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Thread: Chinese air power thread 18

  1. #1201
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    Quote Originally Posted by Marcellogo View Post
    I think this would be absolutely not possible, F-35 is not slow because of a bad T/P ratio a.t.c. it is better on that regard than the same MiG-31:
    it's about aerodynamics a.k.a. being a flying brick.
    .
    Sure marc, so are the Rafale and Gripen which are a whopping 50 KCAS faster.

    The ignorance never ceases to amaze me. Sure, the F-35 is CLAWS limited to 700 knots because of aerodynamics. Any other gems you want to share?

  2. #1202
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    Quote Originally Posted by haavarla View Post
    Say what?

    I do recall one reported test run by a F-35A where it actually had to "unload" in order to reach Mach 1.6
    Unload means it had to point its nose downward compared from a sustained altitude flight.
    Say what?

    Do you actually know what you are talking about? I know the answer to that.... NO

    It was the F-35C that they referred to using a Rutowski profile. And to get to maximum speed quickly, or climb rate, that is common, and efficient. As we all know defense reporting is always accurate and not sensational at all.

    Personally, I’ve always found the F-35C to be compromised, 2 1/2 tons heavier, different wings, wing design, camber. It’s transonic acceleration shows the wave drag impact of increased wing area. Yet it still reaches Mach 1.6. Time to start thinking of the substantial differences between F-35 variants.

    The F-35A has exceeded Mach 1.6. It has been tested with full weapons and fuel to Mach 1.6. It exceeds Mach 1 at sea level. It can easily overspeed even with control laws. Questions?
    Last edited by FBW; 11th June 2018 at 23:54.

  3. #1203
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    The discussion here is one of fluid dynamics. Basically, the fluid flowing through a pipe, or the surface of an airplane, is not uniform. There are boundary layer effects. Fluid (air in this case) is nearly static within the boundary layer. This is bad for a turbofan because if it doesn't get uniform flow then part of it doesn't work as efficiently, resulting in poor fuel efficiency and excess wear. Everyone tries to get around this in different ways. The F-35 uses a DSI because it is a cheap means of reducing RCS. The circular bulge simply forces the boundary layer on the airplane's skin to flow more in uniform with the air outside of the boundary layer. This effect rapidly starts to deteriorate as you approach Mach 2. So the J-20 and the F-35 are likely bound by that no matter how powerful of an engine/engine's they receive. Other designs like the F-22 and the Su-57 use a diverter. This is basically a gap which separates the inlet of the aircraft from the surface so that the boundary layer has no effect. This allows for speeds a little beyond Mach 2, but at a cost of making it more difficult to maintain stealth at lower frequencies (the F-35 is said to actually be stealthier than the F-22 in lower frequencies).

    All of these designs are fixed inlets. To propel a turbofan aircraft up to the velocities where ramjet propulsion is required you need a variable inlet. However, this is practically impossible to implement in a LO or VLO design.

  4. #1204
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    With regard to current DSI testing, your pretty much correct XB-70.

    NASA studied the DSI as early as the 1950’s. There were more than RCS considerations that led to both the US and China adopting DSI on their aircraft; weight, complexity, maintenance, and that testing showed that the DSI had greater pressure recovery at supersonic speeds (up to Mach 1.8 in the case of the F-16 test platform, I believe). It isn’t just the bump, the entire fore body shaping is part of the inlet efficiency in the case of the F-35.

    Irregardless, it has little to do with pervious posters comments about the F-35. As far as DSI belong limited to Mach 2. DSI have been tested to Mach 2, and that testing on the F-16 showed increased flow separation above Mach 1.8. Decreased efficiency and spillage, but that was on the modified F-16. Considering the evolution of DSI shapes and inlet design, I wouldn’t say that’s an absolute limit.
    Last edited by FBW; 12th June 2018 at 02:04.

  5. #1205
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    Some posters here would be surprised to learn that modern 3-D hypersonic inlets are fixed, not variable, and do not require bleed to hold the shocks in place. Multiple small oblique shocks produce better pressure recovery than one oblique shock and a huge normal shock as is found mechanically variable inlets from 50 years ago.

  6. #1206
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    Sure marc, so are the Rafale and Gripen which are a whopping 50 KCAS faster.

