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  • Robbiesmurf
    Rank 5 Registered User
    • Jul 2014
    • 587

    #61
    You throw an awful lot of figures around Andraxxus, do you actually understand them?

    Comment

    • Andraxxus
      Rank 5 Registered User
      • Sep 2012
      • 954

      #62
      Yes. Now question is do YOU?

      If you are questioning my credantials, I am mechanical engineer, I have Turbomachinary design as working area, and I have a (not yet incomplete) thesis half involves Advanced Aerodynamics. In my posts, what I wrote is mostly high school physics, and usage single lift/drag formula. I doesn't require an engineering degree to understand it (or at least I was hoping as such).

      If you are questioning my interpretions, I necessarily make assumptions (how in gods name I am supposed to know L/D curvature of F-22 anyway) so they are subjective. In any case, I try my best to leave a room for interpretions other than mine so people who DO understand them can disagree with me.

      If you are questioning understanbility of my methods, I don't explain 90% of WHYs, or I simply skip the steps which are irrelevant to make comparisons, and just give the conclusions unless someone asks. I do so to keep my already boring and long post more readable.

      For example If I were to make my "ferry" comparison in the long version:

      An aircraft requires lift to maintain any kind of flight, and generates drag; so we have two equations:

      Equation 1: (Lift in Newtons) = (weight in kg) * (Aircraft G) * g = 0,5 * (air density at ferry altitude) * (required Cl) * (Wing Area in m^2) * (ferry speed)^2

      If you divide both sides by Wing area, you will get an equation lets call it 1A: (wing loading kg/m^2) (Aircraft G) * g = 0,5 * (air density at ferry altitude) * (required Cl) * (ferry speed)^2

      Equation 2: (Drag in Newtons) = 0,5 * (air density at ferry altitude) * (Cd at required Cl) * (Wing Area) * (ferry speed)^2

      Now lets divide eqn 2 by eqn 1A;
      (Drag in Newtons) = 0,5 * (air density at ferry altitude) * (reqiured Cd) * (Wing Area) * (ferry speed)^2
      (wing loading kg/m^2) * (Aircraft G) * G = 0,5 * (air density at ferry altitude) * (required Cl) * (ferry speed)^2

      As you can see constant "0,5" and variables "air density" and "ferry speed" cancel each other, and Cl/Cd is the aircraft Lift to Drag ratio at ferry AOA.

      Equation 3: Drag = (Wingloading) * (Aircraft G load) * (Gravitational acceleration) * (Lift-Drag Ratio)^-1 * Wing Area

      Now I strongly stress that this equation is *irrelevant* of aircraft type, and what aircraft is doing. (L/D) is a variable changes with AOA (or aircraft design, if we are talking about different aircraft) , and G load changes with requested maneuverability. Since we are talking about "ferry" G load is "1G", so I am excluding it from this point on.

      As aircraft is at constant airspeed (its not accelerating or decelerating), Thrust=Drag.

      Now we can talk about 2nd part; fuel consumption:

      (Ferry Range in km) = (ferry speed in km/h) * (Fuel quantity in kg) / (Specific fuel consumption in kg/kN-h) * 1000 / Thrust.

      Now instead of "Thrust" I wrote the right hand side of "Drag" equation (#3), and eliminated all the constants, to determine what Ferry range is proportional to.

      (Ferry Range of F-22) ~ (ferry speed of F-22) * (F-22's internal fuel quantity) * (ferry L/D of F-22) / (SFC of F-22) / (Wingloading of F-22) / (Wing Area of F-22)
      (Ferry range of F-15) ~ (ferry speed of F-15) * (F-15's internal fuel quantity) * (ferry L/D of F-15) / (SFC of F-15) / (Wingloading of F-15) / (Wing Area of F-15)

      Fill these and you will get exact, 100.00% accurate data for comparing them. Note in real life, ferry speed, wing loading SFC L/D are variable so they are in differential form. However with available graphs they can be best represented by "d/dx" and iterated by computer.

