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C172S Noise During Flare  
User currently offlineFly2HMO From , joined Dec 1969, posts, RR:
Posted (10 years 1 month 3 weeks 4 days ago) and read 2352 times:

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

19 replies: All unread, jump to last
 
User currently offline320tech From Turks and Caicos Islands, joined May 2004, 491 posts, RR: 5
Reply 1, posted (10 years 1 month 3 weeks 4 days ago) and read 2332 times:

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.
User currently offlineBuzz From United States of America, joined Nov 1999, 697 posts, RR: 21
Reply 2, posted (10 years 1 month 3 weeks 3 days 15 hours ago) and read 2277 times:

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


User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 3, posted (10 years 1 month 3 weeks 3 days 14 hours ago) and read 2251 times:

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.
User currently offlineCFIjames From United States of America, joined Aug 2004, 87 posts, RR: 0
Reply 4, posted (10 years 1 month 3 weeks 3 days 13 hours ago) and read 2242 times:

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.


There are 3 simple rules for making a perfect landing every time. Its a shame that no one knows what they are.
User currently offlineAaron747 From Japan, joined Aug 2003, 8294 posts, RR: 26
Reply 5, posted (10 years 1 month 3 weeks 3 days 9 hours ago) and read 2215 times:

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.


If you need someone to blame / throw a rock in the air / you'll hit someone guilty
User currently offlineFly2HMO From , joined Dec 1969, posts, RR:
Reply 6, posted (10 years 1 month 3 weeks 3 days 2 hours ago) and read 2153 times:

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]

User currently offlineNWA From United States of America, joined Jun 2001, 1200 posts, RR: 3
Reply 7, posted (10 years 1 month 3 weeks 2 days 7 hours ago) and read 2094 times:

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.


23 victor, turn right heading 210, maintain 3000 till established, cleared ILS runwy 24.
User currently offlineRaginMav From United States of America, joined May 2004, 376 posts, RR: 1
Reply 8, posted (10 years 1 month 3 weeks 2 days 6 hours ago) and read 2080 times:

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.


User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 9, posted (10 years 1 month 3 weeks 2 days 6 hours ago) and read 2073 times:

NWA:
"and is loudest when you reach Vy attitude or just before the stall horn goes off"



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineNWA From United States of America, joined Jun 2001, 1200 posts, RR: 3
Reply 10, posted (10 years 1 month 3 weeks 2 days 4 hours ago) and read 2067 times:

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.
User currently offlineSccutler From United States of America, joined Jan 2000, 5617 posts, RR: 28
Reply 11, posted (10 years 1 month 3 weeks 2 days ago) and read 2044 times:

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.



...three miles from BRONS, clear for the ILS one five approach...
User currently offlineNWA From United States of America, joined Jun 2001, 1200 posts, RR: 3
Reply 12, posted (10 years 1 month 3 weeks 1 day 21 hours ago) and read 2029 times:

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.
User currently offlineBrodieBrazil From Canada, joined Nov 2003, 88 posts, RR: 0
Reply 13, posted (10 years 1 month 3 weeks 1 day 11 hours ago) and read 2003 times:

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.


User currently offline320tech From Turks and Caicos Islands, joined May 2004, 491 posts, RR: 5
Reply 14, posted (10 years 1 month 3 weeks 1 day 3 hours ago) and read 1967 times:

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.
User currently offlineBrodieBrazil From Canada, joined Nov 2003, 88 posts, RR: 0
Reply 15, posted (10 years 1 month 3 weeks 1 day ago) and read 1950 times:

Also....

just realized the whistle and the stall horn can come on at the same time... so it's definitely not the same thing.


User currently offlineFly2HMO From , joined Dec 1969, posts, RR:
Reply 16, posted (10 years 1 month 3 weeks 2 hours ago) and read 1912 times:

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]

User currently offlineBMAbound From Sweden, joined Nov 2003, 660 posts, RR: 4
Reply 17, posted (10 years 1 month 2 weeks 6 days 12 hours ago) and read 1875 times:

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

johan



Altitude is Insurance - Get Insured
User currently offlineFly2HMO From , joined Dec 1969, posts, RR:
Reply 18, posted (10 years 1 month 2 weeks 3 days 23 hours ago) and read 1813 times:

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


User currently offlineAdamWright From , joined Dec 1969, posts, RR:
Reply 19, posted (10 years 1 month 2 weeks 13 hours ago) and read 1752 times:

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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