    The ignorance never ceases to amaze me. Sure, the F-35 is CLAWS limited to 700 knots because of aerodynamics. Any other gems you want to share?
    ??????? For what I know the Gripen speed is set at mach 2 and the same Rafale is 1.8 like the F/A-18 (hardly a runner) that's in every case more than 200km or +100 knots more in my book...
    In percentage it means that even the previously slower fighter planes around has almost 10% more speed than our truly, all other have almost a 25%.
    Now to spare the other members of this forum another show of your trademark chauvinism and lack of even a minimum of good manners, let me add that "flying brick" is intended as a ironic/sarcastic reply to another non 100% serious post of F-14 Tomcat as the use of an emoticons should have suggested you.

    In case you still taking a fuss about it, let me explain better what the term was intended to mean: Tomcat said that putting over a F-35 a most powerful engine or a different intake would significatively increase its maximum speed at the point of reach the one of the F-16 (or any other plane around except the two listed above. And the Su-34 also).
    To put it simply, I just think it is not possible to reach such a result short of such radical changes in the plane own aerodynamics to result absolutely not worth the effort.
    While in the case of the other slow movers you can blame the bad T/W ratio or the presence of fixed intakes, both those just doesn't apply to the F-35 as its excellent subsonic performance seem to suggest.
    It has an excellent engine, a more than decent t/w ratio DSI intakes (i.e. still better than a fixed one) still is anyway limited to mach 1.6.
    So what can be except a general aereodynamic shape that it's not more efficient above a certain limit i.e. that would not allow if not a very slight increase of speed even in the case of a consistent increase of thrust or a more efficient air flow?


    Now, if calling such an occurrence " being a flying brick" is something going about political correctness, let's just use another term: what about "aereodynamically challenged"?
    In any case, just not look at it as an equivalent of calling the F-35 "a lemon " or something like so, it's just a critics of a single (and evident) shortcoming of a given design . not something intended to thrash it
    Last edited by Marcellogo; 12th June 2018 at 09:24.

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  8. #1208
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    Quote Originally Posted by Marcellogo View Post
    ??????? For what I know the Gripen speed is set at mach 2 and the same Rafale is 1.8 like the F/A-18 (hardly a runner) that's in every case more than 200km or +100 knots more in my book...
    In percentage it means that even the previously slower fighter planes around has almost 10% more speed than our truly, all other have almost a 25%.
    To put it simply, I just think it is not possible to reach such a result short of such radical changes in the plane own aerodynamics to result absolutely not worth the effort.
    While in the case of the other slow movers you can blame the bad T/W ratio or the presence of fixed intakes, both those just doesn't apply to the F-35 as its excellent subsonic performance seem to suggest.
    It has an excellent engine, a more than decent t/w ratio DSI intakes (i.e. still better than a fixed one) still is anyway limited to mach 1.6.
    So what can be except a general aereodynamic shape that it's not more efficient above a certain limit i.e. that would not allow if not a very slight increase of speed even in the case of a consistent increase of thrust or a more efficientit
    What you describe as “trademark chauvinism” would be fact that I have little tolerance for people who repeat falsehoods and have no idea what they are talking about yet repeat it over and over.

    One- the Rafale is limited to 750knots/ Mach 1.8. Meaning below ~30,000 feet it’s fcs restricts it to 750 knots, above it’s Mach limited.
    Two-Gripen is operationally limited to the same. The E/F says Mach 2, we will see.
    Three- the F-35 is limited by it’s fcs to 700knots/Mach 1.6.
    Not to mention, the F-18 is stated as Mach 1.8. One look at the flight manual shows this to be a largely theoretical speed (as is true of many aircraft with stated Mach 2 performance).

    Fifty knot KCAS. Period. Now why are they all similarly limited by control laws?
    Because the idea is relatively carefree handling and flying, the pilot does not have to be as concerned with overspeed on the deck, thermal loading at high Mach, canopy damage, damage to RAM on leading edges.

    Not to mention, sixty years experience of operating supersonic aircraft. Does it matter that the F-16 and Typhoon are rated as 800 knot aircraft and can achieve Mach 2 (clean x2 AAM in the case of the F-16), does that 50-100 knots make an operational impact 99% of the time? The designers and operators of the latter think not. Mainly because experience tells them that aircraft rarely, if ever require Mach 2 speeds for the types of missions they perform.