      In all the simplicity, I make following assumptions:

      1- I assume ferry speed of F-15 and F-22 are the same. This is not a far fetched assumption, as all 2nd/3rd/4th gen I have data have ferry speed around M0,85. Because: As airspeed increase, necessary AOA to maintain level flight drops, so L/D improves, aircraft gets more efficient with speed increase. However after around M0,85 transonic wavedrag starts to add to basic aerodynamic drag and L/D drops sharply. Now F-22 may cruise a tad faster because its aerodynamics are so called "supersonic optimized" but 5,92% wing thickness compared to 3% of F-15 tells me F-22 may possibly cruise a tad SLOWER than F-15. This can easily go both ways, so IMHO "same" is a good enough assumption.
      2- I assumed ferry SFC of F-15 and F-22 are same. They may or may not. F-22 is newer, designed with better level understanding of fluid dynamics and can be more efficient, but S-ducts and square nozzles are big sources to generate inefficiency. This can also go both ways.
      3- I assumed F-15 and F-22 have same wing loading. Note that it doesnt: From full to empty, F-15E's wingloading change from 364 to 254. F-22's change from 358 to 252. This assumption slightly favours F-22 by 1%.
      4- Now I assumed L/D of F-22 and F-15 are same when in level flight. This is the most questionable assumption made by mere guessing. F-15 has much thinner wing airfoil, has no VLO considerations like internal bay, parallelism or flat surfaces, but F-22 has negative stability and is much newer in design.

      So (Ferry range ratio between F-22 and F-15) = (speed)*(8200/6380)*(L-D)/(SFC)/(Wingloading)/(78,04/56,5)

      So this would assume F-22 will have 93% range of F-22. If you like to; you can use Aircraft weights instead of (Wingloading * Wing area). I've used Wing Area because thats what I've used in my previous post. Reasoning: On similar airfoils, similar wingloading translates to similar L/D.

      Getting back to assumptions, if people thinks F-22's L/D ratio is better, then F-22 would need 7,4% better cruise L/D ratio only to match F-15's internal fuel range.

      @Robbiesmurf: Now instead of posting this wall of text, I write two sentences without going into such details to say the same thing. Was it not better?

      Comment

      • Robbiesmurf
        Rank 5 Registered User
        • Jul 2014
        • 587

        #63
        My working area was also what you call turbo machinery, Known in the RAF as A Tech P.
        My specialists were: BAC Lightning, HS Buccaneer, Hawker Hunter, Sepecat Jaguar and HP Victor. After that it was Boeing 707,737 & 747 plus Douglas DC8,9 &10. If I were to add all the stuff I serviced casually (visiting a/c) I could probably add another 20 types or so.
        Yes I have a good understanding of how a/c work.
        Seeing as you are a turbine man, how does reheat increase the thrust? I don't need the figures, just the basic working.
        Last edited by Robbiesmurf; 27th September 2015, 17:56. Reason: missed word

        Comment

        • mig-31bm
          Rank 5 Registered User
          • Oct 2013
          • 2140

          #64
          Originally posted by Robbiesmurf View Post
          My working area was also what you turbo machinery, Known in the RAF as A Tech P.
          My specialists were: BAC Lightning, HS Buccaneer, Hawker Hunter, Sepecat Jaguar and HP Victor. After that it was Boeing 707,737 & 747 plus Douglas DC8,9 &10. If I were to add all the stuff I serviced casually (visiting a/c) I could probably add another 20 types or so.
          Yes I have a good understanding of how a/c work.
          Seeing as you are a turbine man, how does reheat increase the thrust? I don't need the figures, just the basic working.
          Robbie, if there is some parts you disgree with Andraxxus, just point it out and explain why you disgree, that would save time and alot better than asking everyone about afterburner

