Boat Design Forums  |  Boat Design Directory  |  Boat Design Gallery  |  Boat Design Book Store  |  Thanks to Our Site Sponsors

Go Back   Boat Design Forums > Collaboration > Projects & Proposals
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read Most Recent Posts Gallery Images Search

Reply
 
Thread Tools Search this Thread Display Modes
  #31  
Old 11-09-2010, 09:30 PM
Yellowjacket Yellowjacket is offline
Senior Member
 
Join Date: May 2009
Rep: 438 Posts: 444
Location: Landlocked...
Quote:
Originally Posted by tom kane View Post
some Stealth air intakes are at the top and are controversil at the moment. I would use a water propeller where the water was deep enough ( it would need to be at least 2 feet deep) A horizontal ducted air propeller would not change air direction twice,90 degree in 90 degree out. Trouble with airflow across the horizontal may start above 50 MPH.
Stealth aircraft mount the engine inlet above the fuselage in order to shield the inlet from ground based radar. All of these inlets are basically forward facing, or are what is called a flush inlet, (do a search on flush inlets or NACA inlets and you will learn something about inlet recovery), none of them EVER turn the air 90 degrees from the direction of travel because that is basically a bad idea.

Successful air cushion craft use a two different fan systems, one for lift and the other for propulsion. The reason for that is that you need higher pressure and lower flow for lift, and you want a lower pressure ratio and higher flow for propulsive efficiency. You are trying to do both with one fan and that is fundamentally inefficient because you are bleeding higher pressure air that you have put a lot of energy into and are basically trying to push that air out the back and that is an expensive way to propel your boat.

If you are trying to pressurize an area under the hull, a horizontal fan can do that, but axial fans aren't as good at supplying the required amount of pressure at lower flow rates when compared to a centrifugal blower. The reason for that is that it is harder to get pressure ratio at the inner diameter of the fan where the blade speed is lower, so if you want high pressure ratio at lower flow a centrifugal blower is a better machine.

For propulsion the higher flow rate and lower pressure ratio system suffers from a high percentage of losses in turning the air to create thrust, which is why a conventional fan is used on air cushion vehicles for propulsion.
Reply With Quote


  #32  
Old 11-10-2010, 04:07 PM
tom kane's Avatar
tom kane tom kane is offline
Senior Member
 
Join Date: Nov 2003
Rep: 361 Posts: 1,105
Location: Hamilton.New Zealand.
Airboat_Experiment

Thank`s for you comments. I accept your explaination as being the conventionaly accepted theory, but I don`t think the airflow theory is correct. I want somthing different from the usual air boat design and I am finding designs closer to what I want but they are still too expensive and too noisy for my purpose. I think that many people do not understand even how a water propeller pushes a boat forward,it`s not a new idea but proven hundreds of years ago.

A vaccum cleaner does not suck air but displaces air and atmospheric pressure rushes in to replace that air carrying dust with it. The inlet can be anywhere from verticle to horizontal without affecting the amount of air displaced.

A baby sucking on a mother`s nipple displaces air and atmospheric pressure squirts milk into babys mouth. No air inlet involved here ???
Attached Images
 
__________________
tomkane
Reply With Quote
  #33  
Old 11-10-2010, 05:34 PM
Yellowjacket Yellowjacket is offline
Senior Member
 
Join Date: May 2009
Rep: 438 Posts: 444
Location: Landlocked...
I am sorry that you don't want to accept "conventional theory", but what I am explaining to you is not a theory, it is a simple FACT and that fact is that propulsive efficiency can be quantified and calculated. That means that it is no open interpretation or other "theories". The simple fact is that any means of propelling something through the air using air as the propulsion medium is based on the concept of accelerating the air through the system. You are thinking about the inlet side of the equation, and not the exhaust. However, to induce flow through the inlet it has to come out somewhere and if it comes out at a higher velocity the propulsive efficiency can be quantified.

