Max Speed of P-51H : 487mph or 471mph ?

Discussion in 'Aviation' started by Dawncaster, Mar 30, 2014.

  1. Dawncaster

    Dawncaster New Member

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    P-51H commonly known as a top speed of 487mph.

    But some people say it's just a prototype test results.

    http://www.wwiiaircraftperformance.org/mustang/p-51h-na117.jpg

    NA-117 graph, gross weight 7302lb, 481mph.

    http://www.wwiiaircraftperformance.org/mustang/p-51h-altperf-91444.jpg

    NA-126, Report No. NA-8284, gross weight 8000lb, 491mph.

    http://thehuwaldtfamily.org/jtrl/ve...A, Perf. Calc. for P-51H Mustang (NA-126).pdf

    NA-126, Report No. NA-8284-A, gross weight 9450lb, 471mph at 22700ft without racks.

    http://www.alternatewars.com/SAC/F-51H_Mustang_SAC_-_22_March_1949.pdf

    F-51H Standard Aircraft Characteristics March 1949, gross weight 9430lb(combat weight), 471mph at 22700ft. <= same as NA-8284-A

    http://www.alternatewars.com/SAC/F-51H_Mustang_SAC_-_3_July_1950.pdf

    F-51H Standard Aircraft Characteristics July 1950, same as March 1949 SAC.

    which one is correct?
     
  2. GregP

    GregP Well-Known Member

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    I'm VERY suspicious of the "Standard Aircraft Characteristics" where the max speed is one knot difference when racks for rockets are installed. Racks slow you down more than one knot. Note the top speed is for the "Basic" mission, but the Interceptor mission is a clean aircraft ... the same as the Basic mission except weight. The mission where bombs are carried is also quite suspicious since bombs shackles and sway braces will eat up more than 2 knots, trust me.

    Also 412 knots converts to 474 mph. Altogether, this looks something like "minimum guaranteed performance," not "typical performance."

    But, I am NOT an expert on the P-51H model by any means. I've known two guys who flew P-51H's and neither ever went to top speed, they climbed for a little while at the takeoff rating (was remembered as GREAT fun) and throttled back for economy pretty quickly and were turning hard in ACM, so they weren't going all that fast ... 370 - 390 mph tops while maneuvering at the altitudes they trained at (they didn't say the height).

    I gather that top speed runs are for test pilots. Combat pilots almost never see it except in a dive where the dive limits get to be important limits for personal safety.

    I knew several people who flew F-104's and only 2 or 3 out of about 15 ever saw Mach 2. All of those few were in a shallow acceleration dive to achieve a specific flight profile for speed in a clean aircraft.
     
  3. drgondog

    drgondog Well-Known Member

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    I would tend to trust the 1949 SAC data as the data was used for mission profile and planning purposes and founded on actual flight test data.. the 407 and 412kts are With external fuel tank/bomb racks.. add 8-10mph for increase in speed without racks.


    I also agree with Greg that the difference with and without rocket racks seem off. Offhand I don't recall ever seeing a USAF P-51H without them but they are easy to take off.
     
  4. Dawncaster

    Dawncaster New Member

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    hmm.. but see Report No. NA-8284-A, 30 of 97 page, gross weight 9450lb had no racks. compare to other weight. 471mph at 22700ft was clean condition's performance when november 1945.

    last page of SAC "performance data are flight test values and are based on AMC test and North American Report No. NA-8284-A dated November 1945."

    SAC's basic 9430lb performance curve and value are very similar to Report No. NA-8284-A's. but take-off weight was 11029lb with two 110gal tanks.

    That is why I am confused.

    Report No. NA-8284-A, 50 of 97 page, drag of external load items curves.

    drag of 2 bomb racks for 110gal tank is lowest but..

    case of P-51B, difference between clean and fighter condition(with two bomb racks) was 12mph.

    here is P-51H No. 44-64182 report.

    P-51H Performance Test

    "All tests at the fighter configuration (bomb and rocket racks only) were flown at a take-off weight of 9544 lbs"

    max speed is terrible to compare other tests, only 451mph with 90" hg.

    bomb racks and rocket racks were almost decrease 20mph speed.

    but SAC's mission profile was.. damn! what happen between P-51H to F-51H? o_O <= confused again.
     
