Announcement

Collapse
No announcement yet.

C-130J/C-130J-30 performance figures & inconsistencies. Can they be explained?

Collapse
X
Collapse
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
  • Filter
  • Time
  • Show
Clear All
new posts
  • swerve
    Rank 5 Registered User
    • Jun 2005
    • 13612

    C-130J/C-130J-30 performance figures & inconsistencies. Can they be explained?

    If one looks at the Lockheed Martin web site, one finds that it refers to the USAF fact sheet for the performance of the C-130 & its variants. Looking at the fact sheet, there are a few typos (e.g. the use of the metric equivalent of 123 inches as the metric equivalent of 119 inches), & some puzzling numbers.

    The C-130J-30 appears to fly significantly further (30%) than the lighter basic C-130J, with the same payload. I can't find any mention anywhere on the fact sheet, or elsewhere, about extra fuel in the -30, & I can't think of an aerodynamic reason for this phenomenon. Can anyone explain it?

    The C-130J-30 also appears to be able to take off over 4 tons heavier than the basic C-130J, with the same wing & engines.

    Despite the -30 & basic model range differences already mentioned, rather small differences in all up weight caused by fairly small differences in payload cause large differences in range, according to the fact sheet. Reducing payload by less than 3% (& all up weight by a bit over 1%) is said to improve range by 25% (1700 to 2100 nautical miles) for the -30, but the same 1000 lb payload reduction increases range by half as much for the basic C-130J (1600 to 1800 nautical miles).

    Can anyone shed light on these numbers?
    Last edited by swerve; 2nd March 2015, 08:31.
    Juris praecepta sunt haec: honeste vivere, alterum non laedere, suum cuique tribuere.
    Justinian
  • topspeed
    Get on uppah !
    • Jan 2009
    • 2660

    #2
    Here are the C-130J specs; http://en.wikipedia.org/wiki/Lockhee...Super_Hercules

    15 ft longer C-130J-30; http://www.lockheedmartin.com/us/pro...c-130j-30.html

    http://fas.org/man/dod-101/sys/ac/c-130.htm

    Does it have bigger external fueltanks ?

    http://www.casr.ca/ai-comparison-c130j-stretch.htm

    This says it is nonsense; http://www.casr.ca/bg-af-airlift-c130j.htm
    Last edited by topspeed; 2nd March 2015, 09:21.
    If it looks good, it will fly good !
    -Bill Lear & Marcel Dassault


    http://max3fan.blogspot.com/

    Comment

    • swerve
      Rank 5 Registered User
      • Jun 2005
      • 13612

      #3
      I linked to the USAF factsheet which gives more detailed specs, & is obviously the source of almost all the other measurements I've found, since they all repeat its errors in the inches/metres conversion of the width of the cargo hold - though I note that the www.casr.ca site uses a precise correct feet/metres conversion for the officially stated length of the cargo hold in feet, unlike the USAF fact sheet.

      I wasn't asking about external fuel tanks. I was asking if there's any evidence (not mentioned in anything I've found online) of additional internal fuel tanks. I should have been clearer.

      I just noticed that the USAF fact sheet uses at least three different conversion factors for pounds to kilograms: an approximate (but accurate enough, given that it's converting from numbers in thousand lbs) 2.2 lb/kg, an unnecessarily precise 2.2045 lb/kg, & a downright wrong 2.222 (recurring) lb/kg. Doh!

      The conversion of feet of altitude to metres is ridiculous. 26000 feet to 8000 metres is fair enough, as round figures, but all the others are spuriously precise numbers of metres, converted from ft into metres using the same very rough (3.25:1) conversion factor as is used to get the approximate, rounded number of 8000 metres from 26000 ft, as if that was a precise conversion. Lengths & widths are a mixture of the same inaccurate conversion (cargo compartment length), accurate conversions (cargo compartment height), conversions using a rounded factor of 3.30:1, & some figures which are downright wrong, using conversion factors up to almost 3.4:1.

      I trust this document less & less the more I look at it. It looks as if a rather dim junior clerk did a rushed job of updating it for the C-130J. It's riddled with conversion errors & typos.


