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Guest Disasterman

Too much trim during landing

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Hello everyone I have a big problem when I try to land the big birds like 747-400. The elevator trim is going crazy and the nose of the plane is at 15-20 degrees up and eventually it stalls. What am I doing wrong?Also another question, the trim during level cruise should be 0?Thanks in advance, newbie here :(.I am looking forward to your replies!!!!

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I suppose you are talking about the stock B744 here.Unless the autopilot is active during landing (which it shouldnt in the stock aircraft for the obvious reason: no autoland), the trim aint doing anything you dont tell it to do. At least I have never seen or heard something like that. In real aircraft you usually have multiple trim switches to prevent a trim runaway, that you probably wont have on your joystick. A trim runaway might eventually occur when you have the trim switch stuck. Quite unusual, but might happen, I don't know... Nevertheless you might want to check your joystick/key assignments.The nose isnt simply at 15-20

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The problem isn't that you're doing something wrong.. the problem is probably that you're not doing anything.. ala, letting the autopilot fly the approach before you've mastered landing it manually.That said.. it sounds like you're trying to land too heavy, and as you slow to approach speed, the autopilot is trying to keep the overweight airplane on the glideslope by pitching up.. and of course that starts the deadly cycle of trying to maintain an altitude by pitch while on an approach. Pitch is used to control airspeed.. and power is used to control vertical speed.. (assuming a properly stabilized approach in a jet at landing weight)... so, when the autopilot tries to pitch for altitude.. all that really happens is that the plane slows down even more.. and you see the results :( Along with being at a safe weight.. make sure you're in proper landing configuration for that weight. That would include specific approach speeds and flap deployment, based on the weight.

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Thanks guys! I think that it's happening just exactly as Brett said.In everycase that I had these stalls the gargo load was max I should make the approach with different speed and flaps accordingly thanks again.I use ILS approach only if the airport has one, when I land manually I have not this problem.Thanks again happy new year!!

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I use ILS approach only if the airport has one, when I land manually I have not this problem.
Well yeah thats exactly the problem lol. You should fly the ILS manually. There simply is no other way to land the stock jets than manual, be it on instrument approach or not.On a side note, there is absolutely no problem to land the stock planes at MTOW without breaking them - realism not being the question here. Have fun. :(

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Thanks guys! I think that it's happening just exactly as Brett said.In every case that I had these stalls the cargo load was max I should make the approach with different speed and flaps accordingly thanks again.
In the real world ... of course ... avgas being expensive to purchase and carry around with you ... much effort is expended to minimize the weight associated with spare fuel at landing (balanced against the possible need to divert to an alternate airport or circle a busy airport).In any event, each default aircraft is equipped with a Kneeboard that will suggest landing approach speeds (Vref) and flap settings for several different weight configurations. A pilot can have the kneeboard open to the Reference page on all landings so that the flap placard speeds and Vref info is handy during your descent and approach.referencevref.jpgAs you can see from the image above, the landing approach speeds suggested for the default 747 can vary dramatically - up to 60 knots of difference - depending on your landing weight configuration and flap preferences.Cheers,

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Pitch is used to control airspeed.. and power is used to control vertical speed..
Ok for light aircraft theory Brett, but for airline category aircraft the opposite is correct.

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Ok for light aircraft theory Brett, but for airline category aircraft the opposite is correct.
Yeah.. much like a blind, instrument approach in a small aircraft, the timing and effect of those two controls blur, and even switch roles... especially in a flap-deployed, high-wing-loaded jet, where your approach-speed can be as much as much as 50 knots above stall-speed.I've no time or training in big jets.. so I'll defer to an expert.. but an airplane is an airplane.. a big jet trimmed for level flight will climb, not accelerate when you add just power.. and if I'm nailed on perfect approach-speed in a jet, but a little low, I'd just add some power, and the pitch to keep that airpeed nailed.The OP's problem was the autopilot trying to picht to maintain altitude.

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especially in a flap-deployed, high-wing-loaded jet, where your approach-speed can be as much as much as 50 knots above stall-speed.
Are you sure about that 50kts above the stall speed? Vref is determined by 1.3 x Vs0, so that would mean and aircraft would have a stall speed, fully configured for landing of 167kts, thus a Vref of 217kts
I've no time or training in big jets.. so I'll defer to an expert.. but an airplane is an airplane.. a big jet trimmed for level flight will climb, not accelerate when you add just power
It won't, and it can't. Not to start with anyway. If you look at the lift formulaCL=

