Exhaust diverter to keep fuselage bottom cleaner?

[Eric Greenwell]

I get tired of cleaning the bottom of my Phoenix, so I'd like to find a way to divert the exhaust stream downwards; for example, something like the "turn down exhaust tip" in the picture (it's about 9" long, and comes in several diameters). Any idea if this would reduce the oil goop on the fuselage, and not adversely affect engine operation?

[Andreas Clauss]

Hello Eric, I'll be 49 U15 in April 2018. I've heard about this issue and have personally seen it on a Phoenix in France.

Not sure if your suggestion will work, it depends a lot on the balance of the airflow around the fuselage and exhaust airspeed. I don't think it would effect the exhaust back pressure significantly (still maybe worthwhile to talk to Rotax about this) One thing to watch out for might be vibrations that you introduce through a perpendicular force on the exhaust tube.

I've seen Christian Brondel doing the following. Put a cushion below the nose of the Phoenix and lift it on the tail so the nose is gently sitting on the cushion. This provides you free access to the fuselage to clean it. It's not ideal but it works.

I'll be with Martin in Feb and will discuss this with him! My thoughts are maybe finding a film that can be easier cleaned and put that on the fuselage.

Merry Christmas and greetings from Geneva, Andreas

[Eric Greenwell]

I use a creeper to roll around under the fuselage while cleaning the belly, but it might be easier tipped up on it's nose. Is there any problem with fuel leaking out? Does it stay on the nose without support for the tail? Be sure to ask Martin about keeping the oil off the fuselage with an exhaust deflector, or easier ways to clean of the oil!

I don't know if the exhaust flow pulsations would be problem. We know from Russ Owens experience that even the standard system can develop cracks in the exhaust pipe, so I intend to try it, remove it if it doesn't help, and make inquiries about the pulsations if it does help.

 

[Andreas Clauss]

Hello Eric,

The plane is staying in the position without having a tail support in place.

We had the plane on the nose for about 10 minutes and there's been no evidence of any leaking. BUT I have to say that Christian has a retrofit injection system installed that might behave differently from the standard carburetor. 

So I'll add this question to my To-Do List!

 

 

 

 

[Eric Greenwell]

And please, tell us more about the retrofit fuel injection system!

[Eric Greenwell]

I couldn't find an exhaust tip to divert the exhaust flow downward, so fabricated one from a 180 degree bend tubing piece (1.5" OD tubing, 3" radius bend). The Phoenix exhaust tubing appears to be metric, about 40mm OD, so I had find an exhaust shop that could expand the end of the tubing enough to slip over the Phoenix exhaust. The end has 8 slits cut in it, and a hose clamp holds it to the Phoenix pipe.

I hope to fly with it tomorrow.

[Rob]

I like your chocks .

They look they are made out of plastic

[Eric Greenwell]

I first saw that sytle of chocks at Ed Walker's hangar. It's made out of 1/2" PVC pipe and two right angle fittings that are glued together - standard Home Depot stuff. They are effective, cheap, and easy to make. I carry one in the glider for tying down when away from the hangar. I can get a picture and dimensions later if you like, but it's easy enough to cut the pieces, fit them together, then glue once the lengths are right.

[Eric Greenwell]

The flight test yesterday didn't reveal any problems, nor did it confirm the effectiveness of the diversion. That will take 5-10 hours of flying, I think, so it will be a weather dependent "while" before I'll know if it's keeping the belly clean.

[Eric Greenwell]

It works! When I added the exhaust diverter, I cleaned the area from the bottom opening of the cowling back to the landing gear - an area that gets  oily and brown very quickly. That area, after 20 engine hours since adding the diverter, remains clean. No problems have emerged in the 20 hours: the diverter is still very tight on the exhaust pipe, pipe has no cracks in it or the welds, and the CO monitor doesn't show any CO in the cockpit. Simple, cheap, easy, and now known to be effective - it doesn't get any better than that.

[mikeschumann]

I love it.  I want one.  How can we get a batch made?  Can we get Jim Lee to issue an LOA.  Maybe we should add this to Martin's product improvement list.

[mikeschumann]

I had my local muffler shop manufacture the attached diverter, which I hope to install tomorrow.  Total cost was $50.  He'll make more if anyone else is interested.

