Results 1 to 7 of 7

Thread: Speed relativity in flight? (physics and real life)

  1. Default Speed relativity in flight? (physics and real life)

    Hi. I wonder:

    When plane is very high it appears (for observant in earth) to be almost not moving, while airplane flying at 100 feet would fly above us very very quickly.

    Question 1 : How does it look like from perspective of pilot? Is it the same or opposite?

    Question 2:

    If plane is moving with 150 nm/h at 100 feet, if given plane will fly at 100.000 feet - would his realtive (ground speed) increase because of the altitude(for pilot it would be still 150nm/h) ?

    Extra question 3: does any of it works in flight simulator?

  2. #2
    Join Date
    Mar 2005
    Location
    Westminster, CO
    Posts
    7,067

    Default

    1. It's the same -- horizontally as well as vertically. It's a function of distance.

    2. We have to ask whether the 150 knots (NM/hr) is indicated or true airspeed -- a big difference. The airspeed indicator is a pressure gauge, fed by air pressure through the pitot tube, so it's a good indicator of relative air density transcribed into aircraft performance, that is, stall speed, best rate of climb, etc. roughly remain the same whether near sea level or at 10,000 feet with the same indicated airspeed. But that doesn't tell your actual speed in relation to the air except under standard conditions at sea level.

      True airspeed, is your actual speed in relation to the air, but tells the pilot nothing about how the airplane will fly -- it's only useful (after also figuring wind effects, giving you ground speed) to figure how long a trip will take.

      So if you're discussing indicated airspeed as you climb then the ground speed will, indeed, increase with increasing altitude (assuming winds remain the same). If you're referencing true airspeed, then ground speed will not increase with altitude.

    3. Yes, this works the same in FS as in real life, provided that you have your airspeed indicator set to indicated airspeed (there is a menu choice to use true airspeed, but it's useless to a pilot).

    Larry N.

    As Skylab would say:
    Remember: Aviation is NOT an exact Science!

  3. Default

    1. I'm asking about true airspeed. 150nm/h in both cases.

    2. I'm not asking about effects like effect of pressure, wind, air resistance etc - but more "high level" effects like time dilatation, weaker gravity or advantage/disadvantage of flying in high altitudes - based on curvature of earth.

  4. #4
    Join Date
    Mar 2005
    Location
    Westminster, CO
    Posts
    7,067

    Default

    Well, I think I answered 1), but for the revised 2) any effects from those causes are so small, if any, that they are beyond consideration for a pilot -- negligible as far as practical flight is concerned. For any of that information you'll need a scientist with the relevant background -- it's beyond me.

    Larry N.

    As Skylab would say:
    Remember: Aviation is NOT an exact Science!

  5. #5
    Join Date
    Mar 2005
    Location
    Montreal, Quebec
    Posts
    2,079

    Default

    Negligible effect on such a small scale as a single planet for this branch of physics.
    -----------------------------------------
    Simon

  6. #6

    Default

    Q!1: Answer the same Q2: Answer150 kt. Question 3: Answer Yes

  7. #7

    Default

    Quote Originally Posted by hhans View Post
    1. I'm asking about true airspeed. 150nm/h in both cases.

    2. I'm not asking about effects like effect of pressure, wind, air resistance etc - but more "high level" effects like time dilatation, weaker gravity or advantage/disadvantage of flying in high altitudes - based on curvature of earth.
    I hesitated to do this but now cannot resist the temptation ...

    No effects of relativity theory here - yes time slows slightly if you live (or remain in an airplane) very high up at the equator but what you see is purely your perceived rate of change of the angle of your head (or eyes). Very low aircraft require you to move your head / eyes a large amount in the same amount of time (covering the same distance at the same speed) - angle theta 1; when high up, the same distance at the same speed = same amount of time requires a smaller change in head / eye movement - angle theta 2. So, you rotate through a smaller angle in the same amount of time so your head / eye movement speed is slower and also covers a smaller portion of your full angle of view - so your perception is that the higher altitude aircraft is moving more slowly then the same plane at the same speed at a lower altitude. And you can see that the rate of change of the angle with respect to height (d theta by dh) is - once you get things up there a bit - decreasing by the inverse of the height squared (so for each chunk of height higher up your rate of head movement decreases relatively rapidly). Note that the equation is negative (owing to the negative value in the rightmost term of the right side of the equation) indicating that for increasing height (a movement of height in the positive direction) the rate of change of the angle you need to move your head through is decreasing - and decreasing by the inverse square of the height.

    Click image for larger version. 

Name:	PerspectiveByHeight.JPG 
Views:	29 
Size:	23.7 KB 
ID:	152686
    Last edited by FlyingHorseSindbad; 08-05-2013 at 04:10 PM.
    Dan
    www.vfrprophops.com / www.ifrjethops.com
    Win 8, i7 3770 3.9 GHz, 12 GB DDR3 RAM, NVIDIA GT630 2 GB mem 42" 1080p FSX w/Accell yoke joystick rudder pedals REX TrackIR-5 FlighSim Commander FSUIPC

Similar Threads

  1. Replies: 69
    Last Post: 10-29-2009, 12:38 AM
  2. Replies: 47
    Last Post: 11-25-2007, 04:26 PM
  3. The Physics of flight(for 2006 developers)
    By rpembert in forum FS2004
    Replies: 13
    Last Post: 11-20-2004, 02:12 PM
  4. the law of relativity...
    By sanyok in forum MSFS Screen Shot Forum
    Replies: 4
    Last Post: 11-29-2003, 06:53 PM
  5. A Basic Flight Sim using physics, calc, & C++
    By Dre777 in forum The Outer Marker
    Replies: 5
    Last Post: 03-11-2003, 01:40 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •