Not holding speed at take off?

[copilot767 19]

Example: I want to fly a manuel takeoff, flightdirector is on, V2 is 149.. I set speed at fcu to 159...

I takeoff and climb about 10-15 degrees to 1500 ft and then level my thrust...

Still fly manuel, I sink my nose to about climbing 500 fået pr minut..

But seems the speed continue increasing Even fcu speed says 159 knots..

Why?

Christian from Denmark ☺

[The Dude 6537]

First, you do not set your speed in the FCU during take off. It is not a Boeing.

Only if you are in SPEED mode (FMA most left) and the ATHR is active will it hold the speed regardless of pitch.

Did you fly the step by step tutorial flight?

[Stathis Z. 6]

I don't think you are supposed to hold a specific speed during takeoff. V2 is the minimum safe climb speed, not a target for the fmc. Wouldn't holding speed put the aircraft in potential danger of stalling in the initial climb depending on weather conditions, take off weight etc? The takeoff thrust is maintained up to a certain point (1 minute?) after which you set climb thrust. Only them the fmc starts managing speed. I believe this happens to ascertain the aircraft's climb.

[The Dude 6537]

I don't think you are supposed to hold a specific speed during takeoff. Wouldn't this put the aircraft in danger of stalling in the initial climb? The takeoff thrust is maintained up to a certain point (1 minute?) after which you set climb thrust. Only them the fmc starts managing speed. I believe this happens to ascertain the aircraft's climb

If you do not know how the Airbus flies then muddling of the thread doesn't help either.

[Emi 5161]

I don't think you are supposed to hold a specific speed during takeoff. Wouldn't this put the aircraft in danger of stalling in the initial climb? The takeoff thrust is maintained up to a certain point (1 minute?) after which you set climb thrust. Only them the fmc starts managing speed. I believe this happens to ascertain the aircraft's climb

You're supposed to maintain V2+10 to accelerationaltitude. A typical accelerationaltitude is around 1000ft AGL.

However there's no reason to do this with selected speed in an Airbus as it will do that automatically with managed speed until reaching the accelerationaltitude in the FMGS.

[Stathis Z. 6]

If you do not know how the Airbus flies then muddling of the thread doesn't help either.

What I'm saying is that you are not supposed to hold climb speed some way by setting it, other than maintaining the correct pitch for the initial climb. This happens in any aircraft and takeoff thrust/power is standard and calculated. You don't adjust thrust to maintain speed, which is what happens when you set the speed. Instead you adjust your pitch. The aircraft needs at least enough thrust to maintain the speed at which drag due to lift is minimum. This speed is higher than V2 and there is no standard speed, as it depends on wind, weather conditions and aircraft load. In a bus it's calculated automatically. In older Boeing, you calculate it yourself and set it. Even then, in takeoff thrust only the pitch is altered and not the thrust level. If you could set the speed, you could end up maintaining climb speed with low thrust (in a more shallow angle) which is dangerous. You could also end up not having enough thrust for the chosen angle of attack to maintain minimum drag, because of thrust lag. This is why you can't set speed in flex or toga and also why you takeoff with flex or toga and maintain it until the thrust reduction altitude.

Apart from the acceleration altitude, there is also the thrust reduction altitude which may be the same, or may be different depending on the allowed noise levels in the area you take off from (which would change the acceleration altitude). So below the thrust reduction altitude, you must not reduce your thrust and it is not ok to reduce thrust, even in a Boeing. You are not supposed to force any speed on the aircraft below that and you are not supposed to hold V2+10, but at least V2+10. The SRS will set a pitch, immediately after takeoff, which will guarantee V2+10 with one engine off and there is also a rule for attitude protection. This is the pitch the FD is showing and the pitch the AP will follow if on. As a result, depending on weather and aircraft load, the IAS will most likely be higher than V2+10 and may be as high as +20 or +25, except if you have a failed engine, in which case it would be V2+10. In less automated aircraft (like a 737), the pilot may set climb speeds which provide a more comfortable climb, like V2+20 or 25, but in the airbus these are calculated automatically.

This has nothing to do with me not knowing how to fly a real airbus. This airbus is not programmed like a real one, but in order to imitate one in the first place. In that respect, the end result may be to "fly like the real thing", but it certainly doesn't work the same way in may aspects. In reality, the bus has no trouble keeping a proper N1 for one, or doesn't let you autoland with CAT I/II ILS. I may not be able to fly one, but I certainly know how "it flies", as I am a control systems and avionics engineer and I know very well how the systems work. Yes, if you choose an arbitrary pitch, V2+10 is a great speed to hold, but you are not supposed to do that. So with all respect, you are not supposed to hold the speed, but you are supposed to hold the pitch calculated by the system, and the manufacturer emphasises on this, and going with whichever speed the thrust/pitch combination results in. This is how the autopilot does it also. If your speed isn't stable, then it means you are not holding pitch well and has nothing to do with setting speed or thrust. How is what I'm saying wrong exactly?

[Patrick1246 353]

you can use a certain thrust setting AND hold a certain speed

[copilot767 19]

Thanks for answers ☺