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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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I don't understand this, please clarify. What are airway charges? When a company flies IFR in Europe we are charged for using the nav aids and ATC services that we pass through rather like tolls on a motorway. A typical flight from the UK to Spain can cost in excess of

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I'll have to see what I can get my paws on but I can't see it being a problem, just give me a little time! Kris

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So Kris -Since this is flightsimulator, we really dont need to concern ourselves with calculating the weight for Airway Charges. Is this correct?Essentially, with calculating the assumed temparture, all we need are the charts and our takeoff weight?Best,Chris SmithCompuer Specs:Dell Dimension 83000Processor: Intel® Pentium® 4 CPU 2.80GHz Processor Speed: 2.73 GHz Memory (RAM): 1024 MB Graphics: ATI RADEON 9800 XT (512MB)

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ChrisNo you don't but I was asked why I did it in my real world calcs so I shared why and what purpose it served. In reality there are many things we must take into consideration my post covers just a few! In sim land look up the structural limit weight probably 113200kgs and use that as your limit weightKris

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Also..Kris, you said: We now get our load sheet and see our actual TOM is 95000kgs so we know we are not exceeding our maximum! but how much can we derate the engines? Now here's where we have to make another correction. Because we have a negative factor working against us we must also use this against our actual TOM. so we add the QNH correction to the actual TOM (yes ADD). This effectively is saying we are 920kgs heavier than we actually are. ie we add 920 to the 95,000kgs giving us an assumed TOM of 95,920kgs: 95000 + 920 = assumed TOM 95920kgsMy question:If the QNH is greater than standard, would we subtract instead of add?Also, I would be intersted in knowing the settings for airports with other runway lengths. As the runway 10 is only 6500 feet in your example, im sure there is a difference when the runway is much longer than that. Also, doesn't the actual airport temperature come somewhere in this equation?And my newbie question of the day, what is TORA, TODA and ASDA.. I assume TODA is takeoff distance.Chris SmithCompuer Specs:Dell Dimension 83000Processor: Intel® Pentium® 4 CPU 2.80GHz Processor Speed: 2.73 GHz Memory (RAM): 1024 MB Graphics: ATI RADEON 9800 XT (512MB)

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>And my newbie question of the day, what is TORA, TODA and>ASDA.. I assume TODA is takeoff distance.TORA - take-off run availableTODA - take-off distance availableASDA - accelerate stop distance available

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On the other side of the coin some airlines, like United, just allow dispatch to figure it and the pilots get it either in the Planned Takeoff Data Message or from ACARS. United's 757/767-200 and -300 flight manual I have, dad flew both for a time, has all the speed charts and other performance stuff, but not runway lenegth vs temp charts as Kris's company does, would be interested in having general charts simular to the charts the well known 767 developers made.

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ChrisIf the QNH is greater than standard, would we subtract instead of add?When considering the weight for any assumed temp we only ever add and NEVER take credit. Penalties include Engine Anti-ice on for T/O, low QNH or MEL items that require performance penalties. Also, I would be intersted in knowing the settings for airports with other runway lengths. As the runway 10 is only 6500 feet in your example, im sure there is a difference when the runway is much longer than that. I am working on that, I cannot get any e-data but I have some photocopies which I will take pics of and post ASAP with some examples for you guys to play with! Also, doesn't the actual airport temperature come somewhere in this equation?This is taken care of when we are looking for the maximum weight we can lift. We look up the actual temp and read off the datum weight and QNH correction. Once we've adjusted for the QNH and any other penalties or credits we get the Regulated TOM for the curent weather conditions including pressure, temp and wind! I think the ASDA, TORA etc query has been answered already.Bear with me and I'll try to make a real world example available ASAPKris

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