foil plan shapes

foil plan shapes

Post by David Forsyt » Sat, 11 Oct 1997 04:00:00


Hi all,
I have some questions, but before anyone gets ideas.....
1)  I'm not copying anyones kites, I prefer to design my own, and
am                      currently busy building one to my own design, and have two      
others drawn and awaiting the outcome of the first.
        But it is useful to know what others have done to avoid the     obvious
mistakes.
2)  Can anyone describe the plan shapes of common foils like Peels
        Sky Tigers, Paua's etc?
        Specifically, is the leading and trailing edge curve
mirrored                                        around the centre line or not?  
        How much of the leading/trailing edge is 'straight' before it                  
curves to the tip profile?

thanks

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foil plan shapes

Post by Andrew Beatt » Sat, 11 Oct 1997 04:00:00


Quote:
>I have some questions, but before anyone gets ideas.....
>2)  Can anyone describe the plan shapes of common foils like Peels
>    Sky Tigers, Paua's etc?
>    Specifically, is the leading and trailing edge curve
>       mirrored around the centre line or not?  
>    How much of the leading/trailing edge is 'straight' before it
>       curves to the tip profile?

The Tiger is rectangular, I believe.

The Peel and, I presume, the Paua pretend to be Elliptical, but in fact the
middle few (5?) cells are identical.  For convenience, I assume - they are
so similar to start with that any difference required to make a perfect
ellipse is lost in the underflow.

On the Sputnik 4, the taper is just on the tip 4 (24 cell kite) or 6 (36 cell
kite).  The middle is parallel.  There is twice as much taper at the rear of
the tips as at the front.

On the Chevron, the only the middle 4 cells arn't tapered.  The front and
rear taper is identical.

From a design point of view, you can do whatever you like :-)

If you draw a line from the line throught the primary bridle tow-point and
continue it to the skin, you mark the point of the effective point of pull
on canopy.  You might like to arrange for these points to form a straight
line across your kite.  This is what the Sputnik-4 achieves.

I actually curve this line int eh Chevron (it curves forward in the middle
of the kite) and I *think* that this helps to counter tip-drag induced
bananaing, but this is unproven.

Andrew
--
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foil plan shapes

Post by David Forsyt » Tue, 14 Oct 1997 04:00:00

Hi Andrew

Thanks for your useful reply

Quote:


> >I have some questions, but before anyone gets ideas.....
> >2)  Can anyone describe the plan shapes of common foils like Peels
> >       Sky Tigers, Paua's etc?
> >       Specifically, is the leading and trailing edge curve
> >       mirrored around the centre line or not?
> >       How much of the leading/trailing edge is 'straight' before it
> >       curves to the tip profile?

> The Tiger is rectangular, I believe.

> The Peel and, I presume, the Paua pretend to be Elliptical, but in fact the
> middle few (5?) cells are identical.  For convenience, I assume - they are
> so similar to start with that any difference required to make a perfect
> ellipse is lost in the underflow.

If they are elliptical, then that means the curvature is symmetric about
the centreline.  This means that the centre of pull you talk about below
curves back from the centre of the kite.  
Hmmmm.  
My currently-being-contructed kite is made of 2 ellipses, one for the
front edge and one for the rear, with a straight line running through
the point 30% back from the leading edge of the centre rib (widest point
in a clark-y rib profile, except I'm not using the clark-y directly, I
modified it a bit just for fun, and I've left off the tips to have a
reasonably sized final rib profile)
Therefore, I think the centre of pull is also in a straight line?
Whatever, the design makes sense to me in a gut feel kind of way.

Quote:
> On the Chevron, the only the middle 4 cells aren't tapered.  The front and
> rear taper is identical.

I thought so from your fotos.  One of my designs-to-be-built I admit is
similar, but with no parallel centre section, and different front and
rear tapers.

Quote:
> From a design point of view, you can do whatever you like :-)

> If you draw a line from the line throught the primary bridle tow-point and
> continue it to the skin, you mark the point of the effective point of pull
> on canopy.  You might like to arrange for these points to form a straight
> line across your kite.  This is what the Sputnik-4 achieves.

> I actually curve this line int eh Chevron (it curves forward in the middle
> of the kite) and I *think* that this helps to counter tip-drag induced
> bananaing, but this is unproven.

Well, that's a thought.   I am toying with going the other way, ie
having the tips forward of the centre, as in some more modern fighter
and light aircraft wing designs.
The bridle may become more interesting though (BTW I notice the Chevron
bridle becoming more complicated as time passes, I also notice you are
using some bridle features from the N-Gen....)
I'm also toying with various ideas for reducing the number of bridle
lines in a cross bridle (and still have it fly decently), but it's
probably all been done before.....
I'm also reinforcing every rib so I can switch between bridling every
2nd or every 3rd rib.....

