Take Off N1 Thrust question

[Ray Proudfoot]

I have a question regarding setting take-off thrust. I fly the PMDG737 model but without its panel of course and I have an Aerosoft 747MCP for autopilot control. My throttle is the CH Pro Throttle.

If I set TO1 or TO2 in the CDU the maximum N1 setting will be reflected on the EICAS. But, when I then press THR on the MCP and push the throttles all the way forward N1 exceeds that set on the EICAS. It slowly returns to the N1 value but it doesn't seem right that it should exceed that value in the first place. Things seem better if I don't push the throttles all the way forward.

Is the problem related to the Aerosoft MCP (it's more closely related to the 747 - not a 737) or down to some misunderstanding on my part as to how to engage Take Off thrust?

Guidance would be appreciated by this armchair pilot. :smile:

[Bob Reed]

The way I use takeoff power is, and this may not be right, arm auto throttle, advance throttles slowly until 80%n1 is stable then engage TOGA.

[Ray Proudfoot]

The way I use takeoff power is, and this may not be right, arm auto throttle, advance throttles slowly until 80%n1 is stable then engage TOGA.

Thanks Bob. It seems I should help the autothrottle by manually applying the approximate amount of power. The problem is the green indicator on the N1 EICAS doesn't accurately reflect the power setting and often it needs retarding.

Out of interest do you keep the parking brake set until the throttles have been advanced to the approximate N1 value? I don't and I've often wondered what is the correct procedure.

[Bob Reed]

Thanks Bob. It seems I should help the autothrottle by manually applying the approximate amount of power. The problem is the green indicator on the N1 EICAS doesn't accurately reflect the power setting and often it needs retarding.

Out of interest do you keep the parking brake set until the throttles have been advanced to the approximate N1 value? I don't and I've often wondered what is the correct procedure.

Well the parking brake depends on the length of the runway I am on. If it is long and I have room I do not hold the brake but if it is a shorter runway, and I guess this, I hold the brakes until just before 80%N1 and then engage TOGA. Would like to hear from a real pilot on this.

[Trevor Hale]

I know for a fact on smaller runways, The operators of the Falcon 900 Hold the peddles until engines are at T.O. power. then let em go... But Not the parking Brake!

[Ray Proudfoot]

Well the parking brake depends on the length of the runway I am on. If it is long and I have room I do not hold the brake but if it is a shorter runway, and I guess this, I hold the brakes until just before 80%N1 and then engage TOGA. Would like to hear from a real pilot on this.

That sounds pretty sensible. I too would like to know r/w procedures on this. I can almost see Pete D flicking through his 737 procedural manual now.:) My Mike Ray 737 manual suggests the p/b should be set but in my mind it puts an undue strain on the brakes.

[Bob Reed]

I know for a fact on smaller runways, The operators of the Falcon 900 Hold the peddles until engines are at T.O. power. then let em go... But Not the parking Brake!
I have used both but I did think that the parking brake was probably not the way to do it... But sometimes easer.....

[Peter Dowson]

That sounds pretty sensible. I too would like to know r/w procedures on this. I can almost see Pete D flicking through his 737 procedural manual now.:) My Mike Ray 737 manual suggests the p/b should be set but in my mind it puts an undue strain on the brakes.

The parking brake is merely a physical lock on the brake pressure in any case, so whether you use foot pressure or the parking brake lever is rather irrelevant. If you have your pmSystems programmed correctly you'd find you have to depress the toe brakes to create the brake pressure then pull the PB handle to lock the pressure on. In that sense it is rather similar to the way the parking brakes operate in a humble Cessna.

Regards

Pete

[Bob Reed]

The parking brake is merely a physical lock on the brake pressure in any case, so whether you use foot pressure or the parking brake lever is rather irrelevant. If you have your pmSystems programmed correctly you'd find you have to depress the toe brakes to create the brake pressure then pull the PB handle to lock the pressure on. In that sense it is rather similar to the way the parking brakes operate in a humble Cessna.

