P47 dorsal fillet

Discussion in 'Aviation' started by rogerwilko, Jan 18, 2015.

  1. rogerwilko

    rogerwilko Member

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    Why so long until late series to fit dorsal fillet to P47's? More powerful engines causing extra swing on takeoff?
     
  2. Capt. Vick

    Capt. Vick Well-Known Member

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    Wasn't it on the bubble tops because of the loss of fuselage from the razor backs? And maybe resolving some bubble top turbulence problems?
     
  3. GregP

    GregP Well-Known Member

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    #3 GregP, Jan 18, 2015
    Last edited: Jan 20, 2015
    Yes it was. It was there due to loss of vertical surface area when they went to a bubble canopy. It showed up rapidly after the bubble conversion ... at least according to many sources.
     
  4. rogerwilko

    rogerwilko Member

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    So how many produced before fillets were fitted on bubble tops? I suppose this subject could apply to P51's as well.
     
  5. GregP

    GregP Well-Known Member

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    From: P-47 Thunderbolt variations and production

    The USAAF fitted a standard P-47D-5-RE airframe (serial number 42-8702) with a bubble canopy taken from a Hawker Typhoon. In order to accommodate the bubble canopy, the Republic design team had to cut-down the rear fuselage. This conversion was redesignated XP-47K, and was tested in July 1943. This modification was immediately proven to be feasible, and was promptly introduced on both the Farmingdale and Evansville production lines.

    Ordinarily, the USAAF would have given such a radical modification a completely new variant letter. The USAAF chose instead to designate it simply by giving it a new production block number in the D-series. The first batches to feature this new bubble canopy were Farmingdale's P-47D-25-RE and Evansville's P-47D-26-RA. These batches also had the R-2800-59 or -63 engines, the paddle-bladed propeller, and the "universal" wing first introduced on the "razorback" P-47D-20-RE. Stronger belly shackles capable of carrying a 91.6 Imp. gall. drop tank were fitted. This tank, together with the 170.6 Imp. gall. main fuselage tank, an 83-gallon auxiliary fuel tank and two 125-gallon underwing tanks, made it possible to carry a total fuel load of 595 gallons, providing a maximum range of 1800 miles at 10,000 feet.

    The early "bubble-canopy" Thunderbolts had suffered from some directional instability as a result of the loss of aft keel area. From the P-47D-30-RE production lots onward, a dorsal fin was fitted just ahead of the rudder. This innovation successfully restored the stability.The high diving speeds of which the Thunderbolt was capable pushed the aircraft into the edge of compressibility, and new blunt-nosed ailerons were fitted to improve controllability at these high speeds. In order to help in dive recovery at these high speeds, an electrically-operated dive recovery flap was fitted on the undersurfaces of each wing. Republic Farmingdale produced a total of 2547 bubbletop P-47D's and Evansville produced 4632.
     
  6. rogerwilko

    rogerwilko Member

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    Thanks Greg. Does this apply to the P51's as well?
     
  7. GregP

    GregP Well-Known Member

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    #7 GregP, Jan 20, 2015
    Last edited: Jan 20, 2015
    The P-51 dorsal fin was needed before the bubble canopy, as evidenced by the addition of dorsal fins to the razorback P-51Bs/Cs. Here is one:

    54191.jpg

    And though that image may be modern, there are shots from WWII with P-51B/C models in formation ... some with and some without the dorsal fin. It was definitely needed when the P-51 lost some keel area with the introduction of the bubble canopy, but the earlier B/C models could have used it due to the detabilizing effects of adding power without adding rear vertical area.

    It wasn't catashrophic loss off stability, but it did show up in high power operation. Why not restore the flying characteristics as intended by the designer?

    This sort of thing shows up in even low-powered civil aircraft, too, when rear keel area is lost or when forward keel area is added, such as when a landplane get floats. Most float-equipped planes that started life as landplanes dislpay added keel below the fin or SOMEHERE at the rear to restore lost stability. They could get by without it, but the added area returns the benign flying characteristics of the landplane version.
     
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  8. bobbysocks

    bobbysocks Well-Known Member

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    #8 bobbysocks, Jan 20, 2015
    Last edited: Jan 20, 2015
    from what i understand the dorsal fin was needed because of the merlin engine. the airframe was designed with the allison in mind and when the brits dropped the merlin in with its increased horsepower and torque a few problems cropped up. i have read of empennage failures contributed to the change in engine but have yet to find a definative explaintion of what the failure was. the reports were not very specific...did the airframe twist or break or???

    also the dorsal fin didnt come out until around the 51D-5 or shortly after. all B/C models on the bases that were still airworthy got the mod as well.
     
  9. GregP

    GregP Well-Known Member

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    Here is a formation of C/D models with and without the dorsal fin.

    View attachment 282502

    Here is a pic of a P-51C with the fin. The caption says it was added to counter the stability loss encountered when the fuselage fuel tank was added ... but that is from Wiki and is probably as authentic as my $3 bill.

    View attachment 282503
     
  10. bobbysocks

    bobbysocks Well-Known Member

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    #10 bobbysocks, Jan 20, 2015
    Last edited: Jan 20, 2015
    well did a little digging andf found the tech order for the mod. it is T.O. 01-60J-18 dated april 8, 44 ( page 9 of the PDF on site below ) about a month after the first D models were delivered to some units. TO state right off the top.