High speed aircraft do actually create thrust in the inlet, but that only works at high speeds, like above Mach 1, and we aren't talking about that here. The SR71 spy plane (at a speed of Mach 3.5) actually made more than 70% of its thrust in the inlet. But the engine behind it acted like a pump and moved the air away from the inlet, so there had to be an engine in there to do that work and the air leaving the system was at a higher velocity and the results were consistent with propulsive efficiency calculations.

Propulsive efficiency can be determined based on the velocity of the air exiting the propulsion system (and providing the thrust) and the speed of the vehicle. If you have a very low differential between the velocity of the accelerated air and the vehicle (ie, you move a lot of air but the speed difference is low) you will have an efficient system. If you have a high velocity jet, and the speed of the vehicle is low, the efficiency will be poor. This is why turbofans are more efficient than old fashioned jet engines, they move a lot more air at lower pressure ratios and this gives them more low speed efficiency.

Propellers (either in water or in air) are airfoils that are accelerating medium which is air (or water if the prop is in the water) and the larger the propeller, the better the low speed efficiency will be.

You are trying to invert the frame of reference and think you can "pull" the craft forward and have the depression created in the inlet do that. But it really doesn't matter what your reference frame is, it is the acceleration of the air inside the system that provides you the momentum change to push you forward. I'm sorry if you don't want to believe it, but we all see airplanes flying around us and the performance of these aircraft is calculated and determined accurately, before the airplane is ever built, using these conventional analysis techniques.
Reply With Quote
  #34  
Old 11-10-2010, 08:05 PM
tom kane's Avatar
tom kane tom kane is offline
Senior Member
 
Join Date: Nov 2003
Rep: 361 Posts: 1,105
Location: Hamilton.New Zealand.
Thank you for your time and explanations. One thing which I have learned over the years is not to think what information I have aquired in the past is still correct now so I check for the most up-to-date information available. That is what I am doing now.
__________________
tomkane
Reply With Quote
  #35  
Old 11-11-2010, 03:41 PM
tom kane's Avatar
tom kane tom kane is offline
Senior Member
 
Join Date: Nov 2003
Rep: 361 Posts: 1,105
Location: Hamilton.New Zealand.
Airboat_Experiment

Quote:
Originally Posted by mydauphin View Post
Tom you invented the hovercraft...
It look`s like you are right.. but I have not invented the hovercraft but an Air Boat With a Horizontal Fan..seeing that no one else appears to have done it before. I don`t think I will continue with my Patent Application I shall give it to the World for free'.

As I have put the idea into the Public Domain no one else can Patent It.
Attached Thumbnails
Airboat with Horizontal Fan-small-scale300.jpg  
__________________
tomkane

Last edited by tom kane : 11-12-2010 at 04:53 AM. Reason: more info
Reply With Quote
  #36  
Old 11-16-2010, 02:04 AM
tom kane's Avatar
tom kane tom kane is offline
Senior Member
 
Join Date: Nov 2003
Rep: 361 Posts: 1,105
Location: Hamilton.New Zealand.
Airboat_Experiment

Quote:
Originally Posted by Yellowjacket View Post
You need to change your reference system, try looking at it this way.

The thrust gained by any fan or jet is a direct function of the change in velocity of the air multiplied by the mass flow, or simply put the momentum change across the fan or jet engine.

Since the boat is moving forward, the air around the boat is moving relative to the boat, and therefore has momentum. If you do not caputure this momentum, you have to accelerate the air from zero speed to the speed of the exit air, and that takes more energy than it does to accelerate the air a small mount across a conventional fan that is facing the airflow.

If you are talking about very low speeds, it doesn't matter that much, but a fan drive system is very inefficient at low speeds. This is why you don't see low speed air boats, unless it is a very specialized application where you are operating over a mud flat. Otherwise, a propeller in the water is far more efficient than a propeller operating in the air. Do a search on propulsive efficiency of propellers and you will see that at very low speeds propellers operating in air are simply not efficient.
One of the worlds newest inventions (world acclaimed) has horozontal fans and intakes and moves forward rather fast.
Attached Thumbnails
Airboat with Horizontal Fan-flying-high.jpg  
__________________
tomkane
Reply With Quote
  #37  
Old 11-16-2010, 11:15 AM
kach22i's Avatar
kach22i kach22i is offline
Architect
 
Join Date: Feb 2005
Rep: 1181 Posts: 2,378
Location: Michigan
Tom Kane, have you seen the posts by BMcF in this thread?

