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Updating a Protech Topic 400


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Found this lurking in the loft...

topic 400.jpg

1.5 M span with a Speed 400 - very under powered by today's standards. Got me thinking though. The wing is very good and quite light. All it needs is a new fuselage, motor and prop and ESC, radio gear, and lighter tail feathers.

speadsheet.jpg

Here's my target design spreadsheet. Looking to save over 200 grammes in the process.

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Made a start, thanks to Hyperflight.

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And even dusted off some old drawing skills!

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Nice model, as I remember they float very nicely. The only issue you are likely to have is achieving the CG - with a modern brushless and lipo powertrain you are likely to need a fair bit of noseweight. That new fuse looks a smidge longer in the nose though, so perhaps you will be ok.

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Posted by MattyB on 30/01/2018 16:10:39:

Nice model, as I remember they float very nicely. The only issue you are likely to have is achieving the CG - with a modern brushless and lipo powertrain you are likely to need a fair bit of noseweight. That new fuse looks a smidge longer in the nose though, so perhaps you will be ok.

Yes, you're right re CG. But a few factors work in my favour. The Pod and Carbon boom is very light - so the trick will be to build the stab and fin as light as possible and then adjust the boom length! The new fuselage will be nearly two ounces (54g) lighter - and much of that weight saved behind the CG. There is a trade off that with longer tail moment I can use a smaller tail. The SailplaneCalc design spreadsheet really helps here.

 

Edited By FilmBuff on 30/01/2018 16:57:39

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tailplane.jpg

Simple, light but strong AMT that will fit on the Blaster V mount. Great wood selection from SLEC. In it's naked form (needs more shaping) it's just under 10g, and with covering and the mount will be smack on my 15g target. That's less than half the weight of the original.

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  • 2 weeks later...
  • 3 months later...

Test flew in the calm between thunderstorms. Exceeded expectations. Launched on 20% power initially and then pulled it near vertical to around 150m. Stall and dive tests revealed CG needs moving forwards a smidgeon.

Hang time for a 1.5m glider is amazing. Weighs around 440 grams with a wing loading of around 6oz/sq ft. Funny how we mix units...

Little 2S 1300 battery gave me a 40 min dead air flight with 50% charge remaining.

First time with Spektrum. Liking the programming interface.

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Edited By FilmBuff on 07/06/2018 19:10:13

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