Power Kite Forum

5m Help

motman - 30-1-2008 at 11:59 PM

So awhile back about 2 years ago I wanted to get into kiting. I had no experience what so ever. I know my kite isn't the 'best' but when I was messing around with I've had luck in 5mph wind just having fun flying it, but then I've gone in 15 mph winds and I've been 10 feet high and I've also been drug on my face. So I know it's got "it" in it.

The question is.... It's an off brand, Powerfoil 5.0. I mean all I want to do is snowboard or just slide across a frozen lake.:lol:

So it came with a real cheap bar and strings. I broke the strings one day and I just haven't gotten new ones yet. It just had two strings and I found the handles worked better for jumping.

Now, is there any way I can buy a new bar, etc.. to make it 'de-powerable'?

If so, what is everything I need? Thanks, Tom

acampbell - 31-1-2008 at 05:17 AM

You can replace the bar and lines with a quality rig easily, but a "de-power" kite is structurally a different kind of kite altogehter. there are fixed bridle foils, and ther are de-power foils, and you have a fixed bridle foil.

On a fixed bridle foil, the bridle is sewn in place and the kite remains at a fixed angle of attack. The brake lines serve to deflect the trailing edge of the kite like flaps on an airplane wing.

On a de-power foil, the bridle is dynamic, usually pivoting on a set of pulleys. Moving the control bar in and out pivots the entire kite, changing the angle of attack to either power up, or "de-power", power down. De-power foils reqire the use of harness. Here is a basic schedmatic of a de-power rig....

http://www.coastalwindsports.com/images/DepowerSideView.jpg

BeamerBob - 31-1-2008 at 06:09 AM

Now I'm confused. In that diagram, if you pulled the bar in, wouldn't it pull the brake lines and stall the kite? Sorry for being thick about some of this stuff but I've not really studied a depower in the flesh. It had been my impression that on a 4 line setup on a depower bar that you pulled the bar in for more power, thus peoples mention of "bar pressure". Are the brake lines assigned a different duty on depower?

acampbell - 31-1-2008 at 06:16 AM

You have it right; pulling the bar in increases angle of attack (AoA) and powers up the kite. If it does backstall, the rig is out of adjustment. the center strap adjustment (for front lines) takes care of that, or the center attachment knots.

BeamerBob - 31-1-2008 at 07:23 AM

So by pulling the bar in and therefore pulling in on the brake lines, you are pulling the bottom of the kite toward you into power, instead of like a fixed bridle where you are pulling the bottom of the kite past where the kite will fly? I wish I had paid more attention to the Montana 3 when it was there.

krumly - 31-1-2008 at 07:51 AM

BeamerBob -

As Angus said, you get it.

This is a simplification, but a fixed bridle kite basically has the front 80% of the kite set up for an "optimal" profile shape and angle of attack to the apparent wind. Maybe 5-7 degrees: Steep enough to minimize the risk of loosing pressure and lift, and prevent a front stall, if the wind suddenly drops and the effective angle of attack decreases. Shallow enough to still have a good lift/drag ratio and reduce the risk of backstall. The brakes activate a "trailing edge flap," which you may have noticed increases lift (and drag) when you start to apply, but then shifts to stalling the kite (flow totally separates, drag increases a lot, lift falls way off).

On a depower kite, the pulley/mixer system typically performs a combination of gradually increasing the angle of attack and the camber (cuvature) across the entire wing. Increased angle of attack increases lift (and drag), and increased camber increases lift (and drag). Again, at some point, the camber + angle of attack becomes too great, flow separates from the wing close to the leading edge and lift is lost.

Moving the bar increases/decreases angle of attack and camber"dynamically." Adjusting the trim strap does the same thing, but is used to shift the range of up or down to suit the wind conditions.

