Super cavitating very high speed stealth surface vessel

[Bob Abell 2Participant @bobabell2]

Paul

Notice on your first picture

Ghost is parked up, yet the hull is not touching the water?

That means the pods can float?

Bob

[Paul TParticipant @pault84577]

Bob

It might help to think of this boat as a special kind of catamaran.

On a catamaran the hulls remain in the water whilst the main superstructure is kept above the water, the same basic description applies to the Ghost boat.

Paul

[Bob Abell 2Participant @bobabell2]

Here`s clear picture of GHOST parked up

The pods are circular and have contra rotating props………That`s a challenge for starters!

With my idea of having the motors in the main hull, using timing belts, the contra rotation feature is not a problem

Bob

[Andy StonemanParticipant @andystoneman15177]

No Definatly flash steam, I built a flash steam boiler once and when I saw the amount of steam produced, far more than i imagined I gave it away. Entering another scope of modelling there!

Andy

[ashley needhamParticipant @ashleyneedham69188]

Fraught with difficulty this, as the propulsion will newver emulate the real thing as A) they spent thousands of computer/dollar hours designing it and B) ITS ALL SECRET.

For my money. I would identify the characteristics that make the boat. Its sponson arrangement and underwarter propulsion. These are the things.

I would make the sponson bodies from foam to provide bouyancy, and fit at the rear a ducted prop/jet drive arrangement. I like the belt drive. If the inboard pully was on the wing pivot centreline, then the wings could move without disturbing the drive. I would forget any counter-rotating prop stuff. The pully wheels in the water ducts would create massive loss of thrust I am sure.

Trim could be adjusted experimentally with clear acrylic winglets on the sponsons. They could even be linked by rods to remain parallell to the water independant of wing angle.

I would have thought that rudders of some sort and/or steering tubes on the jet outlet would be the thing to steer with, as adjusting prop thrust as per using differential prop control will result in a loss of thrust when making high speed turns and result in falling over. The rudders do not need to be behind the props….this would ease the linkage situation and allow a clean underwater body shape.

I am sorry but a general arrangement drawing is all I would use personally, and take it from there. . Bit like a certain other project Paul..know what I mean ???   Possibly a crude mockup would be required to sort out some of the features and balance/floatation/effect of wing angles etc etc

As a working model I am sure some…optimising…of certain dimensions will be required.  However I would not be building a true scale ship but more of a life like representation.

Ashley

 

 

Edited By ashley needham on 04/01/2015 09:25:41

[Bob Abell 2Participant @bobabell2]

There`s a lot of sense and logic there, Ashley

But Paul can call the shots at the moment though………He`s our tame Boffin

The pulley on the pivot point is a tried and test method…….I would like to see contra rotation though

Rudders are an unnecessary complication…..Prefer the prop control…….No need for tight turns

Just food for thought at the moment

Wonder if Pauls secret cave has got Wifi?

Bob

[Paul TParticipant @pault84577]

Hi Bob and Ashley

Sorry to say that putting the motors and batteries in the superstructure wont work as it puts the centre of gravity in the wrong place.

The image below shows in very simple terms what happens to the boat as it speeds up and makes a very shallow turn.

The position of the motor / battery mass becomes unsupportable as the legs of the boat close together.

Sorry chaps but the motors and batteries have to be in the sponsons (or pods as Bob calls them)

Paul

[ashley needhamParticipant @ashleyneedham69188]

Hmmm. I see the wings only moving as much as the top three drawings. The wings I would make a bit shorter as well, in fact half that length looks good to me…

Cant remember…does it float on its belly and rise up only when moving??? This would alter the dynamic a fair bit

Ashley

[Paul TParticipant @pault84577]

Hi Ash

Hmmm. I see the wings only moving as much as the top three drawings

All I can say is that the bottom three images show the benefit of doing the full research.

Paul

Edited By Paul T on 04/01/2015 16:56:12

[Bob Abell 2Participant @bobabell2]

Tea Lady to Mr Paul

Please Sir……..On your pretty pictures, the weight on each pod is the same whether the motors are in the pods or in the hull

I think you may have caught a chill, sitting in that cave, Sir

Charmaine

[ashley needhamParticipant @ashleyneedham69188]

Hmmmm…..

