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

Steam catapult and rotating runway for airports

  1. Nov 24, 2008 #1
    What do people think about this

    1. Put steam catapults on all airport runways (or perhaps use Linear Induction Motors)

    2. Get the plane to accelerate all the way from the gate following a track, through to
    launch, so acceleration for take off starts from 'go'. Apply an acceleration profile
    such that passengers don't feel too much discomfort but runway length is
    still reduced considerably

    3. Get runway to rotate to take advantage of wind assistance.

    Doing this will (qualitative assessment)
    - reduce airport space required
    - save on fuel for aircraft
    - already mature technology in aircraft carriers
    - airport land tax costs reduced etc....
    - less noise??

    to name a few benefits.
  2. jcsd
  3. Nov 24, 2008 #2
    1. Steam catapults are large and expensive and need maintenance. A F18 has a max take off weight of 23400kg, a jumbo: 333000kg-440000kg. Ie. you'd need a steam catapult about 10 times the size of the ones they use on carriers. Also, imagine the G-forces tolerance of airforce pilots and those of your standard airline passenger. Perhaps they could be used for smaller planes, like private jets. Not sure what the acceleration of a typical catapult is.

    2. That's a good idea, but flights are often delayed and some are early and there are always queues to use the available runways (especially in busy airports). To have the ability to continue moving from taxi to take off would require a lot more runways, taxi ways and therefore more space. Possible for very small airports with little traffic, perhaps.

    3. A typical runway for large aircraft can be a couple of km long, it may be a little difficult to rotate that much tarmac.

    I don't want to shoot down your ideas, and I'm glad someone is thinking about reducing air travel costs, but there needs to be more analysis of your ideas.
  4. Nov 24, 2008 #3
    once again haven't done the number crunching but

    supposing for take-off you have a set of LIM or LSM tracks that lead up to a 'nascar track' oval. Planes will enter this oval at appropriate times determined by some scheduling algorithm. There can be seperate ovals for international, domestic, rural etc... Now planes are kept zooming around the oval at a velocity close to producing lift to take off but not quite. Then
    you have a small tangential section(s) that contains a powerful LIM/LSM that has some angular freedom. Aircraft cleared for take off come of the oval and hitch a ride on this LIM...

    Landing can be yet another 'nascar oval' (hook on landing gear) or portion of oval which
    can slow aircraft down and then gently exit to gate tracks.

    ...dunno if this is practical at all..just an idea.
  5. Nov 24, 2008 #4


    User Avatar
    Science Advisor
    Homework Helper

    You could simply tarmac the entire area and have the ILS put imaginary lines on it to denote a runway.
    The first airfields were fields, the planes landed and tookoff into the wind from whichever direction it was blowing. then as fields were tarmaced they adopted a compromise of two runways at an angle to cover the most common wind conditions - which is why you see this shape all over the UK. [​IMG]

    The biggest saving would be to tow planes to the start of the runway. Jets are very efficent running at 600mph at 30,000ft, they are terrible running at 10mph at 10 feet - a 747 uses about 2t of fuel and emits a lot of polution taxiing to the start of the runway.
    Last edited: Nov 24, 2008
  6. Nov 24, 2008 #5
    This is what I was going to say. Also, steam catapults aren't going to be much more efficient then a jet taking off at WOT(or near it) so there's not going to be much of a savings in fuel there. Also, tarmacking all of an airport and creating imaginary runways would not only be ridiculously expensive but also rather unpractical. Just think about the snow removal. The airport would probably have to operate for 100+ years in order for it to pay off.
  7. Nov 24, 2008 #6


    User Avatar
    Science Advisor

    It's a lot more practical than rotating the entire tarmac with hige steam catapults attached.
  8. Dec 13, 2008 #7
    Runways are large for a reason: Emergencies.

    The only reason aircraft carriers use catapults is because of space requirements. Catapults break down often, are expensive to maintain, and sometimes fail.

    And with catapults you also need an arrestor system of some type. Also breaks down often and sometimes fails.

    Then you need some sort of emergency baricade system in case the of a damaged aircraft.

    Large runways are safe. Got no landing gear but a large runway? No problem. Got no breaks but plenty of length? Piece of cake. Got a bad catapult shot? your dead.
  9. Dec 26, 2008 #8
    I think your statement "once again haven't done the number crunching" is probably the key here. When you start to make numbers, the problems begin to be evident.

    I worked on electric launch for the US Navy, to design electric catapults to replace the steam catapults used on current carrier designs for the proposed future all electric carriers. It is an very difficult, very expensive task to launch a single aircraft at a time electrically and the energy quanties required are simply huge. This is the thing that makes it immediately prohibitive to consider moving numerous aircraft at once around in this manner. Every thing required can be done -- in principle -- but the amount of power electronics required, and the amount of electrical power consumed, is just beyond reason. We have much better, simpler means today with the small diesel tugs that move aircraft around airports today.

