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

Harrier fuel consumption

  1. Oct 20, 2005 #1
    Greetings!

    Would anyone know about how much fuel does a Harrier aircraft (with the Pegasus Turbo fan engine) consume when taking off verticaly?
    I tried searching the net with no success.

    Thank You
    Chris
     
  2. jcsd
  3. Oct 20, 2005 #2

    Clausius2

    User Avatar
    Science Advisor
    Gold Member

    A lot :biggrin: .
     
  4. Oct 20, 2005 #3

    Pengwuino

    User Avatar
    Gold Member

    A lot? Arent you just re-directing thrust? Seems like at the most, it would consume its normal 100% thrust requirement.
     
  5. Oct 21, 2005 #4

    russ_watters

    User Avatar

    Staff: Mentor

    Since it's non-afterburning, it's probably less than most military jets at takeoff.
     
  6. Oct 21, 2005 #5

    Clausius2

    User Avatar
    Science Advisor
    Gold Member

    Saying "A lot" I am not intending to say "A lot more than other jets":biggrin: (I was just kidding).
     
  7. Oct 21, 2005 #6
    Here's some help for you. The weight of an empty Harrier is 22,950lbs and it provides 23,800 lbs of thrust from its engines Pegasus Turbofan engine. In order to find the amount of fuel needed to take off you now need to find the amount of fuel consumed in order to acheive >97% of it's maximum thrust. I think that it is correct so maybe it should help you. Now all that you need to do is find out how much this Pegasus Turbofan engine fuel consumption at 97% is to acheive liftoff.
     
  8. Oct 21, 2005 #7
    You also have to remember that as the aircraft rises it will be consuming fuel reducing the thrust that is required to maintain a constant upward acceleration. Also as you do this to maintain a steady acceleration you must reduce the thrust to maintain the same thrust to weight ratio.
     
  9. Oct 21, 2005 #8

    Pengwuino

    User Avatar
    Gold Member

    I think they accelerate up as fast as possible (as opposed to steady acceleration) because you can only hover for a limited time. They can (although I may very well be wrong because I remember someone saying something contrary to this idea) hover for about 45 seconds because they have a limited supply of water to cool the engine which would normally be done by the passing air in flight.
     
  10. Nov 4, 2005 #9
    ......It can hover for more than 45 sec. I went to two air shows that had Harriers and one of them was still at about 100-150 feet altitude in front of the crowd for at least 1 min then it slowly turned around and after about 2-3 min of downward thrust it started slowly to move forward until it achieved the required speed to use only the back thrust.
    .....I could not find how much a Harrier consumes at 100 thrust off google.
    Either way it would not be 1 gal/sec like some one mentioned to me would it?
     
  11. Nov 4, 2005 #10

    russ_watters

    User Avatar

    Staff: Mentor

    Well, the Harrier carries about 1000 gallons of internal fuel alone. At a gallon a second, that's more than 15 minutes. It does seem a little high for the consumption rate, but it's conceivable.
     
  12. Nov 4, 2005 #11

    Pengwuino

    User Avatar
    Gold Member

    Well beats me, i read it a long time ago after watching True Lies. Guess hollywood screwed me again.
     
  13. Apr 20, 2008 #12
    is there any one still interested in this question, the thread looks pretty old and i might add a little on it.
     
  14. Apr 20, 2008 #13

    Averagesupernova

    User Avatar
    Science Advisor
    Gold Member

    Add away. The harrier has always interested me.
     
  15. Apr 20, 2008 #14
  16. Apr 21, 2008 #15
    aviation measures in weights rather then gallons and of course in the US it is in pounds, had to mention becuase there are aroung 6 countries that use the harrier. the hover limitation is not solely on a time bases but on liitations of fuel availability and temperature of the engine so as not to damage it, and there is the outside temperature that has a direct impact on engine performance, everything is based on engine performance. Water is not required but it is prefered as it does help cool the engine temperature, more on that next time true believers.
     
  17. Apr 21, 2008 #16

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    The water on a Harrier doesn't diectly cool the engine.
    It is injected into the exhaust after the engine - the purpose is to cool and increase the density of the output jet (a kind of anti-afterburner) it also increases the engine power by condensing the exhaust and so sucking more air out of the engine.

    A lightly loaded harrier (such as at an airshow) with no external stores can hover pretty much indefinately without using cooling water, certainly in the cold wet rainy conditions that are traditional at British airshows. Although they generally try and move slowly forward while hovering for a long time, injesting hot oxygen poor exhaust back into the engine intake is a problem if hovering in still conditions.

