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Hovercraft- Let the cutting begin!
My four-year experiment of modifying a factory built hovercraft, the saga continues. Last time out it operated on ice and land, but not enough lift for deep grass or to operate over water. It was a real hog on water, not quite out of the water, pushing it out of the way like a wounded animal or like primitive boat/displacement craft.
I could not figure out how to put my Roto-Zip back together, so I put one of the drill type cutters into my cordless drill and it worked! Not real clean, fast or with any high degree of accuracy, but it worked. One of the things I did was to cushion my seat and kneepads. I used flat sheets of 1/2" pool noodle material. The domed clear vinyl air splitter was adapted from a basement window cover, ran about $12. I also covered the inside of the duct with sill sealer, to help absorb sound and to make a tighter clearance with the fan. I hope the adhesive I used stays on, if not I'll use mineral sprits to remove it. I also used Great Stuff to build up a foam diverter at the bow. This should direct the tunnel air for lift, need to cut-form and sculpt it yet...............another project, will let flay as it. I'm going to add a few additional clips to the diverter/splitter, maybe make the edge facing the fan more consistent. The original craft used 33% of its power for lift; I'm guessing the current configuration is about 44%, so it will be a little slower. Photos of work done Friday, Saturday and Sunday. Will it fly? http://forums.pelicanparts.com/uploa...1154965702.jpg http://forums.pelicanparts.com/uploa...1154965715.jpg http://forums.pelicanparts.com/uploa...1154965726.jpg http://forums.pelicanparts.com/uploa...1154965735.jpg http://forums.pelicanparts.com/uploa...1154965746.jpg http://forums.pelicanparts.com/uploa...1154965760.jpg |
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Sitting on hard fiberglass, just getting too old for that anymore.
Bring on the foam!:D http://forums.pelicanparts.com/uploa...1154966473.jpg |
Wow. Wish I lived close enough to come over and help. that looks like a fun project (when it's not my $ involved, anyway).
Good luck. JP |
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Last year I tried my best to patch a small exhaust hole in the black metal using Map gas. Big freaking mess, wrong tool for the job, plus I suck at welding. Tim Hancock offered to do a quick weld on it if I swung by, but it's a several hour drive (out of state). Anyone in S.E. Michigan want to give this a try? I'D rather not yank it off and go to a local auto shop, don't want to catch my craft on fire either. What do you think? The protective/perforated heat shield bracket is easy to remove, but there are a half dozen connections holding it all on. The hole is where another bracket used to attach to it, smaller than a quarter in size. The yellow skirt material will melt and leave a hole if a spark gets on it. Take it all off ? http://forums.pelicanparts.com/uploa...1154971001.jpg EDIT: I had a local Auto repair shop weld a patch on the exhaust pipe/muffler. I then painted with a combination of black 1,200 degree paint and yellow 500 degree paint (red letters said "HOT"). The 500 degree paint blistered and turned an ugly brown in under 10 minutes of operation. Guess the muffler runs way hotter than 500 degrees, live and learn. |
Re: Hovercraft- Let the cutting begin!
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I let this project sit for almost two months, but have the old 911 running pretty good. To answer my own question, it did fly. However the saga continues as it did not do very well. The problem is two fold, I need both additional lift and thrust out of my old craft to make the new experimental skirt work. My goal never was efficiency or performance for that matter. My goal was increased obstacle clearance and stability. I can still reach my goal, but have to toss more into the pot to make it go. There are descriptions in the upper right hand corner of the webpage links which describes what I'm facing and my thoughts on how to deal with it all. I just took a saw to the lower front bow of the craft, except for the aluminum supports it's 100% open now. I just pinched the air flow too much before it could enter the plenum under the craft. I will also Gorilla-Tape up some of the side bag feed holes so more lift air actually gets under the craft. The craft is still too stable and will not lean into a banking turn. I don't need all that side pressure in the bags, I need a real air gap to reduce friction. The videos.......... Part 1: http://video.google.com/videoplay?docid=8306791101923106301&hl=en Part 2: http://video.google.com/videoplay?docid=-7414948022879099026 Part 3: http://video.google.com/videoplay?docid=1013029571331310870 Part 4: http://video.google.com/videoplay?docid=6657780685702543190 .................and the journey continues.:) |
WOW, that thing is cool.
