V-Flyer

One for the knowledgeable ones: what is rotating? I see it often on boards and photos. Clearly its something to describe take-off, or something that happens during take-off???

It's point at which the joystick is pulled back the nose lifts, and the wheels leave the ground

Yup. The speed (Vr) at which the sidestick (nee Joystick) on the A340 is pulled back ,or yoke on any Boeing, to rotate the aircraft into the air. The rotation point is roughly in the middle of the aircraft where the trailing edge of the wings meet the fuselage. Usually it only rotates around 10-15 degree's - dependant on weight/aircraft/wind...yadda yadda.

Rotating: cleaning out the fridge! [:o)]

Try and think of it like this:

the x-axis runs through the centre aisle of an aircraft

the y-axis runs from wing-tip to wing-tip

the z-axis runs from the ground to the sky.

when a pilot pulls back on the yoke (or sidestick) the plane rotates on the y-axis, pointing nose into the air.

this is normally followed by a rush to the loo's and a drinks service

Rich.

Or in lamest terms, when the plane takes off...

Or, as imbibing with a VS pilot in a Barbados bar (he was on holiday with his family), and I wish he hadn't told me this - if it (rotating) hasn't happened after 45 seconds you're in trouble....

Carefully checking my watch now every time I take off......

Originally posted by KenUK

Or, as imbibing with a VS pilot in a Barbados bar (he was on holiday with his family), and I wish he hadn't told me this - if it (rotating) hasn't happened after 45 seconds you're in trouble....

Carefully checking my watch now every time I take off......

I remember being on the flightdeck departing JNB on a 744 one warm evening and it certainly felt like more than 45 secs till we nosed up!

Regards

John

I remember being on the flightdeck departing JNB on a 744 one warm evening and it certainly felt like more than 45 secs till we nosed up!

It would do! Jo'burg is at 5500 ft where the air is less dense, but they have provided a very long runway to allow the aircraft to accelerate to the required speed.

Time to rotate depends on, amongst other things, weather, weight of aircraft, length and height above sea level of the runway and thrust setting of the engine.

You will avoid a lot of unnecessary stress if you ignore the 45 second rule!

Regards

Edna

Originally posted by Edna Cloud
You will avoid a lot of unnecessary stress if you ignore the 45 second rule!

Yeah, have another drink

There are essentially four speeds or points in the take-off sequence

V1 is the velocity at which you are committed to take-off (ie there is no longer enough runway to stop the aircraft from this speed

Vr is the rotate speed and is the point at which the pilot will rotate the aircraft - as others have said about its Y axis (whilst trying not to let it rotate about the other 2!) Between Vs and Vr, the pilot is actively holding the aircraft onto the ground.

V2 is the speed at which the aircraft will fly and climb and is computed to be reached at the point that the aircraft is 35 feet into the air

Vs which is the speed at which the aircraft will just fly (stall speed), You can take-off at any point beyond this but the aircraft will be unstable. Vr is chosen to be the point where safe stable flight is possible. Stability etc increase as speed increases between Vs and Vr

So the sequence is Vo (zero speed) at the start of the runway; followed by Vs, V1, Vr, V2

The exact values for these speeds are computed from various factors including load, altitude, temperature, weather etc. Once an aircraft reaches its Vs speed, it will fly because Boeing (or Airbus) say it will! The thrust, lift, etc. of the aircraft is known, thus given the other factors used to compute the speeds the MTOW (Maximum Take-Off Weight) can be calculated. Fuels and cargo (and sometimes, but rarely pax) are adjusted to ensure that MTOW is not exceeded.

There are other calculated speeds to do with flap and slat retraction

Originally posted by Edna Cloud

I remember being on the flightdeck departing JNB on a 744 one warm evening and it certainly felt like more than 45 secs till we nosed up!

You will avoid a lot of unnecessary stress if you ignore the 45 second rule!

Regards

Edna

Thanks for that Edna, otherwise I'd have to up mu valium!!