And yes, this is more about building things than enything else, it
doesn't really matter if one of my kites isn't the next buggy engine of
note, I'm having fun, and I can't afford 'real kites' anyway, building
is much cheaper for me (and I spent most of the weekend waiting for the
wife to finish with the sewing machine....)

And another thing, has anybody ever bridled a foil with dihedral like an
airplane wing, ie the centre closer to you than the tips?  If not why
not?

cheers
--

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foil plan shapes

Post by Steve Batema » Tue, 14 Oct 1997 04:00:00

Quote:


> > I actually curve this line int eh Chevron (it curves forward in the middle
> > of the kite) and I *think* that this helps to counter tip-drag induced
> > bananaing, but this is unproven.

> Well, that's a thought.   I am toying with going the other way, ie
> having the tips forward of the centre, as in some more modern fighter
> and light aircraft wing designs.

I've done this on the last 4 foils I've made, for aspect ratios of 3.8
to
4.7. The middle of the tips averages 38% of the main profile length
down from the "front" of the kite (front being the leading edge of the
center ribs, if that makes any sense).  Seems to work good; those going
to BBT3 will see them there. I've decided to call these foils I'm making
Cocoons, mainly due to the color scheme.

Quote:
> I'm also reinforcing every rib so I can switch between bridling every
> 2nd or every 3rd rib.....

I'd bridle it every rib or every two.  Every 3 ribs deforms the leading
edge of the kite to much (where you get most of the power from).

--
Steve Bateman    geokite at sprintmail dot com
5.2m^2 sputnik4 for sale, Icarex and spectra, $275+shipping.
You might have to remove the blue from the return address to respond

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foil plan shapes

Post by Andrew Beatt » Tue, 14 Oct 1997 04:00:00


Quote:
>Therefore, I think the centre of pull is also in a straight line?

Yep.  I'd say so.

Quote:
>Whatever, the design makes sense to me in a gut feel kind of way.

I agree.

Quote:
>I thought so from your fotos.  One of my designs-to-be-built I admit is
>similar, but with no parallel centre section, and different front and
>rear tapers.

No good reason for not doing that.

Quote:
>Well, that's a thought.   I am toying with going the other way, ie
>having the tips forward of the centre, as in some more modern fighter
>and light aircraft wing designs.

Yes.  I've toyed with that idea too.  In particular, I wonder if it will
improve the steering response (just because it feels like it should
be more unstable)

Quote:
>The bridle may become more interesting though (BTW I notice the Chevron
>bridle becoming more complicated as time passes, I also notice you are
>using some bridle features from the N-Gen....)

*slap*

The design of the bridle on the Chev predates the Ngen :-)

The bridles are in fact, quite different.  What features were you thinking of?

Quote:
>I'm also toying with various ideas for reducing the number of bridle
>lines in a cross bridle (and still have it fly decently), but it's
>probably all been done before.....

Yep.  Can be done and works well.  I was cutting off cross-bridles only the
other week...

Quote:
>I'm also reinforcing every rib so I can switch between bridling every
>2nd or every 3rd rib.....

Good idea.  I hate doing the reinforcing and never do this...

Also on development kites, consider puting the reinforcing down the seam
line, rather(*) than in a zig-zag.  This isn't as strong, but it allows you
to move bridle positions with ease.

(*) or possibly, do both

Quote:
>And another thing, has anybody ever bridled a foil with dihedral like an
>airplane wing, ie the centre closer to you than the tips?  If not why
>not?

 - You might expect it to make the kite more stable and thus be to the
   detriment of the steering.  Maybe.  My experience is that other factors,
   such as how well the wing flies and the design of the cross bridle swamp
   any effect from the front-on profile.
 - The shape will put a compressional load on the canopy.  The shape of
   the canopy and the bridle will mean that it will not be good at resisting
   this force.  Structural integrity will be severely impacted.  (Peter Lynn
   uses this effect on his Rays to make the fins wiggle...)

Andrew
--
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foil plan shapes

Post by David Forsyt » Wed, 15 Oct 1997 04:00:00

Hi

Quote:



> > > I actually curve this line int eh Chevron (it curves forward in the middle
[]

> > Well, that's a thought.   I am toying with going the other way, ie
> > having the tips forward of the centre, as in some more modern fighter
> > and light aircraft wing designs.