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Thanks, it can be fun, it can also be a pain.
As promised more hacking and cutting photos. Thinking of adding more surrounding supports (aluminum). I have to get the air flow sculpted much better than it is now at the bow, just starting the process. I thought I only had a couple air holes each inflated sponson side to seal up. I can see where I need to seal up many holes, don't need the air in the sides, need to get it out the front and under the craft. Tweeking may not cut it, but it will help. I'm more or less set on replacing the drive/lift fan. Plastic gets old and breaks down with age, probably a good thing to replace every 17 years, right? I mean car tires should be replaced every six years no matter how many miles on them, right? http://forums.pelicanparts.com/uploa...1157463715.jpg http://forums.pelicanparts.com/uploa...1157463733.jpg http://forums.pelicanparts.com/uploa...1157463742.jpg http://forums.pelicanparts.com/uploa...1157463750.jpg http://forums.pelicanparts.com/uploa...1157463759.jpg http://forums.pelicanparts.com/uploa...1157463769.jpg |
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So was that a kit or did you build it from stuff you had???? Why not just get a bigger blower to force more air into the skirt and under the craft??
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Bigger blower can mean three things: 1. Improved replacement fan. 2. Bigger engine with better fan, and more blades and higher degrees of attack. 3. Add a dedicated lift engine and fan, and convert the rear fan into thrust only...........aka "Air Commander" hovercraft style. More into the pot anyway I look at it.:cool: The challenge at this point will be getting it to work without major changes. There is a slight chance I can tweek it and get it to work. Then all I have to do is to get it to work BETTER.:) |
Hey George,
I have about got mine back together, ( SCAT 1 ) I'm dropping in a Rotax twin Cylinder water cooled rotary valve 536 pulled from a Ski Doo snowmobile. I got my motor mounts finished. All I need now is a little time to finish things up and run the lines for the radiators. |
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:D http://35heures.blog.lemonde.fr/phot...rized/yoda.jpg I'll never be able to keep up with you now. Get good at it and you will do good when racing it. |
Air distribution is unequal, looking at adding a foil like scoop to balance it out.
What do you think? http://forums.pelicanparts.com/uploa...1157967526.jpg |
UPDATE 09-25-2006
Took it out for a third test flight using the heavy yellow skirt fabric. This is the second time out on water, the first time with video of the stren wake condition. Below is a sketch to show the design and proposed fix to the design flaw(s).............which may be more than I'm attempting to fix at this time. One problem and one fix at a time, just so I can equate results, actions and reactions. http://www.hoverclubofamerica.org/fo...81_6_42848.jpg Links to three videos, the last video is of most importance if you have time to click just one. The hovercraft just about leaps into the water just to encounter massive drag at the stern moments later. Watch for the vortex of water billowing in the form of wake between the twin tails. Part 1: http://video.google.com/videoplay?docid=2874026733268022464 Part 2: http://video.google.com/videoplay?docid=5341781496606431296 Part 3: http://video.google.com/videoplay?docid=2182246473369429912 During water operation the partial stern bag which is fed supply air from pressure under the craft, has been found to act like a drag chute under real life conditions. So much for theory alone. A large central drail hole was unable to get the water out fast enough. I don't want the water getting in there at all, need to rethink this portion of the design - again. Items in blue marker are proposed changes which have been on my mind since I started the project. It's time I made these changes while it's still warm enough to work outside in Michigan. What do you think? The sail like splitter I installed worked very well. Almost too well, I now have slightly more air coming up to the starboard supply air lift hole than to the port side supply air lift hole. It was once double the air on the port side prior to the diverter/splitter modification. The craft had more lift and more thrust than last time out. This improved on-land performance, but was you can tell at-sea performance is still lacking. I could not turn into the wind, nor with the wind, so I went across the lake and used the shore to do a 180 degree turn. I then ran out of gas 2/3 rd's of the way back, one guy (DNR) got my spare gas can, but his boat was too small to tow me. On the way back another but much larger boat gave me a tow as I was not quite up on cushion with the drag chute holding me back - made lots of spay though. Perhaps if anyone ever wants to develop a sea anchor or brake drag chute for hovercraft they will look up my little experiment here. :D I'm learning a lot, so I guess that means I'm having fun.:D |