    As far as the F-35, it is not “aerodynamics” in the case of the F-35A. It has flow to near Mach 1.7. The designers have stated it can overspeed easily in spite of CLAWS. It is a 700 knot/ Mach 1.6 aircraft because that was the requirement. It is limited by said flight control system. The bay has thermal issues at those speeds. All three variants can reach Mach 1.6 (though the B is limited to 630 knots), that alone should tell you that the “A” is not limited by aerodynamics.
    Last edited by FBW; 12th June 2018 at 12:54.

  9. #1209
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    Ok, FBW ,let's do like so:

    I'm not saying any falsehood on pourpose, everything i say i'm convinced to, period.
    In the case I am saying something you retain not correct, just reply to me with the data in your possess like you are doing in this last one post, just don't call names and treat everyone, not just me with a minumum of respect and urbanity, please.

    So it's a the bomb bay that have a thermal issue at more than 1,6 speed.
    Huge if True, much more than call it a "flying brick" IMHO.

  10. #1210
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    I apologize if I offended you, sincerely. I would admit to a prickly demeanor and being combative especially when having to respond to inaccuracies that are oft-repeated on this forum, it isn’t always easy to differentiate those who have read previous discussions on said topic and choose to continue to repeat what has already been addressed and those who have not. Do not mistake this for a lack of respect for the value of a spirited discussion. It is wrong conceptions and opinions I am hostile to, not the poster (mostly).

    As far as the bay issues, these are not unique to the F-35 (and I believe the bay heating is mostly an issue at low level IIRC). A few years ago I posted a presentation from a symposium discussing the thermal challenges faced by this and the next generation of aircraft. The current methods of thermal management have reached their limits, especially on LO aircraft. It isn’t just aerodynamic heating. It is the power requirements for AESA, IRST, EW suites, processors that have pushed current cooling methods, such as using fuel as a heat sink, to their limit. In previous generations, ram air heat exchangers could cope with thermal load. Even if IR/RF signature wasn’t a concern, sustained high speed flight makes these less efficient for cooling.
    Last edited by FBW; 12th June 2018 at 17:12.

  11. #1211
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    FBW: Don't take this as an attack! Just correcting a misconception for the benefit of all readers

    Quote Originally Posted by FBW View Post
    Fifty knot KCAS. Period.
    Except at those altitudes (& Mach numbers), 1kt (CAS) =/= 1kt (TAS) - and obviously it's TAS that is relevant when discussing which is "faster".

    To illustrate why this isn't mere sophistry, refer to the following diagram showing these relationships:

    Click image for larger version. 

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    Red envelope: bounded by Mach 1.6 & 700kCAS limits (F-35)
    Blue envelope: bounded by Mach 1.8 & 750kCAS limits (Rafale)

    Maximum TAS within the F-35 Mach/CAS envelope is 960kts (@ 25kft altitude), whereas for Rafale it's about 1070kts (@ some 27.5kft, 1020kts at the F-35's 25kft) - a deficit of 110kts, rather than just 50. As a percentage, that's a 11.5% margin - not actually too far off the gap you might expect from the Mach 1.6 to 1.8 difference at 12.5%.

    Quote Originally Posted by FBW View Post
    It has flow to near Mach 1.7. The designers have stated it can overspeed easily in spite of CLAWS. It is a 700 knot/ Mach 1.6 aircraft because that was the requirement. It is limited by said flight control system.
    If military certification requirements are anything like civilian in this regard, it would have had to in order to gain approval for a Mach 1.6 placard limit in service. AFAIK safe operation must be demonstrated at a defined margin over and above the certified red line, precisely because control laws (or pilots, as the case may be) can't prevent minor overshoots in all conditions. The fastest business jets today (large cabin Gulfstreams and the like) are pushing Mach 1.0 during testing as a result!

    In other words, in all probability Rafale will similarly be capable of (and have been taken to) > Mach 1.8.

    Quote Originally Posted by FBW View Post
    All three variants can reach Mach 1.6 (though the B is limited to 630 knots), that alone should tell you that the “A” is not limited by aerodynamics.
    What that should also have told you is that your comparison is an oversimplification... if Mach 1.8 to Mach 1.6 really was only a 50kt difference, how could the F-35B with a CAS limit lower by 70kt reach the same max. Mach as the -A?

    (Answer: by climbing to roughly 32kft, where that CAS will equate to a TAS of 930kt rather than 860kt at 25kft. The drop in outside air temperature at that altitude sufficiently lowers the speed of sound that this works out to Mach 1.6. Which shows the TAS/CAS discrepancy due to altitude is way too big to ignore in comparing the F-35 and Rafale.)

