Carmichael low drag bulb

[Submarine Tom]

I've read old, old threads on this site before.

It appears there are some very knowledgeable people partaking.

I need to know the lowest drag form for a 15 knot mini-sub.

I mean mini. 22 inch diameter. Shoulder width.

Think of it like a manned torpedo. Actually, it a sports car,

no, make that a jet fighter style, sub. I'm looking for performance,

manoeuvrability, safety, efficiency, shallow water operation (30 feet max),

pressure hull. Has anyone established what hull form offers the least

resistant, good handling performance?

Thanking you in advance, Tom.

[Guest625101138]

I believe the USN did what you seek post WWII with the USS Albacore. This hull resulted from extensive wind tunnel testing and performed to expectation in prototype and eventually operational subs. I believe over 40kts with diesel power.

I have tested this shape at scale level and at human power level. It is good. Basically an ellipsoid with a fineness ratio of 8. The aft end forms into a parabola for a single drive shaft. You need to keep control surface to a minimum.

If you intend to operate near surface most of the time then smaller diameter and larger fineness ratio will give the best result for the same displacement. Wave drag becomes noticeable within 3 diameters of the surface. At the surface the wave drag is substantial unless much much finer.

You will read about laminar flow hulls that are very slippery but I believe they are intended for speeds slower than you indicate.

One having a diameter of 22" will displace around 0.75 tonne so not that small. Drag say 600N at 15kts. Require about 5kW without allowing for prop losses.

Rick W.

[Guest625101138]

When I was looking for low drag hull designs I did a lot of research on installed power and performance on subs. The objective was to determine best possible Cdv and I could use this for my own calculations.

It became frustrating to get actual speed data on subs. I was just re-reading some of the notes I found on USS Albacore (AGSS 569) and here is a classic:
<Phase V required modification for a final series of tests of a classified system designed to increase speed beyond what had been attained earlier. The nature and the results of this test remain classified at the time of this nomination. Ship design expert Norman Friedman gives Albacore's top speed when built as 26 knots and 33 knots when equipped with the silver-zinc batteries. The top speed of Albacore or any other submarine is stated by the Navy as "in excess of 20 knots." One former Albacore officer, forbidden to state any specific speed, said "Albacore has gone more in excess of twenty knots than any other submarine." [8]>

It would have been a wonderful experience to be in a position to make this statement. Simply knowing you are the best but forbidden to say by how much - maybe there is someone out there who actually knows by how much!

Rick W.

[Submarine Tom]

Rick, thank you for your reply.

It fills my heart to hear (read) someone who knows what they're talking about. I've had a frustrating, lonely few months researching this project.

I've seen a lot of what you posted, but appreciate the context you bring.

I do plan to minimize my control surfaces in an effort to minimize drag.
In fact, my original plan was only two elevators mounted behind a RICE
(Kurtz style) nozzle. These would operate independently to double as ailerons. In order to turn, I would first roll 90 degrees, using opposite elevator input, then using "up" elevator input, turn. I think it would be a thrill to drive.

To achieve these manoeuvring characteristics, it is my intension to superimpose the CG over the CB resulting in zero inherent (intrinsic)
stability and a highly responsive vessel.

I should also note here that my design is axsymmetric. It has no conning
tower. No sail. Very unconventional I know, but what a reduction in drag!
My new term for freeboard is: trailer. Other than in emergency, the only way in or out, would be on the trailer.

Fineness Ratio: I'm most interested in your comments here. I have
determined, certainly not conclusively and only from the vague info I've found, that 5-6 is optimal. Now Albacore showed 8. I am very flexible here. I just want what is going to give me the least resistance in a straight line AND while manoeuvring. I don't intend to operate near the surface, too
many hazards, (boats, logs, flotsom, jetsam, tideline debrit, etc.). It is also my impression that the shape I'm after has very poor performance characteristics at and near the surface.

It's very interesting to me your comment on laminar flow hulls not being practical at my speed objective, 15 knots.

5kw, so about 7Hp net or about 10 gross considering ~80% electric motor efficiency and about the same for a nozzled pair of contra-rotating props.
That's a lot of juice isn't it! ~8kw.

Finally, I'm making some headway here. Yahhhhhhhh

Swimmingly yours, Tom.

[Guest625101138]

Tom
The quoted fineness ratio is for a given displacement constraint. If you have a minimum diameter constraint then shorter might be better.

You will find for airships the optimum fineness is about 5 but the optimum for water is finer. Probably related to the lower kinematic viscosity of water compared with air.

I have doubts about the laminar flow hull actually achieving that condition in a high speed maneuvering hull.

I have no idea what experience you have with these sort of boats but they can be nasty. I think something that you enter/exit from a trailer could be dangerous.

You find dollar for dollar that the A123 Lithium batteries are similar price to VRLA on a power basis. Much more expensive from an energy perspective. So for something that will run 15 minutes you might consider A123 lithium batteries as there will be a huge weight saving. It is a matter of how small can you squeeze into. You may need lead batteries for ballast.

There are many safety issues that need to be considered in such a craft. The thought of being trapped under water would make me a very reluctant submariner. Even free diving is far from my most relaxed activity.

Rick W.

[tspeer]

...

I need to know the lowest drag form for a 15 knot mini-sub.

I mean mini. 22 inch diameter. ...Has anyone established what hull form offers the least resistant, good handling performance?...

I've seen papers on minimum drag axisymmetric shapes, but I've not seen any that also considered the handling qualities. I suspect you can tame the handling qualities by proper fin sizes, but what the tradeoffs would be between wetted area in the fin vs wetted area in the hull, I don't know.

You'd probably want to start here: Parsons, J. S.: The Optimum Shaping of Axisymmetric Bodies for Minimum Drag in Incompressible Flow. Ph.D. Thesis, Purdue University, 1972.

Take a look at Design of Fuselage Shapes for Natural Laminar Flow (http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19860014381_1986014381.pdf) and Drag Reduction and Shape Optimization of Airship Bodies (http://www.iag.uni-stuttgart.de/luftfahrzeugaerodynamik/paper/sanfrancisco_6_97_lutz.pdf)

Also, PARSONS, J.S., GOODSON, R.E., and GOLDSCHMIED, F.R., "Shaping of axisymmetric bodies for minimum drag in incompressible flow," Journal of Hydronautics 1974, 0022-1716, vol.8 no.3 (100-107).

