J vs K with regards to noise level

[mccdeuce]

Looking for PIRPEPS with regards to noise in the cabin when comparing the J and K.  I have very limited K time and it seemed to be a much quieter ride. The K had a 3 bladed prop vs 2 blade in the J.  

Which is more significant though? The prop or the 6 cyl turbo vs 4 cyl muffler.

[carusoam]

Things that effect the noise in the cabin...

1) the J has a muffler... the K doesn’t... it’s noise is adsorbed by a complex turbo system... 

2) Most of the noise you are going to hear is generated by the prop tips as they are going towards the speed of sound, kind of...

3) Check the prop diameter to see which tips are going faster... @ 2700 rpm  Many Mooneys share the same prop diameter... they would be longer if the ground wasn’t so close...

4) The longer nose technically puts that noise much further out front... +1 for a six cylinder engine mounted far away...

5) Some Js And Ks have been outfitted with composite props... the Composite Sound absorber has an interesting sound profile while the plane is in T/O mode... very noticeable on the ground...

6) Window thickness... the more thick and angled the better... J and K are sharing the same geometry, but may have a thicker window installed...

7) Taken to an extreme... Find a Long Body with an MT on the front... with a thick windscreen... and cruise in a low rpm setting...  Long Bodies are amazingly quiet inside compared to other planes with near vertical windshields and the prop mounted nearby...

8) Could be the sound adsorbing materials used inside the plane... Materials cost money, and they come with weight... some planes have this deleted for both reasons...

PP thoughts only, not an aero-audio engineer...

Best regards,

-a-

[gsxrpilot]

Just to add one additional point to Anthony's excellent list.

9) Air density has quite a bit to do with noise. In the thin air of the flight levels between FL200 and FL280 where the K's are at home, the air is too thin to transmit much of the noise from the engine and prop. The result is a quieter ride. The J flying in thicker air 10K to 15K lower will generate significantly more noise.

[Guest]

All Mooney short and mid body lengths tend to be noisier than other brands in my experience, despite having equally poor firewall insulation.

Clarence

[ArtVandelay]

According to my phone app, my J runs about 95-100dB, but I have tried it at higher altitudes.


Tom

[larryb]

I owned a J for 500 hours and now have near 300 hours in my 1997 K model. The K is much smoother and quieter. The 6 cylinder Continental is smoother than the 4 cylinder Lycoming. It also does not have the annoying yellow rpm range that can be an issue on landing in the J. The factory also added more noise deadening in the later years.

[bradp]

Saw a pic of someone’s engine side firewall with insulation material.  Wonder if that would cut some of the noise.  

My plane is loudest at the footwell 95Db or so.  It’s mostly engine noise.  

85 Db or so in the rear. 

The continentals always sound better to me.

Prop noise and vibration is just as much of a factor as engine noise  -  the composite props are notably smoother and a little less noisy. 

[ArtVandelay]

How much engine noise is coming from the exhaust? How much is engine noise vs wind noise? Someone call the myth busters.



Tom

[johncuyle]

First two posts covered it from a technical perspective.  Paul's post is the practical answer.  You fly the K higher than the J, air density is lower, less sound transmission.  The way you actually use the planes, the K is quieter.  If you're planning on flying a K low enough that it's an apples to apples comparison, the noise doesn't matter, you want a J.

As a K owner who transitioned from a rental J, though, I will second Larryb's observation that whatever the dB meter says, the K's engine is a lot smoother and that continuous drone is less unpleasant to listen to than the racket a four cylinder Lycoming makes.  If the Lycomings weren't basically bulletproof, vastly lighter, and much more economical to maintain, I can't see why anybody'd ever use them...

[ArtVandelay]

As a K owner who transitioned from a rental J, though, I will second Larryb's observation that whatever the dB meter says, the K's engine is a lot smoother and that continuous drone is less unpleasant to listen to than the racket a four cylinder Lycoming makes.  If the Lycomings weren't basically bulletproof, vastly lighter, and much more economical to maintain, I can't see why anybody'd ever use them...

My AP tells me my engine is the smoothest Lycoming he’s ever ran FWIW. I’ve never flown a 6 cylinder so I can’t comment on it vs a 6. I have no complaints.


Tom

[johncuyle]

1 minute ago, ArtVandelay said:

My AP tells me my engine is the smoothest Lycoming he’s ever ran FWIW. I’ve never flown a 6 cylinder so I can’t comment on it vs a 6. I have no complaints.


Tom

As flat fours go, I guess the Lycomings aren't that bad overall.  Ever drive a Toyota FRS.  The Subaru powerplant in that is a really nasty, thrashy thing.

[jaylw314]

48 minutes ago, johncuyle said:

As flat fours go, I guess the Lycomings aren't that bad overall.  Ever drive a Toyota FRS.  The Subaru powerplant in that is a really nasty, thrashy thing.

Some of us love the really nasty, thrashy sound from the EJ25 and other Subaru boxers...

But maybe not for 4-5 hours at a time  

[gsxrpilot]

2 hours ago, johncuyle said:

If you're planning on flying a K low enough that it's an apples to apples comparison, the noise doesn't matter, you want a J.

As the proud owner of a K 252, I second this statement. I wouldn't give up my 252 for a J, but then I fly above 15K ft. more often than not. 

Make your decision based on the altitude you typically fly...

[Hank]

3 hours ago, ArtVandelay said:

My AP tells me my engine is the smoothest Lycoming he’s ever ran FWIW. I’ve never flown a 6 cylinder so I can’t comment on it vs a 6. I have no complaints.


Tom

The last IA to work on my plane, responsible for my visit to Joey Cole to fix what he did, was absolutely shocked at how quickly and easily my C cranked up, and by how easily I was able to hot start it . . . . But he will never touch it again.