Valveless PJ powered Hovercraft?

[ace_fedde]

I wrote this post in another topic where I was asked to open a new topic:

Man, I'm getting inspired by these "alternative" applications of the Thunderchine and because of that some turbulence of ideas and questions is taking place in my head.

Let me first introduce myself. My name is Fedde and I'm from The Netherlands. I've been reading and studying this forum for over a year, registered and unregistered, and I did only a couple posts.

Back to my turbulence: Constructing a hovercraft out of a Citroen 2CV, using separate pulsejets for propulsion and maintaining the aircushion...
For this car of 550 kg with a surface of app. 6 sq.m. the raise of pressure in the cushion would be less than 0.1 bar. For a highly tuned pulse jet this might be a problem? (this is more a question than a statement)

For the cushion there is not so much max. thrust needed but max. displacement of air.
I know that for turbines a restriction in the exhaust can cause an increasement of thrust (higher pressure), but probably a slight reduction in displacement.
The same (reverse) effect i noticed when I unscrewed the endnozzle of my high-pressure watercleaner: an decrease of thrust but a increase of waterflow. Unfortunatly I don't know (yet) the physics in this matter.

Would it be possible to design a pulsejet (or a modification) with more displacement but lower thrust than, for example, the thunderchine? Would it help to add multiple augmentors? etc. etc.

I love to post these questions in this thread because all the experts seem to be gathered in this one. But if these are interesting questions to you guys too, it might be better to open a new thread?

Fedde

[ace_fedde]

M. answered me:

PS: The lift cushion is best supplied via a ducted fan; I can help you size one,
but open a separate thread if you want to discuss or build the hovercraft project.

mm, ducted fan, kinda old-fashioned seems more fun to me to use a PJ for that purpose.
Compact and lightweigt!(and bad fuel economy )

Is there any way to construct a PJ more like a pump than a thruster?

Fedde

[milisavljevic]

Hello Fedde,

Ducted fan, kinda old-fashioned. Seems more fun to me to use a PJ for that purpose.

Sometimes "old-fashioned" is best. Today we make noodles the same way we did 4000 years ago,
when the Chinese first invented them. I don't hear anyone complaining about "ancient" spaghetti!

That said, a pulsejet would be more fun!

Is there any way to construct a PJ more like a pump than a thruster?

A pulsejet is a pump. Thunderchine is a prodigious pump, displacing thousands of kilos of air in
an hour. If I added an ejector to the exhaust, its air displacement may be enough for your needs.

I will have to do some modeling to see if one (1) Thunderchine can lift your proposed hovercraft.
Why not post the details for exactly what you want to lift and how fast you want it to go? Thanks!

Cheers,
M.

[ace_fedde]

Hello M.,

Sometimes "old-fashioned" is best. Today we make noodles the same way we did 4000 years ago,
when the Chinese first invented them. I don't hear anyone complaining about "ancient" spaghetti!

I went to the local chinese restaurant and asked for last months noodles and today's noodles. I must say that I could already (what's a month compared to 4000 years!) notice a significant diference! I liked more today's noodles.
After extrapolation my conclusion in this little experiment is that I like more newer ideas, and noodles, than the older.

I will have to do some modeling to see if one (1) Thunderchine can lift your proposed hovercraft.
Why not post the details for exactly what you want to lift and how fast you want it to go? Thanks!

First I would like to say something about me and my project(s): I have skills, materials, objects but at this time I am submerged in problems and don't have work space (for couple years already). I say this because I would hate to see people disappointed because they offered great help, had great ideas, showed great designs but it seems like I'm doing nothing with it.
For the time being this is a theoretical project for me which I hope to realize in the (near?) future. Would love though to inspire somebody else to build a hovercraft like this before I get to build!

My idea started with my love for Citroen's 2cv, we call it "the ugly duck" in Holland. I owned a couple and I still own two of them in parts. Also I own a rotten Fiat 600-like "Zastava" but this car is located in former-Yugoslavia. One of these cars might become the basis for this experiment.

A 2cv can handle pretty rough terrain. But what to do if you end up in a swamp or have to cross a pool? Simple: ignite your PJ's, blow up your cushion and cross! That's the basic idea for this project. And what if Johanson cracks trough the ice? Simple: ignite your PJ's, blow up your cushion and cross! Haha!

Of course I started also thinking about "real" hovercrafts. Easier to construct, lighter, and if equiped for example with one left-right steering PJ for forward thrust, and PJ's on the left- and right front side (also adjustable in direction) for breaking and steering support, it might pe possible to construct a hovercraft with extreme manouvrebility.

Back to the 2cv. The ground-surface of the cushion would be around 6 sq. meters. The weigth of the car is around 600 kg. To my calculations it needs an additional pressure of around 0.1bar to maintain the cushion. Now we can only calculate the needed displacement if we know what's the surface of the effective gap between terrain and cushion on different types of terrain. Maybe this figures can only be obtained by experience?
Of course we can start with theoretical gaps. The skirt would have a length of 11 meters, the height of the gap might vary between 1 and 5 cm. Maybe just 1 cm when the skirt drags through the dirt and the water. So the gap would be between 0.1 and 0.6sq. meter (!) if i see it right.
Now it's a long time since I went to school and I haven't got a clue how to calculate the needed displacement to maintain the 0.1 bar overpressure with such a gap.

I hope I offered sufficient information and inspiration so far!

Fedde

[ace_fedde]

hmm, kilograms, newtons, hmm, always mix up.

So after re-evaluating I have to admit that the pressure will be only 0.01 bar (1000 Pa) and not 0.1 bar

Found the methods of how to calculate the needed air displacement but I didn't study them yet.
Will be back.

Fedde