  5. Aozora

    Aozora Well-Known Member

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    From the P-51H Pilot's Manual, 1946:

    [​IMG]


    The 1949 charts do not allow the use of WEP (War Emergency Power), a rating which allowed boost pressures of up to 76" Hg for 1 minute see http://www.wwiiaircraftperformance.org/mustang/p-51h-na117.jpg the other test used up to 90" Hg with water injection.

    By 1949 the engines were restricted to using Military Power with a maximum boost of 61 Hg (15 minutes); that accounts for the difference between the P-51H and F-51H.

    Also, take a look at the "Compressibility Correction Table" in particular; none of the reports note whether the figures were corrected for compressibility:

    [​IMG]

    Engine chart (note WEP):

    [​IMG]

    Instrument limitations

    [​IMG]
     
  6. Dawncaster

    Dawncaster New Member

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    #6 Dawncaster, Mar 30, 2014
    Last edited: Mar 30, 2014
    SAC [engine ratings] section was not included max power.

    for example, same as F4U-4 SAC http://www.wwiiaircraftperformance.org/f4u/f4u-4.pdf

    so, 1949 SCP's max power(wet) = water injection with 90"hg. (7 mins only).

    mil-power was not called "wet" or "max" power. especially "wet" means ADI.

    and IMO, NA-117 was not standard P-51H. it was prototype. gross weight was just 7302lb, only 105gal fual and 4 guns with 1080rds ammo.

    actual P-51H was NA-127. gross weight 9430+lb, 255+gal internal fuel, 6 guns with 1820rds ammo.

    here is P-51H test report without water-injection.

    http://www.wwiiaircraftperformance.org/mustang/p-51h-64161.html
     
  7. GregP

    GregP Well-Known Member

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    Goes to show how well-defined the flight test reports are, huh?

    The repeatability is variable, even if you use the same plane on two successive days.
     
  8. davparlr

    davparlr Well-Known Member

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    The first three charts are NAA charts and most likely represent engineering estimates, which will also have engineering errors, and possibly optimistic. The last two chart state that they are based on flight test data and should be more reliable. There is a question regarding the test weight, however. 9544 pounds at loaded weight seems heavy. "America's Hundred Thousand" states that the loaded weight of the P-51D configured for fighter operations was 9611 lbs. The empty weight of the P-51H is 540 lbs less than the P-51D. I don't know where the extra weight is. No big deal for speed but would impact climb. My estimates of nominal climb at SL is 5600 ft/min at 8800 lbs and max airspeed is 468 mph at 21k ft. clean. Interestingly, top speed at sea level is a very impressive 410 mph, all plus or minus my error.

    Confusing conflicting data on these aircraft are not uncommon. Take a look at the F4U-4 sometimes.
     
  9. Dawncaster

    Dawncaster New Member

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    #9 Dawncaster, Mar 31, 2014
    Last edited: Mar 31, 2014
    P-51D, gross weight 9611lb was 180gal fuel, empty fuslage tank.
    P-51H, gross weight 9450lb was 260gal fuel, full tank with clean wing.
    P-51H, gross weight 9544lb was 260gal fuel, full tank with x2 bomb racks and x6 rocket racks.

    here is P-51D test reports.

    http://www.wwiiaircraftperformance.org/mustang/p-51d-na-46-130.html

    P-51D, gross weight 9611lb, 180gal fuel.

    http://www.wwiiaircraftperformance.org/mustang/p51d-15342.html

    P-51D, gross weight 9760lb, 184gal wing tank fuel + 25gal fuslange tank fuel.

    and here is P-51 tactical chart.

    http://www.wwiiaircraftperformance.org/mustang/p-51-tactical-chart.jpg

    P-51D, combat weight 10100lb with 269gal full tank.

    92gal x2 wing tanks + 85gal fuslage tank

    but P-51D's common combat weight was around 9600~9800lb, without or less fuslange tank fuel.

    so, of course P-51H was less weight than P-51D. even with full tank and x8 racks, P-51H was lighter than P-51D with empty fuslage tank, 180gal fuel.
     
