Military climbing procedure
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Hey folks,
I stumbled across a question during working on calculating fuel usage for a flight… I found a way to calculate the needed fuel out of a AFM flight model dat file for continous flight.
However, you spend a lot of fuel during climbing to angels 25 or 30, especially with a heavy payload so I need to include this into the calculation.
But… How is it done in real life? Do you climb with…
1. constant pitch (climb angle) with constant mach, but not full MIL
2. constant climb angle with constant CAS, but not full MIL
3. full MIL power and constant mach, climb angle decreasing with altitude
4. full MIL power and constant CAS, climb angle decreasing with altitude?So many possibilities… Thanks for any help
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Hey folks,
I stumbled across a question during working on calculating fuel usage for a flight… I found a way to calculate the needed fuel out of a AFM flight model dat file for continous flight.
However, you spend a lot of fuel during climbing to angels 25 or 30, especially with a heavy payload so I need to include this into the calculation.
But… How is it done in real life? Do you climb with…
1. constant pitch (climb angle) with constant mach, but not full MIL
2. constant climb angle with constant CAS, but not full MIL
3. full MIL power and constant mach, climb angle decreasing with altitude
4. full MIL power and constant CAS, climb angle decreasing with altitude?So many possibilities… Thanks for any help
For training sorties day-to-day, we climb at 350 and set whatever pitch is needed to maintain that.
For a XC it’s whatever you want I suppose, but if gas is tight you’ll reference a climb profile in the checklist. It’s a MIL power climb (they have MAX AB climb profiles too) based on drag index. For a clean Viper with a DI of 0 you’re looking at 445/0.84. A DI of 100 and you’re climbing at 400/0.84.
For a divert the ROTs are 450 for an A/A to config and 400 for A/G. Notice these are similar to the numbers I listed above.
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if gas is tight you’ll reference a climb profile in the checklist
Hey TobiasA, Weapon Delivery Planner will do the “work” for you if you enter the required info. It references the aforementioned checklist and will get you the correct climb profile for any weight and drag.
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MIL climb schedule to optimum altitude or less if cruise segment is < 250nm. It’s all drag index-based with slicker configs being faster. At some point the reference CAS and Mach meet and you switch over to referencing Mach (CAS will be lower than the reference value).
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Thanks for all the replies. Well, the background is that I decided to learn C++ a few weeks ago and tried a few things to see how that works and ended up with a little fuel calculator with a Qt UI.
It reads the FM dat file and calculates the fuel flow, AOA, drag, thrust and all that stuff similar to F4doghouse. But I can’t calculate the climbs yet.It must be possible to read all that stuff from the AFM dat file and calculate the optimum cruise speed, fuel needed for the climb, playtime and such stuff. And also the optimum climb profile since after all it’s just physics described by a bunch of breakpoints and the four forces drag, thrust, lift and weight.
My guess would have been that Frederf’s cheat sheet is based on the optimum drag for each speed so you have for each loadout. Given a loadout with 2 JSOW, 2 600gal tanks, 4 slammer and a jammer you end up with a drag index of 228, stores weight of 10k lbs, fuel 15k lbs.
On sea level it is not.
But on angels 20, my calculations say that the optimum speed for that loadout (least fuel usage for miles) is around Mach 0.67, fuel flow 6100 lbs/h. Which comes pretty close.
On sea level, the optimum speed is around Mach 0.5.
Clean, the optimum drag is around Mach 0.35 if my little program is right, on altitude it is about mach 0.7 to 0.8 again.
So, the most fuel efficient speed can’t be the only criteria one uses to find the right climb speed and angle. Guess there is a rough estimation behind it that is based on simple experience which is then not calculable out of the dat file.Once I figure out how to calculate the right speed, I can build a P/S equation and see how much of my MIL power I have left (can look that up in the thrust table) which is then calculated against the weight of the aircraft which then is a simple sin/cos/tan triangle calculation of forces to find the climb angle.
Then, I build up an array every 1000ft or so, calculate the fuel flow, distance and therefore used fuel for this section of the climb, add all the stuff together and then I would have the duration, fuel burned and distance needed for the climb.At least I hope so.
For the F-16, a Mach 0.8 climb would come close enough I guess…
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For anyone interested: I found out the maths befind it.
Best climb speed is the biggest difference between drag and engine power (Vy that is). So, going along the breakpoints, calculation shows that optimum mach is about 0.6 until about 12-15k altitude and then rises to about 0.8 in most cases which matches that cheat sheet provided by frederf. It is the exact curve- follow CAS until you reach the mach curve, than follow mach.
