Bushwhacker

Alex Whittaker’s own-design homage to traditional R/C aeromodelling, the Boddingtonesque ‘Bushwhacker’ has featured extensively in RCM&E in the recent past as an extended free pull-out plan feature. Now this 55”-span, three-channel (no ailerons) .15-.30-powered trainer/sports model has been kitted by Colin Buckle to join the long-established Ben Buckle range of traditionally-constructed R/C aircraft kits. Speaking as someone with an aversion to ARTF models and a liking for traditional aeromodelling techniques, I was most interested to see if this ‘new kit on the block’ would be a suitable offering to tempt more ‘instant aeromodellers’ to sample the traditional aeromodelling scene.

BUSH CRAFT

The kit vibe is definitely ‘cottage industry’ – the sturdy plain white box features just a colourful label citing the model’s relevant specs, plus a flying shot of the finished product. The label also announces that ‘further items are needed to finish the model’, but annoyingly doesn’t say what the items are.
Looking inside the box it’s obvious that additional components, namely a spinner, fuel tank, fuel-tubing and wheels, are on the shopping list to back up the polythene bag containing basic accessories such as the dural engine mount plate, hinges, control horns, clevises and kwik-links.
A considerable amount of band-sawn and hand-sawn balsa and ply is provided beneath the bubble-wrap. In my sample kit, the wood quality was good but the cutting accuracy was poor – both uneven and inaccurate cutting spoiled many parts. This necessitated edge-sanding and part-tweaking as the build progressed – irritating, to say the least! Luckily, most parts were too big, so they could be ‘reduced to fit’, but there were exceptions – see later.
Paperwork comprises of a reprint of the original ‘RCM&E’ free plan, plus a thirteen-page build pamphlet. Some scribbled hand-written annotations indicating slight build changes are added to the plan which rather detracts from the original professional draughting standard.

FUSELAGE FORMATION

The airframe build begins with the fuselage by first assembling the fore and aft radio bay formers F2 and F3 from strip balsa directly over the plan. This is very simple to do – just ensure that both the vertical and horizontal strips are accurately cut to size before gluing and pinning them together. The note about F3 being built with a ‘reverse’ strip layout to F2 is irrelevant – both formers can be built in the same way and F3 is simply rotated before gluing in place.
A selection of vertical and horizontal balsa strips reinforce the interior of both fuselage sides from F3 rearwards. This layout includes an additional Buckle-modified upright strip each side to anchor the rear face of F3, which is a sensible idea. Don’t forget to add the wing dowel reinforcement doublers around this time too.
As with the strip reinforcement pieces, the positions of the assembled strip formers, plus the ply firewall, are now marked on the inside of both fuselage sides, using the plan and a straight-edge as a guide. F2 is builder-slotted to allow the hardwood beams that support the dural engine mount plate to pass through; this construction method leads to a very rigid interlocking structure when the fuselage is eventually pieced together.
Joining the fuselage sides involves attention to detail. F2 is first glued in place to the right side, then the hardwood beam is dry-fitted to ensure a good fit through the former’s slot. The built-in down-thrust is achieved when F1 (with pre-cut slots) is also correctly dry-fitted over the hardwood beam, whereupon the beam’s downward-slanted orientation is marked inside the fuselage side. Now F1 is temporarily removed and the hardwood beam is epoxied in position. It’s marginally over-long, so you will have to trim it flush later where it slightly extends past the nose.

At this point, the sturdy ply firewall F1 is epoxied in position, followed by F3. The end-result is three formers, plus the hardwood beam, glued to the inner right-hand fuselage side. What that lot are dry, the left-hand hardwood beam is epoxied/slotted into place on the other sides of F1 and F2, just before gluing the left-hand fuselage side to the completed assembly.
I attached the left-hand side with the structure off the board, as the whole thing needed heavy-duty clamping to ensure a good tight fit – especially to get the left beam properly into contact with the left-hand side.
I pulled the fuselage rear-end together over the plan with the fuselage assembly jigged using large set-squares and clamps to a Great Planes building board. I felt this strategy was necessary to maintain an accurate structure, as the joined fuselage is slightly narrow relative to the plan-view drawing.
Add the internal upper/lower tank bay doublers before fitting the ‘windscreen’ and sheeting the nose underside, otherwise the doublers will be impossible to get in place! These doublers needed considerable trimming down to fit accurately.
The ply undercarriage plate and all lower sheeting back to the horizontal tailplane-mounting opening, but excluding the lower cowl area, are now added. Again, part inaccuracy frustrated matters – the undercarriage plate was too big and the ply tail-skid mounting plate was too thin in section! I trimmed the undercarriage plate to size and left sorting out the tail-skid mounting plate ‘til the model was almost fully finished.
Before adding the balsa sheet windscreen, check that your chosen fuel tank will fit between the hardwood beams. I had to trim the beams with a Stanley knife to allow my SLEC four-ounce tank to fit. The tank bay omits a sub-former shown on the original plan, and has some other minor structural differences, but this is of no great disadvantage. Chamfer the windscreen edges before gluing in place. The ‘small fairing piece’ mentioned to top off the windscreen was not needed on my model.
I retained the balsa tank bay hatch with six small self-tapping screws going directly into the fuselage sides. This method worked well and is neat, but you could try the suggested hatch-retention techniques if you prefer.
An opening is meant to be cut out of the supplied dural engine mount plate to allow your chosen engine to fit in place with the recommended amount of side-thrust as shown on the plan. I used a ¼” thick ply plate instead, as I was nervous of tackling the ‘heavy metal’ cutting! After some frenzied hacksaw work, my O.S. 15FP fitted nicely and the ply plate was ready to be attached to the hardwood beams.
Here a conflict arose. The engine mount plate is meant to be screwed to the hardwood beams – presumably for easy removal later on if needed. But, access to said screws becomes impossible because the thick nose bay doublers, added above and below the hardwood beams after the plate is mounted, get in the way! The solution would be thinner nose bay doublers – or permanently attach the engine-mounting plate to the hardwood beams, as I did. Note well: Be absolutely sure that you don’t glue in the upper nose bay doublers until the engine mount plate has been fully sorted and permanently fixed to the hardwood beams!
The actual engine-to-plate union was easily accomplished using 6BA Nyloc bolts. The right-hand nose cheek/tank hatch front top corner needed slight cutting away to allow the silencer to take up residence.
The two sets of length-wise radio bay longerons, which strengthen the cabin area and eventually support the servo-mounting beams, would be more easily fitted before the fuselage sides are joined, but they did squeeze in okay when carefully cut to length. Given a second chance, though, I’d definitely fit ’em at an earlier stage!
I ignored the overly-complicated recommendation to permanently glue in place the horizontal and vertical tail surfaces at this stage. Unless the airframe design makes it absolutely necessary to do so, I usually leave these components off until after covering, as their addition too early makes the finish-sanding and covering processes so awkward, and they are prone to handling damage. I’d also suggest adding all the fuselage top-rear sheeting in one go, as it’s perfectly feasible to measure-up and mount the tail bits when the model is covered.
As for leaving some top-rear sheeting off for better access until such time as the rudder/elevator control linkages are set up, well again I found that particular route completely unnecessary. I can only suggest that you do what you feel is best here!
The fuselage hole-formation method for the wing and undercarriage-retaining dowels is a good technique to avoid ragged edges. I decided however to use clamps to hold the undercarriage on, as it looked so much neater!

The two-part pre-formed wire undercarriage is a major frustration! Though bent accurately to the plan front- and rear-views, the rear wire fails to incorporate the small but essential side-view bends to allow it to mate up with its frontal counterpart. I didn’t have a vice, so had to add brass tube extensions to the rear wire ends, bent to shape and flattened, to allow the wires to mate. When bound and soldered together the arrangement worked okay, but this is a failing that needs to be rectified as it is too much to expect beginners to sort out this oversight unaided!
I used a pair of alluring vintage-type ‘MG Airwheels’ that I bought second-hand many years ago – I knew they’d come in handy one day! When held in place with collets, they really suit the model’s appearance. The over-long wire axles needed hacksawing and filing back just outside the collets.
Liteply infills, added between the assembled undercarriage wires, and Solarfilmed to match the model’s main colour scheme, gave a finishing touch.