  12. #1212
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    I assumed that anyone reading the post would understand what KCAS means. As that is what is used when setting placard limits anyway.

    You are (mostly) correct on all above (except CAS/TAS conversion) I assumed posters would understand speed/alt conversion. The crossover from a KCAS to Mach limit is roughly 30,000 feet depending on atmospheric conditions. Obviously an F-35B is reaching Mach 1.6 at a higher altitude (~35k feet I believe)

    Testing usually exceeds operational limits by 10% or more for safety margin. Hence F-35 tested to 1.67 Mach, 9.9g. Absolutely. Point is, not an aerodynamic limit.

    I would not say it’s an oversimplification because aircraft don’t use ground speed (+\- wind) TAS

    Edit-,Trident why are you using sea level standard day temp to convert CAS to TAS at different altitudes?

    Should be 915 knots vs 970 knots TAS @ 25,000. Difference of 55 knots TAS.
    Last edited by FBW; 12th June 2018 at 21:34.

  13. #1213
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    Let me clarify myself, FBW. There is no physical law that says an aircraft with a DSI cannot go faster than Mach 2. Rather, there is just substantial empirical evidence that when an aircraft such equipped approaches Mach 2 the ability of the DSI to force flow in the boundary layer becomes increasingly reduced and thus engine efficiency plummets. And so there is a practical limit at Mach 2. Why would the engineering team choose to spend upgrade funds to further increase speed in spite of plummeting engine efficiency when they could improve the aircraft in other areas with more bang for the buck - such as better sensors. Engineering is all about tradeoffs.

    The F-35 was conceived as a stealth strike fighter. The DSI provides it with reduced RCS compared with a diverter, particularly at low frequencies. And a strike fighter is expected to do a lot of low altitude, ground support work where high supersonic flight is not of much importance. The J-20 is still mostly an enigma, but many seem to think it is geared for a strike role as well. Personally, I don't think one can tell until we see it fly with the Ws-15 Emei.

  14. #1214
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    Completely understood you post and points XB-70. Was adding complementary points, same page.,

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    Quote Originally Posted by FBW View Post
    Testing usually exceeds operational limits by 10% or more for safety margin. Hence F-35 tested to 1.67 Mach, 9.9g. Absolutely. Point is, not an aerodynamic limit.
    The point is that it's a moot argument, because it works the same way for Rafale - whichever way you slice it, the 0.2 Mach / 100+kt difference won't go away.

    Quote Originally Posted by FBW View Post
    I would not say it’s an oversimplification because aircraft don’t use ground speed (+\- wind) TAS
    For navigational purposes, sure they do - it's the velocity at which the aircraft physically moves from location A in space to location B. CAS is useful for aircraft handling because, being directly related to dynamic pressure, it gives the pilot cues on its aerodynamic behaviour (stall etc.) but for the purposes of this subject it's not applicable.

    Quote Originally Posted by FBW View Post
    Edit-,Trident why are you using sea level standard day temp to convert CAS to TAS at different altitudes?
    Why would I not?

    The effect of temperature variation with altitude is already accounted for in the dashed lines, as evidenced by their slope (and the lack thereof in the stratosphere above 35kft where lapse rate becomes zero). It's why below the tropopause TAS readings at constant Mach number (correctly) decline with altitude. The temperature correction lines are for sea level deviations from ISA standard conditions (15°C) and using any other SL temperature level doesn't appreciably change the percentages I mentioned earlier.

    Quote Originally Posted by FBW View Post
    Should be 915 knots vs 970 knots TAS @ 25,000. Difference of 55 knots TAS.
    Not sure I follow you here.

    Why arbitrarily restrict the comparison to 25kft, rather than each at its optimum altitude, which removes most of the Rafale's advantage from its higher Mach limit (750kCAS is only Mach 1.7 @ 25kft)? Maximum speed is just that, the fastest the aircraft can go, right? If we drop that notion, we also come to the conclusion that the F-35B is not in fact as fast as its siblings, and by a bigger margin than the latter are slower than Rafale.
    Last edited by Trident; 13th June 2018 at 00:03.

  16. #1216
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    Because TAS is based on pressure and temp 1976 standard day at a given altitude. At sea level Mach 1 is 661 knots, at 30,000 feet it is 589 TAS.

    The Rafale has a 100 knot TAS advantage at sea level. 700 KCAS vs 750 (850 vs 950 TAS). TAS and CAS become the same at crossover altitude. Hence why above 30,000 feet the F-35A is Mach limited not CAS limited.