A question to Eric:  When you installed your diverter, did you aim it straight down, or at an angle to the side?

[Eric Greenwell]

I mounted it with exit facing directly down. When I've flown enough t have a deposit on the fuselage, I'll consider changing the orientation, but so far, the fuselage stays clean.

Your diverter appears to be twice the length of mine (and likely double the weight). Mine loosened after a while, so I suggest you check your diverter's attachment carefully before every flight.

[mikeschumann]

Attached is a picture of my installed diverter. The existing exhaust pipe is inserted almost half of the way into the diverter. 

If I was going to have another one built, I would try to have it made shorter, like yours. However, the total weight of my diverter is only 0.8 lbs, so I am skeptical that it would be worth redoing. 

I was a little concerned about using a hose clamp to attach the diverter, so I had the muffler shop weld on two brackets on either side of a single slot cut into the diverter colllar. I am using a bolt with a lock nut to tighten the collar over the exhaust pipe.  It is a very solid connection. It will be interesting to see if it loosens up over time.

Thanks for the inspiration to do this. 

[Eric Greenwell]

Russ Owens Phoenix developed crack at the weld, even with out the weight of the diverter, so I check that weld during the preflight. It will take a year or so of using diverters to know if it causes any problems.

Your tab on the diverter should work well. I now remember it wasn't the screw clamp that loosened, the problem was my slots in the end of the diverter weren't wide enough, so even a tight clamp could not put enough clamping force on the exhaust pipe. I widened four of the eight slots, and no problems since then.

[edwalker]

Just for the service record, I made one identical to Eric’s and it’s been in place now for 2 months with no issues. Bottom of the plane remains clean.

Ed

[Jim Lee]

I have no idea if this diverter changes the back pressure in a way which may be harmful to the engine.

[mikeschumann]

My muffler guy used pipe that is slightly larger than the 40mm OD exhaust pipe on the Phoenix to make sure that we didn't run into that problem.

[Eric Greenwell]

9 hours ago, Jim Lee said:

I have no idea if this diverter changes the back pressure in a way which may be harmful to the engine.

You are probably talking about Mike's diverter, but I recall the ID of my diverter and exhaust tubing are the same size, so the diverter just makes the exhaust pipe a little longer (2"?). With the headers, muffler, and original exhaust pipe in series, that 2" should be insignificant. I did consider cutting 2"-3" off the original exhaust pipe to keep the length and weight closer to original, and still might do that after more hours of testing.

[Andreas Clauss]

Hello Eric,

I got my 49 U15 4 weeks ago. The exhaust is slightly more slanted 2 inches farther away from the fuselage.  Right now I have put on 20 hours and cleaned it only once as the fueselage remained relatively clean. 

Happy Landings, Andreas

[Eric Greenwell]

• I'm glad to hear the factory has apparently responded to owner complaints about the problem. If the exhaust diversion isn't enough, a diverter tip with less curve than I used would easily given it the desired amount.

[mikeschumann]

Just flew from Mpls to Naples FL via Charlotte with my new exhaust diverter.  After a 10+ hour flight, no oil slicks on the fuselage.

[Eric Greenwell]

78 engine hours since installing the diverter, and no grime (or even an oily feel) to the entire belly. I wish I'd thought of this sooner, as I was cleaning the belly every 20-30 hours before using the diverter. No apparent problems, either.

[Eric Greenwell]

110 hours on the diverter - belly still clean, no apparent problems.

I spent about an hour searching for remarks on using diverters, tips, and extensions. I didn't find any remarks about tips, etc, causing problems. I also queried the Rotax owners group (https://www.rotax-owner.com/en/912-914-technical-questions/7470-using-an-exhaust-pipe-with-a-curved-tip") and got 178 views, but no replies.

There are many cars, trucks, and airplanes using diverters like the one I use (and lots of them for sale), but the problems appear to be rare. That doesn't mean my situation isn't a problem, of course. I did find a few articles describing how mufflers reduce the amplitude of the exhaust gas pulsations, and perhaps the Phoenix muffler is doing enough of that to avoid problems. Another mitigating factor is about half of my hours are at idle, because I leave the engine running while soaring.

I wish I had a vibration sensor I could put on the exhaust pipe to measure the amplitude; in the meantime, I'll record video of the tailpipe from idle to full throttle during a ground run.