Compressibility problems

Discussion in 'Aviation' started by MaxQ, Nov 5, 2007.

  1. MaxQ

    MaxQ New Member

    Joined:
    Nov 4, 2007
    Messages:
    3
    Likes Received:
    0
    Trophy Points:
    1
    Occupation:
    jet mech
    Location:
    CT
    I'v read that quite a few US fighters ran in to compressibility problems during dives. Except for the Me262 I don't recall if any other German fighters had this problem, or other fighters from differant countries.
    MaxQ
     
  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
    Max - virtually all of the high performance a/c would enter compressibility in a dive, speed dependin on Critical mach number of the wing. The complications that arose were formation of a shock wave at the point where the velocity was greatest over the wing - leading to separation, change of center of lift, turbulent flow over stabilizer, etc

    all bad things.

    the Me 262 you used as an example would start to mask the horizontal stabilizer effectriveness and move the center of lift aft (IIRC) which in turn would cause the nose to tuck - but at a higher diving speed than the 51 or 47 or 38.
     
  3. mad_max

    mad_max Member

    Joined:
    Oct 4, 2006
    Messages:
    113
    Likes Received:
    1
    Trophy Points:
    18
    The P-51 had a limiting safe Mach of .80-.81 depends if British or American data.

    Atfirst the P-38 was around .65 until dive recovery flaps were installed, then it was
    around .75 from what I gather.

    The P-47 had a limiting safe Mach number of around .79.

    Most Luftwaffe fighters had a limiting safe Mach number of about 0.75 (Bf-109, Fw-190A), while the Dora comes out to 0.77.

    The Spit's was a safe Mach number of 0.83.

    The Me-262's limiting safe Mach is .83.

    Sure most could be dove at higher mach, but your taking a chance of structural
    failure and/or uncontrolled flight.

    So yes the 262 had a slightly higher dive speed. Over the Mustang of approx. 14 mph at
    30,000ft and 20,000 ft. At 10,000 ft approx. 5 mph. All from Mach tables.

    Disclaimer....the above can change with further information.
     
  4. 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
    The primary issue wasn't stucture - it was the aerodynamic forces which caused unwanted control inputs and change in attitude that made airframe structure inadequate.

    At .82-.85 the Me 262 intial shock wave/compressibility effects caused the horizontal stabilizer to start becoming ineffective and the Center Lift moved toward cg, then aft causing a pitch down that would not correct..

    At .78-.81 the Mustang started a severe yaw to right and even the boosted trim tab on the rudder became less effective at controlling that yaw- somewhere in the dive the 51 tail was in danger of failure.. You DID NOT want to use trim to get out of a compressibility dive.

    Etc, etc
     
  5. mad_max

    mad_max Member

    Joined:
    Oct 4, 2006
    Messages:
    113
    Likes Received:
    1
    Trophy Points:
    18
    These limits are supposed to be max. limits for tactical control. Not the max. that
    was higher, but dangerous to perform. My fault if anyone thought this was the Max.
    Mach numbers that a specific airframe could achieve.
     
Loading...

Share This Page