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Old Jan 10, 2011, 05:49 AM
Slip the surly bonds...
Sopwith Mike's Avatar
Christchurch,England
Joined Aug 2004
2,522 Posts
Build Log
Britten-Norman Islander

A few years ago we were on holiday in the Scilly Isles and Wendy and I had walked round St Mary’s (the largest of the islands) in a couple of hours. With a mile or so to go we were sitting at the end of the runway eating out lunchtime sarnies when growling in from the sky came the Britten-Norman Islander G-SSKY, the “Scillies Sky Bus.” This company also operates a couple of Twin Otters, but it was the Islander which took my eye that sunny day. There is another one that ferries flowers and other freight to and from Jersey and flies over our heads most days. The boxy shape is as familiar as the local bus.

The B-N company was located just a short boat ride away on the Isle of Wight, and after a first flight in 1965, over 1100 examples of the type were made in various locations and under a number of owners. Users range from the UK forces for anti-terrorist surveillance to island-hopping for beach-bums like me, and the basic plane has been through a number of variations including the 3-engined Trislander and the Defender, a militarised version that can fire rockets and drop bombs. Its main dimension is a span of just under 50ft (so it is quite a lot smaller than the 65ft span Twin Otter). I can’t find a picture of one on floats, although I have a 3-view and a digitised image. Can anyone confirm that they did actually fit floats to this aircraft?

Following the demise of my Ivan Pettigrew MiniCat I needed a twin of about the same size which could be converted to floats and even, if this weather keeps up, to skis. The Islander plan just cries out to be modelled, so here we go again! The construction will be as simple as I can make it, with the proviso that the wing must be in two halves to assist transportation – perhaps in a box to Chilliwack 2012? The model’s 72” span gives it a scale of about 1/8th.

From a design point of view, it is about as simple as you can get, apart from the undercarriage, which is very stalky and vulnerable. The small wheels will have to be “scaled up” to cope with our flying field but should be OK for the bowling green that our friends of the Fraser Valley MAC maintain. The floats look simple and coupled rudder/throttle will take care of steering on the water.

So, to quote Chris Golds, “to horse.”
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Last edited by Sopwith Mike; Jan 10, 2011 at 08:54 AM. Reason: "Sky Bus" not "Air Bus"
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Old Jan 10, 2011, 05:59 AM
Slip the surly bonds...
Sopwith Mike's Avatar
Christchurch,England
Joined Aug 2004
2,522 Posts
One wing is ready for top sheeting and all the other wing components have been cut, so a week or so should see this component complete. The UC mount still concerns me, and although I have a plan, I wish Messers Britten and Norman had come up with a more modeller-friendly solution.
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Last edited by Sopwith Mike; Jan 18, 2011 at 06:46 AM.
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Old Jan 10, 2011, 09:06 AM
buy a lot, fly a little!
stuart warne's Avatar
Hong Kong, Hong Kong Island, Central And Western District
Joined May 2001
5,659 Posts
Nice project. Always like this plane, looking forward to seeing more.

S.
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Old Jan 10, 2011, 09:21 AM
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RiBell's Avatar
Canada, BC, Abbotsford
Joined Jan 2003
4,670 Posts
Mike:
Will be following along.
Rick
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Old Jan 10, 2011, 04:38 PM
build like there is no 2moz
wallis_100's Avatar
United Kingdom, England, Bristol
Joined Apr 2009
797 Posts
Looking good with the wing Mike

As for the floats, they look about 75% of fuselage length and are about the same length as the full scale twotter ones look.

So long as you keep her light, reasonably powerfull, and the V in the floats fairly shallow, she'dd be fine.

Scott
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Old Jan 10, 2011, 06:21 PM
Tow Dog.
Pilatuspc12's Avatar
United States, CO, Hotchkiss
Joined Oct 2006
1,654 Posts
Mike,

I like the "Defender", it's a turboprop! I have Rich Uravitch's plans for the smaller 70 inch wingspan version. It looks like a fine build.

Cheers,

Randy
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Old Jan 11, 2011, 12:58 AM
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LukeZ's Avatar
Joined May 2001
2,902 Posts
Well Mike, no grass grows under your feet. Signing on!

