Boeing 747 stalling on take off (Bug)

  • Been spending alot of time on the 747 lately (some if it copilot mode) and my position is external view and I didn't pay much attention to the airspeed on takeoff but I did notice a very aggressive climb out angle which is too steep for my liking but it is possible for a 747 to climb out at a crazy pitch. I witnessed a 744 freighter (Atlas) take off on a beautiful blue sky a few years ago, around 8am on a quiet Sunday morning at Sydney Airport and it climbed out like a rocket. It must have been lightly loaded - a rare site particularly as this airline normally flies East out over the Pacific.


    Another reason that the takeoff was spectacular was that the dual runways were operating counterflow, something they rarely do. Meant that he was taking off to the South on 16L (a short runway for a 747) towards oncoming landing aircraft on the opposite runway 34L before he turned left at low level over the ocean. It was a an amazing sight only matched by seeing the Concorde departing Heathrow in my experience. The Concorde was so loud that it would set off the car alarms on our street and if you were on the phone in the office you could not hear the person on the other line.


    The 747 takeoff was so remarkable that even the Tower commented on it. He said something like 'beautiful takeoff mate'. Empty a 747 is a rocket ship. I mention this because these Aerofly guys are pretty smart - they use inertia to calculate performance and I notice that the Aerofly 747 is configured at about 40 ton of fuel. I guess they fixed this weight as it allows for both takeoffs and landings, not to exceed the maximum landing weight (295 ton gross weight if memory serves correctly). At a 185 ton empty operating weight (a typical passenger version 744 empty weight with upto 2 flight crews, 4 pilots and their cabin staff for long haul, about 22 people which alone is about 1.6T of weight!) and 40 ton of fuel, this leaves 295-40-185 = 70 ton for payload (cargo and passengers and baggage). A typical payload of say 40-45 ton people and cargo (passenger 747) leaves a small safety margin with 40 ton fuel remaining. Margin is 70-45= 25 ton, not much of a margin when you consider that a 747 can carry up to 173 ton of fuel on takeoff. There are various reasons you would not want to land a 747 with 40 ton of fuel remaining (4 hrs of remaining possible flying time at 10T/hr burn rate) but that landing limit would be the most important one.


    I am thinking the reason for the steep climb out is the light weight. A 747 configured for landing (little fuel) is a much lighter beast than it was on takeoff as they carry alot of fuel for long flights. I can see Aerofly's problem - they have a fixed weight (no fuel consumption) and must set a light weight for landing. light load, light inertia means an over powered rocket ship. I suspect that is the problem here and it is not a bug but rather a technically correct phenomenon. We have a rocket ship.


    It is customary for pilots to adjust pitch angle on a climb to match a set speed - too slow, they lower the nose, too high they raise it. The guy I saw takeoff at Sydney must have been riding the rocket at a fixed thrust setting and let the airspeed determine the crazy angle.


    I have seen Airbus's do some impressive takeoffs but nothing like that day. I was like watching the space shuttle shooting for space.


    Just a thought. By the way the copilot does do some strange but maybe normal things? First time I flew a STAR into LAX in the 747 he did a holding pattern at one of the first waypoints at 10,000 feet. Only did one circuit of the holding pattern, maybe he missed the turn at the waypoint?, but it was pretty cool - first time a simulator has flown a holding pattern in my arm chair flying. Seemed very real. Not so keen on the occassional missed approach and return to land - still trying to understand why that happens to me at LAX with the copilot flying. He seems a bit of a nervous flyer - the approach looked good enough to me.

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    Edited 6 times, last by HKATER ().

  • A very interesting read!


    The climb out is very steep. Try it with cockpit view - the air speed drops to ~160knots and autopilot disconnects with low air speed warning.


    I've only noticed this with co pilot and B747. The B777 takes off great for me.

  • Yes I see what you mean. Just did a copilot takeoff in cockpit view and it was a pretty alarming takeoff. In external view (my usual viewing location) I have noticed the aggressive climb out before but wasn't watching the speed - as I am not flying.


    At full thrust (a lightly loaded 747 it would seem judging by the very high acceleration on the runway) he seems to let it get away from him, doesn't rotate and leave the ground until almost 180 knots (way too fast and late) and then because of the crazy speed build up on climbout (lighty loaded plane) he has to pitch the nose up at 20 degrees to ride this rocket. A lower rotation speed would have had a slower speed build up on departure - but he does attempt a proper rotation at the bug setting - seems it all happens too quickly for this geezer. Then he dials down the thrust and SETS THE STALL WARNING OFF in the cockpit at about 150 knots - scary stuff and then recovers by lowering the nose.


    Its not a comfortable feeling - quite scary really - I didn't see any of this drama from the outside view before. Seems that the excess power at full thrust is testing this robot pilot to the max.


