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BN2 Islander, Refurb blog

Refurbing a 30 year old BN2 model and converting it to Radio from Control line.

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Andy G.24/10/2017 19:12:16
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326 forum posts
179 photos

Hi all

Some of you may have seen my other posting asking for plans/info on this aircraft so you'll know what's potentially planned here. For those who missed the posting let's start with a brief synopsis. About 30 years ago a good friend of mine started to build a MAP BN2 Britten Norman Islander, The Duncan Knutson one. He built it to be flown control line, 3 line control, for 2 throttled Thunder Tiger 25's. The model got to about 95% finished and then for various reasons the build stalled. I then bought the model, just as circumstances forced me to shelve model flying for a couple of decades, so the model languished forlornly in my attic along with all my other control line and free flight models. I hadn't at that time taken up the 'black art' of radio control. Earlier this year, after an unsucsessful attempt to sell the model on at a control line meeting, I decided to refurb it. My original plan was to just tidy it up, finish off a couple of bits and fly it as intended. But, as my control line flying is limited, due to having to travel quite a considerable distance for a suitable site, it seemed more sensible to re-convert it into the radio plane the designer had originally intended.

So.. the descision was made to strip out the 25's and go electric. and some preliminary exploration work and a strip out began on the airframe. The model had suffered hanger rash and some very serious paint degradation over the years, and wasps had nibbled part of one wing tip away, but all in all the work and expense required to get this to flying state didn't seem too bad, and it would give me something I didn't have in my fleet, a large scale (twin) model.

So.. here goes the build/refurb blog, I'm a little way in now and have taken photos as I've gone, this is basically my 'Winter Project' so the blog will get off to a quick start using the back log of photos etc, then probably slow down a little.

To start with... a few pics of the model as a control liner, before any work started..

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McG 696925/10/2017 07:07:42
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1674 forum posts
730 photos

Subscribed, young man. yes

Cheers

Chris

Andy G.25/10/2017 14:11:34
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326 forum posts
179 photos

Welcome on board Chris!..

One point perhaps I should have made at the start of the preamble was that I live on the Isle of Wight, and my Model club fly from Bembridge Airport where of course John Britten and Des Norman designed, developed and built the Islander for most of it's life. BN have now moved production away from Bembridge although the company still maintains a facility there. So it will be rather nostalgic to fly the model from there and get that old familiar shape back into the air over the site.

The Refurb continued:

Stage one was checking the airframe and noting any obvious damage, There was a large crack in one fuselage side beneath the tail, a small hole and dent in one wing as well as the wasp damage to the tip and the tail fin was a little wobbly.

The refurb continued with a strip out of all the control line related equipment which was no longer needed. The inboard tip line guide was a rather intricately bent piano wire assembly which was bolted to the wing tip, this was easily removed. Over on the outboard tip, the adjustable tip weight box was opened up to see if there was any tip weight in there. Next go to was the Jim Clarkstyle 3 line bellcrank assembly. With 3 line control systems ( where all 3 lines are indentical length) operating the third throttle line makes the 2 elevator control lines go slack meaning no or reduced control. To counter this the bellcrank is a two part device in which the main elevator belcrank is mounted on the secondary throttle bellcrank and physically moves in and outboard as the throttle line is tensioned or released, thus maintaining line tension. A benefit of this is that as you release pressure on the throttle line to decrease power the centrifugal force of the aircraft pulls the assembly backwards and moves the throttle towards the idle position.

Photos of the bellcrank assembly below.dscf0704small.jpg

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First pic shows the bellcrank system with the loop upto the wing fixing area where the throttle pick up point locates into the right angle crank on that cross bearer. The second pic shows a closer view of the 2 part bellcrank, now unobscured by the spreader and throttle pick up which has been cut away, the sliding mechanism is unfortunately concealed by the bellcrank itself. The third pic shows the 3 leadouts exiting the fuselage side.

Once the above was removed the next job was to strip out the two engines and the home made tanks..

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As a matter of interest the motors were then weighed. each Thunder Tiger 25 with silencer, prop and mount weighs 258 gms. The intended brushless motors complete with their mounting cage weigh 203 gms each. The motors I intend to use ( I already have one from an unfinished project) are from Power Max and are 1250Kv 590 watt units. So power unit weights, once tanks or esc's are included are pretty close, although I believe the electric set up will develop more power output, which should more than compensate for Lipo weight etc.

More to follow.

FastFlyer Smyth25/10/2017 15:16:02
294 forum posts
10 photos

yes

Percy Verance25/10/2017 17:48:19
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5713 forum posts
108 photos

Andy

Don't forget to have a little dig into the starboard wingtip, as there will almost certainly be some weight stashed there to keep the lines tight. Ex c/l flyer here...........

Scrub that Andy, I've just re-read the post..........

