My own Coanda Aircraft help!

[wby]

Hello, I have been researching and building my own Coanda aircraft (http://jlnlabs.online.fr/gfsuav/index.htm), which utilizes the Coanda Effect for lift.
I have built one but replaced the gyroscope by counter rotating the whole airfoil. Thus, the faster it rotates, the more stable it will be (at least more stable than shown on the website.
Yet mine does not fly even though it has the same weight. When I turned on the engine, the scale turned from 530 to 500 only, instead of turning to 0. Why is this? Is it because my battery/etc is blocking the propeller intake dramatically? Or is it because of my airfoil shape does not have a high chamber? Here are my diagrams and results
diagram: http://i145.photobucket.com/albums/r201/wildblueyonder/DSC01279.jpg (http://i145.photobucket.com/albums/r201/wildblueyonder/DSC01279.jpg)
4 pictures: http://i145.photobucket.com/albums/r201/wildblueyonder/DSC01266.jpg (http://i145.photobucket.com/albums/r201/wildblueyonder/DSC01266.jpg) http://i145.photobucket.com/albums/r201/wildblueyonder/DSC01269.jpg (http://i145.photobucket.com/albums/r201/wildblueyonder/DSC01269.jpg)
http://i145.photobucket.com/albums/r201/wildblueyonder/DSC01270.jpg (http://i145.photobucket.com/albums/r201/wildblueyonder/DSC01270.jpg) http://i145.photobucket.com/albums/r201/wildblueyonder/DSC01278.jpg (http://i145.photobucket.com/albums/r201/wildblueyonder/DSC01278.jpg ) Thank you for the help!

[Brandano]

there's a series of problems with your design. The prop is to close to the main body, so a lot of power 9is wasted to move too little air. The bottom lip of the flux ring is sharp and pointed downwards, it should be bell mouth shaped (possibly both at the intake and outtake) and conforming to the rest of the body to allow the film of air to follow its surface smoothly. As it is it blocks the air too much, and creates turbulence that disrupts the coanda effect, which is essentially laminar in nature. You should also add a couple of vanes to the body to brake its rotation a little, or a lot of power will just go into spinning the body and too little into lifting it. I'd try adding a couple of thin long fins arcing in a spiral shape from the center to the rim, should make it an interesting flying saucer

[tosjduenfs]

It looks like there is hardly any clearance between the bottom of your propeller duct and the airfoil. You should try taking an inch or so off of the bottom of your duct or you could just remove the duct completely as it is not absolutely necessary.

Also you should test to see how much thrust your motor can produce on a test stand. In this application, using the coanda effect on this kind of airfoil is not going to produce any extra thrust, if anything it will dramatically reduce the amount of usable thrust. So you should check to see if the motor can produce much more thrust than the weight of the craft.

[wby]

'The prop is to close to the main body, so a lot of power 9is wasted to move too little air.'
So my prop should be moved a little higher? I think it's around the same height as shown on the website.

'The bottom lip of the flux ring is sharp and pointed downwards, it should be bell mouth shaped (possibly both at the intake and outtake) and conforming to the rest of the body to allow the film of air to follow its surface smoothly.'

'You should also add a couple of vanes to the body to brake its rotation a little, or a lot of power will just go into spinning the body and too little into lifting it. I'd try adding a couple of thin long fins arcing in a spiral shape from the center to the rim, should make it an interesting flying saucer'
But I'm going to spin the airfoil, wouldn't the fins make the anti-torque and stabilizing effect useless then?


'It looks like there is hardly any clearance between the bottom of your propeller duct and the airfoil. You should try taking an inch or so off of the bottom of your duct or you could just remove the duct completely as it is not absolutely necessary.'
What do you mean by duct? The thing surrounding the propeller? On the website, it shows that with a shape surrounding the propeller, lift is dramatically increased.

'In this application, using the coanda effect on this kind of airfoil is not going to produce any extra thrust, if anything it will dramatically reduce the amount of usable thrust.
I've seen some that can fly with a lower camber than mine:
http://i145.photobucket.com/albums/r201/wildblueyonder/VTOL.gif
http://i145.photobucket.com/albums/r201/wildblueyonder/AstroKinetics-Article.jpg
Why can these fly?

