Purpose

This is a blog containing the build history of an experimental home built airplane. The RV-7A is a two place, piston powered, low wing, tractor configuration, tricycle gear, aluminum and composite aircraft. The original purpose of this blog was to document the construction of my experimental category aircraft in order to satisfy the build log requirement for the FAA. Now it's just for the amusement of friends and family as I document some of our aviation experiences. For more information on the RV series of aircraft see www.vansaircraft.com.

Wednesday, November 20, 2013

Step 10.3, Brake lines

I gave myself a stern lecture about keeping the work area tidy.  In time, it became apparent that I just wasn't taking myself seriously and that the warning was unlikely to have any effect, so I fired myself.

Moments later in an act of diabolical shrewdness, cunning, and business acumen that would make captains of industry blush and Wall street tycoons salivate, I hired myself back at half my former salary.

It's true that I would be receiving half of nothing, but I was happy to be building an airplane once again.


I decided to install a parking brake system.  And by system, of course, I mean a simple valve that can be closed when the brakes are depressed to maintain pressure on the brake calipers.  Sounds easy enough,  I need two valves, actually, because the airplane uses differential braking to steer on the ground. The left and right brakes are completely independent.  But I also want the two valves to open and close and the same time, so what I would really like is a dual valve with a single stem. Fortunately such a valve is produced, albeit at an astronomically high price.


I looked around the internet and found that only about half of the RV7s built are equipped with parking brakes.  I decided to ally myself with the camp that is willing to add 8 oz. to the airplane to prevent it from rolling away before the chocks can be employed.

I found a location for the valve that does not require any linkage to actuate the brake and that location is also generally along the path of the brake lines so very little additional brake line is required.  The location of the valve is behind and just to the left of the auxiliary fuel pump.  The valve lever extends through a slot cut in the fuel tank selector valve cover.

Here is the location on the outside of the cover as I measure for the lever slot.


The valve is supported between the fuel valve cover and a support that is riveted to the floor.


The valve temporarily installed so that the brake lines can be plumbed.


The lines take a few turns, but it's really just a matter of understanding the radius of the tubing bender to make everything come out right.


Here's the first line connected.  It's the left side output.  Note that the aux fuel pump and fuel valve are temporarily removed.


It's tight quarters trying to get flared ends on the tube after it is bent and routed.  There's probably a better way to do this.


From the it goes without saying department: It's much easier to flare the ends when the brake line is still on the bench.  Perhaps we should change that to it goes without reading department.


And now the aux fuel pump and fuel tank valve are re-installed.  The parking valve fits nicely to the left of the fuel selector valve and behind the aux fuel pump.


On the fire wall, the hard lines terminate at these bulkhead fittings.  Flexible lines continue up from here to the rudder pedals where the brake cylinders are mounted.


The rudder pedal assembly is dropped in and the brake reservoir is added to the firewall.


The reminder of the brake lines are flexible nylon.  Here is the routing from the brake reservoir down to the passenger side.


The brake lines then continue from the high pressure side of the passenger brake cylinders to the low pressure side of the pilot cylinders.


The final segment of the fuselage's brake system are the hoses from the high pressure side of the pilot brake cylinders to the firewall mounted bulkhead fittings.  Apparently, they come in the finish kit which has not yet arrived so I'll just call this step complete for now.  Notice the precision impacting instrument in the lower left of the photo above.  It's remarkable how frequently this device is required.  

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