steel 120's for side mount?

[victorzamora]

So it turned out not to be total gibberish; definitely an improvement over 2 posts. Perhaps you want to try it before saying that I've got it wrong?

It is total gibberish. Supersonic flow characteristics are completely counter to what subsonic flow does. We are diving SO immensely far below the speed of sound the entire concept is laughable.

What you're suggesting is that divers frequently experience speeds faster than an SR71 Blackbird's declassified top speed. We're traveling at mach 0.03. Conical shock waves are for Mach 1+ local. Take a class.

 

[djcheburashka]

For some strange reason, animals that move really fast underwater tend to be cylinderish and streamlined, as opposed to really wide but flat... Hmmm...

The thing approaching supersonic speeds is the recession of your credibility.

Anyhow, to the extent this discussion has become about the trans-sonic behavior of objects travelling through water, it's too ridiculous to continue.

Give it a try and get back to us

 

[decompression]

I'm a turtle.....


Sent from my iPhone using Tapatalk

 

[Razorista]

@victorzamora
I am not sure and you are more the expert there, but let me ask at least:
Isn't the point about supersonic flow dynamics in gases (the Blackbird example) that they behave more like liquids then (i.e. water)?

So there may some truth in what he is saying - if the sidemounter used as example really has a larger profile than the backmounter used for comparison.

Sidemount really could have much more drag on the scooter when the profile seen as a whole is not smaller at all than that of a backmount diver.
Most do not bother much about drag when using a scooter anyway, but from the standpoint of using 4 or more stages sidemount badly the scooter might not be able to keep up with a backmounter with stages adjusted more perfectly and a streamlined wing-package.

btw: If I blow the exhaled air in front of me fast enough when my scooter is going Mach 1+, will I be able to make use of cavitation then?
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One additional thing from observation: When my buddy was testing his Gavin Short Tube a month ago I could keep pace with it for 10 Meters and more before I had to give up following the backmounter. In sidemount it carried both of us at comparable speed and I could not let go for more than a moment before being unable to follow.

 

[victorzamora]

@victorzamora
I am not sure and you are more the expert there, but let me ask at least:
Isn't the point about supersonic flow dynamics in gases (the Blackbird example) that they behave more like liquids then (i.e. water)?

No. Water and air act the same at the same Reynolds number. People use water tunnels for airplanes to get better visual effects insert some circumstances. Water and air are just fluids with different properties. Flow acts similarly. Supersonic flow is literally backwards in most ways. Either way, you're not encountering shock waves (the comes he referred to) in any fluid below M1.

Sidemount really could have much more drag on the scooter when the profile seen as a whole is not smaller at all than that of a backmount diver.

Sidemount is a slightly smaller profile, actually. Everything is about the same in terms of quantity of gear. The biggest difference is that in sm, your tanks are partially hidden by your arms/shoulders. Your head is partially hiding doubles, so it should be similar.

As for badly mounted stages in sm versus perfect bm technique..... Yeah, you're right. However, the only good comparison is perfect technique for both.

btw: If I blow the exhaled air in front of me fast enough when my scooter is going Mach 1+, will I be able to make use of cavitation then?

Hahahahaha, that MIGHT work..... until you explode. There's a Russian torpedo that uses super cavitation to achieve the max underwater speed.... of like 200kts, a far cry short of mach 1. Hilarious idea, either way.

 

[Razorista]

No. ... the same Reynolds number.... in any fluid below M1.

Ah, got it, thank you!
He might be referring to something like that, but I do not think the instructor who made the slides he saw was.
He was probably just referring to drag on an 'old-style' setup with the sidemount tanks already hanging as low as stages and the additional stages below that.
Outdated info but not bad at all. Those drawings might have been very interesting.

Sidemount is a slightly smaller profile...

Concur.
But you can do it very badly.
You even called my own setup bad a few days ago and as I described above it is still far superior to a very streamlined backmount system considering drag on a scooter.

As for badly mounted stages in sm versus perfect bm technique..... Yeah, you're right. However, the only good comparison is perfect technique for both.

Concur again.
But sadly nobody is doing it that way.

Even you are flexible yourself I got to see in the other thread: When it concerns the SMS75 you are no less biased than I am about the Razor and are prone to ignore contrary evidence - as I am myself whenever the Razor is mentioned.
You also proved that anyone can show anything he wants to with seemingly convincing drawings.
I do not criticize that by the way, I actually liked it.

Hahahahaha, that MIGHT work..... until you explode. There's a Russian torpedo that uses super cavitation to achieve the max underwater speed.... of like 200kts, a far cry short of mach 1. Hilarious idea, either way.

But..., but I was told sidemount would allow 'supermanning' - was I lied to?

There goes my dream of saving Atlantis from hypersonic torpedos...:blinking:

...
Sometimes at least it feels just like that, that's enough.

 

[djcheburashka]

I looked it up-we're right, Victor's wrong. Drag is proportional to total surface area. The three dimensional object that minimizes surface area for a given volume is a sphere. At a given volume, the surface area of a circular cylinder is smaller than that of a squashed cylinder. So same principle, no shock waves, no supersonic speed, no Reynolds number. Just a little physics and middle-school geometry.

 

[Razorista]

I looked it up-we're right, Victor's wrong. Drag is proportional to total surface area. The three dimensional object that minimizes surface area for a given volume is a sphere. At a given volume, the surface area of a circular cylinder is smaller than that of a squashed cylinder. So same principle, no shock waves, no supersonic speed, no Reynolds number. Just a little physics and middle-school geometry.

No, even I can see that is surely not correct.
This would only be true if there was absolutely no space between elements of the imagined sphere.
Otherwise all objects would have to be considered separately, only turbulence between them would matter: diver separately from tanks.

I would consider the smaller spaces (even eliminated spaces) separating objects an advantage of sidemount there, as this is even closer to approaching the ideal of the sphere than dragging along separate non-spheres a hand-span above you.

Considering your implied insult: I do not know about your school system as a foreigner but learning to see the obvious first was very important to the physics teachers I had.

 

[djcheburashka]

Razorista: think it through again. I didn't say spaces between objects or intricacies of shape are *irrelevant*. I only said drag is proportional to surface area. I.e., other things being equal a shape transformed to have more surface area will have more drag.

There are of course other aspects of drag like how an object cuts the water, but apparently they only matter at supersonic speeds

 

[Razorista]

That's logical (and at last said in a non insulting way again, thank you) and convincing.

But an cannot fully concur:
There is exactly the same surface area on a diver and his tanks considered separately for backmount and sidemount.
One diver two tanks.

Considering the tanks are pushed to the sidemounters sides so tightly water cannot move in-between much they could be considered a unified object.
On the backmounter however the water can move around the tanks on all sides. That would mean what I described above: a non-sphere dragging two seperate non-spheres above it with much more surface area than any sidemounter could have before putting on another two stages.