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 Post subject: Re: 500 mile people hauler 421C vs 425 vs 441
PostPosted: 23 Mar 2021, 14:11 
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Username Protected wrote:
How do cabin noise levels compare between the 441/425/421?


I think the 441 is as loud as my 414, and as the Aerostar that I had. It's definitely louder than the 421. It's not unbearable, but it's not a 421...

I still don't have passengers wear headsets in it unless they want to talk to me.

I have no experience with the 425.

Outside is a different story until takeoff, then I think it's quieter in the air than most piston airplanes.... I pull the power cart from it from time to time, and also did for Metro's for many years and outside requires hearing protection if you are near it. It does not have the howl of a MU-2..


My experience agrees with above. The 421 was the most quiet comfortable plane I've been in. 441 my family still doesn't wear the A20s I provide them but no question it is much louder than the 421.

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 Post subject: Re: 500 mile people hauler 421C vs 425 vs 441
PostPosted: 23 Mar 2021, 14:20 
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Lots of inspections required with jets. Am I reading this right, a Phase 6 exterior airframe check every two weeks? And this has to be done by an A&P? What are they looking for, bullet holes? https://skyway-mro.com/citation-550-551-inspections/

Phase 6:

"Phase 6 - Every 14 days. (Recommended for airplanes that routinely operate from, or are based in, areas subject to saltwater or other corrosion effects.)"

Since it is "recommended", it is optional, and I think it can be done by the pilot. It is basically just a thorough exterior preflight inspection. My plane is not undergoing phase 6 inspections. Just because a phase is listed doesn't mean it is required for your aircraft.

Quote:
I wonder if they really can catch everything (or almost everything) with these inspections.

The legacy planes are VERY well understood by the shops that work on them. Areas of weakness are known and addressed.

Quote:
It seems like if you are dealing with 40 year old metal that (epecially in an engine) has been subject to various cycles and stresses, it's just simply not going to be as reliable as new equipment.

It can be. Planes right off the assembly line have problems, too.

The hours and cycles limits on the metal in the old engines has millions of hours of fleet testing, so those are well understood.

Mike C.

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 Post subject: Re: 500 mile people hauler 421C vs 425 vs 441
PostPosted: 23 Mar 2021, 14:23 
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Username Protected wrote:
441 my family still doesn't wear the A20s I provide them but no question it is much louder than the 421.

Part of this is speed. Just the air flowing past at 300+ knots makes noise as it turbulates over the structure.

Slow a 441 down to 200 knots, it becomes quieter, too.

421 has a slower prop, 441 is a bit faster at 2000 RPM, so prop noise is higher on the 441, but not a huge amount.

Mike C.

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 Post subject: Re: 500 mile people hauler 421C vs 425 vs 441
PostPosted: 23 Mar 2021, 15:22 
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Username Protected wrote:
A new 441 would probably kill the King Air 250/260 in a heartbeat and squeeze the 350.

I doubt it.

The King Air was never about performance, that's a owner flown thing to look at. The corporate world wants reputation and comfort, perceived or not. The King Air reputation will keep them selling even if they have inferior performance, which they have always had.

A restart 441 would be awesome, however. It would be a $6M airplane.

That said, the fact they aren't making them anymore is NOT an issue. You can maintain them and fly them just fine without that. Indeed, the newer planes that ARE in production have been saddled with higher parts costs and more onerous inspections. I realize the 441 has the SIDs, but all the new airplanes have that from the start, effectively.

A well kept older turbine is often cheaper to maintain than a new one though most don't believe that. Just ask anyone with a CJ paying ProParts, ProTech, Williams TAP Blue, avionics program, etc. If new is so much cheaper to maintain, why are they spending $1K/hour just for all these programs?

Mike C.


Cessna is filling the 441 market with the Denali. It's not exactly the same but would probably sell for the same, and I think there would only be a few niche cases where a buyer would take a 441 over a Denali. And those few people would probably prefer a completely redone used 441 for 1/4 the cost than the new one.

I have been in a PC-12 (NG, not the latest) and a Denali mockup. The Denali in particular feels like a midsize jet in size and quality. I'm not a 441 expert but all of the twin cessnas I have been in have more of a high end RV feel to them (I'm a fan, but that's the truth).

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 Post subject: Re: 500 mile people hauler 421C vs 425 vs 441
PostPosted: 23 Mar 2021, 15:48 
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Username Protected wrote:
441 my family still doesn't wear the A20s I provide them but no question it is much louder than the 421.

Part of this is speed. Just the air flowing past at 300+ knots makes noise as it turbulates over the structure.

Slow a 441 down to 200 knots, it becomes quieter, too.

421 has a slower prop, 441 is a bit faster at 2000 RPM, so prop noise is higher on the 441, but not a huge amount.

Mike C.


