure how the line "pops out" of the fuselage and into the elbow between the gear attach lugs. I need to go through the bulkhead under station B, but there won't be a bulkhead fitting. If there's a particularly good routing solution, I'll get Jared to add it to the bearkhawk tips (with the owner's permission, of course).

Thanks guys, it's great to be able to connect with people on this forum, makes your little project feel like part of something big and exciting :-)

James