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Old Jul 03, 2015, 06:44 PM
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Build Log
Hs748

OK - the following will describe an attempt at a scratch build Hawker Siddeley 748 from 3-view drawings I bought a while ago from Nexus and scaled up a lot at the local photocopy shop.

Specs are roughly as follows:
87" Span
Wing area 655 sq in
Root Chord 280mm
Root section NACA4415
Tip Chord 120mm
Tip section Clark Y
2.5 degrees of washout
6 degrees of dihedral
Target weight <7lbs
Wing Cube loading 12-13
Wing Loading <23 oz per sq ft

All balsa and ply construction although Depron would no doubt produce a more sedate flyer. Next time maybe.

Anyway - you'll have to be a bit patient with me as work commitments have kept me away from this project for a month or two. Some peer pressure might help regain some momentum.

Here is a quick update on progress made so far...
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Old Jul 03, 2015, 06:48 PM
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Started with the tail fin - an all built up affair using 2.5mm balsa for the ribs, 1.5mm balsa for the sheeting and some thicker balsa for the uprights that will support the control surface...
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Old Jul 03, 2015, 06:57 PM
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Have also started on the fuselage. I wasted a lot of time and effort by beginning to build a left and a right fuselage half only to conclude that I would be much better off building a top and a bottom fuselage half in terms of later ease in aligning the tail fin, the horizontal stab and the proposed access hatch.

To keep weight down, I've gone to a bit of effort with the lightening holes on all the ribs and keels.
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Old Jul 03, 2015, 07:04 PM
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The fuselage skin is 2.5mm balsa before sanding. Its all light enough so far but I will need to keep a weather eye on weight as things progress; I'm currently thinking I'll go with a fully sheeted wing but can drop that back to D box only if weight gets threatening.
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Old Jul 03, 2015, 07:05 PM
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Old Jul 03, 2015, 07:07 PM
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Top half largely done...
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Old Jul 03, 2015, 07:19 PM
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I always give respect to anyone who can scratchbuild with Balsa. . . . One of the hardest techniques to master.

Beautiful craftsmanship Sir.
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Old Jul 03, 2015, 08:36 PM
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Looking great so far! Keep on it!
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Old Jul 03, 2015, 10:17 PM
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Cool aircraft and excellent balsa work, subscribed!
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Old Jul 03, 2015, 10:26 PM
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To build the lower half of the fuselage I made a cradle out of MDF, flipped the top half of the fuselage over onto the cradle and then starting to build the lower half directly on the top half using plenty of waxy paper to make sure that the two halves didn't join themselves together prematurely.
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Old Jul 03, 2015, 10:38 PM
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You've almost caught up with me now...next came the horizontal stabiliser which, again, is fully built up with three way taper (section depth, chord). It is quite a big unit by itself with just over 32"span.

Like the tail fin, the horizontal stab is built into the structure. The beauty of having a top and bottom fuselage structure is that it makes it very easy to set the tail assembly up level/perpendicular with everything else because the fuselage half is sitting flat on the building board.
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Old Jul 03, 2015, 10:48 PM
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I've just finished planking the remainder of the fuselage. Now ready for the centre section of the wing. Things will slow down now... and I need some advice.

For the wing, I am going to have two spars; a main spar and a rear spar to hang the flaps and ailerons from. The rear spar will be a single piece of 5mm balsa joined to the ribs through a lower slot.

I'm tempted to do the same (a slotted spar in a single piece) for the main spar but then wondered whether I might be better having a top and bottom spar with webbing between the ribs. There may not be much in it but I want the strongest structure given the span. Any firm ideas out there on which of the two is likely to be more bullet proof?
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Old Jul 03, 2015, 10:55 PM
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I should have said already that the finished product will look like this with any luck...
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Old Jul 03, 2015, 11:00 PM
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Quote:
Originally Posted by Rt737 View Post
I should have said already that the finished product will look like this with any luck...
Mount cook of New Zealand. . . . Excellent choice Sir.

I have the feeling your 748 is already finished . . . Hence the fast rapid-fire pace of your build thread.
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Old Jul 03, 2015, 11:34 PM
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Thanks for the compliments. Much appreciated.
No - you've caught up with the build now. This is where I have got to.
I am ready to cut out all the wing ribs which I've printed using one of the wing design software programmes (that was quite good fun all on its own).
It'll be slow progress now as I'm away next week and the building fits in when work and family permit. It's taken about 6 months on and off to get to this point - in elapsed time I'd say 2-3 weeks work. I'm quite quick when I'm on the job but I'm not on the job often!
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