T-Craft
Quote:
Originally Posted by BMcF View Post


OK..I got it now. those were a key part of the propulsion concept that would ahve never worked. And imagine the noise!..as bad as LCAC but with passengers??

Thankfully..some projects die when they need to. I've worked a few that did..and some that didn't die soon enough.
...and have you seen this one yet?
http://www.industrialobject.com/
__________________
George: Architect (land lover type)
Hovercraft & Vintage Porsche Owner
http://www.boatdesign.net/forums/boa...ect-11973.html
Reply With Quote
  #38  
Old 11-16-2010, 11:35 AM
kach22i's Avatar
kach22i kach22i is offline
Architect
 
Join Date: Feb 2005
Rep: 1181 Posts: 2,378
Location: Michigan
Quote:
Originally Posted by tom kane View Post
invented .......an Air Boat With a Horizontal Fan..seeing that no one else appears to have done it before. I don`t think I will continue with my Patent Application I shall give it to the World for free'.

As I have put the idea into the Public Domain no one else can Patent It.
Did a lawyer tell you this?

RE: propulsive efficiency

The formally educated engineers have all been pressed into a conventional mold which says propulsive efficiency is everything, nothing else matters. As I have not been pressed into this mold, but have been squeezed though an education system based on design, which is a decision making process, you must make some decisions. Sure, one decision could be to place propulsive efficiency above all else, but there are other choices.

1. Choose to conceal the fan to limit noise.

2. Choose to provide 90 degree bends before and after the fan to limit noise.

3. Choose noise reduction and safety from spinning blades above all other considerations such as weight or propulsive efficiency.

The very first hovercraft to cross the English Channel used a single fan with not only a 90 degree bend in it, but a series of exposed ducts for multi-directional thrust. To say it cannot be done ignores history, to say it was efficient ignores the laws of physics.

SRN-1
http://www.hovercraft-museum.org/srn1.html
__________________
George: Architect (land lover type)
Hovercraft & Vintage Porsche Owner
http://www.boatdesign.net/forums/boa...ect-11973.html
Reply With Quote
  #39  
Old 11-16-2010, 04:33 PM
tom kane's Avatar
tom kane tom kane is offline
Senior Member
 
Join Date: Nov 2003
Rep: 361 Posts: 1,105
Location: Hamilton.New Zealand.
Thank`s for the replies and info but those craft are getting out of my size and budget
and too big to be bullied by a small light weight 200 HP diesel. Personal transpot cheap to build, reasonably quiet about 15 feet x 6 foot 6 inches hull. I am sure a axial flow style fan (with special design blades) that is easy to balance and light weight will do what I want.
__________________
tomkane
Reply With Quote
  #40  
Old 11-16-2010, 04:59 PM
Boston Boston is offline
Previous Member
 
hey Gonzo I kinda liked your idea of a hovercraft sailboat, cat with hover components but instead of the motorized drive a mast and sails

might end up being pretty fast assuming anyone is crazy enough to build it

cheers
B
Reply With Quote
  #41  
Old 11-16-2010, 09:42 PM
kach22i's Avatar
kach22i kach22i is offline
Architect
 
Join Date: Feb 2005
Rep: 1181 Posts: 2,378
Location: Michigan
Quote:
Originally Posted by tom kane View Post
.........those craft are getting out of my size and budget
and too big to be bullied by a small light weight 200 HP diesel.
What?

You will need less than half the engine for a hovercraft than for an equivalent boat and far less than an airboat.