Airflow around the 441 will rarely if ever be 300kts.
A 421 at FL230 -28C doing 220ktas indicates 153kias.
A 441 at FL330 -50C 300ktas indicates 177kias.
The 25kias difference in wind noise is probably less of a factor vs the prop speed and possibly the engine whine.

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 Post subject: Re: 500 mile people hauler 421C vs 425 vs 441
PostPosted: 23 Mar 2021, 15:52 
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Username Protected wrote:
Part of this is speed. Just the air flowing past at 300+ knots makes noise as it turbulates over the structure.

Slow a 441 down to 200 knots, it becomes quieter, too.

421 has a slower prop, 441 is a bit faster at 2000 RPM, so prop noise is higher on the 441, but not a huge amount.

Mike C.


Airflow around the 441 will rarely if ever be 300kts.
A 421 at FL230 -28C doing 220ktas indicates 153kias.
A 441 at FL330 -50C 300ktas indicates 177kias.
The 25kias difference in wind noise is probably less of a factor vs the prop speed and possibly the engine whine.


Without doing the math I would expect the tip speed of a 4 blade at 2k is at most the same as a 3 blade at 1800. I would think it would then be the engine whine combined with a bit more wind noise. I do notice meaningfully more noise in a fast decent at say 190 indicated in the 340. The turbine whine is probably more annoying than the lower pitched piston, which is more easily filtered out by ANR and also our brains.

I'd love a dB reading from someone's apple watch in either a 421C or a 425 or 441. In the back of the 340 it's something like 86-87db(A) from memory, little louder up front. Comparing with another Apple watch was identical, so I assume that is relatively accurate.

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 Post subject: Re: 500 mile people hauler 421C vs 425 vs 441
PostPosted: 23 Mar 2021, 16:09 
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Username Protected wrote:
Airflow around the 441 will rarely if ever be 300kts.
A 421 at FL230 -28C doing 220ktas indicates 153kias.
A 441 at FL330 -50C 300ktas indicates 177kias.
The 25kias difference in wind noise is probably less of a factor vs the prop speed and possibly the engine whine.


You’re confusing indicated airspeed (which is simply a measure of dynamic pressure, gauged in knots) with the actual velocity of the air (which indeed is true airspeed). That does need to be corrected due to compressible effects when M>0.3 where an error starts to exceed 5% if you don’t.

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 Post subject: Re: 500 mile people hauler 421C vs 425 vs 441
PostPosted: 23 Mar 2021, 17:09 
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Username Protected wrote:
Airflow around the 441 will rarely if ever be 300kts.
A 421 at FL230 -28C doing 220ktas indicates 153kias.
A 441 at FL330 -50C 300ktas indicates 177kias.
The 25kias difference in wind noise is probably less of a factor vs the prop speed and possibly the engine whine.


You’re confusing indicated airspeed (which is simply a measure of dynamic pressure, gauged in knots) with the actual velocity of the air (which indeed is true airspeed). That does need to be corrected due to compressible effects when M>0.3 where an error starts to exceed 5% if you don’t.


Ummmm....ok, so please unconfuse me. As far as I know wind noise is in relation to the volume and friction of air flowing around the aircraft. Hence, at altitude where the molecules are spaced farther apart, making the air “thinner”, the aircraft will indicate a progressively lower airspeed and get progressively quieter while maintaining the same tas. As the aircraft can only “feel” indicated airspeed, the friction and noise will be in relation to its ias not tas.
But I could be way off here of course. :shrug:

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 Post subject: Re: 500 mile people hauler 421C vs 425 vs 441
PostPosted: 23 Mar 2021, 17:41 
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Username Protected wrote:

You’re confusing indicated airspeed (which is simply a measure of dynamic pressure, gauged in knots) with the actual velocity of the air (which indeed is true airspeed). That does need to be corrected due to compressible effects when M>0.3 where an error starts to exceed 5% if you don’t.


Ummmm....ok, so please unconfuse me. As far as I know wind noise is in relation to the volume and friction of air flowing around the aircraft. Hence, at altitude where the molecules are spaced farther apart, making the air “thinner”, the aircraft will indicate a progressively lower airspeed and get progressively quieter while maintaining the same tas. As the aircraft can only “feel” indicated airspeed, the friction and noise will be in relation to its ias not tas.
But I could be way off here of course. :shrug:


From the (now unclassified!) "AERODYNAMIC NOISE AND THE ESTIMATION OF NOISE IN AIRCRAFT"

"Aircraft noise...can be controlled by practical amounts of sound insulation and can be estimated from the indicated airspeed in most jet propelled or multi-engine propeller driven aircraft."

https://apps.dtic.mil/dtic/tr/fulltext/u2/013026.pdf

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 Post subject: Re: 500 mile people hauler 421C vs 425 vs 441
PostPosted: 23 Mar 2021, 18:13 
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Username Protected wrote:

