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" How I Almost Destroyed a 50 million War Plane...'

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" How I Almost Destroyed a 50 million War Plane...'

Old 1st Feb 2016, 17:18
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You're not alone BBK, love the irony!
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Old 2nd Feb 2016, 02:08
  #42 (permalink)  
 
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BBK, discussions often take off on a new direction, and an alert individual may learn something new.

Tourist, being as thick as I am I could make no sense of your post #36. To check we are on the same page a couple of questions. OK, three.

Say we have a skydiver hanging onto the edge of a balloon basket. What "g" is he experiencing under the following circumstances

1. While hanging onto the balloon basket
2. The exact instant he lets go of the balloon basket
3. When he reaches terminal velocity
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Old 2nd Feb 2016, 03:38
  #43 (permalink)  
 
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Say we have a skydiver hanging onto the edge of a balloon basket. What "g" is he experiencing under the following circumstances
1. While hanging onto the balloon basket
2. The exact instant he lets go of the balloon basket
3. When he reaches terminal velocity
1 = 1 g
2 = 1 g
3 = 1 g

assumes balloon is stationary and NOT accelerating up or down AND he does not use a fly suit or wing suit but drops like the proverbial brick

Last edited by CONSO; 2nd Feb 2016 at 03:42. Reason: added constraints assumed
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Old 2nd Feb 2016, 06:32
  #44 (permalink)  
 
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Re: the -1g push that's a side show to the thread:

Wouldn't a push typically be needed when you roll inverted? (Even if the aircraft is a more symmetrical type, and not draggier and less aerodynamic upside down.)

My off-the-cuff aerodynamics isn't the greatest so I won't go into a ton of detail. But I can refer to a what a couple well regarded aerobatic pilots wrote.

Neil Williams in his book Aerobatics in the '70s:

"
The more stable the machine in normal flight, the heavier it will be in inverted flight on the controls; for example, if the tail-plane is set at a high negative incidence on the fuselage, it will give strong longitudinal dihedral, and therefore a powerful restoring force in the event of a disturbance. This, coupled with a forward C.G. can make it very tiring to hold the push force required for inverted flight, and it may be impossible to trim it out. On aeroplanes of this sort, one has to use the trimmer to fly aerobatics, and this will not result in a good performance. Since most aerobatic machines have some positive longitudinal stability , there will always be a push force in inverted flight. By trimming nose heavy, we can compensate to some extent for this."

Eric Mueller in Flight Unlimited similarly writes about trimming for 0g. If one trims for 1g, then one will have to push for level -1g. If one trims for 0g there will be a little pull at 1g (at a given speed) and still some push for -1g. So a push is expected.

============

As for "Normalization of Deviance":

While I like the concept, I think it may be overused, as it is a handy and erudite sounding catch phrase. It seems pejorative about any change, as if there is only one possible correct way. Sometimes that is in a sense true, because if the boss or the manual says there is one way, then that is supposed to be the right way. Or everyone might indeed agree that one way is far more right than another.

If procedures aren't that clear cut though, then it is a kind of 'blame the underling' strategy. If the boss' way results in an accident, well, it's just an unfortunate accident and maybe things will have to change in the future. But if the underling's way results in the accident, then the underling pilot may have been guilty of normalization of deviance.

So one has to be careful about defining what is normal or acceptable. There may be no absolutes involved.

The "How I almost destroyed..." article does talk about Normalization of Deviance as both something that can happen to individuals (like him & his back seater doing the 0g gear up procedure) and something affecting an organization (e.g, Red Arrows procedures getting out of step with other parts of the RAF).

One has to be careful not to conflate the two. If it is something happening in an organization, where it has been accepted as a norm to do things in a way unlike in the dusty manual on the shelf -- and the boss hasn't stepped in -- then it may not be an individual pilot's fault. He isn't normalizing any deviance -- he's just following the de facto standards of the squadron. As far as he knows, his procedures are normal and not deviant.

