20 January 2015

Did a Darwin Award applicant pass through the propellor arc of this aircraft ??

This [very] amateur footage of a serious Runway Incursion on a rural airstrip in Alaska shows our Fairchild C119 FlyingBoxcar taking off on a runway that is too short and too soft on a ferry flight. The plane had forced-landed there years ago to begin with...So this was the first takeoff after the plane had sat there for more than 13 years being vandalized etc. We had changed out one engine, windows and ball bearings and worked on it straight for over half a year. We have been given 7 videos of this takeoff by the locals and the FAA used the footage to teach about the feared "runway incursions". We have it on tape how our pilot preaches from the cockpit window to the assembled villagers that he will use every inch of available runway and THEN SOME beyond that, nevertheless we had a father and son standing in the way of the plane plus two others while a village schoolteacher and professional pilot was arguing with them about getting off the runway...Quite amazing, as said we have 7 camerapositions...Nobody died but the son did actually go through the Prop arc and had the luck to pass through the blades with no harm to him. R3350's run 2950 RPM on takeoff and the reduction gear reduces Prop RPM and at 94 knots it was some space between the 4 blades of the Prop. "
This video link was sent to me by my brother-in-law, who is an air traffic controller.  In the YouTube comment thread the OP responds to a question as to whether someone actually did "go through" the propellors:
From the 6 camera-positions & videotapes, as well as the still photos, That is what we have concluded, there is no other possibility. The 7th tape, being from the camera that the Kid held while he went through the prop-arc, I have never seen. Many people that saw it told me about it, there was no doubt !
I did some rough calculations this morning.  The plane's velocity at the end of the runway was reported at 94 knots = 108 mph = 158 fps.  The "reduction gear" ratio for the propellors is not defined; let's say the RPM were reduced from 2950 to 2400 (anyone know/guess?)  It's a 4-blade propellor, so 2400 RPM results in 9600 blade-passes per minute, or one blade coming by every 1/9600 minute.  Divide by 60 = 160 passes per second.

160 passes per second in a plane moving forward 158 fps would give a space of about 1 foot for the head to pass through.    The person who pulled this stunt probably had a small head to begin with.


A standard, unquestioned rule of airport safety is that nobody should walk through the propellor arc - even if the engine is turned off.
If you never walk through a stationary prop arc due to a conscious decision to avoid it, when you hurry across the flight deck it is less likely that you will walk through a turning prop arc.  FACT: People who have been killed by prop arcs were familiar with the aircraft and flight deck around them, but a momentary lapse of concentration caused them to stray into a turning propeller. 
I suppose there is one possible lesson to be learned here.  If one finds oneself in a real-life action-movie scenario with a propellor blade coming toward you, and if there is no way to stop it and no way to avoid it and a physical encounter is unavoidable, then one's chances are statistically improved by rushing toward the spinning blades as fast as possible.

8 comments:

  1. I happen to believe in miracles. Yes, that might have happened by chance...but that fact that a great tragedy was averted...well, the point goes to God.

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    1. I don't mean to be disrespectful, but given your set of beliefs, how do you explain airline crashes. Does God cause them because some of the people on the plane were evil (killing the righteous ones as well), or does he not know about them (but he's supposed to be all-knowing), or is he incapable of stopping them (he is said to be omnipotent).

      I don't know how you can believe in just the good things, but not the bad things.

      No disrespect intended.

      Delete
  2. Just for accuracy, the R-3350 (Wright Turbo Compound Cyclone 18, also known as "TC18") engine RPM at takeoff is 2900, and the gear reduction ratio is 0.4375:1. A few engines used on the Lockheed Constellation had a reduction ratio of 0.355:1, but they are all gone. Without seeing the other videos referred to (or at least a couple of them), I'm waving the BS flag on this story. Sorry.

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    Replies
    1. I want to make sure I understand... the 2900 RPM refers to the propellor shaft speed, not some other engine component? And is that number before or after the gear reduction is factored in?

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  3. The 2900 is crankshaft RPM at takeoff power, After gear reduction the prop shaft/prop RPM would be 1268, which sounds about right to me. With that prop arc the tips are approaching supersonic speed which kills prop effectiveness.

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    1. Thank you so much. Plugging 1268 into the calculations I made (which assumed 2400) would double the "window" for the idiot to pass through - to about 2 feet. So I would conclude it is possible for him to have passed through the prop arc.

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    2. No chance. The propeller is a Hamilton Standard 6903, so each blade is ~ seven feet long. I don't believe you factored in the thrust effect - the seven foot prop blade is rotating at 2100-2200 RPM, so each blade is continuously delivering thousands of pounds of rearward thrust. I've been behind those props at idle (pulling landing gear downlock pins) and at much higher power settings (maintenance-related), and it's barely possible to stand erect, much less remain perfectly rigid and stationary when the prop generates takeoff thrust. There may in fact be two feet between blades as the prop goes by, but the first blade will generate more than enough thrust to push a stationary object (or person) into the path of the next (or the one after that) propeller blade. Your theory might work with a wooden dowel sticking up from the ground, but not with an object the size and weight of a human head.
      i'm waving the BS flag on this. Didn't happen.

      Delete
  4. As a comparison, I routinely fly an airplane with a big-ass radial engine driving a prop on a reduction of 0.67:1 or thereabouts. At takeoff power the engine is turning ~3000RPM, and the prop RPM is around 2100. It's a much smaller prop arc, so it can turn faster without the prop tips going supersonic.

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