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Author Topic: Doug's Bird of Prey  (Read 4841 times)
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thief
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« Reply #30 on: February 23, 2014, 06:02 PM »

one of the things that really draws me to this one is the shape....the backwards aspect is awesome!!!!
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« Reply #31 on: February 23, 2014, 07:33 PM »

Thank you for the kind words. Grin

The swept forward wing provides some cool flying attributes.  The kite is more responsive to slight changes in line pressure.  The airflow over the wing moves from the tips to the center, so when stalled, it stalls in the center, then recovers quickly.  No tip stall problem with this kite.  This kite can really zoom when you pull on the line.  I love the way I can snap it around in a turn, which looks really cool with the swept forward wings.  The kite settles into a glide as soon as you reduce the tension on the flying.   Most of the gliding is with a slightly slack flying line with the line spooling out of my open hand.  The kite will do a gentle turn just under the weight of the flying line.  I am still learning what I do with this kite and it makes me look better than I am.

Doug
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« Reply #32 on: March 09, 2014, 03:27 PM »

Just finished the sails for 3-24s, 1-36 and 1-48 inch wing span Birds of Prey.  The following picture shows the 5 sails made from Cuben fabric, which are on track to be very low sail loadings.  The three stacked in the center show the 48 on the bottom using orange Cuben, the 36 in the middle using white Cuben, and the 24 on top using orange Cuben.  The two in the upper left and right corners also are 24s using orange Cuben.  These two sails look a lot darker without the white paper template underneath, placed on my smoke colored glass cutting table.  This was done to illustrate the transparent nature of this light Cuben fabric.  The 3-24s are for other glider kite enthusiasts.  The 36 and 48 are ultra-light prototypes.  Trying to see how light I can make this design in these two sizes.

The sails are complete with all of the reinforcements and ready for the frames and lines.  Thief, yes that includes the suture type hand stitching for tip batten pockets on all of the sails.  The weights of the completed sails as show are as follows:

-   24 in. - 1.4 grams
-   36 in. - 3.4 grams
-   48 in. - 5.35 grams

The average sail loadings of the 5 sails as show is 0.0104 grams/square inch of sail area.

Time to build the frames and get flying.

Later,

Doug
« Last Edit: March 09, 2014, 03:28 PM by Doug S » Logged

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« Reply #33 on: March 10, 2014, 04:36 AM »

Those look really nice Doug  Cool  Interested in the construction techniques, do you use typical hem, seam, and sewing techniques while keeping the results light as possible?
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« Reply #34 on: March 10, 2014, 02:33 PM »

stapp59,

That is a very good question.  The following provides my detailed response that is a little long, but it indicates how to use different construction techniques to build ultra-light glider kites.  I learned how to do this with the help of others on this great GWTW Forum.  When I do use PC31, I use traditional techniques.

For the Birds of Prey made from Cuben fabric, I do not use traditional construction techniques that we use with PC31 or ripstop nylon, since this lightest version of the Cuben fabric is too fragile to stitch directly and our traditional techniques would be too heavy.  Although on my Hawks, I do stitch the wing spar sleeves, but the material is atleast doubled.  For the various sizes of the Bird of Prey, the template as shown includes additional sail material that is just folded over to make the wing spar sleeves.  The Cuben fabric is hot cut using the indicated paper template and a steel ruler to absorb the excess heat.  This provides a good finished edge that does not need to be hemmed for these ultra-light low wind glider kites.

The extra material for the sleeve is folded over to make a crease, then taped open for the next step.  The sleeve is held closed with a very thin 1/16 inch strip of double sided tape along its entire edge.  I cutout the 1/16 inch strip of double sided tape very slowly and painfully with scissors from my 1/4 inch roll.  For the 36 and 48 inch versions, I add a small diamond of Tedlar clear tape for reinforcement to where the wing spars enter the wing spar sleeves.  It is a square of Tedlar that is turned 45 degrees, and then placed at the entrance before the wing spar sleeve is taped down.

The Tedlar tape also is used to reinforce where the bridle line goes through the sail at two locations to the center spine, and under the potential wear/pressure point of the center spine/wing spar fitting.  A 1/8 inch wide strip of Tedlar tape is placed on the sail where the center spine goes through the nose reinforcement and into the tail reinforcement pocket on the back side of the sail.  The 1/8 inch of Tedlar tape is about 1/8 inches beyond the black Dacron reinforcements, so I dont accidently push the center spine through the Cuben fabric when installing the center spine into the sail.  Been there and done that!  The Tedlar tape also is used to make the batten pockets, where the Tedlar is wrapped around the edge of the sail material.  I use a very small rectangle of the Tedlar tape to make a pocket on the back side of the sail.  The sticky side of the small piece of Tedlar is placed against the sticky side of the larger piece of Tedlar.  Since the adhesive strength of the Tedlar tape is not that strong, I hand sew a single stitch for the batten tip pocket and a double L shaped stitch for the batten pocket that is next to the wing spar.  The ends of the batten are placed into the pocket and against the stitches.

