Lumenier RB2205C-12 2400KV SKITZO Ceramic Bearing Motor
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Old Dec 18, 2012, 05:54 AM
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The only place the difference in airfoils is going to be noticeable is in competitions when you're down to measuring performance in fine accuracy. Then you have choices to make depending on whether you're going for speed, duration or aerobatics... or maybe a mix of all of them. At that level if you add or save an ounce of weight on the model it might tip you to another section.

I am emphatically NOT at that level, nor do I aspire to be.

I don't even design my airfoils to any known contour - just something that looks about right to the full-size. Even if I did I would be very surprised if my standard of building managed to reproduce it accurately. It's just not worth the effort in my book. My test criteria (with my feet firmly on the ground and transmitter in hand) boil down to 'does it look and fly about right?'

Actually with Reynolds numbers (whatever they are!) militating against smaller wings we sometimes have to cut corners in all sorts of areas to get a really nice-flying model anyway.

'If it works why change it?'
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Old Dec 18, 2012, 10:51 AM
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So how's this build going? You are making me want to build this plane for summer water flying...
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Old Dec 23, 2012, 08:16 AM
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Hello Steve et al.
The build has gone nowhere over the last two weeks, but my wife and I have covered 3500 miles on the good ship Adonia as a way of escaping the English weather for a while! Thanks for keeping the thread alive for me
Old Dec 29, 2012, 10:09 AM
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build like there is no 2moz
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Trevor ... Looking good :-)
Sounds like you had a good cruise. Hope all is well
Old Dec 29, 2012, 04:24 PM
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Looking good indeed!
That tailplane wouldn't look out of place on a H.P. Victor - very stylish.
Old Dec 30, 2012, 04:38 AM
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Thanks for the kind comments guys - a bit of encouragement goes a long way, especially at this stage of the build where things seem to be going so slowly.

Because of its size and vulnerability, I'm thinking about making the tailplane removable. In practice, the model may well be stored in one piece in the garage (assuming it will fit in the car) but I feel that, if the tailplane bolts on, it will be less of a disaster if/when it does get a knock.

There is a pair of bolt-on aluminium tube struts shown on the plan which run from the mid trailing edge of the tailplane to the trailing edge of the fin. I will be fitting these in any case but, when it comes to bolting the tailplane to the all balsa fin top, I would plan to drill a couple of holes in the fin top and glue in short lengths of 1/4in diameter dowel to take small screws. The corresponding holes in the tailplane would be sleeved with aluminium tube to take the compression loads.

What does the panel think?
Old Dec 30, 2012, 05:30 AM
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Slip the surly bonds...
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A detachable tail would be an advantage especially with that very elegant design. Nicely done!

Mike
Old Dec 30, 2012, 08:28 AM
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It would certainly reduce the amount of hangar rash suffered but add a bit of weight at the wrong end - but make sure it doesn't emulate the Victor by having it come off at the wrong moment!
Old Dec 30, 2012, 11:29 AM
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Removable Stab is a good idea, but I would not use small screws. I would use 6-32" nylon bolts. You can tap the hardwood dowels in the fin to accept. Then use 1/16" or 1/8" plywood plate on the stab to take the compression load. It will ruin your day if that stab comes off in flight
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Old Dec 30, 2012, 12:41 PM
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Oh dear, I don't like all this talk of departing tailplanes! In normal flight the tailplane should be pressed onto the fin top but in inverted flight the fixings would be under tension so I agree they need to be up to the job. Funnily enough, I reckon I would be happier with a bolt on arrangement than with glue. The glue would undoubtedly hold but if that tailplane gets a knock the bond could easily be weakened and go unnoticed.

For today, I have been concentrating on the struts. It took a bit of tweaking to get the flattened ends correctly angled but it all seems to be lining up pretty well now. With the struts in place and two pins through the stab into the top of the fin, it feels remarkably solid so I'm beginning to feel more comfortable about the detachable approach. One method I have used before (although I can't remember in what circumstances) would be to glue a couple of pieces of Sullivan snake inner into the top of the fin instead of the dowels. The metric version of Sullivan snakes which I am using will take a 2mm machine screw which definitely won't let go. It will all then come down to how well the snake inners are bonded into the fin and the how well the ali tubes (or ply inserts) spread the load into the tailplane.

However, I can defer the final decision for a while yet, my immediate aim being to get as much done as possible before fitting the fin to the fuselage. This includes sorting out the elevator horn positions and orientations (the geometry of the snakes and the hinge lines isn't ideal, so this will be a ball link arrangement).
Old Dec 31, 2012, 03:06 PM
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Okay, final photo of the year! This was a last trial assembly before gluing the fin on for real (which will be the ceremonial first job of 2013). I couldn't resist putting the control surfaces on so this one picture captures all the work to date.

Weight of what you see is 1lb 8oz, including all servos. It's still hard to estimate an AUW at this stage but I would guess about 4lb 8oz which in my book makes it a 4s x 3000mah aeroplane so I will start looking for suitable motors soon.

Thanks for all the support and comments - keep them coming - and here's wishing you all the best for 2013.

Trevor
Old Dec 31, 2012, 04:24 PM
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Yes, estimating final AUW is not my strong point either Fox Moth's fus was just under 2 pounds a couple of weeks ago, now covered and with doors and wheels added it's suddenly double that. How did that happen?

Not worried though - and I don't suppose you are either. That Aquabird has loads of wing area.

I tried the FM on 2S with scale prop and thought it might just fly at that - but I fully expect 3S to be where I land up with it.

Happy New Year to one and all!
Old Dec 31, 2012, 07:55 PM
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If you are just under 2 lbs at this stage, my guess is your AUW will be just over 3 lbs.
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Old Jan 01, 2013, 07:48 AM
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That was the way I was thinking a week or two back Steve!

Trevor's Aquabird still needs wing tips and floats, covering, Motor, ESC, batteries...


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