REFLECTOR: Re: Falling objects through the prop (Was NOSE WHEEL GOTSIDEWAYS)

[Al Gietzen]

Keith;

 

Yes, I realized as I went back out to the shop that my “thinking-out-loud”
analysis was all wrong; so I’m glad you followed up.  At first your 1.4
inches seemed too small, but the math is correct.  I think the fact that the
object is initially at the speed of the plane makes a huge difference, and
makes it likely a small metal object (small and dense) would clear the prop,
probably by some margin. It only needs a ¼ of a second to make it.

 

Some time ago I remember doing some back-of-the-napkin analysis with a
couple of Long EZ drivers which concluded that a person could safely
parachute out of an elite door Velocity, but it may have been a somewhat
used cocktail napkin.

 

Al

 

Subject: REFLECTOR: Re: Falling objects through the prop (Was NOSE WHEEL
GOTSIDEWAYS)

 

Al,

 

I follow you up through the point where you say the object will only fall 85
msec before the prop comes by.  However, as I recall the position formula
is:

   X = X(init) + V(init)*T + 1/2 A*T*T.   If we use the initial elevation of
the object as our datum, X(init) = 0, and if the initial downward velocity,
V(init), is also zero.  If we further assume that the only acceleration
acting on the object is gravity (32.2 ft/sec^2), then

 

  Distance Fallen = 1/2 * (32.2 ft/sec^2) * (0.085 sec) * (0.085 sec) =
0.117 ft  = 1.40 inch.

 

So does your prop arc extend lower than 1.4 inches below the level of your
nose gear door?  Sure!  

 

However, we have neglected the fact that any object that falls off the plane
is initially at the speed of the plane, not at rest, and it is slowed by air
friction, so it is decelerating horizontally while is is accelerating
vertically downward.  If we know the drag coefficient of the object that's
falling, we could calculate that deceleration due to the relative wind, but
that will be left as an exercise for the reader!  Suffice it to say that the
object will actually fall significantly longer that 85 msec, and will
therefore fall farther.  If the prop arc extends, say, 16 inches below the
belly of the plane, we would need to have approximately 1.0 second of fall
to clear the prop arc.  Is this likely?  Probably not.

 

I think the conclusion is that anything that falls off the fuselage, even
from the nose, is pretty likely to pass through the prop arc.

 

Keith

      

----- Original Message ----- 

From: Al Gietzen <mailto:ALVentures at cox.net>  

To: 'Velocity Aircraft <mailto:reflector at tvbf.org>  Owners and Builders
list' 

Sent: Thursday, March 10, 2005 8:08 AM

Subject: RE: REFLECTOR: RE: NOSE WHEEL GOT SIDEWAYS

 

Subject: REFLECTOR: RE: NOSE WHEEL GOT SIDEWAYS

 

Tom

 

You say believed you lost the "T" fitting in flight.  Did you check the
Velocity high speed rotating strainer that's attached to the engine to see
if it was detected, evidenced by leaving 'memory marks'?  Idle curiousity:
Can anything fall off the plane's fuselage without going through the prop at
rotation speeds or above?

 

Chuck

 

Well, let’s see; at 120 mph that’s 176 ft/sec – so it takes about 85 msec to
travel 15 ft.  If you drop something from the nose gear well, it will travel
downward a max of about 30 – 35 in. before the prop goes by.  It might clear
the prop.

Just thinking out loud, check my math.

Al


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