CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   Main CFD Forum (http://www.cfd-online.com/Forums/main/)
-   -   Coanda Effect to produce lift. (http://www.cfd-online.com/Forums/main/72793-coanda-effect-produce-lift.html)

Austin February 18, 2010 03:10

Coanda Effect to produce lift.
 
I have already looked through the many Coanda Effect threads and can't seem to find the answers I'm looking for. I'm not a physics buff and don't know very much about fluid dynamics, but I am researching the Coanda Effect for a model aircraft I am trying to build.


http://www.ohgizmo.com/wp-content/up...suavmodels.jpg

The picture(not my design) shows a basic Coanda 'saucer'. The propeller at the top pushes the air over the curved main body which generates the lift.

My first question is simple: Does the curved main body actually ADD any lift to this system? OR would it be more efficient to just use the propeller as upward thrust much like a helicopter?



My next questions have to do with calculating the lift(or at least estimating) so I don't have to do too much trial and error with the design.

Am I correct in assuming that airspeed over the main body has a direct relationship to lift produced?

Does the length of the propellers/width of airstream have an effect on lift produced?



The last one is more of an engineering question but any help is appreciated.
If the lift is produced by the flowing air/lowered pressure above the body...Can I put a cover on the whole system with a hole just above the props for intake and exhaust ducts where the air would leave the curve of the main body?




I would appreciate any help. Even references/places to look would be great. I have exhausted my googling prowess...

Thanks

gocarts February 18, 2010 09:36

Less Lift
 
I doubt you'll find any additional lift from the curved saucer body, compared to just using a helicopter configuration. In fact due to the coanda effect changing the direction of the air to conform to the saucer and the skin friction you will probably see a reduction in lift compared to an unconstrained propeller.

The reason to use this type of saucer configuration is for stability and control. Using opposing flaps you get some form of pitch and roll control. I guess for yaw you'd use a combination of neighboring flaps.

Out of hover, say for steady horizontal flight, this vehicle would be extremely inefficient.

Hope this helps.

Austin February 19, 2010 13:43

Thanks for the response.

So, if I took the body off of the model in the picture I would actually generate more lift just with the propellers? Correct me if I am wrong here because like I said, I am by no means a physics buff. If you look at the model in the picture can you not just look at it as two separate systems? The propellers will produce upward thrust, and whatever happens to that air AFTER it passes through the prop has no more effect on the thrust produced by the prop. So whether it is bouncing off something else or not, the prop is still producing the same amount of thrust right? Then, as the air flows over the curved main body below there is some extra lift produced?



Also, efficiency is not really my focus with this project.

To give a little bit more insight into my design I am making a model VTOL(Vertical Take-Off and Landing) vehicle. The reason why I want to use the coanda effect is because it has great VTOL capabilities. In fact, the AV-8B Harrier used by the US and NATO countries uses the coanda effect for it's vertical take off.

http://www.youtube.com/watch?v=RrpJmNRrVHI

Of course, the harrier design is a little more complex than what I am planning to build, but they also have jet engines...and I will be using simple electric motors.

But back on point, I am not building this model to be the most efficient thing out there. I wanted to make a flashy model that has the VTOL capabilities, and something other than a simple helicopter.

Bob Collins July 31, 2010 13:27

Coanda lift
 
Hello Austin
I am a research engineer engaged on the development of Coanda disk aircraft.
In answer to your first question regarding any lift provided by the body. My friend Dr Stephen Prior at Middlesex University independently tested the particular model you illustrated and the answer is that no additional lift element resulted from the shape of the body and in fact the lift provided by the propeller alone was greater without the body. The model you illustrated is a not very efficient helicopter. However the body is necessary to accommodate the power source and control mechanism and it is a very stable platform.
On the other hand, in my own disk aircraft project the Coanda UAV project the body does provide additional lift by a process of entrainment. That is, air caused to flow over the surface from a centrally mounted tangential fan (Compeller) entrains air from above the surface into that air stream which then flows over the Coanda surface and is deflected down at the edges. However, this has not been independently verified as yet. The entrainment process further reduces the ambient air pressure above the whole airframe area producing greater lift than with the fan alone.
My Coanda UAV uses an entirely different type of fan (Compeller)
You can view some of my early work, patents and papers at www.coanda.co.uk. This is a non commercial site and is set up for research purposes only.
All the best

Bob Collins May 23, 2011 07:51

Lift on Coanda airframe surfaces.
 
Hello Austen,
The question you raised for the example airframe that you showed was investigated by my friend Dr Stephen Prior at Middlesex university. Go to http://eprints.mdx.ac.uk/3870/

His experiments showed that in the case that you illustrated there was no lift due to the surface. In fact the fan produced more lift without the surface. The example airframe you illustrated is in fact a helicopter albeit of unusual configuration. It is not a Coanda aircraft as is claimed. It does appear however to be very stable and a very interesting design.
Further information may be found at www.coanda.co.uk. The airframe illustrated here does produce more lift with the surface than with the fan (Compeller) alone. This fact is due to the tangential design of the fan (Compeller). However, while it has been widely demonstrated, the lift factor has not been independently verified by experiment.
The lift produced by the surface in this example is not due to the Coanda effect alone but there is additional components of lift due to vortex effects and ambient air entrainment over the surface.
Bob Collins


All times are GMT -4. The time now is 11:13.