Regards

Pete

Is it possible to program this even with using the Parking Brake release when toe brakes are applied? I have not done too much with PMSystems yet.. Just looking at starting.

[themis]

Real Life Pilots usually set the A/T On when are aligned with the main runway to prevent accidentally press of TOGA button.
Also N1 80% for engine stabilization is way to high...!


The proper way for the 737NG is....(copying from Boeing's FCTM)


"Advance the throttle levers to just above idle (40% N1) as the airplane rolls onto the runway at a slow taxi speed. Once the airplane is aligned with the runway, allow the engines to stabilize momentarily then promptly advance the thrust levers to takeoff thrust (autothrottle TO/GA). Allowing the engines to stabilize provides uniform engine acceleration to takeoff thrust and minimizes directional control problems. This is particularly important if crosswinds exist or the runway surface is slippery. The exact initial setting is not as important as setting symmetrical thrus.

Note: Allowing the engines to stabilize for more than approximately 2 seconds prior to advancing thrust levers to takeoff thrust may adversely affect takeoff distance."

Also,

"A momentarily autothrottle overshoot of 4% N1 may occur but thrust should stabilize at +/- 2% N1 after THR HOLD. Thrust should be adjusted if required by PNF to -0% +1% target N1."


Regards
Themis Katakalos

[Bob Reed]

Thank you for that Themis! Looks like I need to dig out a couple of my manuals....

[Trevor Hale]

Interesting. Actually the Dassault Falcon has a System A and System B braking system. As you hold pressure on the toe brakes and advance the throttles there is a point in which the system itself realized that system A cannot sustain the braking pressure, you feel a little jolt as system a releases and system B engages, Feels like your feet slip off the peddles and when you release the toe brakes the aircraft thunders down the runway!

Amazing feeling.. Like you cannot believe...

[Tomlin]

Trevor, you've actually got to take off in a Falcon jet? Wow, that must have been really awesome. I would love to do the same in a LJ45. Actually, to be honest, I love flying in almost any aircraft. But, the one youre building is such a bonus to the experience!

[Trevor Hale]

Trevor, you've actually got to take off in a Falcon jet? Wow, that must have been really awesome. I would love to do the same in a LJ45. Actually, to be honest, I love flying in almost any aircraft. But, the one youre building is such a bonus to the experience!

Yes, I get to ride in them occasionally. When I travel for Business.

[Ray Proudfoot]

The parking brake is merely a physical lock on the brake pressure in any case, so whether you use foot pressure or the parking brake lever is rather irrelevant. If you have your pmSystems programmed correctly you'd find you have to depress the toe brakes to create the brake pressure then pull the PB handle to lock the pressure on. In that sense it is rather similar to the way the parking brakes operate in a humble Cessna.

Regards

Pete

Hi Pete,

Yes, I remember your system where it was necessary to push both pedals to apply the p/b. Perhaps on my next visit we can try the auto-throttle on t/off instead of manual throttle control. I bet that surprises you.;)

Cheers.

[Ray Proudfoot]

Hi Themis,

Thanks very much for that info. If I understand the instructions correctly during taxiing on the active N1 should be around 40.

Once lined up I switch A/T on and manually advance the throttles to N1 and then engage THR (TO/GA). The a/p will then make adjustments to the throttles to ensure they don't exceed N1.

You haven't mentioned the brakes. Are they touched at all once the aircraft is lined up and before the throttles are advanced to N1?

Thanks.

[themis]

Hello Ray,

When you taxi you try to not speed up over 20knots Ground Speed. If you are close to manouvering areas (near airports buildings) you try to be at 10 knots . In real life I've seen taxi speed up to 40 knots when the Tower is not seeing you..:roll:

The N1 value on taxi is not something to be considered of. Depends on your weight. The 737 doesn't need huge amounts of thrust to taxi. Just an initial push...and it rolls and very easily a bit over idle.