I presume your sub is powered (or is it an underwater glider?). If powered, you may be able to have one or more suction slots around it. A Goldschmied body may be the way to go. These are the axisymmetric analogs of Griffith airfoils.

At the slot, you can get essentially a step increase in pressure. This allows you to have a favorable pressure gradient up to the slot, and then a favorable pressure gradient all the way to the tail. Depending on the Reynolds number, you could have laminar flow over the entire surface. See Aerodynamic Hull Design for HASPA LTA Optimization (attached).

And GOLDSCHMIED, FABIO R., "Fuselage self-propulsion by static-pressure thrust - Wind-tunnel verification", AIAA-1987-2935, AHS, and ASEE, Aircraft Design, Systems and Operations Meeting, Saint Louis, MO, Sept 14-16, 1987. 21 p.

A big problem is, you can get any answer you want, depending on how much flow separation you assume is present at the tail. See "Comments on 'Flow Separation Over Axisymmetric Afterbody Models'", attached.

[Submarine Tom]

Thank you Rick W. and Tom S. for your posts. Greatly appreciated.

Tom S, I will do some research into those publications.

Rick, my experience in, and on, the water is in underwater construction,
SCUBA (PADI) Instructor, Triathlon (swimming), Canadian Certified
tow-boat captain, sailing, windsurfing, Canadian Coast Guard Search and Rescue. I have an expired pilots license (the flying connection), and
a technologists deploma in Mechanical Engineering.

I'm also the father of a two year old, husband, have a healthy fear
of dying, and I'm not claustrophobic (as you may have already gathered).

I am considering epoxy or polyester resin with fiber, vacuum bagged,
as a construction material. I have considered steel but doubt it's feasible.
What really does scare me, is imploding and dying though.

I feel comfortable with my safety measures and certainly appreciate the
concern you have expressed.

Rick, I already have 72 lead/acid, sealed batteries. Each weighing ~2kg
or ~ 4 1/2 pounds. I'm not sure where you got the 15 minutes from.
I do want a 15 knot top speed, however. My displacement comes out a bit lower than your estimate at ~950 pounds. That's measured by a scale model I turned on the lathe and then shoved into a graduated cylinder.

Tom S, your final comments on laminar flow and slots is intriguing,
okay, exciting even. Wow!

Am I able to post a JPG drawing on here? If so, how?

I've got more questions but I thought I'd ask the toughest ones first.
Prop size? Variable pitch? High, flexible pitch? Number of blades?
Contra-rotating? RICE nozzle?
I understand it is a cubic relationship between velocity and battery,
or motor, power. And that cavitation is often a problem getting up to speed (15 knots). Here's an idea: 5 or 6 high pitch blades in a low clearance
RICE nozzle with direct (shaft) drive to an infinitely variable speed, high
torque, electric motor. Infinitely variable pitch would be wonderful,
but so would a million dollars. I've heard about automatically
variable, flex blades made of a plastic composite... Sounds almost
magical!

Tom
Victoria BC

[Guest625101138]

For posting images you click over the paper clip icon on the reply screen and you get a pop-up window. See attached screen dump of part of this page.

Unless you have concerns about hitting objects I would just go for an open prop up around 20" diameter. Counter rotating would be good but you could control prop torque using other methods. Typical design is attached. This is a lightly loaded prop. You get an idea of the possible efficiency.

Counter rotating adds complexity in the drive. I would look to ballast/placement of batteries to keep it oriented. I know what you said earlier but this shape does not need to roll to turn. I expect the low CofG will provide the correct lean anyhow - there are lots of papers on sub dynamics. You could spin the prop faster to reduce torque but the efficiency comes down. You can still get over 80% at 2000rpm. I will leave you to calculate the torque and hence the required righting moment without any control surface input.

I can vouch for the ease of driving these hulls. I got the attached contraption up to almost 7knots and it suffered a lot of wave drag because the main hull was no more than 1ft below the surface. The outriggers also caused a lot more drag than intended. I fitted small foils on them for the second test. I did glide testing and tow tests on scale models as well. I could not get drag as low as Albacore but I was working near surface and did not realise till later how much this was costing me. You will see the hulls on SWATH craft tend to be much finer.

I would not operate the thing near deep water until I was very confident about every aspect of operation. At 8m/s you will go deep fast so you need a soft and shallow place to land.

I am more like 700kg on displacement for 0.55m diameter at 8 fineness??? Can you check your numbers on the model.

There is another thread with Mermaid building a radio controlled torpedo that could provide you with some useful data:
http://boatdesign.net/forums/showthread.php?t=23339&page=2
You might encourage Mermaid to get it done and provide some performance data.

Rick W.

[Guest625101138]

If you intend to operate the sub with you in an air chamber then getting it heavy enough will be a challenge. Probably means a steel hull. You just cannot afford to build it light. Even your 144kg of batteries will not help a lot. You may need foils to get the required down force.

There is a lot of work done on human powered subs and they are water filled so pressure is equalised. Also means there is no unfilled space that has to be ballasted. I think current speeds are around 6kts so 15kts under power is not a particular challenge.

The 15 minutes running time was what I felt would be economic for a lithium battery that did not cost the earth. You are going to lose a lot in battery efficiency if you pull harder than 1C from VRLA. Ratings for VRLA are given at 10 hours. Hence you need about 10kWh of batteries at minimum - about 200kg I expect. These would give about 1 hour at full speed. Much further if you decrease speed. It is indeed a cube relationship between speed and power.

Rick W

[Guest625101138]

You can get carried away with the need for the perfect shape. In the end I think you can get very close to optimum with easy to build developable shape with hard chines. I also think you will want to shape it around the available components within reason. You cannot afford much spare space if you want some sort of air filled cockpit. A 22" diameter tube (at the widest) is tiny inside. Need to mock it up and see what it is like. You will also need some way of "seeing". I know cameras have been tried in recumbent racers but riders cannot orientate. I believe you want a boat that will find the surface of its own accord if power fails.

Surface finish is over rated. I am almost certain you will not achieve laminar flow over much of the hull so a perfect finish is really window dressing.

If you made something that was welded up you could fair it out with heavy weight bog.

Rick W

[Submarine Tom]

Okay, I'll bite. What's "bog", as in "heavy weight bog"? A metal filler perhaps?
If I welded it up, it would have to be made out of 100's of pieces in order to get a teardrop shape.
I'll never get the spherical, cross sectional symmetry I would from a lathe turned, foam blank.