This will provide Vy by altitude.Maybe some time my little calculator will be finished…
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For anyone interested: I found out the maths befind it.
Best climb speed is the biggest difference between drag and engine power (Vy that is). So, going along the breakpoints, calculation shows that optimum mach is about 0.6 until about 12-15k altitude and then rises to about 0.8 in most cases which matches that cheat sheet provided by frederf. It is the exact curve- follow CAS until you reach the mach curve, than follow mach.
This will provide Vy by altitude.Maybe some time my little calculator will be finished…
There are simple tables to find this info in the F-16 performance manuals and supplements. They are not this low and it is not this complicated. It’s simply based off drag factor if you look at Fox3TwoShips post above.
Here’s a table for optimum on the GE:
| Drag Index | KCAS/MACH |
| 0 | 470/.90 |
| 50 | 435/.90 |
| 100 | 410/.85 |
| 150 | 390/.82 |
| 200 | 365/.82 |
| 300 | 340/.73 |
| 400 | 320/.67 |There are also tables for max afterburner climbs. Blend KCAS and Mach once you get some Angels.
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MIL climb schedule is not a best climb rate as in Vy. The math is much more complex. It is a profile for least fuel for the climb and range. It’s a minimization of fuel to that altitude minus the fuel you would have used from the location where you started the climb cruising at that altitude. The instantaneous optimum is a balance of covering ground and marginal increase in cruise economy per foot climbed. The optimum solution is a profile where it is impossible to reach that range and altitude combination with any more excess fuel.
You’ll find that it’s certainly possible to reach a given altitude faster than the MIL climb schedule but having done so and then cruised to the end of the lateral range of the MIL climb you’ll find the fuel used is more. Even the MAXAB climb uses less fuel to altitude than MIL as surprising as that is. However when you consider reaching the distance the fuel use is more.
Similarly MAXAB climb is a best energy-add rate, peak Ps crossing perpendicular to Es lines. Even this isn’t a strict optimization of climb rate but it’s very close being that the kinematic component is relatively fixed.
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Yes I understand, but climbing at vY isn’t usually done. It’s a mil climb on profile or a standard 350 using power and pitch for speed. So while you may use slightly more fuel, the aircraft is further down range, which is a better trade off. The OP asked for the best way to climb the F-16 on a day to day flight. Fox3 gave the answer and I gave a profile that is what is used on that engine type. You would not climb at Vy for most flights. Just my two cents.
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Seeing as Frederf was not arguing for a climb at Vy… just explaining the maths behind the MIL climb profile.
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Don’t worry, Blu3 I don’t believe anyone’s arguing here, his info was super useful. I think it’s spelled “math” brother
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Just like I (and the rest of the English speaking world) spell standardisation without a “z”.
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Thanks for all the replies and help.
I’m currently thinking about a way how the climb profile can actually be calculated from the FM.dat file given thrust, drag, weight and drag factor. I want to be able to read an FM file and calculate fuel usage, playtime, maximum MIL ceiling, maximum sustained G in MIL and so on to allow for a better planning so that when you know your weight and drag factor, you know how much fuel it will take to complete the flight and see what your joker, bingo and power margin you do have. Which is cool for planning and useful when you create your own TE.
And of course, I want to learn C++ 'cause not being able to code a decent program sucks in times of the internet of things and industry 4.0 or whatever you name it. Yes, there are a couple of nicer languages, but C++ is cross-platform and Qt is important for me for a couple of reasons so I’m going the hard way.
But, after some weeks of pain and fail, there is finally something that works to some degree::woohoo:
Which is pretty cool since I have no experience in no programming language except machine PLC’s or Visual Basic. Currently, I only have the F-16C blk52, but it is an array I can fill with any FM.dat file (at least I hope so, F-16’s should work). So, some time I might be able to chose any F-16 variant and calculate how much fuel you use, what power margin one has available and so on. Even the playtime on a waypoint and waypoint actions like refuel or CAP could maybe be added which would be cool. I’ve been thinking about a save and open option, providing templates and so on…
But since I’m an absolute beginner, I might take years to complete it :rofl:
I’m not holding back the source code- if anyone tells me about that license stuff with using Qt Creator community edition and wants to see the source code, I’m zipping it up, compiling it and there you go.
I just want to be able to make subsequent releases on my own since this is my personal training project. I don’t think it is ready to be released to the public although the basic things work. I’m still learning a lot, but sometimes the whole thing chances a lot, some new classes appear, old ones disappear- you know what I mean if you remember your first steps in programming
Well, lot of things are cool, not all of the cool things are useful. The speed converter Mach-TAS-EAS-CAS-EAS-TAS-Mach which is already in the code would be cool and useful once integrated in the UI.
