I have a convertion qustion

[Lt. Nebfer]

I know that jet aircraft engens are rated in pounds of thurast but i was wondering what woud that be in horsepower

ie what woud 100,000 pounds of thurast be in horsepower??

and whats the convertion rate??

[Darth Wong]

I know that jet aircraft engens are rated in pounds of thurast but i was wondering what woud that be in horsepower

ie what woud 100,000 pounds of thurast be in horsepower??

and whats the convertion rate??

I'm not an expert on jet-engine thrust ratings, but "pounds of thrust" must be a measure of force, not power. So there is no direct conversion (note: pounds are a unit of both force and mass in the Old English system; that's one of the reasons the Old English system is stupid, and why America should get with the fucking program and go metric).

[Vympel]

Ha! Try writing the 190,000 word military equipment dossier of the Russian Federation and United States I've been doing for the past 2 years (will put it up on the web with pics one day) and getting really annoyed at having to convert every frigging American pounds rating (i.e. every goddamn American aircraft book) rating to the much nicer, cleaner, and shorter kN (kilonewton IIRC).

What is it with this old English or 'Imperial' system. It's ARCHAIC!!!

GGGGGGGGGRRRRRRRRRRRRRRRRRR.

Ahem.

[XaLEv]

I am reminded of something Bill Nye said once. I can't remember what it was exactly, but I think he had given a measurement in kilometers and then said "That's (x) miles for you old people". I laughed my ass off at that one.

[Wicked Pilot]

I will try to take a shot at this question. The pounds of thrust are a measure of the amount of force exerted on the aircraft by the engines. Consider the following case study, the Northrup AT-38B Talon. Seen below:




This plane has two General Electric J85-GE-5 turbojet engines. Each puts out 3,850 lb (17.13 kN) of thrust at full afterburner. Both engines combined exert 7,700 lb (34.26 kN) of thrust. The aircraft itself has a maxium takeoff weight of 12,050 lb (mass of 5465 kg).

For this calculation, we will assume the airplane is at rest on the ground, and weighs approx 11,000 lb (5000 kg). It then kicks into full afterburner.

If we ignore wind resistance we can calculate that the plane will accelerate at a rate of F/m or 34260N/5000kg which equals 6.852m/s^2.

After 10 seconds of full afterburner, the plane will be traveling at (a)(s) or (10s)(6.852m/s^2) which equals 68.52m/s.

We can then calculate the plane's kinetic energy via .5mv^2 which works out to be (.5)(5000kg)(68.52m/s)^2 which equals 1.173*10^7 Joules.

Since it took the plane 10 seconds to achieve than amount of energy, we simple devide energy by time and get a power of 1.173*10^6 Watts.

One horsepower = 746 Watts. Therefore, the horsepower used for the above example is 1572hp.

There, that is how you convert a jets engine output and it's weight into horsepower. Any questions?

[Lt. Nebfer]

thanks wiked pilot that helps and i know some metric for thos roude pepole (ie the first 3 guys ho responed)

[Wicked Pilot]

thanks wiked pilot that helps and i know some metric for thos roude pepole (ie the first 3 guys ho responed)

They are essentually correct, you cannot simply convert force to power, you need something like mass to do any calculations. Also, using metric for these sorts of things is MUCH easier than using old english. That's why I converted to metric for my calculations.

And last, you must remember that most people on this board are not from the U.S. and will be unfamiliar with with the english system. Metric is the common language, make sure to use it in the future.

[NecronLord]

(note: pounds are a unit of both force and mass in the Old English system; that's one of the reasons the Old English system is stupid, and why America should get with the fucking program and go metric).

Just as well we don't use it anymore, and have gone metric, we have pounds currency as well

[Larz]

American system measurements ... *breaks into convulsion fit*... not to be rude, but metric is so much easier to keep track of and convert in (Chemistry Major... so I'm biased)

[Shadow WarChief]

(Chemistry Major... so I'm biased)

I wouldn't say so, I'm American and I'm having trouble keeping track of the old english system. (partly because I've had to start thinking in metric because of the abundance of calculations on the net).

So all in all, we really should switch to metric.

[paladin]

I read on the Units of Measurement website (http://www.unc.edu/~rowlett/units/usmetric.html) that the US is "soft" metric meaning that measurements in the English system appear with the metric equivalent.

[Vejut]

I'd agree, but mainly because most of how I learned how to do (i.e. change Force times distance to Work...) was in metric...I ain't got no problem with english (but then, I'm an american who has been using it all my life...)

And Sir Wong, isn't the english unit of mass slugs? Pounds is often equated with Kg, but thats mainly because we normally talk about whats in earths gravity....
Thats what I learned in Statics...of course, that was last week or so, which should give you and idea of where I am in school, so feel free to smack me if I'm wrong...

[Darth Wong]

I'd agree, but mainly because most of how I learned how to do (i.e. change Force times distance to Work...) was in metric...I ain't got no problem with english (but then, I'm an american who has been using it all my life...)

It's a bizarre system.

And Sir Wong, isn't the english unit of mass slugs?

And stone, and probably a half-dozen other obscure units. The old system was terrible for having multiple units that describe the same thing.

Pounds is often equated with Kg, but thats mainly because we normally talk about whats in earths gravity....

Actually, no. Pounds are a unit of both force and mass, which is why physics texts will often differentiate by using the units lbf and lbm (pounds-force and pounds-mass).

Thats what I learned in Statics...of course, that was last week or so, which should give you and idea of where I am in school, so feel free to smack me if I'm wrong...

Smack

[Crown]

Why would you want to convert to horsepower from thrust in a jet engine anyway? The only jet engine that is rated in terms of power is the turbo-prob because of its, well propellar...

[Slartibartfast]

I'm not an expert on jet-engine thrust ratings, but "pounds of thrust" must be a measure of force, not power. So there is no direct conversion (note: pounds are a unit of both force and mass in the Old English system; that's one of the reasons the Old English system is stupid, and why America should get with the fucking program and go metric).

While pounds or kilograms is actually a measure of mass, and the correct measure of force (including weight) is either newtons or kilograms-force or pounds-force (I'm translating from my own language so I might be a bit off), it is kinda widely accepted to just say "kg" or "lbs" for weight or thrust. In the metric system, airplanes are also rated for their thrust in "kilograms". (BTW English system sucks anyway )

Basically if you build a device weighing 1000 kg, with an engine capable of 1000 kg of thrust (or pounds or whatever you like) and launch it upwards, it will be barely able to hold its own weight. Planes use aerodynamics and other crap to actually convert most of the thrust in actual thrust (since moving forward will also generate lift). A good example of this is the harrier jet, which can thrust upwards, and will gain altitude very slowly that way.

I know that jet aircraft engens are rated in pounds of thurast but i was wondering what woud that be in horsepower

ie what woud 100,000 pounds of thurast be in horsepower??

and whats the convertion rate??

There's no direct conversion between thrust and "horsepower". With horsepower you can generate a slow, strong motion, or a fast, weak motion, or plug it into your home electric system and generate NO MOTION at all (you're just powering your TV and appliances with it). You can even put it in neutral and accelerate until the engine blows, and will have not moved at all - only generated heat. Thrust is something that directly pushes you in a direction.

[Crazy_Vasey]

Do they actually make you Americans use the Imperial system of measurement in science class? That's fucking sadistic.

[phongn]

We generally use SI in our science classes, but occasionally we use the Imperial system.

[Crown]

The English and American Imperial units are actually slightly different. Go figure!

[phongn]

Well, the American varient of the Imperial system, if you must