Squawk list burn down

I had a week off from work due to the 4th of July holiday, a few vacation days and a summons to appear for a Grand Jury!! I didn't get picked for the Grand Jury, but it sure wasted 1/2 a working day!! All of This means I got to work on my Robin for long uninterrupted periods. My original plan was to assemble the airplane at Midway Airport near Midlothian Texas, but cooling problems, traced to a bad head design, and carburetor leakage side tracked me from all of the small final jobs. The MZ 34 cooling issue was first on my plate, I discovered a few weeks ago that the head was retaining too much heat and when I tried to shut her down, she continued to run in diesel mode. This turned out to be a poorly designed head, why I had to pay for a new head, is beyond me and making me consider my choice of engine, but non the less, I received a new redesigned head from Compact radial engines and when I installed it, It seems to have solved the heating problem.

MZ 34 with new head

The new head has about 40% more cooling fin area, it does however completely screw up my old baffling system. I have not run the new head with a baffling system yet, or the cowl. If I have to, I will do the first flight without a cowl. The engine is cooling very well and it seems I may have to rethink my cowl design. I will however try to run it first with the baffle on to see how it behaves. After I got the engine running with the new head, I discovered that the carb was leaking gas when it was shut down. In addition, the engine was not running very smooth and it was almost impossible to warm start. I started doing some online research and came across a very good web site http://www.aerocorsair.com/index.htm. They also make a good engine!!! Anyway, I determined that the problem was probably an incorrectly set pop off pressure on the main float needle. The web site has a very good step by step troubleshooting guide and for this project I invested in an automotive cooling system tester. The web page shows how to modify this so you can set the pop off pressure. The Tillotson HR carb should have held 8 psi indefinitely. But when I tested it, it started leaking at 3 psi, this obviously was the root of my problem. when I applied the pressure tester to the fuel inlet as I mentioned, it immediately bled down to 3 psi. I then disassembled the pump housing and inspected the gaskets. Nothing seemed amiss. I then applied pressure to an alternate port and I noticed fuel leaking past the needle seat. When I pulled the needle seat out, I noticed a mangled copper gasket. It appeared that the gasket wasn't fully seated before the needle seat was installed. Of course I didn't have a new needle seat copper gasket in the rebuild kit, so I made one by hammering flat and then annealing a section of copper tubing. once I trimmed it and installed it, the carb held 8 psi and "popped off" ay 11 psi just like it should. I then ran the engine for another 45 minutes and almost finished with the ground break in.

Another nagging issue with the design, was the final design of the seat. All along I knew I needed to build a head rest, but I didn't think it would be a big deal. My friend Ed came over and we shot a series of  pictures with mocked up head supports. It became apparent that by just supporting the head, the pilot would be choked, because his upper shoulders were not supported. I decided to modify the seat to add the upper support. This was quite easy because of the way the seat was made.  sanded off a 4 inch wide section of the inner skin and exposed the foam core. I made two patterns out of Styrofoam and then clamped the seat the form blocks. I then lain up another ply of 8 oz fiberglass over the core. 

bonding supports

  The next step was to build a support from the roll over cage to the back of the seat. This part has to be substantial, as it will see heavy compression load in the event of a crash. I made the support and side ribs from .032 aluminum sheet.

upper seat support

I need to rebuild the triangular rib and adjust the flat pattern slightly. But this shows the support clearly. I will build a light weigh aluminum head rest on top of this. That will support the head cushion. The white color by the way, is protective plastic that will come off eventually.









Another project was to do the final rig of the ailerons and cut a cable exit slit in the wing.

Right wing and aileron

This is a picture of the right wing, the left wing was already finished.











Where the wing interfaces with the fuselage, there are slits that needed to be cut in the fuselage skin for the leading edge attach fitting and the aileron cables. I located the areas, added fabric doublers and then added felt seals.

Felt exit seals

I will touch up the paint after I am done adding the seals.

Leading edge felt seal

Before a doubler is added, the old paint is removed with a solvent wipe with MEK. It works quite well!!











I am continuing work on the seat support and head rest. Nest week I should have the final engine run with the cowl and baffle, hopefully this is all I will need to do before the first taxi test.

New head

I have been having overheating problems with my engine. I was completely stumped as to the reasons. I contacted Compact Radial Engines and Leon Massa told me that he had redesigned the head for the MZ 34. Turns out I was not the only one. The difference in the head is huge, there is at least 40% more fin area. One issue I was having was the engine started Dieseling on me, it wouldn't shut off. Initially I thought the reason was the smaller head, but when I started to strip the engine down to replace the head, I discovered the real reason. All of the head bolts were loose and a great deal of exhaust was blowing by the head gasket. This caused the head to fail to transfer any heat, and also heated up the head. Here is a picture comparing the old head (blue) with the new one.



as you can see there is a big difference. it still will fit under the cowl however, but I will need to rebuild the baffling. I am going to install the head and carb without the baffling, cowl and spinner. I may try my first flight in that configuration. I'm spending the next 5 days getting ready for the first taxi tests. I will update again next Sunday














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