    Water cooling is needed for take off with heavy combat payloads or in desert conditions - but becauuse of the fuel required for a VTOL take off, they prefer runways (or catapults) if possible.
     
  18. Apr 21, 2008 #17
    the water is injected in three stages, the first is in the cooling air supply for some early turbines, the second is is in the combustion chamber air flow and the third is directly into the combustion chamber. it does not directly improve thrust but reduces engine temperature allowing the engine to work at higher rpms and indirectly improves thrust, i dont believe that i have ever seen a harrier use a catapult but that does not mean that it has never happened.
     
  19. Apr 21, 2008 #18

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Yes you're right, the Harrier doesn't use a catapult but does have a clever little ski jump on British carriers.
    These were originally designed for helicopters only so a bit of ingenuity was required to operate aircraft from them. http://www.aerospaceweb.org/question/planes/q0281b.shtml The US Marines don't use the ski jump - I think this is because US Navy practice is to store most aircraft on the deck and the ski jump reduces available deck area.
     
    Last edited: Apr 21, 2008
  20. Apr 22, 2008 #19
    your right, the navy is stingy in the space, and now that i think about it i have seen the jumps your talking about.
     
  21. Apr 22, 2008 #20

    FredGarvin

    User Avatar
    Science Advisor

    The US Navy does have roll off takeoffs, but as mentioned, they don't use the ramps the Europeans do.
     
  22. Apr 22, 2008 #21

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Hm - can't seem to edit posts any more?
    By 'these' I meant the carriers were designed for helicopters and so didn't have catapults.
    When the Sea Harrier was introduced it was too expensive and heavy to fit nosegear strong enough to take a catapult launch - so the ski jump was invented.
    Like most new military kit (especially Navy) it took a long time for anyone to accept it.

    One big advantage of a rolling take off is the rate at which you can get planes off the deck - without having to wait for a catapult reset, the Harriers can take off almost nose-to-tail.
     
  23. Apr 22, 2008 #22

    LURCH

    User Avatar
    Science Advisor

    But I had heard that the main advantage of the ski-jump was the reduced fuel consumption. Which is probably what mtivated the OP of this thread. Is thrate of consumtion for hovbering merely the same rate as traveling at full throttle? I assume that, when using the ski-jump, the planes still take off using max thrust, so the rate of fuel consumtion should be the same, yes? And yet, the AV8-B almost always uses a rolling take off, and the reason mentioned is always "to save fuel" (along with the ability to lift a heavier takeoff weight).
     
  24. Apr 22, 2008 #23

    FredGarvin

    User Avatar
    Science Advisor

    In a regular aircraft, the specific fuel consumption (SFC or TSFC) increases with airspeed and altitude. That is because the thrust falls off faster with altitude than fuel flow does. However, I have a gut feeling that this does not cover the hover scenario. My gut tells me that the engine has got to be less efficient at a hover. I say that because I know a hover is not the same as a static engine run at sea level. I'll have to do some digging to see if I can find anything on that.
     
  25. Apr 22, 2008 #24

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    The fuel consumption is a lot higher in hover than rolling take off.
    The ski jump has a couple of advantages - it converts some of the forward velocity into upward velocity more quickly than the wings alone, and since you are flying nose up when you leave the deck there is more time to eject in an emergency such as an engine failure.
    There is an entire site devoted to this unique plane http://www.harrier.org.uk/

    In another Physics link - in 1983 a harrier got lost on an exercise and ended up landing on a Spanish container ship near Teneriffe. The big flat crate it landed on was carrying the base plate for one of the British Telescopes on La Palma. There is a photo of the landing in the tea room there.
     
  26. Apr 23, 2008 #25

    LURCH

    User Avatar
    Science Advisor

    Yes, I too am certain that consumption is much greater in hover than at full throttle in forward flight. Some fo that innefficiency, I'm sure, is due to the movement of air in front of the intakes. Helicopters, for example, never take off straight up unless they have to. Once a helo starts to hover, taking in air from above itself to puch downward and create upward thrust, the collum of air above the bird begins to move. As the blades grab this air that is already moving, they get less of a bite, and less thrust. So, they always prefer to move forward slightly as they climb, so the blades are biting into stationary air. I'm sure the air in front of the intakes of a hovering Harrier must ebhave in a similar fashion.

    It is odd, though, that I did a search and can't find any numbers on how much gas the AV8-B consumes during hover.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook