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Aerospace Super-Birds? Vs Jet-engines

  1. May 2, 2008 #1
    How can a small bird made of bone and flesh manage to shut down a jet engine made from strong metals and alloys??

    R they super-birds?

    Please help me since i have searched for the answer but cant find it anywhere.

    thanks
     
  2. jcsd
  3. May 2, 2008 #2

    mgb_phys

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    The fan blades are spinning at almost supersonic speed so they are under enourmous stress. They are made as thin and light as possible so are only just strong enough for the load.
    Then they hit a bird while flying at 500mph - that's a lot of sjock to absorb.
     
  4. May 2, 2008 #3
    thank you for your time, i understand the sense behind making the engine as light as possible and yet strong enough to withstand the great stresses felt by its components, but does that mean the engine is then damaged and useless?

    if so, wouldnt it make more sense to make the engines slightly stronger (thicker, heavier components) that would be able to withstand such shocks, so that the engines wouldnt need to be "thrown away" if such an event happened?

    also, how often do these accidents happen? is it rare to have some object pass into a jet engine?

    i understand that some fighter planes use a trap door in the inlet that follows through to the back of the jet, in the event of objects entering the duct they hit the trap door and exit without going into the compressor etc....isn't it an idea to have the same mechanism on all planes and thus save thousands of pounds as opposed to wasting engines?

    sorry for the long post :s
     
  5. May 2, 2008 #4
    I can also remember to weight the bolts on a jet to make sure there is a nice axisymetric load distribution. I can only imagine what the off balance of a two pound bird stuck to a blade will do to the vibration
     
  6. May 2, 2008 #5

    russ_watters

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    Airplane engines are, in fact, designed to be able to absorb a bird ingestion under certain conditions. I'm not sure what the exact criteria is, but it is a bird of perhaps 2 or 3 pounds, thrown-in at around 300 mph.
    Dunno what "rare" is, but perhaps a few a year. Here's one recently caught on video:

    The pilots and controllers are so calm, except for the initial "mayday" call (it can be hairy if you lose half your thrust with your nose in the air and speed low), the situation seems downright mundane.


    Here's one I hadn't seen before that took down an F-16 (note the voice of the student pilot): http://jeremy.zawodny.com/blog/archives/006426.html
    No, they don't. Fighter planes may bleed air or bypass it, but they don't do it to pass fod. The engine is sucking in, so you can't direct a bird around it if it wants to eat the bird. Here's what happens if you forget to duck near a jet engine intake:
     
    Last edited by a moderator: Sep 25, 2014
  7. May 2, 2008 #6

    russ_watters

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    Not an issue - it isn't possible for a bird to get stuck in an engine. Think about it like a 30,000 horsepower blender.
     
  8. May 2, 2008 #7
    Ha, yeh an expensive blender...lol..

    well to be honest that is what i thought. i mean to have the titanium alloy blades running at the crazy revs they do, the high temperature and pressure, i would have though the bird would get vapourized and it would just pass through the engine?

    btw russ, expensive camera you have there...saw your site...some great pics you have up!

    WOW, jus saw the youtube vid of the man being sucked into the engine!!!! Not a good day at work i guess....AMAZING he survived!
     
    Last edited: May 2, 2008
  9. May 2, 2008 #8
    looks like a lot of bird but no damage to me?

    now im confused.... so do they damage engines or dont they?

    i think im going to have to question a bird to get the right answer...lol

    i cant post the video but search for Bird vs jet engine (in super-slow motion) on youtube and you will see the vid im talking about....sorry
     
  10. May 2, 2008 #9

    mgb_phys

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    Yes they damage the engine - normally totally destroying it.
    The engines are built to contain a fan blade breaking off, the outer cover of the engine will stop bits of broken engine going into the wing or cabin. But that doesn't mean the engine will survive.
    It's rare enough that there is no need to protect against it. Instead most aircraft are designed to keep flying if they lose an engine for whatever reason.

    It's particulalry a problem for fighters, single engined, flying close to the ground at much higher speeds - usually it means ejecting and losing the aircraft.
     
  11. May 2, 2008 #10
    dont mean to sound silly, but if it damages the engine, worth £10,000's or £100,000's, isnt it time they found a solution for it, as rare as it may seem?

    it would mean more safety for pilots and passengers, and in effect saved money on future damaged engines by little birdies!
     
  12. May 2, 2008 #11

    russ_watters

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    Well, if an engine costs $1,000,000 (they are at least that much), 1 out of every 1,000 engines gets destroyed this way, and it costs $10,000 per engine to make them strong enough to withstand the impact (and assuming the same performance), you could buy 10 engines for the savings to let one get destroyed.
     
  13. May 2, 2008 #12

    FredGarvin

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    Bird ingestion is, in the USA, part of the engine certification process. The test criteria depends on the size of the engine, i.e. fan diameter and thrust. That dictates the weight of the bird and the number of birds to be ingested during the test. Of course, when out in the real world, there's nothing saying that a larger bird can not be ingested. The passing criteria is that an engine remain at rated power (with only a very small percentage of degradation of power) for 5 minutes and then shut down normally. An engine will suffer some very serious damage, but it does not destroy it. A certified engine would have to experience some extra ordinary circumstances to be destroyed by a bird strike.

    The damage that is caused is obvious and not so obvious. The structural aspect is the obvious part. Despite the materials used, an ingested bird does damage blades. That damage does induce some dynamic issues such as imbalance. The fan blades will be bent and twisted and possibly have sections removed because of the strike. The less obvious issue and, really, is more important, is that of flow disruption in the engine. I have had a couple of tests in which the engine violently surged immediately after impact. The engines survived, but the stresses induced were enormous. Imagine the core of the engine turning into a cannon to get an idea of the forces.

    After a strike, the usual requirement is to replace the fan disk since it takes the majority of the damage. A full inspection is required to inspect all other areas. However, the replacement of other items is usually minimal.
     
  14. Aug 13, 2008 #13
    Jet engines are made to withstand ingesting a certain amount of foreign debris. The GE CF34-3A, the engines on the A-10 and Challenger corporate aircraft, are built to withstand much abuse. The A-10 would continually come in with small arms fire all throughout the engines. One of the Challenger's that I worked with came back with a bent fan blade which resulted from a bird strike. These engines are so robust that the crew didn't even know they had hit anything at all, let alone bent a fan blade.
     
    Last edited: Aug 13, 2008
  15. Aug 13, 2008 #14
    When i was working at GE-aircraft engines, the test bed aircraft had taken a bird in 2 of the original JT9D's. still went out test flying, the engines were checked out, looked ok, airplane went back out. Admittedly the airplane flew experimental and was almost in a constant state of emergency (flying with 3 JT9's and 1 test engine)

    so for all practical purposes, 1 bird will not take down a commercial airliner, but could damage the engine. watch out for those birds at 35k feet though

    as far as amz8601's comment about trap doors. F14's and F15's at one time had variable inlets, so if you looked you would see hinges for this system, could be confused as a trap door. almost all fighters have boundary layer diverters, where the useless slow boundary layer is ejected to allow for more useful highspeed air to enter the engine. depending on the model of fighter, these could vary greatly in design. Russian fighters (some) can completely close off their inlets and take air from the top of the wing. this however is not for birds and so forth, but to enable a dirt runway capability. unfortunately i do not know the details, like max thrust with doors closed, speed at which they can be closed, etc...

    but if you could avoid it, keep all hands, feet and other objects clear of jet engines
     
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