Big turboprop west over South London 29/11

[treadigraph]

Anyone know what was heading west over south London at about 7:15pm tonight (29/11)?

Very deep and unusual sounding turboprop, certainly not a Q400 or Herc, nor would I think an AN-12 or AN-26 which are fairly regular over these parts. Might be a Transall, or perhaps an A400 - haven't seen or heard one of those yet!

Nothing on FR24...

Thanks, Treadders

[HEATHROW DIRECTOR]

Q400? I'm not familiar with those.

Did it sound high? I've noticed that thick cloud layers can play havoc with a/c noise. Someone is bound to know..

[DaveReidUK]

RAF C-130J ZH881 was active around that time. And lots of Q400s (marketing designation for the DHC-8-400 Dash 8).

No trace of anything more exotic on Mode S.

[joy ride]

I too heard it in Southwark, was surprised by the deep roar, almost like a huge Swedish freight train crossing our yard. I went outside, but thick cloud prevented me from seeing anything. Weather, especially cloud, can have a very big affect on sound, but this was unusual.

[treadigraph]

I'd would guess it to have been at around 20000 or so. Surprised if it was indeed the C-130J which are regular passers by on their way home to Brize, they seem to have a higher note; and as joy ride says this did sound very unusual - when I first heard it I did wonder if it was the AN-22 but as my fillings didn't start to rattle...

Ah well!

Thanks all,

Treadders

[Big Eric]

It was a GAF Transall that landed at Brize Norton.
Credit : FighterControl

[treadigraph]

Ah, nice one, thanks Eric! Always liked the sound of Tynes!

[Big Eric]

No problem, just happy to help.

[Porky Speedpig]

Solves a mystery - it sounded like a brace of Vanguards over here!

[AeroSpark]

Sure it wasn't a Tu-95?:E

[treadigraph]

We'll Bear it in mind AeroSpark!

(Never seen a Bear in the air, bet those engines/props rattle yer fillings too!)

[Georgeablelovehowindia]

We live 40 nautical miles north of Istres and get our daily dose of Tynes as 'Le Transall' booms its way at climb power, heading I would guess for Bretigny, the other Centre de Essais en Vol south of Paris. Yes, it makes the glasses in the sideboard buzz, but we'll miss it when it's gone. 2018 is the date for their eventual retirement.

The Indian Navy have some TU-142MEs at Dabolim, Goa. To our delight, one started up, and after seemingly interminable checks, took off. It made exactly the sound one would expect!

:ok:

[Wycombe]

it sounded like a brace of Vanguards over here!

Not surprising as they share(d) the same powerplant.

The A400M has a very distinctive sound - more pure-jet-like IMHO.

[treadigraph]

The A400M has a very distinctive sound - more pure-jet-like IMHO.

Mmmm, on a very hazy day during the summer, a turbo prop sounding rather like that went over on much the same route as the Transall. Barely got a glimpse of it through the crud and did wonder if it might be an A400M. Doubtless they'll seem very common soon.

[SpringHeeledJack]

when I first heard it I did wonder if it was the AN-22 but as my fillings didn't start to rattle...


On that note, are there any AN-22's left flying outside of Russia ? There was that Volga-Dnepr(?) one flying for trade, but seemed to be beset with MX issues and not seen for a while.

There's always something highly frustrating for certain people (of which i'm one), to hear such a loud droning above the clouds and to not know what it is being made by :8


SHJ

[DaveReidUK]

AFAIK, there are only half-a-dozen AN-22s still in service, all but one with VTA (Russia's Military Transport Aviation Command), in basic Aeroflot markings plus one at Kiev in Antonov's house colours.

[WHBM]

Solves a mystery - it sounded like a brace of Vanguards over here!
Actually in powerplant terms it's exactly half a Vanguard.

Used to live in The Wirral as a kid, Vanguards on LHR-Belfast were certainly audible from the ground there in the cruise, probably at 20-25,000 ft. Likewise one running up for departure from Edinburgh's old runway 31 could be heard on quiet winter evenings from up at Edinburgh Castle. I don't know why they were so noisy when their close competitor for size and power, the Bristol Britannia, was the opposite, the "Whispering Giant". I suspect the props rather than the powerplant, I believe De Havillands for the Vanguard and Dowtys for the Britannia.

[Midland 331]

Extended ground runs of the Merchantmen at Castle Don. on the compass base eventually took the novelty out of the sound (and feel) of the Tynes. Some days, the whole airfield seemed to resonate for around four hours.

However, only today I was describing to a fellow enthusiast hearing a Merchantman run up at Teesside, over four miles from my house, taxi to the far end, then depart on a still summer's evening, coming into sight looking very heavy indeed. Embarrassingly, I got goosebumps simply describing the event of thirty years ago.

[Chris Scott]

In this post-radial age (talking of big transports), we have to make do with the ever-fewer big turboprops (as well as the occasional RR Merlin and Chinook) to provide the kind of aurally-induced adrenalin rush that makes one abandon PC for the garden in all weathers...

Quote from WHBM:
"I don't know why [the Vanguards] were so noisy when their close competitor for size and power, the Bristol Britannia, was the opposite, the "Whispering Giant". I suspect the props rather than the powerplant, I believe De Havillands for the Vanguard and Dowtys for the Britannia."

Think you are right about the props generating most of the noise on both types. But the Proteus itself was an incredibly quiet engine. As the Brit approached you taxiing, it was virtually inaudible. It was only when the pilot throttled it right back that a momentary "whoosh" was heard: possibly the prop blades going into full-fine (or, perhaps, even reverse) pitch. Then, when the a/c had turned on to the runway and the power levers were pushed forward, there was no noticeable increase in the pitch of the noise - simply a slight increase in the volume. So different an engine from its less-powerful contemporary, the Dart. Oh for a hi-fi recording...

Yes G-ALHI, am familiar with the sound and sight of strings of Transalls en-route at low level from Toulouse-Francazal to the parachute-dropping area near Pau. But most of them seem to be abroad on ops these days, and Francazal has closed.

[treadigraph]

Used to see Dutch Navy Atlantics quite regularly (and Neptunes too in the 70s!) which I recall as equally noisy, presumably the same props on their Tynes?

You can't beat pistons though.

[Discorde]

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.

[Chris Scott]

"Perhaps", Discorde, but think how noisy the Dart is...

[Discorde]

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!

[DaveReidUK]

I seem to recall that the inner Tynes on the Vanguard also drove compressors for the pressurisation which may have generated noise.I believe so.

But we didn't let that get in the way of running all 4 up to takeoff power when doing pressurisation checks. :O

[BOAC73]

Or hitting a hangar door either !!

[Chris Scott]

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)

[bcgallacher]

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.

[Discorde]

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.

Memory's fading a bit here but I think the Vanguard T/O power LP RPMs were 15050-15500 and the max cont HP RPM 17,900 (LP 13500). Prop RPM <1000 at T/O power (950 rings a very faint bell).

[Chris Scott]

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.

[tubby linton]

A number of Proteus engines were used in the West Country as power stations.
http://streaming.britishpathe.com/hls-vod/flash/00000000/00084000/00084489.mp4.m3u8

[SpringHeeledJack]

Looks like we might get to hear one of these again over UK skies in the near future :D

http://www.pprune.org/freight-dogs/572100-refurbished-adb-an22.html



SHJ