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Old Mar 08, 2013, 04:07 AM
AvB
Wind, hill, ... I'm keen ...
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Yep that one's in the panelbeating shop!
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Old Mar 08, 2013, 03:39 PM
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Scratcho.
Hi AvB, having read your thread on your Scratcho, brilliant.
I am interested in scratch building a Scratcho. Is there any chance of getting a 3 view drawing with dimensions ?

Steve 827
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Old Mar 08, 2013, 04:49 PM
AvB
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Yeah Steve, definitely. I have drawings of the wing, stab and fin done in CAD.

I don't have drawing of the fuz but I can take some shots and put some dimensions in.

I'll get onto it and upload them and I can put a link here so you can download them. Gimme a day or so.

I'd love it if other guys started making Scratchos!
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Old Mar 08, 2013, 04:54 PM
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Thanks AvB.
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Old Mar 08, 2013, 09:13 PM
AvB
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This link should give you access to a shared folder which has all the pdf CAD drawings for the wing, stab and fin. They also shows the hingeline and hinge cut positions, bolt holes etc.

There's a hand-drawn sketch that shows the relative positions of wing, stab and fin.

Also a few plan and side view photos.

I have a document that I've been gradually building up where I record notes on the build. If anyone does have a serious go at making one and wants that info, let me know and I'll update it and clean it up for public consumption.

If anyone can make enough of them to sell it would be great! A lot of guys, some pretty big names too, have asked me for one and I just can't do it. Hey if they're made tough I'd buy one!

Before anyone starts yelling about the weird foil used for the fin and stab in these drawings, I'll explain. All of the scratchos so far have used flat profile fin and stab, just tapered at the LE and TE. Even the moulds were made from plugs like that. They fly brilliantly.

When designing these CAD versions, I wanted to increase the foil, but I didn't want to completely lose the flat areas in the mid chord for the simple reason that they are very useful for setting the stab level and the fin straight! By having a flat surface you can use a small spirit level to level the stab. And clamp aluminium angle lengths to the fin and line them up with the nose while the glue dries. If you crash and break the boom it's nice to be able to block up the plane and level the wing on the bench, then use the spirit level and aluminium angles to set the stab and fin straight again while the boom repair sets. I know it's not conventional or beautiful but the Scratcho is designed to be practical and strong and easy to do in the shed, and easy to fix ... like the plaster screws used to hold the wing into thick plaques of carbon in the wing saddle - simple and very effective. And the PU foam expanded in the boom ... ugly but adds so much durability, so you get more flying time and less repair time.

Here's the link to the folder. I hope it works.

https://files.secureserver.net/0fSdZoDHlEWMmJ
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Last edited by AvB; Mar 08, 2013 at 09:24 PM.
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Old Mar 08, 2013, 09:38 PM
AvB
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I also have the drawings for the wing, fin and stab converted into moulds as .stp and .iges files if anyone had access to CNC and wanted to make moulds!
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Old Mar 09, 2013, 05:52 AM
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Very cool andrew... Scratcho's all around the world..

Tim
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Old Mar 09, 2013, 03:23 PM
Where is the inspiration
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Moira
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Note to self
Get cracking on the curved wing tip Scratcho

I will get it done Andrew.

Have you decided to go straight to cavities on the fin and stab? not too concerned about the stab, but how are you going to get around the cutter rad on the fin? do it by hand? or insert?

Will
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Old Mar 09, 2013, 06:35 PM
AvB
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Definitely don't do the curved tip Will. I've decided there are too many projects on the go (for both of us!)

Not sure about the cutter rad ... I'm leaving it to Mike. Yes, straight to cavities.
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Old Mar 09, 2013, 09:05 PM
ERS....Energy Retention System
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Geoff used a 3mm round for my gizmo tail. Had a few small bits had to Finnish by hand around the tip if the tail. If that helps.

Tim
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Old Mar 11, 2013, 02:09 PM
Where is the inspiration
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Moira
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Quote:
Originally Posted by AvB View Post
Definitely don't do the curved tip Will. I've decided there are too many projects on the go (for both of us!)

Not sure about the cutter rad ... I'm leaving it to Mike. Yes, straight to cavities.
I want to do it then you can decide
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Old Mar 15, 2013, 02:41 AM
AvB
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This is the wing that got all the shrubbery smashed into the leading edges DSing at Byron Bay. The fuse also needed patching up at the tail and behind the wing saddle. Completely repaired and bogged up and repainted - only added 60gms to the total weight! Not bad. It's not perfect, but looks a bit more respectable than before. I intended to airbrush a band of black across the curve where the fluoro orange and yellow merge, but haven't got round to it yet. I experimented with using just the airbrush to cover the tips with the fluoro, but it wasn't a great success - it's pretty bumpy due to having to really work to get the coverage with the small jet.

I realized I have 5 Scratchos here all flyable:
1) The one in the pic (half-core light version)
2) Green/ yellow glass with full foam core and Ampreg
3) Very light PU experimental white one (the best light-air fun yet)
4) Very heavy one built for the US last year.
5) Peter's glass one like 2) which is ready to send over to NZ.

Also I have the new PU wing with the solid edges and tips, and I hope to make another fuse for it soon and get it airborne.
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Old Mar 15, 2013, 03:32 AM
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Any light ones for sale? Would like one in Vic
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Old Mar 15, 2013, 04:48 AM
AvB
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I'll let you know if one becomes available Mick.

I got down to the beach for a short fly this arvo. Wasn't big wind, so flew the light white PU one, and the newly repaired half-core (HC) one. Rhys came down too and we swapped the transmitter back and forth. The PU was nice, light, nimble as usual, but today the HC was the star performer. Even in the lightish air it was so fast, so locked in, soared beautifully and really responsive. The pretend F3F turns seemed really fast and neat. I hardly needed to push down to fly inverted, so perhaps the CG could go forward a bit.

We were commenting that we've never yet had a tip stalling problem with a Scratcho. They just seem to stay stable. When we pushed the CG of a Scratcho back too far they start to balloon in lift and get pitchy and over-responsive to camber or flap, but they don't seem to tip stall.
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Old Mar 15, 2013, 06:37 PM
AvB
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Rhys has shaped up some tiplets for the Scratcho! He’s been doing full size gliding and now studying for his private GA license, and everything he saw and read made him wonder if tiplets could make a difference. Yesterday he said he had a “surprise” for me and at the beach, presented me with these 2 nicely shaped tiplets! He’s used his Ampreg Scratcho to shape the mount, and angled them slightly inwards based on some research he did. To say I was impressed would be an understatement!

The pics show one tiplet just taped on loosely with Sellotape. I’m looking forward to trying these out, both frontside and DS.
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