- #36
bob012345
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Thanks. It would be simply fantastic if I actually needed one though.berkeman said:Might be a good idea to add a tether to those experiments...
Thanks. It would be simply fantastic if I actually needed one though.berkeman said:Might be a good idea to add a tether to those experiments...
bob012345 said:I could live with 6 inches.
There isn't a 2 square foot hole. The 6 inches (or the 1ft.) is the total height of the air cushion. The actual air gap may be on the order of a few cm or less which would be the total height of the air cushion in that case without the skirt. So, it's not a 6 inch (or 1ft.) skirt gap, it's a six inch skirt and a very small air gap to the ground.CWatters said:Ok so if it's a 1ft * 1ft square platform a 6" high skirt gap will have an area of 2sqf. Less if the platform is circular.
If we treat this like a hovercraft...
To lift 35lbs the pressure on the underside of the platform would need be...
35/1 = 35lbs per square foot or about 0.24psi.
Your fans would need to maintain this pressure despite having a 2 square foot "hole" around the edge.
I'll let someone else work out the air flow rate needed as that's beyond me. I built small hovercraft as a kid from polystyrene tiles and my gut feel is that a 6" skirt gap is unrealistic on such a small area hovercraft.
I think it will behave more like a helicopter than a hovercraft.
Ok. That's why I asked in #15 how big the gap could be. You replied in #28.bob012345 said:There isn't a 2 square foot hole. The 6 inches (or the 1ft.) is the total height of the air cushion. The actual air gap may be on the order of a few cm or less which would be the total height of the air cushion in that case without the skirt. So, it's not a 6 inch (or 1ft.) skirt gap, it's a six inch skirt and a very small air gap to the ground.
Sorry, I misread your message.CWatters said:Ok. That's why I asked in #15 how big the gap could be. You replied in #28.
bob012345 said:Any thoughts on my pulse jet concept?
I can calculate things but I'm asking general background opinions for direction right now. The project isn't at the stage to debate detailed numbers but I can say I've done back of the envelope calculations. I'm not going to argue that one way is better based on numbers at this point.anorlunda said:Only that it is difficult to make a jet with a thrurst/weight ratio greater than 1. Remember that the vehicle, engine, fuel and passengers all add to the weight.
The F16 and a few other fighter aircraft manage that, but other modern fighters like the F18 don't.
You can see videos of homemade pulse jets on Youtube. It seems that most make only 5-10 pounds of thrust.
So far, your posts on this thread lack numbers. Practicality in engineering means looking at the numbers and the calculations. It is difficult to have a conversation without them. Do you have the background to calculate things like thrust?
Based on the youtube video's, my idea of a pulse jet is somewhat different. I was thinking of a plate that small gas/air explosions push against sort of like Freeman Dyson's Project Orion design for a nuclear bomb powered starship only on a somewhat smaller scale. :)anorlunda said:Only that it is difficult to make a jet with a thrurst/weight ratio greater than 1. Remember that the vehicle, engine, fuel and passengers all add to the weight.
The F16 and a few other fighter aircraft manage that, but other modern fighters like the F18 don't.
You can see videos of homemade pulse jets on Youtube. It seems that most make only 5-10 pounds of thrust.
So far, your posts on this thread lack numbers. Practicality in engineering means looking at the numbers and the calculations. It is difficult to have a conversation without them. Do you have the background to calculate things like thrust?
bob012345 said:Based on the youtube video's, my idea of a pulse jet is somewhat different. I was thinking of a plate that small gas/air explosions push against sort of like Freeman Dyson's Project Orion design for a nuclear bomb powered starship only on a somewhat smaller scale. :)
anorlunda said:Unless you are willing to do the calculations needed to see what it would take to do that, I see no reason to take your project seriously.
My take on this project is that you are looking at it too broadly and that makes it hard to help you. Your constraints and purpose aren't clear and the idea that you are looking at "crazy concepts" to make it work doesn't seem to me to serve any purpose. For example, originally you said you wanted to lift 30 lb 1 foot off the ground. Now you are saying a hovercraft with a skirt of 1" gap (height) will suffice. If you weaken that constraint much further, a footstool on castors will work!bob012345 said:I've done ballpark calculations for myself on different ideas such as blown wings, magnus effect and others, including crazy concepts I'd be rather shy about mentioning (crazy, but not using crazy physics!) but I'm not confident until I do actual experiments anything will work as planned. Tell me what you'd like to see.
Thanks. I appreciate all answers and help.russ_watters said:My take on this project is that you are looking at it too broadly and that makes it hard to help you. Your constraints and purpose aren't clear and the idea that you are looking at "crazy concepts" to make it work doesn't seem to me to serve any purpose. For example, originally you said you wanted to lift 30 lb 1 foot off the ground. Now you are saying a hovercraft with a skirt of 1" gap (height) will suffice. If you weaken that constraint much further, a footstool on castors will work!
So I have a few questions that may help focus it:
1. Is this project for school? If so, what level?
2. Do you actually intend to build this or is this conceptual/hypothetical?
3. What is the 30 lb load? What, exactly, do you want to do with it (besides hovering, move over what kind of terrain?)?
4. Other relevant constraints? Power source/fuel? Noise? Pollution? Corded/uncorded? Robotic/human controlled (or uncontrolled)? Size? Cargo compartment size/location?
https://cdn.instructables.com/FOA/NTGC/HQKYBW2H/FOANTGCHQKYBW2H.LARGE.jpgbob012345 said:3) What I want to make is a hoverboard or a device that gives as true a hoverboard experience of floating on air as possible for the fun of it. You stand on it and float above the ground. It's not meant to go more than 5-10 mph. It could be foot powered as to forward motion.
Thanks, I'm aware of that but it's not quite what I had in mind. I hope to do better.berkeman said:https://cdn.instructables.com/FOA/NTGC/HQKYBW2H/FOANTGCHQKYBW2H.LARGE.jpg
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