    You have to follow the temperature at the top of you graph to convert to TAS. Base temp at 25,000 feet is roughly -50 C international standard day.

    I think your trying to compare relative ground speed. Whole new ballgame.
    “Your killing me smalls”
    Last edited by FBW; 13th June 2018 at 00:26.

  17. #1217
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    Quote Originally Posted by FBW View Post
    Because TAS is based on pressure and temp 1976 standard day at a given altitude. At sea level Mach 1 is 661 knots, at 30,000 feet it is 589 TAS.
    ... and those are exactly the results you get reading the chart the way I did, without reference to the temperature corrections.

    Quote Originally Posted by FBW View Post
    The Rafale has a 100 knot TAS advantage at sea level. 700 KCAS vs 750 (850 vs 950 TAS).
    850, let alone 950kts TAS at SL? Better tell Darryl Greenamyer and the FAI that any stock example of Dassault's finest has his specially modified F-104 (including pre-compressor water cooling) beat by a handsome margin and operational F-35As come within touching distance of the record

    At sea level, the difference between CAS & TAS is nowhere near that big, there remains a Mach number related discrepancy at these high speeds, but it's comparatively minor (i.e. the SL TAS difference between Rafale & F-35 is roughly the same as the 50kts CAS difference, as the chart confirms).

    Quote Originally Posted by FBW View Post
    You have to follow the temperature at the top of you graph to convert to TAS. Base temp at 25,000 feet is roughly -50 C international standard day.
    Again, the dashed lines already factor in the temperature variation with altitude, the corrections are to account for hot/cold day conditions. As it makes no sense to assume a hot day for one aircraft vs. cold day for the other, they are irrelevant here.

    Quote Originally Posted by FBW View Post
    I think your trying to compare relative ground speed. Whole new ballgame.
    For level flight in still air (= no wind), ground speed does equal TAS. No reason to assume anything else for the purposes of this debate, is there?

  18. #1218
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    Trident, I don’t know how else to explain this except that your misreading the chart. In essence, what you are trying to do is convert true airspeed at sea level (which is as you stated ground speed +/- wind) to true airspeed at different altitudes without considering the atmosphere the aircraft is flying in (as that is the very definition of true airspeed). You cannot take TAS at sea level and simply move up to 20, 30 thousand feet. Pressure changes, temp changes, therefore true airspeed changes. Look up NASA charts on true airspeed and crossover altitudes. Then you will get it.

    As far as what I stated about the relative CAS and TAS at sea level for the Rafale and F-35, really? We are talking Mach 1.05 for the F-35 and Mach 1.15 for the Rafale. Unfortunately, I also used your chart to compute TAS and forgot at sea level, there is no conversion (which should give you a hint why your calculations for TAS at higher altitudes are wrong).

    As far what to use for purposes for debate, you based your argument on true airspeed. There is a 55 knot difference between the two at 25,000 feet and 50 knot difference between the two at 29-30k feet (crossover altitude). Above that, say 40k feet the Mach limited difference between the Rafale and F-35 is about 114 knots TAS (918-1032). There is your 11.5 percent margin. But that is because we are talking the difference in Mach/TAS because neither is flying at 700/750 KCAS at that altitude, get it?

    It’s hard to wrap your head around, believe me I am sympathetic on that point. Probably why modern FCS set a placard limit at a calibrated airspeed below 30k feet and a Mach limit above.

    Do it for yourself:
    http://www.rfcafe.com/references/ele...ach-number.htm
    https://www.mathworks.com/help/aerob...orrection.html
    https://www.calpoly.edu/~rcumming/Airspeed.pdf
    http://www.dtic.mil/dtic/tr/fulltext/u2/a801325.pdf
    https://www.pprune.org/questions/333...s-formula.html

    Or cheat with a “good enough” airspeed conversion caluculator:
    http://www.hochwarth.com/misc/AviationCalculator.html

    I cross-checked numbers several times. Honestly, the online one is pretty accurate (or likely more accurate than mine, or my checking it against conversion charts)
    Last edited by FBW; 13th June 2018 at 03:28.