> I've done this on the last 4 foils I've made, for aspect ratios of 3.8
> to
> 4.7. The middle of the tips averages 38% of the main profile length
> down from the "front" of the kite (front being the leading edge of the
> center ribs, if that makes any sense).  Seems to work good; those going
> to BBT3 will see them there. I've decided to call these foils I'm making
> Cocoons, mainly due to the color scheme.

interesting, fotos anywhere on the web?
38% is quite a bit further forward than I thought of....

Quote:
> > I'm also reinforcing every rib so I can switch between bridling every
> > 2nd or every 3rd rib.....

> I'd bridle it every rib or every two.  Every 3 ribs deforms the leading
> edge of the kite to much (where you get most of the power from).

not with 27 ribs in a 3 meter wingspan, rib every 100mm or so......(-:
I've also thought of doing some half ribs, so they only hold the leading
edge shape (a la parafoils/chutes), but this is a sewing time change and
I want the freedom, on this kite, to experiment widely.

Quote:
>            Eye boogers.  The great social equalizer.
>                                                          Opus

(-:  ROFL

--

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Part time railmodeller, kiter, photographer, woodworker etc etc
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foil plan shapes

Post by David Forsyt » Wed, 15 Oct 1997 04:00:00

Quote:


> >The bridle may become more interesting though (BTW I notice the Chevron
> >bridle becoming more complicated as time passes, I also notice you are
> >using some bridle features from the N-Gen....)

> *slap*

> The design of the bridle on the Chev predates the Ngen :-)

> The bridles are in fact, quite different.  What features were you thinking of?

shape of the foil as viewed from the front in particular.
how do you figure the cross bridle lengths to get it like that?
using the rig outlined for the Sput on Emiels web page will not do it,
that produces a curve.

what I don't know is how you've done your cross venting, and I didn't
get long enough with PL's N-Gen in Cape Town to figure his out, but have
a rough idea that not all ribs are vented so that the kite is
'compartmentalized'
I did note that his vents are reinforced by sewing 'something quite
thick' around the holes.  my poor little Singer will not handle
that.....

what is the general theory of where to put the holes?  I know the Sput
is rear vented, I also know some people have augmented that with other
holes.  Where to put them along the length of the rib?  How big?
I think they need to go at the centre of internal pressure to maximize
cross flow when it is needed.  where is that centre of pressure?  or is
the internal pressure all equal?   yeah I know internal pressure is
equal in all directions *in a static body*   Accelerate the vessel and
the pressure changes a bit front to back.

Quote:
> >I'm also reinforcing every rib so I can switch between bridling every
> >2nd or every 3rd rib.....
> Good idea.  I hate doing the reinforcing and never do this...

on later contemplation and a rough drawing one doesn't actually need to
do every rib in order to be able to bridle every 2nd or 3rd.....some can
be left off, like the 2nd one in from the tip.  

Quote:
> Also on development kites, consider puting the reinforcing down the seam
> line, rather(*) than in a zig-zag.  This isn't as strong, but it allows you
> to move bridle positions with ease.

already doing that  (-:   down the rib leading edge, then along the
seam.

Quote:
> (*) or possibly, do both

um, maybe next time....
I'm not sure that one needs the zig zag.   Where is the major lifting
force focused?  on the bottom skin where the bridle attaches.  where
does it go from there?  across the ribs to the top skin.  but where is
the major lifting force acting?  on the bottom skin I think, the top
skin mostly takes inflationary forces, I think(?).  so why the need for
rib reinforcing?  because ribs tear too easily, maybe because of the
cross venting holes.  is the reinforcing needed for spreading the
lifting forces from the bridle, or is it needed simply to keep the ribs
in one peice, and is not really localized to the bridle forces?   bears
some thinking about.   I notice the bottom skin needs no reinforcing,
except at bridle attachments for the point forces, therefore that peice
of cloth is strong enough overall, but why not the ribs?   could one
then make a kite using a lighter cloth for the skins and heavier for the
ribs and not need zigzag reinforcing at all (and avoid overall cloth
weight penalties at the same time, and maybe end up with a lighter kite
entirely)?  

Quote:
> >And another thing, has anybody ever bridled a foil with dihedral like an
> >airplane wing, ie the centre closer to you than the tips?  If not why
> >not?
[]
>  - The shape will put a compressional load on the canopy.  The shape of

[]

yes, a good reason I had not thought of. thanks

steam and wind
--

        David Forsyth                 webmaster A-T Iwr.Ru.Ac.Za
Keeper of the listserver for South African Railways fans
Part time railmodeller, kiter, photographer, woodworker etc etc
http://www.ru.ac.za/departments/iwr/staff/daf/welcome.html
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foil plan shapes

Post by Emiel Stroev » Wed, 15 Oct 1997 04:00:00

Quote:

> Hi Andrew

> Well, that's a thought.   I am toying with going the other way, ie
> having the tips forward of the centre, as in some more modern fighter
> and light aircraft wing designs.