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Are you sure about that 50kts above the stall speed? Vref is determined by 1.3 x Vs0, so that would mean and aircraft would have a stall speed, fully configured for landing of 167kts, thus a Vref of 217kts
Nah.. I'm far from sure, and said that it CAN be as much as 50kias different.... i.e. a jet can fly a good portion of its approach at ~170, and be over the numbers at ~130 and still be at least 10kias above Vso.. hence the 50. I'm sure that in most cases, for most jets, it's much less than 50.. and gets smaller at higher weights; much like the difference between Vs and Vne can shrink to zero, as altitude increases.Again.. I have no jet training, but an airplane is an airplane. The type of airplane, and the situation (ala big jet on approach) will determine the ORDER in which you manipulate controls, and to what degree you can do one, without doing the other, but not the RESULT of each manipulation.. and there's always the confusion between cause, and control... i.e... not understanding that thrust causes airspeed, and pitch controls airspeed..As mentioned.. even in a light single, the order blurs and even flips... especially on an instrument approach. I'll fly an ILS in a C172 at 90kias so that I have the luxury of primarily controling vertical speed by pitch. Not for any aerodynamic reason, but because pitch first can keep me from having to power my way back onto the glide-path. That type of "power for altitude" is fine when you can see the ground, and is THE best way to teach someone how to fly an approach (it's important to drill it into a new pilot's subconscious that power controls vertical-speed, and pitch controls airspeed), but when you cannot SEE anything, you don't wanna power your way back to a glide-path from underneath it.. And in a fast, heavily wing-loaded airplane, falling below a glide-path is a much bigger problem; so you go about it in a manner that allows you to primarily control vertical-speed by pitch, and airspeed by power, but aerodynamically, you're still doing it in the traditional, inverse... and it's well demonstrated, per the OP's problem.

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Nah.. I'm far from sure, and said that it CAN be as much as 50kias different.... i.e. a jet can fly a good portion of its approach at ~170, and be over the numbers at ~130 and still be at least 10kias above Vso.. hence the 50. I'm sure that in most cases, for most jets, it's much less than 50.. and gets smaller at higher weights; much like the difference between Vs and Vne can shrink to zero, as altitude increases.Again.. I have no jet training, but an airplane is an airplane. The type of airplane, and the situation (ala big jet on approach) will determine the ORDER in which you manipulate controls, and to what degree you can do one, without doing the other, but not the RESULT of each manipulation.. and there's always the confusion between cause, and control... i.e... not understanding that thrust causes airspeed, and pitch controls airspeed..As mentioned.. even in a light single, the order blurs and even flips... especially on an instrument approach. I'll fly an ILS in a C172 at 90kias so that I have the luxury of primarily controling vertical speed by pitch. Not for any aerodynamic reason, but because pitch first can keep me from having to power my way back onto the glide-path. That type of "power for altitude" is fine when you can see the ground, and is THE best way to teach someone how to fly an approach (it's important to drill it into a new pilot's subconscious that power controls vertical-speed, and pitch controls airspeed), but when you cannot SEE anything, you don't wanna power your way back to a glide-path from underneath it.. And in a fast, heavily wing-loaded airplane, falling below a glide-path is a much bigger problem; so you go about it in a manner that allows you to primarily control vertical-speed by pitch, and airspeed by power, but aerodynamically, you're still doing it in the traditional, inverse... and it's well demonstrated, per the OP's problem.
I "think" I get what you are trying to say. But what difference is the flight conditions if you are flying an ILS? If you are flying an ILS you shouldn't be looking at the ground.I have over 3,000hrs airline flying, and even from the days of doing my Instrument Rating on the Seneca the opposite is true, Power controls Airspeed, pitch controls ROD/ROC. The reason is simple, if you are "on the Glideslope", but slow, you will add power and then "lower the nose" a fraction to a) speed up, and :( to stop you going above the GS, if you just lowered the nose to regain airspeed and then added power you will go below the glideslope (try doing this technique when you're a mile out). Flying a Glideslope is all about "Attitude", pin the attitude with the required power setting and she'll fly it (remember Power + Attitude = Performance). If you go low, you raise the nose a fraction, if you're low, then the opposite. If your instrument scan is up to anything at all you will never reach

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I think you just agreed with me.. :(

But what difference is the flight conditions if you are flying an ILS? If you are flying an ILS you shouldn't be looking at the ground
That's the difference... you cannot see the ground, so slipping below the glidslope is not an option. But, powering your way back onto the glideslope from underneath is OK, when you CAN see the ground.Sooo.. we fly an ILS a bit diferently. Nailing the glideslope is paramount.. extra airspeed gives us the luxury of "driving" down the glideslope by pitch first... or like you alluded... aiming it by attitude.C172 as an example: IF you were perfectly on glideslope at normal approach speed (~75kias), and then begin to slip below it due to increasing headwind as you descend.. just pulling up would be as "wrong" as it would be on a VFR approach. But at 90kias (being as in front of the power-curve as a heavily wing-loaded jet is at all times on approach), you can "drive" your way back onto the glideslope, and then worry about a power change. That's how the traditional method gets flipped. It's just important (especially for a new pilot), to realize the difference, and that in actuality, he still is controlling airspeed by pitch, vertical-speed by power, no matter the order the controls are manipulated.The order in which you you use the controls for each type of approach, is all about a teaching method. By the time you're in charge of an airplane, and flying it soley by reference to instruments, all of this stuff is instinct. Five+ miles on an ILS in a C172 (or 20+ miles in a jet), can be a dozen different approach conditions before you see a runway... and you'll likely end up flying a single approach in a number of ways.

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