747 bank limiter and descent profile?

[Guest vilius1]

Dear All,I'm new in this huge forum, so I bring my apologies beforehand if my questions have been discussed already. I'm having absolutely great time with PMDG 747, and so far I have only two questions:- If I set bank limiter to e.g. 5 degrees, the aircraft still appears to bank much more in LNAV or HDG modes. While it would be nice to have gentle banks at high speeds and altitudes...- It seems that TOD is too close to final destination, therefore VNAV descent is too rapid, resulting in FMC message "drag required". Therefore I have to extend spoilers, which is almost certainly damaging. Am I doing something wrong here? (Like too much fuel?) I take care not to exceed MLW at all times, typically ending with 30000 lbs of fuel or so...Thanks a lot - Vilius

[744pilot 0]

Hi and welcom to the forum,To answer your first question. The bank angle limiter only works in HDG SEL. mode. LNAV choses there own bank angle.About the TOD point now. Make sure you enter the VNAV DES FORECAST page correctly with wind and etc. This will make sure your descent starts on time and no drag is required then.Good luck soldier, :(

[Guest vilius1]

Thanks!

[Guest iflyby]

>To answer your first question. The bank angle limiter only>works in HDG SEL. mode. LNAV choses there own bank angle.Is it this way in real life? I never sense too much of a bank during cruise.

[744pilot 0]

LNAV bank angle depends on the kind of turn that needs to be taken.For example: If you have to make a 100 degrees turn the bank angle will be around 25 degrees but if you have to turn 10 degrees to the left it will only turn at 5 degrees of bank.

[Chaos81 110]

>Is it this way in real life? I never sense too much of a bank>during cruise.>>It's my understanding that has to do with the speed of the plane. When you are up at Fl350 and doing mach .8x, you don't notice it as much.

[744pilot 0]

exactly

[Guest vilius1]

Well, banking is defined by the bank angle. The perception of changed bank angle has nothing to do with airspeed. If you are going to spill your coffee at 200 KIAS and 30 degrees bank angle, the same is going to happen at 300+ KIAS and 30 degrees bank angle (because bank angle is the same).What is different, is the g load. Steep banking at high airspeed would produce much bigger g load of centrifugal force (and stress on the airframe). Therefore steep banking in cruise can never be seen in practice. It is not because you do not notice it. Due to significant centrifugal force you (or your stomach) would pay attention at once. :-) It is because commercial airliners are not flown that way.(You may even think that a g load which is big enough may prevent your coffee from being spilled. But perhaps it may happen in aerobatics, not in a commercial airliner.)Think of driving a car, for example. You may say that at high speed you cannot really feel the turns, and perhaps it is because at high speed turns are not noticeable :-) The real reason is that at high speed cars cannot be turned abruptly, because the tyres would loose grip due to centrifugal force. (Even if you do not loose control, it is simply uncomfortable).Therefore I'm surprised by the suggestion that LNAV may turn with any bank angle it likes at any airspeed. I would expect that bank angle limitations should apply for higher airspeeds. Sharp turns may be programmed due to pilot error, but I would be surprised to see real 747 banking like a racing bike at Mach 8+ :-)Cheers, Vilius

[Guest ghostrider117]

I might be wrong but an airliner has to obey the same physics than any other aircraft, even the G.A. and gliders that I fly (in real life, I mean).So, about bank angle, g-load etc, it's quite simple. When you bank the airplane to make a symmetric turn (which means you're not sliding or slipping), the sum of weight and centrifugal force (which, as you may know, doesn't exist: it's in fact a fictitious force that we feel because of inertia, the real force being the opposite of the centrifugal force: the centripetal force) will always be perpendicular to the wings. In other words, when being in an aircraft during a symmetric turn, your coffee will be just fine parallel to the floor (not to the ground, though!).The only thing you