          Comment

          • BarnesW
            Senior Member
            • Aug 2015
            • 503

            #65
            Originally posted by Andraxxus View Post
            Getting back to assumptions, if people thinks F-22's L/D ratio is better, then F-22 would need 7,4% better cruise L/D ratio only to match F-15's internal fuel range.
            In operations L/D would be much better because it carries no pylons or external armaments. Ferry range is unimportant because IFR is available. You're also neglecting the affect of TVC on trim drag (~5-7%). And you should note that the petal-free nozzles on the F-15 add 3% to its drag. And the internal capacity of the F-22 is 18,448lbs, which is ~8,400kg (page 10-7 http://www.academia.edu/9336427/F-35...stems_Overview).

            Last edited by BarnesW; 27th September 2015, 12:06.

            Comment

            • Robbiesmurf
              Rank 5 Registered User
              • Jul 2014
              • 587

              #66
              Originally posted by mig-31bm View Post
              Robbie, if there is some parts you disgree with Andraxxus, just point it out and explain why you disgree, that would save time and alot better than asking everyone about afterburner
              I pointed out that there were a lot of figures that can be used to impress others.
              There is a difference between knowing and understanding. I merely asked him and he answered by throwing more figures at me. Nice, if you can't dazzle them with diamonds....
              You're right I have asked a couple of you about reheat and the answers you give appear to come from a Wiki explanation. It's incorrect btw.
              If you take the trouble to read the RR book about the jet engine it explains it very simply and well. The difference between knowing and understanding..
              Seeing as figures seem to impress most of you, a simple question.
              An example jet engine at full rpm has a jet pipe temperature of 1000 degrees Kelvin. The reheat is engaged to full and the jet pipe has a temperature of 1690 degrees Kelvin. What is the thrust increase?
              It's a simple calculation.

              Comment

              • Andraxxus
                Rank 5 Registered User
                • Sep 2012
                • 954

                #67
                That depends. F-15's nozzles are not the most efficient solution (from drag POV), but F-22's nozzles aren't either (from thrust conversion efficiency POV, which increase SFC). As for trim drag, its usage would be in supersonic, not in ferry/cruise speeds.

                I was referring to airforce factsheet as most reliable.
                http://www.af.mil/AboutUs/FactSheets...22-raptor.aspx

                As for "in operations" part, i believe situation gets worse for F-22;

                -All current F-15C/D can be equipped with CFT. All current F-15E already fly with CFT. Too lazy to look at F-15C's specs, but F-15E has 10845 kg fuel capacity with CFT.
                -3x610gal fuel tanks add 5600kg additional fuel, an can be carried (and if needed dropped) in any operational situation.

                For F-22 to have its VLO, it cannot carry EFT. Ferry range is unimportant, but "optimized cruise" is most important factor in combat radius, which is not any different than ferrying. To increase combat radius, IFR may or may not work depending on opposition force. If you equip F-22 with EFT, you are taking away the only decisive advantage of it againist 4+ gen aircraft. This is really problematic if extra range comes with severe survivability cost.
                And remember; F-15E with 3xEFT+CFT will have 16448 kg fuel capacity, F-22's fuel capacity with EFTs is still far less than its predecessor.

                This problem is seen and well adressed in another design:

                F-35 wing area 42,7 m2 F-16 wing area 27,87 m2 = 53% increase.
                F-35 fuel capacity 8390kg F-16 fuel capacity with 2x370gal 5449 = kg = 53% increase.

                I would not think such similar increase is a coincidence, F-35 is designed to carry the fuel to match/exceed range of F-16 with its wing fuel tanks;

                Plus: F-35 fuel capacity 8390kg F-16 fuel capacity with 3xEFT 6370 kg = 31% increase.

                Now, for A-G mission, if you consider extra drag from 3xEFT, external payload, lantirn pods, extra drag from having stores in 3,7 combined with EFTs in 4,6, and with such added weight increasing induced drag on small wings of F-16, F-35 may even match F-16's loaded range only with its internal fuel, and maintain stealthy in the process.