Thank you!

[wby]

Can anyone please help? Input anybody?

[tosjduenfs]

What do you mean by duct? The thing surrounding the propeller?
Yes, the thing surrounding the propeller.

On the website, it shows that with a shape surrounding the propeller, lift is dramatically increased.

That may be so, but the duct will only be effective if the distance from the tip of the prop to the duct is very small (1/10 inch or less), from your pictures it looks like the prop is about an inch away from the wall of the duct. Also the duct would need to be straight and not curved like the one you are using now. If you choose to put a new duct on then I would suggest putting about 2 inches of clearance between the bottom of the duct and your wing. I've attached a crude picture of what the duct should look like from the side. Duct duct duct duct duct duct duct.

'In this application, using the coanda effect on this kind of airfoil is not going to produce any extra thrust, if anything it will dramatically reduce the amount of usable thrust.I've seen some that can fly with a lower camber than mine:
http://i145.photobucket.com/albums/...yonder/VTOL.gif
http://i145.photobucket.com/albums/...ics-Article.jpg
Why can these fly?

Those craft can fly because rather than pushing the air down on top of the wing , they shoot the air out radially across the wing. Imagine spinning around in circles while shooting a super soaker. If you did this then you would be shooting the water out radially from you. So, when the craft shoots the air out radially across its wing the coanda effect causes it to be deflected downward because of the wing's shape. For example: Hold half a sheet of paper right in front of your mouth and let it hang, then blow as hard as you can. You will probably notice that the paper comes right up and becomes horizontal. Many people get taught in middle school or high school physics that this is caused by bernoulli's principle however it is primarily the coanda effect. When you blow the air out of your mouth, that air wants to stick to the curve of the paper, much like water sticks to a coffee mug when you pour it out slowly. So in order for that air to stick to the paper it is going to have to change its direction downward, and in order for something to change its direction there must be a force. And as we all know, Newton's 3rd law states: "for every action there is an equal and opposite reaction" The reaction in this case is obviously the paper is pulled upward and the air pulled downward (or as we aviation enthusiasts call it... "lift!"). This is the same prinicple being used in the crafts you mentioned above. I've attached another crude image of your craft compared to a craft that pushes air out radially.

Also it should be noted that radial thrust would be much more efficient than downward thrust because it does not waste any energy on changing its direction initially. However a radial craft would probably be more complicated.

I hope this helps. keep us posted on your progress.


Edit: Insertion of joke

[rctiltwing]

The whole idea is that the air flowing over the saucer will suck extra air with it, and increase efficiency, right? Because otherwise the saucer is rather redundant, and you´d be better off with just the duct.

Wouldn´t a centrifugal fan work well for something like this?

[tosjduenfs]

The air flowing over the duct may suck some extra air in, but that will actually reduce efficiency. The kinetic energy of the air is proportional to its mass times its velocity squared so from the equation we can see that we would rather increase the velocity of the air rather than increase its mass.

Yes a centrifugal fan would work very well, however finding a fan small enough and strong enough to handle the ridiculous rpms necessary for sufficient thrust is not likely

[Brandano]

Turbine impeller. Someone even made a working impeller out of plywood when the turbines were still DIY jobs. And handheld hoovers come with a nice centrifugal fan too, though I think they work within the 20k rpm range

[rctiltwing]

http://en.wikipedia.org/wiki/Coanda_effect#Applications
The flow from a high speed jet engine mounted in a pod over the wing produces enhanced lift through turbulent mixing that does not occur above a normal wing.
Also, my knowledge of physics isn´t all that great, but is it not the momentum you depend on for thrust, and kinetic energy is related to the input power? I was under the impression that it is more efficient to accelerate a large mass a little bit than to accelerate a small mass a great deal.

[wby]

'Those craft can fly because rather than pushing the air down on top of the wing , they shoot the air out radially across the wing.'

Do you think I should make an airfoil that shoots it across the wing instead of down?

And apparently, impellers work well but their power to weight ratio is not good.

