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notlangley
27th Dec 2011, 03:15
A Boeing 707 jet airliner at the moment of take-off is largely powered by steam. Three times as much water is sprayed into the engines’ burner cans as kerosene (156,000 lbs water per hour compared with 45,000 lbs kerosene), a technique whereby the super-heated steam provides take-off power and the water keeps the temperature from rising above 1,600⁰F.From the book "Fighter" by Len Deighton

WHBM
27th Dec 2011, 07:15
There are probably still a few such takeoffs around. The last built were probably the earlier 747s with JT9D engines, also being constructed into the 1970s were extended range/payload BAC One-Elevens that the Mediterranean holiday operators went for. The water injection was in tanks for each engine, and normally lasted or about 2 to 3 minutes from brake release.

Some used plain demineralised water, others a water-methanol mix. A BAC One-Eleven was lost at Hamburg in 1971 just after takeoff through the water tanks having been filled with the methanol mix in error.

Saying the aircraft is powered "mainly by steam" is a bit misleading, it's like saying it's powered "mainly by air" as this is required for combustion. Power comes entirely from the fuel, with a much greater fuel flow during the injection phase, the water injection just allows this extra fuel to function in a given engine. It's not like the power from a steam railway locomotive at all.

Detailed discussion in the archive here.

Water Injection [Archive] - PPRuNe Forums (http://www.pprune.org/archive/index.php/t-10124.html)

notlangley
27th Dec 2011, 09:12
It's not like the power from a steam railway locomotive at all.
Do you mean a "coal railway locomotive"?

WHBM
27th Dec 2011, 10:42
Do you mean a "coal railway locomotive"?
No, steam. The actual power is produced by the steam. The coal burning is far up the energy chain. This allows the railway steam locomotive, for example, to go uphill producing significantly more measured horsepower than the coal fire can produce as potential energy by evaporating the water, in so doing it reduces the steam pressure in the boiler. This cannot go on for ever, of course. Down the other side it can freewheel with the steam completely shut off, producing zero horsepower but the coal fire is now replenishing the steam pressure. An internal combustion engine (eg a jet engine) cannot do this.

There were a small number of steam locomotives that had no fire at all but were charged at the start of the day from an external supply, eg a factory steam boiler, and then worked around using that "battery" of steam.

Back to water injected jet engines !

Hartington
27th Dec 2011, 10:53
[QUOTE]Do you mean a "coal railway locomotive"?[QUOTE]

And then, of course, there are the oil fired steam locos.

Agaricus bisporus
27th Dec 2011, 14:03
Methinks Mr Deighton is some miles wide of the mark if he imagines superheated steam provides any thrust at all in a water injected engine.
Also shows a serious misunderstanding of where the energy comes from, I fear. If it were the case why would we burn expensive kerosene when burning free water does the same thing?

Steam in an steam engine is merely the transport mechanism that transfers a small part of the energy released from the fuel (Coal? Oil? No! A magnificent smoky American woodburner I think for this example) to the pistons for conversion to thrust. In a jet it is simply to cool the combustion gases so the turbine doesn't melt. Nowt directly to do with providing thrust.

grounded27
27th Dec 2011, 16:09
The weight of water injection proved to negate the system's usefullness. I understood the intent was to cool things down to allow for higher thrust (EPR) with lower EGT.

WHBM
27th Dec 2011, 17:52
I seem to see some correlation in photographs between those types fitted with water injection and some decidedly smoky departures. Is there any feature of the system that causes this ? Does the fuel burn with a more smoky residue for some reason when water injection is in use ?

MathFox
28th Dec 2011, 19:41
The extra water vapor in the exhaust gasses will condense and become visible as cloud (or smoke). The visible component of "white smoke" very often consist of tiny water droplets.

lakerman
28th Dec 2011, 20:51
WHBM

The 1-11 lost in Hamburg was due to the Demin water tank being topped up with water drain fuel which was very cleverly put into empty Demin water barrels. There was an F/O under training doing the take-off and it was decided to do a water take- off. After Take-off, it was decided to completely empty the Demin tank and that's when the fuel lying on top of the demin water then went into the engines. Both engines were lost, and a forced landing was carried out on the autobahn. If memory is correct i think 9 pax were killed at the rear which was damaged when the tail hit a bridge and caught fire, but at least a 100 survived. The airline, Paninternational, had its AOC pulled very quickly by the Luftfarhtbundestampt(apologies if my spelling is incorrect) and the airline went out of business shortly after that.

Hartington
29th Dec 2011, 09:59
Revolutionary railroad: atomic train being developed in Russia — RT (http://rt.com/news/sci-tech/revolutionary-locomotive-russia-atomic/)

PAXboy
29th Dec 2011, 20:18
Well Hartington, the Russians do have form when it comes to interestingly powered trains ...
Russian Jet Train and Ship | English Russia (http://englishrussia.com/2007/04/10/russian-jet-train-and-ship/)

Turbojet train - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Turbojet_train)

So that's the thread back on to the subject of jet engines then ... ;)

Pax Vobiscum
3rd Jan 2012, 21:11
I'm sure I remember seeing one c. 1960 on 'Supercar (http://en.wikipedia.org/wiki/Supercar_(TV_series))'.