      BUT - the questions still stand. The range/payload figures don't look as if they can be explained by poor metric/imperial conversions.
      Last edited by swerve; 2nd March 2015, 11:26.
      Juris praecepta sunt haec: honeste vivere, alterum non laedere, suum cuique tribuere.
      Justinian

      Comment

      • mig-31bm
        Rank 5 Registered User
        • Oct 2013
        • 2110

        #4
        sound interesting, may be they have newer engine?

        Comment

        • swerve
          Rank 5 Registered User
          • Jun 2005
          • 13612

          #5
          I can't find any mentions of a difference between engines in any of the public information.
          Juris praecepta sunt haec: honeste vivere, alterum non laedere, suum cuique tribuere.
          Justinian

          Comment

          • Andraxxus
            Rank 5 Registered User
            • Sep 2012
            • 953

            #6
            Take-off & landing weight are related primarily to landing gear strength. Without changing anything else, stronger landing gear (or simply stronger tires in some examples) can lead to greater take-off weight.

            Havent run the numbers, but only explanation is that due to limited MTOW, C-130J may need to take off with less than 100% fuel at given payload, but C-130J-30 may be able to take off with greater amount of fuel plus the same payload.

            Or simply C-130J-30 has greater fuel capacity and we dont know about it. However, factsheet also says C-130J-30 has ~6% greater MTOW than C-130J, and ~6% less range when both aircraft is at their max payload. This can be explained; same L/D 6% increase in lift (level flight) will also increase drag by 6%, cutting the range by same amount, I dont believe there is mentionable fuel capacity difference.

            Comment

            • topspeed
              Get on uppah !
              • Jan 2009
              • 2660

              #7
              Originally posted by swerve View Post




              BUT - the questions still stand. The range/payload figures don't look as if they can be explained by poor metric/imperial conversions.
              What if the longer fuselage increases lift over drag considerably. Also swans fly really high and cover long distances.

              Here is the "ugly duckling" near the Bothnic Sea on a river ( an hour ago ).
              Attached Files
              If it looks good, it will fly good !
              -Bill Lear & Marcel Dassault


              http://max3fan.blogspot.com/

              Comment

              • swerve
                Rank 5 Registered User
                • Jun 2005
                • 13612

                #8
                Aha!

                I think I've found an explanation for some of the funny range/payload figures figures.

                According to the Defense science board task force report on mobility, at high cargo weights, the C-130 (all models, including J) needs a wing relieving fuel (WRF) load in the wing tanks, to reduce strain on the wing attachment points. This fuel must remain in the wing tanks until the cargo has been offloaded. This explains the sudden decrease in range for small increases in cargo over the 'normal' load: above 36500 lbs of cargo, a C-130H needs to keep about 3 times the weight of fuel unburned in the wing tanks as the extra cargo weight. This also applies to the C-130J, though the weights are slightly different.

                The C-130J-30 can carry slightly more cargo than the basic C-130J (37000 vs 35000 lbs) before needing WRF, presumably because of structural differences - though I'd like to see more details.

                Thus, it seems all the peculiarities are for structural reasons. In effect, the theoretical maximum payload is an overload payload for relatively short distances only, & if you're not loaded to the brim, the basic C-130 should be more efficient & longer range than the -30 - but I've not found any figures which confirm that.

                This -
                Or simply C-130J-30 has greater fuel capacity and we dont know about it
                is sort of true, at high cargo weights. The -30 doesn't need to carry quite as much unusable fuel, so can use more of the fuel it has aboard, & land with less fuel remaining.

                Maximum overload weights (wartime or emergency) seem to be the same for both, though I've not been able to confirm that.
                Juris praecepta sunt haec: honeste vivere, alterum non laedere, suum cuique tribuere.
                Justinian

                Comment

                • Andraxxus
                  Rank 5 Registered User
                  • Sep 2012
                  • 953

                  #9
                  Originally posted by swerve View Post
                  Thus, it seems all the peculiarities are for structural reasons. In effect, the theoretical maximum payload is an overload payload for relatively short distances only, & if you're not loaded to the brim, the basic C-130 should be more efficient & longer range than the -30 - but I've not found any figures which confirm that.
                  I don't think thats the case:
                  "Range with 35,000 pounds of Payload:
                  C-130J, 1,841 miles (1,600 nautical miles)
                  C-130J-30, 2,417 miles (2,100 nautical miles)
                  " says the factsheet.