Wow, that thing is really moving now
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So many toys, so little time.:D |
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Ford Lake, Sunday October 08, 2006. Took it out three or four times into the lake, same result everytime. Gets out there, starts to slow down, nose starts pushing water. From what I can figure the lower front bow skirt drape edge where the pool noodle is, is being sucked down. The bow drape going straight across, and the pool noodle addition were not my first configuration choices for this craft. I wanted to slope it inward like a boat but all the extra cutting and fitting would of taken more time than I wanted to spend this spring. Worked great in the parking lot, and getting it on the trailer was pretty easy to. I think it work just fine on Gun Lake this winter. Come spring time, I'm doing some major modifications for water operation. It's going to look like a boat by the time I'm through with it. The sharp lower tail/sponson corners with their weep holes are catching water too. You can see it in the second video pretty clearly (and in the parking lot video). If I can shape it like a canoe, that's what I'm going to do. 6 Videos: http://www.youtube.com/watch?v=QQkzh0Yd0qE http://www.youtube.com/watch?v=Jq6yx7061lI http://www.youtube.com/watch?v=0S8rW3cmhT0 http://www.youtube.com/watch?v=_eghLJ0dU0w http://www.youtube.com/watch?v=p7YHk0hq7Ek http://www.youtube.com/watch?v=NNUioMLU1_A |
How much weight has been added by your mods, and are you calculating that into your power requirements?
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Why don't you just buy a factory skirt, they work fine. I must be missing something???
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For the fun of it.:) I have a lot to learn, and life is short. I have added weight, from foam and that heavy skirt. I was hoping that the new skirt configuration and fancy splitter/diverter trickery would compensate - guess not all the way. Getting closer all the time, and it's been an interesting trip. |
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I 've just had the throught that perhaps the dome splitter modification on my craft is allowing the spiral of air down, or at least more than a straight one would allow.
This would have the effect of keeping constant yaw on the flight course, meaning driving straight would be difficult and it would also be pushing the nose down. I've experienced both!:eek: http://www.felco.ne.jp/felco/fel/eng...ropeller_1.jpg |
Changes to the model are faster and cheaper than the real thing. A smart person would use one of those fancy 3-D programs, not me - this is too much fun this way.
http://www.hoverclubofamerica.org/fo...81_6_85772.jpg http://www.hoverclubofamerica.org/fo...81_6_17015.jpg http://www.hoverclubofamerica.org/fo...81_6_21583.jpg |
The Big Twin Banana Skirt..................................
Just giving a name to the latest change in the skirt, not that Banana's are an inspiration or anything. :) http://www.cepolina.com/freephoto/f/...ood/banana.jpg http://www.rotonics.com/mathandl/hyd...llow-canoe.gif Additional information is given in the photo's captions under the "Gallery" section labled: Personal Hovercraft Photos. http://www.hoverclubofamerica.org/forum/index.php?automodule=gallery&cmd=sc&cat=6 http://www.hoverclubofamerica.org/fo...181_6_2516.jpg http://www.hoverclubofamerica.org/fo...81_6_20727.jpg http://www.hoverclubofamerica.org/fo...81_6_85415.jpg http://www.hoverclubofamerica.org/fo...181_6_6911.jpg http://www.hoverclubofamerica.org/fo...81_6_79618.jpg Note: As of this date the skirt is untested in this configuration. Roofing tape will cover all seems for air tight fittings. Also tapering of the skirt is in the plans should I have the time to do some refitting. This design is intended to work with elevators in the thrust airflow to insure a "bow up" attitude at speed to help prevent "plow-in". Who knew it would be this much work, or this much fun? :blush: |
More power, Mr. Scott.