    Try putting some numbers together and you will get an appreciation for the problem very quickly. Almost all aircraft heavier than Cessna type will need an air speed of at least 160 mph for take off (strictly ball park), and you don't want to build your catapult too long because that increases the cost and complexity. Try playing with some combinations to see what it get a 400000 lb aircraft off the ground and estimate the cost. It will be an interesting exercise!
  10. Dec 26, 2008 #9


    User Avatar
    Science Advisor
    Homework Helper

    No problem.
    1, Large tower with pulley on top
    2, Very Very big heavy weight
    3, Rope
    4, Aircraft.
    Attach 2 to 4 with 3, drop 2 from top of 1

    Now the only problem left is to raise 2 back to the top of 1 for the next plane.
    Noticed the large number of people standing around at airports?
    You just need to organise them into tug-of-war teams to haul the weight back up
  11. Dec 27, 2008 #10


    User Avatar
    Science Advisor

    I don't understand why anyone is giving this any thought whatsoever. Not to mention the incredible silliness of a catapult to shorten takeoff distances, there are so many holes in this it is silly.

    Let's assume that we did work out an economical catapult device that could handle an A380 (and that the A380 and all others could handle being catapulted) then we still could not shorten any runways. They would still need to be the same lengths. There would be no noise benefits and people think they have enough flight delays without instituting a catapult system? Come on.

    Please let this thread die...
  12. Dec 27, 2008 #11
    Fred, I agree it is an absurd idea. I am puzzled, however, by your assertion that runways could not be shortened. With enough foolhardy assumptions, it seems to me that they could be shortened in much the same way that the Navy makes do with very short runways on carriers for both take-off and landings. What did you have in mind?
  13. Dec 27, 2008 #12


    User Avatar
    Science Advisor
    Homework Helper

    Without arrestor hooks you would still need the same distance to land.
    It needs significant re-enginering for a plane to handle catapult and tailhooks.

    A plan at heathrow to tow 747 to the end of the runway was abandoned because apparently 747 nosegear isn't strong enough to allow it to be towed while fuly loaded.
  14. Dec 27, 2008 #13


    User Avatar
    Science Advisor

    Probably due to some of the passengers not being able to handle the sudden jerk! :rolleyes:

    More realistically, if the plane misses the landing wire (or whatever it is called) the plane probably wouldn't have enough room to stop or even take off again if the runways were shortened.

  15. Dec 27, 2008 #14
    Oh, without a doubt missing the arresting wire could have terrible consequences, just like it does in the Navy (that is why the Navy has at least 4 arresting wires on a carrier). And to be sure, today's commercial aircraft could not begin to stand the loads imposed in either catapult launch or mechanical arrest, so a total redesign of the airframes would be required with that requirement imposed (and sacrificing other qualities in order to achieve this goal). Also, every launch and every trap consumes a measurable amount of the fatigue life of the airframe, so that these aircraft would have very limited useful commercial lifetimes, much like a jet fighter. And the cost would be prohibitive as well, and most passengers would object strenuously to the acceleration loads during both launch and landing.

    But, when we are thinking of such "neat ideas" why not make them really absurd all the way? It goes back to that classic statement that I quoted much earlier, "once again haven't done the number crunching." When people dream without any basis in reality, the results are often totally absurd. One of the best checks is to start making just a few numbers to see if there is any possibility that the idea is realistic.
  16. Dec 29, 2008 #15


    User Avatar
    Science Advisor

    It would be absurd to think of the standard population being subjected to a carrier trap when they land. Small children, the elderly and most adults wouldn't be able to handle it. Grandma's dentures would go flying into the seat in front of her. Plus we would then have to sit through more pre flight demonstrations for how the average gomer is supposed to put on a 5 point harness instead of a regular lap seat belt.

    Plus, the size of the systems required to bring a fully loaded 747 to a stop would be huge. Has anyone ever seen what goes into the arrestor system on an aircraft carrier? They are massive for aircraft the weight probably 1/10th of a commercial transport.
  17. Dec 29, 2008 #16


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Why in the world are we talking about arresting gear systems on land? That is completely nonsensical. Just because a plane is launched with a catapult does not mean it MUST have an arrested landing. Carriers must use arrested landing because of the limited length of the landing strip. There is no such limitation on land, that cannot be resolved in much easier fashion then a arresting system.

    Carrier launch and retrieval systems are complex, requiring a well trained crew of operators and technicians to operate and maintain. The flight deck with these systems in operation is a very busy and dangerous place. To even think about transplanting these systems to a land based airport is simply silly.

    To the OP.
    Generally improvements to existing systems come in the form of simplifications. To attempt to make improvements that are more complex then the existing systems is asking for troubles. Think of the initial troubles with the Denver baggage handling system. In this case with lives at stake and the huge expense of installation, training and maintenance of such systems the idea is more of a joke then anything else.

    since the OP has not posted for over a month there is no point in continuing this rediculus thread.

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Steam catapult and rotating runway for airports
  1. Steam pressure. (Replies: 8)

  2. Steam turbine maths (Replies: 1)

  3. Pop can catapult (Replies: 4)