Edited By Percy Verance on 25/10/2017 17:49:23

Andy G.25/10/2017 19:38:02
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326 forum posts
179 photos

Once the motors,tanks and control system were out more probing and exploring took place followed by the removal of the badly crazed paint from the fuselage. It was during this procedure that the 'wobbly' tail fin became ever more wobbly, and finally parted from the fuselage. In actual fact this wasn't the problem it first seemed, as it made it far easier to work on the fin ( and the fuselage). The first thing was to cut the fixed (biased) rudder part free from the fin and sand the rudder offset out of it, then radius the edges of the rudder and fin ready for later hinging. I took the opportunity to fit a ply 'skeg' into the bottom of the fin which will help to fix the rudder more firmly, plus added some gusseting along the bottom edge. It's a very high fin and the subsequent leverage on it could make it prone to damage.

One of my trusty permagrit blocks was put to good work removing the old paint from the fuselage, it coming off relatively easily. I noticed that the construction method for the fuselage was a little unusual in that instead of fairly sturdy sides and then cross grain top sheeting, this model has very thick top and bottom length wise grain sheeting and ( IMO) far too thin and inadequately supported side sheeting. The friend that sold the the model suggested at the time that before it was ever flown the rear fuselage should be strengthened.

The fragility of the structure became apparent when, whilst sanding my finger and thumb created a split come hole in the centre of the sheet! My first idea was to reach inside, down through the fuselage, push the imprint back out straight, seal with CA then apply a small support doubler inside. This sort of worked, but I certainly wasn't happy with the strength even then. Much pondering took place, part of which included the need to adequately support the snakes going to the tail end. Originally,of course, only the elevator moved, via a dowel pushrod, this needed upgrading and now I needed to operate the rudder as well. So, it was crunch time. I took the bull by the horns and cut a very large opening in the broken side, so that I could fit full size doubler to the other side, and to provide supports for the snakes. The original fuselage is quite high, over 5 inches at one point so it's made from 2 sheets of 3" butt jointed, it's probably 1/8 or 3/32 sheet, and only has 3 formers between the wing t.e and the extreme rear. So I added a thick partial depth former to reinforce the sides and to route the snakes.

Pics follow..

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Attack of the permagrit monster.

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An out of sequence shot, showing the 'control bay' after emptying.

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Internal fuselage structure, showing the side sheet butt joints and general lack of internal support. Dowel pushrod to elevator.

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Open heart surgery on the fuselage, showing the new thick partial depth former and the doublers on the opposite side, this side, when rebuilt had an inner sheet fixed first then the outer sheet to bring it up flush to the existing sheeting.

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One snake in, waiting for the other one to be installed.

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Rudder snake exit.

Andy G.26/10/2017 11:38:26
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326 forum posts
179 photos

A few more photos.....

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The completed additional former, and also additional structure to the next former down for strength and snake support.

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Inner sheeting, supported by the former and with an internal overlap at each end.

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Outer skin, flushed with existing skin. The bay forward of this area, is acsesible from the open fuselage at the wing area so that bay had it's doublers fitted easily.

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You've been Tango'd!!! Once the fuselage had been resheeted, filled and rubbed down I covered it with heavy weight modelspan tissue applied with polyurethane varnish ( Poly C equivalent) to add additional strength and help with the final finish. Why orange? It was the colour I had by far the most of in stock. It certainly won't be this lurid colour when it's finished, so don't panic.. I've been browsing the net for a final scheme, plenty of time to come up with one yet as this is really my winter project, but currently I'm down to a short list of 3, with one scheme having quite a considerable lead..

More to follow if anyone is interested.. ... teeth

McG 696926/10/2017 12:07:06
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1674 forum posts
730 photos

... maybe a Belgian deco scheme, Andy... ??? yes wink

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Cheers

Chris

Andy G.26/10/2017 12:55:22
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326 forum posts
179 photos

Thanks Chris!

That's not a scheme I had seen, and it's rather attractive, plus simple.. I like simple, it reminds me of me!

Maybe the short list has stretched to four now!..

i was going to hold this back until later, but.. here's the current front runner.. A small New Zealand airline..

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Certainly cheap on paint! laugh

McG 696926/10/2017 20:38:36
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1674 forum posts
730 photos

For sure the Kiwi example remains cheap on paint, Andy.

But I keep thinking that the Belgian Survey Islander gives a better view against the clouds.

I bought a very nice ARTF Islander (made in Taiwan, not China) from a German shop some months ago and the quality seems vastly superior than common Shenzhen items.

I then started to collect some deco pics for it, so, if you go for the Belgian one, I can send you some info & pics.

Cheers

Chris

Martian26/10/2017 21:55:54
1612 forum posts
773 photos

Always liked the Islander look forward to following this refurb

Andy G.27/10/2017 08:38:41
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326 forum posts
179 photos

Thanks Chris, that scheme has definitely been added to the short list! I take it you're doing your ARTF in that scheme?

McG 696927/10/2017 10:25:02
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1674 forum posts
730 photos

Not sure about the deco scheme yet, Andy.