But, what I'm hearing here is, that laminar flow may not be achievable anyway on a 15 knot, highly manoeuvrable vessel.
I may as well take a cylinder, put an elliptical bow on and a parabolic tail and go from there. No?

Remember, I want a sub that will be super performance oriented. Rolls, inverted flight, 90 degree banked turns, breaching.
Think of this as a sub you wear. Am I a pacific white-sided dolphin, or a dahl's porpoise, trapped in a mans body? Perhaps.
I want to have fun in the top 30 feet of the ocean without killing myself.

Forward looking sonar, or collision avoidance sonar, may be a necessity here.
Something with a reasonable sweep rate suited to 15 knots.

I considered the camera/screen approach, but that would defeat half the purpose.

Forward looking eyes (horizontal from centre line) and down through 130 degrees or so, with 180 degree side visibility would be fine. If I want to see more to the side or up, I just roll with no affect on trajectory.

No fins, they produce drag. Neural buoyancy a must. I have room for more 4.5 pound batteries but am starting to run out of buoyancy.

I still need 100 pounds or so for ballast/trim tanks. I've already use up 75 pounds in my emerg. drop weight.

I've done the mock-up. 22" at my shoulders is fine. My hands will come down and forward to an array
of controls. I plan foot pedals for my independent elevator control and a couple of hand levels for independent
rudder controls. Independent, as in top half and bottom half. I'll try and get this drawing out.

What I'm after here is crisp roll response using four, independent, control surfaces and that's it.
No fins, no tilting props, no movable ballast. Simple and effective. A lot of driver control.

Also, when rolled 90 degrees, the rudders can act as elevators and the elevators as rudders.

Very unconventional, I know. If you think I'm a nut case, you may be right. Please, challenge my ideas.

It has to be pressurized, as much as I'd like to go ambient, my ears just wouldn't/couldn't take the rapid
changes. Nor could the cabin venting and repressurizing without getting all fancy, hi-tech, expensive, and if it ever fails, once, ouch!

I don't expect I'll run full throttle all the time. If it's low drag, I wont have to. Only to keep up with the seals!

But I wont be outrunning any orca's when they can reach 30 knots! (I spent three years as a whale watching guide/driver).

I picked 15 knots because I thought that's all the thrust I could produce and with calculated drag, that's the number that came out.
I'd welcome 20!

I want a nozzle for stability, like a big fancy rudder, but instead of creating drag, it may cancel out with improved prop efficiency.

Counter-rotating: two fold efficiency improvement. Improved prop efficiency, and no incurred drag from fin, aileron
or independent elevator compensation. I want to roll. Think of the centripetal-neutral feel of riding a motorbike in a corner.

You got what I said about the CofG and CofB being superimposed, right?

I read Mermaid the other day. That's what inspired me to blogg-on.

Okay, now lets see if I can get that drawing up.

Tom, Victoria BC

[Guest625101138]

Tom
A quick response to hit some points.

The numbers I provided are for the elliptical hull shape. If you can create a laminar flow hull then you might do a lot better. BUT, and it is a big one, I think once you start to turn you will lose laminar flow.

The liminar flow hulls that I have seen photos of are for autonomous vehicles that move slowly and in a steady trajectory.

So assuming normal boundary layer turbulence there is no great advantage in a perfectly faired shape or perfectly smooth surface.

There are two ways to make it from steel. The cylinder with nose and tail cone or longitudinal leaves with hard chines. The minimum would be 4 leaves. You might go to 6 to get something like an hexagonal section. Point is you need to sort out what will go in it and where. This might actually have some role to play in the shape.

I do not know of any highly maneuverable underwater animals or boats that do not have some form of forward control surfaces. I am not sure about the Albacore. I think you need to find a good example of what you are doing or build a model before settling on the final design.

If you swing a large diameter prop with high aspect blades then there is no point in putting it in a nozzle. The nozzle just adds extra drag that will more than offset the tiny gain in efficiency. They offer an advantage of you are diameter constrained for some reason. Most of the steering force comes from control surfaces not vectored thrust. The latter only has value at slow speed. Adding the complexity of counter rotating props will likely lose efficiency rather than gain. The drag on foils to counter the torque from the prop will be miniscule I expect. If you ballast downward then there is no cost other than a bit of roll that can be counted with rudder trim. If counter rotating props were highly efficient you would see them on aircraft. Just go to a high efficiency prop in the first place. The loading you have is small. The reason you see them on things like the duoprop is that they are heavily loaded props that are low efficiency to start with.

I still see you will have difficulty getting enough weight into it. I would like to see more detail on the buoyancy model you tested. There is a big difference between your figure and mine.

For a surface boat you aim to keep weight down and I use glass microbubbles for making fairing paste or bog. I think you will want to fair this thing with something more dense like metal filler. Buoyancy will be your enemy.

The power requirement and performance can be determined to reasonable accuracy so the merit of various features can be worked out. I have seen a lot of effort wasted on detail of little merit while some of the main factors are forgotten about. A bit like having tiny ducted counter rotating prop when a large single prop could be fitted and achieve higher efficiency at a fraction of the cost.

I got your point about aligning CoG and CoB but I think you run the risk of being disoriented. Having some righting moment should not alter performance much and my first impression is that this would be a key safety feature.

Rick W

[Guest625101138]

Tom
Attached shows what I consider would be the simplest shape to build from steel plate. It is 4.5mlong and 0.5m square. The drag at a depth of 2m doing 8m/s is 700N. The displacement is 680kg.

A rounded nose would help flow during turns.

If you wanted shoulder room you could make it 6 panels and make it wider than it is high. A matter of what you think you can squeeze into.

If it was 1/4" plate the hull would be 311kg so you are well on your way to the required displacement. It is a whole different story if you are going to operate it flooded. I am still not clear on this aspect.

Rick W

[clmanges]

Tom,
I have a question about the ergonomics. You speak of wanting to roll 90 degrees to effect turns (or just for fun?), and that will mean that you'll be laying full-weight on your side during such a maneuver. It's clear that you'll be laying stretched straight out in the sub, so you won't be able to use knees or elbows to brace yourself. What have you got planned for body support in a steep roll? I'm thinking that if you roll sideways, you'd be laying on your arm and perhaps not be able to operate the controls with that hand. Your legs will flop over as well, so might make it problematic to operate your foot controls.

You could rig a network of webbing to support you in any position, but that sounds really scary if you think of emergency egress.

[Submarine Tom]

Great comments! Thank you Rick and "clmanges".

1 atmosphere air in the cabin, Rick.