Ashley

[Paul TParticipant @pault84577]

Charmaine

The pictures are intended to show that by having the majority of the boats mass (motors, batteries) high up in the model will ultimately and inevitably introduce an unstable centre of gravity to the boat.

You will note from the pretty pictures that the sponsons (for some misleading reason Bob still calls them Pods) are empty, they are empty because of the need to create buoyancy to keep the mass, the afore mentioned motors and batteries, from sinking the model.

As we all know from watching raft races on the TV that those misguided builders who sit upon rafts made from oil drums invariably capsize……..why is this??

BEAUSE THE WEIGHT (MASS) OF THE RAFT IS TO HIGH.

Please tell me that you understand or do I need to get the crayons out.

All of this is basic stuff:

The more complicated engineering required to get your drive belts from the motors and down the very thin legs is to difficult to contemplate, please look at the pictures and try to envisage getting the drive belts into this profile.

Paul

Edited By Paul T on 04/01/2015 18:13:46

[Bob Abell 2Participant @bobabell2]

Let`s rock with the caveman!…..Tral la la

Better get those crayons out, Sunshine!

Don`t understand this lot……

Your second paragraph…….."……The sponsons are empty because of the need to create buoyancy………"

This what I have been recommending

Thinking about it……..Why have pivoting legs?………Fix the legs as your picture No 2

Bob…….Putting up a stiff defence

[Colin BishopModerator @colinbishop34627]

The drawings remind me of the Martian machines from 'War of the Worlds' and is that last one waving or drowning?

Seriously though, even if you overcome the driveline engineering issues I fear you may run into trouble with the fact that the water itself isn't scaled down from the full size to the model and therefore the hydrodynamic behaviour of the model will be different as the water will be 'heavier' (more viscious).

Colin

[Paul TParticipant @pault84577]

Let`s rock with the caveman!…..Tral la la

Thank you Bob although the reference is lost on me

Better get those crayons out, Sunshine!

I feared as much!

Don`t understand this lot……

I gathered as much!

Your second paragraph…….."……The sponsons are empty because of the need to create buoyancy………"

This what I have been recommending

No Bob you have been recommending that the motors be fitted in the cabin

The sponsons will still provide sufficient buoyancy when the motors and batteries are fitted in them but this layout will prevent the model form capsizing every time it made a high speed turn.

Thinking about it……..Why have pivoting legs?………Fix the legs as your picture No 2

The pivoting legs are the main feature of this boat and provide lift, in simple terms the closer the legs get the faster it will go.

Bob…….Putting up a stiff defence

Not really (see reference to crayons) a stiff defence would have taken account of my last paragraph (shown below)

The more complicated engineering required to get your drive belts from the motors and down the very thin legs is to difficult to contemplate, please look at the pictures and try to envisage getting the drive belts into this profile.

Paul……Looking forward to the next comment whilst sharpening crayons: lol

Colin

I agree with your comments and would have listed my own version in one of my earlier postings but I being at the crayon stage I dreaded the prospect of explaining advanced fluid dynamics.

However its all good fun and hopefully Kevin is gaining valuable knowledge from our little performance.

 

Edited By Paul T on 04/01/2015 18:50:20

[Bob Abell 2Participant @bobabell2]

"Rock with the Cave Men" was a 70`s pop song

More confusion here….I was recommending empty pods and you say….

"No Bob, you have been recommending the motors be in the cabin"……..Crayons out here

A tubular channel could be built into the legs for the belts…..It would just look like reinforcement

Must have contra rotation and the belt idea makes this possible

BTW…….We won`t be doing any high speed turns

Bob

[Dave MilbournParticipant @davemilbourn48782]

"Rock with the Cave Men" was a 70`s pop song

That would be 1956.

[Paul TParticipant @pault84577]

Hi Bob

Any channels or ducts on the legs would ruin the models ability to lift (plane) and without lift I would doubt its ability to go any faster than 2m/s (5 mph)

Don't worry about contra rotation, that's the designers problem to solve (the clue is in the word Designer)

Incidentally contra rotation can be achieved by using a simple small gearbox which will quite happily fit inside the sponsons.

