Why are Cessnas so loud?

[Guest Jake.f]

Hey

 

Have been spending a bit of time at the airport recently getting training sorted for a few weeks time, and also on a scenic flight recently (Loads of fun).

 

As the title says though, how come it seems that Cessna aircraft are so bloody noisy at full power on takeoff roll and climb?

 

While I was at the airport recently waiting I watched two Cessna aircraft takeoff and it seemed that their takeoff roll was quite loud. in comparison, from people on the outside, the Cherokee 180 I flew in was "half as loud" as the Cessnas were, and watching the little Foxbat I am training in takeoff it was probably 1/3 as loud.

 

Is this due to the engines or the pitch of the props cutting the air? I expected the Foxbat to be quieter obviously but expected the Cherokee (Being 38 odd years old) to be as loud or louder than the Cessnas around that day.

 

My school is about 1km from the GA runway and I can tell without seeing when a Cessna is taking off (For skydiving, or one of the plentiful privately owned ones) as their distinctive sound fills the air.

 

Any ideas?

 

Thanks.

 

 

[PapaFox]

A little bit of 'A' and a little of 'B'

 

There are quite a few different combinations at play here, but the prop does make quite a difference. Fixed pitch vs Constant Speed... CS will just about always be noiser, due to the higher power output of the motor and higher prop RPM.

 

IIRC, Cessna's also generally don't have as much in the way of mufflers in comparison to the Pipers.

 

 

[turboplanner]

Depends on the Cessna, a 182 will scare the birds for miles

 

 

[Guest ozzie]

C185 has a real rasp to it and as good neighbour policy we asked our jump pilots to come back a litttle on rpm as soon as they were airborne. The C182 was a little quiter. We had a three bladed (ex amphib) and a two bladed 185 and the threee blade was louder. From memory they pulled around 2700 rpm on TO and the 182 was a little less.

 

 

[Guest Jake.f]

The one I watched takeoff was listed as a 206, there was another one which might have been a 172,182 etc etc.

 

You would think if it is the high revs causing noise that rotax engines would be a lot louder.....

 

 

[turboplanner]

Depends on the engine - a Chev 350 makes most of its distinctive noise from resonence of the manifold, I've noise tested and got a higher reading from the front than directly from the exhausts at the rear. Loudest aircraft noises - the one you hear from a kilometre away usually come from the prop.

 

 

[Guest Jake.f]

Yeh it sounds like the noise of the props I always hear not the engine, you can kind of just tell as it sounds like that 'cutting' through the air sound.

 

I have no complaints about it anyway

 

 

[facthunter]

On the bigger engined Cessna's, the prop tips run supersonic, entirely due to a combination of prop diameter and revs. A slight reduction of RPM cuts the noise down considerably. They are a bit anti-social. Nev

 

 

[old man emu]

You would think if it is the high revs causing noise that rotax engines would be a lot louder.....

Don't forget that Rotax engines are noise suppressed to meet strict European noise regulations, so even though they rev high, their muffling system makes them socially acceptable. By the same token, it must be said that Jabiru engines are reasonably quiet too.

 

You can also consider the amount of noise a 2 litre/4cylinder engine will make compared to a 4 litre/4 cylinder engine, simply due to the amount of gas pushed out during each exhaust stroke. (Notice I didn't say that it's due to the bigger "bang" during the power stroke.)

 

The major source of noise from an airplane is caused by the prop tips, and this is a product of the blade diameter. That's why putting a three or four bladed prop quietens a plane down. The extra blades share the engine power, so each blade does not have to be so long. The tip does not have to travel as great a distance per revolution, so it is slower. It all boils down to the old:

 

speed = distance/time, where the distance = pi x diameter.

 

OME

 

 

[facthunter]

Well, the Rotax is geared down, so the prop RPM is lower. Nev

 

 

[Guest Jake.f]

I figured it was the prop tips, I remember reading somewhere that the tip of the props on some engines can travel at 80% of the speed of sound, where the engine revs nowhere near that much.

 

Probably the same principle as something I was reading the other day, theoretically if you built a tall enough tower on the Earth the tip would be traveling faster than the speed of light (and moving back in time, but that's a whole other story).

 

Makes sense that a 3 blade prop makes less noise than the two blade cessnas too.

 

 

[kgwilson]

Engine noise is a bit subjective as individuals have different preferences or perhaps dislikes as the case may be. Personally I love the sound of big radials, also Merlin V12s and in the RA arena the Jab 3300 is hard to beat. As has been said the real raspy noise which seems to travel the furthest comes from the prop tips. This turns into a real cracking sound when prop tips become supersonic so there are multiple mini sonic booms. C185s & C206s seem to be the loudest when at full throttle & fine pitch.

 

 

[PapaFox]

One of the worst offenders recently appears to be the Cirrus SR22. Man do those thing develop a howling scream.

 

 

[Guest Howard Hughes]

Lucky there were no C-206's departing that day, at 2850 RPM they just scream!

 

 

[Guest Jake.f]

There was a 206, and it was loud!

 

 

[Guest Jake.f]

Yeh I personally don't have a problem with aircraft noise, that louder the better! Except when certain pilots choose to fly over our house (Which is just out of controlled airspace) at what surely is lower than 500ft on Saturday mornings, although granted they may be on approach to a small grass strip not far from where I live which could explain the height, or lack thereof.

 

 

[IanR]

Love the sounds of a Harvard on takeoff !!

 

On the C180 I fly the tip noise is very loud on takeoff so we always reduce RPM - makes a huge difference - very noise sensitive residents round here (who moved in after the airport was built)

 

 

[kaz3g]

The one I watched takeoff was listed as a 206, there was another one which might have been a 172,182 etc etc.You would think if it is the high revs causing noise that rotax engines would be a lot louder.....

The C206 with a 3 blade CS prop is shockingly noisy. A jump ship C206 operates out of Lilydale weekends and you can hear it clawing its way up every one of the 10,000 feet until it evicts its load. We have one operating out of Coldstream, too but it generally just comes and goes as it is used for pilot training by the MAF.

 

kaz

 

 

[Guest Jake.f]

The good thing here is that no one really complains about noise if it is at a reasonable time, probably to the fact the airport is often used for training. A fighter jet doing a low pass or a C17/C130 practicing an aborted landing kind of drowns out the Cessna's....