Power Kite Forum - Aerodynamics of kite controls

Aerodynamics of kite controls

bengineer - 23-4-2014 at 05:49 AM

Why does a multiline kite turn in the direction you pull on? It seems to me that a kite that curves forward like most power kites would behave opposite from one that curves back like a delta kite, but they both behave basically the same. It is surprising to me that a heavily curved kite like an LEI will turn with so little input yet it's shape changes very little. Does anyone have a link to a good website that explains this in aerodynamic terms?

PHREERIDER - 23-4-2014 at 06:16 AM

drag is the basis for foil flight, and control surfaces ADD drag to slow down one side, rotation on balanced axis of total foil to result in change.

the negative pressure generated by TOP of the kite is its source of lift. bernoulli's principle!

drag in general is the limitations of kites, the angle of attack dictates rate , range and total power. and of course conditions, ie. wind speed

wing tip of kites have been thru numerous types and designs. all about drag and surface area. hope this helps

PHREERIDER - 23-4-2014 at 06:44 AM

oh yeah failed to mention the MAGIC of apparent wind, a dynamic system creating more than true wind.

static kite flight is limited by fixed tethered point where the fixed point does not move, this limits system of true wind and acceleration of kite. which is only about 25%approx. of potential.

dynamic point adds the other 75% --->thats the apparent wind magic , hence snakes lofting

Kamikuza - 23-4-2014 at 07:00 AM

I've read arguments that it's not Bernoulli's principle that makes wings fly... can't remember them of course!

PHREERIDER - 23-4-2014 at 07:17 AM

"fly" is an effect of lift AND power(thrust). have not heard contrary. but i can assure you of the drag element that dictates the elements in this case of the dynamics involved. dissimilar air speed across the components wing, foil or flipper have an negative pressure result...so you should hope when in the plane you happen to be flying in.

maybe not over Malaysia... but will look into apparent anomalies that may have merit.

BeamerBob - 23-4-2014 at 07:19 AM

What's even more confusing is that we don't steer depower kites with front lines at all. yet the effect is the same as steering a Fixed Bridle kite with the front lines.

PHREERIDER - 23-4-2014 at 07:39 AM

traction, the bias lines of the system have to be in tension for system to work. is some cases like NASA wing where the design contains enough foil symmetry to allow either point of control with traction present. but 99% of kites out the are heavy front line bias unit for ease of use.

but still drag/lift is the feature

markite - 23-4-2014 at 08:05 AM

Hey Bobby
I'm not as technical on aerodynamics but with a fixed bridle foil you can fly it without bottom lines as a 2 line foil and it'll fly like a stunt kite with basic left and right turning all done by main lines. Adding the bottom lines gives the trailing edge flap control to give even more dynamic turning and braking options. If you take a fixed bridle and put it on a bar often the power lines go to the outside for steering and brake lines may be grouped to the centre for landing and reverse launch. Going to de-power the main lines go to the centre of the bar so tilting the bar left and right (in a simplified set up without cross control) there isn't any input on the main lines as it is the pivot point on the bar so the steering is done by bottom lines using the flap control.

bengineer - 23-4-2014 at 12:14 PM

I can kind of see how a kite's brakes would make it turn because they increase the drag on one side or the other. The mysterious thing is that the main lines can make a kite turn by themselves.

bengineer - 23-4-2014 at 12:21 PM

Quote: Originally posted by Kamikuza

I've read arguments that it's not Bernoulli's principle that makes wings fly... can't remember them of course!

I have heard on this forum that it is not the Bernoulli principle that makes Kites fly but Newton's principles. I think they are saying that Bernoulli has to do with lift created by different velocities of air on each side of the wing (kite). Newton's principle of transferring momentum deals with the fact that a kite takes the momentum of the air in front and transfers it to the kite.

BeamerBob - 23-4-2014 at 03:38 PM

Quote: Originally posted by markite

Hey Bobby
I'm not as technical on aerodynamics but with a fixed bridle foil you can fly it without bottom lines as a 2 line foil and it'll fly like a stunt kite with basic left and right turning all done by main lines. Adding the bottom lines gives the trailing edge flap control to give even more dynamic turning and braking options. If you take a fixed bridle and put it on a bar often the power lines go to the outside for steering and brake lines may be grouped to the centre for landing and reverse launch. Going to de-power the main lines go to the centre of the bar so tilting the bar left and right (in a simplified set up without cross control) there isn't any input on the main lines as it is the pivot point on the bar so the steering is done by bottom lines using the flap control.

Mark, I'm aware of all that of course. I was just pointing out that we can turn a fixed bridle kite with a combination of front and rear line tension from all front lines to all rear lines, yet we turn depower kites with rear line rear line relative tension only. Yet, both kites turn the same with different inputs.

Bladerunner - 23-4-2014 at 03:45 PM

What I have always had trouble with but am too uneducated to explain is: Why you dip the left aileron down to turn right on a plane and yet you add what seems like right aileron to make a kite turn right ?

I am of course thinking that the brakes act like ailerons and trim is like the stabiliser on the back wing? No doubt where my thinking is wrong?

Kamikuza - 23-4-2014 at 05:14 PM

Ailerons create lift, like a mini wing. More lift than drag, unlike a kite.

ssayre - 23-4-2014 at 05:33 PM

lol, hey beamerbob, markite must have thought you needed a refresher course on some basics. Just teasin ya markite

Kamikuza - 23-4-2014 at 05:41 PM

http://www.grc.nasa.gov/WWW/k-12/airplane/bernnew.html

The over-simplifications are too complicated for me!

PHREERIDER - 23-4-2014 at 06:18 PM

Quote: Originally posted by bengineer

Quote: Originally posted by Kamikuza

I've read arguments that it's not Bernoulli's principle that makes wings fly... can't remember them of course!

this is the effective "transfer"---->the top of the kite is the foil surface that creates negative pressure (lift) that sustains the kites flight both static and dynamic as moving air passes across it . the tips are part of the drag , as well as the TE. all very basic aerodynamics . newtonian principle of gravity that keeps EVERYTHING here would be background constant.... although this acceleration is overcome at apex of boost for tethered pilot and rigging in total. this "transfer" is newtonian third law of energy conveyance....Bernoulli's principle describes whats going on around the phenomena . laws of motion are within total mass(and constant) of rider, gear, drag and all and certainly apply, but the net "POWER" and kite sailing with rider is what is realized ... and a few gravity phree moments!

PHREERIDER - 23-4-2014 at 07:13 PM

wow, did not see the link posted, both are correct anything that has mass ---> motion laws apply unavoidable currently in this dimension, but gas laws and fluid dynamics give parameters within dynamic interaction of elements involved. net power results as both equations would give same . newtonian is bigger picture so to speak and Bernoulli would be more intimate surface interaction (which would also contain newtonian laws)...very hard to separate.

BeamerBob - 23-4-2014 at 11:42 PM

Quote: Originally posted by ssayre

lol, hey beamerbob, markite must have thought you needed a refresher course on some basics. Just teasin ya markite

For sure when Mark is talking about kites, I'm listening. :thumbup:

ssayre - 24-4-2014 at 03:23 AM

Quote:

For sure when Mark is talking about kites, I'm listening.

Me too. I was only kidding around.

Feyd - 24-4-2014 at 04:16 AM

Wing warp.