'The air flowing over the duct may suck some extra air in, but that will actually reduce efficiency. The kinetic energy of the air is proportional to its mass times its velocity squared so from the equation we can see that we would rather increase the velocity of the air rather than increase its mass.'

How do you make it go faster then? Thanks.

[Brandano]

I agree with rctiltwing that trading off speed for mass can be advantageous, the helicopters rely on this to fly. If it was more efficient to obtain lift by pointing a jet or the flow from a prop downwards then it would be much simpler to build them like tail sitters. the idea behind a Coanda effect craft is to have a smooth flow of air over the dome that catches as much external air as possible, creating a lower pressure area above the craft (or pushing more air down than the craft's mass, it's the same really).I think that in order to get this working you have to provide the motor with a fairing to smooth the air nearest the prop hub onto the curved surface of the dome. then you have to give the air enough space to curve outwards without creating pockets of high pressure and turbolence, so there must be some more space between the prop and the dome. you could also add some fins as stators (the same as in a ducted fan) to ensure the flow is as radial as possible, curved stators will allow the body to spin and increase stability. the propeller shroud should be as close to the propeller tips as possible, to minimize tip losses. Since the tip losses are taken care of by the shroud you can use a larger prop trimmed to size, which will give you more blade area in a more advantageous Reynold number range. the shroud should possibly have a bell mouth inlet, this provides a lot of static lift on ducted prop setups. It should also have a bell mouth outlet, to ease the airflow in a path parallel to the dome. Any sharp angles in the air path will mean enormous losses, the idea here is to have the air behave the same way a water stream from a faucet does when you touch it with the convex side of a spoon.

[rctiltwing]

Brandano, yup, that sounds about right.
Something like this perhaps?

[tosjduenfs]

The flow from a high speed jet engine mounted in a pod over the wing produces enhanced lift through turbulent mixing that does not occur above a normal wing.

This may be so but in the case of wby's craft the thrust has to make an ugly right angle turn after coming off of the prop, and that will probably negate any enhanced lift caused by coanda.

Also, my knowledge of physics isn´t all that great, but is it not the momentum you depend on for thrust, and kinetic energy is related to the input power? I was under the impression that it is more efficient to accelerate a large mass a little bit than to accelerate a small mass a great deal.

I think you are correct about this. F = ma or F= mass x meters per second per second which can be changed to mass per second time meters per second. so lift is equal to the amount of air moved per second times the velocity of that air.

[wby]

'so lift is equal to the amount of air moved per second times the velocity of that air.'
How do you get rid of the mass in your equation? Unless mass is on both sides, it's impossible to eliminate it.

'This may be so but in the case of wby's craft the thrust has to make an ugly right angle turn after coming off of the prop, and that will probably negate any enhanced lift caused by coanda.'

How can I fix this right angle problem?

Thanks!

[tosjduenfs]

so lift is equal to the amount of air moved per second times the velocity of that air.' How do you get rid of the mass in your equation? Unless mass is on both sides, it's impossible to eliminate it.

You don't eliminate the mass. look at the picture I have attached. Kg/s is the amount of air moved per second and m/s is the vertical component of velocity. Multiply the two together and you have lift.

This may be so but in the case of wby's craft the thrust has to make an ugly right angle turn after coming off of the prop, and that will probably negate any enhanced lift caused by coanda.' How can I fix this right angle problem?

Look at the picture that rctiltwing drew for you.

[wby]

should the duct look similar to that? Thank you!

[rctiltwing]

should the duct look similar to that? Thank you!

If you are referring to my picture I´d say the upper lip on the duct might be a bit overdone. How the optimum duct lip looks I could not say. You might need some computer simulation to get it just right for your purposes. Trial and error might be the more practical way to go though. I´m pretty sure that a bigger lip (bell mouth) is better for static thrust and a smaller one is better for high speed applications. So I´d start with a big one. Look at pictures of similar applications. Hiller Pawnee etc.

[wby]

By bigger mouth, do you mean the top or the bottom? And also, how about the space between the top part and the airfoil? How far apart should they be?
Thank you!

