OMS and their Bungeed Wing

[100days-a-year]

Don't own an OMS wing so I can't say anything about how they work.There is an entanglement hazard,that's obvious.But ,is it serious enough to diss it?And for anyone to question if GI has any care about the credibility that anyone may give him is sure funny.In his field ,he is the top of the food chain.If he says something, rest assured he ain't gonna deign to lie to you.What he says is his experience.I have double bladders,but rarely need thier lift.No,they are not any bulkier.More failure points,yes.I have a variety of old bladders around,new bladders will be halcyon...period.I have one and everyone elses at the site is junk when compared side by side(OMS,Dive-Rite,S-P,Cressi,Zeagle,Dacor)My buddies and I often compare stuff,but workmanship is not subjective.We all like our stuff,but if my life is on the line 1000' back 300' down I remember my coach yelling 2nd place is 1st loser.

 

[omar]

Roak,

You don't need to go to the training center. You can go up to CSU and use their flume in the hydraulics lab. CSU has the capability to determine the drag on a set of wings. A wind tunnel would work as well. Air and water flow is pretty much the same. The difference is the viscosity of the medium.

If a fluid or gas is flowing over a surface, the molecules next to the surface have zero speed. As you get farther away from the surface the speed increases. This difference in speed is a friction in the fluid or gas. It is the friction of molecules being pushed past each other. This amount of molecular attraction or friction is called viscosity. Thus, viscosity determines the amount of friction, which in turn determines the amount of energy absorbed by the flow.

Viscosity is the principal factor resisting motion in laminar flow. However, when the velocity has increased to the point at which the flow becomes turbulent, pressure differences resulting from eddy currents rather than viscosity provide the major resistance to motion. That is why the prop wash test is flawed. The prop creates such a turbulent flow that they are not measuring the drag of the wings.

Also, turbulent flow is more pronounced with bungeed wings simply because of the bunches of material pulled in by the bungee and the bulge of uncompressed material. These areas behind the bulges allow vortexes and eddy currents to develop.

What you have is in effect is the difference in flow across a boulder river bed versus a sand bottom. Go and look up the coefficient of friction for each and you will see that the friction on boulder bottom is greater because the turbulent flow in the boundary layer is much more pronounced.

This is also why you see race cars with smooth sheet metal. It is generally intuitive that a smooth surface will cause less drag. Do you see Formula One or Indy or stock cars with rumpled bodies? Of course not because there is greater drag than a smooth surface.

omar

 

[FredT]

Drag testing with a scooter provides good data, provided the entire dive is done with a "scooter positioned" body. Angle of flow across a free-swimming diver will be different; thus the drag factor will be different, as will the efficiency of fins in the turbulent flow of the diver's wake. What is true for a scootered diver will probably NOT hold for the free swimmer. Although the data sets may be related there is a leap of faith necessary to tie the two cases together without detailed testing.

Proper drag testing is done in a still water tow tank with the diver in the proper position for both propulsion methods.

The three "public access" tow tanks with well-calibrated gantry instrumentation I know of are:
1. Scripps (La Jolla, CA.?)
2. The huge David Taylor Tow Tank (USN research facility in MD?)
3. The USGS calibration tank at Stennis Space Center in MS.

There are several others, but they generally are attached to commercial ventures such as oil companies and shipyards. They can be had occasionally, but "in house" projects have priority and protection of proprietary IP often makes these harder to get into than the government tanks.

"Rental" with operators and calibrated gantry speed instruments runs between $1k and $10K per shift depending on facility, staff, and equipment needed. The David Taylor tank is large enough the earth's curvature was calculated and matched during the gantry rail installation to provide a constant depth for equipment under test. Gantry attachment to equipment under test is the responsibility of the "customer" and often runs tens of thousands of dollars all by itself in sophisticated testing programs.


FT

 

[The Chairman]

"Leap of faith" so aptly describe how some view their equipment and how that equipment performs. Very good post Fred!

 

[Lost Yooper]

Originally posted by NetDoc
"Leap of faith" so aptly describe how some view their equipment and how that equipment performs. Very good post Fred!

Yeah? On who's part?

 

[TwoBitTxn]

I am beginning to hear the sounds of the beaten dead horse.

