Maatco parking brake

[Pbruce]

I plan to mount a Maatco parking valve in my QB Patrol. It’s the dual-brakes model with the lever which can go on either side. Trying to decide location. Looking for recommendations.

Also, it came without instructions. I have seen one schematic of installation online, but it can’t be considered installation instructions. Does anyone have a picture of an installation or other resource to guide me? Thanks in advance.

[jaredyates]

It's not too late to omit it... But if you really want to install it, I thought it was useful to put it in the transition from the pedal flex lines to the hard aluminum lines that lead to the top of the gear leg. You are going to end up with some kind of fitting there, so it mitigates the parts count a little. This will probably end up being somewhere between the pedals and near the floorboard and firewall intersection.

[Pbruce]

Thanks. Most helpful. Not sure why I want to omit it? I want to keep the plane from rolling away/swinging in wind on sloping ramps.

[whee]

The reason to omit is because it is the source of a potential failure with significant consequences. Consider Rob C’s experience from not too long ago. I left it out because knew of two BHs and a couple planes that were wrecked due issues with the parking brake. Some pilot caused, some mechanical failures. But there are likely more airplanes flying WITH parking brakes that have not issues than those that have.

My plane hasn’t rolled away yet.

I didn’t use any hard lines in my brake system. Summit racing flex lines were too cheap and easy to work with for me to mess with hard lines. If I were to install a parking brake I’d put in on the firewall between the two sets of pedals and run flex lines accordingly.

[Nev]

Hey Whee, any details on the the aircraft that were wrecked due to parking brake issues so we can learn from them ?

[whee]

Nev, I truly wish I had the information in front of me so that I could share details but that isn’t the case. It was too long ago and I don’t want to share inaccurate info. My takeaway was that enough airplanes had been wrecked due to parking brake issues and I’d never had one before so I elected to not install one. I had planned on installing one till a fellow BH builder shared his experience wrecking his BH due to a failure of the brake. I then looked into it more, NTSB reports, asking the pilots in my sphere, and there where ample examples of wrecked airplanes. One brand of parking brake showed up more often but they have since re-designed their parking brake so I think it is a nine issue.

[Nev]

Thanks Whee. I gather that with designs such as Matco and similar, prior to having a choice of two arms, the cable could flex into an over-centered position which would reverse the function (from OFF to ON). This concerned me alot. I gather they've introduced the additional arm so the best position can be used to preclude this.

[Nev]

Respectfully, I have a different position on this. If we decide to omit various aircraft parts because one caused an issue on someone else's aircraft, I wouldn't have many parts at all left on my aircraft. However, if there was a documented history of the same part failing on many different aircraft then it'd have my full attention.

The Matco and other similar park brakes come with two arms, each is designed to suit a different installation position, and is designed to reverse the panel knob position from ON to OFF to accommodate different installation positions. One arm will have the Park Brake ON in the knob OUT position. If you change to the other arm, it will offset by 45° and the park brake ON will be in the knob IN position. Obviously, correct installation is paramount to avoid the brake being ON when in the OFF position. (Same for the engine, fuel system, etc etc). It can be a good idea to use lock wire on the park brake cable to prevent it from slipping during flight.

I was very lucky to learn from the experiences of others posted here (huge thanks Rob). As a result of that, prior to first flight, we raised the wheels clear of the ground and ascertained that the Park Brake was operating in the correct manner. Rob also caught the issue prior to his first flight, during the test phase. That's exactly why we have a test flying phase. Likewise I found other issues with my own aircraft and rectified them during this time.

One thing to be aware of with the park brake is that if it is set to ON and no pressure has been applied to the brake pedals yet, the aircraft will taxi just fine. However with each subsequent application of brakes as you steer it etc, the pressure will build in the system. Eventually you won't be able to taxi at all. Turning the park brake OFF will release all system pressure. This is not a problem, but if the knob activation was accidentally reversed by using another arm, the issue may not become apparent until brake pressure is applied.

Here's how I did mine:

8C86C403-75B3-4F07-8E48-9E93A657264D.jpg

6E680148-2FBB-4371-99A2-7DD481EE0C6D.jpg

4E340769-C7E8-4E8D-A6CF-B5B827980859.jpg

[svyolo]

I bought one, installed it, then omitted it. Parking brakes are not counted on in any military/commercial application other than the few seconds it takes to install chocks. We had a squadron a/c damaged by a Harrier where they forgot to install the chocks. Larger aircraft have a hydraulic accumulator to maintain pressure, for a while, but they bleed down.

