A drag issue : to bungee wings or not to bungee

[Blackwood]

I didn't want to quote an entire article on golf balls, here on a diving forum... but that effect is evidently not appropriate as a metaphor to what happens with water resistance and a diver.

Maybe, maybe not. It's impossible to make that determination without doing some work.

The dimples reduce the speed needed to cause turbulence. This turbulance, at speed, creates a 'pocket' behind the ball... a 'turbulent flow'.

No, they cause turbulence directly.

What's happening in essence is this: turbulent flow has more energy and a higher velocity gradient (relative to the surface) than an equivalent laminar flow. This increases drag due to skin friction, but it also allows it to make more headway against the adverse pressure gradient.

Turbulent flow (generally speaking) will therefore stay attached longer than will laminar flow (all else being equal).

Separated flow (wake) behind the ball causes form drag. A wake fed by laminar flow is often larger than that fed by turbulent flow since laminar flow detaches sooner.

It's a balancing match between friction and form drag.

I'm not suggesting that a bungeed wing makes more or less drag than a non-bungeed wing of the same geometry. Rather I'm simply poking at the "common sense" notion that bumpy surfaces definitely create more drag than smooth surfaces.

 

[danvolker]

I call Shenanigans#3. I have yet to see any real deaths attributed to the bungees, and I have dove them with a HOLE without perishing or even struggling. Considering your source, I am not surprised.

Look, if you don't like bungees: don't use them. Calling them "BWOD" is simply stupid on several levels. The "if you don't dive my way, you will surely die" line of argument is as vapid as is it is egotistical. They are specious at best.

Disclaimer... I have dove OMS bungeed wings as well as many unbungeed wings. My current sidemount rigs (both Hollis and Zeagle) use bungees to help with my profile.

Net Doc,

I do not believe you or anyone else on this board would accuse me of posts on here telling people to "dive my way or DIE!".

The "bungeed wings of death threads on Cavers and techdiver, had a very large number of technical divers weighing in on this issue, so historically and educationally speaking, it was worthwhile and on-point for being included in this discussion.
In the Jane Orenstein death, when George and I recovered her body the day after her death ( arguably contributed to strongly by the incompetence of her dive instructor, more than having anything to do with the bungee wings she was wearing) , we experienced first hand the failure of the bungeed wings to inflate to capacity as we tried to lift her off the bottom. George used his gas to attempt inflation of her wings, and the bungeed setup did not allow anything close to full inflation before the dump valve let go....George and I together were able to lift her off the bottom to the boat, but the failure of her bungee wing to inflate to rated capacity was a clear indication that this wing "could" cause someone to have a fatal mishap.

I could recount several other stories with equal or greater significance to the threat issue, but this really misses the point..
The point is, the bungees only "look cool"...they do not improve the function of the wing, OR the safety of the diver. Even if you like diving your OMS bungee wings, you must agree the bungees do nothing to improve your safety or performance.
REgards,
DanV

 

[The Chairman]

, you must agree the bungees do nothing to improve your safety or performance.
REgards,
DanV

I don't agree. Air shift is next to nothing on a bungeed wing. They increase stability dramatically and in a way that most don't realize until they dive one. Can you accommodate air shift in a non-bungeed wing? Sure. Even now, I use bungees to keep my side mount rig as LOW AS POSSIBLE on both my Hollis and Zeagle rigs. I know that I have it a bit too tight on my Zeagle Express Tech, but it works for me.

Now, my OMS bungeed wing lies in the corner feeling neglected. There are better designs, at least for me, and I dive them.

My point was, calling them "BWOD" is stupid. If a diver over-tightens the bungees so that they can not work properly, that's not the wing's fault. That's diver/technician error. I have yet to see where a properly configured wing has caused a death. Mind you, these discussions have been going on here since the turn of the century. I know for a fact that a 1/4" puncture will not kill you. In fact, since I was so close to being neutral, I didn't even notice it for a couple of dives.

 

[rjack321]

A diver never reaches a speed where the turbulance creates a pocket around him.

You should work out more


:d

 

[danvolker]

I don't agree. Air shift is next to nothing on a bungeed wing. They increase stability dramatically and in a way that most don't realize until they dive one. Can you accommodate air shift in a non-bungeed wing? Sure. Even now, I use bungees to keep my side mount rig as LOW AS POSSIBLE on both my Hollis and Zeagle rigs. I know that I have it a bit too tight on my Zeagle Express Tech, but it works for me.

Now, my OMS bungeed wing lies in the corner feeling neglected. There are better designs, at least for me, and I dive them.

My point was, calling them "BWOD" is stupid. If a diver over-tightens the bungees so that they can not work properly, that's not the wing's fault. That's diver/technician error. I have yet to see where a properly configured wing has caused a death. Mind you, these discussions have been going on here since the turn of the century. I know for a fact that a 1/4" puncture will not kill you. In fact, since I was so close to being neutral, I didn't even notice it for a couple of dives.

I have to say I have never experienced "air shift" in my Halcyon wings..though I would add that I rarely add much gas to the wings...perhaps this could be an issue when diving a 7 mil suit at great depth, when also using heavier tanks....In any event, I guess I can't dispute your experience with something I have never dealt with....

As to the whole "stupid" thing, come on Pete, the name "Bungee Wings of Death" adds huge Drama and FUN to our threads here on scubaboard...Its a great title! We could have a movie from this

Regards,
DanV

 

[cool_hardware52]

The slow speed turbulance is just resistance... more akin to the flaps on a plane causing 'stall effect'.

Not sure I follow you here. Deploying flaps reduces the stall speed and increases drag.

Fowlers alter the area, curvature and cord of the wing.

Spoilers OTOH add drag and reduce effective wing area.

Tobin

 

[scjoe]

Those reports seem likely and believable.

It doesn't take a great leap of faith to accept that
this...

....is more streamlined than this....

Is it just me....or does that just seem like a whole heap of common sense??

Common sense and relying on what you see (or think you see) doesn't work as often as you might think. For example, common sense may tell you that the main reason one person runs faster than another is that they are moving their legs faster, but that isn't the reason, nor is it necessarily true.

 

[cool_hardware52]

I don't agree. Air shift is next to nothing on a bungeed wing.

Shift can be managed with overall wing shape without any bungees.

Tobin

 

[The Chairman]

Shift can be managed with overall wing shape without any bungees.

Tobin

They increase stability dramatically and in a way that most don't realize until they dive one. Can you accommodate air shift in a non-bungeed wing? Sure.

I believe I stated as such, Tobin. That doesn't mean it's not there.

 

[TSandM]

I don't understand this. I WANT to be able to park gas in one part of my wing rather than another; when I've got a couple of bottles hanging off one side of me, putting more gas in that side of the wing is how I avoid tipping over. Why would I want a wing that evenly distributed the gas?

To me, there is a fundamental flaw in the design. The wing is oversized, and the bungies are used to make it smaller. Choosing a wing with a very large capacity implies that, at some point, you think you are going to need that much lift. But when you have to use it, the bungies are most stretched, and therefore are most likely to exhaust gas from the wing in the event of a puncture. So when you need the most lift, the risk is greatest that you won't have it. Doesn't make sense to me.