In the PDF below you can see a 9.5 meter craft (almost 30 FT) with only a 140 hp Diesel engine (Griffon1050TD).
http://www.griffonhoverwork.com/imag...pdf?1259771992

In general, hovercraft use half the fuel at speed than boats use (and airboats are worse). However the surface area must be about twice as large, so you will be loading it half as much which really upsets some people's mindset.
__________________
George: Architect (land lover type)
Hovercraft & Vintage Porsche Owner
http://www.boatdesign.net/forums/boa...ect-11973.html
Reply With Quote
  #42  
Old 11-17-2010, 10:57 PM
Techecho's Avatar
Techecho Techecho is offline
newbie to boat design
 
Join Date: Nov 2010
Rep: 10 Posts: 5
Location: Vancouver BC Canada
kach22i's post a thread from BMcF showing the www.industrialobject.com showing the ASV-X1. My question would be if you consider a squirrel cage fan, is that consider as taking a 90 deg. turn from intake to exhaust.

What I would look at is replacing your prop design and either using a back to back squirrel cage ( one motor connection, two side air draw ) or two vertical cages with top draw ( reverse motor connections ) in both cases you eliminate side torque.

If all this sounds like I flew in from lala land It true. I be a newbie
Reply With Quote
  #43  
Old 11-17-2010, 11:13 PM
Techecho's Avatar
Techecho Techecho is offline
newbie to boat design
 
Join Date: Nov 2010
Rep: 10 Posts: 5
Location: Vancouver BC Canada
To follow on if you can balance the the boat for angle of attack of the air flow if the air stream is direct at an angle towards the water surface lets say down turn 20 to 30 deg you will get some thrust from the resistance of the the water ( back pressure ) most prop boats are looking to plain so the are looking for speed, the prop is directed at 90 deg to the water for maximum forward thrust at speed you would be looking for slow speed thrust less volume less horse power
Reply With Quote
  #44  
Old 11-18-2010, 08:00 AM
kach22i's Avatar
kach22i kach22i is offline
Architect
 
Join Date: Feb 2005
Rep: 1181 Posts: 2,378
Location: Michigan
Quote:
Originally Posted by Techecho View Post
down turn 20 to 30 deg you will get some thrust from the resistance of the the water
It would be nice to be able to direct it upward as well (pitch control). That way you could pop the bow up to plane once you get enough speed started. Otherwise with the thrust being set at 25 degree downward, the craft stern would start to lift up thereby sending the bow plowing in at speed.

Like a see-saw.
http://www.deltasigtu.com/philanthropy.htm


http://www.langleyflyingschool.com/P...Movements.html
__________________
George: Architect (land lover type)
Hovercraft & Vintage Porsche Owner
http://www.boatdesign.net/forums/boa...ect-11973.html
Reply With Quote


  #45  
Old 11-18-2010, 09:15 AM
Techecho's Avatar
Techecho Techecho is offline
newbie to boat design
 
Join Date: Nov 2010
Rep: 10 Posts: 5
Location: Vancouver BC Canada
I like the pitch idea at start up you can get good thrust ( stirs up the water ) then feather it out to not lose energy into disrupting the water.
If it was the horizontal squirrel cage it could be swivelled and not require redirecting the air flow pattern.

TOM in reading your posts you have made reference to 16' x 6'6" and 200 HP diesel are these items you already have.
How much of the platform are you allowing for your propulsion, an outboard will only take up 1 or 2 feet but an air system will need at least a third of your length. 200 HP is a lot of power and weight, my 17' speed boat has 90 HP and can do 45 MPH. From pictures I have seen of air boats ( everglade style ) they are probably only using from 30 to 80 HP gas engines ( small and light ) I would think that should be the direction to go, maybe a 50-60 HP gas. Maybe a motor cycle engine 650 -750 cc they can be quiet enough with good mufflers.
Reply With Quote
Reply



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
Can these fan boats perform ? Externet Powerboats 2 09-23-2009 08:19 AM
Horizontal Keel adbert Stability 17 02-15-2009 07:22 PM
Can FreeShip give me horizontal slices? alexlebrit Software 18 06-09-2007 02:38 PM
Fan Craft Johnny Boat Design 0 10-15-2005 09:28 AM
Horizontal strongback jonathan Boatbuilding 14 11-22-2003 04:36 PM


All times are GMT -4. The time now is 05:21 PM.


Powered by: vBulletin Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Web Site Design and Content Copyright ©1999 - 2014 Boat Design Net