  19. #1219
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    By all means, let's verify using other sources then then. What's the TAS of Rafale doing Mach 1.8 at 27.5kft on a standard day according to your reckoning? The value I read from that chart, as stated above, is 1070kts.

    https://www.digitaldutch.com/atmoscalc/

    Input 27.5kft and get a temperature of 233.667K (which works out to -39°C, plausible enough to you?), for a speed of sound of 306.4m/s. Convert to km/h by multiplying by 3.6, further convert to kts by dividing by 1.852 which yields 595.7kts. Finally multiply by 1.8 to get the TAS of an aircraft flying at 27.5kft on a standard day (15°C SL temperature) at Mach 1.8 and you get... 1072kts. Not too shabby, reading from such a low-res chart!

    What happens at a SL temperature other than 15°C, say 40°C (we now have Rafale flying over the blazing desert heat of Qatar)?

    Repeat the above, but input +25K for the temperature offset (relative to 15°C). This yields a speed of sound of 322.4m/s and a Mach 1.8 @ 27.5kft TAS of 1128kts. If using the chart, draw a line due right from the intersection of my blue TAS line with the TAS scale along the SL altitude line until you hit the 40°C line, then go straight up to read the TAS scale at the top of the chart. Result? I make that something roughly halfway between 1100 and 1150kts - I rest my case

    Just because the standard day TAS scale is drawn along the SL altitude line doesn't mean it actually gives TAS for sea level only - any more than the Mach number scale at the bottom gives Mach number for altitudes in excess of 100kft or something.

    The CAS/Mach/TAS/EAS Conversion calculator on the site you suggested (http://www.hochwarth.com/misc/AviationCalculator.html) is only reliable for subsonic speeds, as stated explicitly there. Case in point, the CAS value for an input of 27.5kft altitude and Mach 1.8 is way too high (although the TAS does match the chart and the other site above).

    If you don't trust the speed of sound calculation, revert to first principles: speed of sound = sqrt(gas constant (air) * ratio of specific heats (air) * temperature), where the gas constant is 287J/(kg*K), the ratio of specific heats is 1.4 and temperature is any of the values above. You'll get the same results.
    Last edited by Trident; 13th June 2018 at 04:36.

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    One last time, why are you looking up Mach 1.8 at 27k feet when it is limited to 750 CAS below crossover altitude, 750 knots CAS. Read the Rafale specifications.
    Two, you obviously didn’t cross reference with temp on naca conversion chart. The one I gave you matches perfectly +/- 5 knots with naca. It may say not for use above Mach 1 but probably due to compressibility. It’s accurate. Did you even look at first link? That one basically shows you that your dead wrong, end of story, convert to temp. Scroll down to TAS relationship with Mach. What is Mach 1.5 at 30,000 feet? See? why did early airspeed record attempts always occur in morning when the air is cool and calm?

    To be continued, but simply put, you used a crap calculator that does not adjust for pressure/ temp unless you look up international standard day for a given altitude it’s online (should be 217 ish k) I’ve given You all the info you need, use it.

    Here try this, a simple google True airspeed Mach 1 30,000 feet. Then use your method of reading conversion chart without temp conversion. It’s right in front of you.
    Last edited by FBW; 13th June 2018 at 05:17.

  21. #1221
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    Quote Originally Posted by FBW View Post
    One last time, why are you looking up Mach 1.8 at 27k feet when it is limited to 750 CAS below crossover altitude.
    What is the crossover altitude for 750kCAS & Mach 1.8 according to you?

    Crossover altitude is the point where a given airspeed coincides with a specified Mach number. So according to the chart it IS 27.5kft for 750kCAS & Mach 1.8 and I'm perfectly ok to do what I did.

    Why does http://hochwarth.com/misc/AviationCalculator.html suggest it is higher than that? Because the underlying equations are not valid for Mach numbers greater than 1, as is pointed out clearly enough on the site itself. Plug the erroneous CAS value from the CAS/Mach/TAS/EAS Conversion into the Crossover Altitude calculator and it miraculously gives the correct altitude - but that doesn't make the CAS value any less wrong.

    Quote Originally Posted by FBW View Post
    Two, you obviously didn’t cross reference with temp on naca conversion chart. The one I gave you matches perfectly +/- 5 knots with naca
    All the calculators and charts I consulted agree on the temperature value for 27.5kft which I gave. That NACA table dates from 1943, so it's hardly the Standard Atmosphere we know today, but temperature interpolated between 27kft & 28kft works out to -39.4°C, speed of sound to 592kts - close enough, all things considered.