When you reach holding point if there is traffic you can use the parking brake to fully stop the aircraft and not applying toe brakes as you waiting for clearance. In critical phases (holding point, line up) if you think that there is gonna be a delay before the clearance arrive, you can use parking brakes for safety that the aircraft would not "slip" on the runway. After you get the clearance and release the brakes you advance the throttles to taxi for line up and *when you feel comfotable* you advance the Throttles up to 40% N1 waiting for the engines to stabilize... then TOGA... autothrottle does the rest.

When you get used to the procedure you can advance the throttle to 40% starting from the holding point and not after lining up as the real experienced pilots do...:)

In short runways I'll use brakes at the stabilization period to gain some meters.

Themis

[Peter Dowson]

Is it possible to program this even with using the Parking Brake release when toe brakes are applied? I have not done too much with PMSystems yet.. Just looking at starting.

Provided you program your parking brake lever to operate the pmSystems switch, not the FS one directly, the option code in the current 737 pmSystems logics handle the checking to see if you are pressing the pedals enough before engaging. I'm not so sure they currently offer automatic release on pushing the toe brakes, if that's what you mean, but that should be easy enough -- I haven't got that in operation here.

Of course the braking should, in any case, be dependent upon having sufficient brake pressure, but I've no dial for this in my cockpit so I've not got that implemented. For this to be truly correct the toe brakes should also be routed via pmSystems, which isn't so easy considering they are normally axes not buttons. Really I would need to add axis-disconnection facilities in FSUIPC, similar to those for other axes (for "fly-by-wire"), where the input axis value is supplied in a different offset but not applied to the real FS controls. Something else for my list I suppose.

Regards

Pete

[Peter Dowson]

Yes, I remember your system where it was necessary to push both pedals to apply the p/b. Perhaps on my next visit we can try the auto-throttle on t/off instead of manual throttle control. I bet that surprises you.;)


Not half! You have always been so steadfast inn refusing to use TO/GA! ;-)

Pete

[Thomas Richter]

For this to be truly correct the toe brakes should also be routed via pmSystems, which isn't so easy considering they are normally axes not buttons. Really I would need to add axis-disconnection facilities in FSUIPC, similar to those for other axes (for "fly-by-wire"), where the input axis value is supplied in a different offset but not applied to the real FS controls. Something else for my list I suppose.

Regards

Pete

Hi Pete

Oh ja. Hopefully it is near the top of the list (Vers. 3.xx + 4.xx) :-)

[Thomas Richter]

The major problem of all is a known behave of pmMCP that has to be corrected. It is on Enrico's todo list.
It means A/T works Okay and fast, but in ToGa/N1 mode it increases to slow. Normally you should get the power in oround 2 seconds, but actual it takes much longer but will be corrected.

Also there are sometimes different checklists from company to company and A/C's and engines. So if you have different engines in the same A/C type the handle can be different because the manufacturer gives the line.

e.g. in a CRJ
- center the A/C on RWY
- depress toe brakes
- increase N1 up to minimum of 50%
- hold toe brakes depressed for 30 seconds minimum to stabilize N1
then go

But in any case the different engine parameters gives you the GO when they are Okay, like EGT; N1/N2, Vibration ...
There are also some other factors to use ToGa or NOT, e.g. with strong tail wind you don't use ToGa because it doesn't work correct ....

[eudoniga]

I once heard a 737 pilot saying he'd use some pedal brakes to keep the a/c steady during spool up, but never dare to use the p/b: if it remains locked for any unforeseen reason, you have temporary paralyzed that runway !

And if it's a single runway airport, you have temporary ... closed the airport !!!

:p

[Thomas Richter]

I once heard a 737 pilot saying he'd use some pedal brakes to keep the a/c steady during spool up, but never dare to use the p/b: if it remains locked for any unforeseen reason, you have temporary paralyzed that runway !

And if it's a single runway airport, you have temporary ... closed the airport !!!

