Twin boom question

Discussion in 'Technical' started by Velius, Oct 25, 2008.

  1. Velius

    Velius Member

    Joined:
    Sep 4, 2007
    Messages:
    263
    Likes Received:
    0
    Trophy Points:
    16
    Occupation:
    "Mechanical installer" is my official title- a fancy way of saying that I work on A/C structures.
    Location:
    Central Texas
    Hello everyone,

    I was wondering about this the other day- what are the structural/aerodynamic advantages and disadvantages of twin boom aircraft like the P-38, Fokker G.1, FW-189, etc.?
     
  2. drgondog

    drgondog Well-Known Member

    Joined:
    Jun 28, 2006
    Messages:
    7,359
    Likes Received:
    561
    Trophy Points:
    113
    Gender:
    Male
    Occupation:
    Executive, Consulting
    Location:
    Scurry, Texas
    Can't think offhand of an advantage other than two engines when one lets go (maybe - the bromide about the purpose of the second fan is to carry you safely to the crash site) - and frequently you can not only carry a larger payload but have more room for fuel and also have the potential for more power/wt ratio for acceleration and climb. Armament packaging is more efficient

    In general, the cons are -

    It is difficult to reduce drag of a twin to anywhere close to a well designed single.

    It is heavier

    It is bigger and easier to see

    It has a higher rolling intertia

    It is more expensive

    It is more complicated and requires longer training

    With twin engines in nacelles you have 'three' fuselages to create parasite drag.

    Fuel transfer typically is more complicated

    These are not universal truths... but food for thought?
     
  3. Watanbe

    Watanbe Member

    Joined:
    Apr 24, 2007
    Messages:
    526
    Likes Received:
    0
    Trophy Points:
    16
    Occupation:
    Student, Casual
    Location:
    Adelaide
    you can load up the nose with some serious firepower, peace of mind having two engines
     
  4. comiso90

    comiso90 Active Member

    Joined:
    Dec 19, 2006
    Messages:
    3,672
    Likes Received:
    2
    Trophy Points:
    38
    Occupation:
    Video and multi-media communications expert
    Location:
    FL
    I always wondered what the performance of the P-38 would have been if it had a conventional fuselage like the mossie.

    .
     

    Attached Files:

    • p38.png
      p38.png
      File size:
      28.5 KB
      Views:
      259
  5. Velius

    Velius Member

    Joined:
    Sep 4, 2007
    Messages:
    263
    Likes Received:
    0
    Trophy Points:
    16
    Occupation:
    "Mechanical installer" is my official title- a fancy way of saying that I work on A/C structures.
    Location:
    Central Texas
    Interesting concept Cosimo. The horizontal stabilizer looks a little too small for the rest of the plane.
     
    • Useful Useful x 1
  6. comiso90

    comiso90 Active Member

    Joined:
    Dec 19, 2006
    Messages:
    3,672
    Likes Received:
    2
    Trophy Points:
    38
    Occupation:
    Video and multi-media communications expert
    Location:
    FL
    I spent 73 seconds on it... I wast designing a new aircraft,,, just a quick sketch..
    copy and paste
     
  7. kool kitty89

    kool kitty89 Well-Known Member

    Joined:
    Aug 29, 2007
    Messages:
    3,069
    Likes Received:
    36
    Trophy Points:
    48
    Gender:
    Male
    Location:
    San Jose, CA
    In the case of the P-38 the booms may have allowed more internal space than "normal" nacelles. This is significant as turbochargers were installed, and it allowed the radiators to be mounted farther back on the boom. It allowed the use of a larger and higher AR horizontal stabilizer than would normally be practical for a fuselage mounted tail.


    A twin boom configuration is also important in cases other than twin-engine a/c. Such as in a pusher configuration with the engine mounted on the rear of the central pod. This provides space for a central (unsynchronised) mounted armament like a twin, but the smaller size of a single engine a/c.

