Reduced thrust takeoff

[forthbridge]

HI All,

Reading up on Laker Airways earlier, I was amazed to read that they used 'reduced power' for taking off - resulting in their engines being in superb condition when going for maintenance. This was obviously a fuel saving measure, but I can't find any more info on how this was actually put into practice.
Did they always takeoff at less than MTOW?
What thrust settings did they use?

Anyone have any ideas? Just a nice 'correct' piece of flying to try in the DM1-11!!!

[Garry Russell]

They also reduced the pax capacity and had different techiniques in the climb

This enabled Laker to use aircraft direct when the competition had to make fuel stops.

They used similar methods to operate transatlantic flights with DC 10-10 aircraft

Garry

[Chris Trott]

Well, it appears my original reply was lost in the netherregions of the internet, so I'll try it again.

Almost all jet-powered aircraft have reduced thrust takeoff settings available to use and today, it's a standard practice within the airline industry to use reduced thrust whenever possible on takeoff. However, the purpose is not fuel savings, it is wear savings. What fuel you do save is largely offset by the longer takeoff period, but you greatly reduce the wear on the engine during that period so when the airplane is in for maintenance you have to do less to keep the engines running well and thus you save costs on the most expensive part of the airplane.

Airplanes with reduced thrust takeoff settings have two methods of determining the proper setting charts or FMC. FMC only works with planes which are equipped with FADEC (Full Authority Digital Engine Controls), so none of Laker's aircraft did this. All of their reduced thrust settings were determined by charts. What you simply do is take your actual outside air temperature, add a given amount (say 15*C) and read your chart as if it is that temperature. That gives you the reduced settings to use for that situation. This is the old way. Newer aircraft (after about 1970) have reduced thrust takeoff charts that are used and since about 1980, airlines have been using a thing called ATOGS that looks at the runway, the weather, and your airplane's performance and determines if and what thrust reduction is available and how heavy you can take off in those conditions from that runway.

I have not seen a free 1-11 manual that includes all of the engine charts, but if you look at Matt Zagoren's DC-10 manual availabele at AVSIM and Flightsim.com, it does include all of the charts used to determine your takeoff thrust and derated thrust settings.

[cstorey]

This is now almost universal. There are a number of ways of achieving it, but the most common one is to use a performance setting for the engines appropriate to a higher than ambient temperature. Thus the engine epr/%N1 settings are calculated from a table using ambient + perhaps 10 or 15 degrees C up to a maximum of say 36 C. This results in lower epr/n1

Unfortunately, without the tables there is no reliable way it can be simulated. If you want to try,one way you could do it is see what JPT/ITT readings (whichever is shown on the instruments) are at full power, and then knock 25 or 50 degrees C off this and restrict your power to that lower setting

Incidentally, the Speys in the 1-11 had a 5 minute limitation which allowed higher than normal jet pipe temperature to be sustained to cater for hot and high/max gross weight operations. I do not know whether this also applied to the Trident

Chris

[DaveB]

Jim..

Have a look at the thread started by Brendan asking for EPR/Thrust index info We don't have the Flight Performance Manual for the 1-11 but it used two methods of takeoff.. 510 and 511. 510 uses a rolling start and 105%N1/99.5%N2.. 511 is from a stopped start and is 106.6%N1/100.1%N2. Needless to say, a rolling start was the prefered method.

Chris's reply is bang-on.. it is used to reduce engine wear ;-)

ATB

DaveB :tab:

[forthbridge]

Thanks a lot Guys - as usual very informative! How long before I report falling out the sky on takeoff.....? ;-)

[Motormouse]

Just a little addendum, the 'wear' is damage to the engine 'hot section'
which is reduced, and therefore the time between hot section inspections and engine tear-down can be increased,
and this saves money.

ttfn

Pete

[MALTBY D]

If you use 100% on the thrust index gauges during takeoff, you'll nearly always be doing a reduced thrust takeoff.
97% I think is the minimum takeoff thrust - it can usually do way more than 100% if required.

I can't remember if it was set for 510 (proper reduced) or 511 rating though (it was a long time back). Probably 511. ?
We did have the charts for the Trident & I assumed a reasonable estimate of the pod engine figures to be good enough for all Trident & 1-11 engines in FS.

It works the index number out depending on pressure & temperature. Click the top of any one of the thrust index gauges to make it set the correct number.
Attain 100% thrust within six seconds or so & off you go.

DM

[forthbridge]

Cheers David, working an absolute treat

[Techy111]

I read somewhere that Sir Freddie Laker and his bods at Laker Skytrain were the pioneers of this for commercial aircraft is this right ?

Techy