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Feb 29, 2012, 02:41 PM
Multi-Platform Pilot
barracudahockey's Avatar
Discussion

Sagitta 900 Build


After casually searching high and low I finally found an untouched Sagitta 900 kit. I've lusted after one of these since they were introduced but at the time they were out of my 16 year old budget.

Ironically the one I bought was less than 2 miles from my house.

Anyways, I want to stay true to the kit and design but also incorporate any modern building techniques or mods that were popular at the time but without redesigning anything. What are the popular suggestions for building this thing? I also got one of the original fiberglass fuselages with it (wooden hatch for the front, and ballast hatch by the wing saddle.

I'll post progress here for anyone that cares, but I have one event article and 2 product reviews ahead of it so its going to be an "as I have time" project.

Thanks in Advance
Andy


**Note, I searched months of historical posts and didn't really find anything useful but if you have a link to existing information, I'm all ears**
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Mar 01, 2012, 11:37 AM
Known Wind User
Martini's Avatar
The Sagitta 900 is truly a builders kit! Loved the machined ribs. Enjoy! Subscribed
Mar 01, 2012, 12:19 PM
LSF303-AMA Fellow
tkallev's Avatar
  1. Lengthen tail moment 4-5 inches
  2. Lengthen nose moment 2 inches
  3. Remove "balance" portion of rudder (makes fixed fin larger)
  4. Airfoil the stab rather than the flat plate design (less pitch sensitive)
  5. Full-length fuselage side doublers made from 1/64" plywood (strengthens the tail where it gets so small in cross section)
Have fun building, it was Airtronics' greatest kit!
Mar 01, 2012, 09:20 PM
Kurt Zimmerman ≡LSF 4461≡
kzimmerm's Avatar
If you follow Tom's advice then let me offer one more to throw on the coals... I would consider changing out the airfoil making it into a S3014. Here is why, the E205, although is a great airfoil apparently has a nasty stall characteristic. However by reshaping the airfoil to the S3014 you can greatly improve the overall performance with very little effort. See attached.

Kurt

Source: http://worldofkrauss.com
Mar 06, 2012, 10:22 PM
Helmet...check!!!
AndyRice_WI's Avatar
A NIB kit was just put up for sale tonight for anyone wanting to tag along on another build. I'm tempted. but, the kits are piling up.
Mar 07, 2012, 06:28 PM
fa2
fa2
Registered User
say, i noticed your recommended 5 changes - what's the worst kit they made?
Mar 07, 2012, 06:29 PM
fa2
fa2
Registered User
excuse me - 6 (airfoil) - sounds like it was not so great
Mar 07, 2012, 08:25 PM
Registered User
Steve Bailey's Avatar
Having built 4, one modified quite a bit and one from scratch. I can honestly say that you will probably be happy with it "built to print".
Mar 08, 2012, 07:46 AM
Multi-Platform Pilot
barracudahockey's Avatar
Yea, I want to stick with the original design. The fuselage work is out because I've got a fiberglass fuse for it in any case.

Just wondering about...."if i built another one I might put some carbon here or a doubler there...."

How about the spoilers? I haven't been through the book yet but was thinking I have a pile of micro servos laying around, how about just sticking a micro in each wing?
Mar 08, 2012, 08:23 AM
AMA 353531
rdeis's Avatar
That's the easiest answer, especially if you want to avoid opening a wing hatch in that nice glass fuse!

When I get going on my Pantera refit I plan to use 5-pin plugs so I can drive both a spoiler servo and embedded LED strips. Should make a nice Cayote airplane. (-:
Mar 08, 2012, 03:08 PM
Kurt Zimmerman ≡LSF 4461≡
kzimmerm's Avatar
Quote:
Originally Posted by barracudahockey
Yea, I want to stick with the original design. The fuselage work is out because I've got a fiberglass fuse for it in any case.

Just wondering about...."if i built another one I might put some carbon here or a doubler there...."

How about the spoilers? I haven't been through the book yet but was thinking I have a pile of micro servos laying around, how about just sticking a micro in each wing?
I really like the idea of having micro servos mounted in the wing. However, if you follow the building thread of the Duet, Jack uses U-Control cable and a magnet. I've used dial chord for about a gazillion years with great success. When I get to building my Sagitta I may use Jack's method since it looks to be real simple. I like simple.

