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Guest Chris Smith

Takeoff Thrust Calculator?

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Is PSS going to develop a 757 takeoff thrust calculator?I know the 737 has the TOMAFLEX program and the 747 has TOPCAT. Anyone know if there is a 757 version out?Best,Chris Smith

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There is one. It's the thrust rating computer that is near the gear handle.

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I am sorry, but that is not what I was referring to; I already know where to set my assumed temperature to calculate reduced takeoff thrust. However, I am curious to know if there is a program available that will help me determine what assumed temperature I can use given my aircraft's weight and a the runway length so I can use a setting that reduces the wear and tear on the engine.

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Unlikely, as they didn't with the 777.I plan on doing a few tests at some weights just to get an idea of how much derate I can use - but it won't be an exhaustive test and will therefor not be accurate.It takes a load of time to do as well. What we need is some pilots to post some pages from their own manuals (if they can) for some different runways lengths. Thats how I made my charts for the PMDG 747 - just from posts in the forums.

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Thanks Phil. I have done a bunch of tests too. However, there are so many variables involved.

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British Airways use 60'c with a climb 2 de-rate as standard (varies very slighty if conditions require), if thats any help to you.Cheers

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If someone decides to do himself a useful take thrust calculator, I could provide him with some very useful information.BRGDS,Javi

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Sorry Chris. I misunderstood you. Finding the assumed temp on any jet involves a lot of variables such as gross weight, temp, pressure altitude, runway length, climb gradient, flap setting, runway condition (wet/dry/icy), slope, etc. There are a lot of performance charts involved, but most airlines have an airfield analysis in which they have standard assumed temps they use. Unfortunately, the guys I fly for require me to calculate the assumed temp manually LOL. I wasn't aware of any program that will crunch the numbers for you, but it will sure be a great one to have.-Dwayne

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Thanks Dwayne. Do you know how real pilots or dispatchers crunch the numbers to get the assumed temparture? This would make takeoff much more realistic.

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In the real world we have airfield and runway specific charts detailing the available weights against temperatures. We first take the current temperature and work out from the chart what the MAXIMUM load we can lift is be that performance limited or structurally limited. We then find out our actual intended take off weight as supplied on the load sheet. From this we can enter the chart and find the temperature which allows us to lift that weight. This temperature is the one we use to set the assumed temperature. The entry for the weight in the table also gives us the QNH correction and V1/r/2 speeds for that weightSo for exampleToday at Malaga in Spain the runway in use was 13 with the following weather:160/6 CAVOK +27 / +20 1020We look up in the chart the weight corresponding to the given temperature in calm wind as we don't take credit for headwind unless we REALLY need the performance although we always take any penalties for tailwinds! +27C - 119540 (76) Which tells me I can lift 119540Kgs and must correct +/- 76kgs per millibar above or below standard so in this case I could (but I don't as I don't NEED the performance) add 76x7 = 532kgs to the given max weightSo all told I know I can lift 119540kgs (or 120072kgs if I add the pressure correction). However we limit our 757-200's to a max take off weight of 107999kgs for airways charges so my max is my MTOW of 107999kgs! Now we get the loadsheet and find our actual take off weight is 95000kgs. I go back to the performance and look up 95000kgs in the weights for a calm wind and find the following:+54 - 93554+52 - 94669+50 - 95123+48 - 96211EtcI know I have to lift 95000kgs so I cannot use +54 or +52 degrees as they both lift less than I have to lift. +50 allows me to lift 123kgs more than my actual load so I can use this derate! The box with the weight also gives me the speeds so it actually looks like this :+50C 95123 (76) 140 - 142 - 144 so my V1 is 140, Vr 142 and V2 144 (which you put in the MCP speed window). Hope that helps. I'll try to find a page or two of our performance in electronic format to do a better example! Kris

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Kris, really helps a lot.. I made a better translation for my own understanding. Also, I have imbedded a couple questions I still have. Thanks again for all your help!Today at Malaga in Spain the runway in use was 13 with the following weather:160/6 CAVOK +27 / +20 1020First, we look up in the chart the weight corresponding to the given temperature in calm wind (We don't include headwind unless we really need the performance. Further, if tailwinds are present, we need to calculate penalties.).+27C - 119540 (76)As you can see, the temparture is 27 celcius and the given weight for the tempature is 119540kgs. If the QNH (or Altimeter) is above or below the standard setting 1013 QNH (Altimeter 2992), you must add/subtract 76kgs per millibar. The QNH in the metar is reported as 1020, which is 7 milibars above (greater: +) the standard altimter setting of 1013. So we need to multiply 7 by 76 and add that to our weight of 119540. So, the max weight we can depart with is 120,072 kgs.(However we limit our 757-200's to a max take off weight of 107999kgs for airways charges so my max is my MTOW of 107999kgs!)I don't understand this, please clarify. What are airway charges? Also, when do we take into account runway length and flap setting? Is that the "27C - 119540 (76)" figure you produced earlier? So is the max takeoff weight for runway 13 119540kgs, or 120,072 after taking into consideration the pressure?Now we get the loadsheet and find our actual take off weight is 95000kgs. I go back to my performance charts and look up 95000kgs in the weights for a calm wind and find the following:+54 - 93554+52 - 94669+50 - 95123+48 - 96211EtcI know I have to lift 95000kgs so I cannot use +54 or +52 degrees as they both lift less than I have to lift. +50 allows me to lift 123kgs more than my actual load so I can use this derat.The box with the weight also gives me the speeds so it actually looks like this :+50C 95123 (76) 140 - 142 - 144 so my V1 is 140, Vr 142 and V2 144 (which you put in the MCP speed window). But what is the flap setting? Wouldn't a derate temperature, or assumed temperature) be based on flap setting?Thanks for what you have given us so far Kris, any further assistance appreciated!Best,Chris Smith

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I could get some airport analysis to know the specific speeds for some weather-airport conditions.

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