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Old May 17, 2011, 07:13 AM
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Damian Couzoff's Avatar
Melbourne,Victoria,Australia
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Kestrel 17-4.25 Metre span(1/4 scale)

Hi all,l was fortunate enough to purchase a southern sailplanes Kestrel 17 KIT,today.Its complete,minus the wing rod and grommets,and rudder,the seller even threw in a fema retract(new).The wing rod is 1/2 inch in diameter according to the 100 page instruction manual,no plans required.The wing tube is preinstalled in the wing cores with subrib reinforcing.There is also an aluminium tube preinstalled that runs between the wing rod tube and the leading edge,this is meant to be a spar arrangement.I will be adding Australian tasmanian oak- 6mmx6mm sq spars, top and bottom,above and below the wing rod tube,from rootrib to tip,and a 3/4 ounce layer of cloth and laminating resin,before skinnning in either balsa 1.5mm thick sheets,or obeechi.The skins will be covered in 3/4 oz cloth and laminating epoxy resin,sanded,then primed and finished in white auto enamel topcoat.There is a considerable amount of flex in the wings,according to the manual,so by incorporating proper tas oak spars,glass layer under the skins,and on top,will hopefully reduce this flex.The fuse will not have to be painted,the gelcoat is in good condition,l am going to just polish it.The fuse is chop strand/polyester resin,light,these kits were first manafactured in 1977,hence different materials were used.I am going to purchase 370mm graupner spoilers for installation,and have short direct linkage for rudder and elevator(metal gear servos mounted in the fin).Flaps are long,ailerons run along the taper to the tip.There are no winglets,only balsa shaped wing tips.Anyway,there is no rush on this build,l still have other gliders of similiar size to fly,during the building process.-,ASW 27-4.2 metre,DG 808S-4 meter,among others.regards damo
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Old May 17, 2011, 08:40 AM
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North Yorkshire UK, on a big hill facing the prevailing wind. Coincidence?
Joined Oct 2007
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That's a lovely looking kit there Damian. The Kestrel has just about may favourite fuselage shape, although the full size was later criticised for having such a sharp taper into the boom that it caused big flow separation and turbulence. When Slingsby took over production, they reworked the wing roots to help with this. And as a trivia fact, the Slingsby Vega shares the same fuselage as the Kestrel, back to the wing leading edge. Errr... in case you were wondering.

Enjoy it!

Rog
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Old May 17, 2011, 11:48 AM
yyz
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USA, CA, Paso Robles
Joined Dec 2004
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What a great find! You're really going to like this glider. I had the full-scale one and the geometry of the 17m version makes for a very sweet flying ship.

Enjoy,

Mike

ps: Reconsider not painting the fuselage. The older gelcoat will yellow with time.
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Old May 17, 2011, 12:21 PM
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SF Bay Area, USA
Joined Feb 2003
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Nice find. I would first glue in a test piece of former or any structural material using epoxy adhesive in that polyster fuse. Come back a few days later and try yank on it. Special prep may have to be done to the fuse to use epoxy.
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Old May 17, 2011, 09:56 PM
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H Damo yep good find, one word of caution with the model, if the wing cores are the originals get the outboard panels recut with zero washout as the original wings loved to bend down at any speed above cruising. In short they just don't need physical washout and flies great without any. I also remember seeing a kestrel of the same kit snap the wing at the flap aileron joint, but don't worry they fly fine with 3/4 of thr wing remaining. From memory thr joiner in these is where the dihedral was applied, Ie bent in the middle. The wings are thick enough to have dihedral built into them with a straight joiner and would allow you to replace the joiner with a heavier or lighter version to suit the flying conditions. Given the "cheap" price and benefits offered buy obeichi and it's availability thr obeichi is the better option.

Cheers Rossco look forward to the build.
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Old May 18, 2011, 02:59 AM
gizzo don't tweet
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Adelaide, Australia
Joined Jan 2008
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Is that a terrazzo floor Damo? noice! Where you gonna buy obechi?
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Old May 18, 2011, 05:20 AM
I failed linkage geometry
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Melbourne, Australia
Joined Jun 2002
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so rare they can still be purchased brand new from Ralph...........

