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Sound - High pitch whine


RogueRunner

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  • 9 months later...

Sorry to bring back to live this "old" thread.

I think in fact its a total hazardous mix between all explanation.

 

Maybe a resonance between several sound.

 

From one side without open gun port the mustang don't to this sound at high AOA, in another side other mustang still do it in high AOA with gun port, sure things the gun port have an important role.

The air intake also, at high AOA the sound are not constant and pitched higher than the rare occasion where we hear it from a level flight.

At high AOA its for sure the gun port, gun the blade can also help this sound, and at level its the radiator, but during high AOA i'm sure its a resonance between sound from supercharger, gun port, prop and radiator, all of them have an important role, that why with one of this element removed its rare to hear it but not impossible.

 

The prop and the supercharger have a secondary role, but it still important and its cause of both of them that we can hear this sound without gun port, together they do the same effect with the radiator than the couple : gun port -> radiator.

 

The constant sound with always the same pitch was the radiator and the sound who are some time pitched really high (depending of the AOA) come from the gun port.

 

Cause of the number of gun ports, they don't need sound from radiator, supercharger or prop, but the radiator need sound from prop, supercharger or even gun port for scream, cause i think its a sound induced resonance.

All Mustang have the "same" gun port, they don't have so much difference, its always the same caliber after all, but the ventral radiator are different depending of the Mustang, the Reno one have a flat and small one like you can clearly see it here :

http://www.airportjournals.com/Photos/0810/X/0810021_10.jpg

 

Like the gun port it is at 90° of the "gun cross" unlike other mustang where the radiator are inclined :

 

http://www.flightglobal.com/airspace/media/baron_inchcape1/images/818/north-american-p-51d-mustang-susy-flying.jpg

 

 

For this Reno's Mustang only the speed count cause the radiator intake are in the right condition for do a sound, for other Mustangs with inclined radiator intake it need sound resonance from engine for be hear and its only in rare conditions, high AOA help it.

 

 

Its still a theory but my conclusion is :

 

1. Gun ports make the bigger sound, the whistle sound who have different pitch regarding AOA, cause of the number of canon they is (almost?) always one who whistle and cause of the size and the number the pitch can change.

 

2. With or without gun port when the radiator's air intake are flat the sound are more a problem of speed but a really light AOA can in rare conditions amplified the sound but it will not be loud as the gun port's sound, the sound are always at the same pitch.

 

3. With or without gun port when the radiator's air intake are tilt the sound can only be hear in a certain AOA and speed and only in certain conditions who cause a sound resonance between the air intake itself and prop/supercharger and its whistle, a little more low pitched than the gun port's whistle sound but still the same, its louder than the flat air intake direct sound (who can't enter in resonance i think) but not as the gun port's sound and its always at the same pitch...

 

Don't blame me if i'm wrong its still a theory based on...nothing but its better than a dispute between everyone ^^"

And it can be right, who know...

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Just to add my two bits--when I saw three Mustangs doing aerobatics at Oshkosh, I heard no whistle at all. Now the Corsair whistle is loud as heck, but none of the P-51s I've ever seen fly had a whistle. However, I was to the side of the aircraft during their loops, not to the front; the direction may make a difference.


Edited by Echo38
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One culprit might also be the Supercharger ?

High RPM of the blower produces a whine.

 

On Turbocharged engines, like in the Messerschmitt it's more pronounced.

 

Or so i've let myself be told..

Sometimes I Amaze even Myself!
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I have seen many variants of Mustangs flying at airshows over the years and observed the following.

 

1) Merlin engined P-51s all exhibit a very low level 'ambient' whistle in level flight regimes at high speed. This could be airframe or supercharger, but I doubt the latter as Spitfires with equivalent Merlin types do not make the same noise. Cannot confirm if Allison engined Mustangs do the same as I only saw an A-36 once several years ago and cannot recall.

 

2) The loud and very noticable scream-moan-whistle is only active on P-51D with gunports when the aircraft is pulling G during the display; this means AoA and is reinforced by observation that the scream is more intense the more vigorous the pitching manouevre.

