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Using autopilot to take off

Pro Member First Officer
HowardsRock First Officer

I've found that using the autopilot to take off is the only way the airplane can keep itself trimmed during flight. This is the only way I've found to keep the nose from shooting way up or down upon disengaging the autopilot in flight.

Here's my procedure:

1. Before takeoff, set speed, heading, target altitude, and vertical speed in the autopilot. None of the activation buttons should be pressed except for the A/P master (CMD) at this time.

2. Perform all activities on checklist before takeoff.

3. When cleared for takeoff, release brakes and press the IAS button on the autopilot console. This will fire up the engines and get you moving down the runway.

4. At takeoff speed, press the ALT button on the autopilot console. This lifts the plane off the runway on its way to the target altitude at the set vertical speed.

5. Now whenever you disengage the autopilot for whatever reason, the plane maintains its trim (since it set its own trim to begin with). At this point, the plane would flare sharply up or down according to the manual trim if you had taken off manually.

If you take off manually, you MUST level the plane MANUALLY to zero the trim before engaging the autopilot. Otherwise, the trim would not be level, and the autopilot would retrim the plane based on the trim settings FROM THAT POINT. The plane assumes a level trim when autopilot is not engaged.

Example: You're flying the 747 manually at 15,000 feet on your way to a cruise altitude of 30,000. You've manually trimmed the plane to maintain a 1,500 ft/min climb (I'll come back to this later). Now say you want to turn on the autopilot and let it finish the climb and level out for you. You hit the appropriate buttons on the autopilot console, and the plane climbs and eventually levels out at 30,000 feet. So far, so good. You fly your route using the autopilot, taking your instructions from the ATC. Now let's say it's time to land. You've descended to 1,500 feet using the autopilot. You've reduced speed, added appropriate flaps, and you're smooth on the glideslope. You're getting ready to cross the threshold, so it's time to disengage the autopilot. You press the CMD button and OH MY GOD!! The nose of the plane has shot up to 25 degrees! I stall out and crash on the runway!! Why? Because you did not manually level out the trim before you engaged the autopilot after takeoff. Remember, the plane assumes a level trim at the time you engage the autopilot. So when the autopilot is DISengaged, the plane will automatically return to whatever trim was set when autopilot was turned on, assuming it was level flight (even if it wasn't level).

So what's the point of this post? To show you that if you let the autopilot maintain the trim ALL THE TIME (from takeoff clearance to landing clearance), you will never experience any unexpected flares up or down.

25 Responses

Pro Member Captain
Bindolaf Captain

That's a strange way to fly a plane. I've never had issues trimming, I don't quite understand your procedure or the problem. Just take off manually. Set the trim at "TO" for take-off (or zero, or whatever else), then while climbing trim the plane so that you don't need to pull on the stick. When you level off, trim again for the current speed/attitude. And so on.

. You're getting ready to cross the threshold, so it's time to disengage the autopilot.

The time to disengage the autopilot has come and gone many times if you're over the threshold. By then it's better just to auto-land or pray or something.

You press the CMD button and OH MY GOD!! The nose of the plane has shot up to 25 degrees! I stall out and crash on the runway!! Why? Because you did not manually level out the trim before you engaged the autopilot after takeoff. Remember, the plane assumes a level trim at the time you engage the autopilot.

Are you going (way) too fast? Do you have correct flaps? What is the A/P configuration? Is it set for level flight? Is it set to descend? When A/P is engaged, it regulates trim. If you are in level flight and disengage the A/P, you keep flying level. If you were climbing, you keep climbing. However, if - for example - you are on approach doing 300 kts in a descent and suddenly disengage the A/P, the trim might have been "out of range" or at a very high or low range to keep up. This might get bad.

So when the autopilot is DISengaged, the plane will automatically return to whatever trim was set when autopilot was turned on, assuming it was level flight (even if it wasn't level).

I'm not sure this is accurate, I think A/P off just leaves the trim where it was las with A/P on. Correct me though.

