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Tuning aircraft engines

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Hi Andre,

Can you give some more details on the aircraft you have tuned? I've flown both experimental and certificated GA airplanes, and the engines are pretty agricultural by comparison to car engines! Lots of fun though, and It's certainly something different. I'm interested to hear more about what you tuned - was it an electronic magneto or injection system, and what gains did you see?

The Lycoming in the Pitts I used to fly was a stump puller - 540 cubic inches, and 260HP at 2,700RPM. It sure gave a good shove in the back and it made the power at an RPM that allowed the prop to keep its tips subsonic..

Anyway, would love to hear more about these experiences..

Cheers,

Matt

Many years ago I was involved with an experimental home built where the owner/pilot didn't want to go down the age old lycoming path. He fitted a Subaru EZ30 flat 6 and it was controlled via an M800. The difficulty with automotive engines is that you need to gear the prop down so that the engine can work at the sort of rpm it's designed to work in. I tuned the engine initially on the ground which was quite challenging since it used variable cam control and variable lift, but with the ability to also adjust the prop pitch I actually had a pretty decent 'dyno' albeit with no numbers.

The owner needed to complete the first 10 hours (from memory) solo and everything went perfectly. I ended up going for a flight with him after this period to confirm that the air fuel ratio was where I wanted it. The problem was that under cruise conditions the engine ended up at something like 4500 rpm (again I'm stretching my memory) which was above the high cam switch over point. I'm not sure the engine liked constantly running in high cam mode and as the owner clocked up hours and had oil samples analysed, they were finding metal in the oil. They didn't have the engine fail but that was sufficient for them to stop running it. The engine was an unknown wrecking yard engine so they fitted a second engine but had the same result. In the end the owner decided to swap to the tried and tested lycoming. He hated it. Power and torque took a dive, as did fuel economy.

In hindsight there's probably plenty of aspects we could have tried that may have improved engine reliability. I'm still convinced that the issue was to do with the constant high cam operation - Something you just wouldn't see in automotive use. If I remember correctly the metal in the oil was analysed and found to be related to the valve train, hence that deduction on my part.

The second plane I've been involved with was a Spitfire replica that was powered by an LS3 and controlled via a Link G4. Not quite the same sound as a Rollys Royce Merlin V12 but much cheaper and easier to source :) I've really not heard much back after I tuned this plane other than reviewing some data logs. It was fitted with 8 EGT sensors so I had the ability to monitor those and adjust individual cylinder tuning.

With the Spitfire I was adjusting an existing tune and we used a strap with a load cell in it to tie the plane down on the ground. I could then monitor the load from in the cabin and watch the load change as I varied the ignition timing - Really this is not much different than having the engine on a dyno.