Sport CARF Pitts - Engine Upgrade

[reyn3545]

Its been a while... holidays, and just generally being lazy. I finally decided to get started on the baffling. My excuse for waiting was that I ordered a new lower cowl, and I was going to wait for it. So, I ordered one a few weeks ago from CARF, knowing that it would be at least a month before it ships. Then, I started thinking about re-drilling all of the mounting holes in exactly the same place as the original holes, whether or not the paint and paint lines would match up, etc... and I quickly came to the decision that the best thing to do (probably) would be to finish the plane with this cowl and live with a few extra holes on the bottom of it from previous exhaust systems.

Soooo... I cut out the first panels from some CF sheeting and glued them inside the cowl opening. I'll piece-meal this together gradually, and in the end, I should wind up with baffling that creates almost a plenum of air to run over and under all 4 cylinders. That's one of the good things about round cowls, you can direct air on the upper and lower sides of the cylinders.

If all works well, the upper cowl will have not much more than a "lid" that fits on the lower cowl baffling. I'll use one side of some velcro to create a good fit between the lid and the side walls. Should be interesting. Anyway, while the glue dries, here's a picture of the first step.....

 

[dhal22]

Round cowls only for me.

 

[reyn3545]

It does seem a shame to block off most of the cowl, just creating a wall of drag to overcome. Fortunately, there should be plenty of motor to accomplish that.

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[Jetpainter]

Mike, I am certainly no expert on this, but I'd be afraid the rear cylinders might not cool as well as you'd like. A flat plate that splits the cylinders at the plugs and causes all the air to flow over all 4 cylinders from the top and out the bottom, seems to be the choice for most people.

 

[reyn3545]

I had a CARF Extra 330sc with a DA200, and baffles that looked much like yours, but I also had a hood over the top of the cylinders. I thought the air would be forced across all cylinders and out behind them. As it turned out, there was so little airflow under the cylinders that beat from the headers would bubble fuel back towards the tank, making the engine die. I had to cut a 1 1/2 inch hole in the cowl below the spinner, just to get enough airflow to keep the motor cool and running. Several people had the same issue and same resolution.

You might have the entire area between the cylinders and firewall blocked, which I did not.
CF CF
This setup should bring in plenty of air and keep it moving over the top and bottom. If not, maybe it's time to fit that new cowl!

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[Jetpainter]

The picture I posted is my flying buddies Carf Sukhoi. It also has a small hole in front of the carbs just for the reason you said. There is also a plate out of view in the picture that makes sure all of the air entering the open area of the cowl has to go out through the cylinders. It works like a charm even on those mid 90's humid days. If it's hotter than that we stay home. I've become a sissy in my old age.

 

[reyn3545]

Well, my new lower cowl showed up today... only took maybe 2 weeks to get here from Taiwan, and that was including painting. I wasn't expecting it for at least another month. The colors look like an exact match, and the lines are very close on one side and just barely off on the other. Makes me think about moving the baffles over to the new cowl...but those kind of projects always turn to schidt for me... so I'll stick with the old one for now.

 

[49dimes]

The picture I posted is my flying buddies Carf Sukhoi. It also has a small hole in front of the carbs just for the reason you said. There is also a plate out of view in the picture that makes sure all of the air entering the open area of the cowl has to go out through the cylinders. It works like a charm even on those mid 90's humid days. If it's hotter than that we stay home. I've become a sissy in my old age.

WOOSE!. Don't worry....I'm a woose too .

 

[Hinckley Bill]

It does seem a shame to block off most of the cowl, just creating a wall of drag to overcome. Fortunately, there should be plenty of motor to accomplish that.

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How far forward is the back of the spinner plate from the front of that big round cowl, can't quite tell from the 'front view'?

 

[reyn3545]

Just about 2 inches.

That's why I decided to not put a spinner on it. The motor mounts are sitting on the firewall, so no way to improve on that without hacking up the motor dome.