    Twin boom push-pull aircraft (Fokker D.XXIII) are also something to be noted, and generally easier to arrange than the configuraton used on the Do 335. (and is occasionally used on modern aircraft)


    It's advantageous for jets as well, as in the case of the Vampire (Venom, Sea Vixen) this allows for an aircraft with short intake and exhaust which minimizes thrust loss. (particularly important to early jets with relatively low thrust engines) Although single boom designs like the Me P.1101 gave similar advantages.
     
  8. SoD Stitch

    SoD Stitch Banned

    Joined:
    Jun 19, 2007
    Messages:
    981
    Likes Received:
    2
    Trophy Points:
    0
    Occupation:
    Heavy Equipment Rental
    Location:
    Pine Mountain Lake, California
    kk is quite right. In the case of the P-38, half of the reason for going with the twin-boom configuration was so that there was a place to put the (fairly large) turbo-superchargers; a conventional nacelle would not have worked for the Allison V-1710 engines AND the turbo-superchargers, there simply would not have been enough room. It also incidentally provided a convenient place to house the main landing gear.
     
  9. kool kitty89

    kool kitty89 Well-Known Member

    Joined:
    Aug 29, 2007
    Messages:
    3,069
    Likes Received:
    36
    Trophy Points:
    48
    Gender:
    Male
    Location:
    San Jose, CA
  10. kool kitty89

    kool kitty89 Well-Known Member

    Joined:
    Aug 29, 2007
    Messages:
    3,069
    Likes Received:
    36
    Trophy Points:
    48
    Gender:
    Male
    Location:
    San Jose, CA
    Stich, I think it could have worked, but the nacelles would have had to be long to have space (and proper positioning) for the landing gear. (or switch to a taildragger) The radiator could have gone under the foreward part of the nacelle, like the one on the P-40's nose.

    However, with the large nacelles (probably weighing almost as much as the previous booms) and the added weight of the fuselage, the aircraft would probably have been somewhat heavier.


    The push-pull twin boom configuration is interesting as it eliminates the extra drag and rotational inertia (though the small booms will still add some) of outboard placed engines, and is significantly simpler than the Do 335's arrangement. (however, only a small armament would be able to be sone mounted, and -except for an engine cannon- would have to be synchronized)


    And, Bill, most of what you discussed was common to all twin engined aircraft. I think the question was what was the advantages of the twin boom configuration compared to wing mounted nacelles with a central fuselage. (though, as I introduced, there are many other possibilities for the twin boom arrangement)
     
  11. Marcel

    Marcel Well-Known Member

    Joined:
    Sep 19, 2006
    Messages:
    6,977
    Likes Received:
    570
    Trophy Points:
    113
    Gender:
    Male
    Occupation:
    Bioinformatician
    Location:
    Dordrecht
    In the G.1 the configuration was made like this because the rear observer/gunner got a good view to all side (even under) while still being very close to the pilot, which was preferred by Fokker.
    [​IMG]
     
  12. Micdrow

    Micdrow “Archive”
    Staff Member Moderator

    Joined:
    Aug 21, 2006
    Messages:
    7,716
    Likes Received:
    424
    Trophy Points:
    83
    Occupation:
    Manufacture Tech
    Location:
    Wisconsin
    As a side note after listening to lectures on the P-38 glacier girl and Ruff Stuff another advantage was that with the weapons in the center they where easier to aim. Conventunal fighters with the engine in front are subject to more vibration in the nose making it harder to aim. There is very little if any vibration in the nose of a P-38 when it comes to aiming during battle.

    Also with all your guns in central locations they pack a greater punch then say a mustang that has to offset there guns to a certain range or distance to bring all guns into play to hit the target at the same time.
     
  13. Watanbe

    Watanbe Member

    Joined:
    Apr 24, 2007
    Messages:
    526
    Likes Received:
    0
    Trophy Points:
    16
    Occupation:
    Student, Casual
    Location:
    Adelaide
    Also has advantages of range, don't forget!
     