I still could pick some 'exotic' version or even 'invent' a small airline from Bora Bora featuring some vivid colours... sometimes I become a victim of my own imagination. blush

My first idea was a Belgian Army Islander as we used to have some for transport & liaison back in the seventies. But then their colour scheme is really ugly (for me it is). Have a look here at the Belgian Wings site.

In fact, the Sea Survey one (OO-MMM) is the former military B-02, refurbished at Bembridge (Isle of Wight, UK) and modified with special equipment (SLAR, IR, UV) for maritime pollution control in 2004. BMM also owns B-09 that is used for spare parts. They operate from Ostend Airport with nearly daily survey flights.

Cheers

Chris

Andy G.29/10/2017 09:53:14
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326 forum posts
179 photos

@ Chris... Any additional info you have on that scheme would be appreciated.. Did you pickup from one of my earlier posts that I actually fly at Bembridge airport, Isle of Wight where B-02 was refurbed, ( and probably built) ?.

..................

On with the blog pics.

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First explanatory openings into the wing. Having no idea of the actual internal structure due to no plan, I did some probing with a pin before cutting a small hole, then increasing it on either side of the centre rib. In this pic you can see the piano wire linkage that goes to the throttle bellcranks.

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Close up of the linkage mechanism. Don't think it's going to be worth the effort of trying to get this removed, especially as the bellcranks are inside the wing under the engine nacelles, so I'll probably just cut off the short external pick up arm.

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Trial lay up of the proposed motor and mount cage in one nacelle. Seems to fit quite nicely only requiring a small addition to the height of the firewall to pick up the top fixings.

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Motor details. If anyone is interested... the 2 Thunder Tiger 25's are available....Very cheap.. they were bought new for this project and were apparently bench run / run in but have not been flown in anything. They turn over OK but have been in the stored plane since it was put away.. The carbs need stripping and de-gumming.

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More to follow..

Percy Verance29/10/2017 10:04:30
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5713 forum posts
108 photos

Wow, a little bit of overkill in the power department maybe?

Andy G.29/10/2017 10:12:01
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326 forum posts
179 photos

Percy...

There will certainly be enough power, I think! Truth is, I had that motor over from an unfinished project, and it will be easy to get another one to match. Plus they fit physically quite nicely. I am going to be a little limited as to prop diameter by the physical gap between the nacelle and the fuselage, so may not be developing quite as much urge as it might appear. Failing that, it will be down to the prudence with the left hand stick!..... ...devil


McG 696929/10/2017 11:35:35
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1674 forum posts
730 photos

Hi Andy,

So, is the OO-MMM getting a higher ranking in your deco list? smiley

To be honest I didn't make the link with Bembridge and your actual flying area. The Belgian Islanders (and a lot of others) were built in Belgium at the former Avions Fairey (now Sonaca) at Gosselies Airport (now Charleroi Airport / EBCI).

If you want some info about this 'special' Islander, try the link here. It's dedicated to the OO-MMM.

Its first livery in early 2000 was like this, already equipped with 2 SLAR lateral tubes:

islander_b02_bierset_june2000.jpg

The legend of the pic says >

"SLAR equipped Britten Norman BN2B-21 B-02 operated by the Light Aviation of the Belgian Army seen at Bierset airbase on June 3rd 2000.

The SLAR (Side Looking Airborne Radar) was used during pollution control flights over the Belgian territorial waters of the North Sea".

I've been reading somewhere that OO-MMM got some new colours (still red & white) early this year.

I can have a look for more pictures if you decide to take OO-MMM's deco scheme.

Cheers

Chris

Andy G.29/10/2017 11:45:18
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326 forum posts
179 photos

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Chris.....

Britten Norman's facility in the background of this airborne shot.. Actually, BN have moved a lot of their operation across the Solent to Lee on Solent airfield ( the old HMNAS Daeddelus ) , but they still maintain a small presence here at Bembridge..

Percy Verance29/10/2017 13:01:39
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5713 forum posts
108 photos

Well Andy, if I tell you that one of those motors should fly a 50 odd inch 3 1/2 pound model in a fairly sprightly fashion, then two ought to fly a 6 to 7 pound twin quite easily - in theory....... what size props were on the ic engines?

Left hand stick? That operates the elevator on my tx's.......

 

Edited By Percy Verance on 29/10/2017 13:04:41

Andy G.29/10/2017 14:02:45
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326 forum posts
179 photos

Hi Percy...

The Islander is 62" span... and so far, I haven't actually weighed it, but I'd guess we're probably going to come out somewhere around the 6 pound mark so potentially it has 200watts/pound depending on what size battery pack I finalise on. As you say, it should be sprightly!

The original IC motors were fitted with 9x6 props...

******** Left hand stick? That operates the elevator on my tx's....... ************* I'm down south so the left hand stick controls the loud pedal!.. LOL..

This is the model that the motor was originally bought for. A semi scale Predator type drone. ( sorry, despite several attempts the forum insisted on posting it sideways!)

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