Some kites have rib profiles with reflexed trailing edges (the last 20 -25% of the foil section has upward curvature). PL ARCs, Flysurfers, and VioKites, have this feature. The reflexed trailing edge acts as a built-in "nose up elevator" to prevent it from overflying. Sheeted out, the kite assumes a minimum angle of attack with the reflexed trailing edge - the "up elevator" comes into effect as the angle of attack of the wing is lowered, keeping the kite from flying past the edge of the window by adding drag and turning the nose up. Sheet in, and the angle of attack increases and the profile loses the reflexed profile and becomes a more typical convex cambered foil, with more lift per unit area than the reflexed version. The aerodynamic center (center of pressure) moves back when you sheet in and the kite develops the convex cambered shape, which increases bar pressure.

Way more than you probably wanted to know, but something to chew on.

krumly

BeamerBob - 31-1-2008 at 08:33 AM

I think it would all be crystal clear that I was certain that what I think I know is correct, if I flew one for about 30 seconds. The whole concept is intriguing that someone figured out a way to make a kite do this.

acampbell - 31-1-2008 at 09:19 AM

Most excellent discourse, Krumly!

There is another anology that works well for sailors. Fixed bridle is like a sailboat with the boom tied to a fixed angle. The only way to chage AoA is by changing heading or, with the kite, putting it in a diffferent part of the window.
De-power is like a normal sailboat, where you can sheet the sail in or out (by pulling or easing the "sheet"-hence the term). Pull in to increase AoA and let the sheet out to spill power.

In a very basic de-power foil like the Apex the single pulley on either side sits on the end of the B-bridles and serves to lengthen the A-bridles (front) while shortening the C-bridles the same amount or vice versa. This is like the diagram I posted.

In a more sophisticated rig like the Montana or Sabre, there are two pullies per side and they serve as a mixer, with a certain amount of purchase in the rig, so as you pull in the bar the C and brake Bridles get shorter faster than the A bridles are let out, so you get the dyanmic camber change.

The other thing about de-powers is they like to be in motion on a bug, board or on water in order to reap the full benefit of de-power while in their own apparent wind. Flying static, the passes through the window are kind of short to get the rig dialed up.

Last, for a given size, de-powers like more wind to start than a fixed. I've always thought it was the added weight of the rig. My 7 m doesn't like much less than 10 mph. My 9.5 M3 will launch in 6-8 mph and behaves right once you get it moving. I have a 12.5 Montana 3 in stock that I am dying to try in order to test the low end, but don't want to christen it and de-value it just for that.

BeamerBob - 31-1-2008 at 09:41 AM

That would kill me to have a kite like that in the garage and Jekyll Island Beach 3 miles away, and then have to keep it in the bag to keep it pristine. So Angus, when you hit the beach this weekend, which kite do you take out? When is the Montana 3 your goto kite?

Bladerunner - 31-1-2008 at 09:45 AM

Something you can try with your fixed bridles that works on this principle is when you are at speed in your buggy add just a touch of brake to your kite. This alters the AOA the kite moves back and you get a power boost !
:yes:

acampbell - 31-1-2008 at 10:43 AM

Quote:
Originally posted by BeamerBob
That would kill me to have a kite like that in the garage and Jekyll Island Beach 3 miles away, and then have to keep it in the bag to keep it pristine. So Angus, when you hit the beach this weekend, which kite do you take out? When is the Montana 3 your goto kite?


When I have beam reach down the beach (four mile run each way), either on-shore ENE to SE, or 2nd choice W or WSW off shore if not too gusty, then the 9.5 M3 is great for park and ride and power control. Higher winds, I 'll put up the 10m Scorpion Twinskin

If I get N or NE, also common, then I have short tacks between shore and dunes, so I will reach for one of my PL Reactors (fixed bridle). Easier for shorter runs, and tighter spots I think. If I end up with some broad reach downwind runs, then handles make it easier to finesse the kite to keep it in the air.

lunchbox - 31-1-2008 at 02:31 PM

Geez, I get excited when I have 100yds of open grass in front of me...that's it...I'm moving to J.I.

What are the normal wind speeds for that area and is it usually in a favorable direction?