                You can't say similar things about F-22. And in my subjective opinion, lack of internal fuel capacity is only Achilles' heel of F-22.

                Comment

                • BarnesW
                  Senior Member
                  • Aug 2015
                  • 503

                  #68
                  TVC affects fuel economy at all speeds. As for nozzle efficiency, there is no evidence of that. The af mil site also says the B-1B can do Mach 1.2 at sea level. If you ask me, 18,000lbs sounds like a rounded figure and 18,448lbs sounds like an accurate figure.

                  When considering operational deployment you have the false conception of flying a first day mission deep into a peer adversary's territory with fuel bags. Never going to happen unless you enjoy heavy losses, the progress will be far slower and shorter in radius that that. Deeper targets will be hit with cruise missiles but the focus from an aircraft PoV will be SEADing back their IADS and knocking planes out of the air. After that, you either have the choice of using that region for IFR, or mounting a ground offensive in that region and capturing airbases.

                  Add internal fuel and you increase the size and weight of the aircraft, increasing drag and reducing performance. As an air superiority fighter, the aim was to remain lethal in air combat, rather than extend range.

                  Comment

                  • haavarla
                    Rank 5 Registered User
                    • Dec 2008
                    • 6693

                    #69
                    The internal fuel on F-22 is not terrible bad.
                    But those F119 do gobble a lot of fuel, especial on Full AB

                    In what way does TVC affekt fuel consumption?
                    Last edited by haavarla; 27th September 2015, 13:56.
                    Thanks

                    Comment

                    • Andraxxus
                      Rank 5 Registered User
                      • Sep 2012
                      • 954

                      #70
                      Originally posted by BarnesW View Post
                      If you ask me, 18,000lbs sounds like a rounded figure and 18,448lbs sounds like an accurate figure.
                      Its possible, I am not denying it as inaccurate, I merely showed the source I am taking. No point debating over +200 kg of extra fuel anyway

                      Originally posted by BarnesW View Post
                      Add internal fuel and you increase the size and weight of the aircraft, increasing drag and reducing performance. As an air superiority fighter, the aim was to remain lethal in air combat, rather than extend range.
                      Its interesting why this very same logic does not apply when we are talking about internal bay and F-22's kinematics. Su-27 has 47% more fuel than F-15C. Granted its climb and acceleration is not as good at most parts of flight envelope, but I don't think anyone would call it less lethal due to its kinematics.

                      You can say Su-27 is bigger than F-15 (21% by weight 10% by planform area), but F-22 is way bigger than Su-27 (21% by weight 26% by Planform Area) and carries 1 ton less fuel than Su-27.

                      Originally posted by BarnesW View Post
                      When considering operational deployment you have the false conception of flying a first day mission deep into a peer adversary's territory with fuel bags. Never going to happen unless you enjoy heavy losses, the progress will be far slower and shorter in radius that that. Deeper targets will be hit with cruise missiles but the focus from an aircraft PoV will be SEADing back their IADS and knocking planes out of the air. After that, you either have the choice of using that region for IFR, or mounting a ground offensive in that region and capturing airbases.
                      F-22 has no role in that scenario anyway. You are talking all-around technological and numerical superiority againist your enemy. I don't like running such scenarios but; on a more equivalent adversary like Russia, A patrol of MiG-31 will easily neutralize cruise missiles (this is its purpose anyway), and Su-27S doing CAPs and MiG-29s doing GAI will neutralize SEAD aircraft.

                      At the same time, Russian SRBMs and cruise missiles will target your deep targets, and their Su-27/30/35 will try to achieve air superiority. In the end USAF F-22s will find themselves engaging RuAF Su-27/35, no doubt F-22 will have an edge, but it doesn't help if it has 1/2 to 2/3 combat persistance of Su-27/35.

