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Author Topic: Scalded Cat 18  (Read 1161 times)
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BG
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Me with F1B - epic retrieval (flew 10km after DT)


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« on: May 22, 2012, 10:46:49 PM »

Hi All,
So I am doing a new scalded cat for Craig Limber (least I can do considering all of the effort that he has poured into electronic gadgetry for our modelling efforts). Since I am doing this build and since the design is new and incorporates a few humble innovations i thought i would post some photos and the plan (which will appear in the next issue of the NFFS digest along with a short article.

In the first photos you see my patterns (thin card from cereal boxes) and the parts drawn on the balsa sheet. The wing is on a piece of 4.5# 1/4" C grain. The other bots are on 1/16th. Next photos you see the cut parts ready for the next steps.
Next I add a thin strip of bass to the TE, leaving a little space for sanding washout (don't want to sand the bass away when I add washout). After this I add bass or some other hard wood to the LE.

Last photo shows me adding washout to the underside of each wing tip (1/32 on the inside wing and 1/16 on the outside wing).

Attached files Thumbnail(s):
Scalded Cat 18
Scalded Cat 18
Scalded Cat 18
Scalded Cat 18
Scalded Cat 18
Scalded Cat 18
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F1B guy but its not my fault, Tony made me do it.
BG
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Me with F1B - epic retrieval (flew 10km after DT)


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« Reply #1 on: May 22, 2012, 11:15:16 PM »

So after prepping the blanks etc. I move on to shaping. For the wing I usually shave the blank to nearly the correct thickness using a razor plane and then finish with sand paper. Then I mark the high point line and tape the blank to the table with masking tape. Next I start shaving the rear portion of the airfoil until I am close to the thin strip of bass that I attaches to the TE. THe last pert of this section is to carefully sand the final airfoil in with medium ti fine (350-400 grit) sandpaper. Be careful to cut on the strokes towards the wing and glide on the away strokes. If you cut while pulling away you will tear you TE strip off (ask me how I know this  Roll Eyes ). I sand the wing now until I have a nice smooth flat surface from the TE to the high point. Also note how I set the wing relative to the glass edge...this stops me from cutting too mush off and ensures a nice ~1 mm thick TE.

I follow the same procedure for my stabs and fins. On the Stabs I try not to make em too thin because this makes them floppy and unreliable when it comes to trimming. For these I basically taper the blank from the centre line to tip and then sand the rear to a flat surface. The LE is simply rounded and smoothed.

Back to the wing; for the LE I first shape the upsweep. Here I am using my old SWE36DII upsweep tool .....I really should make a custom tool for this foil.

For the top surface of the LE I use my custom shaping tool (see the templates on the plan for this).

Finally a completed wing held upto the light for a quick check of thickness and evenness.

Next on to the fuselage:
First shot is of the climber timer....this beasty has to go into a cavity in the fuse (see plan).

Attached files Thumbnail(s):
Re: Scalded Cat 18
Re: Scalded Cat 18
Re: Scalded Cat 18
Re: Scalded Cat 18
Re: Scalded Cat 18
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sweepettelee
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Simplicate & add more lightness. Keep sanding!



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« Reply #2 on: May 24, 2012, 12:20:31 PM »

As Gene Wilder said in Young Frankenstein, "Nice grouping."
Am anxious to see SC 18 progress. And THX again!  Grin

Leeper
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BG
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Me with F1B - epic retrieval (flew 10km after DT)


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« Reply #3 on: May 27, 2012, 11:28:53 AM »

Hi All,
First my apologies for my horribly sloppy post above....I was in a bit of a rush Roll Eyes

Now continuing with the build photos....
first you see the balsa fuselage core which has been sandwiched together using thick CA and then squared all round. To square stuff I use either my 90 deg sanding block from my angle sanding tool (I simply place the part on the plate glass and then resting the base of the 90deg. block on the glass surface run the tool around the edges of the part to be squared). Or I use my home made squaring tool which is just a hard balsa angle (90 deg) with sandpaper glued to the inside of one side. With this tool I can square edges by placing the smooth inside surface of the tool flat on the side of the part to be squared and running the side with sandpaper along the edge of the part.

After squaring I taper the nose of the fuselage core. Then I glue the carbon cheeks into place (thick CA). Be careful to use a minimum of glue , but also make sure you get it everywhere it needs to be.
A different approach would be to laminate the carbon onto the core before tapering the core. THen when you are happy with the laminate you use a dremel disc saw to cut the center of the core out. When you do this you have to make sure your slot widens towards the nose. Also while at it you can cut a slot for the ply reinforcement. For the core in the second and third photos I used the latter process.

Attached files Thumbnail(s):
Re: Scalded Cat 18
Re: Scalded Cat 18
Re: Scalded Cat 18
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sirkis
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« Reply #4 on: May 27, 2012, 11:27:20 PM »

Bernard!
thanks for the build report
it's very interesting for me because your CLG's are very light and very well finished
keep going!
Omri
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climber
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« Reply #5 on: June 03, 2012, 09:16:55 PM »

Bernard dropped off two of his Scalded Cats saturday.  They look just fabulous.  It blows me away that a glider with that much wing area can be so light.  I saw one of Bernard's other designs fly for 90 seconds or more quite reliably and expect these will be even better. 
 
I have to build some timers for them before I can fly so I need to try and keep my excitement in check.  As I do I will document the installation here.

Thanks, Bernard!  More timers for you!
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« Reply #6 on: June 08, 2012, 05:46:20 PM »

BG,

Oh wow, please tell us what kind of carbon you are using for the cheek plates, source would be nice too.

Dave
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sweepettelee
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Simplicate & add more lightness. Keep sanding!



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« Reply #7 on: June 08, 2012, 05:57:22 PM »

FYI, thin Fiberglas sheet(.010) or .015 ply works quite
well, & should be easily procured. Weight is comparable.
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Leeper
sweepettelee
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Simplicate & add more lightness. Keep sanding!



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« Reply #8 on: June 10, 2012, 11:42:47 AM »

OOPS! You stated CHEEK plates, what I thought you meant was body SIDE plates.
The cheek plate material should be 1/32 plywood, with grain at 30 degree bias angle for best strength.
If carbon used, I recommend thkns of .010-.015. More thkns will raise weight quickly.
Contact the Gewains at CST for carbon of all sorts. See ads in Model Aviation, etc., or google CST, I imagine.
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Leeper
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