TAIL TRIFLES

The tail surfaces are ultra-simple flat sheet components butt-glued together. I wondered what pattern was used to cut the horizontal stabiliser parts, but thank goodness there was too much instead of too little wood! Be careful hinging and chamfering the rudder and elevator, as the wood section is quite thin.

WING WOBBLES!

The wing is a homely flat-bottomed constant-chord affair, built in two separate panels then joined with a ply dihedral brace. Dreadfully simple to put together, eh? In theory, yes, but inaccuracies again clouded the horizon!
For starters, all leading/trailing edge sheet and strip was about ½” too short span-wise and needed extending or replacing before the build began. Add to that, ribs of a slightly greater chord/depth than shown on the plan and it only left the offset spar slots to add the final, maddening touch! None of these inaccuracies were particularly debilitating, but again I pondered why the actual plan drawings were seemingly ignored when forming these crucial kit bits? And, how many people would be prepared to laboriously adjust for a better structural fit as I did?
The actual wing panel build sequence should be second-nature to traditionalists. The lower leading/trailing edge sheeting, cap-strips and centre section sheet are first laid down over the plan. The lower main-spars, ribs, leading/trailing edge stock, plus the upper main-spar, follow on quickly afterwards.
The exact position of the rear-lower main-spar is determined by dry-fitting some ribs onto the previously glued-in-place lower-forward main-spar and spot-cyanoing the rear-lower main-spar to the underlying balsa bits using the ribs as a guide, before permanently gluing almost all the ribs in place.
The initially rectangular-section trailing edge ‘core’ stock needs to be carved to a triangular section before being glued to the underlying sheet. This is an awkward job and pre-sectioned stock should be included for those with an aversion to carving – or for people like me with a shaky hand!
I replaced the kit leading edges with timber of the correct span-wise length from my own stock. The leading edge strips eventually need intensive carving and sanding to match the main wing section. Make sure you concentrate well when tackling this ‘wearing’ task!
Additional ¼” thick sheet balsa ribs cap off the panel’s root and tip ribs. That’s often standard practice at a wing-tip, but is much less common at the root rib location. The thick centre section ribs, which act as ‘doublers’ to the actual thinner root ribs, play an important part in achieving the correct dihedral angle – more later.
The upper leading/trailing edge sheet and cap-strips finally almost tops things off. One is advised to add the top sheeting later with the framework off the board. I strongly disagreed on the grounds that warps could creep in, so did the business with the panel still pinned to the board. Many clothes-pegs were used!
The second panel follows a similar route and then both items can be joined up. But, a couple of grey areas are evident in the instructions which could really confuse the unwary before they get to this point.

No mention is made of adding the top spars at all, yet they are briefly mentioned as being already in place at the dihedral brace joining stage! In case you are in doubt, add the top spars when the ribs are glued in position on the bottom spars.
The method described to fit the second centre section ribs (the ones next to the ‘laminated’ root ribs) is impractical and contradictory, given the confusion about the addition of the top spars. Do this instead…
Simply cut these ribs vertically with a razor saw behind the main-spar slots before starting work on each panel. Then fit the forward pieces along with the full rib compliment during each panel build, and slot in the off-cut rear rib portions after adding the dihedral brace when the panels are finally joined.
The instructions need serious reworking in these areas!

MATING RITUAL!

