Hovercraft Design and Theory - Excercise 1

Collaborative adventure - 1

FYI: I've started a sister thread over at the Hoverclub of America, where you have to be a member to participate.

Link:
http://www.hoverclubofamerica.org/index.php?showtopic=368

So here is the proposal:

We compare hovercraft designs from around the world and analyze them for strengths and weaknesses. Pick them apart; toss them around exploring both concept and application. This process may or may not and develop a fusion design, new ideas and/or a consensus of principles to springboard from.

These efforts may lead to a description or list of desirable features in future design exercises. At the very least it can be a history lesson of "do's and don'ts".

Anyone game?


[/B]Background/ where I'm coming from/going to:[/B]

I am rebuilding my 1989 Scatt II HP to test out some theories (owned since 1990). Also I have many sketches and concept models which may never get built, but are still fun to theorize and dream about. I've been building hovercraft study models since I was 11 years old, and have been aware of the existence of hovercraft since I was six years old - I'm 44 now and never grew up.

[/B]Idea flow and blatherings[/B]

I have noticed that Sevtec hovercraft kind of function like a catamaran- but not exactly. This got me to thinking if there was any tri-pontoon type surface effect ships. I know that the solid sidewall wall cushion vehicles are a form of non-displacement cat, in a general way.

If the hovercraft bag side skirt is made to be of such high pressure that it acts as a inflatable pontoon - or RIB (rigid inflatable boat), then it would act like one, right?

The wave impact on a RIB is turned into mechanical energy by the air-spring effect which then allows for higher speeds, right? So even a non-displacement hovercraft should be able to deflect more of the wave energy impact, or so it follows to think so.

What would a tri-pontoon type surface effect ship really look like?

I have drawings and built a non-working model. Just trying for a little feed back before I post it or do more work on it.

[/B]Example craft - 1 (Sevtec)[/B]
http://members.aol.com/sevtec/sev/skmr.html

[/B] Example craft - 2 (AKS "Mars")[/B]
http://www.aks.r52.ru/eng/mars.phtml

NOTE: My design started out as a catamaran type as above, however it soon became apparent that it should be develop into a tri-hull because of it's pointed bow. I will post model photos eventually, but want to explore concepts of others before picking away at my own work in public.

Personel criteria

I have chosen the above designs because they seem to hold the most promise for rough sea conditions, and yet are still fully amphibious. This conclusion may become more apparent when side by side comparisions are made to simple bag skirts, traditional fingered/segmented skirts, and or combination skirts.

 

Hovercraft Design and Theory

We know that helecopters and hovercraft work,so why not combine the principle of the two into a Hovercopt.A horizontal fixed pitch ridgid rotor would assist lift and provide direction control by tilting in the direction required,and could be shrouded,usual skirts with lifting fans for hull lubrication.

 

Wow, I finally got a bite on this thread, kind of like fishing in a boat.

About the Hovercopter..............I think for fair seas condition the more common "WIG" airplane type combination is faster and more efficient. Not that should stop you from having fun with a novel idea, always something to be learned. You should know that someone has posted a computer model of a similar concept on the internet - it's blue. There is a thread somewhere on this site about it - the boys bashed it around a lot - no takers.

When I was 13 years old (1973) I saw the inablity of the traditional hovercraft to overcome tall obstacles (as viewed by me) as a serious short coming. I mean the hovercraft could not crush or roll over things that got in the way like a heavy tank could. The hovercraft could not fly overhead like a helicopter and escape danger by going over the next hill or tree line.

Here is what I came up with 32 years ago - have to admit may of been influenced by "Speed Racer's" flying car. There would be underbelly retractable ski powered by an explosive charge or compressed air which would contact the surface at allow the craft to "jump" over things........lets say about 12 feet (4 meters) high. The varaiation on this was out board arms looking like the landing pipes of helicopters which would swing down and hop the craft up. I know this is a crazy idea, but the weight of the craft is already floating on air (weightless in a sense), how much extra force would be required to gain a little altitude?

In retrospect the mass and weight of the craft never changes, so my partially undeveloped brain (unbiased mind) and lack of understanding eventualy grew to understand this (I hope).

I think that low altitude "Ground Effects" could play a role in a hovercopter design (if done right)......................build it and they will come?