 

3) P-51C Princess Elizabeth did NOT exhibit same noise when manouevering in similar manner - note radiator housing configuration in this aircraft is identical to P-51D but has different gunport configuration.

 

4) Old Crow from Scandinavian Historic Flights is a P-51D without gunports; during high angle of attack manouevres this aircraft did NOT make the scream/moan/whistle normally associated with such manouevres by a P-51D with gunports.

 

5) Just as an observation different P-51Ds scream differently - Ferocious Frankie for example always seemed to be a particularly vocal aircraft in this respect, whereas Big Beautiful Doll (ex- of Rob Davies) was consistently not quite so (but still pretty loud) and Jumpin Jacques of Peter Teichman still very noticable but not so intense again with a different tone too. A degree of this must be considered as pilot technique (agression of manouvering etc) but it could equally be something like how deep the recess of the gunports are etc. - more likely than differing radiator configs IMHO.

 

So after 16 years of observing many different Mustangs at airshows across the UK, I'd be putting my money on the gunports. :D


Edited by DD_Fenrir
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Just to add my two bits--when I saw three Mustangs doing aerobatics at Oshkosh, I heard no whistle at all. Now the Corsair whistle is loud as heck, but none of the P-51s I've ever seen fly had a whistle. However, I was to the side of the aircraft during their loops, not to the front; the direction may make a difference.

 

Direction does not; I heard Ferocious Frankie scream coming out of a loop a she aerobatted over Leeds castle whilst I, two miles away, was stood in my mates front garden enjoying the show with a beer!

 

You'll find that because formation aerobatics call for progressive steady manouevres so that wingmen can hold their positions more easily, the aircraft in formation rarely fly in the manner to reach the AoA that causes the onset of the whistle, at least at volumes and frequencies to be noticable above the engine noise.

 

I noticed the same as you during a Horsemen routine several years ago at Duxford. Could catch just a trace fleetingly as one of the wingmen briefly corrected with enough pich angle to cause a momentary pulse - an irregular 'whoop---whoop-whop---whoooop------------whoop' as they pulled out from a dive and up into another verticle manouevre which was cool, but no sustained screams of the calibre shown by some of the solo displays as linked in this thread.

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  • 5 years later...
  • 1 month later...

Interesting video. I am glad he mentioned 2 times you hear the whistle because high AOA does not really happen in a dive or high speed pass. On pull up for the loop, yes, when the actual angle of attack, not angle with horizon, gets higher. It's the angle of the chord to the relative wind that makes AOA. And here is where the gun ports catch the relative wind at an angle and whistle more than pass air smoothly. The other time is landing, and this is the big one. Low speed, high angle of attack to maintain lift. Think of the modern jet fighter demos and testing. Slats, cobras all that stuff.

 

And I believe it is a combination of sounds, or at least the supercharger compressor is getting overlooked a bit. The rotors will whine when they are under load. The sounds come from the bearings and the blades. On cars, you hear it when the vacuum system closes the bypass valve when load is put on the engine. When the load is off, you can hear some of the rotor whine, but it is much stronger when the blower is loaded down pushing boost. Now this may differ on the Merlin since I think the system is gear and not belt driven, of course. Someone please fill us in on how this would effect rotor sound. Also placement of the air intake. The Spit intake system is different and the inter-cooler location is as well. The Mustang's central scoop being so famous. Also remember how the sound is stronger when the plane is facing you and much less as it is flying away. Think of where the sound must be coming from in those instances. In front you hear the blower, in back you hear the exhaust.

 

Supercharged engines all whine. The Spit, Emil and Mustang all do it but these Mustangs are extra loud with the gun port whistle. Hey, what about early Mustangs with the 4 50s. Don't they have a streamlined blister on the leading edge? B types?


Edited by Squiffy

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It's perfectly ordinary banter Squiffy, "Bally Jerry, pranged his kite, right in the 'how's your father.'" - Monty Python, RAF Banter Sketch.