  10. Aozora

    Aozora Well-Known Member

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    As GregP and daveparir and others have been saying, it is possible to get all sorts of variables from flight tests; how aircraft performed from day to day depended on all sorts of variables that are not necessarily explained in the data that has been presented - it just has to be accepted that the top speed of the P-51H varied according to the conditions under which it was tested. This is why the Pilot's manual provided 11 charts to allow the pilot to calculate his aircraft's likely performance; eg

    P-51H Weight with 2 110 gal combat tanks = 11,400 to 10,000 lbs. Maximum cruising speed @ 2,700 rpm 46" Hg 375 mph @ 25,000 or 30,000 ft

    [​IMG]

    Ditto with 2 110 gal combat tanks = 10,000 to 8500 lbs. Maximum cruising speed 2,700 rpm 46" Hg = 410 mph @ 35,000 ft or 380 mph @ 20,000 ft

    [​IMG]
     
  11. tomo pauk

    tomo pauk Creator of Interesting Threads

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    Hey, Aozora, anywhere to download that manual for the P-51H?
     
  12. mig-31bm

    mig-31bm Member

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    this one is with 2 fuel tank
    North American's Lightweight Mustangs
     
  13. Aozora

    Aozora Well-Known Member

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    Hi tomo; I got the manual via Avialogs: Aviation E-Library and more US $14 is required for 6 months of access (that reminds me I have to update!) The P-51 section includes the Pilot's manual for the XP-51J.
     
  14. Dawncaster

    Dawncaster New Member

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    #14 Dawncaster, Mar 31, 2014
    Last edited: Mar 31, 2014
    http://thehuwaldtfamily.org/jtrl/ve...A, Perf. Calc. for P-51H Mustang (NA-126).pdf

    see Report No. NA-8284-A, page 30 of 97(PDF page 33 of 106). gross weight 9450lbs without racks. of course no drop tanks.

    gross weight 9450lb, 471mph at 22700ft and 413mph at S.L

    http://www.alternatewars.com/SAC/F-51H_Mustang_SAC_-_22_March_1949.pdf

    see 1949 SAC, last page.

    c. cruise out with long range operation at 25000ft (external tanks are dropped when empty)
    d. combat at 25000ft for 5 minutes with maximum power (fluid injection) and 15 minutes with maximum power (dry)

    "performance data are flight test values and are based on AMC test and North American Report No. NA-8284-A dated November 1945."

    performance I, gross weight 9430, 410kn(471mph) at 22700ft and 359kn(413mph) at S.L <= same as NA-8284-A report

    ------------------------------------------------------------------------------------------------------------------------------------------------------------

    http://www.alternatewars.com/WW2/Aircraft/P-51HML.htm

    474mph with two 165gal tanks? serious? see "from Standard Aircraft Characteristics, F-51H Mustang, 22 March 1949"

    SAC 1949, 410kn(471 mph) with 9430lb (full internal tanks), 412kn(474mph) with 8283lb(less fuel). mission profile, take-off with two 110gal drop tanks and jettison when before starting acceleration to max speed. + basic I performance values are based on NA-8284-A report.

    so, there is no P-51H, 474mph with two 165gal tanks.
     
  15. pbehn

    pbehn Well-Known Member

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    can/could you measure it so accuratelt what about head tail winds, difference in power output and the planes surface finish?
     
  16. Aozora

    Aozora Well-Known Member

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    Ah, of course! #-o The tests in which only 451 mph was reached were taken with the "coolant shutter flush", meaning there was no ram effect...
     
  17. Dawncaster

    Dawncaster New Member

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    #17 Dawncaster, Mar 31, 2014
    Last edited: Mar 31, 2014
    but, flush position had better performance than open position.