    1. To reduce possiblilty of empennage failure of horizonal stabilizer and fin......

    TO 01-60J-18 Reinforcement of horizontal stabilizer and fin - P-51B, P-51C, P-51D and P-51K

    i know the B/C had them as some of them were still flying almost up till the end of the war. but there were also a bunch of D models that were delivered that did not have them from the factory and the mod had to be fitted on them as well.

    on the crazy horse photo site he posts that tails were ripped off due to the 51 going into a snap roll while performing a slow roll....but i dont believe everything people post. i cannot find the actaul reports stating tails were ripped from the fuse...

    *** CRAZY HORSE AVIATION PHOTOGRAPHY ***
     
  11. GregP

    GregP Well-Known Member

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    #11 GregP, Jan 20, 2015
    Last edited: Jan 21, 2015
    According to recent Crazy Horse graduates, that snap roll in the middle of a slow roll was true and that WAS one of the reasons it was added. The pilot is cautioned not to slow roll the P-51D. They also stated it wasn't the ONLY reason, but didn't elaborate any further.

    Perhaps we'll locate all the info in it. I'd bet Bill (Drgondog) knows. Someone please ask him who doesn't automatically piss him off whenever they post anything, as I seem to do.

    Personally I am somewhat amazed at how simple the P-51D tail is and feel that it probably should be strengthed. I have seen one drilled off the rear fuselage, repaired and reinstalled. It is currently flying on the Museum's P-51D "Spam Can." Not much structure there!

    Of course the same can be said for quite a few planes of the time. They were strong enough but not overly strong, as befits an optimized design.
     
  12. rochie

    rochie Well-Known Member

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    Surely a Typhoons canopy would not fit on a P-47 !
    Did a bit of digging and from what I can see, the USAF liked the Typhoon bubble canopy and adapted the idea for their P-47 and P-51's but didn't fit actual Typhoon canopies to them.

    They look totally different on all three machines to me
     
  13. GregP

    GregP Well-Known Member

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    They took the concept and ran with it ... but DID credit the Hawker Typhoon designer with the idea. It seems to have been a VERY good idea since almost all modern fighers, 75 years later, are still using it. Every time they don't, they finally realize they SHOULD have ... and go back to it.
     
  14. rochie

    rochie Well-Known Member

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    Agree 100% Greg but that website gives the impression that stock Hawker Typhoon bubble canopies were fitted, very different to what really happened
     
  15. BiffF15

    BiffF15 Well-Known Member

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    And with the F16 / F22 they finally put it on properly (with the canopy bow at the back)!

    Cheers,
    Biff
     
  16. GregP

    GregP Well-Known Member

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    I wonder why THAT part took so long?

    Hey Biff, maybe you can answer these quewstions ...

    1) Why is the canopy tinted with gold?

    2) Does it affect evening and mornign vision in low light but still light enough to see?
     
  17. bobbysocks

    bobbysocks Well-Known Member

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    i wonder if the snap roll issue became more pronounced when the fuse tanks was added or was a result because it was?
     
  18. GregP

    GregP Well-Known Member

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    #18 GregP, Jan 21, 2015
    Last edited: Jan 21, 2015
    Not too sure, but it IS in the POH. Also, the Mustang has a really nasty developed spin. It can eat up 10,000 feet recovering! If the pilot ctaches the spin in the first turn, recovery is almost immediate. When it develops, the nose oscillates from almost vertically downward to just about slightly nose up, and it can take more than a few turns to get the recovery timed so it works.

    Fortunately, the P-51 is well mannered and gives the pilot a good warning before it stalls. If you pay attention you can avoid the stall-spin easily. If you are pulling some g's and feel the stall warning, you'd best not pull any harder and would be well advised to back off the back pressure slightly for saftey. Most really good flying planes gave a good stall warning.

    The Fw 190 was famous for having almost no stall warning at all. It is an example of a good-flying plane that was difficult to fly near the limit due to the lack of stall warning. Maybe the experts could do it, but more than a few stalled and went in at low altitude in a vertical reverse.

    The Bf 109 had no such issue and gave a very pronounced warning near the stall. You could horse it around right at the edge of stall and be comfortable doing it. In fact, you could still point the nose even IN a stall. That was one of the reasons why the top scoring aces of the Luftwaffe stayed with the Bf 109 ... they were very familiar with its stall characteristics and were not impressed by the Fw 190's stall at all. Familiarity lends comfort in a tight situation.
     
  19. BiffF15

    BiffF15 Well-Known Member

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    Greg,
    1. You will have to ask a Viper guy...
    2. No. Doesn't impede vision at all.
    Cheers,
    Biff
     
  20. fubar57

    fubar57 Well-Known Member

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    From Cybermodeler...The canopies of production F-16A/B aircraft were clear, though with the introduction of the gold-tinted canopies with the F-16C/D (designed to reduce the aircraft’s radar cross-section), the tinted canopies quickly found their way into the F-16A/B fleet.

    You’ll see many photos of F-16A/Bs with tinted canopies and clear rear canopies as the fixed rear sections were not changed out as quickly. Ironically, these aircraft (along with most of total F-16 fleet) are being switched back to clear canopies to make the aircraft night vision goggle (NVG) compatible.

    Geo
     
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