Squiffy, a. slang. 1. Intoxicated; drunk. 2. Askew, skew-whiff. - OED

 

"Put that sucker in a 4G turn and keep it there!!" - Maj. Gen. "Boots" Blesse

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I'm a bit late to this topic, like 6 years late :lol: , and I'm not any "audiophile" as somebody says at some point but I'm a classical musician besides pilot and I think my hearing is good enough.

 

 

I think Fenrir is quite right. Here there are two different sounds, one the whine of the supercharger or whatever aerodynamic effect which is mostly soft and subtle (like the Rheno race gunless P-51 in videos at the thread start) and that can be hear in many aircraft and not only P-51 but changes over in different situations.

 

 

Take a look here where many Spitfires sound different, and some of them (few) features the subtle whine while others don't. Pay attention to 0:50, is that a Mk.XVI with a Packard engine perhaps? But also 1:00, is that MH434 parhaps? So no Packard I think.

 

 

 

And a second whine or better said a whistle by the gun ports as stated at some point by pilots and people knowing the subject here. That video also at thread start of Ferocious Frankie in a foggy day is so obvious and maybe that weather contributed to some extent to the wild whistle heard there.

 

 

Those two effects can be confused in videos as sometimes they can sound alike when only subtle as well as we have to bear in mind they are just recordings so who knows mic quality and recording conditions in every one of them. But those are definitely different sounds and that can be said with a bit of a good listening in the many videos shown here.

 

 

S!


Edited by Ala13_ManOWar

"I went into the British Army believing that if you want peace you must prepare for war. I believe now that if you prepare for war, you get war."

-- Major-General Frederick B. Maurice

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Great vid Ala13! I am a musician too. I realized the supercharger whine is subtle yet quite high, like jet whine and not the howl of the gun ports.

 

I remember in Rowan Software's second great flight sim Batlle of Britain, that the Emil flyby sound was very cool with the supercharger whine. You heard it all the time on merge.

[sIGPIC][/sIGPIC]

It's perfectly ordinary banter Squiffy, "Bally Jerry, pranged his kite, right in the 'how's your father.'" - Monty Python, RAF Banter Sketch.

Squiffy, a. slang. 1. Intoxicated; drunk. 2. Askew, skew-whiff. - OED

 

"Put that sucker in a 4G turn and keep it there!!" - Maj. Gen. "Boots" Blesse

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I remember in Rowan Software's second great flight sim Batlle of Britain, that the Emil flyby sound was very cool with the supercharger whine. You heard it all the time on merge.
Yep, but DB engine is known for its supercharger whine. I guess intake location and fan revs make a difference in that.

 

 

S!

"I went into the British Army believing that if you want peace you must prepare for war. I believe now that if you prepare for war, you get war."

-- Major-General Frederick B. Maurice

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  • 3 weeks later...

Hey guys, I just watched Kermit preflight the P-51 on Fantasies of Flight on YouTube. I have seen it before but I noticed that the inboard guns are set back in the wings, leaving a big tube of hollow sheet metal sticking out into the slip stream. Sure it is about the same reveal as the other guns but no barrel for several inches. I think this might be the main resonator in the high AOA whine noise. It's great that we have these high def videos now with sound on YouTube. I have been practicing a good bit and getting better against the Dora. The AI never makes a mistake at these AOAs but I am still stalling around out there. The whine noise is actually helping as a clue that kicks in before buffeting (external view) I was used to the Sabre with a good buffet onset but you need to be more careful in the Pony with that big prop and Pfactor+. It's still tough to do a loop and hard steep turns. But turning left is of course easier due to Pfactor+ :D

[sIGPIC][/sIGPIC]

It's perfectly ordinary banter Squiffy, "Bally Jerry, pranged his kite, right in the 'how's your father.'" - Monty Python, RAF Banter Sketch.

Squiffy, a. slang. 1. Intoxicated; drunk. 2. Askew, skew-whiff. - OED

 

"Put that sucker in a 4G turn and keep it there!!" - Maj. Gen. "Boots" Blesse

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