BeechTalk - BT - Wow! MU-2 ground noise is insane

Username Protected · **Posted:** 01 May 2015, 18:02

Username Protected wrote:

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"!
:cheers:

Yeah baby! MIN EPR takeoffs were a blast! Literally.

Username Protected · **Posted:** 01 May 2015, 18:15

Username Protected wrote:

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.

The front of the TPE331 is basically the same for all aircraft, yet only the MU2 has the howl. A 441, Commander, Merlin, B100 do not sound like the MU2 during taxi.

Thus, I don't think it is the intake side that is the issue, I think it is the exhaust side which varies a lot from airplane to airplane.

Mike C.

Username Protected · **Posted:** 01 May 2015, 18:34

Username Protected wrote:

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.

Username Protected · **Posted:** 01 May 2015, 20:16

Username Protected wrote:

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.

The front of the TPE331 is basically the same for all aircraft, yet only the MU2 has the howl. A 441, Commander, Merlin, B100 do not sound like the MU2 during taxi.

Thus, I don't think it is the intake side that is the issue, I think it is the exhaust side which varies a lot from airplane to airplane.

Mike C.

Username Protected · **Posted:** 01 May 2015, 20:54

I always thought most of the noise from the MU-2 was from the compressor. At least to me the sound is very similar to the Honeywell centrifugal compressors we have tested in out laboratory.

Username Protected · **Posted:** 01 May 2015, 23:03

My apartment is about 300yards from the GA ramp at KFAR. If the owner of the local gas-station chain fires up his Mu2 in the morning, I am awake too

Username Protected · **Posted:** 01 May 2015, 23:34

Username Protected wrote:

It seemed to me as soon as he went to fuel cut off it actually got louder for a second or two as the engine started to spool down. There was one spot between us with me being off the end of the left wing.

You are correct. That is the EPA kit firing. Gets rid of excess fuel so it doesn't leak on ramp. All Garrett's do it. Unique to the engine not the airframe. A P&W powered machine can sneak up on a man. Something no one ever said about Garrett powered machine.

Username Protected · **Posted:** 02 May 2015, 03:03

Seem to recall from my old Merlin 2B days that on shut down SOP was to go into reverse as the stop buttons were pushed. The reason was to engage the spring loaded start locks so that the props would not go into feather once the oil pressure dissipated. Otherwise, you would have to engage the unfeathering pump(s) while holding the power lever(s) in reverse in order to drive the prop blades out of the feathered position and reengage the start locks. Attempting a ground start on a TPE-331, or other direct drive turboprop, with a prop feathered would undoubtably result in a hot start. On starting, after the start cycle was complete and with condition levers at max, the power levers would be placed into reverse to release the start locks as oil pressure would now keep the props from feathering. The placement of the props into Beta and reverse on either shutdown or startup resulted in a higher prop speed and momentarily additional noise. Also, if my memory serves me correctly, prop blade angle was a great contributor to ground noise. Even as noisey as aircraft equipped with the 331 are, they were never in the same league as G-1's, F-27's, ect., that were equipped with the shrill sounding RR Dart engines and Dowty Rotol props, as mentioned earlier. For max noise, the GE CJ-610 powered Jet Commander had the highest take-off dB rating, even exceeding that of the 4 engine P&W powered JetStars, for any aircraft in the under 75,000 lb. GW category. Surely, these old noise makers of yesteryear, are at least partially the reason for the deafness that most of us old farts now suffer.

Username Protected · **Posted:** 02 May 2015, 11:23

Username Protected wrote:

Seem to recall from my old Merlin 2B days that on shut down SOP was to go into reverse as the stop buttons were pushed. The reason was to engage the spring loaded start locks so that the props would not go into feather once the oil pressure dissipated. Otherwise, you would have to engage the unfeathering pump(s) while holding the power lever(s) in reverse in order to drive the prop blades out of the feathered position and reengage the start locks. Attempting a ground start on a TPE-331, or other direct drive turboprop, with a prop feathered would undoubtably result in a hot start. On starting, after the start cycle was complete and with condition levers at max, the power levers would be placed into reverse to release the start locks as oil pressure would now keep the props from feathering. The placement of the props into Beta and reverse on either shutdown or startup resulted in a higher prop speed and momentarily additional noise. Also, if my memory serves me correctly, prop blade angle was a great contributor to ground noise. Even as noisey as aircraft equipped with the 331 are, they were never in the same league as G-1's, F-27's, ect., that were equipped with the shrill sounding RR Dart engines and Dowty Rotol props, as mentioned earlier. For max noise, the GE CJ-610 powered Jet Commander had the highest take-off dB rating, even exceeding that of the 4 engine P&W powered JetStars, for any aircraft in the under 75,000 lb. GW category. Surely, these old noise makers of yesteryear, are at least partially the reason for the deafness that most of us old farts now suffer.

What did you say???? Speak up

Username Protected · **Posted:** 02 May 2015, 11:35

Username Protected wrote:

Seem to recall from my old Merlin 2B days that on shut down SOP was to go into reverse as the stop buttons were pushed.

Most pilots I know of go to STOP, the engine briefly spools up a bit from the EPA kit firing, then flames out, and then as the RPMs decline through about 50%, they go to reverse. The idea behind waiting to reverse until 50% is to not blast reverse airflow on the line people at higher RPM, or risk having the prop pick up something like the welcome mats. 50% is where there is sufficient oil pressure to put the prop blades behind the locks, but not enough RPM to cause a lot of airflow.

Quote:

Attempting a ground start on a TPE-331, or other direct drive turboprop, with a prop feathered would undoubtably result in a hot start.

In most cases, at least for TPE331, probably not. The fuel and ignition are introduced at 10% RPM and I don't think you can get to 10% with feathered blades, the air drag would just be too high. So the engine would get to 7% RPM or so and stagnate with no fuel or fire.

The only case I could imagine you might be able to reach 10% with feathered props is a series (48V) start. Even then, I am doubtful. Due to the wear and tear this would cause on the starter, I'm not going to test it on my plane.

Mike C.

Username Protected · **Posted:** 02 May 2015, 11:55

You've got to be kidding me... I am the ONLY one who loves the sound of the MU-2 on the ground???

(And the GII crackle)

Really??? :shrug:

Username Protected · **Posted:** 02 May 2015, 12:36

Username Protected wrote:

You've got to be kidding me... I am the ONLY one who loves the sound of the MU-2 on the ground???

(And the GII crackle)

Really??? :shrug:

No.

Username Protected · **Posted:** 02 May 2015, 12:38

Nope. I like it too. Think my noise is a nuisance? Go stand someplace else, out of range of my awesomeness.

Username Protected · **Posted:** 02 May 2015, 12:42

Quote:

Go stand someplace else, out of range of my awesomeness.

Now yer talkin'.

Thank you, sir. :thumbup:

Username Protected · **Posted:** 02 May 2015, 13:50

Username Protected wrote:

We have regular MU-2 traffic. Reece Howell, MU-2 recurrent instructor brings his pilots to our field for practice and re-fueling. They have become a real nuisance. The noise is deafening. They are louder than the Lear 35 without hush kit also based on field.

No such thing as nuisance airplane noise!