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Another 727 exit video with pressure thumps clearly audible as each jumper exits. Don’t need a stair rebound. Stairs not lowered.

On my DC 9 jump I could have accurately counted every jumper exit from my seat in the forward section of the cabin, even blindfolded

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377

Still curious what accounts for the 'pressure thumps clearly audible'. If not stairs closing hole then what? Presence of a moving body obstructing the hole then opening the hole - opening of chute close to the hole - ??
 

That is a good question.

377, did you actually feel a pressure change or was it a noise change or both?

I can't think of any reason for a pronounced pressure change under these conditions.

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Another 727 exit video with pressure thumps clearly audible as each jumper exits. Don’t need a stair rebound. Stairs not lowered.

On my DC 9 jump I could have accurately counted every jumper exit from my seat in the forward section of the cabin, even blindfolded

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377

Still curious what accounts for the 'pressure thumps clearly audible'. If not stairs closing hole then what? Presence of a moving body obstructing the hole then opening the hole - opening of chute close to the hole - ??
 

That is a good question.

377, did you actually feel a pressure change or was it a noise change or both?

I can't think of any reason for a pronounced pressure change under these conditions.

DEFINITELY a pressure bump felt. All sound of course involves pressure waves but this was a feel it in your gut "THUNK". I'll bet a rate of climb gauge (dP/dT) would have shown a big needle excursion.

377

Perception can be tricky, but it sure felt like a positive pressure excursion.

377

Perception can be tricky, but it sure felt like a positive pressure excursion.

377

Thanks.  Let me now make a wild eyed guess about the pressure and noise.

Consider an empty wine bottle with a cork in the top.  Assume that the cork has been replaced sufficiently to just completely seal the opening.  At this point the air inside and outside the bottle will be at the same pressure.  If the cork is pushed in further, the air in the bottle will have a greater pressure than the air outside the bottle.  In either case, if the cork is suddenly (repeat, suddenly) pulled out of the bottle, there will be both a "pop" and pressure changes inside the bottle.

When the rear stairs of a 727 have been removed and with the cabin's aft pressure door wide open, the pressure inside the cabin and just outside the aft stairwell are essentially the same.

When a skydiver, in free fall, goes through the stair opening, he/she apparently blocks enough of the opening for split second to create a slightly lower pressure in the cabin.  The skydiver clearing the opening is about the equivalent of pulling the cork out of the bottle.  It will cause a "pop" (or some kind of noise) and cause a pressure disturbance in the cabin.  In addition, the skydiver free falling through the stair opening will block some of the external engine and aerodynamic noise for a split second.

And remember that 377 states that the sound of the skydiver going through the stair opening is different from the ambient noise.

   

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Perception can be tricky, but it sure felt like a positive pressure excursion.

377

Thanks.  Let me now make a wild eyed guess about the pressure and noise.

Consider an empty wine bottle with a cork in the top.  Assume that the cork has been replaced sufficiently to just completely seal the opening.  At this point the air inside and outside the bottle will be at the same pressure.  If the cork is pushed in further, the air in the bottle will have a greater pressure than the air outside the bottle.  In either case, if the cork is suddenly (repeat, suddenly) pulled out of the bottle, there will be both a "pop" and pressure changes inside the bottle.

When the rear stairs of a 727 have been removed and with the cabin's aft pressure door wide open, the pressure inside the cabin and just outside the aft stairwell are essentially the same.

When a skydiver, in free fall, goes through the stair opening, he/she apparently blocks enough of the opening for split second to create a slightly lower pressure in the cabin.  The skydiver clearing the opening is about the equivalent of pulling the cork out of the bottle.  It will cause a "pop" (or some kind of noise) and cause a pressure disturbance in the cabin.  In addition, the skydiver free falling through the stair opening will block some of the external engine and aerodynamic noise for a split second.

And remember that 377 states that the sound of the skydiver going through the stair opening is different from the ambient noise.

 

Chute is opened or not on exiting! ? IT MATTERS!

Area of person/body vs area of a chute vis a vis the hole air stream.

Until that is answered you haven't defined the whole problem.

Do they stand at the hole and open a chute or do they jump and open the chute later - further away from the hole?

In the jumps that 377 describes, the skydiver does about a 10,000 foot free fall before opening his chute.  So no open parachutes are involved.

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Perception can be tricky, but it sure felt like a positive pressure excursion.

377

Thanks.  Let me now make a wild eyed guess about the pressure and noise.

Consider an empty wine bottle with a cork in the top.  Assume that the cork has been replaced sufficiently to just completely seal the opening.  At this point the air inside and outside the bottle will be at the same pressure.  If the cork is pushed in further, the air in the bottle will have a greater pressure than the air outside the bottle.  In either case, if the cork is suddenly (repeat, suddenly) pulled out of the bottle, there will be both a "pop" and pressure changes inside the bottle.

