Few questions about PMDG 737-800

[martin-w 3,234]

:( Well that explains it then.

[FirstOfficera320 1]

Yes, I am using TOGA thrust (as I said several times in my earlier posts).FirstOfficer320: are you saying therefore to disregard the pitch in the FD?I really don't believe that anyone has yet been able to explain why following the FD leads to a speed decay. What might I not have programmed correctly in the FMC? If programmed correctly, surely the pitch angle shown on the FD will reduce at acceleration height? There should be no need to have to use tricks to get around this.Also - can someone explain how I know that the aircraft is maintaining V2+20 knots? There is only one speed showing on the IAS indicator!Nick

hi Nick,I'm indeed saying that. Here's a quote from the FCTM:"For optimum takeoff and initial climb performance, initiate a smooth continuous rotation at VR toward 15° of pitch attitude. After liftoff, use the attitude indicator as the primarypitch reference. The flight director, in conjunction with indicated airspeed and other flight instruments is used to maintain the proper vertical flight path.Note: The flight director pitch command is not used for rotation."so aim for 15 degrees after 5 sec then when passing 100agl follow the flight director. It shouls give you V2+20. provided that you are in TOGA pitch mode.kind regards,

[nicholas49 0]

Thanks kevinh. I have noted what you have said. If you say using VNAV would make speed control easier, I would like to try that. But it will not arm on the ground. The green LNAV light on the PFD lights up briefly and then goes out again. I don't see why this should be the case, given that the route is correctly programmed in the FMC.As for the stab trim, I do not see how you can accurately input the figure (5.50 in this case) on the stab trim next to the throttles, even if I could find the correct keyboard inputs!?

[kevinh 409]

Thanks kevinh. I have noted what you have said. If you say using VNAV would make speed control easier, I would like to try that. But it will not arm on the ground. The green LNAV light on the PFD lights up briefly and then goes out again. I don't see why this should be the case, given that the route is correctly programmed in the FMC.As for the stab trim, I do not see how you can accurately input the figure (5.50 in this case) on the stab trim next to the throttles, even if I could find the correct keyboard inputs!?

LNAV and VNAV won't always arm on the ground. If there is a turn soon after takeoff in the route for example. You can select them after takeoff when lined up with the first waypoint. VNAV might not arm for other reasons, check the manual for a full description.Stab trim setting doesn't have to be precise. Just judge it by the white index marks in the green band. That's all pilots have to go by too. You should be OK if you are within half a unit. To find assigned the keys, you need to get into the FS9 settings menu options\controls\assignments... choose the control surfaces category then scroll down until you find elevator trim up/down. Make a note of the keys assigned by default. You can select the joystick or yoke you have and assign buttons to the up down inputs. Most joysticks have a pair of buttons arranged fore and aft by the hat switch. I use the front one for trim down and the rear one for trim up. That replicates the trim pickle switches on the real yoke, and it makes it really easy to trim in manual flight.

[Fabo 213]

When you feel confident enough to try using VNAV the speed bug will move automatically (the speed window will be blank), but you still have to retract flap manually as you accelerate.

Bear in mind that legacy NG does not simulate an FMC software version that will allow VNAV arming on the ground, unfortunately.

The FMC TAKEOFF REF Page 1 shows you current CG in %MAC and the recommended takeoff TRIM position in units.

Unfortunately, this is not simulated in the legacy NG, although 5.5 will work most times.Also I have reported the thread, so if it is not here later, you know to look in the legacy section...

[zubart 5]

Guys, I am still really struggling with this. Can I just explain what happens:Before I start the take-off roll, the only green lights on the MCP are the A/T armed (showing in PFD too) and the FD. Is this correct?I am using TOGA thrust. I rotate and follow the FD (which seems to show 20 degrees pitch up - seems a bit steep?). By about 1,000 agl, the speed is decaying. This is definitely happening even before the thrust reduces to CLB thrust. Following the FD = a speed decay. This cannot be right!On a separate note, when I select CMD A, this activates: 1) HDG select; 2) N1 and 3) LVL CHANGE on the MCP (assuming I'm not using LNAV/VNAV). Is this correct?Also, what do people mean by the 'acceleration height' and also how do I do this:I can't adjust anything on the speed tape and I see nothing in the MCP about flaps?Help!Nickfile:///C:UsersChrisAppDataLocalTempmsohtml11clip_image002.jpg

Boeing recommends all normal takeoffs be with TOGA thrust engaged, and FD on.IAS speed decreases or increases because pitch attitude is changing, when you rotate and takeoff, the initial IAS usually shoots past the MCP window V2 speed. The AFDS is commanding a pitch increase or decrease to match the FD pitch bar. The FD pitch bar is directing you to the V2 speed set in the MCP airspeed window +15. For example, if V2 146 is set in the MCP window, then the AFDS will command a pitch attitude that will result in 151 IAS when everything settles down. When the FD pitch bar is satisfied, speed should remain constant as long as no other modes are selected.Steep angle of pitch attitude is not unusual on a light airplane using high thrust settings. For example, KSNA has a noise abetment procedure which on a light airplane (<125,000 LBS) , the FD bars will initially command about a 23 degree pitch attitude to hold V2 +15 Knots.A standard Boeing procedure in the NG is to clean the airplane up first before engaging the autopilot. Keep operation of the airplane simple.Acceleration height is usually 1000 feet AGL for most airlines. It is the height that the flaps are retracted and the airplane is cleaned up and power is reduced to climb speed. The FAA minimum Acceleration height is 400 feet AGL for any transport airplane. This is a pretty low altitude for a jet with lots of reserve power so most airlines use 1000 feet AGL for acceleration height. An airline operating a turboprop airplane will probably use 500 AGL as the acceleration height altitude. Acceleration height becomes real important during an engine failure. Flaps degrade climb performance on a transport, so with an engine failure it’s important to clean the airplane up as soon as possible to improve climb performance.Good luck,John Floyd Edited February 22, 2012 by zubart

[zubart 5]

The FD pitch bar is directing you to the V2 speed set in the MCP airspeed window +15.

the FD bars will initially command about a 23 degree pitch attitude to hold V2 +15 Knots.

I want to corredt myself. After lift-off, the FD Pitch command bar will command MCP speed (V2) + 20 knots.John Floyd Edited February 27, 2012 by zubart

[chris41 0]

Any luck on your problems?

 

Couple things I noticed with the other posts. You questioned whether or not 20* pitch up was a bit much. Lighter the aircraft, the higher pitch you will get to maintain V2 +20. 20* pitch up is common with my short flights or if I am practicing touch and go's with very little cargo/passengers, if any.

 

There should be no need to activate the LNAV mode while on the ground. In most videos I've seen and from what I've read/researched, this mode is never activated until aprox. 400 off the ground.

 

Once off the ground pitch to V2 +20. Soon after takeoff the MCP speed window will automatically change to show what that V2+20 speed should be. Select your takeoff mode (LNAV, HDG etc). You say that following the flight director bars gives you speed decay. Not sure why. I'm pretty sure pilots are instructed that should those bars show something different that they should maintain that V2+20 regardless (fly the airplane 1st, troubleshoot 2nd). While that doesn't solve your particular problem, try first to maintain that V2+20 and then monitor the bars to see what they show soon after.

 

Sidenote: FsPassengers and FS2Crew are great additions

 

Chris Porter

[WilloW_737 5]

The tutorial you are seeking can be downloaded from my website

 

http://www.flaps2approach.com/training/flight-training-b737-aircraft-related/

 

PMDG Flight Tutorial.

 

PM me if you want Tim's tutorial, Iain