 

On the helo, I would worry about the relatively wide top surface of the vehicle taking a lot of the pressure. As kach says, the WIG would use area to the side & so not interfere with the center.

 

The heliferry concept similar to Tom's sketches:
http://www.boatdesign.net/forums/showthread.php?t=4605&highlight=helicopter



This is a cool thread too - 10 pages long.
http://www.boatdesign.net/forums/showthread.php?t=1658&highlight=helicopter

 

That one's not a hovercraft. The spaces between the hulls, plus the larger blades, allow the prop to rest more directly on the water.

 

Skippy, I said it's "similar", or what I meant to say; it has more in common with Tom's idea than anything else I've seen.

Not a huge stretch if you look at his lower image/sketch.

Perhaps the aircraft landing systems of Bell Aerospace (1970's) should be referenced.

Here is an associated thread on that topic (see page two) "Lake" & "Buffalo" :
http://boatdesign.net/forums/showthread.php?t=5885

Note: These landing systems were very high pressure, operated with tiny holes all over the bottom of a closed bag skirt allowing escaping air to lubercate the path. I don't know if they landed on water, they did land on ice & snow, and they did traverse puddles along the airfield with ease (and some spray).

 

For the too busy to bother crowd (yea that's right "Time" magazine):


Landing Without Wheels
http://www.time.com/time/archive/preview/0,10987,841078,00.html
Aug. 25, 1967
Everything seemed normal when Test Pilot David W. Howe eased the LA4 "Lake" amphibian toward Niagara Falls International Airport earlier this month. So he radioed a highly abnormal report to the tower: "Bag down and inflated." Seconds later he landed—without wheels—on a cushion of air.

Howe was testing a new air-cushion landing gear (ACLG) developed by Textron's Bell Aerosystems Co. of Buffalo. Based on the British Hovercraft principle (TIME, June 2) and conceived by Bell's T. Desmond Earl and Wilfred J. Eggington, the system employs an elastic bag made of laminated nylon and rubber attached to the underside of the plane. For takeoffs and landings, the bag is inflated through louvers in the plane's underbelly by a fan on board. Air is forced through hundreds of openings on the underside of the bag, producing an air cushion that holds the aircraft off the ground for silky take-offs and gentle touchdowns.

Bell's ACLG permits landings on the most rudimentary runways and also on ice, water, sand, swampland, and terrain dotted with obstacles, such as rocks half the height of the inflatable bag. Deflated in flight, the ACLG hugs the bottom of the aircraft without causing aerodynamic drag. "We consider the ACLG a complete technological breakthrough in landing systems," says David Perez, civilian project officer in the Flight Dynamics Laboratory at Wright-Patterson A.F.B., Dayton. And so last year, the Air Force awarded Bell a $99,000 contract for wind-tunnel tests of the ACLG. Now Bell has won a second contract for $98,700 to study possible use of its ACLG on the Air Force's C-119 "Flying Boxcar" transport.



This guy has a good site, pleantly of related information - look at that WIG!

http://www.geocities.com/air_mech_strike/aircraftphotos.htm



Look for Jane's Surface Skimmers 1976-77 for pictures.

 

Hovercopt is not intended as a multimillion dollar project,but a reasonable project for an experimenter at home,and safe form of cheap transport to take the family for a picknic.The roto system is not the usual helecopter design and is simple and the mechenics have been used for years.In effect a horizontal propulsion thruster.You fellers are not going to spend my money.I want a finance price cap on such a project.

 

I'm sure you know something about "Gyrocopters" and their not so stellar safety record so I'll leave that alone for you to research and decide.

Below is the coolest gyrocopter ever........and insult to even call it one:

http://www.cartercopters.com/

 

Hovercopt has no autogyro attributes,air flows down through the rotor (propeller) and there is no need for cyclic-pitch-control,but a pitch control would be useful.Unequal litf is cancelled out by the tilt ability of the rotor,and the rotor adds lift effect to air cushion of craft and tows the hull with a wheather vane effect.Torque effect is limited by keel effect of the hull and controlled discharge of air cushion air.Hovercopt is not intended to fly but can be likened to a air-boat with a horizontal propeller in place of a vertical one.

 

Tom, I don't want to try to change your mind on your design - my only intent in mentioning the gyrocopter is that is one of the cheaper answers to heavier than air flight. Well, so is powered para-sailing but that is very far removed from your design topic.