Kurt
Mar 08, 2012, 05:01 PM
LSF303-AMA Fellow
tkallev's Avatar
Depending on the glass fuse you have, most of the dimensional changes are likely already there.

A micro servo in each wing is the really easy way, especially if you set them up on separate channels and then tie them together in the radio.
Mar 09, 2012, 03:24 PM
Multi-Platform Pilot
barracudahockey's Avatar
I fly an 11x and I have a pile of little servos laying around from reviewing electric planes that....uh...didn't live an excessively long life lets say
May 26, 2012, 09:02 AM
Registered User

Saggita build


Two things not mentioned, Move spoliers out one bay. Double thickness of stab. I have built eight sagitta,the last one flys the best. laminate carbon fibre to spar pryor to build. I vacum bag carbon to spar. Also replace balsa ribs with plywood were spar block is installed
May 26, 2012, 07:24 PM
Segelflugzeug esgeht nach oben
AllThumbs's Avatar
All good stuff...I always heard they flew pretty good built the way designed, but I think that there is at least one thing that ought to be considered along with all the other mods .....

If you do nothing else... this may be the mod that ought to be No. 1. on the list of mods for the 900 (maybe for the 600 too, but I'm only building my first 600 now).
I will be doing this critical mod when I build my next 900 soon ...(yes, just can't not have one 900 in my stable).

You need to address the wing joiner box at the root of each wing where it slides onto the steel wing rod ...this is the failure point that got mine on a winch, along with several others where I flew.
On the wing plans it is called the "pine tube carrier block"...located at the ply wing root and ending at the third rib W-1 inside the sheeted root of each wing. Section 2 B shows it clearly - it is seated between the upper 1/8 spruce spar and lower spruce spar, just like a shear web. It comes drilled with a diagonal hole to receive the brass tube which is where the steel wing rod goes in - this is where you mount each wing and where the wing rod eventually breaks out of the pine carrier block under winch load...
You can consider several ways to fix this...carbon thread wrapped around it soaked in CA, ply laminate on the face of it...or get radical and throw the part out altogether and replace with something beefier (rohacell?) but don't leave it as is - unless you enjoy watching wings fold on launches...(I didn't)
Even though I reinforced it with a laminated ply plate before I planked the wing roots (as suggested in RCM Soaring column at the time - it eventually fractured under load...allowing the wing rod the break out of the wing and the wings to fold.

That said.....I built my 900 with the popular "club mods" at the time in 1989....

-thicken the horizontal stab from the 3/8 by about 50 - 60 %. sanded to a symetrical airfoil shape, with sharpened trailing edge. Also increased stab area by about 10% and you can lighten the tail by putting lightning holes on thickened part

- move spoiler bay out ward to wing tips at least one bay to keep airflow to the stabs clean and help control it during low speed landings using spoilers

- straighten rudder..remove the flying counterbalanced portion of the vertical stab/rudder and mount the rudder perpendicular to the fuselage centerline (ever notice that most modern hi perf. sailplanes appear to have a straight vertical rudder and not that sexy canted LE on the rudder...?)

-sand two pieces of 3/16" hard balsa to the stab root shape and glue to each side of the vertical fin on a neutral line of the horizontal stab root..this will get rid of the notorious stab wobble that develops over time...(you'll need a longer brass tube for the stab mounting music wire joiners ...(I put in a nice little RC car ball bearing in the vertical fin where the stab wire joiners mount in the vertical fin and trued it up during the build ..which made for a very clean fixture for the stab to rotate on...very solid).

- drill out nose block and fill with lead - you'll be putting on more nose weight later anyway...

- if you don't have the replacement FG fuselage...thicken the skinny fuselage where it narrows back near the vertical fin, it is a failure point on hard landings. ...(you have a FG fuse so thats good...I fiberglassed my entire fuse and will do so again so I never had a problem, even when it came in hard after the wings folded and destroyed everythng else....
Last edited by AllThumbs; May 26, 2012 at 07:56 PM.


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