All,

 

I was wondering if someone could lend me a hand or point me in the right direction so I can get this problem sorted.

 

So I started a flight in the 777 the other day from Heathrow to Copenhagen. As I was only going over to Copenhagen I was quite light. 

 

The issue is that I simply don't know how to perform a derated take off. Every time I take off I apply full power and the aircraft's off the ground within about 6 seconds (obviously I am doing something wrong). I can derate with no problem on the NGX. I just click the option underneath the top one in the FMC which is 24k I think or something along that line. I try to do this in the 777 but it's not working for me :(

 

Also on the climb out due to full power being applied I am straight over 250 knots. Could someone tell me:

 

1. How to calculate my takeoff thrust 

2. Where to enter this into the FMC so I take off with the correct thrust setting according to the aircraft's weight.

 

Thanks.

Full names in the PMDG forums please.

 

You are just scratching the surface of an interesting subject.  The easiest way to calculate thrust for takeoff is to use TOPCAT, the calculation must include weather conditions and runway in use as a minimum.

 

There are pages in the FMS to select thrust for takeoff (ie TO, TO1 TO2) and to apply the flex temperature(an assumed temperature).  The former reduced thrust as if it were a smaller engine, the latter reduces thrust as if the OAT were higher.

 

You will only need full takeoff thrust when at maximum weights on relatively short runway at high altitude on a hot day.  Best to try out TOPCAT.

In addition to what Dan mentioned (especially the full names - first and last - thing):

 

 

 

2. Where to enter this into the FMC so I take off with the correct thrust setting according to the aircraft's weight.

 

Depending on the livery you are flying, TO1/TO2 derates might not be available, so you would have to use an Assumed Temp takeoff. This is because the various liveries automatically import the options the airline has installed in their aircraft. If the airline does not allow anything other than TO, then TO1 and TO2 will not be offered on that page.

Alright guys, thanks. I noticed that the flight I did, I selected the top option which was TO as described above and that gave me a rotate speed of about 140 however the one underneath gave me a rotate speed of around 132 and the 3rd and final option underneath, that gave me a lower speed to rotate at. I selected the top option as I didn't want to get of the ground any sooner than 140 as I would have used even less of the runway! so selecting the TO 1st option on the thrust settings page was the best option. I just want to know if that's the right way of doing it, by selecting it from that page.

Alright guys, thanks. I noticed that the flight I did, I selected the top option which was TO as described above and that gave me a rotate speed of about 140 however the one underneath gave me a rotate speed of around 132 and the 3rd and final option underneath, that gave me a lower speed to rotate at. I selected the top option as I didn't want to get of the ground any sooner than 140 as I would have used even less of the runway! so selecting the TO 1st option on the thrust settings page was the best option. I just want to know if that's the right way of doing it, by selecting it from that page.

 

You are not taking into consideration the fact that a TO1 or TO2 derate will produce less thrust than a TO setting. So a TO2 setting would use up a lot more runway than a TO setting even though your V speeds may be lower.

 

As others have said, you should be using an assumed temperature thrust setting (enter this in the top left of the thrust limit page)  either with or without a derate. TOPCAT will give you all the details you need to use the right settings. In the meantime experiment with TO1 and 50 degrees celcius and see if you notice the difference.

I selected the top option as I didn't want to get of the ground any sooner than 140 as I would have used even less of the runway!

 

Hi, may I ask that silly question: why? What is the reason why you don't want to takeoff at less than 140kt and use less runway?

Actually, the choice of TO thrust will depend on the following parameters:

_ Weight of the aircraft (the heaviest, the highest thrust)

_ Flaps

_ Weather conditions (temperature, pressure, weather phenomenons expected like windshear, rain/snow, runway wet/dry...)

_ Runway parameters (length, elevation, condition)

_ Obstacles on the departure path

 

Basically, using the lowest thrust as safely possible will help reducing wear of the engines which is sensible choice.

The Vr is not a factor to choose the TO thrust but a consequence of that choice.

 

Also, don't get confused between Vr and the runway length used. A lower Vr doesn't necessarily mean a lower takeoff distance.

A lower Vr if it is the consequence of a lower thrust setting may even mean a longer takeoff run as the acceleration will be lower too.

 

Pay also attention to the fact that selecting a too high thrust for a certain weigh may be prohibited as you may loose control of the aircraft in case of an engine failure. Some aircraft have an indicated minimum takeoff weight so that the ratio Weight/thrust doesn't exceed the safe margin.

Charlie,

 

The reason for the difference in speeds at very light weights may have to do with minimum controllable airspeed.

Most probably at that weight, you need 140 knots to have the margin needed in the event you suddenly lose

115.000 LBS of thrust on one side. With the derate settings you have less thrust to overcome with the same

rudder. Thus a lower speed can be rotated at (with all other things equal).

 

Cheers,

137kt is the Vmcg speed - velocity for minimum control on ground - with an engine out, as pointed out by Xander.

 

The FMS will never give you a speed lower than this, as rudder authority would not be enough to overcome asymmetric thrust.

137kt is the Vmcg speed

 

I think you’re thinking of the VREF speed floor, which exists as an extra buffer to VMCA if an engine fails right at the moment you’re going around.

 

VMGC like VMCA is variable based on weight, altitude, temperature, thrust, and (unlike VMCA) runway condition.  On the ground the tire friction helps in keeping you straight (although not so much in the sim) so the speed will usually be lower than VMCA.  In the 77L it can be under 100 knots at a hot high airport with a 20 percent thrust reduction.

 

As Xander stated, a thrust derate is a requirement in the 77L at lighter weights for MCA protection.  At sea level on a standard day the minimum weight for a full thrust takeoff is 190.7 KG.

I'll try a derated thrust setting on my next flight and see if it works out better. Thanks guys

Sorry my terminology may have been a bit wrong, you are probably right on that. The point remains the same.

Since it is winter in the Northern Hemisphere and currently -4°C outside where I am, I thought I might mention what a Singapore captain told me after we landed in Manchester. We had hopped over from Munich on the last leg of the trip from Changi to Manchester with a scheduled stopover in Munich. We needed de-icing prior to takeoff and we left the runway in record time...

 

Turns out we were light, low fuel weight and only half the passengers, but a derate or assumed temperature takeoff is prohibited as soon as de-icing fluid has been used... so we rocketed out of Munich on 08L... was impressive to say the least!

 

A

 

 

but a derate or assumed temperature takeoff is prohibited as soon as de-icing fluid has been used

 

I guess it may because of the lift degradation that is induced by the de-icing fluid. I'm reading a very interesting theorical study done in a tunnel called "Effects of Anti-icing Treatment on Lift Degradation during Simulated Take-off".
I don't know whether I'm allowed to post a link here because of copyright and forum rules so in doubt I will refrain from doing it but it can be easely found on google for whose are interested.

Do we have a freeware take off data calculator? I don't have the money to buy TOPCAT after buying the 777.

Do we have a freeware take off data calculator? I don't have the money to buy TOPCAT after buying the 777.

Have alook at TOPER 777 on simmarket.com

I think it's about 12 euros. I find it very good.