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may the FAN BE WITH YOU! too much. looks like a hell of a good time. now where do the quad .50 cals. go? i'd warn the neighbors and wear a mask going down the street if i were you!
WHO WAS THAT MASKED MAN??????? |
UPDATE 11/29/06
I did some major modifications to get the lift air to behave the way I wanted it to. I'm not going to post the details of this. I'll just say that I've went past way beyond the point of no return and this will never be a finger skirt craft again. The center of lift was shifted way back when I made the bow more boat-like. I'm struggling to correct for the balance and weight shift - looking for ideas short of adding weight to stern. Funny thing is that a major engine swap/upgrade would shift it back into balance (I think). If I were to do this it may look similar to what Ralph Debouse (sp?) did to his Scat-1 (a radical redesign). How do you determine the center of gravity on an existing craft? How do you determine the center of lift on an existing? Is it best to have the two the same? What happens if they are not? The first video is without the 2x12 for balance. The piece of lumber was the heaviest thing I had around to strap to the craft via bungie cords, but it does look like a wing. For more information be sure to read the captions posted with the videos. Off Trailer-1: http://www.youtube.com/watch?v=cQtK1jHAHh0 Parking lot run-2: http://www.youtube.com/watch?v=bU0Xnlru-qo&mode=user&search= Parking lot run-3: http://www.youtube.com/watch?v=lIc9vYyar6E The video comes to a stop before the hovercraft hits a wood post at the end of the parking lot. I did that twice and now have some hull repairs ahead of me. I have more videos taken the same day which was the day after Thanksgiving, but they don't show much more. To do/install: 1. Longer handle bars 2. Seat 3. Elevators 4. Access panels plates to fix hull damage 5. Windshield 6. Gas tank rethink/replacement 7. Bow thruster/leaf blower.......someday 8. NOS kit.................just dreaming :P EDIT: Test flight 11/25/06 results: Not once but twice I slid into a post at the end of a parking lot. The second time even harder than the first. My latest revisions to my craft means it slides much further than ever before after I let off the gas. Plow-in is no longer a quick fix reaction to objects coming up on you. On the up side, I have an excuse to cut a big hole in my deck and have air tunnel access via aluminum diamond plate. http://www.hoverclubofamerica.org/fo...81_6_34913.jpg |
You need to perform weight and balance calculations just like you'd need to do if you were building an airplane. On fixed wing, the datum line is typically the firewall. The the weight is measured, and the moment arm (the distance from the datum line) is calculated and the effect of the weight based on its' location can be known. This is why modifications to certified aircraft are illegal without engineering calculations, and a full new weight and balance being completed. When I was an aircraft mechanic, years ago now, we had to redo the weight and balance on every helicopter during it's major maintenance cycle.
Look at this: http://home.new.rr.com/trumpetb/alph/ Tim Hancock does this way more often than I do. He'd be the one I asked for suggestions. However, I believe on your craft, the datum line would be the nose. Maybe. |
Well, I do not know where the CG is supposed to be on any paricular hover craft, but since you altered the center of lift you obviously will need to alter the center of gravity. On a given airplane design the center of lift, is somewhere in the vicinity of 25% aft of the leading edge of the wing. Once this is determined, the designer makes an educated guess at the range of where the center of gravity needs to be to make the airplane safe. Thru actual testing then the safe CG envelope is proven.
You are going to have to guess then experiment with your altered center of lift hovercraft. By using weight placed in various locations, you can using math, figure out what permanent components you can move around then to duplicate the temporary weights that produced the desired results. |
Thanks for the information. At the HCA site Dave Reyburn posted what I needed to correct my problem, or at least to get started.