We have different design techniques you and I, and that's okay.
I would first like to define my hull form and then design the filling.
My overall design objectives are efficiency, handling/performance
and safety. I'm pondering your dissorientation concerns.
Our buoyancy numbers do differ substantially, you're right.
I haven't really got to the details yet because I need to finalize
my hull shape first. I realize this may be a back and forth process,
but it's still where I've chosen to start. Hard chines are out for me.
No offence, and I may end up with them, but not for now.

I embrace your large prop ideas and would gladly dump all that other
stuff.

Clmanges, rigid bracing and g-force will keep me positioned.
I only anticipate the more radical manueovring at speed,
otherwise, the more conventional turning approach would be
implimented. I don't plan on ever exiting the vehicle in the water.
It will be possible if all other emergency measures fail.
I would lose the vessel to sinking if I were to exit due to flooding.
A scuba regulator and mask will be very close at hand.
Blowing the forward (and perhaps only) ballast tank.
Shallow water, close to the beach operation. As Rick has pointed out,
this will be a slow evolution to deeper , riskier operation.

Gentlemen, all of these points you raise are excellent pointsand I appreciate them more than you know, but what I need is to finalize my hull form before I can even begin to answer to them in detail.

I'll try again later (when my two year old isn't pestering me) to
get it up (so to speak...).

Tom.

[Leo Lazauskas]

But, what I'm hearing here is, that laminar flow may not be achievable anyway on a 15 knot, highly manoeuvrable vessel.
I may as well take a cylinder, put an elliptical bow on and a parabolic tail and go from there. No?


It might work. Or the boundary layer might separate at the join of the elliptical bow and middle section, or near where the middle section joins the tail.

Here's another paper for your burgeoning collection :)

MATTNER, T.W., TUCK, E.O. and DENIER, J.P. " Optimal nose shaping for delayed boundary-layer separation in laminar plane-symmetric and axisymmetric flow ", 15th Australasian Fluid Mechanics Conference, Sydney, 13-17 December 2004. Proceedings edited by M. Behnia, W. Lin, & G. D. McBain, The University of Sydney, 2004, paper AFMC00078.

http://internal.maths.adelaide.edu.au/people/etuck/pdfiles/AFMC00078.pdf

Good luck!
Leo.

[Guest625101138]

Leo/Tom
The referenced paper has a couple of qualifications concerning angle of incidence. For example:
< Another important factor is sensitivity to
angle of incidence. The optimized forebody geometries exhibit
rather sharp corners. We expect that such features would pro-
mote separation in the presence of small angles of incidence.
This is also the subject of future work. >

This supports my understanding that it will be difficult to retain or promote laminar flow over a large portion of the hull if it is intended to do high speed gymnastics.

Irrespective of this the axis-symmetric shape is interesting as it does not exhibit the same shape as the Carmichael body. I need to take it in a bit more and understand the differences here.

Rick W

[Submarine Tom]

You guys are awesome. I was about to give up on outside help and just start experimenting. I know I sound like a wealthy man from my life experiences (all my bragging) but I am not. I wasn't even going to build a working test model, but am now reconsidering. Can radio control be used underwater? I'm thinking not. OR, is the range just reduced?

Rick, what is your background? If in a previous post, please direct me.

Leo and you have made me think about this transition (drift) and angle of incidence. This is angle of attack? One reason I'm leaning toward a spherical leading "edge" (nose) is angle of attack. When manoeuvring,
or performing my gymnastics, flow direction will change over the "wing" and the apparent shape will become chubbier. I'll bet you're loving the technical terms here! A sharp pointed nose, like what you attached Rick, would be disastrous with eddies popping up an the lee side of the nose, no?

Okay, what is snap roll? I can find lots of references to it but no definition.
I'm assuming it is a sudden, negative effect of a cumulative affect of turbulent flow around protrusions on a submerged hull form making way.
Am I close?

In my last closing I mentioned I was going to try and get it up. What I neglected make reference to was my drawing. So, stand-by...

[Guest625101138]

You guys are awesome. I was about to give up on outside help and just start experimenting. I know I sound like a wealthy man from my life experiences (all my bragging) but I am not. I wasn't even going to build a working test model, but am now reconsidering. Can radio control be used underwater? I'm thinking not. OR, is the range just reduced?

Rick, what is your background? If in a previous post, please direct me.

Leo and you have made me think about this transition (drift) and angle of incidence. This is angle of attack? One reason I'm leaning toward a spherical leading "edge" (nose) is angle of attack. When manoeuvring,
or performing my gymnastics, flow direction will change over the "wing" and the apparent shape will become chubbier. I'll bet you're loving the technical terms here! A sharp pointed nose, like what you attached Rick, would be disastrous with eddies popping up an the lee side of the nose, no?

Okay, what is snap roll? I can find lots of references to it but no definition.
I'm assuming it is a sudden, negative effect of a cumulative affect of turbulent flow around protrusions on a submerged hull form making way.
Am I close?

In my last closing I mentioned I was going to try and get it up. What I neglected make reference to was my drawing. So, stand-by...

Radio - do not really know but I think Mermaid has knowledge on it.

Background - boats for hobby and recreation since as long as I can remember. I am the fifth generation of a sea-going family but my older brother is the only one in the current generation working on boats. I play with them. I am an electrical engineer by profession and get paid to be the devil's advocate and work out how things will fail before they do with the objective of preventing failures.

Incidence - A pointy nose is most streamline in-line but a small angle of incidence will cause detached flow. A rounded nose is more tolerant. JavaFoil is a very useful tool for playing with these things and getting an understanding. It only gives wing sections rather than bodies of revolution but I believe it will give insight:
http://www.mh-aerotools.de/airfoils/jf_applet.htm
The shape I gave you in wing section form has detached flow on the low pressure side from about 1.5 degrees of incidence. This will increase drag over a hull with rounded nose. Maybe a beneficial aspect is that it will help the hull turn as the turning moment will be lower than if you had nice attached flow. I expect a rounded nose will produce a large moment that counters rapid turning. So my proposed shape might actually turn a lot easier. Might be Dolphins have a pointy nose for good reason. There are certainly a lot of cues in nature that you can learn from with these things.

This is the sort of area where Tom Speer or Leo might be able to comment meaningfully.

I also expect there are simple relationships for drag on a body of revolution with respect to a wing of the same section. If you had this then JavaFoil would be very useful for analysing shapes and forces imposed with some angle of incidence.

Rick W

[Submarine Tom]

Rick, thank you once again for your input.

