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Big ships can be fast but big planes cannot.

  1. Sep 20, 2004 #1
    Just before world war 2 there were many big planes and tanks that had lots of guns but were slow. People were trying to make the equivalent of battleships which had lots of guns and armor and were often faster than than smaller ships. however large planes and tanks were impractical. Why?
     
  2. jcsd
  3. Sep 21, 2004 #2

    Integral

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    It is not clear what you mean?

    Tanks grew through out WWII, compare a King Tiger to a PzIII or better yet a PzII, it was the PzIIs and PzIIIs that went into Poland in '39 and France in '40. The Tigers were not introduced until '44 and '45. Likewise for the Planes compare a Super fortress to the bombers used in The Battle for Britain.

    Now what is your question.
     
  4. Sep 21, 2004 #3

    Gokul43201

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    Most Carriers (big) can do about 30 knots on a sprint. The HSVs (fast) do about 50 knots. Speed ratio (big/fast) = 0.6

    The C5 Galaxy (big) does about 500 mph, while the SR-71 has a top speed of over 2000 mph. Ratio < 0.25 (Ratio's small, < 0.3, even if you compare with an F-15).

    Is this the question ?
     
  5. Sep 21, 2004 #4
    @Gokul43201 that is in essence is my question. I would like it answered in general and I want to know why the speed ratio was even more drastic in the 1930s.

    @Integral
    I am talking about land battleship tanks with many turrets experimented with before world war 2 such as the t32
    http://www.nemo.nu/ibisportal/5pansar/5sidor/t321.htm
    similar mistakes were made with experimental planes.
     
  6. Sep 21, 2004 #5

    russ_watters

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    A ship that doesn't plane has what's called a "displacement hull." Displacement hull ships have a top speed that's proportional to the square root of the water line length. At "hull speed" (the max speed for that ship), the ship sits in a trough between the bow and stern waves and going faster means lifting the ship out of the water to ride up the bow wave. So while a frigate tops out at 29 knots - and I know from experience that doubling the engine output at 25 knots only pushes you up to 29 - a carrier actually tops out at about 45.

    For airplanes, all subsonic jets go about the same speed plus or minus 10% (mach .8 or so). And then, the difference is only due to wing cross section and sweep.

    One of the first SR-71 sketches was of a hydrogen powered monster that would have been 300 feet long. Size is not a major factor in airplane speed.
     
    Last edited: Sep 21, 2004
  7. Sep 21, 2004 #6
    Hey thanks, I learned something new today.
     
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