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karakayab

Lifting off before VR

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Hi,I tried to find clear solution or an advice for my problem but no clear info anywhere.... so as you can see topic title aircraft lifts offf automatically before Vr.... everything is ok ( FMC settings, speed and fuel calculations and trim )Problem accours every take off.... automatically lifts off and I lost control but I try to manage good climb but almost it is tail strike :(you can find below some value from my latest test flight to show you problem... I think it is trim problem but I didn't understandI have been using Level-d 767 since 2004 and I haven't this kind of problem with 767... everything is ok....Units: LbsLPPT / Runway03ZFW: 486.268Payload : 92.180 ( pax+cargo)Fuel : 265.880 ( calculated for LPPT>SBGR )Reserve Fuel : 33.4Flaps: 10 ( or 20 it doesn't change )V1:148 VR: 162 V2:175Trim: 6.0 CG: %23Thanks

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Trim: 6.0 CG: %23
You set the trim to 6 up? This setting is way too high. Try a lower setting like 4 and it will change.

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You set the trim to 6 up? This setting is way too high. Try a lower setting like 4 and it will change.
6 seems to be a correct trim setting as per the table in page 1-4 of the manual for a CG of 23% and a TOW of 320000 kg.

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Remeber at lift off befor VR happends in real life to. Especially if it's windy. Trim calculation does not take into account windSteinar Grindstein

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Remeber at lift off befor VR happends in real life to. Especially if it's windy. Trim calculation does not take into account windSteinar Grindstein
That raises an interesting question: Suppose for simplicity that VR is 150kts and you have a headwind blowing down the runway at say 25 kts. When you reach VR, your ground speed is only 125 kts. What's your airspeed when the wheels leave the ground? And more importantly will the plane fly then?

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That raises an interesting question: Suppose for simplicity that VR is 150kts and you have a headwind blowing down the runway at say 25 kts. When you reach VR, your ground speed is only 125 kts. What's your airspeed when the wheels leave the ground? And more importantly will the plane fly then?
You are ready to go lined in the runway end, and there is a headwind of 150 kts, now you just pull back the yoke to raise the aircraft nose and...ooops you are flying, aren't you?.

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Hardware trim axis assigned?
through FSUIPC ? No.... I haven't enough info what do I do about it

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To those discussing airspeed, remember that it is AIRspeed. This has nothing to do with wind at all. Vr is an airspeed, not a groundspeed, so winds are irrelevant. V1 may take into account winds in its calculation, because it should take into account the amount of ground covered on that particular runway (or a runway of that length), but after its calculation, there is no wind adjustment. That's a slight simplification of everything, but for all intents and purposes, once you have the numbers, ignore the wind's effect on them.If you're standing still (not moving) and the wind is blowing by you at 40 knots, your airspeed is 40 still knots, despite your lack of movement across the ground. I can take a 152, put it in slow flight with a stiff headwind (at altitude) and fly "backwards" (relative to the ground) if the wind speed is greater than my airspeed.

through FSUIPC ? No.... I haven't enough info what do I do about it
A trim axis assigned in FS would be enough. A trim axis defined anywhere really. The post earlier about your trim (6.0) being too high is more likely the answer, however.

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The post earlier about your trim (6.0) being too high is more likely the answer, however.
I've put the approximate figures in a small excel I've done (based on the PMDG manual) and it calculates, given the weight and the CG, that the trim should be 6. Was wondering whether the 23% CG is correct. Seems a bit low to me. Maybe somebody can tell us the range of normal CGs...

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If the wind speed and direction have changed after the FMC has been completed and the new wind is not loaded into the box, the speed you got the first time may be too high in relation to current conditions at take-off, and when you will get the lift off before a calculated.Steinar Grindstein

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If the wind speed and direction have changed after the FMC has been completed and the new wind is not loaded into the box, the speed you got the first time may be too high in relation to current conditions at take-off, and when you will get the lift off before a calculated.
You will lift off before the calculated runway distance, but not the calculated speed.As mentioned above, the speeds are airspeeds. As such, if the wind is stronger, your airspeed will be higher from the very start (standing still at 0GS with a 10KT headwind means your airspeed is 10), and you will still lift off at that calculated speed.

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Just out of curiosity, I plugged those weights into the PMDG load manager & both CG and trim are correct. On the Takeoff Ref page on the FMC I got trim:6 @ 21% cg.I was using the sliders & fudged the numbers a bit, but they're pretty close, maybe 1-2k lbs change each on zfw, pax/cargo & fuel load.

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Takeoff may seem easy but I have a small question. How much do I pull back on the yoke? Defiantly not all the way back. On videos I see the elevators and They don't go up much. Only 1/4 or something. How much do you guys pull back on the yoke and how long for on average?

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Takeoff may seem easy but I have a small question. How much do I pull back on the yoke? Defiantly not all the way back. On videos I see the elevators and They don't go up much. Only 1/4 or something. How much do you guys pull back on the yoke and how long for on average?
Pull back far enough to achieve 3 degrees of pitch per second. The amount changes with differing COG.

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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

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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?

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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.

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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?

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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.

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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

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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).

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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.

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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.

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

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