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Old May 18, 2011, 05:40 AM
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Damian Couzoff's Avatar
Melbourne,Victoria,Australia
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Quote:
Originally Posted by gizzo View Post
Is that a terrazzo floor Damo? noice! Where you gonna buy obechi?
Yes,its a terrazzo floor.The obechi can be purchased from wayne jones,hes ordered a large batch recently, for skinning the cores hes been cutting for customers.
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Old May 18, 2011, 05:47 AM
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Melbourne,Victoria,Australia
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Quote:
Originally Posted by salisbug View Post
so rare they can still be purchased brand new from Ralph...........

The kestrel 17 is not kitted anymore by ralph.I spoke to ralph late last year-quote-the fuse mould is long in the tooth.......unquote.Ralph obviously has not got around to deleting the kestrel 17 from his website.
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Old May 18, 2011, 07:06 AM
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Melbourne,Victoria,Australia
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tip panel join and washout

.The end of the flap and start of the aileron bisect the tip panel join.The aluminium tube spar ends about six inches before the tip panel join,hence prone to breaking at the join-NO SPAR-inherent design flaw by ralph learmont.I am going to have my 6mm sq tas oak spar running from root to the tip on the top.On the bottom it will run also from root rib to approx halfway along the outer tip panel-both over the join.The bottom spar can only go halfway to the tip panel,as the thickness of the tip reduces considerably.However,the spars will flex with the wings and skins,they should not break.The washout is geometric 3.50 degrees-not aerodynamic washout,the wing cores are the original cores,and they do have the washout,as l have checked both,the only cores, not original, are the tailplane cores-naca section.I can get the outer panel cores recut without washout,and in blue foam,not white.l will call andy and he can offer his advice on whether washout is good or no good for the kestrel.regards damo.
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Last edited by Damian Couzoff; May 18, 2011 at 08:35 AM. Reason: Regarding geometric washout-It can cause problems at excessive airspeed
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Old May 18, 2011, 12:55 PM
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Melbourne, Australia
Joined Oct 2005
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One of my all time favorites, this is my second Southern Sailplanes Kestrel, this one nearly 20 years old. This is one kit you will enjoy all the way through! Interested to see the progress.
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Old May 18, 2011, 06:25 PM
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Melbourne, Australia
Joined Aug 2003
309 Posts
Damo,

Its up to you how you build it, But I have one that I bought second hand that is a bit rough. Every time I bring it out I have great flights on it and wonder why I don't clean it up and fly it more. It is built as original, and in fact the tailplane was built inverted.

My wing does tuck at the tips at high speed, but this is NOT what the model was designed for. I regularly have thermal flights greater than 45 mins with this model and often just come down because my neck gets tired. Build it as you will but note that Ralph did an excellent job at the time this model was designed and if flown as designed is fantastic as is.

Steve
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Old May 20, 2011, 06:44 AM
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Damian Couzoff's Avatar
Melbourne,Victoria,Australia
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Great pics andrew.Steve-i agree,the kestrel was not designed for flying at high speeds.I have decided to build the kit as is,l am not going to get new tip panels cut-without the washout,and use the original cores that l purchased with the fuse and tailplane.I have sourced the aluminium wing rod-grade 7075/ T6-12.75mm in diameter-1/2 inch.I still have my spar tools, specially made, when l made my 4 metre DG808S foam core wings,l will save time by not having to make them again.This sunday i will commence work,using the spar tools,and begin inlaying the spars,l will be flying slope tommorow.
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Old May 20, 2011, 07:18 AM
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Australia, VIC, Leongatha
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Quote:
Originally Posted by Damian Couzoff View Post
Great pics andrew.Steve-i agree,the kestrel was not designed for flying at high speeds.I have decided to build the kit as is,l am not going to get new tip panels cut-without the washout,and use the original cores that l purchased with the fuse and tailplane.I have sourced the aluminium wing rod-grade 7075/ T6-12.75mm in diameter-1/2 inch.I still have my spar tools, specially made, when l made my 4 metre DG808S foam core wings,l will save time by not having to make them again.This sunday i will commence work,using the spar tools,and begin inlaying the spars,l will be flying slope tommorow.
Where are you tomorrow flying damo ?

Ant
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Old May 20, 2011, 01:37 PM
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Melbourne, Australia
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I have never had a problem with the wing tips tucking under, then again I don't push it too fast either. From memory I put in a top spar only (full length) then glassed the wings once they were sheeted. The only thing I would do different now is put servos in the wings for the flaps, ailerons and airbrakes. I did replace the kit retract and spoilers with Graupner items. It fly's beautifully and is a great fun build. Attached photo goes back to Bordertown 2000, no less than 8 x Southern Sailplanes Kestrels!
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