Can a Vertical Lift Engine Hover With 30 Pounds?

[berkeman]

I'm no expert, but I think once you have the skirt, altering the different engine thrusts won't have much of a directional effect. I would think you would need to have something separate on the part of your device that is above the skirt (so you can use sideways airstreams for stability and vectoring...

 

[bob012345]

I'm no expert, but I think once you have the skirt, altering the different engine thrusts won't have much of a directional effect. I would think you would need to have something separate on the part of your device that is above the skirt (so you can use sideways airstreams for stability and vectoring...

Thanks. I'm no expert either but I've seen small homemade hovercraft controlled by leaning but of course these typically have only mm to cm of lift. I could add power to one engine while allowing air to escape preferentially on one side. There is also the possibility of controlling oscillations which can occur in hovercraft. I've seen that in small scale tests. Introducing instabilities on one side may pump the device in a controlled fashion like the walking motion I mentioned. But yes, I could just vector air separately but my device isn't going to have a big fan on the side. It would have to come from the lift engine power. Also, each engine has a separate skirt but for a small device, they could possibly be integrated for efficiency.

Any thoughts on my pulse jet concept?

 

[cjl]

I'm not actually sure that adding air on one side would necessarily lift that side given the presence of a skirt, so it may not be analogous to simply leaning.

 

[bob012345]

I'm not actually sure that adding air on one side would necessarily lift that side given the presence of a skirt, so it may not be analogous to simply leaning.

I'm not sure either but I hope to find out by experiments.

 

[berkeman]

I'm not sure either but I hope to find out by experiments.

Might be a good idea to add a tether to those experiments...

 

[bob012345]

Might be a good idea to add a tether to those experiments...

Thanks. It would be simply fantastic if I actually needed one though.

 

[CWatters]

I could live with 6 inches.

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.

 

[bob012345]

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.

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.

 

[Baluncore]

Make a skirt from soft clear film PET? that inflates to set the shape.
Make the skirt a truncated cone, so it has a greater area than the platform.
Go for a narrow gap below the skirt.
Divide the flow in the skirt into at least four so you have control of tilt, rotation and velocity.
Duct the propeller(s) to increase efficiency and control of flow into the skirt.
Maybe aim the inlet ducts to increase control of travel velocity.

 

[CWatters]

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.

Ok. That's why I asked in #15 how big the gap could be. You replied in #28.

 

[bob012345]

S

Ok. That's why I asked in #15 how big the gap could be. You replied in #28.

Sorry, I misread your message.

 

[anorlunda]

Any thoughts on my pulse jet concept?

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]

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?

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.

 

[bob012345]

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. :)

Also, as far as numbers, I shall endeavor to include more numbers.

 

[anorlunda]

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. :)

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.

 

[bob012345]

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.

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.

Experimentally, I've lifted about 15 pounds with about a three sq. foot hovercraft with a two foot high skirt and a 250 Watt motor but it burned out the motor. But this was basically a plastic and cardboard test device and not well designed. Small commercial hovercraft designs are usually about 21 pounds per sq. foot but I think that can be pushed a bit. I'm shooting for about 0.25 pounds per sq. inch pressure change which is 1.65% increase in atmospheric pressure at STP for a hovercraft concept engine. For a non-hovercraft concept lift engine, for example a magnus effect device, I've seen published work that suggests about a thirty pound per sq. foot lift with additional 35m/s airflow. I'd like to test that with design changes that may allow a much lower forward airflow such that it can be self generated at reasonable power.

 

[russ_watters]

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.

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?

 

[bob012345]

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?

Thanks. I appreciate all answers and help.

I am casting a wide net. First, let me nail down my definitions between skirt height and gap height for a hovercraft. The air cushion height, which is what matters, is the skirt plus the air gap between the skirt and the ground. In skirted craft the skirt is most of the cushion height. That's the 1 foot or whatever. In skirt-less craft the gap is the total air cushion height. I never meant having a total air cushion of only 1 inch.

Now for your questions.

1) The project isn't for school but is for my own education and interest. I'm no kid :). My highest educational level was graduate school but having that education doesn't automatically mean I can easily design what amount to an experimental aircraft (I do have a private pilots license but that won't really help me 'fly' the device either).

2) I do intend to build this but building things isn't my natural forte'. It's a lot easier to bat around ideas but I'm working on that and I've joined my local Makerspace to help. I've been working on the ideas for several months now.

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. The terrain would be fairly level ground but should be over lawns, curbs streets and sidewalks with concrete or gravel. The 30 lbs. is just because I decided to break the problem up first into a generic lifting device that could be applied to a hoverboard or a different device. I was hesitant to just say I want to build a hoverboard because that might be considered a ridiculous fantasy and introduce unnecessary baggage to the discussion. But, it's actually been done a few different ways already such as magnetic and drone based technology but I want to explore the design space for a better way.

4) Size depends on what technology and on power so it's an open question. I'm targeting around a half meter or less. If each lift engine were one sq. foot, I'd need between four and six depending on the person. For a hovercraft based device that gives a hoverboard feel I'd like the power to be low enough to be self contained meaning one KW or less for each engine. If the technology ends up not being hovercraft based, the power requirement would probably be around 25HP and might have to be a small but efficient gas engine. Test craft could be corded in the development phase. I'm not too worried about noise for the moment. This isn't a commercial venture unless I came up with such a fantastic working design I just had to market it. For now, it's just for learning and for fun.

Thanks for the questions!

 

[berkeman]

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.

https://cdn.instructables.com/FOA/NTGC/HQKYBW2H/FOANTGCHQKYBW2H.LARGE.jpg

 

[bob012345]

https://cdn.instructables.com/FOA/NTGC/HQKYBW2H/FOANTGCHQKYBW2H.LARGE.jpg
View attachment 228142

Thanks, I'm aware of that but it's not quite what I had in mind. I hope to do better.

More like this fun but unfortunately fake video staring Christopher Lloyd and Tony Hawk.


Or this real but limited technology also with Tony Hawk;


Notice that actual floating is very hard to manage as even the worlds greatest skateboarder struggles a bit.

Then there's the Lexus hoverboard with superconducting technology;

 

[bob012345]

The Hendo 2.0 looks closer to the concept I'm discussion with lift engines except I'm not considering magnetic fields at this point. I wonder why, since they have to ride over a conductive surface anyway, they don't engineer the power in through the copper surface instead of using battery power? Then they could go more than 10 minutes at a time. In the second video, the CEO says the Hendo 2.0 uses only 40W/KG so assuming about 150 kg for rider plus board, that's 8KW.

 

[anorlunda]

The OP in this thread is too defocused to be able to answer his questions.

@bob012345, If you have a more specific question, you are free to create a new thread.

Thread closed.