*


All times are UTC + 1 hour



Post new topic Reply to topic
 [ 45 posts ]  Go to page Previous  1, 2, 3, 4, 5  Next
Author Message
 Post subject: Re: Unexpected telltale results
PostPosted: Fri Aug 23, 2013 11:38 pm 
Offline
Very Frequent Poster
User avatar

Joined: Sun Sep 04, 2011 5:37 pm
Posts: 1723
tautologies wrote:
...

I've always wondered about the slots..do they actually work? Intuitively it makes little sense to me, but intuition and science is not the same :-)


When you add, ( Angle Of Attack ) to a normal un-slotted wing, the airflow
will start to separate on the upper surface, then reverse causing the
wing to stall. Kinda like the rotor on a cliff, the air reverses .

Doing the same on a Slotted flap will also add AOA, but the air on the upper
surface tends to stay Stuck to the wing thus delaying that stall and Adding Lift !!!

It works because your actually sucking the High pressure off the bottom of the
airfoil, then tossing into the Low pressure on top of the airfoil. As a result
the air hitting the wing actually Thinks the airfoil is Thicker than it really is, and
the air tends to stay stuck to the wing's skin.


http://www.utility-aircraft.com/planes/dornier.htm

It works the same way on the Leading Edge also, there called Leading Edge Slot's
from :
http://www.allstar.fiu.edu/aero/wing33.htm

Sewing a 1.5 inch wide screen fabric to the skin of a LEI, and attaching it to where
the skin is sewn to the LE Bladder, SHOULD work the same way as a sloted Leading
edge ?

They actually do that to the REV ll ; has it bin done to a modern kite ?


Attachments:
Adding AOA = flow seperation.jpg
Adding AOA = flow seperation.jpg [ 2.4 KIB | Viewed 509 times ]
Adding AOA with slotet flap = laminar flow.jpg
Adding AOA with slotet flap = laminar flow.jpg [ 2.94 KIB | Viewed 509 times ]
Leading Edge Slot.gif
Leading Edge Slot.gif [ 8.7 KIB | Viewed 509 times ]
Top
Profile
 Post subject: Re: Unexpected telltale results
PostPosted: Sat Aug 24, 2013 12:03 am 
Offline
Very Frequent Poster
User avatar

Joined: Wed Aug 03, 2005 6:25 pm
Posts: 837
Location: Vancouver
MikeYQM wrote:
... I would gradualy move the telltales forward by testing when they flutter according to a full stall. Only then will you get an indication of the critical angle of attack.

I appreciate your suggestion , but...

I'm not trying to determine the point of total stall. I can detect that easily by feel and sight. The point of telltales near the trailing edge is to keep the kite generating maximum lift. Those telltales indicate exactly how tightly a kite can be sheeted before it begins to lose efficiency.

Cheers,
James


Top
Profile
 Post subject: Re: Unexpected telltale results
PostPosted: Sat Aug 24, 2013 12:13 am 
Offline
Very Frequent Poster
User avatar

Joined: Wed Aug 03, 2005 6:25 pm
Posts: 837
Location: Vancouver
tautologies wrote:
Do you think the flow would be more parallel if the canopy section where flatter?

I don't know that flatness of the chord is significant, but a kite that's flatter spanwise will have more parallel flow. A so-called c-kite, for example, has very skewed, non-parallel flow.

tautologies wrote:
I've always wondered about the slots..do they actually work? Intuitively it makes little sense to me, but intuition and science is not the same :-)

They work, but they're only one way to balance performance and ease of handling. The slot effect is similar to a jib and mainsail combination on a sailboat, or a biplane. Both have their advantages, but in terms of pure maximum performance, a single (high aspect) aerofoil on a sailboat or airplane will be the configuration to break performance records.

This isn't intended for an instant to take away from the potential practical advantage of Ocean Rodeo (or Flysurfer, etc) slots.

Cheers,
James


Last edited by JS on Sat Aug 24, 2013 12:17 am, edited 1 time in total.

Top
Profile
 Post subject: Re: Unexpected telltale results
PostPosted: Sat Aug 24, 2013 12:14 am 
Offline
Medium Poster
User avatar

Joined: Tue Oct 20, 2009 9:04 pm
Posts: 113
Location: Moncton NB Canada
In theory the Venturi system should work. On aircraft wings slots are added to basically allow a secondary flow of laminar air over the wing to increase lift at low speeds. These are only used in specific flight profiles (usually landing) and only on specific airplanes (usually high speed/low lift wings). Personally, I think the effective window for a slotted canopy to be effective on kites os so small its inconsequential ans mostly a marketing gimick.

If it were more beneficial, more companies would use it. Like most companies pay lucensing to Slingshot for One Pump systems, if it was worthwhile, they woyld use it.


