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triple777

takeoff advice

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Hey guys I just have a question can you take off in the same way as x plane in prepar 3D Or do you have to go full speed all the way because like in the Airbus a 320 or 737 series Do I have to put up to full speed Or you could just put it to half speed like in x plane If anyone could help me figure this out That would be great thank you from triple 777

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Do you mean de-rated takeoff / flex temperature?


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Concerning basic operation there's no difference between x-plane, P3D, FSX etc.  Don't know what you meant with 'half speed' but you don't take off with 50% throttle in any sim. 

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There are a few reasons why you might not use full throttle for a take-off, but you need to understand what these reasons are if you want to make use of that technique. So here's all about it...

It was Laker Airways which pioneered the technique, on its BAC 1-11 airliners in the late 1960s, and they initially did that to save money rather than in an attempt to make their take offs more efficient (which was an added side benefit), since using reduced thrust for the take off puts less wear and tear on the engines, prolonging the engine's life and increasing the amount of time between overhauls for their engines. They also encouraged their pilots to also climb quickly to their assigned cruise altitude (even if that meant using higher thrust settings for their climb) because even though the thrust is high during the climb phase of a flight, if you climb quickly, you reduce the amount of time your engines are running at high RPM, so it doesn't wear them out as quickly. Rolls Royce reported that Laker's Spey engines on its BAC 1-11 fleet were among the best maintained engines they had ever seen, and so the techniques which Laker used to keep their engines in good condition in order to save money, began to be widely copied by other airlines and it is nowadays done by almost every airline. But not for the sole reason of saving money, it also makes your take offs a lot safer and quicker too.

So, what makes a reduced thrust take off better for actually taking off? As you may  know, when you take off, there are several critical moments in the take off roll before you get airborne. The first is when you reach 80 knots and both pilots look at their airspeed indicators and agree that they are both displaying the same speed (this is called the cross check and is important because it shows that your instruments on both sides of the cockpit are in agreement). The next critical speed you reach, is V1, this is the speed at which if you are going to abandon the take off because of a problem (such as the cross check not matching on both instruments), at the point where you reach V1 speed on the runway, that is the latest you should try aborting the take off because of the amount of remaining runway you have in front of you will still be enough to allow you to safely stop. If you decide that are continuing the take off when you reach V1 because you have no problems with your aeroplane, the next critical speeds you reach are V2min (the minimum safe take off speed) and Vr (the speed at which you begin bringing the nose up by easing the stick back at a rate of about 1 or 2 degrees per second until you get to about 10 or 12 degrees nose up, so that the aeroplane will take off. These last two critical speeds (V2 and Vr) often come quite close to one another.

So, how are these important speeds calculated? Years ago the crew would have had to consult paper charts to figure all that out, but in a modern airliner with a flight management computer (FMC), the pilots input a lot of data into various fields and pages on the FMC and it calculates these speeds for you. This includes telling the flight computer things such as payload weight, fuel weight, air temperature, runway condition, runway length, runway slope, wind speed etc. With all this information entered into the FMC, it can calculate the important take off speeds of V1, V2 and Vr, and if you want to use a reduced thrust take off, it can advise you about that too. But a reduced thrust take off is not simply about saving money, it can also mean that you reach those V speeds quicker than if you simply pushed the throttles all the way forward. But how can that be? Surely using full throttle would make you accelerate faster wouldn't it? Well surprisingly, the answer is no, it won't, and here's why...

Two of the really important things you enter into the FMC, are the air temperature, and the airfield's ICAO identity (such as KJFK for Kennedy International), which will confirm the airfield's height above sea level. From this, the FMC can calculate how dense the air is along the runway, and with jet engines, it needs to know the air density in order to calculate the most efficient throttle setting. This is because if, for example, the air temperature is very high, the air will not be very dense, so if you advance the throttles all the way forward to maximum, you will actually be putting too much fuel into the engine for it to be able to handle because it won't be able to suck in enough air to get an efficient mix of fuel and air to create the best amount of thrust. Similarly, if the air is very cold, the engine might suck in too much air and not be able to pump enough fuel into the engine to match the large amount of air going into the engine. You car does that too by the way, you might have noticed it runs a bit faster in cold weather for example - a lot of motorbikes do.

