Happy-flier
Topic Author
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Joined: Sat Dec 25, 1999 4:41 pm

Did Turbojets Ever Produce A "buzzsaw" Noise?

Thu Jun 17, 2004 10:57 pm

I'm hoping that all you folks who remember the old turbojet-powered (JT3C, JT4A) DC-8s and 707s can help me with this one.

Did these engines make that familiar forward "buzzsaw" noise that we hear on the JT8Ds that power the old-generation 737 and DC-9, or even that we hear on the JT3Ds?

I have never heard the old turbojets in operation (born too late for that), but I noticed that the Concorde certainly did not have any buzzsaw noise when it took off - just a reverberation of the thunder-like boom from the hot exhaust (not considering afterburner use - I only saw it take off without this feature). The only reason I bring up the Concorde here is that it is a four-holer turbojet.

Many thanks.

[Edited 2004-06-17 16:03:14]
May the wind be always at your back . . . except during takeoff & landing.
 
N766UA
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RE: Did Turbojets Ever Produce A "buzzsaw" Noise?

Fri Jun 18, 2004 3:21 am

I've never heard a 707, DC-8, 727, or DC-9 engine buzz. They sound more like fighters when they take off... very throaty rumble. NASA flies their 720 here often and it just roars. Aircraft that buzz typically have high-bypass engines like the 737NGs, A320s, 757s, 777s, etc. Even the CRJ has a bit of a buzz to it.
This Website Censors Me
 
411A
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RE: Did Turbojets Ever Produce A "buzzsaw" Noise?

Fri Jun 18, 2004 12:45 pm

B707-320B (advanced cowl) models wth JT3D engines, the 'buzzsaw' noise can only the heard from INSIDE the aircraft, from the flight deck and in the first few rows of pax seating.

The older models of B707, without fan engines, did not have the 'buzzsaw noise' that was common with later models.
 
tu114
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RE: Did Turbojets Ever Produce A "buzzsaw" Noise?

Fri Jun 18, 2004 6:43 pm

I didn't think Concorde was able to take off without afterburners selected?
 
QantasA332
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RE: Did Turbojets Ever Produce A "buzzsaw" Noise?

Fri Jun 18, 2004 7:57 pm

As far as I know, normal Concorde takeoffs do indeed always involve "activated" afterburners; they're employed for up to 30 seconds after takeoff...

Cheers,
QantasA332

Edit: I checked my books to confirm and yes, afterburners are normally used on takeoff. Unless you saw a special demonstration or test flight, chances are the afterburners were on on takeoff. They remain on for around 30 seconds after takeoff, as I said, and then turn of to help reduce noise while accelerating through Mach 1.7 or so...

[Edited 2004-06-18 13:17:58]
 
Klaus
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RE: Did Turbojets Ever Produce A "buzzsaw" Noise?

Fri Jun 18, 2004 9:15 pm

At low weight (non-transatlantic), it should have been possible to take off without reheat, would it not?
 
Happy-flier
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RE: Did Turbojets Ever Produce A "buzzsaw" Noise?

Fri Jun 18, 2004 11:21 pm

Thanks, 411A. You kind of confirmed my suspicions about the difference in the forward sounds made by the JT4A- vs. JT3D-powered jets. It makes sense to think that the buzzsaw sound would be absent in the non-fan engines, because it is, after all, the fanblades that make the sound (and produce a much deeper tone in the larger turbofans than in the narrow-diameter ones, like the JT3D & the JT8D).

As for the Concorde takeoff - I must have thought that the afterburners were not on, but then I am even more surprised that the noise did not linger as I thought it would. The sound of the Concorde on takeoff - to me - was like a fighter jet, but it did not linger. On the other hand, watching a 732 or a 722 takeoff - man, does that crackle ever linger and reverberate!!  Smile
May the wind be always at your back . . . except during takeoff & landing.
 
sovietjet
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RE: Did Turbojets Ever Produce A "buzzsaw" Noise?

Sat Jun 19, 2004 2:30 am

If the "buzzsaw" is what I think it is, then I definetly hear it on A320s and B737-300 and above and all the planes that have "fat engines" or high-bypass engines. Low bypass turbofans I've never heard them make buzzsaw noise. MD80, Tu-134, they all have a deep roar when they approach. Tu-154 whistles alot but doesnt have the buzzsaw noise. But all the Airbuses and new Boeings do. I can only imagine what a JT3C sounds like or better yet, 8 of em on a B52.
 
Happy-flier
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RE: Did Turbojets Ever Produce A "buzzsaw" Noise?

Sat Jun 19, 2004 2:57 am

Here's how I distinguish the sounds made by various jet engines.

Forward sound: "buzzsaw" -- This sound is indeed very common in the P&W-powered 762's, in pretty much all 757's, certainly in the early-series 747's, and also on the L1011 and DC-10. But - as Sovietjet pointed out - these are all "fat" or large-diameter turbofans, and so the "buzzsaw" noise is quite deep and guttural. In "slimmer" turbofans, like the JT3D, there is definitely a buzzsaw forward noise - but it's of a much higher pitch than the large, high-bypass engines that I mentioned above. It makes sense to me that turbojets (in other words, "straight-pipe" or no-bypass engines) would not make a buzzsaw noise, since the first "fan" blades in the intake are part of the compressor, and the overall air intake space is much smaller in turbojets compared to turbofans. It's not to say that there is absolutely none of this noise produced by turbojets - I've never heard them up close - but the few sound files that I have heard of turbojets starting up or taxiing, have had more of a plain "hiss" or air-being-sucked-in sound, with the "fighter-jet" thunder reverberating from behind - in other words, from the very noisy exhaust.

Lateral sound: "scream" or "whistle" -- The few sound files that I've seen of turbojets in operation (e.g. Comet) have had an intensely painful scream - a kind of shrill whistle, if you will. Now, I have picked this up pretty much in all jet engines - even the most modern, quiet turbofans. They all have a bit of a whistle as they pass by. The JT3D's that powered the 707 and DC-8 had a particularly resonant, melodious "whine" as they landed - quite the sound. The IL-62 had a similar kind of sound as well.

Aft sound: "thunder" or "crackle" or "boom" -- The aft sounds produced by various jet engines can be quite variable. The Concorde had an intense, fighter-jet-like thunder. The JT8D's on the old-generation 737's and DC-9's really crackled (though the hushkitted engines in recent operation now seem to produce more of a "muffled hiss", if I can use another term). I never heard the aft sound of a JT4A with sound suppressors, so this I don't know. But most high-bypass fans today seem to cover up the "boom" of the hot jet exhaust quite well with the cool air.
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