                      Comment

                      • bring_it_on
                        2005-year of the RAPTOR!!
                        • Jun 2004
                        • 12480

                        #71
                        For F-22 to have its VLO, it cannot carry EFT. Ferry range is unimportant, but "optimized cruise" is most important factor in combat radius, which is not any different than ferrying. To increase combat radius, IFR may or may not work depending on opposition force. If you equip F-22 with EFT, you are taking away the only decisive advantage of it againist 4+ gen aircraft. This is really problematic if extra range comes with severe survivability cost.
                        And remember; F-15E with 3xEFT+CFT will have 16448 kg fuel capacity, F-22's fuel capacity with EFTs is still far less than its predecessor.
                        Depends upon the operational scenario, but the F-22's can carry EFT's during cruise to the area of operation and ditch them along with the pylons well before entering the fight. With the pylons ejected, the impact on the stealth should be well worth the the added range if that is required for a mission.

                        http://theaviationist.com/wp-content...s-jettison.jpg
                        Last edited by bring_it_on; 27th September 2015, 16:03.
                        Old radar types never die; they just phased array

                        Comment

                        • BarnesW
                          Senior Member
                          • Aug 2015
                          • 503

                          #72
                          Originally posted by Andraxxus View Post
                          Its interesting why this very same logic does not apply when we are talking about internal bay and F-22's kinematics. Su-27 has 47% more fuel than F-15C. Granted its climb and acceleration is not as good at most parts of flight envelope, but I don't think anyone would call it less lethal due to its kinematics.
                          Well the Su-27 is almost a decade removed from the F-15 for a start but the empty TWR did take a hit due to the extra internal fuel. However Russia has to cover a vast amount of airspace with relatively few planes, so range is a strong driver there.

                          Originally posted by Andraxxus View Post
                          You can say Su-27 is bigger than F-15 (21% by weight 10% by planform area), but F-22 is way bigger than Su-27 (21% by weight 26% by Planform Area) and carries 1 ton less fuel than Su-27.
                          But theoretically, you could put extra fuel in the weapons bay, that's what you're missing. The F-22 is larger because it carries 8 AAMs plus attachments internally and the means to launch them under high g or upside-down. TVC also adds a little weight over the original Su-27. You can't carry weapons and more fuel internally and add TVC and still be as light, obviously you can't, unless the gap in technology is exponential. Does the Su-27 have built-in jamming?

                          Originally posted by Andraxxus View Post
                          F-22 has no role in that scenario anyway. You are talking all-around technological and numerical superiority againist your enemy. I don't like running such scenarios but; on a more equivalent adversary like Russia, A patrol of MiG-31 will easily neutralize cruise missiles (this is its purpose anyway), and Su-27S doing CAPs and MiG-29s doing GAI will neutralize SEAD aircraft.
                          Some yes, all no. The Su-27s will be shot down by F-22s and the MiG-29s have proved no match even for F-15s thus far. Even on a 1vs1 basis.

                          Originally posted by Andraxxus View Post
                          At the same time, Russian SRBMs and cruise missiles will target your deep targets, and their Su-27/30/35 will try to achieve air superiority. In the end USAF F-22s will find themselves engaging RuAF Su-27/35, no doubt F-22 will have an edge, but it doesn't help if it has 1/2 to 2/3 combat persistance of Su-27/35.
                          The SRBMs have a range of 480km. They can be targeted by a variety of cruise missile from surface or air. They can also be shot down by several US and European systems - Patriot, THAAD, SM-3, SM-2 Dual Capability, Aster 30 etc. What usually happens is fierce fighting for the first night and then the enemy get demoralised by being shot down BVR by an enemy they can't see and give up. Combat persistence of a dead aircraft is zero.

                          Comment

                          • haavarla
                            Rank 5 Registered User
                            • Dec 2008
                            • 6693

                            #73
                            Can.. could.. Should. .