:p

Like Pete described, Toe brake and Parkbrake is exactly the same !!
The difference is that the Parkprake is a mechanical blocking of the Toe brake pedals in there depressed position. So the Toe brakes are in both cases depressed.
If you enter a Cockpit with Parkbrake set, the Toe brakes are in depressed position because the Parkbrake Lever blocks "only" the pedals in depressed position.
To unlock it is NOT possible to release the Park brake Lever only !
You have to depress the Toe brakes full and then release the Parkbrake Lever.
It is not like in a car where you have two different brake systems. In A/C's there is only one.

To set the Parkbrake or only hold the Toe brakes depends on the roles of the company and the day-feeling of the Pilot. No one will notice what he did :-)

[Peter Dowson]

Oh ja. Hopefully it is near the top of the list (Vers. 3.xx + 4.xx) :-)

Well, it wasn't on at all till last night -- oddly no one had asked for it. It only occurred to me as I was writing to this Forum.

It should be easy enough. Flags someplace, like in offset 310A. Would it be okay if these are cleared after 10 secs if not replenished, like the others? pmSystems should be able to re-set the flags every second or two?

There will be a Byte somewhere with separate Left and Right Brake disconnect flags, and two 16-bit words containing the current axis input value. When intercepted pmSystems would have to read those and apply them at offsets 0BC4 and 0BC6, but in a weakened form depending on brake pressure availability.

I'll look at doing this before the next major release if you think you can make use of it?

Regards

Pete

[eudoniga]

the Parkprake is a mechanical blocking of the Toe brake pedals

In fact I guess he was referring to the ... blocker's block !!!

;)

[Ray Proudfoot]

Hi Themis,


When you taxi you try to not speed up over 20knots Ground Speed. If you are close to manouvering areas (near airports buildings) you try to be at 10 knots . In real life I've seen taxi speed up to 40 knots when the Tower is not seeing you..:roll:

I stay within the speed limit when taxiing.... just.:D Some people are the aviation equivalent of Lewis Hamilton! :lol:


The N1 value on taxi is not something to be considered of. Depends on your weight. The 737 doesn't need huge amounts of thrust to taxi. Just an initial push...and it rolls and very easily a bit over idle.

The PMDG737 model that I use is very close to those values.


When you reach holding point if there is traffic you can use the parking brake to fully stop the aircraft and not applying toe brakes as you waiting for clearance.

That would be traffic on the active - not inbound.


In critical phases (holding point, line up) if you think that there is gonna be a delay before the clearance arrive, you can use parking brakes for safety that the aircraft would not "slip" on the runway. After you get the clearance and release the brakes you advance the throttles to taxi for line up and *when you feel comfotable* you advance the Throttles up to 40% N1 waiting for the engines to stabilize... then TOGA... autothrottle does the rest.

That's just what I was looking for. Brilliant! Thanks.


In short runways I'll use brakes at the stabilization period to gain some meters.

Roger!

Now that we've got a standard lne-up and take-off sorted what's the procedure for an immediate departure? Radar Contact v5 will feature this with inbounds a certain distance out. Obviously things are more time-critical. I'd be interested to know the procedure please.

[Tomlin]

Hi Ray

Also, if youre not already privy to it, here's an excellent source from the horse's mouth: http://www.smartcockpit.com/plane/boeing/B737/

[Ray Proudfoot]

Hi Ray

Also, if youre not already privy to it, here's an excellent source from the horse's mouth: http://www.smartcockpit.com/plane/boeing/B737/

Hi Eric,

Perhaps I'm a bit slow but I can't find anything there relating to an immediate departure clearance if that's the correct term to use.

I believe the word 'take-off" is only used when clearance is given to take-off. It's never used in any other instruction so as to avoid any misunderstanding.

I'm going out shortly but will return later tonight or later tomorrow after Pete D and I go on Concorde G-BOAC at Manchester (EGCC). Unfortunately it won't get airborne and even though I've never ben inside one I'm really looking forward to the trip.

Cheers.

[Peter Dowson]

Some people are the aviation equivalent of Lewis Hamilton! :lol:

Hey, I rarely do more than 35-40 on the straight! Except maybe in O'Hare when the really really long straights almost demand at least 50 -- and I'm sure I've seen them doing it for real too!

