Can anyone give me a back of the envelope conversion between the thrust of a jet engine and the horsepower of a piston engine please. I understand horsepower. When somebody tells me that a Sea Fury has 2,000 odd horses under the bonnet I can see a lot of Clydesdales eating a lot of grass. 2,000 Clydesdales munching through ovals and ovals of grass. When folk talk of jet engines and thrust my eyes remain glazed and uncomprehending. I appreciate that a number of RR Trents pulling an Airbus A380 into the sky with 800 odd passengers, 34 cases of champagne, 680 rolls of toilet paper and 2,000 packets of salted peanuts must have a lot of thrust but it doesn’t seem to grab me the way Clydesdales do. I understand thrust. Thrust is how you make babies. So if you take the three minutes, if you are lucky, of thrust it takes to make a baby, how many hours of thrusting and how many candlelit dinners does one Trent generate in equivalent effort?
Now I think Whittle, in pleading and promoting his jet engine, would have had to couch his pitch in terms the disapproving, fox hunting, public school types in the Air Ministry would have understood. He would not talk of thrust in the way modern engine salesmen do, he would have had to compare it with horsepower. It goes back to James Watt pitching the steam engine to Luddite farmers chewing a stalk of wheat as they listened to his mad expositions on what a steam engine could do in comparison to a trusty old nag. Surely Whittle would have held up an apple in one hand that could do X horsepower, and his orange in another that could do the equivalent of Y horsepower, in the same airframe.
Now I don’t need an expostion of why the two measurement terms cannot be directly compared. I will just get on my Clydesdale and saunter away, chewing on my wheat and muttering. Please tell me something that I can tell my seven year old the next time we stare out the window at a Trent, so I can masterfully compare it to Clydesdales eating grass, as we eat out peanuts.
By: smirky - 21st October 2015 at 21:46
Then explain why for autos Torque is a better measure of acceleration / speed than HP?
Torque is good but I can’t because it is not really true.
If you look at the power/torque curves for your engine you will see that the power equals the torque times the rpm.
To put it another way, the torque is equal to the slope of the power curve.
So if you have lots of torque you will get lots of power. If you have lots of torque at lots of rpm you will get loads of power!
Diesel is preferred for trucks because of high torque.
High torque but over a limited rpm range, hence trucks have loads of gears to keep the engine rpm within the power band.
(The torque is the power divided by the rpm so high torgue at low rpm gives good power at low rpm.)
And I realize there is ways to convert the values.
It is not a conversion as such, it is two sides of the same coin since one is equal to the slope of the other.
Hope this is helpful 🙂
By: paul178 - 21st October 2015 at 21:27
Wiki’s definition:
https://en.wikipedia.org/wiki/Horsepower
And while we’re on the subject, here’s 1 horsepower. 1999 model Clydesdale gelding. Zero to 30 in…. depending on how hard you kick him!
[ATTACH=CONFIG]240919[/ATTACH]
What are you doing wearing jeans? You ain’t half going to have bad thighs without the proper rig!:D
By: Flying_Pencil - 21st October 2015 at 19:30
NO 😡
Power can be expressed in angular units asPower = torque x angular velocity
or in linear units as
Power= force x velocity
It is meaningless to say that one thing uses power and another uses torque because they are different physical quantities.:)
Then explain why for autos Torque is a better measure of acceleration / speed than HP?
Diesel is preferred for trucks because of high torque.
And I realize there is ways to convert the values.
By: smirky - 19th October 2015 at 16:19
Horsepower is a LINEAR measurement, not an ideal measurement for most machines because they use…
TORQUE for movement, translated into linear movement by wheels or cogs to a rack.
NO 😡
Power can be expressed in angular units as
Power = torque x angular velocity
or in linear units as
Power= force x velocity
It is meaningless to say that one thing uses power and another uses torque because they are different physical quantities.:)
By: Vega ECM - 17th October 2015 at 09:53
I didn’t know that the 199 has vapourisers, ……..did the Proteus have vapourisers?
The RB199 is a Bristol designed engine, so has vapourises, it was where the design teams expertise was/is, l’ve spent a bit of proffessional time on this very component;- pretty sure the Proteus was where Bristol’s vapouriser journey started. Also Bristol’s ramjets, Thor & Odin also vapourised which was fun getting them started. I was aware the former A/S & DHe engines Bristol inheritied vapourised, but not sure about the early DHe (Ghost, etc) and Napier(Eland).
By: Robbiesmurf - 17th October 2015 at 06:47
Jets (rockets, and other Reaction engines) do not create movement by contact or aerodynamic means, but by Newtons action/reaction, or Force.
Now a Turbo Shaft engine that powers a propeller, that can be measured as Torque (and by extensions HP).
Good points. Reaction engines do run by virtue of Newton’s 2nd and 3rd laws of motion. I was told by an engineer that when Rover built a jet powered car they did find out about the second law when they tried to turn it around a corner…
Turbo shaft engines are measured in SHP (Shaft Horse Power), sometimes with an e in front (estimated). Horse power is calculated by rpm x torque.
By: Robbiesmurf - 17th October 2015 at 06:32
In UK terms, Rolls Royce Derby use atomisers and pretty much everyone else use vapourisers;- i.e. Olympus, Orpheus, Pegasus, RB199, Gem, Viper,etc all vapourise .
I understand most US atomise whereas most Russian vapourise.
