brndiar

Noise Certificate M20C with 3 Blade Hartzell Prop

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Hi,

Please, what should be a Take -Off Noise Level  for M20C with Lycoming O 360A1D  and new 3 Bladed Hartzell (HC-C3YR-1RF/F7282) Prop?

I replaced the original, old 2 bladed Hartzell HC-C2YK-1BF/F7666A-2  with the new 3 blade Prop.

Unpleasant surprise for me is a new Noise Certificate (Foto) with 85,5 dBA, while in the old one there was 75 dBA.

According the Hartzell Page new prop.  should  dramatically decrease noise. 

lg,m.

 

 

Noise certificate.jpg

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I've not noticed my 3-blade being especially loud, but I'm also not listening from the ground. 

While you're at it, check the muffler too.

 

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Looks like you need some info from a European M20C owner...

Where is our Swiss M20C...  @Urs_Wildermuth


Are you a member of the European OPA, similar to AOPA...

Best regards,

-a-

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Hi,

From Hartzell I got a link to EASA  database
and explanation:

"Whatever the reason, for the listings in the EASA noise level archives, you can bet that we had nothing to do with it. Here’s what I can tell you about it

Prior to 1988 noise was measured at 1000’ AGL (overflight). In FAA speak, this was FAR 36, Appendix G. EASA, or more specifically the Authorities that preceded EASA called in ICAO Annex 16, Chapter 6.

After 1988 both organizations changed to a noise measuring system that took take-off and climb performance into account. The better a plane climbed, the higher it would be at 8200’ from where the airplane started rolling, and the microphone is set up. This Take-off method is called FAR 36, appendix G, or ICAO Annex 16, Chapter 10.

I can tell you that Hartzell never tested a M20C with any prop on it for the FAA or EASA. Both of these prop TC/STC’s were validated in Europe well before EASA was established. Hence they were grand-fathered in without any noise testing on our part.

The note that EASA has pertaining to the three blade entry is “”9/24/201 Engine designation revised”.  

Looking at the numbers themselves, the Chapter 6 numbers are on props that were TC’ed. Maybe these numbers came from Mooney from the TC process? I can only guess. The 7282 three blade is approved on an older STC. In 2010 we added eligibility for the Powerflow exhaust to the STC. The only thing I can think of is that when Powerflow applied to validate their STC it must have initiated some noise discussion. If you will note, 85.5 dB(a) is the maximum allowable under Chapter 10. That seems like allot for un untested unit that is the same diameter as the two blade??

So, to get to the bottom of your questions, The props are the same diameter. They should be about the same noise-wise, except the 3 blade climbs better (CHAPTER 10). The numbers in the archive compare two 74” props at the same RPM, using two different methods, one of which may be considerably closer to the mic, and the Chapter 10 listing is as high as it can be to pass. It seems almost arbitrary?? The three blade certainly is not 10 dB(a) louder than the two blade."

lg,

m

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Noise levels have become more of an issue in Europe than the US...

Prop manufacturers have demonstrated great results by changing the materials of construction...

When comparing props, see what the MT company has... their composite props are noticeably different during the T/O run...

No measuring device needed for the comparison...

Hartzell also has composite props. I don’t know if they publish noise data on their site...

Best regards,

-a-

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23 hours ago, brndiar said:

Please, what should be a Take -Off Noise Level  for M20C with Lycoming O 360A1D  and new 3 Bladed Hartzell (HC-C3YR-1RF/F7282) Prop?

I replaced the original, old 2 bladed Hartzell HC-C2YK-1BF/F7666A-2  with the new 3 blade Prop.

Unpleasant surprise for me is a new Noise Certificate (Foto) with 85,5 dBA, while in the old one there was 75 dBA.

According the Hartzell Page new prop.  should  dramatically decrease noise. 

Just a little googling on the specs of these two props tell me that they are both 74" in diameter.  What you did is add an extra high speed tip to your prop.  I wouldn't be surprised if it is nearly half again as loud as your previous prop.  Prop tips near supersonic make up a lot of our airplane noise.

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I guess you will need to find a way to do an official measurement and hand the result to your caa. In Switzerland there are possibilities for this. Your maintenance organisation should know but certainly AOPA.

I have the 2 blade prop. 

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74 " in Diameter= 187,96 cm in Diameter.

At 2700 RPM speed tip is: 3,14*1,8796*2700/60= 265,59 m/s.

Sound travels at 343 m/s in air.

lg, M

 

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11 hours ago, brndiar said:

Sound travels at 343 m/s in air.

Assuming stp, thats a mach number of .78.  With the compressibility of air and lower pressure areas changing the speed of sound, that easily makes a higher mach number and locally supersonic flow.  Not as loud as a T-6, where they like to make the prop tips actually go supersonic (that's what the BRAAP noise they make is), but the propeller and especially the speed of the tips make much of the noise in our small planes.

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