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Ben Buckle/KeilKraft Falcon

Vintage 8 ft wing span.

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Robert Foreman11/04/2012 21:33:09
71 forum posts
45 photos

I purchased a set of Ben Buckle plans for the Falcon. The plans come on 3 sheets, each over 4ft long. I've also got an A3 version of the original KK plans. So my Falcon will be a hybrid. I started building the Falcon about 7 months ago.

I started with the wings. To avoid spoiling the plans I drew the spar positions on the building board and spaced the ribs out evenly. I produced the ribs using the 'sandwich' method with the ply centre ribs as the template.

I had to produce two sets of ribs as the sandwich was too wide to handle otherwise.

The two halves of the wing are joined by a complex arrangement of joinery.

Here's the left wing:

And here's the right wing:

And here they are joined. I've yet to sheet the centre section - it seems a shame to hide all that work.

Eamonn Fahey11/04/2012 21:41:55
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529 forum posts
58 photos

Beautiful work Robert. Keep it up. yes

Alan Cantwell11/04/2012 21:46:03
3039 forum posts

nice, i dont like a lot of vintage models, but this ones ticks every box,

Robert Foreman11/04/2012 21:52:21
71 forum posts
45 photos

Next up is the stabiliser. This has a 3 ft wing span. I found it easier to cut the ribs as rectangles and then sand to shape after the whole thing is assembled. In this shot the elevator has not been fully seperated into two halves. As the elevator is so long and seems to twist easily I have not decided yet whether to use 1 servo or 2 servos for the elevator. Either way the mini servo(s) will be built into the tailplane.

The rudder servo will be built into the fin.

Alan Cantwell11/04/2012 22:12:57
3039 forum posts

carefull with the 2 minis down the back end, the falcon, and others, was designed to be free flight, with the balance point WAY back on the wing, its flight pattern was to spiral upwards, then settle into a gentle glide, the engine was also a heavy sparky, the short nose will need balllast, me personally, i would closed loop both the rubdder, and elevator, and have standard servos up the front end, with maybe a servo link to a bellcrank for the back end left right, and uppy downny bits

Tom Richardson 212/04/2012 09:12:56
2 forum posts

Wish I could build as neat as you Robert. I do try to produce a clean build but somehow it never turns out as neat as yours. Well done and keep it up !

Tom

Jim Carss12/04/2012 09:48:11
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2073 forum posts
82 photos

Nice job Robert, I built this model over 30yrs. ago and I had a bog standard OS40 up front and it flew like a dream.

As Alan has said keep the rear end as light as possible to avoid too much ballast up front,thats a mighty big tailplane.

I had three standard servos up front,made the cabin area removable for radio access.

The pic was taken on a box brownie so that tells you how old it was,keep up the good work.

Jim

Robert Foreman13/04/2012 22:18:14
71 forum posts
45 photos

Thanks for the comments chaps. I've got a long way to go yet before I make a decision of servo placement. My gut feel at the moment is that there's a lot of weight in the wings and the front fuselage with the back end relatively lightly built.

Here's some shots of the fuselage.

Former cut out for fuel tank, snake installed for throttle. I've angled the engine bearers to produce side thrust so that the propellor shaft ends up central at the front.

Looks a log bigger with the stringers added.

Geoff Smith 114/04/2012 09:47:04
avatar
545 forum posts
88 photos

Hiya Robert. I would just like to add my admiration for an excellent build. Oh how I wish..but that's another story. Keep up with the pictures, I am following this build with a green tinge in my eyes. lol

Geoff.......envious dept

Braddock, VC14/04/2012 11:30:40
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1634 forum posts
82 photos

My falcon has a laser 70 up front with no lead in up front and I sold my other one with a saito 62 up front again with no lead.

The plane is VERY tolerant of c of g position and if it's around the 50% chord position the plane will let you know when it hits a thermal (or sink).

On my laser powered one the cg is 1/2 way between where BB says it should be and the 50% chord and it flies well with adequate thermal indication.

The one I sold had the c of g at the 50% mark.

One thing that you may want to consider is that both those engines are massively overpowerful for the falcon, the original exposed rocker OS 60 fs is too but is a much better match, the net result is the plane tries to fly vertically up when anything over 1/2 throttle (with the laser) is applied, this with 7 degrees of downthrust added. Point I'm making is that you could build in the downthrust.