    Quote Originally Posted by FBW View Post
    Use your head, why did early airspeed record attempts always occur in morning when the air is cool and calm?
    Very early? Because once your (piston) engine has reached operating temperature (tolerances & lubricant viscosity nominal), cold air with its higher density will benefit volumetric efficiency and hence power output, not to mention better waste heat rejection in the radiators. Compressibility was not yet a significant concern. Later on? It depends TM. Low altitude jet records were actually flown in the *highest* possible temperatures (New Mexico & the Mojave Desert for Sageburner and Greenamyer's efforts) because a Mach limited aircraft will achieve the highest TAS with the highest speed of sound (which is proportional to the square root of ambient temperature, as stated earlier).

    Quote Originally Posted by FBW View Post
    To be continued, but simply put, you used a crap calculator that does not adjust for pressure/ temp unless you look up international standard day for a given altitude it’s online (should be 217 ish k) I’ve given You all the info you need, use it.
    Well, your suggested Standard Atmosphere calculator (http://hochwarth.com/misc/AviationCalculator.html) gives the same temperature as the one I used. Since I've shown why I did it the way I did pretty exhaustively, maybe you can make your case for an OAT of 217K in similar detail.

    As for crap calculators, I'd submit that I'm not the one using a source which explicitly states it's only valid for Mach <1...
    Last edited by Trident; 13th June 2018 at 05:55.

  22. #1222
    Join Date
    May 2004
    Location
    Germany
    Posts
    3,920
    Quote Originally Posted by FBW View Post
    Here try this, a simple google True airspeed Mach 1 30,000 feet. Then use your method of reading conversion chart without temp conversion. It’s right in front of you.
    I did, first result is another calculator which only offers a small number of altitude levels for selection. I tried 30kft & Mach 1.8 and got 1062kts TAS. Using my method of reading the chart I get 1060kts - still fail to see the problem.

  23. #1223
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    Jan 2018
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    Chinese Y-30. To be equipped with DSI intake plus engines, like on their fighters, drones, trainers, etc

  24. #1224
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    Germany
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    Chinese Y-30. To be equipped with DSI intake plus engines, like on their fighters, drones, trainers, etc
    Nope ... if you look at the c/n of that bird it's just an older Y-20 static test frame.
    Attached Images Attached Images  
    ...

    He was my North, my South, my East and West,
    My working week and my Sunday rest,
    My noon, my midnight, my talk, my song;
    I thought that love would last forever; I was wrong.

    The stars are not wanted now; put out every one:
    Pack up the moon and dismantle the sun;
    Pour away the ocean and sweep up the woods:
    For nothing now can ever come to any good.
    -------------------------------------------------
    W.H.Auden (1945)

  25. #1225
    Join Date
    Oct 2010
    Posts
    476

    Talking

    I have difficulty on which part of photograph to focus..the plane or the creature in front corner..
    Last edited by ananda; 13th June 2018 at 12:52.

  26. #1226
    Join Date
    Jan 2018
    Posts
    115
    compare the size of the person next to the plane

    here is the y-20


  27. #1227
    Join Date
    Mar 2012
    Location
    London
    Posts
    563
    The girl is clearly Photoshopped into that picture, look at the quality of the background image of the Y20 compared with the foreground pic of the girl.

  28. #1228
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    "Where the fruit is"
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    It's not the same plane, period.
    There is plenty to detail that will bring anyone to the right conclusion. See cockpit windows profile, wiper size or wing root section (this one is for a slower plane, probably turboprop) for example.

  29. #1229
    Join Date
    Oct 2015
    Posts
    89
    I don't know how anyone can believe that the very clear picture Deino provided is even connected to that transport aircraft in the picture.. which is quite blurry.

  30. #1230
    Join Date
    Jan 2000
    Location
    Germany
    Posts
    4,096
    I don't know how anyone can believe that the very clear picture Deino provided is even connected to that transport aircraft in the picture.. which is quite blurry.
    Simply since there were several more images posted at several Chinese forums and one guy even was so close to post detail shots ... IMO anyway better than posting ps'ed fake images only to mislead the size of that bird.
    ...

    He was my North, my South, my East and West,
    My working week and my Sunday rest,
    My noon, my midnight, my talk, my song;
    I thought that love would last forever; I was wrong.

    The stars are not wanted now; put out every one:
    Pack up the moon and dismantle the sun;
    Pour away the ocean and sweep up the woods:
    For nothing now can ever come to any good.
    -------------------------------------------------
    W.H.Auden (1945)

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