Small Detail to consider

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tom kreiner
Posts: 38
Joined: Sat Feb 25, 2017 9:49 am

Small Detail to consider

Post by tom kreiner »

OK - my LAST POST of the year!

A couple of days ago, I was at the field grabbing some stuff for my Piet project, and came across the Cub shown in the pic. It turns out the Exhaust pipe was miter cut (cut on diagonal) backwards, which caused a pretty significant problem.

Cub Exhaust.jpg

When the open end of the pipe is either perpendicular or mitered the wrong way, the pipe will produce a very smooth & tight stream of hot exhaust gasses which will disperse rather slowly. In fact the exhaust stream is so tight, that it has burned the covering on the gear leg!

Think of this as a stream that doesn't break up - kinda like water coming from a hose... Consider that a 4 cylinder engine (i.e. a small Continental), running at 2500 rpm produces some 80+ exhaust pulses per second! With a temperature of around 1200 F, it's easy to see that the stream of gasses will create havoc on anything in their way.

To eliminate this from happening on your project, you'd ideally cut the same miter - but with the open end oriented towards the direction of flight. Done properly as described, both the apparent wind and the prop wash tend to disperse the exhaust stream, thereby reducing or eliminating the heating effect of the exhaust gasses.

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Richard Roller
Posts: 52
Joined: Mon May 22, 2017 11:14 am
Location: Olathe, Ks.

Re: Small Detail to consider

Post by Richard Roller »

That is a standard J-3 exhaust system for a Continental engine. Something else is causing the burning on the gear vee. Mixture problem?

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Lownslow
Posts: 26
Joined: Wed Mar 08, 2017 9:56 am

Re: Small Detail to consider

Post by Lownslow »

I agree Richard. I checked the exhaust stack on my Tri Pacer with an O-320 yesterday and it is cut the came as J-3's. The bevel faces aft.
Rick Schreiber

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