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Old Apr 04, 2014, 12:05 AM
Kurt Zimmerman ≡LSF 4461≡
kzimmerm's Avatar
Montrose, NY
Joined May 2003
1,349 Posts
Build Log
Sagitta 900 with some mods

Greetings all;
Well this is the first installment of my building log for a long awaited Sagitta 900. This build is going to include some changes to the original design. These are some of those changes:
1) Change the airfoil from E205 to S3014
2) Increase the main wing spar from 3/8" to 1/2"
3) Laminate carbon on upper & lower spars
4) Increase length of joiner rod and joiner rod tubes in wing
5) Wrap inner spar and polyhedral with Kevlar
6) Increase LE top sheeting by about 1" to reduce covering sag in rib bays
7) Use Quality Fiberglass fuse
8) Remove rudder balance
9) Considering using separate spoiler servos (still deciding this mod)


I'm hoping with these changes I'll see greater ranging along with a wider speed range. Also I'm planning on winch launching the Sagitta. I want to have the comfort level that I can load up the winch without concern of doing damage.
That it for openers. I have a few pictures that I took of the carbon capped inner spars.
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Old Apr 04, 2014, 01:58 AM
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Hawaii
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Love it.
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Old Apr 04, 2014, 04:37 AM
Detail Freak
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Harbor City, CA
Joined Oct 2003
21,331 Posts
Hi Kurt-
Will you be using a larger diameter joiner? Like 1/2"?
I'd assume if you did that, you'd have to use a dihedral joiner.
An aluminum one would work.
Or carbon!

R,
Target
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Old Apr 04, 2014, 05:02 AM
Kurt Zimmerman ≡LSF 4461≡
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Montrose, NY
Joined May 2003
1,349 Posts
Quote:
Originally Posted by target View Post
Hi Kurt-
Will you be using a larger diameter joiner? Like 1/2"?
I'd assume if you did that, you'd have to use a dihedral joiner.
An aluminum one would work.
Or carbon!

R,
Target
No and here is the reason why. I have an "injector pin" that measures the same diameter as the original joiner rod, just longer. I highly doubt even infer heavy loads that joiner rod will hold up without the slightest signs of bending. I did think of using a larger joiner rod but when I got this pin I decided against it. The big advantage in using the same diameter pin is I get to use the preformed block along with extra wedges to hold the joiner tube in place. Finally I'll be able to pot that section of the spar with a slow cure epoxy/fiberglass mix. Finishing that section of the spar with Kevlar wrapping should hold things together.

The other advantage of the extra width of the spar allows a longer ply shear web along both sides of the joiner tube boxed area along with a thicker I beam for the remainder of the inner wing panel.

Final note on the spar I plan on building up the center of the I beam with 1/8" balsa on a bias of 45 degrees. I'll sandwich the balsa together making for a stronger core.
Kurt
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Old Apr 04, 2014, 05:03 AM
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Nova Scotia, the East Coast NA
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Popcorn ready


Are you gonna eliminate the wooden wing tube carrier, and build like the Aquila ?



whacker
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Old Apr 04, 2014, 06:34 AM
Kurt Zimmerman ≡LSF 4461≡
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Montrose, NY
Joined May 2003
1,349 Posts
Quote:
Originally Posted by whacker View Post
Popcorn ready


Are you gonna eliminate the wooden wing tube carrier, and build like the Aquila ?



whacker
Im planning on using the wood carrier. By widening the spar by the 1/8" allows me to encapsulate the wooden carrier along with additional wedges with longer ply sheer webs. Net result will look just like the finished Aquila as you shown. The biggest design flaw I see in the original joined/spar box design is the abrupt transition from a width of 1/2 inch to 3/8 at tv he end of the joiner tube.
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Old Apr 04, 2014, 07:02 AM
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Hi
That should work really well then

Actually that's the Elio I have shown with S3021 Ribs

I believe you are correct, and that block did form a stress riser at that point in the finished spar.
I reckon though this block was added to streamline the build, as it's use is significantly easier then the "floating tubes" that really need to be jigged to have aligned properly..

