Hovercraft- Let the cutting begin!

[kach22i]

Originally posted by lendaddy
Why don't you just buy a factory skirt, they work fine. I must be missing something???

From the guy that made his own jet pack for his kid, you have to ask?

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.

[lendaddy]

Originally posted by kach22i
From the guy that made his own jet pack for his kid, you have to ask?

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.

Fair enough.

[kach22i]

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!

[kach22i]

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.

[kach22i]

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.





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







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:

[fastpat]

More power, Mr. Scott.

[charleskieffner]

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???????

[kach22i]

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.

[fastpat]

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.

[Tim Hancock]

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.

[kach22i]

Thanks for the information. At the HCA site Dave Reyburn posted what I needed to correct my problem, or at least to get started.

http://www.hoverclubofamerica.org/forum/index.php?showtopic=962

QUOTE
How do you determine the center of gravity on an existing craft?


Place a steel pipe 8 feet long under your hull and slide the craft forward and back until it balances. Have
a friend do this while you sit in the craft.

QUOTE
How do you determine the center of lift on an existing?


You need to calculate the center of area of your skirt. Not trivial in your case.

QUOTE
Is it best to have the two the same? What happens if they are not?


If the center of lift if forward of the CG then you have nose up, aft you have nose down.

[kach22i]

UPDATE 12/17/2006

I've posted the pictures with captions here:
http://www.hoverclubofamerica.org/forum/in...ry&cmd=sc&cat=6






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.

[kach22i]

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.





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.

[Seahawk]

George,

Very cool. As with all flight test, build to the crescendo!

[fastpat]

Well, I did say "more power Scotty" didn't I? Looks like you're getting there, but still on the uphill side of the slope.

Enjoyed the videos.

[azasadny]

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!!!

[kach22i]

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.

[Aurel]

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

[kach22i]

Originally posted by Aurel
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

Yes and no. What you need for wings to work is "take off speed".

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

[fastpat]

Originally posted by kach22i
the same inventor is now making 100 foot long hovercraft in Florida (Atlas Hovercraft).

See if you can determine his power to weight ratio. I'd think looking for an engine that overpowers your experiment would be just right.