Thrust to horsepower?

[Nick_Walczak]

Anyone know how to convert thrust into horsepower? Not that I'm thinking of putting a jet engine on my car or anything you understand :D

[Billy]

You can't convert directly, since horsepower includes time and thrust is just a force.

Having said that 1hp =33000lb/ft per minute

Torque is more like thrust. It is the ability to do work, whereas hp is the rate at which it is done.

The trouble is a jet engine produces thrust even when the plane is stationary, at which time no work is being done, so no power can be calculated. You could measure the torque at the wheels (you'll need a very big torque wrench!) but you're not really measuring the engine torque, 'cos jet engines don't use torque as such (not even turbojets).

[Nick_Walczak]

OK, so how do you convert from torque to thrust? I'm just trying to compare small jet engines to piston engines. :)

I guess that a jet can run at full chat all the time whereas an engine only hits peak torque at one specific rpm so you'd have to work out the average torque through all the gears.

[Billy]

I'm not sure you can convert in any meaningful way.

As an example of futility:

One compressor blade in a modern turbo jet measures about the size of a credit card, and produces the equivalent of a Formula 1 engine (approx 800hp). There are several hundred of them in each engine, which gives astronomical power figures, and equally astronomical power to weight ratios, well above any piston engined vehicle. Yet the F1 car will out accelerate any plane in existence from a standstill.

I'm sure you could measure shaft torque in a turbo jet, (they do) but to compare it to a cars power output, you need to know the efficiency of the whole caboodle (which changes with altitude) and you would have to invent a constant to factor in the de-coupling of the drive medium (air), which acts like a huge soggy torque convertor.

Thrust is much easier to work with in planes, since you can factor in drag as negative thrust without problems. As long as you are left with positive thrust at your desired speed, the plane will go that fast. Try that with a car!

[Vez]

Not if the plane has its breaks on with full reheat it wont, as soon as the plane releases breaks it would kick its ass ;)

But if we take into account running at 0% throttle then a car will win, the f1 car would beat it to 200mph but beyond that it would be destroyed (sorry starwars moment there).

[Billy]

Originally posted by Vez
Not if the plane has its breaks on with full reheat it wont, as soon as the plane releases breaks it would kick its ass ;)


'Fraid not!
Don't you remember Clarkson racing an F-15 in, er, something or other? It wasn't an F1 car, but it still beat the plane hands down, until it didn't!
Not that that's very scientific, but it proved the point....

You need rocket power to accelerate stupidly fast. Jet engines just don't cut it at low air speeds, mainly because they can't suck enough air. It's like a turbo in that sense. The forward speed equates to boost. At a standstill it's limited to atmospheric pressure.

[Vez]

The jet wasnt on full reheat, both vehicles wre running at 0% throttle before they started, the F15 definetly didnt have 20 foot flames out the back whilst it was stationary therefore didnt have full reheat ;)

Have you seen Typhoon take off from full reheat, ITS AMAZING!

[Nick_Walczak]

Yeah and what does an F16 weigh? :) I bet at least 15 tonnes.

[Vez]

Werent we talking F15 here?

[Nick_Walczak]

Yeah we were. I've been to teh pub so what of it? :)

[Billy]

Well it's all pretty meaningless really. But...

If a plane can accelerate that fast, why do they still use steam catapults on carriers?

The F1 car wouldn't be my first choice for outright acceleration, it was just a handy benchmark for the power, and shedloads faster than whatever Clarkson was pedaling! How would a plane match up to a top fuel dragster doing 0-250+ in 5 seconds? I reckon that would be a fairer match, given the proportional weights of the engines etc.

What's a Typhoon? Apart from a WWII piston engined crate, or a funny little car made in Rochdale.

I'm afraid "It's amazing!" doesn't convince me. F1 cars are amazing. Drag cars are gob-smackingly amazing.
It's like I said, you can't compare them in any meaningful way without knowing the weights of everything. Show me some 0-100 times and I'll be happy to admit I'm wrong....

[andyf]

Originally posted by Billy
What's a Typhoon? Apart from a WWII piston engined crate, or a funny little car made in Rochdale.



Eurofighter Typhoon innit ?

Also there was an ESPN clip which had an Indy car racing a jet, the Indycar won on that too..


TopGear had a Tornado vs. TVR didn't it?

The tornado over took it eventually after like 2 miles or something


As for accelerating against each other, surely it's absurd to compare them based on the way they use the power, jets pushing against air, cars twisting driveshafts.

[Billy]

Originally posted by andyf



Eurofighter Typhoon innit ?

Also there was an ESPN clip which had an Indy car racing a jet, the Indycar won on that too..


TopGear had a Tornado vs. TVR didn't it?

The tornado over took it eventually after like 2 miles or something


As for accelerating against each other, surely it's absurd to compare them based on the way they use the power, jets pushing against air, cars twisting driveshafts.

Oh good, it's not just me then. :)

[andyf]

Originally posted by Billy


Oh good, it's not just me then. :)

haha no,

it's like the jet-powered drag cars.. although they still do rather fast times, the fact is they start off slow and build up - top speeds, given enough room, would be aeronautical - they'd probably take off without enough downforce. But top fuel dragsters have those immensely large wheels.. acceleration comes from spinning the wheels via the driveshafts EXTREMELY fast, and the rubber then translates this to the road. It's always going to be a faster acceleration because of the way the power is used.

[andyf]

Well, faster than anything other than some future technology where you can literally detonate something right behind you and be accelerated by the shockwave of it.


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BOOO! the 60-second-between-posts rule is haunting me :( is this forum specific ??

[piglet]

Billy and andyf are right.