I have limited GA experience, but lots of experience in mil/com. We don't trust them there, so I deleted it in my build.

If it is not there, it doesn't weigh anything, and can't fail.

[Archer39J]

Not coming up when I search, what issue was discovered with the matco valve to make folks not install it? Seems pretty straightforward to me.

[Pbruce]

Thanks for the info (and opinions) all. Good points raised about not relying on it, and understanding its limitations. I’m sticking with it. The unit I have has only one arm, but I gather it can be oriented as desired by rotating the two halves of the brake body relative to one another. No sure about this though.

Nev, does your park brake lock pressure on when cable is pulled? (when used normally, as intended)? Releases pressure when pushed? Must foot brakes be applied while engaging the parking brake and releasing it? Or only when engaging?

[Nev]

Not coming up when I search, what issue was discovered with the matco valve to make folks not install it? Seems pretty straightforward to me.

https://bearhawkforums.com/forum/bea...ve-brake-issue

and

https://bearhawkforums.com/forum/bearhawk-general-discussion-news/64261-need-brake-bleeding-education

[Pbruce]

I’m wondering about mounting the unit on or under the plate holding the gascolator and fuel valve. This would eliminate the cable, requiring only a handle or grip on the lever. Besides the issue of kicking it, is this a valid idea for the PATROL?

[Nev]

Nev, does your park brake lock pressure on when cable is pulled? (when used normally, as intended)? Releases pressure when pushed? Must foot brakes be applied while engaging the parking brake and releasing it? Or only when engaging?

Mine is a valve that closes the brake lines when I pull the knob out. Then if brake pedal pressure is applied, it is locked and holds the pressure. Then when the valve is turned OFF (push the knob in), the pressure is no longer held so the brake is released.

To set the park brake, I can pull the Park Brake knob to the ON position while holding pressure on the brake pedals. Or, I can pull the knob ON with feet on the floor (the wheels are still free to move), then press the brake pedals to build pressure.

To release the Park Brake, you just need to push the knob in (not like the Boeing where you stomp on the pedals to release).

The situations that are being discussed in the threads above, is where the Park Brake is inadvertently set ON during flight, or a malfunction occurs such as the cable slipping or going over-center that causes the brake valve to go to the ON position. Then when the brake pedals are pressed, the brakes will lock on. When landing, if the pedals haven't yet been pressed, the wheels are free to rotate. But during normal braking the pressure will build and cannot be released until the PB is pushed back in.

So for this to occur it requires the PB to be set ON prior to landing(or a malfunction), AND enough brake pressure to be applied to flip the aircraft.

[Lee]

Well Pat, once again your timing is impeccable. I have that same Matco valve about 90% installed under the floor as described by Jared. That Matco valve is just a simple ball valve so it's installation is really pretty straight forward if one pays attention. For me front seat brakes only and the lines take a continuous uphill path all the way to the reservoir. Just need to weld in tabs for the mounting bracket. Now I am wondering if I really want to finish it or just leave it out. One of the local serial builders that's a regular visitor to my hanger keeps telling my that I don't need a parking brake. Guess I need to think on this some more. Attached some pix of the mounting bracket early in the build. Thanx for the links Nev.
Lee

[zkelley2]

I'm pretty sure I know of over 10 airplanes that are now at the scrap yard from a parking brake. Mostly cessnas and pipers. I've even seen big jets have brake failures and end up blowing most of the tires.

I'd be willing to bet I land and park on significantly steeper slopes than most, and wildly more than any ramp has ever been. I've never needed one, or had an issue with the airplane rolling away.
If it's steep enough, I chalk and tie it down, there's not a chance I'd trust that to a parking brake. I'd be worried I'd come back to an airplane at the bottom of a canyon.

[rodsmith]

I recall a Bearhawk rolling into a hangar and damaging the tail before the pilot could get it chocked. With or without a parking brake it pays to be vigilant in choosing parking spots. I like Nev's approach to carefully checking the function before starting taxi tests. I have one installed, will probably stick with it, with awareness of possible issues.

[spinningwrench]

Here is the installation of a Grove brake valve. Has the same two position function as the Matco. I have fueled my Citabria on many windy days and not having a parking brake would have made it very difficult especially if there is any slope to the ramp.

Patrol Brake Valve-S.jpg