Military recon powerboat concept

[kach22i]

The reason I was thinking axial fans are better than centrifugal fans for amphibious hovercraft (when considering heave acceleration) is that someone once told me axial fans have a flatter HQ curve.

Some info here (non-hovercraft):
http://ateam.lbl.gov/Design-Guide/DGHtm/fans.htm

Example (non-hovercaft):
http://ateam.lbl.gov/Design-Guide/DG....axialfans.htm

Centrifugal vs. vane-axial fans

The choice of forward-curved centrifugal or backward-inclined centrifugal or airfoil centrifugal fans versus vane-axial fans will affect the energy efficiency. Standard centrifugal fan systems are typically very inefficient (50 percent to 60 percent), and their actual installed efficiency is usually much worse than the manufacturer's ratings. Efficiencies as low as 30 to 40 percent have been measured in the field. It is recommended that high-efficiency (80 percent to 90 percent) axial airfoil fans be considered with direct drive and static regain devices. However, flexibility of adjustments will be compromised. [Naughton, "HVAC Systems… Part 1," 1990; Micro-Electronics Facility Efficiency Workshop, 1995]

Sometimes the less you know, the more open to learning you are. I'm an open book, tell me what you know.

[BMcF]

Originally Posted by kach22i

Just to clear up a long standing confusion on my part;

1. The "Jeff-A" (LCAC prototype) lift fans which are tied into the bow/stern thrusters were originally "Mixed-Flow Impellers" - right?

The two Jeff craft, A (Bell)and B(Aerojet General) were competing propotypes for the LCAC. The 'B boat' won. The B had air thrusters over centrifugal (HEBA) fans. The B had two airscrews in the stern. The 'A' had mixed-flow lift fans and four air-screw propulsors, each 'module steerable through 360 of rotation.

2. Were they axial or radial? See above

3. Were they single or dual on a common axle? Not as familiar with A boat..the B has two DWDI fans on common shaft line, two port and two starboard.

4. These were the ones which you could see straight though when spinning at speed, right? No..beign DWDI, you cannot see through them due to center disk unless yr Superman.

5. The mixed-flow fan(s) were drawing in air from the port and starboard as well as the cargo well area, right? Again..I'm not as familiar with A-boat details....although I have them aroudn the archives here somewhere

6. The mixed flow fans worked fine but were switched to higher pressure centrifugal fans when the military once again stuffed 10 lbs of organic fertilizer into a 5 lb bag, right? Other way around..

7. I mean to say that the Navy raised the system requirements (added weight) and even larger mixed-flow fans would not fit, or that centrifugal fans had some kind of other advantage yet not discussed.

Mixed-flow and RD (radial diffuser) lift fans were proposed for several concepts (3KSES for example) that got a bit..er..obese as they approached final design completion stage. We now know from building many SES' since then that it was a pointless exercise for the most part. What I mean by that is that if you need fans that have higher pressure ratio than the HEBA centrifugal can deliver, yr already exceeding rational cushion loading ..and zee design will be a peeeg.

[kach22i]

Originally Posted by BMcF

Mixed-flow and RD (radial diffuser) lift fans were proposed for several concepts (3KSES for example)

I'm assuming that Mixed-Flow fans would of been considered as a compromised in between axial and centrifugal fans (best of both) and not as something to provide even more pressure than a centrifugal fan.

What am I missing here?

[BMcF]

Originally Posted by kach22i

I'm assuming that Mixed-Flow fans would of been considered as a compromised in between axial and centrifugal fans (best of both) and not as something to provide even more pressure than a centrifugal fan.

What am I missing here?

Mixed flow designs (witness turbochargers) are used to create higher delta-P across the 'machine' than can typically be achieved by purely radial centrifugal fans. That is a gross simplification that ignores so many other design factors...but one factor that seriously mitigates against using mixed flow whels is their complexity of construction. Airfoil centrifugal wheels are SO much easier to build.

[kach22i]

Originally Posted by BMcF

Mixed flow designs (witness turbochargers) are used to create higher delta-P across the 'machine' than can typically be achieved by purely radial centrifugal fans. That is a gross simplification that ignores so many other design factors...but one factor that seriously mitigates against using mixed flow whels is their complexity of construction. Airfoil centrifugal wheels are SO much easier to build.

The rubbery plastic injected ones (vacuums and blow dryer type) are limited to what size and power?

I'm building a scale hovercraft model, looking to use about a three inch diameter.

Has CNC machining rewritten the rule book on what can be made and scaled up?

[BMcF]

Originally Posted by kach22i

The rubbery plastic injected ones (vacuums and blow dryer type) are limited to what size and power?

I'm building a scale hovercraft model, looking to use about a three inch diameter.

Has CNC machining rewritten the rule book on what can be made and scaled up?