So, the answer here is to carefully put all the correct information into your FMC and then let the aeroplane's systems determine the ideal thrust setting. To do that, having put all the correct information in, you line up on the runway, turn on the autothrottle and engage the TOGA (Take Off, Go Around) button. When you do that, the FMC links to the autopilot's autothrottle and puts the throttles up to the most efficient high thrust settings it can for the current conditions, which might be perhaps something such as 87 percent of full throttle or something like that, depending upon the weather and your info that you put into the FMC.

In the days before FMCs were available, or if your airliner does not have an autothrottle or an FMC, you would consult paper charts in the aircraft's manual and find out what the best EPR (engine pressure ratio) setting is for the current conditions and then adjust the throttles as you begin your take off roll until your EPR gauge is reading that setting. Engine Pressure Ratio sounds complicated, but it is simply a measure of the difference in pressure between the front of the engine where the air is going in, and the back of the engine where the exhaust is being forced out. Some modern aeroplanes use a FADEC (Full Authority Digital Engine Control) system to help with this stuff as well, and that is a bit like an ECU on a fancy modern car.

As you can tell from all that, it seems like a complicated subject, and it kind of is, but on an Airbus or a Boeing with an FMC, all the hard work and calculations are done for you so long as you put the correct bits of information on the Index pages of the FMC. This is why it is important to listen to the ATIS (Air Traffic Information System) announcement on your radio when at the airport, as it will tell you a lot of that stuff you need to know so you can enter it into the FMC.

Hope that helps you understand it all a bit better. It's really not as complicated as it appears at first and it's kind of interesting to learn about all that stuff if you like aeroplanes.

Edited by Chock
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Alan Bradbury

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Edited by FDEdev

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54 minutes ago, Chock said:

Hope that helps you understand it all a bit better. It's really not as complicated as it appears at first and it's kind of interesting to learn about all that stuff if you like aeroplanes.

Chock I love reading your posts over the years.. I feel like a kid sitting at grandpa's feet ,wide eyed listen to a good story. You can make just about any subject interesting. Do you read a lot?


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5 hours ago, reecemj said:

Do you read a lot?

Yup, and I seem to be able to remember most of it lol

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Alan Bradbury

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This is a situation where Concorde is so much simpler than these fancy glass cockpit aircraft. No derated takeoffs and no flap settings. For every flight the throttles were slammed fully forward with reheats engaged. Vr varied according to weight and to a lesser extent, air temperature.

Slowest rotation speed was 139kts and fastest 190kts. Just a pity you can’t buy it from FS Labs until / unless they build a 64-bit version. 3-2-1-now! 😁

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Ray (Cheshire, England).
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19 hours ago, triple777 said:

Hey guys I just have a question can you take off in the same way as x plane in prepar 3D Or do you have to go full speed all the way because like in the Airbus a 320 or 737 series Do I have to put up to full speed Or you could just put it to half speed like in x plane If anyone could help me figure this out That would be great thank you from triple 777

This is not sim dependent. It depends on the addon plane in the sim (if the systems are coded to simulate limited thrust). But even if they are not you can do it manually (on paper) if you own right performence specification charts and now the calculation techniques for given plane. For example for Dc-10-30 and A33x-A34x series i always do it on paper. And in real world even in aircrafts with such FMC capability crews were often obliged or prefered to make manual calculations themselfs.

