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Old Feb 05, 2006, 10:47 AM
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Build Log
Sagitta XC Build

Am hoping to document and complete a Sagitta XC glider. Purchased a rib set from DreamCatcher before it was sold. So...except for the ribs, all the parts need to be handmade...... oh boy lucky me. This is one Big plane. Span is about 14' with a root chord of 13". Fuselage is 4" longer than my workbench, which is about 52". The whole plane will be built using only wood. Well maybe a little kevlar around joiner area. Have plan only, no manual or directions, except what's on the 3 page plans. So if anyone wants to wade in with advice, am more than willing to listen.

Will probably make a few minor changes over what the plans show. Intend to make fuselage 1/4" longer. Will be making a full height rudder (no balance) which will be 1/2" higher than plans show. Spar will be kevlar wrapped in area of joiner. Joiner tube will be 5" in each wing as opposed to 3" shown on plans. TE will be 1/2" carbon strip laminated between 1/16" balsa sheets, as opposed to the spruce TE, on plans. The tip / main panel, joiners, are shown as 5/16" steel joiner rod, will probably use carbon rod here, although, will still use a steel one for wing / fuselage mating.

Have redone my work bench to accommodate a 13" chord wing. Pinnable work area was only 12" wide. Purchased some great lumber from a place called, National Balsa Co., (which just happens to be 30 miles from my house) so am pretty much ready to go.

Will start, by building the main panel spar. This is built in total with no break in the ply webs from root to wing tip. That's 48" of a 1 1/4" x 3/8" spar. It has 1/16'" ply shears on front and back of spar, which go the full 48". The spar caps are 1/8" spruce which is doubled for 24" on top cap, and doubled for, 18" on bottom cap. Between caps are 3/8" balsa shears.

Have glued the doubled spar caps for both wings, Used Titebond then let sit under weight for a day or two, to make sure glue doesn't warp the wood.

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Old Feb 05, 2006, 10:55 AM
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This will be an interesting build..looking forward to it.
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Old Feb 05, 2006, 04:55 PM
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This is great Erich, love following your build threads especially since I have so many of these sailplanes in my hangar. Great reference for when its time to build my Gentle Lady, Olympic II and Mirage. I might not have a Sagitta XC but I'm sure my Sagitta 900 will benefit from this. Your ideas and methods, such as scalloped trailing edges, look like they could be used in many applications. Thanks.

Tom
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Old Feb 05, 2006, 06:20 PM
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double post
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Last edited by tw126a; Feb 05, 2006 at 06:21 PM. Reason: double post
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Old Feb 05, 2006, 06:45 PM
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I was just about ready to start mine, when I relized my pinable area wasn't wide enough for the wing cord! Back to Home Depot I go ;^)
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Old Feb 05, 2006, 07:54 PM
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Yea, had to cut a 3" wide strip and tape it alongside my "not wide enough 12" wide" ceiling tile area. Had some left over from when I first put down the ceiling tiles. Have built 6 planes on the same tiles. The whole building board is getting pretty ratty looking. Well one more plane, then it'll be time for a new board. Are you building a Sagitta XC or another Windsong? Either one sounds cool to me (can you tell I'm from the sixties).

Made some reductions (40%) of the plans.



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Old Feb 05, 2006, 09:26 PM
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Making parts

While waiting for spar caps to fully dry, worked on making some of the parts for fuselage. Had full size copies made of the plans at a Kinkos. Also made a 40% copy of fuselage and wing sheets. The smaller size makes it MUCH more convenient to check out plans. On the full size copy, cut out the fuselage side view. Cut this in half, where break is between front 1/8" birch ply and rear 1/8" lite ply, sides. Taped paper template to ply sheet using one of the straight sides to line up with edge of ply sheet (less cutting that way). Cut out with a small scroll saw. Taped & temporarily glued the two forward fuselage halves together. Planed and sanded till sides were as close as possible to plan, and identical to each other. Drilled out holes for front and rear joiner tubes (while sides were taped together). Using ply root rib as template for the holes.

As to photo 3....please don't ask what that big hole just in front of forward joiner hole, is!!