Even if you don't want to do high speed turns somebody else might and we mustn't forget that the idea is to produce an easy to build design that provides decent performance.

Paul

[Bob Abell 2Participant @bobabell2]

Look here you!

We don`t want motors and stuff inside the sponsons whatsoever!…..Cried a member of the design sub committee

We don`t want any of that silly submarine nonsense!

The timing belts can pass down the leg practically touching each other…..They would travel down a 1/2" gap quite easily

The legs could have restricted movement from flat out to about 45 degrees and would not be too top heavy

How long is the hull and the sponsons

If we don`t get our skates on, that Southern usurper may get the drop on us!

Bob

[Paul TParticipant @pault84577]

Bob

We don`t want motors and stuff inside the sponsons whatsoever!…..Cried a member of the design sub committee

We don`t want any of that silly submarine nonsense!

Imagine that I am writing in crayon

Putting the motors and batteries in the sponsons is the best place for the equipment, but to avoid the pages and pages of complicated calculations proving this fact I will simply point out. The designer of the real boat put the heavy equipment there

The timing belts can pass down the leg practically touching each other…..They would travel down a 1/2" gap quite easily

The belts might pass through the legs but they wont get around the hinge that connects the leg to the cabin.

The legs could have restricted movement from flat out to about 45 degrees and would not be too top heavy

Restricting the movement of the legs will also restrict the lift and speed of the model (already discussed this)

How long is the hull and the sponsons

Don't know how long the model will be as due to answering and re-answering questions I haven't been able to do any actual drawing work.

If we don`t get our skates on, that Southern usurper may get the drop on us!

I refer you to my point of answering and re-answering questions and will merely add that you don't get anywhere by trying to second guess the designer especially when the designer hasn't even started.

The drawing office welcomes questions and advice from everyone but there comes a time when work has to proceed.

Paul

[Mark Jarvis 2Participant @markjarvis2]

Paul.

Refer to all past statements, DESIGNER. – CONSTRUCTION MANAGER. – cant build it till you have designed it.

All designs from or by committee are a disaster.

Mark

[Bob Abell 2Participant @bobabell2]

Hello Mark

We are not falling out, we call it light hearted banter

Paul is the designer and I just keep stickin' my nose in, every now and then with outrageous suggestions……..Sometimes it works out ok

Carry on Paul

Bob

[Paul TParticipant @pault84577]

Hello Mark

Our little chuckle brothers routine allows us to explain the design and build process, even if Bobs questions might seem silly (especially to the more experienced builders) but hopefully they will help explain the process to the many beginners who visit our site.

Paul

[Bob Abell 2Participant @bobabell2]

Paul

When the legs are vertical and pigs might fly, an aerofoil section is pointless

So make the legs wide enough to take the batteries, low down

Put the motors in the hull or the legs with belt drives to contra prop shafts

The belts and pivot action will be similar to a motor cycle chain drive to the back wheel

This idea will allow plenty of room in the hull for the pie in the sky pivoting mechanism

Bob making a robust suggestion…….. Before you get too far down the lane!

[Paul TParticipant @pault84577]

Bob

I give up…………..

Here is a nice cross section for you to show me how you intend to get twin drive belts, a dynamic hinge and leg operating system into the model.

But remember you CAN NOT increase the size or change the overall shape of ANY of the component parts, in doing so you will also have to detail the twin servo leg operating system (including all rods and connecting arms) the construction of the dynamic hinge which will allow the legs to move as the speed increases but hold them firmly in position when the operator lets go of the stick.

And whilst you are figuring all of this out you might as well indicate just where in the cabin you intend to put the batteries (the motors shown are scale MFA 850) or if the batteries are going in the sponsons please show where the power leads will run and how you intend to get them past the leg operating system, the dynamic hinge and twin drive belts.

All of the above are critical design considerations that I have already taken into account and worked out answers for which also work very nicely with the critical centre of mass problem.

Answers on 24 foolscap pages including all details, sections, calculations and proposed equipment

[Author]

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