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Interestingly, on the subject of 'reading a lot' and engine thrust settings for take off, I think the only really major criticism I had of the Captain Sim FSX Boeing 707 and 727 simulations, which I reviewed for Avsim ages ago, was that the replication of the JT8D and JT3D/4A engines on them, didn't really have a good stab at simulating varying the EPR, and so if you studied and used the PDF of charts which came with the thing and set the correct thrust based on the EPR on the gauges, it didn't really work very well. To check that, I went to the trouble of finding genuine manuals for the aircraft and buying them, and also bought a couple of training books on those aircraft in order to be as clued up about them as possible and tested it out very thoroughly.

From all that reading a study of the real things, I was able to confirm that the engine simulation on those Captain Sim classic airliners with their low bypass ratio turbojets, was not as detailed as it could have been, although in the case of their 727, part of that was really because they made the decision to  'fluff it' a bit by using only one engine simulation thrust rating for several different 727 variants, when in reality those different 727 models had very differently-rated engines from one another.

Ironically, with the better simulation of air mass which is allegedly on the way in the new MS flight simulator, I'm kind of hoping that eventually someone will get around to making a Boeing 707, 727, Douglas DC-8 or even a Convair 990 for that sim which has a genuinely good stab at simulating the management of the engines with the EPR settings, so one day those rather pricey 727 and 707 manuals I bought might come in handy and we'll be able to actually use those paper charts realistically to calculate take off settings.

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Alan Bradbury

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22 hours ago, Ray Proudfoot said:

This is a situation where Concorde is so much simpler than these fancy glass cockpit aircraft....For every flight the throttles were slammed fully forward with reheats engaged. ....

Sadly I was never able to fly on Concorde, but I would have loved to experience her acceleration once the reheat kicked in. I believe the reheat was a simple on-off affair being activated by 4 "piano keys", one behind each of the throttles, operated by the Flight Engineer (no two crew cockpit for that beauty!). I believe standard operation was to flick two switches (engines 1 and 4 , or 2 and 3 I'm not sure), then follow up with the remaining two, for passenger comfort. However, I wonder how vicious the kick in the pants would be if all 4 were engaged simultaneously?! :cool::biggrin: Yes, I'm still a hooligan...

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Mark Robinson

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@HighBypass, sadly me neither. Just didn’t have the 500GBP for the cheapest subsonic flight around the Bay of Biscay.

You’re correct in how the reheats were engaged at FL280 / Mach 0.95. Done for passenger comfort as there was quite a kick when they were engaged. But the greatest effect would have been at takeoff when all four engaged within a couple of seconds.

I had the next best experience. Stood in the Airport pub garden at Manchester back in July 2000 when a BA Concorde visited. I was around 150 yards from the engines when full takeoff power was applied. No exaggeration to say my chest cavity vibrated with the power. Absolutely awesome. 😎

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Ray (Cheshire, England).
System: P3D v5.2 & v3.4, Intel i7-8086K o/c to 4.6Ghz, Nvidia GTX 1080 Ti 11Gb, Samsung 970 EVO M.2 SSD, 1Tb Samsung 860 EVO SSD, Asus Prime Z370-A mobo, 32Gb G.Skill DDR4 3000Mhz RAM, Win 10 Pro 64-bit, BenQ PD3200U 32” monitor, Fulcrum One yoke.
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11 hours ago, Ray Proudfoot said:

@HighBypass, sadly me neither. Just didn’t have the 500GBP for the cheapest subsonic flight around the Bay of Biscay.

You’re correct in how the reheats were engaged at FL280 / Mach 0.95. Done for passenger comfort as there was quite a kick when they were engaged. But the greatest effect would have been at takeoff when all four engaged within a couple of seconds.

I had the next best experience. Stood in the Airport pub garden at Manchester back in July 2000 when a BA Concorde visited. I was around 150 yards from the engines when full takeoff power was applied. No exaggeration to say my chest cavity vibrated with the power. Absolutely awesome. 😎

I remember that "chest vibration" effect when I was a kid at the 1978 Farnborough Air Show. Concorde made a touch and go on that day, and the sound was body shattering!

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Christopher Low

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