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Old Feb 05, 2006, 09:32 PM
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Looking forward to the build. Are these plans available commercially?
Enjoyed your Challenger build too. Its a great looking airplane with interesting construction methods. Im from the sixties too, but actually started life in the fifties...
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Old Feb 05, 2006, 09:38 PM
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The stock fuselage is very short! You should increase the tail boom by 6".
See:
http://www.qualityfiberglass.net/
"Quality Fiberglass offers an excellent line of both r/c sailplane kits, and r/c power kits."

I'll bet that they have the better fuselage length with the molding tooling XL Sagitta. Ask them to build a better epoxy-glassfabric fuselage from their old tooling.

Check the small tail moment arm and tail areas. This comes from Dr. Mark Drela.

"Ch = (A_hori/A_wing) * (tail_arm/avg_wing_chord)
Cv = (A_vert/A_wing) * (tail_arm/avg_wing_span )

A well-sized tail will be in the range...
Ch = 0.35 - 0.50
Cv = 0.02 - 0.035
If the Ch and/or Cv are below the minimum values, the handling will suffer."

The Sagittas all have problems with the stab mount to the fin. The problem of small music wire jointer rods have high bearing stress in the fin. Eventually the stabs wobble in the fin mounting. The solution is bigger 1/8" diameter and brass tubing nesting (5/32, 3/16, 7/32, 1/4" brass K&S tubing in epoxy) up to 1/4" diameter brass tubing in the fin mounting. Another way is to change the 1/8" music wire with a 3/16" diameter carbon rod jointer.
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Old Feb 05, 2006, 10:03 PM
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Ollie

Thanks for the help. And the link to "quality fiberglass" But as to using a fiberglass fuselage...................

One of the main reasons I am building this plane is the wood fuselage. It's my favorite part. Will only work on all fiberglass fuselages if forced to. Have increased the fuselage by a small amount, but not 6 inches. Hey my trunk is only so big. Will be using a bigger dia. stab pivot wire, also longer. May also make stab a little bit thicker. Had a Sagitta 900 which had the wobble in the stabs. Am planning on making fin and rudder 1/2" taller, with a NONE balanced rudder. Appreciate you giving me the proper numbers, but those kinda things just make my head hurt. It's probably wrong most of the time, but I go with the TLAR method. I do however listen to what others have to say. So Ollie, if I do anything too weird, please let me know.

Just measured it, the fuselage is going to be 58" overall (not counting rudder). Please let me know if that's within acceptable limits.

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Old Feb 05, 2006, 10:05 PM
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I got the plans and ribs from DreamCatcher, which went out of business awhile back. RCM or Flying Models might have plans.

Just checked them both, no plans. Sorry

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Old Feb 06, 2006, 01:18 AM
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Just a remember of the Dreamcatcher line of kits to those just in case do not know, but "Aerosphere" company took over, and they will be reproducing the kits. As to when? No one knows, but they will....especially paying $$$ for the rights... so, if you wait a while, then maybe you can get the plans...and kit too.
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Old Feb 06, 2006, 03:11 AM
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Quote:
Originally Posted by erich
Are you building a Sagitta XC or another Windsong?
erich
Building a Sagitta XC this time.
It's interesting that the Airtronics building instructions for the Cumic Plus noted the thicker stab in this plane as an improvement over the Sagitta stab. I guess I'll have to do that also.
Quality Fiberglass does make a longer f/g fuse for $125.
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Old Feb 06, 2006, 04:55 AM
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erich,

There is another way. If you don't want to stretch the fuselage 6", you could increase the tail area about 20%. If you do with a stock design, with small tail areas, it fly but it will handle poorly. With a longer fuselage and more tail area, it will fly groovy and, in gusty thermals, it will return to trim quicker.

Without enough tail moment arm and tail area, in the gusty conditions, the porpoising flight is not groovy. It is hard to control the flight smoothly at long range. It increases the pilot's work load on long flights.
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Old Feb 06, 2006, 06:32 AM
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Ollie

Thanks a bunch. I will increase tail area. Am assuming you mean BOTH H. stab and V.stab + rudder. To re-cap: I need to figure area of H.stab, then increase that by 20% PLUS do the same for the rudder & fin area? Is that what you mean?


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