Pete

[themis]

Now that we've got a standard lne-up and take-off sorted what's the procedure for an immediate departure? Radar Contact v5 will feature this with inbounds a certain distance out. Obviously things are more time-critical. I'd be interested to know the procedure please.

The ATC asks you:"Are you ready for an immediate departure?"
You must have finish all the check lists (and BEFORE T/O) to be really ready.

Once you get the clearance...

From Holding Point you start entering the Main RWY by advancing the Throttle to 40%. Until you line up with the runway the engines should be stabilized. Then TOGA.

So the use of main runway is limited.

Themis

[Thomas Richter]

Hey, I rarely do more than 35-40 on the straight! Except maybe in O'Hare when the really really long straights almost demand at least 50 -- and I'm sure I've seen them doing it for real too!

Pete

It seems we need "radar traps" to brake you bit down on Taxi ways :-)

[Ray Proudfoot]

Hey, I rarely do more than 35-40 on the straight! Except maybe in O'Hare when the really really long straights almost demand at least 50 -- and I'm sure I've seen them doing it for real too!

Pete

:lol: And I never even mentioned your name Pete! Just as well they don't have Gatso cameras on taxiways ;-)

[Ray Proudfoot]

The ATC asks you:"Are you ready for an immediate departure?"
You must have finish all the check lists (and BEFORE T/O) to be really ready.

Once you get the clearance...

From Holding Point you start entering the Main RWY by advancing the Throttle to 40%. Until you line up with the runway the engines should be stabilized. Then TOGA.

So the use of main runway is limited.

Themis

Thanks Themis. Clearly no brakes are applied and checklists are completed in double-quick time.

You've been very helpful, thanks.:D

[Thomas Richter]

Thanks Themis. Clearly no brakes are applied and checklists are completed in double-quick time.

You've been very helpful, thanks.:D

You will also find this.
*******************************
To initiate taxi, release brakes, smoothly increase thrust to minimum required
for the aircraft to roll forward and reduce thrust to idle. Under normal
conditions, 45% N1 should be considered the maximum N1 for breakaway
thrust. Do not start a turn until sufficient forward speed has been attained to
carry the aircraft through the turn at idle thrust.
Thrust use during ground operation demands sound judgment and technique.
The air blast effects from the high bypass engines at relatively low thrust can be
destructive and cause injury. Avoid following other aircraft too closely. Jet
blast is a major cause of foreign object damage.
The tendency is to taxi faster than desired. This is especially true during runway
turnoff after landing. The appropriate taxi speed will depend on turn radius and
surface condition. Nose wheel scrubbing indicates excessive steering angle
and/or taxi speed for surface condition. The normal straight away taxi speed
should not exceed approximately 20 knots. Speeds in excess of this, when
combined with long taxi distances, cause heat buildup in the tires. When
approaching a turn, speed should be slowed to the appropriate speed for the
conditions. On a dry surface, use approximately 8 to 12 knots.
===============================
Later .
===============================
SETTING TAKEOFF THRUST
A rolling takeoff is recommended. As the aircraft is aligned with the runway,
the Pilot Flying will smoothly advance both throttles to approximately 40% N1
(thrust settings between 35% and 45% N1 are satisfactory) and allow the
engines to stabilize. The throttle position will be about ¾” forward of idle.
Unrestricted advancement of the throttles can cause asymmetric thrust with
directional control problems, especially on slippery runways.
Caution: The nose wheel steering (tiller) should not be used above normal
taxi speeds (20 knots).
After the engines are stabilized, the PF will manually advance the throttles
toward the takeoff power setting, and engage TOGA when satisfied that engine
acceleration is normal. ....
*******************************

[Ray Proudfoot]

Thanks Thomas. After our tour of G-BOAC Pete D and I spent a short amount of time trying these procedures with the PMDG737-900.

