The old lady had her fifty hour check-up the other day and is in perfect health.
There were a couple of us there to help out, which is cool because there’s some parts that are two person jobs. Like the cylinder pressure test – one person needs to hold the prop in place at top-dead-center (the point where both valves in the cylinder are closed) and one person turns on the air hose and reads how much pressure is being lost. That test cam out very well – Leon, the AME (aircraft mechanical engineer) said that he had done a pressure test on this very plane and engine shortly after the cylinders were replaced, and the results were not nearly as good. Apparently that’s one of those things that improves if the plane is being flown regularly.
The one thing that’s still a little bit sketchy is the mixture, and Leon figures the valve could be twisted a bit, or worn. The issue is the engine doesn’t shut down, but sputters when the fuel mixture is cut off, meaning there’s enough fuel getting to the engine to keep it just barely turning over. When it sputters and doesn’t die like that, they call it “dieseling.” The trick to getting it to shut down in that situation is to push the throttle in a little, and run the engine a bit harder to burn the fuel faster so that it starves and shuts down.
Worst case scenario, you can turn off the mags, and then there will be no spark in the cylinders to ignite the fuel, then the engine shuts down instantly. The problem with that, though, is it leaves unburned fuel in the cylinders, and firstly, that can cause fouled mags, as well as making it more likely the engine will start, and run longer in the case of a ground wire failure.
I haven’t had too much trouble getting the engine to shut down myself, but Leon figures some of the girls may have had more trouble due to pushing the throttle in too fast. If you push the throttle in fast, you engage the accelerator pump. It’s for when you need power fast, and gives the engine an extra shot of fuel if you ram the throttle to the firewall really fast. In case you’re abandoning a landing and need power to climb right away after having had the engine running on low power for a while. If if you do that when you’re trying to shut the engine down and starve it of fuel though, then suddenly you’re dumping a bunch of extra fuel into the engine.
Anyway, enough rambling about engines. Hopefully I can get out and do some circuits with the old lady today. She’s also got a new paint job.
Looking at the picture she doesn’t look like an ‘old lady’, that looks like a pretty smart plane.
So am I right in thinking you have to go through this routine for every fifty hours of flight the plane has? That sounds very frequent!
She does look pretty snazzy with the new paint. And yes, this has to be done every fifty hours of wheels-off-the-ground time. Reasons. Good reasons. If you have a failure, you can’t pull over to the side of the road and call CAA. You want all the parts in the plane working. Fifty hours is plenty of time for something to become worn, start leaking, etc.
Also, normally planes are inspected every 100 hours – or yearly, at which point, the engine is removed and dismantled. If a plane is flown frequently, and the owner doesn’t want to fuss with having the cylinders removed and inspected, there is the option of doing a lower level inspection every 50 hours instead, which doesn’t require the engine to be dismantled. Flight schools do that a lot, to keep their planes in rotation. Harv’s has AME’s onsite to make sure the planes are seldom out of action for more than a few hours.
That totally makes sense – you pilot’s can’t just pull over and pop the hood can you 😉