Fly2HMO
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C172S Noise During Flare

Wed Nov 03, 2004 1:02 pm

I'm working on my PPL at ERAU, and so far I've flown 8 different (all pretty new, oldest is 1998) C172S and they all make this whining noise during flare.

This noise begins when at flare the nose goes up through the horizon, and is loudest when you reach Vy attitude or just before the stall horn goes off, and disappears as soon as you touchdown. I think I also recall hearing this "whining" during slow flight, but I don't remember if in a dirty or clean config.

Could it be turbulent airflow through the flap gaps that makes this noise?

Thx!!!  Smile/happy/getting dizzy
 
320tech
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RE: C172S Noise During Flare

Wed Nov 03, 2004 1:33 pm

Well, I don't get to fly nice new C172's, but the 70's versions make a low whining sound as the stall is approached. If you pull back just before the stall horn comes on, the sound gets louder and higher pitched.

I assume that's the same sound you hear.

It's obviously caused by changing airflow, but around which component, I have no idea.
The primary function of the design engineer is to make things difficult for the manufacturer and impossible for the AME.
 
Buzz
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RE: C172S Noise During Flare

Wed Nov 03, 2004 10:25 pm

Hi Fly2HMO, Buzz here. I haven't flown a plane that's less than 25 years old... and i prefer Classic Taildraggers. So take my advice with a grain of salt.

Do those new Cessnas have the wing root fresh air vents? Might it be an airflow harmonic through there? Close 'em and let's find out.

I'm thinking that it's caused by an airflow from higher pressure to lower pressure (OK, that's a redundant thought) The higher the angle of attack, the greater the pressure differential... whines more?

g'day
 
FredT
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RE: C172S Noise During Flare

Wed Nov 03, 2004 11:45 pm

Air will flow from lower pressure to higher pressure just fine... it just won’t accelerate, which it will do going the other way.  Big grin

If you blow down the neck of a bottle, you won’t hear much. Blow over the neck at the right angle and it whistles. It’s the same mechanism. At high angles of attack, the air hits something at the right angle to make it whistle. Never mind the pressure difference, angle and velocity are the crucial parts.

Cheers,
Fred


I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
CFIjames
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RE: C172S Noise During Flare

Thu Nov 04, 2004 12:29 am

One of our 172sp's at my flight school had the same issue, only it was constant throughout flight. VERY annoying. We tried closing the air vents, taping the air vents, etc. Turns out it was the wing root fairing between the windshield and the wing itself. When we put some tape along that seam there the noise stopped completely. Musta been some kind of harmonics or something when the wind whistled through there.
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Aaron747
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RE: C172S Noise During Flare

Thu Nov 04, 2004 4:22 am

It's definitely something harmonic. I fly a '79 172N, '82 172P and '97 172R at my school and all have the wing root air vents and the weird whining sound while flaring.
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Fly2HMO
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RE: C172S Noise During Flare

Thu Nov 04, 2004 11:24 am

Must be some weird harmonics then, because today I flew in the morning and I did stalls and slow flight (clean and dirty) and outside it was at 0 celsius, I had the vents closed and I still remember hearing this.

Thx for your responses  Smile

[Edited 2004-11-04 03:26:17]
 
NWA
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RE: C172S Noise During Flare

Fri Nov 05, 2004 5:52 am

I am surprised your flight instructors have not told you what it is. Its the stall horn. Landings are to be done, most of them anyways, to a FULL STALL. If the stall horn does not go off, you did it wrong. On newer models, the flow over the wing changes, which creates a suction. This in return makes the stall horn go. In older models with an electronic stall horn, its not a vent in the wing like on the newer models, its a little switch. When the flow over the wing changes like in a stall of moments leading up to it, it will throw the switch up and connect the circut, allwing for the horn to sound. The stall horn will go off from stall to 10 knots above stall I believe. If I am incorrect, I am sure one of the CFI's here could explain this in MUCH better detail than I can.
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RaginMav
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RE: C172S Noise During Flare

Fri Nov 05, 2004 7:08 am

The 1967 150 I fly does the same thing, and yeah it does it during slow flight as well. No it is NOT necessarily the stall horn! that's an entirely different whining sound.