All of the black reinforcements are made from Dacron, which are mounted to the sail using double sided tape.  The Dacron maybe a little over kill, where I could have used 3/4 oz. ripstop, but I just like the durability at these key stress points on the kite.  I use the double sided tape to help spread the load at the ends of the sail, so all of the tension is not solely on the stitching discussed below.  Please note that no double sided tape is placed were the center spine goes through the nose and into the pocket at the tail, both on the back side of the sail.  The Dacron is hot cut using stainless steel washers of the appropriate size, where I only use half of the cut circle diameter.  For example, if I am using a 1 inch washer, then the Dacron will be mounted 1/2 inch onto the sail.  On the wing tips, I fold the Dacron circle over the leading edge.  The crease in the Dacron is made first to assist in alignment.  At all of the other reinforcement locations, the Dacron reinforcements are separate for the top and bottom of the sail.  Once the Dacron reinforcement is in place on the top side of the sail, I hot cut it slightly larger than the final size.  I then place the bottom side in place, then hot cut to the final size using a steel ruler.  There is a bit of waste using separate pieces of Dacron, but I build this way because the Dacron is so stiff as compared to the Cuben fabric, and this style of construction allows me to carefully get the pieces aligned.  Please note that you cannot remove the Dacron with double sided tape from the Cuben fabric without damaging the Cuben fabric.

Now for the only machine sewing I do on these kites.  The stitches are straight 8 stitches to an inch, except as noted.  Using my sewing machine, I very carefully stitch two single stitch lengths on the nose, which allow the center spine to slide between them.  I very carefully stitch the U shaped pocket in the tail, which is two stitches, 90 degree turn, two closer space stitches, 90 degree turn, then two stitches.  Finally, I very carefully stitch about three stitches along the outside of the tip reinforcement, where the wing spars will be applying pressure from the inside.  I use stitching because I have seen the double sided tape shift under load and a little sun light.

There is a lot of fine detail work to make these kites, but it is well worth the effort.  Also, you have to be in the right frame of mind to do this type of detail work, because one mistake and you just wasted an expensive piece of Cuben fabric.  Been there done that!  The reinforcements are more than sufficient and very light, which protect the Cuben fabric when the kite is framed and in flight.  In flight, I have actually nose-dived the Bird of Prey 24 numerous times into the hard icy snow and other indoor objects without a problem.  I am not recommending others to do so.

If you have any other questions, just let me know.

Doug
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« Reply #35 on: March 10, 2014, 05:22 PM »

some detail shots...hope to get some more up in this folder...... https://picasaweb.google.com/110977665158917743177/FalconAeroDesigns#


tiny stitching at the tail


wing tip detail showing the cuben


tiny stitch holding in the batten


nose details
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« Reply #36 on: March 11, 2014, 03:04 AM »

Wow. Very nice work Doug.

Thanks for the thorough explanation Doug and for the pictures Rob.  Certainly quite detail oriented and very different from ripstop techniques.  Reminds me of the indoor microfilm free-flight model airplanes.  Those always seemed a bit beyond me. For those curious:

http://www.freeflight.org/Indoor/index.htm

As you said that type of construction requires a different mindset, skills, and lots of patience.  Nice to see the details, thanks again.

Steve
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« Reply #37 on: March 15, 2014, 08:49 AM »

Finally finished the three Bird of Prey 24s for other glider kite enthusiasts.  The attached picture shows how they look using the orange Cuben fabric.

Doug
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« Reply #38 on: March 15, 2014, 08:50 AM »

Here is a shot from the nose.

Doug
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« Reply #39 on: March 15, 2014, 09:00 AM »

Looks like the Boeing plant floor  Grin

Here is a shot from the nose.

Doug
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« Reply #40 on: March 15, 2014, 09:23 AM »

Just finished the prototype of the Bird of Prey (BOP) with a 36 in. wing span.  It's made from my last piece of the white/grey Cuben fabric.  My goal was to build this one as light as reasonably possible.  To do so, it uses minimal reinforcements, framed with 0.04 in. carbon rods for the center spine and wing spars and 0.01 in. carbon rods for the tip battens.  Was able to get it to balance at the desired location with only a two layer nose piece.  I was shooting for 6 grams, which would yield the same sail loading as the BOP 24.

Placed in on my scale this morning, held my breath and was pleasantly surprised that it weighs only 5.8 grams, which yields a sail loading of 0.0198 grams/sq.in.  The attached picture shows the BOP 36, with a BOP 24 in front as a point of reference.  Since the wind is howling outside, I flew it in my family room and this one is definitely a keeper!  Grin

Time to frame the ultra-light version of the BOP 48.  I am using 0.059 in. carbon tube frame for this one.  Need to find a local place with a higher ceiling to fly these indoors.

Later,

Doug
« Last Edit: March 15, 2014, 12:01 PM by Doug S » Logged

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« Reply #41 on: March 15, 2014, 09:54 AM »

stapp59,

Love your comment.  I am way too slow a builder for Boeing, but would love to play in their work space! Cheesy

Later,

Doug
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« Reply #42 on: March 15, 2014, 12:00 PM »

Very nice, and good work on the big ultra light Smiley
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« Reply #43 on: March 15, 2014, 01:46 PM »

Thank you for the kind words.  Grin

Doug
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« Reply #44 on: March 15, 2014, 03:25 PM »

Just finished the ultra-light version of the Bird of Prey (BOP) with a 48 in. wing span.  It's made from orange Cuben fabric.  My goal was to build this one at this size as light as reasonably possible.  To do so, it uses minimal reinforcements, framed with 0.059 in. carbon tubes for the center spine and wing spars and 0.02 in. carbon rods for the tip battens.  I was shooting to be below 15 grams.

Placed in on my scale and was pleased that it weighs only 11.3 grams, which yields a sail loading of 0.0217 grams/sq.in.  Not bad for a glider kite with a wing span of 48 in. and projected sail area of 520 sq.in.  The attached picture shows the BOP 48.  Since the wind is still blowing outside, it went for a test glide in my family room.  Nice slow floating glide.  Looking forward to getting this one in the air in a larger area.

Later,

Doug
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