747 0-60mph/100kph
 

Time for a silly question!!
Does anybody have any idea how fast a average loaded
747/777 etc could do the 0-60? Ive owned some pretty
fast cars in my time but a couple of take-off rolls seemed to
come fairly close to them!
Somebody must have an idea:)

Re:
 

Aerosim shows 12-13 seconds for a GW 294.5 ZFW 267.6 no reduction TO ;) I am sure this is somewhere close.....


crvm

It depends a lot on the weight of the plane and how much derate you use.
There's a HUGE difference between a max-weight take-off with full derate and a light take-off with no derate.
I once used a gadget called a G-Tec to measure the horsepower of a 747 on take-off - it's a thing you can use in a car to measure the 1/4 mile time or power of a car, but it'll work on any machine - and I came up with roughly 100,000hp odd.
Perhaps not very accurate, but it'll be roughly right.

Cheers guys! :ok:

(non pilot speaking) When asking this question, you may wish to specify the altitude of the a/c, as well as the loading of the machine and the thrust rate that is to be used.

At LHR, a 744 is motoring for (typically) around 45/50 seconds before rotation whereas, at JNB with an elevation of some 5,000' the wheels are working for (sometimes) another 20/25 seconds. In this matter, everything depends upon other factors and there are many of them to be considered.

Thrust/horsepower
 

While we're at it, can somebody please explain the formula for converting pounds of static thrust to horsepower. More specifically, if a big P&W or GE is rated at 50,000 lbs. static thrust
how much horsepower is the engine actually producing?

rotornut,
As a rough(very) about 2 to 21/2 pounds of thrust per HP for a turbine.

Rotor: Thrust and horsepower are different things entirely, there is no direct conversion, a bit like torque and horsepower in a car. You can provide a rough conversion, as fruit has, but it makes some major assumptions.
I'd started posting a fuller explanation but then realised I'd probably mess it up. The great thing about Pprune is that there's always a real expert coming along soon.

I did read somewhere once (might have been Airliner World or Aircraft Illustrated, something like that), a 777 is capable of accelerating to 60 from a standing start in around 6 seconds. I have absolutely no idea if that is true, but I can only see it being a theoretical figure at min weight, max t/o thrust.

Rather impressive if true. Imagine the fun you would have racing away from the lights in that!:ooh: :ooh: :E

My latest F1 mag reckons the concorde could
do 0-200mph in 12secs!! F1 car in 11.8 secs
OMFG! that cant be right!!

Slightly off-topic, but Smoketoomuch : note that there is a direct conversion between torque and horsepower:

(Torque x Engine speed) / 5,252 = Horsepower

(assuming Torque is in pound-feet)

See How Stuff Works for more...

cbl.

Right off the line it is a lot slower, but once rolling the 747-400 is gaining about 3 kts of speed per second.

Standard day, sea level, O mph headwind, MTOW of 875k, Vrot is around 185 kts. 185 kts/3 = 61.67 seconds. Typically there is some headwind so PAXboy is correct, the takeoff roll will usually be around 50 seconds.

:)

Great thread for us number crunchers !

747FOCAL - Your numbers look realistic to me. A bit of trivia, how does 95 sec to Vrot in a 747-400 at Singapore sound ?

witchdoctor - Based on 747FOCAL's logic, your 6 sec looks optimistic. I estimate 15 sec to 60 mph (52 kts)

anti-skid - I think your F1 car info looks OK, but I doubt the Concorde numbers. I've never had the privilege of seeing a Concorde take off. What's it's Vrot and how long to achieve it ? Then we could work out the numbers.

Work is the result of a force moving something by a distance over a time. 1 HP = 550 ft.lb/sec hence the direct conversion from torque to power, but thrust is only force. So, as mentioned earlier, more info is needed to calculate the power generated by a certain thrust.

Keep the info coming to exercise the grey matter.

Spec

Specnut727,

That would probably be from derate, hugh humidity, and high heat. 95 seconds, that is almost a lifetime to be banging along the ground at 875k. :)

CBLong, that's not a direct conversion as such because it also involves a third variable, ie speed upon which it is also proportional. I think what Fruitloop meant is that for a given shaft horsepower within the turbine the output thrust it can provide is in the range (note the wide range) he/she said.

Thrust/Horsepower
 

I've found some info in my P&W Aeronautical Vestpocket Handbook.

For turbojet or turbofans, Thrust Horsepower = Pounds Thrust x MPH / 375

For piston or turboprop, Pounds Thrust = 300 x Shaft Horsepower / MPH (assuming 80% prop efficiency). For static conditions the equation doesn't work, so rule of thumb is 2.5 pounds per SHP.

For turboprops I've heard the term ESHP (equivalent shaft horsepower) used. I understand that there's energy in the exhaust after the turbine, which provides thrust. Adding this to the SHP gives a better indication of the engines output. On some engines this thrust must be significant. I spend a bit of time in Dash 8's (as SLF) and am always impressed by the exhaust size on the PW 123's.

Spec

Sounds wrong to me. Add 4 or 5 seconds till the wheels leave the ground, thats 100 seconds. Cant see it.

Having read this thread I kept an eye on the clock out of Hong Kong yesterday.

Wind L/V
OAT 24
QNH 1020

No derate
394.6T (868k lb)

60 sec from thrust set to V2 (180kt) which is about when the wheels leave the ground

I reckon we used about 10,500ft to get to that point.

jtr,

Thats kinda what I was thinking. After 160 kts you are doing about 260 ft per second increasing to 301 fps at 180 kts. Your going to need a lot of runway to stay on the ground for 30 more seconds. Even if you stayed at 180 kts after 10,500 and kept it on the ground for another 30 seconds you would burn up +9000 ft of runway. I am speculating that the answer to specnut727's trivia question is that you end up in the water. :}

Thanks for the comments jtr and 747FOCAL.

Early 90's I was SLF on a QF 747 Singapore/London. Captain announced to the PAX that the take off would be longer than usual, so I reached for my stop watch. Yes, 95 seconds until rotation.

Spec

Specnut727,

With Singapore Changi Airport being:

ELEVATION: 22 ft.
RUNWAY INFORMATION Orientation Length (m) Displaced
Threshold (m) Glide Slope(deg) Width (m)
02L 4000 - 3 60
20R 4000 740 3 60
02R 4000 - 3 60
20L 4000 - 3 60

It must have been REAL hot and muggy to accelerate that slow. That could have been a bit scary.
:)