                  Without WRF, C-130J-30 still has longer range. I think IMHO, my explaination is more valid; with numbers:

                  C-130J = 85000lbs empty, 35000lbs cargo, 155000 lbs MTOW. On board fuel = 35000lbs.
                  C-130J-30 = 88000lbs empty, 35000lbs cargo, 164000 lbs MTOW. On board fuel = 41000lbs.

                  Standard reserve fuel for C-130 is 4500lbs;
                  (41000-4500)/(35000-4500) = 20% greater non-reserve fuel capacity.

                  As this 20% additional fuel would be used solely for cruising (both aircraft will use similar fuel for take-off/climb/landing), it could easily explain the additional 31% range.

                  According to C-130T manual; C-130T (equal to A/B/E/F/G/H/K models) has following fuel capacity;
                  33646 lbs main tank only.
                  45900 lbs main tank plus auxillary tanks.
                  64654 lbs main tank plus auxillary tanks plus external tanks.

                  Fuel capacity is by itself irrelevant, as both aicraft will be half filled while lifting 35000lbs due to MTOW.

                  Comment

                  • swerve
                    Rank 5 Registered User
                    • Jun 2005
                    • 13612

                    #10
                    According to the factsheet, normal maximum for a C-130J is 34000lb. This is consistent with the DSB publication figure, if we add a few extras such as crew arnour. At 35000lb cargo, it is 1000lb over normal maximum, & therefore needs to keep about 3000lb of extra fuel unused in the wings. At the same load, the C-130-J-30 is below its normal maximum load (apparently a structural limit), so can burn that 3000lb of fuel.

                    That's 10% of the total fuel load you calculated. Allowing for reserves, it has 36500 lb to burn, while the C-130J has much less. 35000 less reserves = 30500. Less 3000 lb it has to keep in wing tanks because of the 1000 lb over normal maximum load = 27500 lb.

                    Being able to use 36500 lb of fuel rather than 27500 lb should explain the greater range even allowing for extra drag from the extra weight & longer fuselage. It's 33% more.
                    Last edited by swerve; 2nd March 2015, 19:17.
                    Juris praecepta sunt haec: honeste vivere, alterum non laedere, suum cuique tribuere.
                    Justinian

                    Comment

                    • PhantomII
                      Phantoms Phorever
                      • Jan 2000
                      • 8292

                      #11
                      Fellas,


                      Let me clarify a few things.

                      First off the C-130J and C-130J-30 have the exact same configuration when it comes to fuel tanks. There are a total of eight tanks, including the two underwing tanks. The biggest difference in the two is the 15 ft. fuselage stretch, which allows for an extra pair of pallet positions (6 vs. 8...including the ramp position).

                      Maximum take-off weight for both is 164,000 lbs. The 155k number is outdated and applies to legacy C-130 variants only. 175,000 applies to all variants (J & legacy) but must be in extreme circumstances only...requires waivers.

                      Engines are also the same between the two variants (Rolls-Royce AE2100D3)
                      Last edited by PhantomII; 3rd March 2015, 02:18.
                      Fox-4!

                      Comment

                      • topspeed
                        Get on uppah !
                        • Jan 2009
                        • 2660

                        #12
                        Originally posted by swerve View Post
                        Being able to use 36500 lb of fuel rather than 27500 lb should explain the greater range even allowing for extra drag from the extra weight & longer fuselage. It's 33% more.
                        Sounds like the Herc longer fuselage is not a lifting body type in your view ?

                        We just concluded in an other thread that even the external fueltanks create lift.
                        If it looks good, it will fly good !
                        -Bill Lear & Marcel Dassault


                        http://max3fan.blogspot.com/

                        Comment

                        • swerve
                          Rank 5 Registered User
                          • Jun 2005
                          • 13612

                          #13
                          Originally posted by PhantomII View Post
                          Fellas,


                          Let me clarify a few things.

                          First off the C-130J and C-130J-30 have the exact same configuration when it comes to fuel tanks. There are a total of eight tanks, including the two underwing tanks. The biggest difference in the two is the 15 ft. fuselage stretch, which allows for an extra pair of pallet positions (6 vs. 8...including the ramp position).

