David -- I was/am one of those folks. Was there about a month ago for recurrent training and probably spent an hour doing various approaches/landings/rejected takeoffs/rejected landings/etc. at Shelbyville. Great airport!

Dave

Yes, this is normal. It is called the "EPA kit".

Back in the early days, when the engine shutdown, the fuel was simply shutoff and the engine flamed out and the engine spooled down. This left unburned fuel in the lines to the fuel nozzles. This caused unburned fuel to drain on the ground (hence the EPA concern), and the unburned fuel coked onto the fuel nozzles resulting in streaking nozzles that burn up turbine wheels.

To fix this, there is a small air pressure reservoir in the engine which is discharged through the fuel lines at shutdown. This causes a momentary jump in fuel flow from the air pushing all the fuel out of the lines, which is the increase in power you noted. Now the fuel lines are empty so they don't drip unburned fuel on the ground or coke the fuel nozzles.

If your EPA kit doesn't work, your engine will be damaged over time from streaking fuel nozzles, so this is very important.

Even with the EPA kit, there is a little residual fuel in the system. To help dissipate that, TPE331 owners rotate the props after shutdown to blow some air through the engine. This helps evaporate any unburned fuel before it cokes on the fuel nozzles.

Mike C.

The PT-6's in the RC-12 never seem to make any change in noise when shut down. Must be a Garret thing. I've always like the looks of the MU-2. Just have never been around one running. Seems like they are always in the chocks shutdown when I see them.

The PT6 has an "EPA kit":

http://digital.turn-page.com/i/30832-ki ... ne-2011/23

Apparently, early EPA kits for PT6 used a collector tank, later ones had an air purge like TPE331.

Mike C.

There's a reason they call it the "MU2 Solute"

FIFY.

Mike C.

The PT6 has an "EPA kit":

http://digital.turn-page.com/i/30832-ki ... ne-2011/23

Apparently, early EPA kits for PT6 used a collector tank, later ones had an air purge like TPE331.

Mike C.

I was with Dave at Shelbyville in my awesome noise machine with Jerry. Nice airport.

I'm not used to noise being called a nuisance by other pilots. Damned kids and their MU2s these days

If I had the coin and the need, hell, maybe not even the need, the MU-2 would be on my short list.

According to the FAA, a B55 Baron is louder than the MU2 when it comes to overfly noise.

http://www.faa.gov/documentLibrary/medi ... 036-1H.pdf

The objectionable noise is taxiing on the airport. It is loud, but not really THAT loud.

This video captures the difference between flight and taxi noise:

https://www.youtube.com/watch?v=ihUXDW2Uy0s


Once you go to zero or near zero thrust and taxi RPMs, the MU2 develops a characteristic howl. The exhaust is no longer surrounded and isolated by prop airflow.

I wondered if making a new tailpipe with serrated trailing edge would reduce this noise. The theory is the howling is a resonance from the tailpipe length (much like a wind instrument) and by having a serrated trailing edge, it would detune the resonance.

Kind of like this:



Mike C.

Agreed at idle they are loud but as soon as they are pulling air into themselves, they are not. From an airport noise standpoint, they are quieter than the old stage III jets like a Lear 35.

My mistake. It is an older Lear 25. Thx for correcting me. We also have a Lear 35 (much quieter)with hush kits on the field. Owners were partners in the 25, however , both own their own Lears now.

As was already pinted out, Lear 35's do not have/need hush kits. They are already stage III.

I am convinced that the "ramp noise" of the TPE-331 Garrett engines, is primarily the result of the exposed intake turbine, at the front of the engine, just aft of the propeller.
I do not have the db stats, but I believe that the MU-2 is much less "noisy" than a Baron during takeoff!
Too bad, I miss the "crackle" of the old Rolls Royce Spey's on my old G-II; wow what a cool sound! I always called it the "sound of money"!

In my town basically everyone says that the piston traffic is louder than my Merlin on overflight. Startup at sunup, well that is a different story.