Ummmm....ok, so please unconfuse me. As far as I know wind noise is in relation to the volume and friction of air flowing around the aircraft. Hence, at altitude where the molecules are spaced farther apart, making the air “thinner”, the aircraft will indicate a progressively lower airspeed and get progressively quieter while maintaining the same tas. As the aircraft can only “feel” indicated airspeed, the friction and noise will be in relation to its ias not tas.
But I could be way off here of course. :shrug:


From the (now unclassified!) "AERODYNAMIC NOISE AND THE ESTIMATION OF NOISE IN AIRCRAFT"

"Aircraft noise...can be controlled by practical amounts of sound insulation and can be estimated from the indicated airspeed in most jet propelled or multi-engine propeller driven aircraft."

https://apps.dtic.mil/dtic/tr/fulltext/u2/013026.pdf


I gotta tell ya. Feels quite nice to have my aerodynamic breakdown endorsed by the Wright Air Research Center.

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 Post subject: Re: 500 mile people hauler 421C vs 425 vs 441
PostPosted: 23 Mar 2021, 18:15 
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You say the following (bold is mine for emphasis):

Username Protected wrote:

You’re confusing indicated airspeed (which is simply a measure of dynamic pressure, gauged in knots) with the actual velocity of the air (which indeed is true airspeed). That does need to be corrected due to compressible effects when M>0.3 where an error starts to exceed 5% if you don’t.


Ummmm....ok, so please unconfuse me. As far as I know wind noise is in relation to the volume and friction of air flowing around the aircraft. Hence, at altitude where the molecules are spaced farther apart, making the air “thinner”, the aircraft will indicate a progressively lower airspeed and get progressively quieter while maintaining the same tas. As the aircraft can only “feel” indicated airspeed, the friction and noise will be in relation to its ias not tas.
But I could be way off here of course. :shrug:


Noise in the cabin is no doubt proportional to dynamic pressure (q), but is not otherwise liberated from velocity. That is, the noise created inside a fuselage in aircraft A will be higher than in B for the following situation: q_A = q_B , V_A > V_B
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 Post subject: Re: 500 mile people hauler 421C vs 425 vs 441
PostPosted: 23 Mar 2021, 18:40 
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Username Protected wrote:
"Aircraft noise...can be controlled by practical amounts of sound insulation and can be estimated from the indicated airspeed in most jet propelled or multi-engine propeller driven aircraft."

The Avantis must be noisy as hell!

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 Post subject: Re: 500 mile people hauler 421C vs 425 vs 441
PostPosted: 23 Mar 2021, 18:51 
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Username Protected wrote:
I doubt it.

The King Air was never about performance, that's a owner flown thing to look at. The corporate world wants reputation and comfort, perceived or not. The King Air reputation will keep them selling even if they have inferior performance, which they have always had.

A restart 441 would be awesome, however. It would be a $6M airplane.

Mike C.


I don't know many new King Air buyers, but the few who I do know got them far below "list." 350i's ended up being roughly PC12 money plus a few bucks.

To jump in the ring, a 441 should go for PC12 money and no more. To bring some converts over from TBMs, maybe slightly less.

You're right about the 441's cabin/comfort. That'd be the biggest knock on it compared to PC12 or KA. Or P180.


The sales hook seems crazy:

300 knots
Two engines
Under 70 gph fuel burn
2100 nm (!!!) max cruise range with 5 people aboard, or 10 people aboard with something absurd like 1200 or 1400 nm range. Sardine flight, but hey!


Crazy that it holds speed so well at 35k feet.


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 Post subject: Re: 500 mile people hauler 421C vs 425 vs 441
PostPosted: 23 Mar 2021, 18:55 
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Username Protected wrote:

Ummmm....ok, so please unconfuse me. As far as I know wind noise is in relation to the volume and friction of air flowing around the aircraft. Hence, at altitude where the molecules are spaced farther apart, making the air “thinner”, the aircraft will indicate a progressively lower airspeed and get progressively quieter while maintaining the same tas. As the aircraft can only “feel” indicated airspeed, the friction and noise will be in relation to its ias not tas.
But I could be way off here of course. :shrug:


Noise in the cabin is no doubt proportional to dynamic pressure (q), but is not otherwise liberated from velocity. That is, the noise created inside a fuselage in aircraft A will be higher than in B for the following situation: q_A = q_B , V_A > V_B


But if calling me confused improves your day then I accept.

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 Post subject: Re: 500 mile people hauler 421C vs 425 vs 441
PostPosted: 23 Mar 2021, 19:52 
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Whatever Israel, didn’t mean to insult your manhood.

By the way, calling you confused is quite different than saying that you have confused ...but I think an aero lesson is enough for one day

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