    Was reading Mike Ray's legendary 747 manual recently and I noticed that he warned the real 747 pilot of the perils of pressing the TOGA (full thrust) on a go-around. He suggested it should only be used if absolutely necessary. He mentions something about being left with a handful of rocket ship. Its obviously a well known problem of a lightly loaded 747 coming in for landing. Seems that we have some hard physics in this simulator. Not surprised as I have come to expect nothing less from these guys - proper engineers, a few Doctors of Engineering as well.


    Below is a link of a commentary on the rotation and climb out speeds and angle of the 747 for those who are interested. Its highly variable and needless to say our copilot is not up to the task.


    In a 747 is it normal for the Vr (takeoff speed) to vary greatly depending on fuel load and ambient temperature?
    I was reading one of the documents linked on this question, particularly I was reading case study number 8 of this particular document. In the conclusion the…
    aviation.stackexchange.com

    Favourite album: In The Aeroplane Over The Sea

    My ride: R22, Eurocopter, Aerofly FS2022, Ipad Pro 2022/11 1TB ipadOS15

    XBox Series X/S wireless controller (model 1914)

    Edited 9 times, last by HKATER ().

  • Well just did some takeoffs on the Aerofly 747 and I am very impressed. The closest thing I have come to flying a 747 on a computer.


    Based on Boeing data with RR RB211engines, flap 10

    Region C (approximately at sea level and normal ambient temperatures)

    Assuming 40T payload, 40T fuel, 185T OEW = approx 270T TOW

    V1-120, VR-131, V2-149

    say VR (130 knots) rotation speed

    150 knot climb out speed, flap 10


    Was able to acheive and maintain a 150 knot climb out at 20 degree pitch angle at maximum rated thrust TOGA leaving the flaps out. The copilot retracts the flaps which explains the stall warning alarm.


    If you leave the flaps out you can climb to 10,000 feet, the flight director bars guiding you all the way from the runway. If you cut the thrust you will discover a cool looking amber stall warning indication (not the alarm like your pants are on fire of before) commencing at 130 knots.


    Its a vastly different experience to the copilot and feels very real. Fantastic flight model. Very impressed.


    I doubt I could do this takeoff without the wireless Xbox as its quite challenging with everything happening much faster then normal. Great job at this plane. I would recommend takeoffs at a derated thrust, it would be much easier.


    Boeing data state a pitch angle of 16 degrees, and 18 degrees at no payload (230T TOW), as high as 20 degrees at the lightest weight, but I was at times well above 20 degrees. Only because the speed gets away so fast you have to raise the nose almost 30 degrees to bring the speed back to the 150. But once you get to 150 knots you can hold it there happily at 20 degrees pitch. Fantastic.


    EDIT: just read a 747-400 reference manual for simmers which states that a -15% thrust de-rate is recommended for a lightly loaded 747. Options are full thrust, -5% and -15%. It also states that the climb angle on takeoff for light loads is not fixed but dependent on acheiving the set climb out speed or V2. (V2+10 in some cases).


    Seems that though the plane can do this, passengers would not appreciate the wild ride and most real pilots would struggle to perform this rapid takeoff - as we can witness with this copilot. This guy likes to live dangerously. Its a good thing that us sim pilots are not allowed near the real thing. But I recommend doing this takeoff on Aerofly. It is quite an experience and a challenge. My advice - don't let the copilot takeoff!


    Anyway I now know the speed targets for this 747 on takeoff for a more realistic simming experience.

    Favourite album: In The Aeroplane Over The Sea

    My ride: R22, Eurocopter, Aerofly FS2022, Ipad Pro 2022/11 1TB ipadOS15

    XBox Series X/S wireless controller (model 1914)

    Edited 4 times, last by HKATER ().

  • Did some takeoffs in the 777-300ER last night. Was a bit wary and expecting the copilot to have an even worse problem of excess thrust. Reminds me of the line from that TOOL song (Vicarious): "I like to watch things die - from a safe distance." Unlike the 747, each engine is capable of flying a 777 on its own and have heard that some airlines takeoff at 50% thrust routinely as the engines are so over powered. Seems that a max rated thrust MRT takeoff in even a fully loaded 777 is rare thing.


    He actually did a good job at MRT. I was surprised.


    My estimates are:

    OEW = 168T (this figure may not include crew?)

    Fuel = 54 T

    Payload estimate at 365 pax@100kg per pax = 37 T

    TOW = 168+54+37= 260 T approx


    Managed to get some takeoff data for the ER at flap 15 from a pilot forum:

    V1/Vr/V2 of 142/149/162 at flap 15

    https://www.pprune.org/tech-log/273815-where-find-b777-flaps-15-takeoff-speeds.html


    Say rotate at 150 knots and

    climb out at 165 knots, at max rated thrust.


    Managed to climb out at 165 kots (about 20 degree nose up) at flap 15 and after cutting the thrust an amber stall warning began at 149 knots just like the 747 did. That the stall warning begins at 149 knots, exactly as per the Boeing data at this weight is seriously impressive. A lower thrust would have been a sedate and comfortable take off and a lower angle of climb at the 165 knots, before flap retraction and speed up.