Learned a lot of physics on the way. Like what is a compressibility error or the difference between TAS, EAS, and CAS.
But that climb thing is giving me a serious headache… For the fuel usage, it does not matter this much. I don’t even calculate descends, no turns, nothing, just plain level flight and the climbs. But originally, I wanted to calculate the profile out of the dat file since it differs depending on weight, drag factor and of course the airplane and engine used to fly it.
Now, I am thinking about making some file in which the table for the “real life climb” is stored. But hey, someone must have calculated it and some jetplane engineer said “if you do is that way, it will be the best way to do it- write it in that manual” and he said that based on math and numbers. My personal guess is that it is simplified by only using the drag factor for easier use + a few % for fuel effectiveness (climb is not so steep- total flight profile is more fuel efficient).
Basically, I now have calculated the best climb rate, but not the most fuel efficient one.Maybe I’ll just create a table for each variant, display that in the UI and calculate all climbs based on that…
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Hi Tobias,
I’d recommend looking into Python / QT which is much more friendly to the beginning programmer than C++… yet I see you’ve some results to show already, good work!
I think the QT licensing is rather lenient when not making money off of the resulting product, but I’d have to check that in detail. QT has been around for ages alongside GTK in the Unix / Linux world, so I’d be quite confused to find out their licensing sucked.
All the best, Uwe
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errrr not 100% sure but ain’t WDP doing this already?
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But don’t tell anybody, thats classified…
Gr Falcas
Don’t worry it will be a secret between me and you… I’ll take it to my grave…
:lol: -
Don’t worry it will be a secret between me and you… I’ll take it to my grave…
:lol:So will do everybody here
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I’d recommend looking into Python / QT which is much more friendly to the beginning programmer than C++… yet I see you’ve some results to show already, good work!
…Thank you very much! I already noticed the C++ is rather hard for a beginner. About 15-20 years ago, I tried to learn C (was about 15 years old or so) but I gave up back then. C++/Qt is used in our machine controls too (cross-platform Linux and Windows), so I decided to go for this option.
A couple of months later, I remember my trouble with C back then and all the advices about Java and Python- and decided to go for one of these next… I think I should have chosen the other way 'round.
However, making strict use of the C++ OOP features finally provides a good way to solve all those things that really limit C in the more modern environment nowadays. Like having a decent UI which is rarely ever seen in pure C applications. I heard that it is pretty easy to provide an UI with Python, but well- decisions are made, the path is set and there we go.
Since I “grew up” with machine controls and coding PLC’s which is pretty much like assembler basically, the whole OOP thing is rather new to me. But I think that good programming is always a way of thinking, not a way of the language you are using. After all, I must say that knowing how to create and keep an OOP structure without getting lost in the code you wrote 2 months ago is actually harder than learning the language itself. But developing some sort of clean code structure and following the OOP approach also holds the biggest potential and saves work afterwards.
Still, I’m pretty sure that if I look into that code two years later I will facepalm myselfYep, WDP has the RL climb profiles for each F-16 block (depending on engine) from there RL manuals.
But don’t tell anybody, thats classified@TobiasA, Keep on going and enjoy coding.
Gr Falcas
Thank you very much! I am using WDP which is an outstanding program. My thought was that it was possible to calculate that best climb profile out of the FM.dat file, knowing that WDP uses the RL manual table made me think different about that approach.
The difficult thing is that the Vy climb is a real profile with various mach numbers and altitude figures you need to follow and the RL table is way easier- hold CAS until Mach matches, then hold Mach.
I think I will include those RL tables for all the F-16 variants in a special file. So, whenever I have a table, the table is used and if not, I assume a Vy climb.
Still, the calculation might come in handy if there is no table provided (thinking about non-viper airframes).My co-worker told me that if you use Qt for an open-source application and do not change the libraries you could even release it as beerware or so. Well, I could just provide the source code for it as a zip file and there we go.
Thank you all for your kind help!
Regards, Tobias
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Instead of maximizing excess thrust for each chunk of altitude, maximize climb rates (ft/min). If you look for best excess thrust, like you did, you’ll get slow, steep climbs that make it to the required altitude using the least amount of fuel, but like Frederf said, it’ll end up costing more fuel by the time you get to the target because of the increased cruise length. If you try to maximize your climb rate and therefore minimize time spent at each altitude, then the answers that pop out are shallower, faster climbs that are a lot closer to the IRL falcon climb schedule. Now, idk if this is the absolute minimum or not, but it certainly results in less fuel being burned by the time you reach the target area (climb and cruise combined).
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