                          Maximum take-off weight for both is 164,000 lbs. The 155k number is outdated and applies to legacy C-130 variants only. 175,000 applies to all variants (J & legacy) but must be in extreme circumstances only...requires waivers.

                          Engines are also the same between the two variants (Rolls-Royce AE2100D3)
                          Thanks for that.
                          Juris praecepta sunt haec: honeste vivere, alterum non laedere, suum cuique tribuere.
                          Justinian

                          Comment

                          • djcross
                            Rank 5 Registered User
                            • Jan 2000
                            • 5464

                            #14
                            Having the outer wing tanks feed next to last is a decades old trick to reduce wing bending/fatigue. (The feed tanks feed last and are typically held as reserve in case of a divert). All the wing fuel still gets consumed.

                            Comment

                            • swerve
                              Rank 5 Registered User
                              • Jun 2005
                              • 13612

                              #15
                              But so far, the retention of fuel in the wing tanks when heavily loaded is the only explanation I've seen for the sudden drop off in range when loads go up, & the difference between basic C-130J & -30 published ranges at high loads.

                              Are you saying that the Defense Science Board report is wrong? If so, do you have an alternative explanation for the puzzling cargo/range figures?
                              Juris praecepta sunt haec: honeste vivere, alterum non laedere, suum cuique tribuere.
                              Justinian

                              Comment

                              • Cherry Ripe
                                Rank 5 Registered User
                                • Jul 2009
                                • 564

                                #16
                                The -30s have slightly lower drag than both shorty lengths ( the basic military length and the civil -20 ).

                                Not enough to account for the discrepancy but enough that Lockeed documented it.

                                Comment

                                • Andraxxus
                                  Rank 5 Registered User
                                  • Sep 2012
                                  • 953

                                  #17
                                  Originally posted by swerve View Post
                                  Are you saying that the Defense Science Board report is wrong?
                                  After spending half hour skimming through the C-130T flight manual, I am starting to think all the Wing relieving fuel thingie is full of crap due to wrong numbers and estimates..

                                  Aircraftweight limits may be divided into two categories: grossweight limits and limits on cargo-fuel combinations.
                                  The grossweight limits in this chapter are designweights onwhich airframe strength is based. Taxi and landing gross
                                  weights are limited by the strength of the landing gear and the related fuselage structure. Takeoff and flight gross
                                  weights and cargo weight are limited by wing strength and the effects of fuel weight and distribution, airspeed,
                                  maneuver, and turbulence.......... Alternatively, airspeed andmaneuver load factor may be limited bywing and empennage strength, cargoweight, and
                                  fuel weight and distribution. Fuel weights for taxiing and landing are limited by wing strength and landing gear
                                  shock-strut reaction.
                                  In short, DSB is right about there IS a limitation about fuel and cargo weight combinations.

                                  Click image for larger version

Name:	c-130 f46.JPG
Views:	1
Size:	273.5 KB
ID:	3660203

                                  And according to the Sheet2 of figure 4.6, there really is a need for a Wing relieveing fuel. Following "not recomended" area E; any payload greater than 49000 lbs to 60000lbs, (not 35000lbs as DSB predicts) there is a need for 3000 to 25000lbs of fuel to stay in "recommended" Area C.

                                  Operating below 49000lbs, Fuel/cargo weight relation appearantly doesn't really affect take-off/landing performance, but it both affects maximum allowed load factor, and maximum recommended airspeeds. according to sheet1 of figure 4.6.

                                  Click image for larger version

Name:	C-130 sec fuel.JPG
Views:	1
Size:	116.8 KB
ID:	3660204

                                  Also this graph is self explainatory; more fuel the outboard fuel tanks have, more MTOW the C-130 is capable of. However with secondary fuel flow (means manually operated by pilot) C-130 can take-off at 155 lbs, deplate all inboard fuel first, then gross weight drop sufficently so deplating outer fuel tanks completely is still allowable.

                                  Heres the further text from the manual regarding limitations.

                                  Click image for larger version

Name:	C-130 txt1.JPG
Views:	1
Size:	218.6 KB
ID:	3660205Click image for larger version

Name:	C-130 txt2.JPG
Views:	1
Size:	259.5 KB
ID:	3660206

                                  Comment

                                  Unconfigured Ad Widget

                                  Collapse

                                   

                                  Working...
                                  X