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Aerospace Aerospace people get in here quick, i need help w/ a question.

  1. Jan 22, 2005 #1
    most airplanes are designed so that the outer tips of the wing are higher than the wing roots attached to the fuselage in order to:

    streamline the fuselage.










    i remember that's the reason, but i think i'm wrong.
     
  2. jcsd
  3. Jan 22, 2005 #2
    The angling of the wings upwards is known as dihedral. Its main purpose is for stability. It produces a coupling between roll and yaw, that makes an aircraft more pleasant, and safer to fly.

    There may be other advantages, such as keeping the wings clear of ground obstacles when taxiing, but the stability effect is the main reason AFAIK.
     
  4. Jan 22, 2005 #3
    thanks! another question if you could help please:

    the standard weight for gasoline used in an airplane is: ?
     
  5. Jan 22, 2005 #4
    by the way is that: lateral stability or longitudinal stability?






    thanks
     
  6. Jan 22, 2005 #5

    Astronuc

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    Staff: Mentor

    AVIATION TURBINE FUEL (JET FUEL)

    CIVIL JET FUELS

    Aviation turbine fuels are used for powering jet and turbo-prop engined aircraft and are not to be confused with Avgas. Outside former communist areas, there are currently two main grades of turbine fuel in use in civil commercial aviation : Jet A-1 and Jet A, both are kerosine type fuels. There is another grade of jet fuel, Jet B which is a wide cut kerosine (a blend of gasoline and kerosine) but it is rarely used except in very cold climates.

    JET A-1

    Jet A-1 is a kerosine grade of fuel suitable for most turbine engined aircraft. It is produced to a stringent internationally agreed standard, has a flash point above 38°C (100°F) and a freeze point maximum of -47°C. It is widely available outside the U.S.A. Jet A-1 meets the requirements of British specification DEF STAN 91-91 (Jet A-1), (formerly DERD 2494 (AVTUR)), ASTM specification D1655 (Jet A-1) and IATA Guidance Material (Kerosine Type), NATO Code F-35.

    JET A

    Jet A is a similar kerosine type of fuel, produced to an ASTM specification and normally only available in the U.S.A. It has the same flash point as Jet A-1 but a higher freeze point maximum (-40°C). It is supplied against the ASTM D1655 (Jet A) specification.

    (see http://imartinez.etsin.upm.es/dat1/eCombus.htm for a comparison of fuel properties including Jet-A).

    JET B

    Jet B is a distillate covering the naphtha and kerosine fractions. It can be used as an alternative to Jet A-1 but because it is more difficult to handle (higher flammability), there is only significant demand in very cold climates where its better cold weather performance is important. In Canada it is supplied against the Canadian Specification CAN/CGSB 3.23

    MILITARY

    JP-4

    JP-4 is the military equivalent of Jet B with the addition of corrosion inhibitor and anti-icing additives; it meets the requirements of the U.S. Military Specification MIL-PRF-5624S Grade JP-4. JP-4 also meets the requirements of the British Specification DEF STAN 91-88 AVTAG/FSII (formerly DERD 2454),where FSII stands for Fuel Systems Icing Inhibitor. NATO Code F-40.

    JP-5

    JP-5 is a high flash point kerosine meeting the requirements of the U.S. Military Specification MIL-PRF-5624S Grade JP-5. JP-5 also meets the requirements of the British Specification DEF STAN 91-86 AVCAT/FSII (formerly DERD 2452). NATO Code F-44.

    JP-8

    JP-8 is the military equivalent of Jet A-1 with the addition of corrosion inhibitor and anti-icing additives; it meets the requirements of the U.S. Military Specification MIL-T-83188D. JP-8 also meets the requirements of the British Specification DEF STAN 91-87 AVTUR/FSII (formerly DERD 2453). NATO Code F-34.

    ============================

    The wings are angled up (dihedral) for lateral stability. Longitudinal stability is produced by sweeing the wings back, in addition to stablilizers, and counterweight.
     
  7. Jan 22, 2005 #6
    thanks, but i need the weight in lbs. like is it 6lbs./U.S. gal. or 7.5 lbs./U.S. gal.?




    thanks
     
  8. Jan 22, 2005 #7

    Astronuc

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    Staff: Mentor

    Well the fuel comparison has Jet-A fuel density in the range of 780..840 kg/m3.

    I think one should have access to a English (Bristish) to SI conversion table.

    1 kg = 2.2046 lbm

    3.785412 E-03 m3 = 1 gal

    I would strongly encourage all US students in engineering to become fluent in SI as well as English units, and be able to easily and accurately conver between the two systems. In a global market, where most of the world uses SI, it is advisable to know both. I work in both systems, but prefer SI (mks, cgs).
     
  9. Jan 22, 2005 #8
    My major is geoscience, and i'm taking the AFOQT (air force officer qualifying test) in which i'm on the aviation information part, and since i'm working for a fighter/bomber track, i have to make a good score on it.





    :frown:
     
  10. Jan 23, 2005 #9

    FredGarvin

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    The specific gravity of JETA which is the most common fuel used is, on average, about .82. That means it's equivilent to about 6.8 Lbm/gal.

    You're on the fighter/bomber track and you're asking what dihedral is for? You've got some serious studying to do.
     
    Last edited: Jan 23, 2005
  11. Jan 24, 2005 #10

    russ_watters

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    Staff: Mentor

    Indeed, in engineering, even just in college, you will likely need to use both.
     
  12. Jan 26, 2005 #11
    Just an added note!
    I don't know how many in the US are aware, but several years ago, Congress decided to make a complete conversion to a Metric standard, however some unions decided to throw their weight around. (In those days unions were much stronger in the US than they are now). These unions demanded that taxpayers be made to pay for all metric tools required by tradesmen, so Congress decided to forget it. As result, we are changing but very slowly and irregularly. Additionally we have to concern ourselves with the added step of constant conversions back and forth.

    KM
     
  13. Jan 27, 2005 #12

    FredGarvin

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    Science Advisor

    Personally I could care less what system of units I use in calculations. They are both equal in my opinion. The one thing that we have not done is go over to metric in our designs. That to me is OK too. I have a much better feeling for what a thousandths of an inch is versus a tenth of a millimeter and such.
     
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