Saturday, October 15, 2005

Swapping the engine on the MX

I arrived about 8:00 and made preparations to install an engine on my MX. Last weekend, I took the provision 8 503 off of the MX and moved it to it's perch on top of the Phantom's keel tube. Of course, this left me in a non-flyable condition which can't be tolerated very well.

Some time back, before and during my neck surgery recovery, I rebuilt a points-type 503 engine that I purchased on eBay. This was the engine that I was going to swap back on to the MX. It's the first Rotax that I've completely rebuilt, even replacing the PTO-side crank bearings. I've pulled heads off of Rotax engines before, and completely disassembled a few, but never re-assembled one until this 503. Of course, I was very carefully during assembly and had no problems. I was a bit paranoid about the case sealing, but it went well as did everything else.

While I was working on the details, my friend Dean drove up and I took a break and sat down and chatted with him for an hour or so. Dean is a great guy. He told me that he had decided that he would re-build the wings from his Ultra-Piet that he sort-of crashed last month after his engine quit after take-off. He was at about 300 feet AGL and had to put the plane down in a short field. He ran out of room an had to put the wings between two trees. The fuselage, prop and engine escaped damage. See my post from Saturday, September 17th for pictures. When Dean left, I got back to working on the MX.

It took me slightly less than one hour to actually mount the engine on the MX. Getting the angle relative to the coupler and driveshaft took a couple more hours. Everything was going just fine until I installed the exhaust manifold. One of the bolts stripped out as I was tightening it. I left it as tight as I could with the intentions of fixing it at a later time. Everything else went according to plan when noon came around, I was ready to test run. After I pulled the plane out of the hangar, I gave a squirt of primer and pulled the rope. The engine didn't fire, so I pulled again. Gas started pouring out of the fuel line, which I had forgotten to attach to the carburetor. Idiot! After securing the fuel line, I squirted another shot from the primer and pulled the rope. It fired! It died of course, but after a bit more priming and another pull, it started right up! I pulled the throttle up to a very high idle and this is when I noticed my Tiny Tach reading was way off! Oh, I guess I need a model 1C for a points engine...not a 2C for a Ducatti CDI like I used to have on the MX. I wrapped the tach lead around only 1 plug wire and the readings dropped back to normal.

I taxied the MX to the windsock pole where I tied the tail so I could do some run-up. I didn't specifically follow the Rotax break-in procedure, but the important thing to remember when breaking in an engine is the heat-up, cool-down cycle of expansion and contraction. I strapped in and advanced the throttle to 3500 for about a minute while observing that the CHT and EGT were within range, then I let the engine idle until the CHTs dropped to 250 degrees. Then I revved the engine to 4000 RPM for about a minute, then let it cool. I followed the same cycle to 5500 RPM when the tach started acting screwy. After that, I decided to go full-throttle for a minute, during which time the temps were fine. I wouldn't expect anything different because the prop pitch and jetting were already set for a 503 engine. I let the engine cool back to 250 on the CHTs and untied the tail and taxied back to the hangar. I was quite happy with the engine test.

I worked on the Phantom for a while, allowing the MX engine to cool completely, all the while waiting for the windsock to drop down a bit. While I was running-up the rebuilt engine, the sock was going through periods of 45 degree angles and up! I didn't want to fly a new engine with winds that strong, so I kept waiting, while working on the Phantom.

I switched the shoulder harness belts around so they were correctly position. I had installed them backwards. I installed the lap belts. I worked out a mock-up of a pushrod system that I'm going to use for the nosewheel steering instead of the stock springs, that I don't like. I installed the new throttle cable bracket that came with my custom 3-way splitter for dual carbs and oil injection. When I started to route the cable through the front strut, I couldn't get the splitter to fit. This means that I have to remove the tube to allow room to push the cable through. I really didn't want to do that. It's a bitch getting a bolt through both ends with spacers both on the inside and the outside. I'll save that for later.

The winds died down a bit, but were still stronger that I prefer. I could test fly the MX, but the winds were strong enough that I wouldn't be flying anywhere. I only had about two gallons (maybe less) of fuel in the tank, so I decided just to fly some patterns, getting some real-life wide open throttle/cruise/idle cycles in. I took off uneventfully and the engine seemed to be working well. I climbed to about 500 AGL, pulled the throttle back and then performed the cross-wind, down-wind, base and final legs of the pattern. As I approached the numbers, the wind suddenly eased up, causing me to drop to the surface hard enough that I bounced about two feet. I shoved the throttle forward quick enough that when I came back down from the bounce, the next bounce was only a few inches high as I pulled the throttle back to idle. The right wing came up...I shoved the stick right to deploy the spoiler and I pushed rudder to the right. The right wing came down, I straightened up and then the left wing came up. I pushed left rudder and it came down and I was finally planted on the ground. I've had things like this happen so many times that I didn't even think about what I was doing as it was happening. It is only as I write this that I really realize how many things we do when piloting our craft that become natural reactions.


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