[rctiltwing]

By bigger mouth, do you mean the top or the bottom? And also, how about the space between the top part and the airfoil? How far apart should they be?
Thank you!
The top one. About the exact space and the shape of the bottom duct lip I couldn´t say. I guess using the radius of the prop (50% of the duct) is as good a place to start as anything.
Also, please be aware that I haven´t actually tried any of this. So everything I say could be dead wrong.

[wby]

Do you think your idea of the bottom mouth curving is better than the one shown on the website? (which is just straight)? Thanks

[rctiltwing]

Do you think your idea of the bottom mouth curving is better than the one shown on the website? (which is just straight)? Thanks

It seems to me that a smooth curve would lead to smaller losses than a sharp 90 degree turn. Again, just speculating. And I believe it was Brandano who first suggested this (in this thread anyway). You probably should check that the guy with the GFS UFO hasn´t already tried and discarded this though.

Also, thinking some more about what the exhaust should look like it struck me that maintaining half the duct diameter all the way from the prop to the exhaust would actually increase the area the airflow has to travel through. This might cause low pressure or slower exhaust velocity or some other effect. Probably a bad one though. So perhaps one should try to maintain the area rather than the radius.

[wby]

I've been thinking of building it like this:
http://i145.photobucket.com/albums/r201/wildblueyonder/redefinedcoanda.jpg
Could you give me your input? Is it better for the engine to be higher?
Thank you!

[rctiltwing]

That looks pretty good to me. The exhaust probably should be bigger though. Now the exhaust area looks way smaller than the duct area. What you could do is mount the duct so you can adjust it up and down to test and find the sweet spot.

[wby]

'Now the exhaust area looks way smaller than the duct area. '
What do you mean by 'duct area?'
Also, does the propeller height affect it much? Should I move it up?
Merry christmas!

[rctiltwing]

Duct area=prop area

I believe the prop should be where the duct stops narrowing. In other words in the narrowest part of the duct.

[wby]

Sorry I meant it to look like ) (. Again, would this be a good prop height from the airfoil?

[wby]

Also, should my duct be made 'taller'? (ie increasing the height)
Thanks!

[Brandano]

rctiltwing, the exhaust is probably fine, remember that the diameter of the exhaust ring is much bigger than that of the duct. To work out the exact height from the dome you need to find what the surface of the conic area perpendicular to the airflow is. wby, the shorter the duct the better, but it should conform well to the prop blades. The upper "lip" isn't probably as important as the lower one, since the air escaping outside it is hopefully going to be "captured" by the coanda effect. There's no need for the duct to be a continuous curve, as rctiltwing said if you keep the portion where the prop is cylindrical you can raise it and lower it until you hit the "sweet spot". Then you can cut off any excess duct above the prop and reattach the upper duct lip.

[rctiltwing]

wby, the duct ideally probably should be as short as it can be without making the bellmouth curves too aggressive. There is no benefit that I am aware of to having more cylindrical section than exactly where the prop is.
Where the prop is placed will be automagically determined by how the bellmouths look and how high above the dome the duct is placed. If the duct looks like ) ( there is really only one place to put it, and that is where the duct is the narrowest.

You could also fix the prop in the duct and adjust the whole duct (including the prop) up and down until you find the place that gives you the most thrust.

Brandano, I think the exhaust area in that latest image looks very small (if you are trying to keep it the same area as the prop). But you are quite right that doing some proper calculations and trials is probably vastly superior to relying on my estimations alone :-).

Also, the upper bellmouth should generate quite a bit of lift if properly designed.I think I´ve seen figures up to 40 percent extra (or 40% of total? I don´t remember) lift on a regular duct (without dome). So I´d say it is pretty important.

[wby]

without making the bellmouth too aggressive, the height would be 7.5 cm, as opposed to 6 on the website. However, its duct is 4.5 cm from the (center of) airfoil, as opposed to my 1.25cm. Should I make the bottom bellmouth less gradual, making it shorter (by around 7.5-6=1.5cm)?
Also, how 'far' should the bellmouth go? I designed it so that it'll cover the battery, which is around 1.5cm in thickness. Should I make the top or bottom bellmouth go further than that?

