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Thread: Help I cant figure it out!!

  1. Default Help I cant figure it out!!

    Can anyone help me out here. I am trying to figure out:
    If the final approach speed in a C172 at Daytona Beach Intl. is 65 knots... then what would it be at Denver Intl? What airpseed will increase? And what will this effect during the landing of the aircraft?

    I am sure the airspeed will increase but im not sure by how much. And I have no idea what it means by "which airspeed will increase?". And I am also unsure about how this will effect the landing of the aircraft. If anyone could help me that would be great.


    http://comm.db.erau.edu/media2/galle...os/erauelk.gif

  2. #2
    Join Date
    Mar 2005
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    Anchorage, AK
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    Default RE: Help I cant figure it out!!

    The speed is the same. My home airport's at 4475 ft, and I fly 65 in a 172 for my speed on final. The only difference is that we're leaning our mixture as part of the runup. Another effect is that on hot days, our density altitude will be up around 6-7,000. Doesn't affect speeds at all, it just takes longer to get to those speeds and overall decreased performance.

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    Commercial Pilot ASEL - Instrument Rated
    Air Traffic Controller - Anchorage

  3. #3
    Join Date
    Mar 2005
    Location
    Indianapolis, Indiana, United States.
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    Default RE: Help I cant figure it out!!

    ^
    |
    |
    |

    Listen to him, he knows what he's talking about. The only airspeeds in a 172 that vary with altitude (IAS), that I can think of off the top of my head are Vx and Vy.

    -Khir
    Private ASEL
    "When logic and proportion
    have fallen sloppy dead,
    and the White Knight is talking backwards,
    and the Red Queen's 'Off with her head!'
    Remember what the dormouse said:
    'Feed your head. Feed your head.'"
    -Jefferson Airplane, White Rabbit

  4. #4
    toddrf Guest

    Default RE: Help I cant figure it out!!

    So are you saying that an indicated airspeed of 65 knots in Miami on a standard day has the same ground speed (no wind) as does an indicated airspeed at Denver on a standard day with no wind?

    Todd :-wave

  5. #5
    Join Date
    Mar 2005
    Location
    Indianapolis, Indiana, United States.
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    725

    Default RE: Help I cant figure it out!!

    No, but ground speed is not what we're discussing. You don't look at the GPS or DME and fly your approach at 65 kts over the ground, do you?

    GS and TAS will change, but I was thinking in terms of reference speeds for the aircraft, not in terms of different ways of measuring speed.

    -Khir
    Private ASEL
    "When logic and proportion
    have fallen sloppy dead,
    and the White Knight is talking backwards,
    and the Red Queen's 'Off with her head!'
    Remember what the dormouse said:
    'Feed your head. Feed your head.'"
    -Jefferson Airplane, White Rabbit

  6. Default RE: Help I cant figure it out!!

    Think of your indicated airspeed (IAS) as reality in terms of what keeps your airplane functioning as it should while in the air. No matter what your altitude, an IAS is an “indication” of the pressure of the air on the pitot tube and the surfaces of the airplane. You should expect the same function and feel of the aircraft at 65 knots IAS whether you are at sea level or 10,000 feet and regardless of wind speeds.

    What is very important for you to understand is that your True Airspeed (TAS) and your ground speed increase dramatically as you increase altitude. When you land at Daytona at 65K IAS (notwithstanding any winds) you will contact the ground at a significantly lower ground speed than the same landing at Denver. You will have to physically move faster relative to the earth to generate the same air pressures in Denver than in Daytona simply because there is less air in Denver.

    Actually, I would like to hear from other pilots on this one. I have, off and on, flown GA aircraft for many years. I have yet to figure out what good true airspeed is to the average pilot. IAS tells me where I am in relationship to my in-flight envelope. Ground speed tells me where I am relative to going somewhere and where I am in relationship a transition into or out of my flight envelope (you know, take off and landing). True airspeed has always impressed me as some meaningless math exercise.

    I suppose it could be used as a means of approximating ground speed knowing density altitude and winds aloft but by the time I made that calculation, I would be in the wrong county anyway.

    Dick


  7. #7
    Join Date
    Mar 2005
    Location
    Indianapolis, Indiana, United States.
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    725

    Default RE: Help I cant figure it out!!

    TAS is used most often in the IFR environment. If you file a flight plan, you are asked to provide your TAS. Why? For simplicity's sake. As you move through weather systems your GS is going to change, in a lot of cases, it's going to change quite a bit. Which is easier for you, controllers, and FSS personnel? "Ground speed is 130 until I hit OOM, then it should be about 160 until I hit VHP. After that if the forecast is right I'll be at about 110....etc....etc...."

    -or-

    "True Airspeed will be 120."

    ;-)

    -Khir
    Private ASEL
    "When logic and proportion
    have fallen sloppy dead,
    and the White Knight is talking backwards,
    and the Red Queen's 'Off with her head!'
    Remember what the dormouse said:
    'Feed your head. Feed your head.'"
    -Jefferson Airplane, White Rabbit

  8. Default RE: Help I cant figure it out!!

    Thanks Khir,

    Now I don't think I have missed much. My flying as PIC has been very much limited to severe-clear VFR. My instrument training has been limited to what might bail me out in an emergency. So far I have been smart enough to not need it.

    Dick


  9. Default RE: Help I cant figure it out!!

    [font size="1" color="#FF0000"]LAST EDITED ON Mar-22-03 AT 08:16PM (EST)[/font][p]All performance numbers are based on TAS. When flight planning, IFR or VFR, and finding groundspeed (and hence range, endurance, flight time, fuel-burn, etc) you start with a TAS value, which can be found using a cruise performance chart. TAS will also allow you to compare actual and stated aircraft performance, as well as performance between aircraft. And important for commercial certificate students....pivotal altitude is based on TAS not GS:)

    Your true airspeed will change during the flight and during different phases of the flight's profile. It is typically lower on climb and approach than it is during cruise in descent. This simply has to do with the airplanes' capabilities. A climb at 100 KIAS and full power will yeild a slower TAS then cruising at 135 KIAS. Airplanes do typically accelerate to cruise speed after all. You give FSS only your estimated cruise TAS. This allows them to calculate ETA and any deviations from it. This is especially useful in a non-radar environment.


    Brad

  10. Default RE: Help I cant figure it out!!

    To add to the rest......

    Since it's already been mentioned that your ground speed would be higher at Denver, although indicated is the same; you'll also find that most high altitude runways are longer & your pattern may even be wider depending on aircraft.

    Ladamson

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