I am the first genertion to make a living on the water. However, it only lasted 12 years. About seven years ago, I found work in earthquake research here on the west coast, (Canada) in earhtquake country.
That ended two years ago and I am primarily a stay at home Dad that dabbles in boat sales, woodwork and gardening.
I just got off the water from demo-ing a high speed Zodiac replica (made locally) to a German police agency. It was great to be out on the water again. Especially at 52 knots!!

Thanks for the JavaFoil tip, should prove interesting.

I'm not able to get my silly drawing up. I have a MAC and don't know how to use it I'm affraid... Can I post it somewhere else on this site?

Tom, Victoria BC

[Guest625101138]

If you can get a drawing on the screen then you can post it. To get a screen image of the drawing you have follow this:
http://www-rohan.sdsu.edu/~scc/web/screencapt.html
It will produce a png file that can be posted.

Just follow the logic of the window that comes up when you click on the paperclip icon on the Reply to Thread screen.

This is being done on a MAC.

Rick

[Submarine Tom]

JPG of drawing.

[Submarine Tom]

Rick I get the F*£@%^!*^@!! image up on a JPG.

But get a Invalid File response from the "Manage Attachments"

paper clip window.

[Submarine Tom]

I have to go break something now before I piss all over this computer.

[Submarine Tom]

Imgp4552.jpg

[Submarine Tom]

Is there a webmaster that can hold my hand through this infuriating process?

[Guest625101138]

Imgp4552.jpg

I have attached an image of the Manage Attachment window.

You <Choose File> the file. Then <Upload> it. If it is a large file it will take time. The window looks like the second image when it has uploaded. Simple as 1,2 and 3.


Rick W

[Submarine Tom]

Thanks Rick, but it wont do it.

I'd love to be able to show you what happens, but that would require me getting the image up, and well that's not working now is it...

Would you please email me directly and then I can send it to you and, if you would be so kind, post the f-ing thing for me.

Thanks

[Guest625101138]

All
These are thoughts on paper, but you get the general idea.

This is page 21 of the process. Page 19 follows, showing the elevators only idea.

A hard, clear ballast tank in the nose. Likely, a bunch of lead shot as a drop-weight (so it can flow out a small hole). The little rectangles are 2" X 6" X 4", 2 kg batteries. If room allows, I'll add more.

I think the rest is obvious. If not, please let me know.

Tom

[Submarine Tom]

Well, that went over like a lead balloon.

"A picture tells a thousand words" and silenced everyone...

I have researched all the references kindly given above

and am no further ahead with my hull form.

Surely, someone out there has some feedback to offer.

Again, my design objectives are zero to twenty knots,

great handling and manoeuvrbility, fun to drive, low drag,

minimize cabin volume (buoyancy, and therefore, mass).

If no further critique, could anyone suggest where else I look

for assistance with this hull form design?

Thanking you once again in advance,

Tom.

[Guest625101138]

A. You have not shown how you intend to get in and out of it.

B. I do not understand how you will set up the breathing system. How do you discharge waste gas. How do you separate the CO2.

I have already given my other views on the following.

1. Build it with positive buoyancy and forget the lead shot stuff. Could use small wings/vanes to generate the extra down force and improve control.

2. Remove the cowling on the prop unless you are certain you will hit something. It just adds drag.

3. Keep high density components low so at rest the boat is oriented. Will also likely provide enough righting moment to avoid counter rotating props.

4. Do a precise calculation on the buoyancy and all the component weights.

Another point after looking at the drawings. Bring the rudders further forward so the controls are not interfering with flow around the prop. They can just be fins coming out of the aft body. Vectored thrust is only of value at very low speed.

Rick W

[Guest625101138]

You can get a lot of design cues from things like this:
http://www.youtube.com/watch?v=xL8UCPPAWEQ
You can bet they have explored all the avenues in search of efficiency.,

Most of what I have pointed out about props and controls can be seen here.

I know these are flooded vessels. On the other hand one of the things to realise is that the pilot has to generate the power with limbs working in water.

I believe the best speeds are about 6 knots. Not a lot better than an olympic swimmer at about 4 knots. I have noticed some of the swimmers are doing very deep dives on turns now to reduce wave drag. One guy in 200m backstroke was almost hitting the bottom of the pool on turns.

The HPS events are highly controlled activity because the dangers are significant.

I think you are overly concerned about the shape. It simply does not make that much difference once you get the fineness in the ballpark.

I have posted this link to a fellow who has been actively involved in the HPSs to see if he cares to contribute.

Rick W

[Submarine Tom]

Hi Rick, thanks for your response. I appreciate your continued efforts.

A. No, I haven't shown in and out procedure. Mostly because I don't feel it's relevant here. I need to finalize my hull form before I can get into that. But, to try and answer your question: on the trailer. Probably the nose cone will pop off in a symmetrical fashion. I suspect the tail assembly will be removable as well, or, I may make the entire inside assembly removable through the nose cone opening depending on where the widest point is on the hull. That depends of hull design.

B. Again, not important at this point, but, to try and answer your question: perhaps through a mouth piece from the 80 cft scuba tank. In the ambient design it was great. Compressed air would have passed through the motor compartment, cooling it, and then be ducted to the viewing window for condensation reduction, breathed, and then made it's way aft to the tale cone for venting. With the 1 ATM design, it may have to be vented directly from my mouth to the outside via a through-hull. I don't know, but I'm open to suggestion.

With your other points, it appears you and I are at a stand-off because:

1. I want neutral buoyancy so as not to waste thrust on staying down. Wings and vanes double the drag of the vessel for each protruberance as I understand it. Lead shot drop wieght is a saftely feature I'm not willing to compromise on. Besides, as you've pointed out, I may need added weight to overcome excess buoyancy.

2. I've been encouraged to have some sort of rudder by a fluid dynamics engineer. Are you familiar with the R300 submarine recently built in Texas?
His concern is instability without some kind of rudder. I feel the RICE nozzle will provide that stability while improving prop efficiency, giving a point of purchase to mount control surfaces on while minimizing drag by keeping those sufaces downstream of the props, in turbulent flow. If these surfaces are in front of the prop(s), they will decrease prop efficiency by disturbing the clean flow of water into them, no? My intension is to make those surfaces flexible so they curve, not pivot, to provide control and decrease drag. They would be fixed along the longitudinal axis of the vessel and curve the most at their outboard end. Also, by keeping these control surfaces so far aft, they have a greater moment arm for accentuated affect. No, I am not certain I will hit something.