Interesting. The Olympus, Orpheus, Pegasus and the Viper were all Armstrong/Siddeley or Bristol/Siddeley designed/built. I didn’t know that the 199 has vapourisers, the Adour used what they called a tulip spray atomiser. Tulips and vapourisers have shorter flame lengths than atomisers, so shorter combustion chamber. It must be old age but I can’t seem to remember anymore, did the Proteus have vapourisers?
By: Flying_Pencil - 16th October 2015 at 23:08
This is engines that power light aircraft
[ATTACH=CONFIG]241225[/ATTACH]
Not sure if noted, and crude description:
Horsepower is a LINEAR measurement, not an ideal measurement for most machines because they use…
TORQUE for movement, translated into linear movement by wheels or cogs to a rack.
Jets (rockets, and other Reaction engines) do not create movement by contact or aerodynamic means, but by Newtons action/reaction, or Force.
Now a Turbo Shaft engine that powers a propeller, that can be measured as Torque (and by extensions HP).
So, when it comes to Jets, its FORCE.
[ATTACH=CONFIG]241226[/ATTACH]
By: RPSmith - 9th October 2015 at 22:49
What I’d like to know is if the calculations using horsepower takes into account the thrust from the horse when it lifts it’s tail and f*rts?
Roger Smith.
By: Vega ECM - 9th October 2015 at 13:33
Gas turbines normally had atomisers. An exception I know of was the AS Sapphire series engines which had vapourisers (‘hockey sticks’)
In UK terms, Rolls Royce Derby use atomisers and pretty much everyone else use vapourisers;- i.e. Olympus, Orpheus, Pegasus, RB199, Gem, Viper,etc all vapourise .
I understand most US atomise whereas most Russian vapourise.
By: powerandpassion - 9th October 2015 at 12:16
Thank you for all your contributions to this table, probably would be better hosted in a pub with free flowing beer, horses tied up at the front to take everybody home after! The Hives rice puddin’ reference is starting to get the picture, in the sense one Merlin equals 1,000 Clydesdales equals the Whittle jet engine. The whole enquiry relates to turning to a more innocent companion, a child or somebody capable of putting petrol into a diesel tank, and saying with an air of quiet, undeserved confidence : “that there is the equal of 50,000 Cydesdales,” or the Hivian 50 Merlins. Now we all know a Merlin with a broken crankshaft can generate 0 horses, and something off a Hornet a few more, but 1000 horses will do. The beauty of a thrust comment is that it can only arise in the moment, when something thrustworthy occurs. I am thinking of that time when the Russian pilot at Avalon Airshow in Australia in 1998 parked his Su-27 vertically 30 feet above the runway, then opened a bottle of vodka with his eye socket, then hit the gas and Yuri Gagarined the jet into the ******** of a seagull flying at 20,000 feet. I think he drained his tanks in 5 seconds, but it was an extremely THRUSTY moment. I wonder if anybody knows what sort of motor there is in an Su-27, and how many Merlins or Clydesdales spewed out of the tailpipe. I would also like to find out how many Merlins or wing’d Pegasi draw a single Trent through the sky at cruise of 700km/h at 30,000 feet, so I can converse with the 7 year old and impress him for 3 seconds. I do love the horse photos by the way, and have gained new ideas on attending airshows on a horse’s back, why pay for VIP seating when you can bring it under you?
By: bazv - 7th October 2015 at 18:52
I knew a guy who owned a TVO (tractor vapourising oil) – he just ran it on petrol and did not use the other tank !
By: adrian_gray - 7th October 2015 at 15:54
No, there are so few paraffin tractors around these days I think most people just burn heating oil instead, perhaps with a dash of petrol or RedeX. Diesel took over very rapidly in the 1950s and 1960s.
Adrian
By: Robbiesmurf - 7th October 2015 at 15:43
The tractor paraffin, is it coloured red?
Gas turbines normally had atomisers. An exception I know of was the AS Sapphire series engines which had vapourisers (‘hockey sticks’) and a couple of atomisers for starting. The combustion chamber was annular.
By: adrian_gray - 7th October 2015 at 14:10
I
The problem with shoving AVTUR into an AVGAS engine is the fuel needs to be better atomised (high pressure).
…which is why paraffin engines (eg RAF Fordsons) had to be started on petrol – this got a vapouriser attached to the exhaust hot and once it was hot enough you could turn the paraffin on, the hot plate in the vapouriser would vapourise it, and away you’d go, smelling like a jet as you ploughed the fields and scattered. I don’t know what the difference in grades between vapourising oil (aka tractor paraffin) and AVTUR, but I ahve seen the later being sold to run the former…
Adrian
By: charliehunt - 7th October 2015 at 05:44
Thanks Daz – I know! But I reckon the OP was already trotting with his first post!!;)
By: DazDaMan - 6th October 2015 at 22:59
It is indeed, Moggy. It started at a trot, broke into a canter and is now positively galloping along!!:D
Sorry to be the pedantic equestrian, but it’s walk, trot, canter, gallop.
😉
By: Robbiesmurf - 6th October 2015 at 19:00
Would that be US gallons or Imperial gallons?
Is it an African or European Swallow?
Fortunately, US and imperial pounds are the same.
By: Robbiesmurf - 6th October 2015 at 18:58
ISO standards are insidious……
By: Arabella-Cox - 6th October 2015 at 17:03
Millibars? These days its hectopascals and time is UTC instead of GMT (Bl###y French……..)
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October 5, 2015 at 1:44 pm