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Aerospace How are these crafts engines protected from ingress of debris?

  1. Feb 18, 2009 #1

    wolram

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    How are these crafts engines protected from ingress of debris?
     
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  3. Feb 18, 2009 #2
    Re: Vtol

    I assume you mean ingression or ingestion of debris (it's been a while since i've seen the word ingress :wink:, but then again my vocab suffers from my having to speak a second language most of the time)

    Referring to question, I guess it kind of depends on the type of engine.

    I saw on a documentary on the x-33 and x-32 that they often took off and landed on pits in the ground that were covered by a grate. This was apparently more to protect the engines from ingesting heated air and exhaust gases.

    I think that most engines are realtively resilient to dust and debris intake (take a look at most helicopters) and I'm not sure if there are any special measures taken to protect a VTOL's engines. If anything, the intakes are probably geometrically positioned to reduce interaction from the exhaust and flying debris that is induced by exhaust.

    I'm pretty sure FredGarvin will have a great reply for you. He specialises in jet engines.
     
  4. Feb 18, 2009 #3

    mgb_phys

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    Re: Vtol

    It should be less of a problem than a regular aircraft.
    The planes forward speed at take off is zero, so there is only the 'suction' of the engine to pull in debris. The harrier at least has a large intake for the relatively small engine so the inlet pressure (or however it is called) is going to be lower than a regular jet fighter.
    And I'm guessing the nose up stance helps keep the inlet away from anything thrown up.
     
  5. Feb 18, 2009 #4
    Re: Vtol

    Actually, its far worse. The VTOL pushes a column of air down and blows any loose material back up into the engines. I'm currently doing work on this:

    10034.jpg
     
  6. Feb 18, 2009 #5

    mgb_phys

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    Re: Vtol

    That's what I would have thought, but Harriers operated for years from woods in Germany eating the occasional tree branch! The US harriers have inflatable intake guards - I suppose they might have more powerful engines.

    Apparently the only Harrier lost to fod was a navy one that sucked in some tools.
    I also found out that most engine damage on fighters is on landing with thrust reverses that blows stones back into the final stage of the engine.
     
  7. Feb 18, 2009 #6
    Re: Vtol

    Sorry, I don't believe this. This is a crock. On aircraft carriers they go to great pains to remove things as small as nuts and bolts. A tree branch......not buying it.
     
    Last edited: Feb 18, 2009
  8. Feb 18, 2009 #7

    FredGarvin

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    Re: Vtol

    Some aircraft have some small form of FOD protection on the inlets, but those are helicopters. The worst thing that I ever had to deal with was sand ingestion. I know the Apache and Blakhawk guys had a horrible time with sand. It plays hell with the first few compressor stages and can actually glass coat parts of your combustor and turbines. That is why a lot of aircraft now have particle seperators as options.

    The Russians were pretty smart with aircraft like the MiG-29 that has special intakes on top of the fuselage that are opened for takeoff on unapproved airstrips.

    In most cases, especially with aircraft like the F-35 they must have plenty of margin for the size of ingested debris because there isn't really anyhting that can prevent it. I think the tradeoffs performance wise are too great. Yeah, you don't want to ingest a tree branch, but it's not like that is going to bring an aircraft down. You'll shake like the buhjeezus but it shouldn't be a killer.
     
  9. Feb 18, 2009 #8

    FredGarvin

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    Re: Vtol

    I can somewhat believe it. An aircraft carrier is a controlled airfield. Of course they do FOD checks. However, when you are landing in some LZ out in the middle of nowhere, you get what is there. No one goes out and cleans up a field before you land or takeoff.
     
  10. Feb 18, 2009 #9

    mgb_phys

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    Re: Vtol

    I meant the Harrier was originally designed to operate without runways -on the assumption that the UK airfields would be radioactive craters 4mins after a war started.
    They were always shown taking off from tiny clearings in the woods, so unless German woods are meticulously clean or the clearings were tidied first by a bunch of horticulturaly minded squaddies they have got to be FOD nightmares.

    My only direct experience of this is that they invented a clever inflatable shelter/hanger that we were trying to adapt as a telescope dome that would completely retract.

    Whether the number of dead engines in gulf/Afghan is because they are now more powerful, are near end of life and getting worn out or sand is bad I don't know.
     
  11. Feb 18, 2009 #10

    wolram

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    Re: Vtol

    Thanks guys, i think i won't be buying a second hand engine from a VTOL craft.
     
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