Hovercraft B/C

[cool hand luke]

This is our first year to attempt Olympiad. All the other builds are going well but we can get NO movement on this one. We have some of the fans of digikey that produce plenty of pressure. If we have a full bag it easily lifts it but every skirt system we've tried has failed. what materials are you making skirts out of? I'm not kidding myself that we will be competitive this year, but I don't want to fail to get something to function and have the kids embarrassed.

[chalker]

This is our first year to attempt Olympiad. All the other builds are going well but we can get NO movement on this one. We have some of the fans of digikey that produce plenty of pressure. If we have a full bag it easily lifts it but every skirt system we've tried has failed. what materials are you making skirts out of? I'm not kidding myself that we will be competitive this year, but I don't want to fail to get something to function and have the kids embarrassed.

Try putting LOTS of little holes in the bag. I'm talking hundreds to thousands of them. You want to ensure air flow out of every portion of the bottom surface.

[Zioly]

Can someone explain to me the different kind of skirts? I'm really confused as to what the difference is between a "bag skirt" or an "open skirt." What materials seem good for skirts? Garbage bags? And how is the skirt supposed to inflate? I'm just really confused, so all help is appreciated!

[retired1]

This is personal opinion!
A full bag skirt covers the entire bottom which makes it more of a skid than a hovercraft. By putting a number of small holes in it, the bag will allow some air to escape-hopefully uniformally, which will reduce the friction. It is far easier to have this type of bag and with enough work it can be as effective as the next one. With a virtually unlimited amount of "push" power available, more friction is not a kiss of death.

The next one is the edge skirt which is far more difficult to make. It has to be big enough but not too large. It has to be able to trap the air uniformally on all 4 sides and not leak at the corners. I found that putting the edge skirt over a 3/8" dowel gave a decent amount material and made it possible to keep all 4 sides reasonably close. The dowel should not be difficult to remove. The trick is in how do you attach the material to maintain the skirt and not leak at the corners. It took a number of trials to get that right. That I will not share.

If you search long enough on google or bing, you can find a pattern for a superior one. This is really difficult and not necessary to be competitive.

[HandsFreeCookieDunk]

Still need help with a propeller motor for a 2kg hovercraft...

I guess I'll add a little bit to this since I'm still not sure myself. Does anyone know how to calculate thrust based on the specs that are available on Digikey? I've seen people say that it's correlated with RPM and air flow, but I've yet to see a general relationship that I can use to determine what I'm looking for to move the craft for a given acceleration (and therefore force).

There hasn't been a lot of talk about the rear propeller on here, but I'll be curious to see if the majority of them will allow for the full range of speeds, since I imagine attempting slower times might result in the propeller not being able to move the hovercraft at all.

[retired1]

One approach is for a plain DC motor(no brushless), A shaft adapter for propellers and a prop of choice that is a legal size. Add to this a potentiometer of appropriate capability (and affordable) and a small digital volt meter (also affordable).
The motor is a 12 volt motor as 9 volt ones are not plentiful with about a 5,000 rated RPM. You determine the voltage required for the fastest run and then the slowest run. You may have to trim the ends of the prop off a bit and start over.
If your hovercraft is repeatable, you can find the voltage for each time and or distance. Some interpolation may be required if you can not test for all possibilities. This will allow you to nail a good score.

[HandsFreeCookieDunk]

One approach is for a plain DC motor(no brushless), A shaft adapter for propellers and a prop of choice that is a legal size. Add to this a potentiometer of appropriate capability (and affordable) and a small digital volt meter (also affordable).
The motor is a 12 volt motor as 9 volt ones are not plentiful with about a 5,000 rated RPM. You determine the voltage required for the fastest run and then the slowest run. You may have to trim the ends of the prop off a bit and start over.
If your hovercraft is repeatable, you can find the voltage for each time and or distance. Some interpolation may be required if you can not test for all possibilities. This will allow you to nail a good score.

Right, that's more or less the plan. My concern is making sure that the propeller I choose will be strong enough to hit the max speeds and still overcome static friction at the lowest speeds.

[windu34]

Has anyone found a proven design for an edge skirt design?

[bob_the_unicorn]

Does anyone have suggestions for adding weight to the hovercraft while still allowing it to hover?
thanks

[HandsFreeCookieDunk]

Does anyone have suggestions for adding weight to the hovercraft while still allowing it to hover?
thanks

Uhhh..... get a stronger fan? What exactly is the issue here? If you're adding weight and it makes the hovercraft unable to hover, then there's not really much you can do other than finding a fan that generates more pressure.The only other thing I can think of is to make sure the hovercraft is built to max dimensions.