  14. kool kitty89

    kool kitty89 Well-Known Member

    Joined:
    Aug 29, 2007
    Messages:
    3,069
    Likes Received:
    36
    Trophy Points:
    48
    Gender:
    Male
    Location:
    San Jose, CA
    Micdrow,

    I noted that already in post #7. The twin-boom (single engine) pusher also allowed this. (the push-pull obviously would not)

    Of course, you could still mount nose (or wing root) guns on a/c with a tractor propeller on the nose, but they would have to be synchronized (except for an engine gun) which reduced RoF and excluded weapons not able to be synchronized. The size and number of weapons are also more limited given they all have to fit around the engine and compete for ammo space. (except for wing root guns)
     
  15. Marcel

    Marcel Well-Known Member

    Joined:
    Sep 19, 2006
    Messages:
    6,977
    Likes Received:
    570
    Trophy Points:
    113
    Gender:
    Male
    Occupation:
    Bioinformatician
    Location:
    Dordrecht
    You are all talking about the advantages which are shared between all twin engined fighters. I think the question was why a twin boom construction. I believe in several cases this was because of the visibility for the gunner in the rear. Could the P38 configuration been chosen because of the tricycle gear?
     
  16. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
    Staff Member Moderator

    Joined:
    Apr 9, 2005
    Messages:
    23,206
    Likes Received:
    788
    Trophy Points:
    113
    Gender:
    Male
    Occupation:
    Aircraft Maintenance Manager/ Flight Instructor
    Location:
    Colorado, USA
    I believe that Kelly Johnson wanted to build an interceptor that could carry a big gun and could climb extremely well. At the time the P-38 design team thought the only way to achieve the design goals was with a supercharged twin. Using the twin boom alleviated bulky nacelles and lended it self for a nice turbocharger installation. Also remember - those responsible for the design of the P-38 thought that no more then a handful of the aircraft would be produced.
     
  17. Marcel

    Marcel Well-Known Member

    Joined:
    Sep 19, 2006
    Messages:
    6,977
    Likes Received:
    570
    Trophy Points:
    113
    Gender:
    Male
    Occupation:
    Bioinformatician
    Location:
    Dordrecht
    Good point Joe, I forgot about the superchargers. Twin booms was a neat solution indeed.
     
  18. comiso90

    comiso90 Active Member

    Joined:
    Dec 19, 2006
    Messages:
    3,672
    Likes Received:
    2
    Trophy Points:
    38
    Occupation:
    Video and multi-media communications expert
    Location:
    FL
  19. Graeme

    Graeme Well-Known Member

    Joined:
    May 31, 2007
    Messages:
    2,729
    Likes Received:
    170
    Trophy Points:
    63
    Gender:
    Male
    Couple of illustrative advantages.

    In the case of the ANT-23, the booms provided access for the recoilless cannons...

    [​IMG]

    For White Night, it allowed a large payload to be carried...

    [​IMG]

    And it remains an active concept in Homebuilts. The latest(?) being The New Horizons design. In their words, eliminating visibility problems...

    "Our design is a pilot-forward design, keeping the wings and propulsion system aft of the pilot thereby eliminating visibility issues common in the traditional "tractor" designs."


    New Horizons Aircraft Inc. | Prototype Aircraft, Light Sport Airplane, Experimental Airplane


    [​IMG]
    [​IMG]

    Some of their future designs...

    [​IMG]
    [​IMG]
    [​IMG]
     
  20. SoD Stitch

    SoD Stitch Banned

    Joined:
    Jun 19, 2007
    Messages:
    981
    Likes Received:
    2
    Trophy Points:
    0
    Occupation:
    Heavy Equipment Rental
    Location:
    Pine Mountain Lake, California
    Good point, Joe. The requirements the USAAC were looking for virtually ruled out the use of a single engine; at that time (1938 ), there was no single engine (yet) on the market that provided adequate performance, hence the use of twin engines. Since twin engines were required (and also twin turbo-supercharger), Lockheed's airframe options were extremely limited.

    And, yes, at that time Lockheed figured they'd be lucky if they got an order for 50 (yes, that's right, I said 50) from the USAAC, instead of the over 5,000 that ended up being produced before War's end; the first models were virtually "hand built" before the institution of the assembly line in 1942.
     
Loading...

Share This Page