                            So when will we see the next incremental upgrade on F-22?
                            Thanks

                            Comment

                            • bring_it_on
                              2005-year of the RAPTOR!!
                              • Jun 2004
                              • 12480

                              #74
                              The F-22 already has the capability to ditch tanks and pylons. At the moment Increment 3.2B is funded and is expected in 2017. Increment 3.3 (formerly, 3.2C) comes next but there is no timeline or list of features defined yet and a lot will depend on how the threat pans out or is expected to pan out in the mid to late 2020's. A lot will also depend on when sequestration is lifted and what the long term budgetary outlooks are. Stuff like side arrays and HMS have been mentioned in the article below. HMS may be brought in earlier to a formal Increment 3.3 however but it isn't its pretty much a set capability for whatever follows Inc. 3.2B. Whatever they do decide to eventually ask in 3.3, it should be available around 2023-2025.

                              https://www.scribd.com/doc/282900306/F-22-AFA-4-12
                              Last edited by bring_it_on; 27th September 2015, 19:05.
                              Old radar types never die; they just phased array

                              Comment

                              • Robbiesmurf
                                Rank 5 Registered User
                                • Jul 2014
                                • 587

                                #75
                                Originally posted by Andraxxus View Post
                                That depends. F-15's nozzles are not the most efficient solution (from drag POV).
                                They are from a thrust POV. They are con-di..

                                Comment

                                • FalconDude
                                  Rank 5 Registered User
                                  • Sep 2010
                                  • 1172

                                  #76
                                  Originally posted by Robbiesmurf View Post
                                  I pointed out that there were a lot of figures that can be used to impress others.
                                  There is a difference between knowing and understanding. I merely asked him and he answered by throwing more figures at me. Nice, if you can't dazzle them with diamonds....
                                  You're right I have asked a couple of you about reheat and the answers you give appear to come from a Wiki explanation. It's incorrect btw.
                                  If you take the trouble to read the RR book about the jet engine it explains it very simply and well. The difference between knowing and understanding..
                                  Seeing as figures seem to impress most of you, a simple question.
                                  An example jet engine at full rpm has a jet pipe temperature of 1000 degrees Kelvin. The reheat is engaged to full and the jet pipe has a temperature of 1690 degrees Kelvin. What is the thrust increase?
                                  It's a simple calculation.
                                  well it has been a while since I done all that stuff but I believe your question is not complete. I believe you need the two stagnation ratios and some other values to calculate that. I'm almost 99% sure of that, but I could be wrong. I am an old man.

                                  Comment

                                  • Robbiesmurf
                                    Rank 5 Registered User
                                    • Jul 2014
                                    • 587

                                    #77
                                    Originally posted by FalconDude View Post
                                    well it has been a while since I done all that stuff but I believe your question is not complete. I believe you need the two stagnation ratios and some other values to calculate that. I'm almost 99% sure of that, but I could be wrong. I am an old man.
                                    I'm not so young myself...
                                    Ok good point. Let's make it simple and complete. Thrust = M x delta V. M= mass airflow. Delta V= velocity differential (airflow in/airflow out)
                                    Example jet engine. Variable reheat. SLS (sea level static).
                                    Ambient: 15 degrees Celcius
                                    PR (pressure ratio) 9:1
                                    Mass airflow 156 lb/s
                                    Rpm maximum 100%
                                    Jet pipe temp 1000 degrees Kelvin

                                    Reheat engaged to full
                                    Ambient: 15 degrees Celcius
                                    PR 9:1
                                    Mass airflow 156 lb/s
                                    Rpm maximum 100%
                                    Jet pipe temp 1690 degrees Kelvin
                                    Simple figures. Simple calculation, it's a ratio. It is a percentage. It's the simple answer as to how reheat works.
                                    pressure doesn't rise when engaging reheat, it is modulated by turbine pressure.

                                    Of course when actually moving, due to the dynamics, values change. However, the ratios remain the same.
                                    As I said, it's about understanding, not just looking it up on wiki or wherever. Andraxxus likes to bamboozle me and others with figures, I'm just asking for clarification...

                                    Comment

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