acerc

I have a Valach 170cc 4 cycle in a Pitts and have come to the conclusion that I need to baffle the airflow around the engine. But, seemingly in a manner unheard of, it is running way to cool. So, any one have any ideas as to which would be better, reducing the intake opening or the exit opening?

CK1

My Feedback: (60)

acerc , without seeing what you have to work with it is pretty hard to be sure which would work better , but in general I would say regulating the outflow would give a more uniform mode of restricting flow as it has been done that way on full scale very successfully .

acerc

The front opening's are very large, as seen in the pic, nearly larger than the engine head. The left head is 1" inch from the opening and the right is 1-1/2". The exit opening is larger than the two intake's combined, about 3" x 8", I don't have a pic of the exit.

CK1

My Feedback: (60)

The inlet areas look fine to me as they are ,I am not sure I would restrict them in an attempt to get the engine to run warmer . Is there an issue resulting from the engine running to cool ? Perhaps you could speak with Goetz Vogelsang to address any particular issues with the Valach engine .

Vogelsang Aeroscale

372 Legacy Falls Drive North

Chapel Hill, NC 27517

919 533 6275

acerc

The issue namely is it is not hot enough to burn the fuel/oil cleanly and the exhaust gasses do not turn smoke oil to smoke very well.

Truckracer

My Feedback: (19)

Full scale planes use both techniques to reduce cooling airflow. Many planes have cockpit adjustable cowl flaps that restrict the outward airflow to control engine temperatures. Others use airflow restrictors in cowl inlet openings with some only being installed during winter operation. Most full scale planes that use the flat opposed engines restrict airflow into the cowl to less than the full size cowl opening. Find a small airport and go look at something like a Cessna, Decathlon, or even a Pitts, etc. and you will see what I mean. Its part of the cowl baffles on the full scale.

For your Pitts, I believe I would restrict the intake a bit. A side benefit, it would even make your cowl air inlet openings more scale.

acerc

After your post Truckracer I remembered it seemed like I saw intake restriction baffles on the full scale. So I went and looked, here is the pic where a portion of the opening is blocked so to speak. This effect would be easy to replicate, but, being I am flying in an event currently duct tape and a piece of flat aluminum will do to find out.
Thanks for jogging that memory Truck!!

John_M_

Ace, you don't want to run that engine above 300-320 degrees... 280-290 would be in the normal range... but having said that, raising the operating temperature of the engine a few degrees, isn't going to change what is happening in the exhaust system... as you already know a four stroke only produces an exhaust pulse every 720 degrees of rotation; where as a two stroke is every 360 degrees of rotation, so a two stoke produces a hotter exhaust than a four stroke.

What I think is happening, is the exhaust system is cooling off by the airflow through the cowling, since the exhaust system doesn't have a lot of metal mass to hold on to the heat... you can try a couple things, like baffling to keep the airflow off the exhaust system... the other thing you can do, basically what the performances engine builders use to do (and are still doing) when running thin walled tube exhaust headers... was to raise the temperature of the exhaust gasses inside the headers to increase the gas velocity by wrapping the exhaust headers in a fiberglass thermal wrap.... the fiberglass wrap insulated the exhaust header tubes and kept the heat from dispersing through the thin walled exhaust tubes.

If you were to wrap the entire exhaust system from the head all the way to the end, except the tips sticking out the cowl with a thick strip of heavy fiberglass, overlapping each wrap as you go, and then secure it with some wire at each end, that along with a baffle to keep the airflow off the exhaust headers would help hold the heat in the exhaust system... its worth a try anyways.

Cut a strip of fiberglass and fold it over in half so the frayed edges meet so when you wrap it around the exhaust tubes. the overlap will hide the frayed edge... wrap it tight!



John M,

TJC333

I think those baffles are there to direct the flow of air into the cylinder fins. My Piper Cherokee had the same ones.