When the rear stairs of a 727 have been removed and with the cabin's aft pressure door wide open, the pressure inside the cabin and just outside the aft stairwell are essentially the same.

When a skydiver, in free fall, goes through the stair opening, he/she apparently blocks enough of the opening for split second to create a slightly lower pressure in the cabin.  The skydiver clearing the opening is about the equivalent of pulling the cork out of the bottle.  It will cause a "pop" (or some kind of noise) and cause a pressure disturbance in the cabin.  In addition, the skydiver free falling through the stair opening will block some of the external engine and aerodynamic noise for a split second.

And remember that 377 states that the sound of the skydiver going through the stair opening is different from the ambient noise.

 

Chute is opened or not on exiting! ? IT MATTERS!

Area of person/body vs area of a chute vis a vis the hole air stream.

Until that is answered you haven't defined the whole problem.

Do they stand at the hole and open a chute or do they jump and open the chute later - further away from the hole?

In the jumps that 377 describes, the skydiver does about a 10,000 foot free fall before opening his chute.  So no open parachutes are involved.

Robert, if you see this ... have you got anything on Columbia water column temps near TBar? Surface to channel bottom?  I looked around a little and was surprised to find the Columbia as warm as it is, apparently? But I have yet to find any water column temps say in ten foot intervals? It matters if the money and bands were ever in the main river at some depth ... for example melt transition (gooey stage) of the bands is at 68F !    anything would helpful ...

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Perception can be tricky, but it sure felt like a positive pressure excursion.

377

Thanks.  Let me now make a wild eyed guess about the pressure and noise.

Consider an empty wine bottle with a cork in the top.  Assume that the cork has been replaced sufficiently to just completely seal the opening.  At this point the air inside and outside the bottle will be at the same pressure.  If the cork is pushed in further, the air in the bottle will have a greater pressure than the air outside the bottle.  In either case, if the cork is suddenly (repeat, suddenly) pulled out of the bottle, there will be both a "pop" and pressure changes inside the bottle.

When the rear stairs of a 727 have been removed and with the cabin's aft pressure door wide open, the pressure inside the cabin and just outside the aft stairwell are essentially the same.

When a skydiver, in free fall, goes through the stair opening, he/she apparently blocks enough of the opening for split second to create a slightly lower pressure in the cabin.  The skydiver clearing the opening is about the equivalent of pulling the cork out of the bottle.  It will cause a "pop" (or some kind of noise) and cause a pressure disturbance in the cabin.  In addition, the skydiver free falling through the stair opening will block some of the external engine and aerodynamic noise for a split second.

And remember that 377 states that the sound of the skydiver going through the stair opening is different from the ambient noise.

 

Chute is opened or not on exiting! ? IT MATTERS!

Area of person/body vs area of a chute vis a vis the hole air stream.

Until that is answered you haven't defined the whole problem.

Do they stand at the hole and open a chute or do they jump and open the chute later - further away from the hole?

In the jumps that 377 describes, the skydiver does about a 10,000 foot free fall before opening his chute.  So no open parachutes are involved.

Robert, if you see this ... have you got anything on Columbia water column temps near TBar? Surface to channel bottom?  I looked around a little and was surprised to find the Columbia as warm as it is, apparently? But I have yet to find any water column temps say in ten foot intervals? It matters if the money and bands were ever in the main river at some depth ... for example melt transition (gooey stage) of the bands is at 68F !    anything would helpful ...

I doubt if such information is routinely collected.  But there may be special papers or projects that checked into this matter.  Maybe the Washington State or Oregon State Fish or wildlife departments have done something along this line.  Perhaps the Portland area fishermen who are online here can help.

An eon or so ago, I spent a lot of time swimming in a tributary of the Columbia River about 200 miles upstream of Tina Bar.  Amazon and I discussed this on DropZone, but even in July and August the water in that river was essentially just melted ice and I can guarantee that the water temperature was never anywhere close to 68F degrees.

And I suspect that the water at Tina Bar is also going to be essentially just melted ice and quite a bit colder than anything you would see in a central or mid-western river during the summer.

Also, keep in mind that the deepest part of the Columbia in the Tina Bar area is the 40 foot deep shipping channel that is close to the Oregon side of the river.  I doubt that there is much variation vertically in water temperature.

Meyer, and maybe Bruce, have ventured a few feet into the river to cool off, so maybe they can provide some input on this.

ok, let me see what I can find. Thanks. Will keep you posted. All of this matters as far as money and band deterioration IF the money spent time in the river.

Find someone who is monitoring invasive species; zebra and quagga mussels begin reproducing at 54 degrees so most AIS specialists monitor water temp to understand where and when to look when doing assessments and surveys. They might have the best info.