    "Opening coolant flap wide open from flush position slowed the airplane from 349 M.P.H. I.A.S. to 325 M.P.H. at 18,000 Ft." from P-51B-1-NA AAF No. 43-12093 report.

    and even with flush position, mustang's rear scoop is not completely sealed.

    http://www.goodday.co.nz/files/attach/images/5141/117/061/bdf646d9b53cb8310b2ec621ac647531.jpg
    P-51D, flush.

    http://livedoor.blogimg.jp/p51_mustang/imgs/5/d/5d8819ee.JPG
    http://air-and-space.com/20040813 Hawthorne/DSC_2231 P-51H N551H left rear landing l.jpg
    http://cdn-www.airliners.net/aviation-photos/photos/4/5/5/0782554.jpg
    http://www.simflight.com/wp-content/uploads/2012/03/p-51h_annoucement_stiz_chopped.gif
    P-51H, flush.

    http://www.air-and-space.com/20080517 Chino/BL2_1933 P-51H N551H left side l.jpg
    P-51H, open.

    http://www.avialogs.com/en/aircraft...ight-handbook-usaf-series-f-51h-aircraft.html
    F-51H handbook, page 11 (pdf page 17)

    so, P-51H's coolant shutter is short to seal.

    in my opinion, flush position was requirement for maximum performance. if not, why they did use flush position and result called "Max"?
     
  18. Aozora

    Aozora Well-Known Member

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    #18 Aozora, Mar 31, 2014
    Last edited: Mar 31, 2014
    Note the words "wide open" - the radiator shutter was fully open, thus contributing drag http://yolo.net/~jeaton/Propplanes/p51/086p51.jpg

    That should go without saying - if the radiator exit was completely sealed the engine would overheat almost immediately.

    Read what the flight manual says (1946 edition):

    [​IMG]

    [​IMG]

    The reason for having an automatic shutter was to ensure optimum airflow through the radiator consistent with keeping the engine at its optimum temperature; the shutter's optimum position would be somewhere between fully open and flush - fully open contributes drag and reduces ram effect - fully closed and the airflow is less effective. The aircraft was tested with the radiator shutter flush to determine how this configuration would affect performance; "Max" simply means the maximum speed achieved in this configuration, as opposed to the performance with the shutter in its optimum position.

    The coolant flap emergency release was added to later production P-51Hs to ensure that the exit flap would not close to a position where the engine could overheat, probably as a result of these flight tests; not forgetting the P-51H was modified in the eight years between 1946 and 1954.

    The P-51H's radiator scoop and exit shutters were of a completely different design to that of the B/C/D/K so the test results of the H with the shutters in different positions would be different to those of the earlier models.
     
  19. Dawncaster

    Dawncaster New Member

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    #19 Dawncaster, Apr 2, 2014
    Last edited: Apr 2, 2014
    you said

    I wanted to say "P-51H had ram-effect even with coolant shutter flush position."

    P-51B/C/D/K and P-51H had completely different design or not, their radiator had same basic mechanism, so that's not problem for what I want to say.

    51H_coolant_radiator.jpg

    see P-51H pics, even with coolant shutter flush position, rear scoop had enough size.

    P-51H with no ram-effect at 450mph? how? how "coolant shutter flush position" = "no-ram effect"?

    51h_coolant.jpg
    9726797019_890daf651e_51H_coolant.jpg
    F-51_coolant.jpg
    F-51H-10-NA Mustang 44-64633_coolant.jpg
    noram-p51h.jpg
    p-51h_annoucement_stiz_chopped.jpg
    il2fb 2014-04-02 10-47-16-56_coolant.jpg
    il2fb 2014-04-02 10-47-26-06_coolant.jpg
    il2fb 2014-04-02 10-47-10-97_coolant.jpg
    il2fb 2014-04-02 10-16-35-74_coolant.jpg
    5d8819ee_coolant.jpg

    agree. and it's same as P-51B/C/D/K. but important thing is "which position make best performance?"

    As far as I know, mustang's radiator effect is follows.

    close to flush position = airflow/cooling effect low but compression high so make high thrust with low drag.
    close to wide-open position = airflow/cooling effect high but compression low so make low thrust with high drag.

    so, in my opinion, flush position had best performance or close.

    ps. damn.. I just wanted a simple way for make P-51H's FM...
     
  20. mig-31bm

    mig-31bm Member

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