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UPDATE 12/17/2006
I've posted the pictures with captions here: http://www.hoverclubofamerica.org/forum/in...ry&cmd=sc&cat=6 http://www.hoverclubofamerica.org/fo...81_6_76445.jpg http://www.hoverclubofamerica.org/fo...81_6_21261.jpg http://www.hoverclubofamerica.org/fo...1_6_111814.jpg http://www.hoverclubofamerica.org/fo...81_6_13352.jpg Almost time for test flight number seven, but for safety reasons I'm going to install the flow straighteners and elevators first. The zig-zag path though the parking lot makes me real nervous - I have to try to solve this next or more damage will be done. |
UPDATE 12/25/06 Chirstmas
Test flight No. 7 went alright yesterday, there is good and there is bad to report. Good: Elevators gave me much needed control Craft was balanced Parking lot trials were good, I did not hit any wood post this time. Straight line water travel and large arc turns were good to fair Bad: Elevator clips for adjustable angles slipped up the shaft(s). Balance still allowed some mid-ship/mid-bag spray blasts of water when coming off cushion. I found myself sliding sideways when letting off the gas going down a steep drive. Tight water turns were slow to respond and resulted in coming off cushion. Conclusion: About the last "bad" item. This may indicate there is still large amounts of skirt drag under certain conditions. These conditions get worse very quickly because of the heavy skirt material. This heavy skirt drag once it happens does not allow the hovercraft to "recover" and get back on cushion. Weather Conditions: Christmas Eve, sunny 47 degrees F, and very little wind. What state am I in? Michigan, I know it's crazy - unheard of. Merry Christmas everyone. :) http://www.hoverclubofamerica.org/fo...1_6_102375.jpg http://www.hoverclubofamerica.org/fo...81_6_55928.jpg http://www.hoverclubofamerica.org/fo...1_6_138691.jpg Video going out on to the lake: http://www.youtube.com/watch?v=UEWQS8TCnDo Video coming back in and dragging it: http://www.youtube.com/watch?v=55L1HwYOvKQ I went in and out of the lake several times, and "at will". The results were always the same. Sharp turn would slow the craft down and force me off cushion, dragging the skirt. Large arc type turns did okay (270 degrees) until facing a slight headwind then there was no way to keep speed up, not enough thrust. There is not enough lift and thrust to overcome the problems the heavy skirt material has caused. What I have now will make a fine "ice skirt" but I don't see it ever see it becoming a good water skirt without more development. As it is now I can just experiment with it, and not enjoy it in any other manner. |
George,
Very cool. As with all flight test, build to the crescendo! |
Well, I did say "more power Scotty" didn't I? :cool: Looks like you're getting there, but still on the uphill side of the slope.
Enjoyed the videos. |
George,
Merry Christmas! Weren't you cold? I drove Helga to my inlaws yesterday and didn't take the targa top with me. It rained hard on the way home and it was about 35 degrees and I still feel cold today!!! |
I've been thinking about the rear wake which follows the hovercraft up to shore.
What would cause that? There is no bow wake, so the skirt must be catching/contacting at the tail end. I thinking of removing what I've called "The Cape" (large anti-drag flap) under the stern of the craft. I will then put a new stern bag skirt on the craft, one designed to seal the rear corners by it's self - trapazoid in shape. 1. Yes, more power would most likely cure all ills. 2. Skirt used to be too stiff (it was bouncing), but no longer is after closing off some air feed holes. I may have to soften the bag skirt further still. 3. Too stiff of a skirt will not conform to irregular surfaces such as waves which in turn will cause air to escape, getting you all wet and losing lift in the process. I did get wet, and it was cold out there. 4. Because you've lost lift, the skirt drags in the water and this will lower forward speed. In the turn, air leaking out and getting you wet represents a loss of lift, which results in even more skirt drag, which slowed the craft down below "hump speed", the speed in which you fly over the water not through the water. 5. Hump Speed for boats is also called planing speed, it the point where it takes less energry to skip over the water than to plow through it, once you have climbed over the bow wave. |
Once you get enough lift, you could put a pair of wings on it, and get a result like that: http://www.hovercraft.com/content/index.php?main_page=index&cPath=53
Aurel |
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Here is a RIB with wings, no hovercraft lift air required, the same inventor is now making 100 foot long hovercraft in Florida (Atlas Hovercraft). http://www.seair.com/flyingboat.htm http://www.seair.com/images/SeairWingSmall.jpg |
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