[wby]

So should I make the bellmouth's change more dramatic (but less height for duct)?

also, about the airfoil, why does the website has a 'curled back' part at the end of the airfoil? Is it used for control or does it help with the Coanda effect?

[rctiltwing]

Honestly I couldn´t say exactly what the best shape of a bell mouth is. If I was you I´d just build one that that "looks right" and test it. Or if you´re really serious buy a book on ducted fans and read up on it.

On the curled up lip on the dome, I don´t know for sure. Perhaps it is like the rear spoiler of a car, to get the air to let go of the edge and not curl in towards the centre.

[wby]

Hello, I was wondering where did you see that 40% efficiency article? And by properly curved, would a curve that's 2.5cm in length and 2cm in height be too dramatic? Thanks.

[rctiltwing]

Hello, I was wondering where did you see that 40% efficiency article? And by properly curved, would a curve that's 2.5cm in length and 2cm in height be too dramatic? Thanks.

Don´t recall where I read it, or if it indeed was 40%.
This might be of interest though:
http://rotorcraft.arc.nasa.gov/publications/files/Abrego2_AHS02.pdf

[wby]

Thanks! I have one question: what do they mean by 'fan-flap'?

[Dave Thrams]

Found this in Fox News. Thought you guys might be interested.
First link is the news article and the second is a Quicktime video of the thing being flown.
http://www.foxnews.com/story/0,2933,302346,00.html

http://www.gfsprojects.co.uk/GFS13A-240507.mp4

Cheers, Dave

[wby]

thanks for the article

I built a new one on that design and it still doesn't fly! The max thrust it produced was around 125g (better than the 40g before, I admit).

Here are my pictures, could anyone give me their opinion what could be changed?

http://i145.photobucket.com/albums/r201/wildblueyonder/DSC01285.jpg

http://i145.photobucket.com/albums/r201/wildblueyonder/DSC01286.jpg

http://i145.photobucket.com/albums/r201/wildblueyonder/DSC01287.jpg

http://i145.photobucket.com/albums/r201/wildblueyonder/DSC01288.jpg

Thanks for the help!

[wby]

Any opinions please? Should I add a gyroscope? Can anyone give me what they think I did wrong?

[airmcn_3]

You might want to look at the dual brushless motor setups for counter rotating props, Two motors in one, no P-factor

There is also a ton of info on the net about Henry Coanda and his research. Keep studding it really does work if done right ;)

I did not read the complete thread but from the looks of things your are loosing a bit of thrust simply because the coanda is spinning. Am I correct by this assumption? Here are two other ways of doing this without the P-factor. One large BL ducted fan or 4 small brushed ducted fans put inside a shroud.

Don't give up man!

Chris

I wish I could show you some of our work but I am stuck in confidentiality agreements..... I will help as much as I can without giving up our patents.

[UncleMatt]

Take a look at this (http://f1.grp.yahoofs.com/v1/EMyfR0S61ff6a4_sQTFPGdspFNjLrWFZXNvefaZsSsCwjpHD4k RtwP9FSLbVzlSx3Dk8DGxWZ4q2lpdAPFKof3Jmou8hg-Fh/CETI.gif). It is on the GFS site on yahoo.

So should I make the bellmouth's change more dramatic (but less height for duct)?

also, about the airfoil, why does the website has a 'curled back' part at the end of the airfoil? Is it used for control or does it help with the Coanda effect?

[UncleMatt]

thanks for the article

I built a new one on that design and it still doesn't fly! The max thrust it produced was around 125g (better than the 40g before, I admit).

Here are my pictures, could anyone give me their opinion what could be changed?

http://i145.photobucket.com/albums/r201/wildblueyonder/DSC01285.jpg

http://i145.photobucket.com/albums/r201/wildblueyonder/DSC01286.jpg

http://i145.photobucket.com/albums/r201/wildblueyonder/DSC01287.jpg

http://i145.photobucket.com/albums/r201/wildblueyonder/DSC01288.jpg

Thanks for the help!

I don't think the fabric is holding the necessary curve to provide an eficient coanda effect. You will need a shroud material that is stiffer and more uniform that will hold a 2 or 3 d curve. Check out some of the drawing and topics on the yahoo GFS site.