You would know more about the scale fans than I probably. We use either axial muffin fans or FC (furnace blower or squirrel cage) types in the models we build...or a combination fo the two. The 57' radio-controlled 1/20 scale model SES that we are currently building has two 1.5 HP FC squirrel-cage blowers for lift air and 3 Rotron axial muffin fans to act as 'boost fans' for stern seal inflation.

I'm partial to the FC fans for full-scale application as stern seal inflation boost fans. Great pressure rise and flow in a compact min-diameter package..not so great in efficiency but that gets lost in the 'noise' when you consider they average only about 15-20 HP each.

As far as I know..all the mixed flow wheels are/were cast...

[kach22i]

Originally Posted by BMcF

The Jeff-A used mixed flow lift fans, IIRC. They were purched later by Gentry, intended for use in his aborted trans-Atlantic record attempting SES design

I could find nothing on the second SES, but found this on the Gentry Eagle boat.

FOR SALE:
"Own a Piece of History. This is a rare opportunity to be the only person in the world privileged to experience the speed, adventure and prestige of owning Gentry Eagle."
http://www.gentryeagle.com/

Transatlantic crossing record
Ambrose Lighthouse at the entrance to New York Harbor to
Bishop Rock on England's Isles of Scilly.
Boat: Gentry Eagle
Record time: 62 hours & 7 minutes

The SES you are working on is over one thousand feet long?

57 x 20 = 1,140 feet long................or is the model about three feet long?

57 x 12 divided by 20 = 34.2" long?

What good is 1/20th scale?

I thought it had to be at least 1/6 scale to be of any use.

[BMcF]

Originally Posted by kach22i

I could find nothing on the second SES, but found this on the Gentry Eagle boat.

FOR SALE:
"Own a Piece of History. This is a rare opportunity to be the only person in the world privileged to experience the speed, adventure and prestige of owning Gentry Eagle."
http://www.gentryeagle.com/



The SES you are working on is over one thousand feet long?

57 x 20 = 1,140 feet long................or is the model about three feet long?

57 x 12 divided by 20 = 34.2" long?

What good is 1/20th scale?

I thought it had to be at least 1/6 scale to be of any use.

1140 feet LOA..you got it! 1:20 is fine..1:6 is better..1:1 is best.

Gentry and his team never got to finish the SES..the project collapsed when he went in to teh coma and never recovered.

[kach22i]

Originally Posted by BMcF

1140 feet LOA..you got it! 1:20 is fine..1:6 is better..1:1 is best.

The 57' radio-controlled 1/20 scale model SES that we are currently building has two 1.5 HP FC squirrel-cage blowers for lift air and 3 Rotron axial muffin fans to act as 'boost fans' for stern seal inflation.

Maybe my math is wrong; let's say a total lift of 10 HP assuming a useable 7.5 HP of lift, right? (1.5 x 5 = 7.5)

I think 20 foot long hovercraft (not an SES) uses at least 20 HP for lift.

Example:
http://www.hovercraft.com/content/in...ex&cPath=35_55

Therefore, a 60 foot long hovercraft might be using 60 HP (I'll check an old Jane's Surface Skimmer's - 1976 or 1987, later).

The SES uses 1/6 the lift which a fully amphibious hovercraft uses?

I could believe 1/2 the power requirement, but 1/6?

Is this more of a air assisted cat?

[kach22i]

Found this..........................no good pictures though.

http://www.globalsecurity.org/milita...s/ship/hss.htm

Surface Effect Vessel (SEV)

Surface Effect Vessel (SEV) are hybrid surface effect ships that incorporate rigid catamaran-like sidehulls and bow and stern seals to create a plenum pressurized by air. The result is a craft which is 80 percent supported by pressurized air and 20 percent supported by buoyancy. When the plenum is pressurized (on-cushion), the wetted surface of the sidehulls is reduced, reducing drag and allowing high speeds.

Litton Ingalls Shipbuilding has designed (concept design) a transoceanic SEV capable of average transit speeds of 70-75 knots with payloads of 5,000 short tons over a range of 8,700 nautical miles. Ingalls is also designing a smaller coastal SEV (container/RO/RO) as a possible contender for the Army Theater Logistic Vessel (TLV) requirement, and a fast ferry SEV (RO/PAX) that may have intra-theater or riverine warfare applications. The transoceanic and coastal SEV designs are gas turbine powered, water jet propelled and have shallow drafts. They can transport both track and wheeled vehicles as well as containers and will be self-sustaining (i.e., can offload itself) vessels that can rapidly offload in damaged or austere ports, or directly across a beach without the aid of JLOTS. The speed and payload of the vessel would provide the JFC with the capability to strategically maneuver forces into positions of operational advantage on a global basis. The vessel's shallow draft, coupled with its other features would make it useful for maneuvering forces within the theater. It could provide the JFC with the element of surprise and keep the adversary "off balance" because his entire shoreline would be vulnerable to attack.

