Lifting off before VR

[Chock 17,769]

Boeing recommend that you should be aiming to go through a rotation rate of approximately two-three degrees per second for most airliners, which should see you off the deck after four seconds from commencing the rotation and at a pitch up angle of between seven and eleven degrees at the point where you leave the ground (the actual angle will depend on the type and how long the fuselage is: 737-900 at 9 degrees, 747-400 at 10 degrees, 757 and 767 at 11 degrees).Once off the deck, the climb out should be at somewhere between fourteen to twenty-five degrees nose up when thirty-five feet AGL and at a speed of V2+10-15 (again, depending on the aircraft type). Note that the 25 degree value is pretty unique to the MD-11, most airliners should be at a climb out angle of fifteen degrees or so, which is a good average to aim for.Boeing have found through various studies with the 747-400, that if you are just one degree per second slow on your rotation rate, you will lift off at between four and five knots over the optimum speed for lift off, and that can risk overheating the tires a bit, which is not only a fire hazard, but also wears them out a lot quicker and may even make maintenance action necessary. If you under-rotate, you will lift off sooner than rotating too slowly, but in both cases you will take, on average, a ground distance of seven hundred feet to make it up to thirty-five feet AGL for the climb pitch up when compared to a normal on target rotation in a 747, so you can see that it is worth getting it right for obstacle clearance.The 747's tires are typically rated to be able to handle up to speeds of 235 miles per hour, since a B-747 can have lift off speeds of nearly 200 knots when heavily loaded, so there has to be a safety margin built in for late rotations, plus the capability to land without flaps at high weights.A lot of that stuff is not simulated in FS (tire overheats and tread damage for example), but if you want to do it properly, the above values are the things to aim for.Al

[captainklm 1]

Thanks Alan,I was wondering about beyond MTOW takeoffs. I know its not done in real life but I tried with the 747-400. On the Zero fuel weight colum in the FMC I put down 999.9 cause thats the highest it can go and fill the fuel up to the top. I flew with that and it worked. If it did with the pmdg 747 can it be done in real life?

[Vollie 11]

The rule for flying is: lift - you can get lift if you have enough wind trough the wings. (Blowing wind in front of the airplane)My experience with this is light weight and to much trim up. I don't think dat wind is pulling your aircraft earlier then VR speed, this will be the same. Because if you stop the airplane, lined up the runway and you get headwind of 50kts, you will see the indicated air speed raising up to 50 kts. When the VR speed is 154 kts (ground speed), you need 104 kts on the ground to fly, because you get 50 kts a gift. If I''m right, you must fill this in the fmc and fmc corrects the speed.

[captainklm 1]

The rule for flying is: lift - you can get lift if you have enough wind trough the wings. (Blowing wind in front of the airplane)My experience with this is light weight and to much trim up. I don't think dat wind is pulling your aircraft earlier then VR speed, this will be the same. Because if you stop the airplane, lined up the runway and you get headwind of 50kts, you will see the indicated air speed raising up to 50 kts. When the VR speed is 154 kts (ground speed), you need 104 kts on the ground to fly, because you get 50 kts a gift. If I''m right, you must fill this in the fmc and fmc corrects the speed.

really, with 50 knots wind and your at 100 knots wouldn`t you still rotate. Does that wind count as speed?

[Paul_Smith 92]

really, with 50 knots wind and your at 100 knots wouldn`t you still rotate. Does that wind count as speed?

How fast your tyres are turning has nothing to do with flying. The only thing that counts is the speed of the air over the wings.

[captainklm 1]

How fast your tyres are turning has nothing to do with flying. The only thing that counts is the speed of the air over the wings.

thats my point, with 50 knots of wind and your speed without that 50 knots of wind being 100 knots thats when you lift off

[yos233 1]

Then we should specify different speeds. With a 50 kt headwind, moving at 100 kts groundspeed will give you an overall 150 kts of airspeed, which is enough for some lighter weights. But using that same 50 kt headwind and an airspeed of 100 kts, that is not sufficent as you are only moving at 100 kts through the air (50 kts groundspeed).

[Paul_Smith 92]

Then we should specify different speeds. With a 50 kt headwind, moving at 100 kts groundspeed will give you an overall 150 kts of airspeed, which is enough for some lighter weights. But using that same 50 kt headwind and an airspeed of 100 kts, that is not sufficent as you are only moving at 100 kts through the air (50 kts groundspeed).

No, you only specify one speed! If Vr is 164Knots, then you rotate when the IAS (indicated AIR speed) says 164. It really is that simple.

[scandinavian13 5,192]

No, you only specify one speed! If Vr is 164Knots, then you rotate when the IAS (indicated AIR speed) says 164. It really is that simple.

Exactly. As I've specified several times in this one thread. Airspeeds are the speed of the air over the wings. Forget everything else, including wind. The only issue with wind is gusts.

[captainklm 1]

So can I clarify if there is 5 knot headwind and VR is 155 you can rotate at 150 knots ground speed

[scandinavian13 5,192]

Yes, but are you really looking at the GS indication? Doing so would only serve as a distraction, and neglects the only speed we really need to know as pilots to remain in the air: airspeed.

[captainklm 1]

No I never really but from time to time my eye catches it

[El padrino 2]

No I never really but from time to time my eye catches it

There is absolutely no reason for your eye to catch it, especially during busy times like takeoff or landing... In general though you got it correct:GS=IAS + tailwind component orGS=IAS - headwind component

[Paul_Smith 92]

So can I clarify if there is 5 knot headwind and VR is 155 you can rotate at 150 knots ground speed

Actually, no (sorry Kyle). You rotate when your AIR speed is Vr. If your Vr is 155 then you rotate when your IAS is 155. You can not measure ground speed accuratly and even if you could, how would you know that you weren't experiancing a 20knt gust from behind. Unless you want to talk about about V1 or time on target, there really is no place for groundspeed in aviation.

[scandinavian13 5,192]

Actually, no (sorry Kyle). You rotate when your AIR speed is Vr. If your Vr is 155 then you rotate when your IAS is 155. You can not measure ground speed accuratly and even if you could, how would you know that you weren't experiancing a 20knt gust from behind. Unless you want to talk about about V1 or time on target, there really is no place for groundspeed in aviation.

That's what I've been saying this whole entire time. If you go back and read it, every post I've been saying airspeed, airspeed, airspeed, don't even care about the groundspeed.Seeing that the post was technically correct, as the 155 airspeed minus the 5 knot headwind would result in a 150 groundspeed, I conceded that technically, yes, you can rotate at 150 groundspeed, provided your airspeed was 155 (on a 155 Vr). Why you would ever try to argue that point, that you could or ever would rotate based on groundspeed is rather amateurish and ignoring the fundamentals of flight, but the point is technically correct. Practically, and intelligently is another matter.To drive the point home, I could technically drink beer out of a martini glass with a straw, but why would I?...and groundspeed does have its place around here: flight planning for ETE, and it's all over the ATC side. I do see the point you're trying to get at, though. Related to keeping the plane in the air, groundspeed has no place. Ever.