Parking brake idea

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Dana

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My plane currently doesn’t have a parking brake. It has the low pressure Scott diaphragm master cylinders that include the heel brake pedals, paired with the usual Cleveland brakes. Normally, the parking brake is a valve that blocks the lines to the calipers after applying the brakes with your feet, which would involve some replumbing and additional lines.

The Scott cylinders have a hole in the arms intended to link them to a second set of brake pedals (normally the master cylinders are installed for the back seat of a tandem ship, with a link going to additional pedals for the front seat). I don’t need front seat brakes, but I was thinking of adding cables from the arms connected to an over-center lever like this one (just an example, not necessarily the one I’d choose). I’d probably add a spring for some compliance in the system.

Thoughts?
 

Dan Thomas

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My plane currently doesn’t have a parking brake. It has the low pressure Scott diaphragm master cylinders that include the heel brake pedals, paired with the usual Cleveland brakes. Normally, the parking brake is a valve that blocks the lines to the calipers after applying the brakes with your feet, which would involve some replumbing and additional lines.

The Scott cylinders have a hole in the arms intended to link them to a second set of brake pedals (normally the master cylinders are installed for the back seat of a tandem ship, with a link going to additional pedals for the front seat). I don’t need front seat brakes, but I was thinking of adding cables from the arms connected to an over-center lever like this one (just an example, not necessarily the one I’d choose). I’d probably add a spring for some compliance in the system.

Thoughts?
Would work OK but you might want to use an adjustable overcenter lever like one might see on forklifts and some other equipment. Eliminates the uncertainty of the spring.

Handle control lever by Cablecraft Motion Control | DirectIndustry

Make one out of aluminum instead of the steel used in commercial units.

I flew a SuperCub that had those Scott low-pressure masters and Cleveland brakes. Wasn't impressed. Couldn't hold the airplane against runup RPM.
 

cluttonfred

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This is absolutely no help to you, but the absolute simplest parking brake I ever saw was on a Sky Ranger microlight which has a single center-mounted stick and a single hand-lever for the brakes. The parking brake was a loop of rope to slip over the brake lever.
 

wsimpso1

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I don’t need front seat brakes, but I was thinking of adding cables from the arms connected to an over-center lever like this one (just an example, not necessarily the one I’d choose). I’d probably add a spring for some compliance in the system.

Thoughts?

Dana,

I like it. In an attempt at avoiding a constant chase on the adjustment, you would want a springy connection. Once you have a spring (or a rod with two little kinks in opposite directions to give some compliance) the forces might be a lot lower than the 1200 pounds the original is designed for. So yeah, fab one up out of aluminum, and consider more stroke and less weight. With a springy element in it. I did not invent the double bend - it is has been in car hand brake linkages for decades, and for the same reason.

Bill
 

Dana

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My Scott brakes work pretty good, they hold my plane at runup and even more, though maybe not full power.

I like the Z-bend idea, though an extension spring on a cable would work as well. As I said, the clamp I posted was just an example, I certainly don't need 1200 lbs! It doesn't take much force on the pedals to hold the plane at idle, or against any wind I'm likely to be flying in when stopped at the pumps.

There are a lot of ways the linkage between the pedals and the hand lever could be arranged... pulleys, cables in tubes, bellcranks, etc.
 

Dan Thomas

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In my Jodel I had heel brakes. I needed to hand-prop it, so I either had to tie the tail down or have capable parking brakes. The first affair was a hydraulic dual shutoff valve I built; both brake lines ran through it and a shaft, ground to form a cam over each of two poppet valves, was rotated by a push-pull control on the panel.

But that required climbing into the airplane, getting seated, mashing the brakes and pulling the control. Basic laziness combined with an engineering mind changed that. I used a big heavy vernier push-pull control to pull on a short cable between the two heel brake levers. The control was in the panel, ran through the firewall and looped back through to pull on the brakes. Reach into the cockpit, push the vernier button and pull the brakes on, then give a couple of counterclockwise twists on the knob to pull the brakes on hard. In the end I usually used it and tied the tail down, too. Age = conservative.

1642533410934.png

Available online or at heavy truck shops.
 

Doran Jaffas

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My plane currently doesn’t have a parking brake. It has the low pressure Scott diaphragm master cylinders that include the heel brake pedals, paired with the usual Cleveland brakes. Normally, the parking brake is a valve that blocks the lines to the calipers after applying the brakes with your feet, which would involve some replumbing and additional lines.

The Scott cylinders have a hole in the arms intended to link them to a second set of brake pedals (normally the master cylinders are installed for the back seat of a tandem ship, with a link going to additional pedals for the front seat). I don’t need front seat brakes, but I was thinking of adding cables from the arms connected to an over-center lever like this one (just an example, not necessarily the one I’d choose). I’d probably add a spring for some compliance in the system.

Thoughts?


I keep a set of wheel chocks in the airplane. Less hassle. Not very good in windy conditions though. In which case I had tie-downs LOL
 

Vigilant1

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Is it tough on the hydraulic seals in airplane brakes to keep them under pressure whenever the plane is parked? Any problems with the cylinder bores/oxidation if the brakes are on all the time (so the seals are now parked within their normal "working range", not at one extreme). Okay for the disks and pucks if they are kept in contact (maybe wet)?
Over all, if small aircraft brakes weren't designed to be used continuously as parking brakes, should we expect increased maintenance or other issues?
 
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BJC

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Is it tough on the hydraulic seals in airplane brakes to keep them under pressure whenever the plane is parked? Any problems with the cylinder bores/oxidation if the brakes are on all the time (so the seals are now parked within their normal "working range", not at one extreme). Okay for the disks and pucks if they are kept in contact (maybe wet)?
Over all, if small aircraft brakes weren't designed to be used continuously as parking brakes, should we expect increased maintenance or other issues?
I find parking brakes very useful for entering / exiting the aircraft, for starting and mag checks, and for stopping at fuel pumps, tie-down spots, etc. But I don’t leave them set. Like DJ, I carry chocks, and use them.


BJC
 

Dana

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I find parking brakes very useful for entering / exiting the aircraft, for starting and mag checks, and for stopping at fuel pumps, tie-down spots, etc. But I don’t leave them set.
Thatone
 

Dan Thomas

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Is it tough on the hydraulic seals in airplane brakes to keep them under pressure whenever the plane is parked? Any problems with the cylinder bores/oxidation if the brakes are on all the time (so the seals are now parked within their normal "working range", not at one extreme). Okay for the disks and pucks if they are kept in contact (maybe wet)?
Over all, if small aircraft brakes weren't designed to be used continuously as parking brakes, should we expect increased maintenance or other issues?
Those seals are usually O-rings, and constant pressure on them deforms them and they will start to leak when relaxed. I worked regularly on one airplane in which the owner used those parking brakes all the time, and we had to replace the caliper seals constantly. Didn't do the masters any good either. The parking system pulled on the masters.

The caliper seals gradually move outward as the lining wears. Corrosion in the bore is a problem anytime moisture can get in there, and any other pollutants only add to the corrosion process. The small, normal amount of oil that seeps past the seals also mixes with water and forms acids that eat the metal. These things have no dust boots on them like car calipers do.
 
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