The need for high speed, heavy payload capable, long distance transportation has led to the investigation of alternate ship designs capable of performing highspeed sealift. Several options are being explored including hydrofoils, multi-hulls, air cushion vehicles, and semi-planing hulls. A proposed commercial example of the latter variety is thought to be capable of 40+ knots with a payload of over 8,000 long tons. Appraisals of the technical feasibility of developing a 50-kt displacement-hull type ship capable of delivering a 12,000 LT payload over a distance of 9000 nm concluded that this ship will have a length of 1500 ft, a displacement of 64,000 LT, a draft of 30 ft, a length/beam ratio of 12.6 and a transport efficiency factor nearly twice that of any existing 50-kt ship. Further, it will require nearly 600,000 hp, which is substantially larger than that in any existing marine vessel.

[BMcF]

Originally Posted by kach22i

The 57' radio-controlled 1/20 scale model SES that we are currently building has two 1.5 HP FC squirrel-cage blowers for lift air and 3 Rotron axial muffin fans to act as 'boost fans' for stern seal inflation.

Maybe my math is wrong; let's say a total lift of 10 HP assuming a useable 7.5 HP of lift, right? (1.5 x 5 = 7.5)

I think 20 foot long hovercraft (not an SES) uses at least 20 HP for lift.

Example:
http://www.hovercraft.com/content/in...ex&cPath=35_55

Therefore, a 60 foot long hovercraft might be using 60 HP (I'll check an old Jane's Surface Skimmer's - 1976 or 1987, later).

The SES uses 1/6 the lift which a fully amphibious hovercraft uses?

I could believe 1/2 the power requirement, but 1/6?

Is this more of a air assisted cat?

Yes..the air leakage is much lower for an SES than for an ACV. An since the leakage is mostly from the bow and stern, it is not greatly affected by increasing the cushioni Length to beam ratio by lengthening the cushion..thus this 10:1 L/B high-speed sealift 'thing' we are building has very low flow requirements for its size. We just completed a program review on the model build phase and I'll get some pictures posted up here soon. At 57' LOA, it is one of the larger remote-controlled scale models ever built.

[kach22i]

Originally Posted by BMcF

At 57' LOA, it is one of the larger remote-controlled scale models ever built.

Largest I know of, including boats and aircraft.

Your competition....................?

SES pictures...................models too.
Blyth Bridges Marine Consultants Limited
http://www.blythbridges.co.uk/projects_column.html

[BMcF]

ah yes..my old friends Andy Blyth and David Bridges. Been quite some years since we worked together on some of those SES concepts.

Our competition for..what?

[kach22i]

Originally Posted by BMcF

Our competition for..what?

Model testing?

Solving ride, stability and buoyancy issues for surface craft of unconventional design?

I thought there was some overlap of services, my mistake?

FYI:
Right now I'm building a five foot long hovercraft model. It started out as a mock-up study for the cabin area only, and just to see if it would work as intended. I enjoy taking plan and section sketches beyond the 2D and into model form, real models (3D) not computer models.

I kind of got carried away and now there is no turning back.

I just picked up three (3") mixed flow fans from a vacuum cleaner repair shop ($15). I also picked up two (4") axial fans for thrust ($10) from an appliance repair shop.

I have the electric motors and NICAD batteries from a few years ago and now have to make it all come together somehow.

[BMcF]

Originally Posted by kach22i

Model testing?

Solving ride, stability and buoyancy issues for surface craft of unconventional design?

I thought there was some overlap of services, my mistake?

FYI:
Right now I'm building a five foot long hovercraft model. It started out as a mock-up study for the cabin area only, and just to see if it would work as intended. I enjoy taking plan and section sketches beyond the 2D and into model form, real models (3D) not computer models.

I kind of got carried away and now there is no turning back.

I just picked up three (3") mixed flow fans from a vacuum cleaner repair shop ($15). I also picked up two (4") axial fans for thrust ($10) from an appliance repair shop.

I have the electric motors and NICAD batteries from a few years ago and now have to make it all come together somehow.

Sounds like a sweet model..and big. I like big..

No mistake on your part..I just didn't know who or what you were referring to as far as competition. We have competitors..but few and we compete in a very small market. Collaboration is as often the case as direct competition..

Our biggest source of work is supporting the 'big boys'..US and foreign navies and larger design houses and shipyards that don't have the expertise in-house to design and build the 'weird ones'..SES, ACV, SWATH, hydrofoils, cats, and hybrids thereof. Stabilization, or 'ride control' used to be our main specialty and primary business, but that morphed in to 'whole ship' design over the last 20+ years and now the ride control systems are a secondary part of our business today..even though we are one of only a handfull of companies worldwide that produce such systems.