SonexBuilders.net

The AeroVee instructions don't say much about where the cut the lower exhaust pipes. They say 'not too much' and 'not too little." Any helpful insight into where to cut them, relative to where they exit the lower cowling of my Sonex tail dragger?

Mike Smith

I don't think there really is one set length of pipe that you need to cut to, but from my own experience I would recommend that you cut the pipes long enough that they stick several 4"-6" below the bottom of the cowling/fuselage line. I cut mine so I only see around 2"-3" of pipe and every once in a while, when I'm at a really high angle of attack, I can smell a little exhaust entering the cabin. Not enough to worry about and it goes away as soon as i add power, but still enough to make me wish I had left my pipes a little longer.

While we're on the subject, I also recommend you head to your nearest Jegs and get automotive exhaust pipe wrap and wrap your whole exhaust system. I've done this and it's amazing how much cooler your cowling is after the exhaust is wrapped. It really goes a long way in keeping everything in the cowling much cooler, including fuel lines which may help reduce or eliminate "burping" from the engine.

I cut mine off just a little past flush with the bottom of the fusealage. It is somewhere between the bottom of the fusealage and the bottom of the deflector lip you install on the cowel (maybe 1/4" proud of the fusealage bottom) Take a look at the latest aerovee assembly manual on the aerocoversions website. There are some pretty good pictures in there of where Sonex cuts theirs.

Keith
#554

On my Sonex they are about 1.5" lower than the cowl "ejector lip" and it seems to work well--no hint of exhaust smell under any flight condition so far. While every bit of drag reduction helps, I think this is an area where it's best to be on the conservative side.
Mark W.

Interestingly, the Sonex instruction sheet shows their exhausts cut ABOVE the level of the lower cowl, such that the ends of the pipes are within the cowl. I've emailed Sonex to ask their current recommendation.

Mike Smith

Sonex tech support says:
The pipes can be cut off as short as will still assure the gas are exhausted out of the cowl. Ours tend to be up inside a bit more than the lips, but slightly longer is probably better.

I originally left mine full length, about 8 inches below cowling. I later cut them off about 1" below the cowling and picked up 8 mph. No I'll effects.