Won't this encourage the banana effect? The tips have less drag than the centre
and will have a natural drive to go faster. I think that's why they don't form a
straight line, it will keep them back a bit.

My next foil will have:
- thick profiles (18-19%), I think they improve the lift more than the drag.
- X-venting to improve inflating.
- A clark-y like profile.
- Different shape vents
- Every profile bridled (don't now how much profiles yet), with the centre 5's
X-bridled
- Tune it like a 2-liner (they *are* more fun) and quad for use on crowded buggy
beaches
- Use the standard high-tech materials, what else?

I can't wait for the tuning to begin, it will only take about 80% of the
time-to-make-a-foil

any comments?

way cool,

Emiel

--
-------------------The-Kite-&-Buggy-Site--------------------
Skylon foil design         Sputnik tuning         Buggy tech

----------------------Made-In-Holland-----------------------

 
 
 

foil plan shapes

Post by Andrew Beatt » Wed, 15 Oct 1997 04:00:00


Quote:
>shape of the foil as viewed from the front in particular.
>how do you figure the cross bridle lengths to get it like that?
>using the rig outlined for the Sput on Emiels web page will not do it,
>that produces a curve.

To the best of my knowledge, Emiel and I use similar bridle jigs, but
probably with different dimentions.

Quote:
>what I don't know is how you've done your cross venting,

I cross-vent at the trailing edge, only.  With propellor-spinning quads,
the cross-venting requirements may well be different.

Quote:
>get long enough with PL's N-Gen in Cape Town to figure his out, but have
>a rough idea that not all ribs are vented so that the kite is
>'compartmentalized'

I *think* that the middle rib isn't vented, but my NGen is in the garage
and it's raining, so I'm not goig to check.

Quote:
>I did note that his vents are reinforced by sewing 'something quite
>thick' around the holes.  my poor little Singer will not handle
>that.....

Spectra.  He fits his bottom bobbin with Spectra.  I need an industrial
machine...  (Won't work in the top bobbin, of course)

Quote:
>Where to put them along the length of the rib?  How big?

Dunno.

Quote:
>I think they need to go at the centre of internal pressure to maximize
>cross flow when it is needed.  where is that centre of pressure?  or is
>the internal pressure all equal?   yeah I know internal pressure is
>equal in all directions *in a static body*   Accelerate the vessel and
>the pressure changes a bit front to back.

Dunno about acceleration, but when *filling*, the air goes in and fills up
the trailing edge first.  Observe the kite (particularly a large kite)
carefuly and you'll be able to see this clearly.

Quote:
>on later contemplation and a rough drawing one doesn't actually need to
>do every rib in order to be able to bridle every 2nd or 3rd.....some can
>be left off, like the 2nd one in from the tip.  

Of course, then you'll realise that you should be bridling every *prime* rib.
1, 2, 3, 5, 7, 11, 13

Quote:
>I'm not sure that one needs the zig zag.   Where is the major lifting
>force focused?  on the bottom skin where the bridle attaches.

BZZZT!

Nope.  The net force on the skin at the bridle point is *downwards*!  Just
look at how the skin billows.  All of the force from the bridle is
transferred to the rib.  Surprising, huh?

The zig-zag spreads that point-load on the rib across a wide area.  When I
build, I make this re-inforcing over-spec because it is *so* inconvenient to
fix.

Quote:
>then make a kite using a lighter cloth for the skins and heavier for the
>ribs and not need zigzag reinforcing at all

You are trying to tackle a point-load issue by making the whole rib stronger
rather than just the point that needs to be re-inforced.  This is very
inefficient - I think you will loose.

Andrew
--
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free to drop me a line...

 
 
 

foil plan shapes

Post by Steve Batema » Wed, 15 Oct 1997 04:00:00

Quote:

> > I've done this on the last 4 foils I've made, for aspect ratios of 3.8
> > to
> > 4.7. The middle of the tips averages 38% of the main profile length
> > down from the "front" of the kite (front being the leading edge of the
> > center ribs, if that makes any sense).  Seems to work good; those going
> > to BBT3 will see them there. I've decided to call these foils I'm making
> > Cocoons, mainly due to the color scheme.