I'd say a 48 surpass would be almost perfect or, with a bit of a breeze, a 40 surpass or 45 saito.

Just my 2p.

Edited By John Gibbs on 14/04/2012 11:31:07

Braddock, VC14/04/2012 11:45:35
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1634 forum posts
82 photos

BTW, forgot to say that the reason this plane is so tolerant of cg position is that there is, in my opinion, a fair amount of lift coming from the tailplane. I have other vintage jobs where I have the c of g at 70% again with a lifting section tailplane as opposed to a flat plate ditto.

Edited By John Gibbs on 14/04/2012 11:46:02

Alan Cantwell14/04/2012 12:59:43
3039 forum posts

John, sounds like the original free flight angles of attack etc have been retained, does it have the undercamber thick airfoil as well? cant tell off roberts pics, would it be better, do you think, to re-jig the thing for modern radio flying?

Braddock, VC14/04/2012 15:32:09
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1634 forum posts
82 photos

Al it's been flying since 2003, I can live with the climb, just to watch it bump when it hits a thermal.

With the cg that far back, it lands at less than walking pace in the calm and, if there's a bit of a breeze, it'll land going backwards though I have to be absolutely honest and say I've only done that once as I bottle it and prod the revs up as it took forever to build.

Alan Cantwell14/04/2012 16:54:48
3039 forum posts

i was thinking more of roberts build on here, would not make sense to butcher yours

Robert Foreman16/04/2012 15:58:11
71 forum posts
45 photos

Neither the BB or KK plans make much sense regarding the sub-fin. In the end I choose to use a 3/16" core with spruce to strenghten and provide anchorage for the tail wheel wire. Then I covered the core both sides with more 3/16" and finally 1/16" sheet to make up the required thickness.

Here's the finnished item.

Rex Keene16/04/2012 20:15:22
80 forum posts

Lovely looking build quality.

what type of building board is that you're using?

Robert Foreman17/04/2012 12:09:14
71 forum posts
45 photos

Rex,

The white stuff is just melamine covered chipboard as sold in B&Q etc for shelving. The benefits of it are that it's available in several widths and flat and true. The downside is that you can't push pins in by hand - you need a small hammer. I've used a piece of it for the SLEC fuselage jig, where I've covered it with the red squared sticky stuff that SLEC supply.

Robert.

Robert Foreman17/04/2012 12:20:03
71 forum posts
45 photos

The underside of the fuselage is in-filled with balsa sheet.

The undercarriage uses 3 pieces of 8 SWG wire. I tried to soft solder a trial joint first but could not get the solder to flow properly with my 75W soldering iron, so I ended up using silver solder and a blow lamp. Not perfect but it should look ok once painted.

Here's the rear undercarriage mounting.

Rex Keene17/04/2012 12:21:49
80 forum posts

Ah, OK, I noticed the "graph paper" markings and your jigging fixtures and naively assumed it was some kind of purpose built jigging board.

But thanks anyway

(always looking for a better way to do things...)

Edited By Rex Keene on 17/04/2012 12:22:25

Mike Etheridge 117/04/2012 15:56:34
1536 forum posts
429 photos

Excellent build!

A few years ago I bought my Falcon on E-bay. When I went to collect it the seller warned me that a mouse had been in the fuselage (May have set up home?) and the result was that it had chewed up the rear fuselage balsa bulkheads and stringers which meant the fixed tailplane and fin assembly just 'flopped about'. I thought it was necessary at the time to remove all the nylon covering to repair the damage. However using the balsa cement techniques for tissue repairs from the past I managed to carry out key-hole surgery to the stringers and bulkheads and glue-up the incisions to the nylon. Once I had emptied out the mouse droppinngs from the fuselage and repaced the front cockpit cellophane it was 'ready for radio'! A repair was also necessary to one wing.

I am not sure it was necessary but I fitted high torque servos to operate the rudder and elevators as they had large surface areas.

The plane has flown a few times in the last 3 years but I have had trouble with the Merco 49 engine which keeps cutting out. However I have been most impressed with the plane's performance otherwise.

MJEKK Falcon

Edited By Mike Etheridge 1 on 17/04/2012 15:59:36

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