Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Aerospace Cruise is the level portion of aircraft travel where flight

  1. Sep 15, 2010 #1
    Source

    http://en.wikipedia.org/wiki/Cruise_(flight [Broken])

    then totally opposite statement
    What essentially is cruise speed
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Sep 15, 2010 #2

    boneh3ad

    User Avatar
    Science Advisor
    Gold Member

    Re: Cruising??

    Those statements do not contradict each other. The cruise portion of a flight is the most efficient, but usually the longest portion by a long shot. It can still use the most fuel despite being the most efficient. Driving a Prius from Chicago to LA will still use more fuel than driving a pickup from your garage to Wal-Mart, for example.
     
  4. Sep 15, 2010 #3
    Re: Cruising??

    @boneh3ad

    Thnx
    by the way when applied to warplane what is cruising speed??
     
  5. Sep 15, 2010 #4

    boneh3ad

    User Avatar
    Science Advisor
    Gold Member

    Re: Cruising??

    Off the top of my head, I am not really sure. It depends on the plane. Most of them cruise just below Mach 1 somewhere... the number of 0.85 or so seems to stick out in my mind. However, I believe it is either the F-35 or F-22 that can do supersonic cruising.

    I would have to look it up later though when I have more time. The bottom line is that it is different for every plane.
     
  6. Sep 16, 2010 #5
    Re: Cruising??

    The term "cruise" has different applications. The term "most economical cruise" uses the least fuel over the greatest distance. That's called "best range," and it's way below what most aircraft fly, including military aircraft.

    As time is money for the pax, they're willing to pay a few more dollars to travel across country or the oceas in a few less hours of time, thus, the pilots push things up beyond best range. Then there's the salaries of the flight crew, so a few more knots are added until an in-flight mini-max solution is obtained. Then there's wear and tear on the airframe and engines as both a function of time in flight was well as an inverse to the square of the velocity, so that's added in as well.

    Finally one has to deal with lost airfare if the pax don't make their connections on time, along with the lost goodwill from both them, the media, and potential future pax.

    The calculations aren't difficult, but the result is an optimax solution which allows the airlines to turn the largest net margine possible.

    From what I've been able to gather, airlines have yet to achieve the most economical target. It may be because of several factors, but I think your average airline could easily increase nets by $1 M a year.

    If you'd like to speak about it further, I'm available for hire (inquire within) :)
     
  7. Sep 16, 2010 #6
    Re: Cruising??

    @mugaliens

    Thnx
    I just am a student & questioned it out of curiosity. However; can any plane cruise at low altitudes which is beneficial for stealth warplanes. I think cruising/super-cruising only is obtained at very high altitude
     
  8. Sep 16, 2010 #7
    Re: Cruising??

    Any time. :)

    Whether or not cruising stealthily and efficiently at low altitude is included in the design of an aircraft depends on the mission. For something like the B-2, a high-altitude weapons delivery platform, it's not part of the mission.

    The reason military aircraft in the 60s through the 90s flew low-level was to fly below the radar, using terrain masking to help hide the aircraft from enemy search radar. These days stealth technology is so good that aircraft can fly at altitude without showing up on radar, so they do.

    All aircraft, including reciprocating props, turboprops, turbojets, and turbofans, fly more efficiently at a higher altitude than sea level*, but only to a point, and that point is both an entering argument in the aircraft's design, as well as a result of that design. For example, practical considerations such as FAA regulations requiring the flight crew being on 100% oxygen above FL 430 render flight above the FL 430 fatiguing. Therefore, most airliners are designed such that at average pax/cargo weights, min fuel, and temperatures, FL 430 is the most efficient cruise altitude.

    This depends mostly on the weight of the aircraft and the outside air temperature. The weight changes throughout the flight as fuel is burned, and temperature changes with decreasing altitude, but only to a point. At any given weight, there is a most efficient altitude. Flying any higher than that actually decreases per-mile efficiency. A fully-laden airliner, therefore, might start at FL 280, but throughout the flight it will step-climb to successively higher altitudes as it burns fuel and becomes lighter. As it nears it's destination, having burned all that fuel, it might be at FL 420.

    * In the rare case of a very heavily-laden aircraft on a hot day, the most efficient cruise altitude can actually be below sea level. In fact, the service ceiling, which is the safest altitude an airplane should fly, can be below sea level! When that happens, it's safer to take the bus.
     
  9. Sep 22, 2010 #8
    Re: Cruising??

    ^^Thnx
     
  10. Sep 22, 2010 #9
    Re: Cruising??

    The speed at which the aircraft is comfortable and also economical is known to be crusing speed.
     
  11. Nov 15, 2010 #10
    Re: Cruising??

    Generally speaking, max range airspeed/mach is used whenever something else isn't required tactically. Get's you the longest distance using the least amount of gas. This airspeed is a function of altitude, ambient temperature, external stores (how much stuff you are dragging through the air on the wings), as well as fuel load/gross weight. Bottom line is that you fly the angle of attack that corresponds to max range, as this does not vary with any of the above parameters.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Cruise is the level portion of aircraft travel where flight
  1. Human Flight (Replies: 63)

Loading...