The Vr speed (velocity) on a 744 changes quite dramatically, depending on the conditions at take-off:

Empty plane, cold weather (or low altitude) = c. 120KIAS
Empty plane, hot weather (or high altitude) = c. 130KIAS
Full (max) plane, cold weather (or low altitude) = c. 160KIAS
Full (max) plane, hot weather (or high altitude) = c. 175KIAS [:0]

(KIAS = Knots Indicated AirSpeed)


Basically, if you're on a full flight, in a hot country, at a high altitude, you'll be rolling down that runway for quite a while

Originally posted by VS-EWR
Or in lamest terms, when the plane takes off...

LOL, you think nice and simple like I do:D

Phil

Last time I flew out of Joburg, we were certainly rolling for some time. And the time before that, the EK flight had not rotated in time and had hit the lights a little way down from the runway when they lifted off. They had to make an emergency landing (and dump fuel) but everyone was ok.

Cheers,
VS045

Originally posted by VS045
Last time I flew out of Joburg, we were certainly rolling for some time. And the time before that, the EK flight had not rotated in time and had hit the lights a little way down from the runway when they lifted off. They had to make an emergency landing (and dump fuel) but everyone was ok.

Cheers,
VS045

Hopefully the dump fuel was before the emergency landing:D

In case anybody is wondering, the dumping of fuel is not to reduce the chance of fire or anything similar. It is purely to reduce the weight of the aircraft. The maximum take-off weight far exceeds the maximum landing weight (which has additional determinants of load on undercarriage and braking distance compared to runway length). For example MTOW is around 340,000 kgs, MLW is 255,800 kgs. In the normal course of events, the excess fuel weight will have been burnt off in the journey. Some aircraft do not have the ability to dump (Airbus 320 springs to mind) and must therefore burn off the fuel.

There was a case I read about some time back where a pax had a suspected heart attack soon after take-off. Normally, this would cause a divert to get the pax medical attention. However, the aircraft could not dump fuel and since it had to burn off, carried on towards the destination; declaring a medical emergency for a priorty landing slot

Thanks for the informative answers guys, esp Pat and Paul, what a lot of information can be gleaned from this site [y][y][y]

Am amaxed at your collective knowledge, thank you. Will consider my next question ... now I know about multiple axis and vs and v1 etc I'll be measuring it on next take off.

Now, when will it happen that we're all weighed before boarding to see what the MTOW is???

Originally posted by slinky09
Now, when will it happen that we're all weighed before boarding to see what the MTOW is???

I can't find the actual CAA document for it (as strangely, each country has a different "standard" weight to assume for PAX), but here's an example one from the OZ CAA.

Bear in mind that they also factor in whether it's Summer/Winter to "guess" the weights of the PAX onboard (heavier in Winter, lighter in Summer - clothing, plus our "winter layers" I believe ).

Now, the FAA has a higher assumed weight (apparently, they're generally larger [:p];)) than we do in the UK. But still, they've done studies, and even with the natural errors that occur when assuming weights, the MTOW is very rarely THAT out from what they calculate as a result of the latest specs. (I believe, thanks to a couple of not-so-happily-ending incidents from the past).


Incidentally, on the same subject - you might find this article interesting! [:p]

Indeed. But realise that MTOM is the structural mass that the aircraft can take off with. For example, it's 77000kgs for our A320's. We use 89kgs per person in general of European flights and 92k for internationals. Eventually, after check in, the EZFW is calculated baring in mind the number of women (less mass), men, kids and infants. The EZFW (estimated zero fuel weight) is the DOM (dry operating mass (mass of the aircraft ready for operation minus fuel (so weight of empty aircraft, crew, crew bags, catering....etc))) plus the weight of all the passengers added. This is why, of course, check in closes when it does and after it closes - bugger off. From this the fuel required can be calculated and this becomes the TOM. (Take off mass). If this exceeds the MTOM/MTOW, then you either tech-stop (stop for more fuel), boot off pax or drop bags. Once the TOW/TOM is calculated, say 77000kg on the dot for an A320, then the V speeds can be calculated. Amazingly classy and high tech airlines, such as the one I work for have laptops where you input the aircraft, aircraft type/reg, airport, runway in use, weather (wind/condition/pressure/systems in use during take off (air con utilises engine power). It will then work out V1, Vr and V2 and another speed which I forget. Somtimes, these speeds are not achievable with the runway in use, and then, tech-stopping/bump take off's, kicking off pax (always fun), or asking for a different runway, become an option. I could go on.....

Yeah, Im a member of a.net.