Top
Profile
 Post subject: Re: Unexpected telltale results
PostPosted: Sat Aug 24, 2013 3:16 am 
Offline
Very Frequent Poster
User avatar

Joined: Fri Jul 16, 2010 6:27 am
Posts: 2315
Location: Ford Lake, Michigan
you can add telltales to a racing kite but it won't go faster. they can feel every puff of wind thru the bar, unlike a 49er where without telltales you can't tell what the wind is doing. It's actually a much better interface feeling the wind thru the bar. Imagine you are driving a car with stiff suspension (a racing car) and you can feel when the road is slick because the wheels slip you can feel when there is a rough patch, and adjust your steering and gas accordingly. Now imagine you take away all that feel, put in a really soft suspension and now you put a computerized indicator that tells you everything about the road. It's a much worse interface. Your eyes have to do a lot, they have to look out for other people, they have to look ahead for the next curve, they have to watch the speed, and now you ask them to watch an indicator that tells you the condition of the road. If you can offload some of the visual processing and give it to the sense of touch you are a more efficient racer. Another example is when you are racing and have to decide when to shift. If you are driving a very quiet car and can not hear the engine at all, you need to use your eyes to peek at the tach all the time to decide when to shift. If on the other hand, you can hear the engine, you can use your sense of hearing, offload some of that visual processing to another sense, it makes you a better racer.

Telltales make a kite racer less efficient because now he is putting more demands on his eyes which should be used for other things, instead of using the sense of feel which is already in his hands. Most sailboats need telltales of course because they cant hold the sail in their hands to feel the wind.

Kite designers should probably be using telltales, but I don't think they do. I think they rely on their modeling software that spits out all the information about the airflow.


Top
Profile
 Post subject: Re: Unexpected telltale results
PostPosted: Sat Aug 24, 2013 4:33 am 
Offline
Frequent Poster

Joined: Mon Mar 07, 2011 2:26 am
Posts: 275
Bla bla bla just get all the brands into a Wind tunnel Shootout.

No more Bullshit claims - just graphable Results.


Top
Profile
 Post subject: Re: Unexpected telltale results
PostPosted: Sat Aug 24, 2013 4:33 am 
Offline
Frequent Poster

Joined: Mon Mar 07, 2011 2:26 am
Posts: 275
Bla bla bla just get all the brands into a Wind tunnel Shootout.

No more Bullshit claims - just graphable Results.


Top
Profile
 Post subject: Re: Unexpected telltale results
PostPosted: Sat Aug 24, 2013 4:39 am 
Offline
Frequent Poster

Joined: Mon Mar 07, 2011 2:26 am
Posts: 275
OHH but that cost money huh ?? Well $1-3000 is alot of money too.
Maybe cancel one of your team Dangle dork trips to a luxury promo vid spot and youll have more than enough ;)


Top
Profile
 Post subject: Re: Unexpected telltale results
PostPosted: Sat Aug 24, 2013 7:08 am 
Offline
Very Frequent Poster
User avatar

Joined: Wed Aug 03, 2005 6:25 pm
Posts: 837
Location: Vancouver
edt wrote:
Most sailboats need telltales of course because they cant hold the sail in their hands to feel the wind.

Absolutely to the contrary... accomplished sailors can feel the effects of every wind nuance through all interfaces: hull, tiller, rig and controls (not least continuously trimmed, handheld mainsheet - common in many classes). In many cases this can make windward leading edge (impending luff) telltales redundant, but not leeward trailing edge ("slightest stall") telltales.

edt wrote:
Kite designers should probably be using telltales, but I don't think they do.

Your impression of kite designers is apparently radically different than mine.

Cheers,
James


Last edited by JS on Sat Aug 24, 2013 9:44 am, edited 1 time in total.

Top
Profile
 Post subject: Re: Unexpected telltale results
PostPosted: Sat Aug 24, 2013 7:46 am 
Offline
Frequent Poster
User avatar

Joined: Mon Jun 25, 2007 8:15 pm
Posts: 296
tautologies wrote:
eree wrote:
oh, so that is why so many world cup races are won by the kiters riding ocean rodeo kites! :bravo:

impressive...


jesus dude whats up with the constant sarcasm?


I'll bite. The guys at Crissy can tell you that a few years back the OR Rise kite was a serious contender in their races. Or should I say, racers on OR gear (kites don't win races). The Rise was a medium AR kite never purposely designed for course racing. When others brands started designing specific racing kites with maxed out ARs that was over.

Designing competitive racing gear takes serious R&D efforts only a few brands can afford, for that juicy 0,1% chunk of the market most brands tend to leave it alone.

Kiters expect a kite to do everything, and everything unhooked. Most of us are flying compromises. James is spot on with his comment that adding venturis is only one way of balancing performance and ease of handling.

On the OR kites, the vents do work. Try one and you know it.


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic
 [ 45 posts ]  Go to page Previous  1, 2, 3, 4, 5  Next

All times are UTC + 1 hour


Who is online

Users browsing this forum: Bing [Bot], Google [Bot], Séb and 13 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group