Suffice to say:

One side says the bungies pose an entanglement hazard and increase drag. Also if the wing were to be punctured it would completely deflate leaving you with nothing.

The other side says:

The bungies are too snug to the wing for anything to easily get up under it. If something were to get under it the tubing could easily be broken or cut thus getting the diver out of the situation. This side doesn't have a great response to the drag issue other than prove it. Both sides agree the OMS testing appeared flawed but it is all we have. Fred blew the scooter issue out. As for the final point; LY I think offered up a very good idea to puncture a bungied wing and see it it didn't totally deflate or if it would as I was told only deflate to the nearest bungie and stop or greatly slow. If someone is willing to offer up their wing to try this test please do so, but not with mine as I would like to dive it before punching holes in it. I would also like to see the test done at depth with a bungied wing and a non bungied wing to see which one emptied first as I believe (maybe wrongly) the end result with both BC's would be an empty BC leaving you with the same predicament.

This whole discussion (IMHO) has gotten to the point it reminds me of a past friend of mine that HATED Fords. You could have shown him the best car ever made in all of auto history, but if it was a Ford he still never would have driven it as he would have found an excuse to hate it.
I'm not saying the OMS is the best ever made and maybe at some point I will find some of the Con arguements are right and I remove the bungies, but I do hope that if it could be proven the con arguements are flawed those detractors here could at least admit it.

Tom

 

[large_diver]

Tom -- excellent summary.

And to be clear: it's Chevys that suck...Fords are fine ;-)

 

[roakey]

Originally posted by Tom Vyles
Fred blew the scooter issue out.

Wishful thinking at the very least.

He said what's applicable at scooter speeds and body attitude may not be applicable at swimming speeds and body attitude.

I agree, in fact I'll go as far as to say that I don't think there's a noticeable difference at swimming speeds between the two (given the same lift wing).

However, to say it again, I buy for the endgame, and I may scooter someday and the best and most accurate testing to date has been done by the WKPP (FredT even goes out on a limb and calls it “good data”) and the non-bungee wing wins. If someone wants to agree that OMS’ data is flawed and ignore the WKPP’s “good data” and still buy OMS, go right ahead.

But it’s all noise when you think about the bungee “power leak” feature. Would a bungee-wing proponent like to defend that flaw? I should add, other than the “spend more money and add more complexity to compensate for an introduced problem!” defense?

The WKPP is very good at many things, one being the philosophy that a “solution” that introduces another problem that you have to solve is no solution at all.

As in bungee-wings ("solution")->power leak (introduced problem)->dual bladders (solution to introduced problem).

Roak

 

[The Chairman]

about the alleged disastrous effects of a Bungeed power leak... I will not dive that over weighted! If I can not make it safely to the surface with -NO- air in my bladder then I did something wrong. I thought, perhaps erroneously, that this was a DIR precept as well.

In fact, when I do choose to ascend, I deflate my BC completely, so there is no possibility of a runaway ascent. The incumbent kicking action (according to BillP) will help my off gassing as well!

As for un-answered benefits, no one on the "other side of the bungee" has commented on the reduced air shift with a bungeed system, and how you can easily adjust your trim as well. The increased stability will probably make it less likely for you to puncture your BC anyway. It’s almost like the big car/compact car scenario... Big is great if you are actually in a crash, but the nimble compact may very well avoid the crash altogether.

Tom, that WAS a mighty fine job of clarifying just where we do disagree!

Ford? Chevy??? Give me my AMERICAN BUILT Nissan Truck!

 

[Uncle Pug]

Originally posted by NetDoc
In fact, when I do choose to ascend, I deflate my BC completely, so there is no possibility of a runaway ascent. The incumbent kicking action (according to BillP) will help my off gassing as well!

Pete,
I think you have taken this farther than Bill intended...
You can ask him....
But vigorous muscle movement...
Especially the large leg muscles...
Is the best way to generate BIG bubbles....

Movement to promote circulation through the pumping action in the capillary beds is helpful if not too vigorous....

I know you won't believe me without data & bungees to back me up...
But I do care for your safety...
Please ask the Doctors about this...
I know you don't do tech diving and deco stops...
But this is just as important after a rec. dive...