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BERGFALKE IV CABRIO 1:4.7 SCALE**

Posted: 05 Jun 2021, 21:32
by chris williams
This has proved itself to be a very practically-sized model & a smooth performer. As far as I know, there are no IV's in this particular configuration, although there seems to be a variety of Bergfalke 3's thus modified. The unusual scale is due to the 1/4 scale version being scaled down to a size that suits existing stock material dimensions. The last minute decision to hide a motor in the fuselage has proved well-founded, as last weeks inaugural slope flights demonstrated in the light conditions...

Construction starts on the jig: note that the longerons are cut longitudinally at the front to ease the curvatures...
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 06 Jun 2021, 11:48
by chris williams
Once all the longerons are in place, the tail mount can be added, and then a template made up for the top sheeting...
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 07 Jun 2021, 10:53
by chris williams
Once the front planking & the top deck are in place, the fuselage can be removed from the jig. Note that there is a slight compound curve at the front of the top decking, hence all the masking tape. An alternative would be to separate the panel at F8...
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 08 Jun 2021, 11:56
by chris williams
To allow for the tapering thickness, the tailplane is built inverted on the board, than sheeted on top. Then it's inverted once again, with jigging supports spot-cyano'ed to the top sheeting, placed back on the board, and the bottom sheeting added...
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 09 Jun 2021, 10:57
by chris williams
The making of the 'cab'...
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 10 Jun 2021, 10:17
by chris williams
With some 5mm sq balsa added to increase the glueing area, the ply side panels are added, followed by the top panels...
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 11 Jun 2021, 11:04
by chris williams
Now, the ply sheeting can be finalised at the front...
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 12 Jun 2021, 11:08
by chris williams
Now the wheel mount can be finalised...
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 13 Jun 2021, 10:13
by chris williams
Now for the elevator: the first job is to hinge up the false LE to the tailplane and sand it flush. It can then be removed, and the elevator built over the plan. Then the final LE is added and rounded off...
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 14 Jun 2021, 11:03
by chris williams
Details of the elevator actuating pushrod arrangement...Now, construction of the fin/rudder starts.
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 15 Jun 2021, 11:04
by chris williams
Followed by the rudder: once again, the false LE is hinged up before construction commences...
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 16 Jun 2021, 11:05
by chris williams
Now the tailwheel assembly can be added, prior to ply-sheeting the rear of the fuselage...
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 17 Jun 2021, 10:10
by chris williams
Moving on now to the wings...using my current wing-build practice, the lower main spar is built over the plan. Once the upper spar is added, the ply webs are glued to the front of the spar and the sub-spar dropped in in front of them.
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 18 Jun 2021, 10:14
by chris williams
The second wing joiner sits between the sub spars: when fitting two joiner boxes like this, it's always prudent to insert the blades into the boxes to ensure that they are exactly parallel as the epoxy cures...
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 19 Jun 2021, 10:05
by chris williams
Once the lower sheeting has been added (not forgetting the ply plate to accept the rubber band retention hook) the wing can be placed on its jigging supports, weighed down and the top sheeting added...
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 20 Jun 2021, 10:06
by chris williams
Now the wing root can be finalised and lined with 0.8mm ply...
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 21 Jun 2021, 11:10
by chris williams
The wing root fairing on the fuselage is simply a 1.5mm ply profile: this is best made by offering up to the wing root and marking around. Also, it's best to leave the wing joiner boxes and incidence tube proud of the wing root up to this stage. This way, a ply blank can be pushed into the wing root with two layers of masking tape in the appropriate places. The resultant marks in the tape will show where to cut and drill, then, when you mark out the profile it will be accurate in relation to the protruding brass...
Once fitted, it was time to add the 6mm half-round dowel from my nearly diminished stock to simulate the metal tube of the full size. Then, at this stage, it was time for the obligatory test rig!
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 21 Jun 2021, 15:44
by Jus Gordon
Hi Chris,

Another great build thread, will you be flying this at Whitesheet this weekend, weather permitting?

Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 21 Jun 2021, 16:56
by chris williams
Of all the sad words of tongue & pen...'weather permitting' are the saddest... ;)

Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 21 Jun 2021, 17:12
by Barry_Cole
Not looking good at present...

:roll: :roll: :roll: :roll:

BC
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 21 Jun 2021, 19:12
by Peter Balcombe
Depends which weather forecast you look at ;)
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 22 Jun 2021, 11:09
by chris williams
It's often best to make up the combined brass boxes for the fuselage with the wings joined together as the epoxy cures. The boxes extend into the wing root fairing and are trimmed off at the end of the process...
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 23 Jun 2021, 11:57
by chris williams
The ailerons are fairly simple: just built over the plan. Then it's time to fettle the winglets. (These at least are scale, as there is one Bergfalke 4 on the 'net fitted with them)
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 24 Jun 2021, 09:54
by chris williams
Now for my favourite bit: the airbrakes...
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 26 Jun 2021, 11:48
by chris williams
Continuing with the airbrake saga...
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 28 Jun 2021, 19:56
by chris williams
That's the airframe pretty much complete...
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 29 Jun 2021, 11:21
by chris williams
In a last-minute decision I decided to fit the spare Turnigy G32 that I had lying about. (A wise move as it later turned out)
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 29 Jun 2021, 12:00
by Cliff Evans
And it was all going so well!! :lol: :lol: :lol: :lol:

Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 30 Jun 2021, 09:53
by chris williams
I've used my usual finishing method: Solartex and 2k paint on the fuselage, and HK film on the flying surfaces...
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Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 30 Jun 2021, 12:23
by Cliff Evans
Nice Chris.

Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 30 Jun 2021, 19:30
by SedB
Your Bergfalke looks stunning! That thin chatline does it all!

Daniel

Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 30 Jun 2021, 21:30
by Jus Gordon
Very nice, great job!

Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 01 Jul 2021, 11:28
by chris williams
And the coop de grass...le video


Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 01 Jul 2021, 11:34
by Barry_Cole
You made a nice job of Cooping de grass...

8-) :D 8-) :D

BC

Re: BERGFALKE IV CABRIO 1:4.7 SCALE

Posted: 01 Jul 2021, 13:17
by Max Wright
That's what it's all about.

Trez beanie. 8-)

Re: BERGFALKE IV CABRIO 1:4.7 SCALE**

Posted: 04 Sep 2021, 10:59
by ddlawrence
nice! that is really something.

Re: BERGFALKE IV CABRIO 1:4.7 SCALE**

Posted: 04 Sep 2021, 11:47
by Alex Tankink
Thatโ€™s a lovely ship. The Cabrio is so unique. Great choice for a project and inspiring๐Ÿ‘๐Ÿป

Re: BERGFALKE IV CABRIO 1:4.7 SCALE**

Posted: 08 Sep 2021, 14:29
by Alex Tankink
Found this on a vintage glider site on FB today

Thought of you and your build.

Cheers ๐Ÿป