3. I want zero intrinsic stability for superior manueovrability/handling. This would, as you've pointed out, make counter-rotating props very attractive. My understanding is CR can improve prop efficiency markedly.

4. Doing a precise buoyancy calculation would involve knowing what size and shape my hull is. I can't do that with out knowing the shape, then I can work out the size and know what my buoyancy figure will be. Then I can finalize what's going in and where.

It frustrates me that we think so differently Rick, and it must frustrate you too. For that, I appologize. I could be completely wrong with my whole idea/concept here, but I am going with it because I think it could work, dispite being so unconventional and, apperantly, unpopular.

I understand if your done with this and appreciate your most sincere efforts thus far.

Do you know of anyone else that may be interested and could help me out with my "outside the box" ideas?

All the best, unconventional, Submarine Tom.

[Submarine Tom]

Rick, I didn't see your second post until I had already replied to your first.

I too noticed those deep turn-around Olympic swimming dives, interesting.

I beg to differ on the importance of the hull form. Of course, in my case it appears obsessive because I have chosen this as my starting point and can't move forward until it's finalized. I believe in straight line speed you are right, it may not be so important, but, as soon as I start turning at speed, things are going to happen. I don't want to be sluffing speed off in turns, snap rolling (whatever that is), spinning around in circles, suddenly diving. All these possibilities have been expressed to me as concerns by those in the know??? I am really struggling here and this is starting not to be fun. All I have learned thus far about hull design is that further study is necessary and that it is incredibly complicated. You know, I am a marginally above average IQ, guy that has some pretty good street sense for 47 years of age. I've built lots of unconventional things in my life of which some have performed better than expected and some have seen me fall flat on my face. Someone out there has tried what I want to do before, probably lots of people. Where are they. Once I pick a shape, I'm committed to it. Lots of time, money and effort will go into this and I'd be tickled pink if it works. Wish me luck.

[Guest625101138]

Tom
You need to look very closely at the video of the human powered subs. There are a lot of useful cues that you can take. Notice not many have counter rotating props or control surfaces behind the prop. You can bet that by the time you set up control levers on your rudders you will have much greater drag than that of simple blades ahead of the the prop with through-hull shafts and seals.

Your understanding of foils and props is limited and incorrect.

Sure if you stick a gun on the deck of a sub it will contribute significantly to drag but not a foil. A sail that is as wide as the hull will cause more than a little drag as well. All these things can be determined precisely.

The lift to drag on a moderate wing could be 20:1 so if you made the boat with 100kg of positive buoyancy it would cost 50N in drag to submerge it. Only 0.5kW at 20kts.

Compare the maneuverability of a jet fighter to a blimp. Large control surface equate to high forces that can change direction quickly. Have a look at some of the video clips of dolphins, sharks and wales. See how effectively they use forward control surfaces.

If you want something that is highly maneuverable make the body as small as you can and use large control surfaces.

I have attached the performance data for a NACA 3510-34 foil with an aspect of 4. You can see even with this moderately slim planform you can get L/D of 20.

Have a look at the forward control surfaces on this underwater flyer:
http://www.youtube.com/watch?v=fGf_LGX0594
Roughly around aspect of 4 and planform like a jet fighter wing.

Like I say, way too much emphasis on the fuselage. You need to understand the propulsion and control surfaces. These are the things that will give you the performance you seek.

If you want blimp maneuverability then stick with what you have. If you want to soar and turn with ease then look at what does that well in water or air and replicate as much as you can.

Rick W

[Guest625101138]

Rick, I didn't see your second post until I had already replied to your first.

I too noticed those deep turn-around Olympic swimming dives, interesting.

I beg to differ on the importance of the hull form. Of course, in my case it appears obsessive because I have chosen this as my starting point and can't move forward until it's finalized. I believe in straight line speed you are right, it may not be so important, but, as soon as I start turning at speed, things are going to happen. I don't want to be sluffing speed off in turns, snap rolling (whatever that is), spinning around in circles, suddenly diving. All these possibilities have been expressed to me as concerns by those in the know??? I am really struggling here and this is starting not to be fun. All I have learned thus far about hull design is that further study is necessary and that it is incredibly complicated. You know, I am a marginally above average IQ, guy that has some pretty good street sense for 47 years of age. I've built lots of unconventional things in my life of which some have performed better than expected and some have seen me fall flat on my face. Someone out there has tried what I want to do before, probably lots of people. Where are they. Once I pick a shape, I'm committed to it. Lots of time, money and effort will go into this and I'd be tickled pink if it works. Wish me luck.

I have a saying that I think is appropriate here - "polishing the turd". If you have a concept that is rubbish then it does not matter how much effort you put into it it is still rubbish. That is not to say what you have is rubbish. Clearly you have given clear thought to many aspects.

However design is an iterative process. You start with a concept and bring along all aspects together. Getting ever finer detail on every aspect. You cannot do one part in isolation of the others. It can be frustrating because sometimes you have to let go of something that you feel important. This is part of the learning process.

As an aside, my first foray into pedal boats was with a flapping foil. I got this to be a very efficient method of propulsion but I was speed limited because my boat started to bounce at about 70rpm. I kept at it for about 2 years until a guy asked why didn't I use a propeller. I pointed out that it was the way dolphins move and they are fast in the water. He simply said that if they could replicate a rotating shaft they would have propellers. Anyhow I started to make propellers and determined he was right. Not all of what I had learnt was nonsense because a prop is a rotating foil so I was able to apply what I had already learnt about foils to props. I now make very efficient props.

Some of your understanding is flawed. Or you have overemphasised certain features.

I think the quickest way to develop is to get your hands dirty. Do it in an easily affordable scale. Find out what is important and what is not.

Absolutely no point in getting the minimum drag hull if it does not respond to controls. Control surfaces give control not the shape of the fuselage.

Foils in water will generate huge forces for their size and do not contribute much to drag when in line. All can be determined in a matter of minutes to within a few percent.

Quite honestly I think the hull without forward control surfaces will be a tub of lard compared to what it could be with a couple of wings.

Rick W.

[Submarine Tom]

With all that said, I still don't have a hull form.

I've seen these videos. I've been researching this for five months now, and I'm just going around in circles. This is water, not air. A fineness ratio of four IS a blimp. Your obviously not understanding what I'm saying. My fault, not yours. An athlete can produce about 400 watts for up to about ten minutes. My calculations show I need about 8 000 watts (80% efficiencies means about 10 000 watts gross) to go 15 knots. That's a difference of an order of 20 from a HPV. Quite a bit more torque wouldn't you say? Especially from an electric motor.