I'm guess that you are also familiar with the flying platforms/flying jeep of the 1950's-1960's - pretty cool stuff, right? Have you seen the latest effort in this school of thought? I found it by doing an image seach on Google "hovercopter".



Here is the link:
http://www.hovercopter.us/

The reason I like to make similarties between different designs is to learn what works and why. I feel that if one only looks at the differences the larger picture gets lost in minor details. Commor problems solved in different ways are also very exciting to examine (for me).

Looking at your project with a more critical eye, one may ask; What is the problem you are trying to solve?

If I could project my own personal thoughts into this - just do it because it can be done, and has not been done before!

Well, that's good enough for me as long as it's not a cash or time hog impending on other worthy projects.

In a practical sense your design even on a good day has limited applications, but then again so does a basic hovercraft. Let me tell you about operating a hovercraft in:

A: Inland lake: Curiosity seekers on jet ski's getting too close, boats towing skiers across your path, running out of lake and docks, noise to residences, choppy water, and the inablity to turn with other caft who are inaware that you don't even have brakes......really sucks.

B: Great lakes: Lake Erie a choppy shallow lake with anoying winds (not much fun).

Lake Michigan has big rolling waves which are a blast to ride on like mogals or hills at a snow ski resort - that is until they break and crest crashing a torent of water into your plastic fan blades which are spinning at near supersonic speed/rotation (a bad thing). Once again - mightly gust of wind may come at unexpected moments.

Lake St. Clair, it's not really a "Great Lake" (kind of a extention of the Detroit river, which is not really a river but a connection between to large bodies of water) but it's much better than an inland lake...........boat traffic and winds may be problems at times.

C: Rivers........river are "da bomb", can't be beat. However horsepower limits (5 hp) are very common, hard to get a nice stretch without hitting a dam or low bridge in most cases. Narrow rivers may become completly blocked by fallen trees. Wide rivers can become partialy blocked by fallen tress and have powerlines and bridges crossing them. On the wide rivers the birds - poor crane's get confused and can fly into your path. More often they fly along side terrified that they can't out run you and exhaust themselves until banking off (your design would chop them up in a worst case). Again there are fly fishermen, canoeist, kids swiming and low water levels can expose some pretty big rocks/obsticals.

In the end, I can't see large whirling blades of a low flying, not very manuverable craft being safe or economical - sorry. Form strictly a design study viewpoint you may want to address some of the day to day operating problems I've described in my hovercraft experiences. It could only make your design better, safer and more fun. Plus it's always nice to learn new things, try new things develop and grow. Good luck, cheers - George/kach22i.

 

Hovercraft design and Theory

Thanks Kach22i,what you describe is a universal problem with hovercraft in general built along the design of the image shown.This is the reason for the hovercopt concept which has progressed far beyound that basic idea.The black and white image is an aircraft built by a New Zealand inventor Richars pearse 1877-1953 and possibly the first person to fly a heavier than air craft,a VTO.From a book Kiwi Ingenuity by Bob Riley.

 

This is a good link to hovercraft sites:
http://www.hoverclubofamerica.org/HCA_Matl/Links/Links.html

How close is Pacific Hovercraft in Belfast, Christchurch to you Tom?

Hover people are a tight nit group (so few of us) perhaps you could get a tour or free test ride.

I know New Zealand is very different from Michigan, and it's not just the sheep (haha). The remote and wide open spaces may make an idea location for testing out your ideas.

One thing that I know from watching the Universal WIG craft is that the constantly inflated skirt (while in flight) is a huge safety feature. Nothing like coming down on any surface with a cushion of compressed/pressurized air for unplanned touch downs.

People always say helicopters are more manuverable than fixed wing craft, I have to agree as I almost lost my lunch (felt sick) in a helicopter when I was 16 years old. Perhaps this may be true for your craft, just remember you can only bank up, banking down is a crash, and no banking is a just a wide arc/turn.

 

Pacific Hovercraft www.hovercraft.co.nz is in the south island of New Zealand,and Hamilton is in the middle of the north island,just a short trip by copter,and you can see all 65 million (I think),down from 75 million sheep on the way.Unfortunately you may get the very scenic route in amoung the trees and waterfalls,and you can have a bungie jump just to add excitement.