Just my opinion as an amateur observer of aviation human factors.
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Old 2nd Feb 2016, 12:29
  #45 (permalink)  
 
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Originally Posted by CONSO
1 = 1 g
2 = 1 g
3 = 1 g

assumes balloon is stationary and NOT accelerating up or down AND he does not use a fly suit or wing suit but drops like the proverbial brick
No.

2 is zero if we use the only sensible reference frame.

You can check this by fitting a g meter to the man. It will read +1/0/+1

We can go into a little more depth if you want, but if you disagree, be aware that you are arguing with Einstein, not me.

The elevator, the rocket, and gravity: the equivalence principle ? Einstein Online
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Old 2nd Feb 2016, 16:42
  #46 (permalink)  
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Beat me to it on Equivalence. The fascinating thing is that the instant his fingers stop resisting gravity, he is weightless (no real airflow yet.) No transitional time.

I'm perplexed by the thread drift since it sometimes seemed to veer, erm, bunt off into talking of negative g rather than attaining 0 g. Thread drift is usually beneficial, nit-picking, quite different.

I'm sure the pilot was able to fly level inverted without much thought and then the issue becomes - what would be shown on a g-meter?

Neil Williams. For those not around back then, the man knows a little about inverted flight. Having suffered what might be called, asymmetric dihedral, i.e. a broken wing, he flew back to base inverted, flipping the right way up for the landing. Nifty.

Zlin wing Structural Failure Report - Neil Williams
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Old 2nd Feb 2016, 18:30
  #47 (permalink)  
 
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1. There is no need to "gently push up" once inverted to get -1G. You are already there just by being inverted.
Surely I'm not the only in this thread who's flown inverted. There is indeed a need to "push" once inverted. I'll see if I can explain it.

A trimmed aircraft in level, unaccelerated flight is usually presented in basic aerodynamic texts books with four opposing vector arrows pointing up, down, forward, and aft representing, in order, lift, gravity, thrust, and drag. We can ignore thrust and drag for the moment. The g meter will read 1 in this instance.

If the aircraft is rolled inverted without making any other changes then the lift vector and gravity vector arrows are both pointing in the same direction. The aircraft will accelerate toward the earth rather rapidly unless the pilot does something to prevent it.

If level inverted flight is the goal, then the pilot will push forward on the stick far enough to produce a lift vector equal the the weight of the aircraft or, put another way, he will produce sufficient negative lift to offset the force of gravity. A new drawing will show the same four vector arrows, but this time the lift vector will be extending from the belly of the aircraft; i.e. the vertical forces on the aircraft are reversed. To maintain level inverted flight in a conventional aircraft, you gotta' push to overcome the significant out of trim condition.
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Old 2nd Feb 2016, 18:57
  #48 (permalink)  
 
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Mozella

It is possible/probable you may have to re trim when inverted, but that is different from "lets just roll inverted and get a gentle push up"

I would describe the action required to fly level inverted as applying forward pressure to maintain straight and level until re-trimmed. Once re-trimmed, no push will be required.

I believe I am correct in thinking that when the phrase "lets just roll inverted and get a gentle push up" was used he meant to push the nose of the aircraft up from the horizontal to get negative g.
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Old 3rd Feb 2016, 00:52
  #49 (permalink)  
 
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Tourist & Loose rivets, no fooling you two. The instant he lets go he is experiencing zero g. This fact was used to good effect in the production of lead shot and musket balls in days of old, since a liquid in zero g will form a perfect sphere.

NASA has what is called a "drop tube" at Brook Park, Ohio, in which they conduct zero g experiments in a vacuum environment. The working area of the tube is 432 feet in depth and 20 feet in diameter, allowing 5.18 seconds of zero g when the experiment is dropped.
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Old 3rd Feb 2016, 11:43
  #50 (permalink)  
 
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Originally Posted by megan
Tourist & Loose rivets, no fooling you two. The instant he lets go he is experiencing zero g.
Though not all of him, obviously.....
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