The construction looks straight-forward enough, I bet you have this one done in record time. A lot less curvy stuff than your P-51, which was also built in record time!


Luke
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Old Jan 11, 2011, 06:38 AM
Slip the surly bonds...
Sopwith Mike's Avatar
Christchurch,England
Joined Aug 2004
2,522 Posts
When I said the build was "typically Ivan" I have made a couple of small changes to the way the wings are constructed which I think makes for a stronger structure without any weight penalty. I use 1.5 x 20mm balsa sheet top and bottom for the trailing edge, sanding the bottom one to a feather edge before gluing on the top sheet. This is much easier to handle than shaped TE and gets away from the unsightly notching that's needed to locate the rib ends. It's also lighter and makes a much firmer joint, so that the flap and aileron can be cut away with no fear of the semi-built structures falling apart.

I also use rib cap strips. This makes each rib an I-beam and calms those "surely he can't be serious, using 1/16th ribs on a 100" wing" fears when approaching one of Ivan's larger designs.

Which is a long way round of saying that the flap and aileron are separated from the starboard wing!
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Last edited by Sopwith Mike; Jan 11, 2011 at 10:07 AM.
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Old Jan 12, 2011, 01:08 AM
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Quote:
Originally Posted by Sopwith Mike View Post
I also use rib cap strips. This makes each rib an I-beam and calms those "surely he can't be serious, using 1/16th ribs on a 100" wing" fears when approaching one of Ivan's larger designs.
Or even worse, "surely he can't be serious, using a 1/16th SPAR on a 100 inch wing!"
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Old Jan 12, 2011, 03:06 AM
Slip the surly bonds...
Sopwith Mike's Avatar
Christchurch,England
Joined Aug 2004
2,522 Posts
That's right Luke, I'm using 1/16th for the vertical spar on this model, but have extended the 3mm sq spruce caps right out to the tip - blasphemy!

In my defence, I propose that we design and build models for the prevailing conditions at our strips, and living on the S Coast here, the mean windspeed is around 8-10 kts during the day, whereas at Chilliwack, it seems to be 2-3 kts.

I rest my case.
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Old Jan 12, 2011, 03:21 AM
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Trevorh's Avatar
Hampshire, U.K.
Joined Jun 2008
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Mike, I don't remember wind speed figuring in any equations I have seen for calculating spar size - but you do read a lot more than I do
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Old Jan 12, 2011, 05:44 AM
Slip the surly bonds...
Sopwith Mike's Avatar
Christchurch,England
Joined Aug 2004
2,522 Posts
Quote:
Originally Posted by Trevorh View Post
Mike, I don't remember wind speed figuring in any equations I have seen for calculating spar size - but you do read a lot more than I do
Perhaps I should have been more honest, but I was hoping to preserve a vestige of respect in the RC Groups community. What I should have said was that I have an addictive need to "strengthen up" any design, against its eventual demise. I'm learning to do without 3mm hardwood main spars, but it's been a long hard struggle.

Just in case my description of the "My-van'" TE construction method was not clear, here is a sketch of the way I build them.
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Old Jan 12, 2011, 09:15 AM
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RiBell's Avatar
Canada, BC, Abbotsford
Joined Jan 2003
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Quote:
Originally Posted by Trevorh View Post
Mike, I don't remember wind speed figuring in any equations I have seen for calculating spar size - but you do read a lot more than I do
The only reason that I can think of is that with higher wind speeds. The flight can get a lot more bumpy. A beefier spar will handle a higher "G" loading that can be present in bumpy conditions.
Rick
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Old Jan 12, 2011, 09:17 AM
Slip the surly bonds...
Sopwith Mike's Avatar
Christchurch,England
Joined Aug 2004
2,522 Posts
Quote:
Originally Posted by RiBell View Post
The only reason that I can think of is that with higher wind speeds the flight can get a lot more bumpy. Rick
...and the landing!
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Old Jan 12, 2011, 10:19 AM
The Hun in the Sun
vonJaerschky's Avatar
Canada, BC, Comox
Joined Nov 2003
7,226 Posts
...and the trees.

Looking good Mike!
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