It appears you can't help me Rick, and I'm not finding your comments terribly motivating at this point, although I really do appreciate all your efforts. I will ask you one last time, do you know of anyone that can?

[tspeer]

...I have researched all the references kindly given above and am no further ahead with my hull form....

You're not going to be able to go right to the answer in a straight line. You have to design in several spirals. The first lap around doesn't have to be all that accurate - its main purpose is to clarify your thinking and develop requirements.

I think you're a bit hung up on the hull form at this stage. There simply isn't a single best shape - only the most suitable shape for your particular requirements. Pick a hull shape that is sort of like what you envision. One way to do this is to adapt a two-dimensional section by taking its coordinates to the 2/3 power. Or start with an existing high-performance shape like this one (http://www.boatdesign.net/forums/attachment.php?attachmentid=9563&d=1160351957).

Scale it to the approximate dimensions to hold the pilot, and calculate the volume. From your 15 kt speed and the cube root of the volume, you can calculate the volume Reynolds number [Re_vol = (volume)^1/3 * speed / knematic viscosity]. Take a look at the Lutz & Wagner paper on drag reduction of airship bodies and see what Reynolds number range you fall into. That will tell you roughly what kind of shape would be best, and also how much laminar flow might be possible. If you look at Figure 8 in their paper, you can see it's better to over-estimate the design Reynolds number than it is to under-estimate it.

You won't have the computer programs to design an optimal shape, but you can look at where the maximum thickness ought to be and adapt a suitable airfoil section using the 2/3 power relationship. Chances are there will be more drag in the details of things like your prop shroud & struts, etc., than there will be between similar hull shapes, as long as the flow is fully attached.

Now you really do need to get concerned about packing everything inside. Designing the systems for your sub will take a lot more time and effort than will the hull itself. You'll need to see if you can fit everything into the volume you assumed. If not, you'll have to resize the hull and maybe even iterate on the shape. For example, the maximum thickness may be too far back, forcing you to go with a larger than desired frontal area to get adequate thickness where you need it. The shape of the nose for laminar flow may be incompatible with the need to have a hemispherical transparency there. The weights and ballast capacity have to be consistent.

Propulsion efficiency will be important, so you'll need to properly size the prop and design the shroud. From the power available and your estimates of drag of the hull, you can start to see if you'll meet your target speed. If not, something's got to give.

You'll want to develop a spreadsheet that has the key geometric parameters, weights, and performance calculations. If you can develop relationships for the weights and performance based on the geometry, you can use Excel's Solver to find optimum combinations.

If there are some design parameters that are crucial to achieving your objectives, then you may need to devise some tests to reduce the uncertainty in those parameters.

For example, say the drag coefficient of the hull is critical to hitting your speed bogey. You may want to build some subscale models and test them to determine the drag. Carmichael used a comparatively inexpensive method of testing by lowering buoyant subscale models to the bottom of a deep, still lake. When the model was released from the ballast weight, he timed how long it took to come to the surface. From that, he was able to calculate the terminal velocity and knowing the buoyancy, he had the drag at that velocity. That's a technique that doesn't require tow tank or wind tunnel facilities. By making repeated runs with different amounts of buoyancy, you can cover a range of speeds or Reynolds numbers.

Or you may need to measure propulsive efficiency. You might be able to adapt an electric trolling motor by mounting it in a model of your tail unit and measuring the force it produces and the electrical power it consumes.

So don't worry about optimizing at this stage. At this point, you don't even know what the really important aspects are. First you need to get to a feasible design. From there, you can move to a better design, and a still better design, and ...

[Guest625101138]

.... Quite a bit more torque wouldn't you say? Especially from an electric motor.
...........



NO. Power is torque times angular velocity. Those big HPS props are running around 100rpm. I suggested you run your prop at 1000rpm maybe 2000rpm if you are prepared to lose a little in efficiency. At 2000rpm, 8000W requires the SAME torque as 400W and 100rpm. You don't see the HPSs with single prop spinning uncontrollably. Just minor adjustment on the control surfaces to offset the small torque. Maybe even ballasted to give sufficient righting moment to overcome torque. If counter rotating props were far superior as you seem to think then all those HPSs would have them. They are the exception rather than the norm.

As I said you need to do the calculations and bring it all along together. You are making assumptions and design decisions based on insufficient understanding of the engineering.

No one can help you if you are not open to understanding and doing the sums. None of it is magic. It can all be calculated with great precision or adequate precision with little effort.

Saying things like this is water not air shows a lack of understanding. The behavior of bodies in air or water is similar (remember the Albacore hull was developed in a wind tunnel). There are adjustment made for the density and viscosity but otherswise exactly the same principles apply. If you want a hull to behave like a jet fighter in water it will look like a jet fighter but the control surfaces will be a bit smaller in proportion. If you want it to be ponderous and slow to respond as is a blimp it will look like a blimp.

If you do build a model or actual sub you will come to learn about the detail of what I am trying to point out. I have not built a sub so I do not have all the answers but I do understand the physics and engineering detail that you need to work through.

I also notice that virtually all those HPSs have the same fineness and shape I originally proposed. Keep in mind that they are designed to go in a straight line with little deviation other than to maintain course. If you want to maneuver at high rates then your control surfaces will need to be bigger.

Rick W

[clmanges]

Submarine Tom,
For what it's worth, you've got my sympathy. As Tom Speer just said, You're not going to be able to go right to the answer in a straight line.I had the same experience very recently with my own project; I asked questions which I thought could be answered straightforwardly, but they couldn't. It didn't take long for me to feel like I was being given the run-around, but that is not the case. Rick, and tspeer, and others here have immense experience and knowledge about this stuff, and put out tremendous effort to help people here. Believe this: if a simple answer were available, they'd much sooner just hand it over than to write thousands of words, taking time away from their own projects.

You've obviously got a personal (perhaps emotional) investment in a particular notion of your project; you're attached to it. Buddhism says that attachment leads to suffering (I have no religion, but they all have some useful wisdom). Let go of that notion and start over. These guys can --and will -- still help you, but it's really hard to suffer and accomplish anything at the same time.

And -- (sly grin) even though I have no religion, if you want, I'll give you a suggestion for a 'detachment ritual.'

Your concept is delightful, and I'd like to see it succeed.