With the aircraft aligned down the runway I advanced the throttles to 40% N1 and after a few seconds engaged TOGA. The engines took quite a long time to reach N1. Longer than seems safe if I'm honest. With a lightly fuelled aircraft it was 2/3 down a 10,000ft runway before we got airborne. I would have expected it to get to Vr around half-way down.

[Peter Dowson]

With the aircraft aligned down the runway I advanced the throttles to 40% N1 and after a few seconds engaged TOGA. The engines took quite a long time to reach N1. Longer than seems safe if I'm honest. With a lightly fuelled aircraft it was 2/3 down a 10,000ft runway before we got airborne. I would have expected it to get to Vr around half-way down.

I was also surprised at this, as it hasn't happened to me that I've noticed -- it is usually too quick and overshoots a bit. Mind you, I'm using FSX now, not FS9.

Of course we both got it wrong today in any case -- as Thomas said

" After the engines are stabilized, the PF will manually advance the throttles toward the takeoff power setting, and engage TOGA when satisfied that engine acceleration is normal."

I do actually manually advance at the same time as engaging TO/GA, but possibly we are both trying to engage TO/GA too early in any case?


Regards

Pete

[Ray Proudfoot]

I was also surprised at this, as it hasn't happened to me that I've noticed -- it is usually too quick and overshoots a bit. Mind you, I'm using FSX now, not FS9.

Of course we both got it wrong today in any case -- as Thomas said

" After the engines are stabilized, the PF will manually advance the throttles toward the takeoff power setting, and engage TOGA when satisfied that engine acceleration is normal."

I do actually manually advance at the same time as engaging TO/GA, but possibly we are both trying to engage TO/GA too early in any case?


Regards

Pete

Hi Pete,

Yes, I was possible a bit too eager to try this during your short stay but I didn't have access to this forum for the precise rules. I will try again and advance the throttles slowly and as N1 approached I'll engage TO/GA.

It wouldn't be as much fun if it worked first time anyway.;)

PS. I've reviewed the pictures of today's Concorde tour and some are quite good. The one of you sat in seat 2D has come out well. I hope the one I took of you in the captain's seat turned out okay.

Cheers,

[Peter Dowson]

PS. I've reviewed the pictures of today's Concorde tour and some are quite good. The one of you sat in seat 2D has come out well. I hope the one I took of you in the captain's seat turned out okay.

I've had a quick look and I think they are okay. I'll sort out the better pix and email you copies -- at about 2Mb they could mount up but I know you have a good broadband connection so you'll be okay. ;-)

Best regards

Pete

[Ray Proudfoot]

I've had a quick look and I think they are okay. I'll sort out the better pix and email you copies -- at about 2Mb they could mount up but I know you have a good broadband connection so you'll be okay. ;-)

Best regards

Pete

Thanks Pete. Look forward to seeing them.

Cheers.

[themis]

With the aircraft aligned down the runway I advanced the throttles to 40% N1 and after a few seconds engaged TOGA. The engines took quite a long time to reach N1. Longer than seems safe if I'm honest. With a lightly fuelled aircraft it was 2/3 down a 10,000ft runway before we got airborne. I would have expected it to get to Vr around half-way down.

I've noticed this to my latest flights using PM. (N1 Slow at TOGA) I think Thomas mentioned in a previous post that is a well known bug, and Enrico will fix it soon.

Themis

[Ray Proudfoot]

I've noticed this to my latest flights using PM. (N1 Slow at TOGA) I think Thomas mentioned in a previous post that is a well known bug, and Enrico will fix it soon.

Themis

That's good news. :D Last night I tried advancing the throttles to 40% at the start of the take-off roll and coninued to advance them slowly until N1 approached. When it did I engaged TO/GA. The aircraft soon reached Vr and the overall effect was very smooth.

Now how does this compare to an actual flight as a passenger when I experience a small amount of thrust being applied followed within a few seconds by a large increase in thrust. I'm not aware of a gradual increase in thrust during the take-off roll. It seems to come in two distinct parts.