Big turboprop west over South London 29/11
The Tyne is considerably more powerful than the Proteus was which perhaps accounts for some of extra decibels. For an insight into operation of the Vanguard (in its 'Merchantman' freighter config), try the novel "The Damocles Plot" by Julien Evans.
The Dart had a centrifugal compressor rather than an axial compressor IIRC - did that contribute to noise? I seem to recall that the inner Tynes on the Vanguard also drove compressors for the pressurisation which may have generated noise. I knew this stuff 40 years ago!
I seem to recall that the inner Tynes on the Vanguard also drove compressors for the pressurisation which may have generated noise.
But we didn't let that get in the way of running all 4 up to takeoff power when doing pressurisation checks.
Quote from Discorde:
"The Dart had a centrifugal compressor rather than an axial compressor IIRC - did that contribute to noise? "
You're right about the Dart having a centrifugal compressor, but as a non-engineer I've no idea what effect that would have on noise. As you imply, the Tyne seems to be straight-through axial-flow.
Been trying to get my head around the "reverse-flow" path of air through the Proteus, which was said to make it more susceptible to icing (e.g., in cu-nims over Africa in the early days - 1957). Although there is a 12-stage axial-flow compressor at the front of the N2** shaft (and two turbines at its rear), the air intake is behind them, and the air flows forwards through them. After that, it enters a centrifugal compressor as a final compressor-stage before turning outwards and then aft through the eight combustion chambers, which are mounted annularly outside the compressors to minimise the length of the engine.
I'm wondering if the Proteus may have been so quiet because the compressor noise is partly shielded by the combustion chambers? (The exhausted air then drives the two N2** turbine stages, followed by two more turbine stages on the N1* shaft. The N1* shaft is referred to as a "free turbine", because it has no compressor at its front end - only the reduction gearbox that drives the propellor.)
"I seem to recall that the inner Tynes on the Vanguard also drove compressors for the pressurisation which may have generated noise."
Yes, and FWIW I reckon it's the (four) ED compressors and/or air-conditioning packs that produce the characteristic whine of a taxiing VC10. (BTW, most of the noise on an idling A320 is the shriek from the air-conditioning packs, run in their case by engine bleed-air.)
** For N2 read HP (high pressure)
* For N1 read LP (low pressure)
"The Dart had a centrifugal compressor rather than an axial compressor IIRC - did that contribute to noise? "
You're right about the Dart having a centrifugal compressor, but as a non-engineer I've no idea what effect that would have on noise. As you imply, the Tyne seems to be straight-through axial-flow.
Been trying to get my head around the "reverse-flow" path of air through the Proteus, which was said to make it more susceptible to icing (e.g., in cu-nims over Africa in the early days - 1957). Although there is a 12-stage axial-flow compressor at the front of the N2** shaft (and two turbines at its rear), the air intake is behind them, and the air flows forwards through them. After that, it enters a centrifugal compressor as a final compressor-stage before turning outwards and then aft through the eight combustion chambers, which are mounted annularly outside the compressors to minimise the length of the engine.
I'm wondering if the Proteus may have been so quiet because the compressor noise is partly shielded by the combustion chambers? (The exhausted air then drives the two N2** turbine stages, followed by two more turbine stages on the N1* shaft. The N1* shaft is referred to as a "free turbine", because it has no compressor at its front end - only the reduction gearbox that drives the propellor.)
"I seem to recall that the inner Tynes on the Vanguard also drove compressors for the pressurisation which may have generated noise."
Yes, and FWIW I reckon it's the (four) ED compressors and/or air-conditioning packs that produce the characteristic whine of a taxiing VC10. (BTW, most of the noise on an idling A320 is the shriek from the air-conditioning packs, run in their case by engine bleed-air.)
** For N2 read HP (high pressure)
* For N1 read LP (low pressure)
Last edited by Chris Scott; 5th Dec 2015 at 18:04. Reason: N1/N2 terminology explanations added.
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I suspect that the very high RPM of the Dart was a major contributor to the noise - Dart 510 ran at 14,000rpm while the 520 ran at 14500 at max power. Centrifugal compressors require to run at much higher rpm than axial. The Garrett TPE 331 in the Skyvan runs at a max of 43,000rpm - I saw one let go on a max power run it was spectacular to say the least.
I suspect that the very high RPM of the Dart was a major contributor to the noise - Dart 510 ran at 14,000rpm while the 520 ran at 14500 at max power. Centrifugal compressors require to run at much higher rpm than axial.
My only source for Proteus rpm is a small book on the Britannia by Derek Harvey that states the maximum compressor speed (i.e., HP rpm) as 12000. It also gives the free turbine (LP) speed as "about" 11000 rpm at take-off power, reduced by the reduction gear to about 1000 rpm at the propeller.
A number of Proteus engines were used in the West Country as power stations.
http://streaming.britishpathe.com/hl...84489.mp4.m3u8
http://streaming.britishpathe.com/hl...84489.mp4.m3u8