    Maybe the V speed bugs on the 747 are wrong - hence why the copilot rotates too late and too fast? On the 777 they appear to be correct.

    Favourite album: In The Aeroplane Over The Sea

    My ride: R22, Eurocopter, Aerofly FS2022, Ipad Pro 2022/11 1TB ipadOS15

    XBox Series X/S wireless controller (model 1914)

    Edited once, last by HKATER ().

    • Official Post

    In the existing version the copilot retracts the flaps too early and that causes a stall. I've just tested this again with the next major version and it took off without retracting flaps :)

    The default v-speeds set in the aircraft are values that work well for the present weight. I think these speeds originated from some manual but I'm not sure anymore (long time ago). Once we add weight and balance we will find a way to compute the correct v-speeds.

  • No worries Jan. Its a good and impressive flight model, both 777 and 747 based on my arm chair charts (I am not a real pilot) - only the copilot actions seem questionable. Good to hear that he has had some remedial training! Very nice, thank you.

    Favourite album: In The Aeroplane Over The Sea

    My ride: R22, Eurocopter, Aerofly FS2022, Ipad Pro 2022/11 1TB ipadOS15

    XBox Series X/S wireless controller (model 1914)

  • In the existing version the copilot retracts the flaps too early and that causes a stall. I've just tested this again with the next major version and it took off without retracting flaps :)

    The default v-speeds set in the aircraft are values that work well for the present weight. I think these speeds originated from some manual but I'm not sure anymore (long time ago). Once we add weight and balance we will find a way to compute the correct v-speeds.

    Would weight and balance be added to Aerofly as an app update with Aerofly fs2022 or would it be added for a future Aerofly like fs 2023.

  • A final comment on MRT and TOGA and heavy airliners. Years ago an engineer told me that an aircraft turbine is most efficient at sea-level. Something I could not understand as all aircraft fly as high as possible so surely that is the most efficient place to be? It took me years to understand what he meant. I had no interest in aircraft at the time but was studying aerodynamics. I remember being in a lunch room around that time full of Aeronautical Engineers joking that any time an aircraft crashed, like its wings fell off, it was the fault of a mechanical engineer not an aeronautical one.


    He was not talking about fuel efficiency of course but power efficiency. That all aircraft turbines develop their maximum power at sea-level due to a higher air density. Its good news for the loss of an engine and when taking off but bad news for fuel economy.


    This is the reason that all pilots should be wary of using maximum thrust at low altitudes or on the ground. A turbine's power has to be respected. Same applies to Aerofly. And of course this thrust is not the actual maximum - emergency power - that is something else entirely. The maximum 'rated' thrust that can be safely used.


    Never had the time to fly the A380 on a sim but found a great article on this topic, link below for those who like to:

    Flying the Airbus A380 – Takeoff!
    Thank you to everyone for your feedback on the first two posts. I think it is time we took the A380  into the air, don’t you?!   Before we go blasting off down…
    captain-daves.com


    and V speeds at a lower weight, link below

    http://www.srs.aero/wordpress/wp-content/uploads/2010/08/SRS-TSD-005-Rev-0-A380-Flex-Take-Off-Analysis.pdf

    Favourite album: In The Aeroplane Over The Sea

    My ride: R22, Eurocopter, Aerofly FS2022, Ipad Pro 2022/11 1TB ipadOS15

    XBox Series X/S wireless controller (model 1914)

    Edited 3 times, last by HKATER ().

    • Official Post

    Jet engine power is defined as velocity times thrust. So at takeoff engine power is nearly zero by definition! That's why in engine specifications you can only find static sea level thrust for different ratings like max takeoff thrust, max climb thrust, etc. and no power specifications in terms of horse power or kilowatts (other than engine accessories).


    It's different to a propeller driven plane or helicopter where engine power is defined as torque times rotation speed of the propeller/rotor. When talking about jet engines it doesn't really make sense talking in terms of power. It's thrust and thrust efficiency. Specific fuel consumption for jet engines is fuel mass flow divided by thrust which is different to specific fuel consumption for propeller driven aircraft which is FF divided by engine power and time (if I remember correctly).

    Turboprop aircraft are usually just handled like propeller driven aircraft but if you want to include the small residual engine thrust they produce then there are also formulas for that.


    But at some point engineers just give up. Let the pilots say weight when they mean mass even though one is a force and the other is a mass. Let them say power instead of thrust. Let them use imperial units for their altitudes, speeds and distances...

  • Great Jan, makes sense. Also explains why I see 'power' all the time on this topic used as though it were interchangeable with a force (thrust), which it isn't.



    Favourite album: In The Aeroplane Over The Sea

    My ride: R22, Eurocopter, Aerofly FS2022, Ipad Pro 2022/11 1TB ipadOS15

    XBox Series X/S wireless controller (model 1914)