> interesting, fotos anywhere on the web?

Mabe after this weekend, I'll let the group know when they are.

Quote:
> 38% is quite a bit further forward than I thought of....

Just in case, 38% means the following: say the center of the kite has
a chord of 100cm.  The center of the planform is at 50cm across the
kite.
The center of the tip rib is 12cm above this line (50-38).
--
Steve Bateman    geokite at sprintmail dot com
5.2m^2 sputnik4 for sale, Icarex and spectra, $275+shipping.
You might have to remove the blue from the return address to respond

           Eye boogers.  The great social equalizer.
                                                         Opus

Check out the San Diego Kite Club at
http://www.geocities.com/Colosseum/Field/5841/target.html

 
 
 

foil plan shapes

Post by Bernhard Mall » Thu, 16 Oct 1997 04:00:00

Quote:

>Also on development kites, consider puting the reinforcing down the seam
>line, rather(*) than in a zig-zag.  This isn't as strong, but it allows you
>to move bridle positions with ease.

Ahh, here we go. I knew that once upon a time in the future, Andrew would
admit that my way of sewing the reinforcement line is the better way....

Bernhard

 
 
 

foil plan shapes

Post by David Forsy » Thu, 16 Oct 1997 04:00:00


Quote:

>Subject: Re: foil plan shapes
>Date: Wed, 15 Oct 1997 07:05:35 +0200

>>Also on development kites, consider puting the reinforcing down the seam
>>line, rather(*) than in a zig-zag.  This isn't as strong, but it allows you
>>to move bridle positions with ease.
>Ahh, here we go. I knew that once upon a time in the future, Andrew would
>admit that my way of sewing the reinforcement line is the better way....

(-:
So tell us more then.  You mean you do big serious traction kites with seam
reinforcing only?  What strength line?  How far down the seam from the
leading edge?  Ever have any rib failures (not due to crashing)?  why?

thanks

 
 
 

foil plan shapes

Post by Andrew Beatt » Thu, 16 Oct 1997 04:00:00

Quote:


>>Also on development kites, consider puting the reinforcing down the seam
>>line, rather(*) than in a zig-zag.  This isn't as strong, but it allows you
>>to move bridle positions with ease.

>Ahh, here we go. I knew that once upon a time in the future, Andrew would
>admit that my way of sewing the reinforcement line is the better way....

This is a good technique for *development* kites, where you might want to
change things.  I wouldn't dream of doing it in a production kite.

BTW, Bernhard:  Your mail server has dissapeared from the net.  We can't
mail you.  (and no, I'm not confused by "Please-Edit")

Andrew
--
Have you got your rec.kites Tshirt yet?  http://www.kfs.org/kites/shirt
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free to drop me a line...

 
 
 

foil plan shapes

Post by Andrew Hawke » Thu, 16 Oct 1997 04:00:00


writes
...

Quote:
>I'm also toying with various ideas for reducing the number of bridle
>lines in a cross bridle (and still have it fly decently), but it's
>probably all been done before.....

I have played with reducing the size of the cross bridle until its silly
small but quite vicious, then putting extension lines between the
primary bridles and the cross bridle.  This is roughly what Andrew has
done on the chevron (I think its the bit he credits me with?) but
Andrews are not as extreme as mine.  This kind of thing saves loads of
line (drag).

Quote:
>And another thing, has anybody ever bridled a foil with dihedral like an
>airplane wing, ie the centre closer to you than the tips?  If not why
>not?

One of the things I tried was a gull wing shape.  Kinda

/\/\

The idea was that the steering input would be to two small wings rather
than one huge one.  In that respect it worked, problem with it was that
the dihedral could not support the compressive load, especially while
turning, and the kite would fold in the middle.

--
Andrew Hawken

 
 
 

foil plan shapes

Post by Andrew Beatt » Fri, 17 Oct 1997 04:00:00


Quote:
>Won't this encourage the banana effect? The tips have less drag than the
>centre and will have a natural drive to go faster. I think that's why they
>don't form a straight line, it will keep them back a bit.

Pardon?

As a general rule, the tips have *more* drag than the centre, because of
the tip-vortex problem.

Tips bending forward are generaly a steering-related cell-compression
problem.

Quote:
>- Tune it like a 2-liner (they *are* more fun)

Amen.

Andrew
--
Have you got your rec.kites Tshirt yet?  http://www.kfs.org/kites/shirt
For sale:  Prototype Lynn N-Gen 3.6m^2.  Excellent price.  Mail for details.
I offer free advice by email on all aspects of traction kiteing.  Feel
free to drop me a line...