Pro Member Chief Captain
CrashGordon Chief Captain

Umm... Wouldn't it be more appropriate to properly trim the plane? Even on those models that do not have a good indicator for trim, It is pretty easy to bring it down the same number of "notches" you brought it up originally.

Pro Member First Officer
HowardsRock First Officer

Quote:
So when the autopilot is DISengaged, the plane will automatically return to whatever trim was set when autopilot was turned on, assuming it was level flight (even if it wasn't level).

I'm not sure this is accurate, I think A/P off just leaves the trim where it was las with A/P on. Correct me though.

I promise you this happens. I've has FS9 for over 2 months now, and this unexpected flare happens to me EVERY TIME, unless I do the things I mentioned.

Pro Member First Officer
HowardsRock First Officer

All these things you guys mention I'm sure will work. The important thing to remember is to level the plane manually before you turn on the autopilot.

Pro Member First Officer
HowardsRock First Officer

OK. I tried taking off manually, then manually trimming the plane for a climb so I don't have to keep the stick pulled back. Once I reached my cruise altitude, I trimmed manually for straight and level flight.

The I turned on my A/P to hold the altitude I was at. As soon as I hit the A/P switch to turn it on, the plane took a nose dive.

I leveled the planed out using the vertical speed setting in the autopilot. Then when I turned off autopilot, the nose shot up again like it always does.

Dammit I am so frustrated with this damn thing!!

What the hell am I doing wrong??

Pro Member Captain
Bindolaf Captain

Could it possibly be the plane? What are you flying? Does it happen with all planes? In any case, the best way to get acquainted with trimming is the Cessna 172 and not a Boeing 747. The latter has so many other issues and mainly power management. It's really easy to go into overspeed or stall in a 747.

Let us know.

Pro Member First Officer
HowardsRock First Officer

I like to fly the 747, but this happens in all planes - 737, 747, Cessna 172, you name it.

The autopilot uses trim control to climb, descend, or hold altitude. So when the autopilot levels out, it uses the trim to do so.

Level is level, right??

Apparently not, because it reverts to some kind of screwed up trim when the autopilot is turned off.

Pro Member Chief Captain
Alex (Fire_Emblem_Master) Chief Captain

Ok, buddy. I've had FS9 for over a year now, and with far over 500 hours in on the B757-200 I can promise you that what you're doing isn't what will work best. In all my flying experience, I've not found a single plane that actually requires manual trim in order to stop the autopilot from "Shooting" you up or down so many degrees. Here's something to consider:

When you set the autopilot, the FIRST thing you need to do, is set the altitude, and heading, or NAV button if you want to follow VOR/GPS. then ENGAGE both those buttons. Do that FIRST. After you've gotten the plane up off the ground, all you need to do is flick the AP master switch (Hit Z on the keyboard) and slowly bring the stick to center. Don't just let it go and expect the A/P to suddenly keep you level. Trim for takeoff is different than trim for level flight/climb/descent. Don't forget that. 😉

Pro Member First Officer
HowardsRock First Officer

I don't have a stick. I am using the keyboard. Any other suggestions?

Pro Member Chief Captain
Alex (Fire_Emblem_Master) Chief Captain

THAT would be why. Main suggestion is that you get one. I'm not downplaying it if you can't afford one, but it makes it so much easier.

OH HELL! Just remembered

if you use the NUMPAD to control the alierons and elavator, DO NOT FORGET to hit NUMPAD 5 to center everything, otherwise it all stays how you put it. like if you tap NUM 2 to raise the nose, the elavators will NOT center themselves out, ONLY NUM5 will do that. 😉

Pro Member First Officer
HowardsRock First Officer

Wow...what a difference that would make. I didn't even know about NUMPAD 5. Between takeoff and cruise, when should I press 5 and center everything?