Curtis

[tspeer]

...Wings and vanes double the drag of the vessel for each protruberance as I understand it.
This is exactly the kind of thing we're talking about. Clearly, this statement cannot be true. A tiny fin added to the hull will not double the drag. The amount of drag will be proportional to the area of the fin, so it's probably not going to double the drag until the wetted area of the fin starts to approach the wetted area of the hull.

Since you want to maneuver, there will have to be side force developed by something. If it's not a wing or fin, then it will be the hull. The drag due to lift is inversely proportional to the square of the span of the lifting surface/object. Since the hull is narrow, the drag due to lift of the hull alone will be high. Adding wings will dramatically reduce the drag due to lift when maneuvering. And the hull can only produce a small amount of lift before flow separation sets in, also raising the drag and quite possibly not allowing you to maneuver sharply at all.

Is that important? It depends on how much maneuvering you do vs straight line cruising, and how much wing you have to add to get the turning radius you need. Design is all about trade-offs - how much can you give in one area to get what you want in another area? You won't be able to do that without making some quantitative estimates.

This is where engineering requirements come in. You've really only give us three: single occupant, 15 kt, human power (~1/3 hp). Qualitatively, you've said you need to maneuver, but you haven't expressed that in quantitative engineering terms, yet. How sharply does the craft have to turn (turn rate or turn radius) at what speed? Does it have to be directionally stable, or what is the maximum time-to-double you consider acceptable for the pilot to stabilize manually? These aren't easy questions to answer, but they are critical to coming up with an acceptable design.

Even for just the requirements you've stated, you can start to flow the requirements down to various subsystems. For example, thrust horsepower is thrust times velocity. Thrust equals drag in steady state operation. There will be various losses between your power source and the thrust horsepower delivered to the water. So, say the drive chain is 90% efficient and the prop is 85% efficient. That means you can deliver maybe a quarter horsepower to the water. Convert horsepower to suitable units, divide that by the speed, and you get the drag. If I've done my sums right, that's 5.4 lb/24 N at 15 kt! Divide that by the dynamic pressure, and you have the drag area. Divide that by the skin friction coefficient you think you can achieve, and you have the maximum wetted area. From that you can estimate the maximum volume and see if you can begin to get into the craft.

If not, you have to go back to the beginning and up the horsepower or improve the efficiency of the drivetrain, or improve the efficiency of the prop, or reduce the skin friction. Once you have a set of values that all hang together, you have the requirements for the subsystems. You'll know how much power is delivered to the prop and what its efficiency has to be at what speed, which is what you need to design the prop. You'll know what kind of loss you stand in the drivetrain, and the prop design will tell you how much torque the drive has to withstand. And so on. Then you flow those requirements down into more detailed requirements for each part.

I know that isn't sexy, but it's what engineering is all about. You'll be able to come back to the forum and ask, "I need to design a prop that does X under Y conditions. How do I do that?" You'll be able to look at a shape in a technical paper and know if it's suitable or not, based on the design Reynolds number and the drag coefficient. Until you've done your homework, nobody can help you very much.

... I feel the RICE nozzle will provide that stability while improving prop efficiency, giving a point of purchase to mount control surfaces on while minimizing drag by keeping those sufaces downstream of the props, in turbulent flow. If these surfaces are in front of the prop(s), they will decrease prop efficiency by disturbing the clean flow of water into them, no?
Not necessarily. Surfaces in the prop wash also have higher drag than they would have in the outside the flow. It may be better to mount them on the outside of the shroud where they get clean flow and also don't shed their wakes onto the prop.

You may well get enough stability from the shroud, but that will depend on how big the shroud is. It's going to depend on your hull form. That's another thing you have to estimate from sources like text books on submarine or aircraft fuselage design. In general, the hull by itself will be quite unstable.

My intension is to make those surfaces flexible so they curve, not pivot, to provide control and decrease drag. They would be fixed along the longitudinal axis of the vessel and curve the most at their outboard end. ...
This is not the most efficient way to design a control surface. You will be loading the outboard end excessively, and the drag due to the lift produced by the deflection will be high because the effective span will be short. Its better to load the surface more evenly along its span, unless it's rolling moment you're trying to produce. Technically, the minimum drag will be obtained when the normal-wash of the flow is uniform along the span of the surface.

All-moving or hinged surfaces are not much more drag than a flexible surface would be. I'd definitely accept the profile drag of a hinged flap over the induced drag of a continuously twisted surface like you're proposing.
3. I want zero intrinsic stability for superior manueovrability/handling.
Neutral stability and good maneuverability do not necessarily go hand-in-hand. For good handling, you will probably want to have a certain amount of positive stability so the craft will track straight, not burden the pilot excessively with having to control it, and not pick up drag by wandering around. Performance in the maneuver is also a separate issue from stability.
...Doing a precise buoyancy calculation would involve knowing what size and shape my hull is. I can't do that with out knowing the shape, then I can work out the size and know what my buoyancy figure will be. Then I can finalize what's going in and where....

Exactly. So you need a candidate shape to start, then do the calculations, revise the shape, and do the calculations again. Don't think that you will be able to do the calculations once. You're going to do them dozens of times.

[Submarine Tom]

Curtis,

You make me laugh my friend.

Thank you.

As for the rest of you, you have offended me. You have created a monster.

I am no monster.

You know I appreciated your attempts to help me, this I have made abundantly clear.

Speaking of clarity. Would you please go back to my first post, on page one, as I have just done, and, carefully, reread it. Twice, as I have just done. Indulge me. Please. Then, have a beer, and rethink how you can best answer my plea.

Thank you, Tom.

P.S. Interestingly, the unsubscribe instructions for this forum are
impossible to figure out.

[clmanges]

Tom,
Glad I could get a laugh out of you, but don't give up yet. No one has created any monsters here, and I don't think anyone has offended you. Look at it from their viewpoint; it must get frustrating at times, dealing with noobs like me (and you) who don't know what questions to ask because we're on the steepest part of the learning curve. And we get frustrated when we can't get simple answers to what we think are simple questions.

I just went back and read your first post again, and, having read all the rest of this thread, it looks to me as if the answer you seek is conditional, and you haven't stated all the conditions! Not your fault, because you probably didn't know there were so many (I sure didn't!). So, don't quit now; you're getting a free education, and I doubt if you'll find a better source anywhere. These guys impress me.

Take a break for a little bit, and then study all you can find. This isn't easy; it takes concentration and work, but it's worth it.

Curtis