Had you considered plug in wing tips?
I know it adds weight a little further out, but does make the plane very portable!
I also completed a Skybird last fall with plug in tips.
Really slick

whacker


Quote:
Originally Posted by kzimmerm View Post
Im planning on using the wood carrier. By widening the spar by the 1/8" allows me to encapsulate the wooden carrier along with additional wedges with longer ply sheer webs. Net result will look just like the finished Aquila as you shown. The biggest design flaw I see in the original joined/spar box design is the abrupt transition from a width of 1/2 inch to 3/8 at tv he end of the joiner tube.
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Old Apr 04, 2014, 07:13 AM
Kurt Zimmerman ≡LSF 4461≡
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Montrose, NY
Joined May 2003
1,349 Posts
Although the plug in wing tips sounds like a great idea I would gain little benefit. I transport longer wings than the 49-50" panels of the Sagitta. For me it isn't worth the extra time spent along with the extra weight gain. Keep in mind the spar will be taking on additional weight just by the fact I'm increasing the width by 1/8" along with the carbon and Kevlar. For me the disadvantage outweighs the advantage .

Kurt
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Old Apr 04, 2014, 07:21 AM
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United States, KY, La Grange
Joined Feb 2006
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You might also consider increasing the thickness of the flying stab halves. It's a popular mod which will settle down the pitch sensitivity with that short tail moment.

Been flying my 900 for 6 years now, and it's still one of my favorite airplanes.
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Old Apr 04, 2014, 07:34 AM
Kurt Zimmerman ≡LSF 4461≡
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Montrose, NY
Joined May 2003
1,349 Posts
Quote:
Originally Posted by dion9146 View Post
You might also consider increasing the thickness of the flying stab halves. It's a popular mod which will settle down the pitch sensitivity with that short tail moment.

Been flying my 900 for 6 years now, and it's still one of my favorite airplanes.
Interesting. Somehow I missed that suggestion along the way. Thinking "out loud" I'm wondering how the Drela stab airfoil used on his Bubble Dancer would work.
Kurt
Nice looking ship!
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Old Apr 04, 2014, 10:22 AM
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United States, MD, Lutherville-Timonium
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Thanks for sharing, Kurt. I ordered a set of Sagitta 900 plans from RCM 18 months ago. They took the money and then, well, we all know what has been happening there. I have chocked it up as a loss. The upshot is that I can now watch your build and live vicariously through it.
W
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Old Apr 04, 2014, 10:41 AM
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United States, CA, San Jose
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great timing, I just ordered 2 of these fuses! Gonna ALES one! Are you going to use a bellcrank for the stab Kurt? I am just going to use an existing set of wings and stabs I have. will be following this thread for sure!

Al
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Old Apr 04, 2014, 11:34 AM
Kurt Zimmerman ≡LSF 4461≡
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Montrose, NY
Joined May 2003
1,349 Posts
Quote:
Originally Posted by alstrahm View Post
great timing, I just ordered 2 of these fuses! Gonna ALES one! Are you going to use a bellcrank for the stab Kurt? I am just going to use an existing set of wings and stabs I have. will be following this thread for sure!

Al
Hi Al;
A bellcrank for the stab seems to be the logical choice. It is easy to fabricate and install. Several tricks I've used in the past:
1) Cut the bellcrank out of 1/16" ply
2) drill the proper holes for the pivot along with the secondary pin and pushrod
3) wick thin CA into all holes then ream them for a tight fit without binding.
4) I use small pieces of nyrod (red seems to be the right size) as bushings on either side of the bellcrank to insure the bellcrank doesn't walk along the brass tube and up against the fin causing it to bind.
5) I use small washers on either side of the fin to support the brass tubing pivot. This gives a larger surface area that keeps the brass tube in place. Before doing this I've pulled out brass tubes when removing the stab. It becomes a real pain re-installing it.

That arrangement seems to be the "right stuff" and has not failed me. My Grand Esteem has that arrangement and has been working flawlessly for almost 20 years.

Kurt
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Old Apr 04, 2014, 12:40 PM
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United States, CO, Hotchkiss
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Sounds good. I'll be watching as I have Aerosphere plans for the 900 but they wouldn't sell me the kit. Oh well.
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Old Apr 04, 2014, 12:48 PM
Kurt Zimmerman ≡LSF 4461≡
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Montrose, NY
Joined May 2003
1,349 Posts
Quote:
Originally Posted by Pilatuspc12 View Post
Sounds good. I'll be watching as I have Aerosphere plans for the 900 but they wouldn't sell me the kit. Oh well.
This is not a very difficult plane to scratch. A flying buddy of mine not only built one from scratch but also made a 3m version which flies awesome!

Kurt
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