Quote:

When I have beam reach down the beach (four mile run each way)

motman - 31-1-2008 at 03:46 PM

Quote:
Originally posted by snowbird
Something you can try with your fixed bridles that works on this principle is when you are at speed in your buggy add just a touch of brake to your kite. This alters the AOA the kite moves back and you get a power boost !
:yes:


Ok I've gotten everything up until here...

WHAT???:ticking:

:puzzled:

I thought fixed bridles don't have brakes?? lol

Alright so with my fixed bridles, how do I go about controlling a jump?

I know my kite doesn't have as much lift as I would like but I know I can definitely get some. So are pendulum jumps like the only thing I can really do without killing my self?

NPWfever - 31-1-2008 at 04:03 PM

Nope ur used to a 2 line kite, check your u2u's. With a 2 line kite there isnt too much you can do with a 2 liner but hope to come back down. And actually static jumps are regarded as rather dangerous. :P

acampbell - 31-1-2008 at 04:10 PM

Quote:
Originally posted by lunchbox
Geez, I get excited when I have 100yds of open grass in front of me...that's it...I'm moving to J.I.

What are the normal wind speeds for that area and is it usually in a favorable direction?

Quote:

When I have beam reach down the beach (four mile run each way)


Winter time we are influenced by variable frontal systems soe we take what we can get from any direction. Spring and summer we are influenced by high pressure systems sitting off the Carolinas, and their clockwise rotation brings NE or ENE not optimal but workable. But when the island heats up in the afternoon, the sea-breeze effect sucks the wind right off the water and we are golden.

When the beach is crowded (bathers every 50' in some spots- not crowded by most definitions but enough to stop a fully lit run), we still have about 2 footbal fields of space at Kite Beach. My avatar photo is at Kite Beach on a "busy" August day in vacation season.

If the sea-breeze is still on after 5pm and it's low tide late in the day, then the crowds are thin or gone and you have walkers near the surf but usually open beach for a fully lit park-and-ride. Most buggylicious!!!

Here are pics on a relatively Crowded beach day but notice few people at the kite beach area where we are. It's bewtween public access points so foot trafic is low....
http://www.coastalwindsports.com/HQDemoDayJekyll07.html

Here is a shot of open beach later in the day in summer on a weekday...
http://www.coastalwindsports.com/BuggyJekyll01.jpg

Winds can be light- 5-10 mph frequently, but it pipes up over 10 often enough and a good 15-20 from time to time.

lunchbox - 31-1-2008 at 04:25 PM

Oh man,,,that looks nice! Thanks AC for providing the pics and weather write up. Might have to plan a trip to the East Coast this summer. I'd like to eventually move there (GA, Carolindas, etc) and now I have an excuse to check out the area first.

acampbell - 31-1-2008 at 07:44 PM

I have hijacked this thread enough so this is the last. But you are welcome to contact me and visit. Real estate values are just awsome. They are not making any more coastline and we are the last of it. We decided to move to the coastal south from Mid-town Manhattan two years ago and have not looked back.
Thanks to the Astor/ Carnegie/ Rockefeller families, the island is state owned. The Jekyll Island Authority that administers the Island has embraced the kiting comunity wholeheartily, both land and water.
I even get to chase and tease the Georgia Highway Patrol (State Troopers) when they patrol the beach in their 4x4

I welcome anyone to come and visit.

BeamerBob - 31-1-2008 at 08:26 PM

Ok, this is my last on this hijack as well. Jekyll island has to be the best beach I've been to (limited) yet. It is as nice as Angus says. Very non commercial and that awesome kite beach area that you can get away from the crowds if you can call it that. Here is a shot of me with the Beamer for its maiden flight on Jekyll Island.

big beach shot

Bladerunner - 1-2-2008 at 10:38 AM

Hey Motman,
I'm confused about how I confused you :puzzled:

I was talking about 4 line fixed bridles on handles ( or a bar )

Is it possible you only have a 2 line ?

I find it simpler to think of the back lines on a depower kite as the steering lines rather than brake lines although you are basically doing brake turns.