Pro Member Chief Captain
Alex (Fire_Emblem_Master) Chief Captain

Before you activate the autopilot I'd guess ❓

Pro Member First Officer
HowardsRock First Officer

And after pressing NUMPAD 5, do I need to wait a period of time for everything to center out before engaging the autopilot?

Pro Member First Officer
vlad (tiger7881) First Officer

Guys if u are taking off by using the auto pilot 😂 guys u have to practice by urself its better cuz sometimes the auto pilot get crazy cuz in take off has to be the following :

engine 95% n1

in 155 knots to get ur nose to 20 deagreas pitch up

light on.

but the auto pilot dont do that cuz in real life that what u hve to do but if u are flighin not like in real so it not interesting so........ 😛 have a good flight ❗ ❗ ❗



Last edited by vlad (tiger7881) on Wed Oct 26, 2005 6:11 pm, edited 1 time in total
Pro Member Chief Captain
Alex (Fire_Emblem_Master) Chief Captain

And after pressing NUMPAD 5, do I need to wait a period of time for everything to center out before engaging the autopilot?

No, it's just like letting go of the stick in a real aircraft, it will center nearly immediately.

WEL TIEGR I THINK TAHTS GOD AND AL BUT IT D3P3NDS ON DA ARECRAFT1!!11!1! WTF LOL IF U TRY AND ROTAET AT 15 IN A FULY LOAEDD 747-40 U WONT G3T IT OF DA GROUND!1111 WTF B SURE U CHEK UR INFO

ALSO111!!1 WTF 95% N1 ISNT NESESARY FOR SOME ARECRAFT TEH B757-20 ONLY NEDS 87-89% N1 FOR PROPAR TAEKOF THRUST1!1!1 WTF

Guest Guest

so the point is that we have to trim the aircraft for a level flight before engaging the Autopilot to prevent the nose of aircraft going up and down after disengage the Autopilot ?

Pro Member Chief Captain
Alex (Fire_Emblem_Master) Chief Captain

No, the Autopilot will naturally Re-trim the aircraft anyway. All you have to do, is if you're flying with ONLY the keyboard, hit NUM 5 and then activate the autopilot

Guest

Tried NUM5 before engaging autopilot. Didn't work.

Pro Member First Officer
HowardsRock First Officer

According to the default keyboard settings in FS9, NUM5 only applies to ailerons and rudder, not elevators.

Guest

how many times do i need to press 5 so that the aircraft won't go up and down after i disengage the A/P ?

Pro Member Chief Captain
Manuel Agustin Clausse (Agus0404) Chief Captain

Only once.

Pro Member Chief Captain
Alex (Fire_Emblem_Master) Chief Captain

well, what I would then do is try and find the elavator center button and hit that too i guess.

Pro Member First Officer
HowardsRock First Officer

No such luck. I had to download the newest version of FSUIPC. It has an option to center the elevators when A/P is engaged.

Works like a charm now...I just wish it hadn't cost me $26.00.

Guest

are you sure that press 5 num lock only once? i've already press it just once, but i figured out that my plane shot up again once i disengage the autopilot...

where do i go wrong?

Pro Member Chief Captain
Tailhook Chief Captain

Have we mentioned and emphasized strongly enough the importance of the Num Lock??

It's easily overlooked and the same mistake easily repeated over and over again. I know this because I've had many months of practice in this.

This is of utmost importance for simmers using a keyboard only. Why?

Because you're using the Num Pad not only for trimming but also for looking around as in flying your downwind- crosswind leg etc.. In the absence of a flightstick (where most likely you would be using your hat switch) you're confined to your Num Pad. Soo...

The Num Lock light has to be OFF for trimming!

The Num Lock light has to be ON for looking around!

This is a rule that leaves no room for exceptions!

The 5 key to neutralise your trim : If you hit it more than once that should not cause any problems. Flying the heavies you tend to do just this because the response time seems to be longer and we tend to get impatient.

Hoping that this is within the context of this debate
and hoping someone finds it useful,
Rick 😎

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