Funny though, the Cherokee 180 I flew a month ago didn't do it.
 
FredT
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RE: C172S Noise During Flare

Fri Nov 05, 2004 7:44 am

NWA:
"and is loudest when you reach Vy attitude or just before the stall horn goes off"
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NWA
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RE: C172S Noise During Flare

Fri Nov 05, 2004 9:02 am

Sounds like the stall horn to me. Other than that, i have never heard this noise.
23 victor, turn right heading 210, maintain 3000 till established, cleared ILS runwy 24.
 
sccutler
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RE: C172S Noise During Flare

Fri Nov 05, 2004 1:08 pm

Recall that the 172's have a non-electric, reed-type stall warning device. It starts out with a sort of thin, reedy squeal and morphs into a robust bleating calf squall noise.

Kind of ridiculous-sounding, but very simple, and works no matter what happens with the electrical system.
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NWA
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RE: C172S Noise During Flare

Fri Nov 05, 2004 3:57 pm

the electrical system I was refering to is that on the 1980 172RG.
23 victor, turn right heading 210, maintain 3000 till established, cleared ILS runwy 24.
 
brodiebrazil
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RE: C172S Noise During Flare

Sat Nov 06, 2004 2:23 am

I dont think he's referring to the stall horn...

I too have noticed almost a whistling noise right before the stall horn starts as I begin to flare on all of the 172S models i've flown. It increases when there is a gust of headwind too, so I guess it could be related to the reed-type warning device, but most likely is just air blowing over something else.
 
320tech
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RE: C172S Noise During Flare

Sat Nov 06, 2004 10:39 am

As I've heard the sound too, I would like to emphatically state that it is NOT the stall horn. If you can't tell the difference between airflow noise and the stall horn by the time you've finished your private pilot's licence, you are a dead man flying!  Smile
The primary function of the design engineer is to make things difficult for the manufacturer and impossible for the AME.
 
brodiebrazil
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RE: C172S Noise During Flare

Sat Nov 06, 2004 1:13 pm

Also....

just realized the whistle and the stall horn can come on at the same time... so it's definitely not the same thing.
 
Fly2HMO
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RE: C172S Noise During Flare

Sun Nov 07, 2004 11:34 am

I think I discovered what it is, I was practicing at an emergency landing, and had 68 kias. It was getting hot in there and I opened the overhead vents. Then the whistle started. Interesting enough though, it seemed to be produced by the propeller's wash, because as I changed the throttle setting, the whistle pitch changed, even though I was still at 68 kias.

Anybody here flying Cessnas would care to confirm this in an experiment? I have a flight on monday, i'll mess around with the vents and see what happens (if I remember).

Cheers  Smile/happy/getting dizzy



[Edited 2004-11-07 03:44:56]
 
BMAbound
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RE: C172S Noise During Flare

Mon Nov 08, 2004 1:03 am

I'm going to fly a 172R tomorrow (monday) as well, I'll try to check it out.

johan
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Fly2HMO
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RE: C172S Noise During Flare

Wed Nov 10, 2004 2:41 pm

OK, I think I finally confirmed this.

Today (Wed.) I had a flight with all the vents closed since it was chilly outside. I never heard the whining noise, and I did several in-flight stalls and several full stall flares. Never heard it. So I guess the vents have something to do with that whining. In reply 6 I said I heard this with the vents closed, but I was thinking maybe my instructor had his vents open, because the whinning wasn't as loud. This time I was sure I had all of them closed, and I didn't hear the whining.

Makes sense?  Smile/happy/getting dizzy
 
AdamWright
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RE: C172S Noise During Flare

Sat Nov 13, 2004 11:58 pm

I've flown the riddle fleet... N501ER Yesterday as a matter of fact.

I believe I know what "whine" you are talking about. i'd say that the airvent deal is probably what it is. It's definately an airflow issue. Don't worry though, I've heard it lots of time on landings.. and I'm still here  Big grin

Good luck with your PPL man.

-Adam

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