As previously mentioned, both root ribs feature a thicker balsa rib companion. When each panel is propped up by the required amount using a card template, these thick ribs are sanded vertically chord-wise using a large sanding block to produce angled centre section ribs. This has the same effect as slanted ‘thin’ root ribs but is stronger owing to the extra wood laminations.
I was initially suspicious of achieving a good result. But, in fact, both wing panels mated up beautifully, thanks to the abrasive action of my large Perma-Grit sanding block, while each propped-up panel was carefully positioned at the edge of a Great Planes building board.
The panel joining is a two-step process. First, the wing halves are glued together and allowed to dry. Then, the front/rear ply dihedral braces are pushed up from beneath via slots cut in the lower centre section sheeting and root ribs and glued in place against the spars. Use plenty of clothes-pegs and adhesive tape to hold the braces against the forward/rear spars, so that they grip firmly.
An unpleasant surprise surfaced here – the larger ply dihedral brace was too shallow for the quoted dihedral angle! This meant that the brace couldn’t reach the top spars and it stuck out beneath the lower centre section! I made a new dihedral brace of the correct angle, but this flaw needs addressing PDQ in future kits!
The top centre section is finally sheeted when the aforementioned second centre section rib rear pieces are sitting pretty.
Owing to the dimensional discrepancies between the original wing plan drawings and the pre-cut wood parts, the chord width and trailing edge thickness turned out slightly wider and thicker than designed. I consoled myself that the extra area, brought into being by inaccurate kitting, would add even more flying stability…

FINAL FIDDLING

A thorough sanding session emphasised the charm of this model’s totally traditional airframe! Before long, a simple but effective Solarfilm scheme and appropriate registration code hid all that lovely woodwork. Previously, the engine and tank bays received several applications of Clearcoat to fuel proof the exposed timber; then the engine bay received yet more post-covering paint and proofing layers to both beautify and protect it from the nasty engine exhaust goo.
The tail parts were then aligned and glued in place, having first gently cut away the fuselage film from where the fin would sit. The fin base features triangular fillets to increase its gluing area – a wise move. I also added triangular fillets over the underslung horizontal stabiliser after it had been stuck in place to also further increase its attachment area.
The rudder and elevator easily located in place using the supplied ‘fibrous Mylar’ hinges and thin cyano.

The tail-skid assembly comprises of a piece of builder-cut/bent wire sewn to a Liteply triangle mounted on a ply base-plate, the components formed using the pattern shown on the plan. It was easy but time-consuming to do. I used a ‘needle gauge’ bit, in a hand-turned twist drill, to form the thread holes in the Liteply. The ply base-plate is supposed to lie flush with the balsa fuselage underside sheet, but as mentioned it was too thin, so I glued the base-plate on top of the balsa sheet instead. The completed assembly was Solarfilmed to finish it off.
Very little information is given for the tail-skid manufacture and fitting in the instructions. More re-writing needed!
The engine was finally bolted in place and the tank, well packed in rigid foam, was plumbed up to the carb and silencer nipples through the builder-formed firewall hole. I added a soldered-on needle valve extension, made from cut/bent-up brass fuel tube, for easier ‘screwing about’ with the fuel mixture!
There’s ample room for average-size gear in the radio bay. My model was turning out nose-heavy, so I placed the beam-mounted servos as far back as possible with the well-foam-packed receiver and battery further forward. The switch was mounted on the fuselage side opposite the exhaust blast and the receiver aerial was ran out via plastic tube through the fuselage top behind the wing to anchor on the fin tip.
I used a conventional wood/wire elevator pushrod, exiting directly through a hole cut in the fuselage rear end, to minimise slop. The rudder linkage is a closed loop system, with a cable-in-tube throttle connection waggling the carb arm. No rudder and elevator control throws are quoted, so I aimed for ‘best guess’ factors and waited to see what would happen in the air!
The balance point came out spot-on without the need for additional ballast, which made a nice change! The model’s finished and ready-to-fly statistics are quoted elsewhere.

BUCKLE UP!

A gentle but firm solo fling saw the Bushwhacker airborne and climbing away quite strongly. Apart from a nudge of right rudder and down elevator trim, the model was quite happy to fly about by itself. Some rudder/elevator inputs at the appropriate times ensured that it didn’t disappear into the distance, while yet more constantly-held-on slight forward stick generally kept it from climbing too rapidly too soon.
At this stage, I was reminded of my powered-glider sorties in the early days. At full chat, the awesome thrust of the .15 (!) rapidly pulled the model to a great height, whereupon the power was cut back to high idle and a graceful, unhurried descent followed.
That was all well and good, but what about the general handling?
It’s been ages since I flew a non-aileron model and the Bushwhacker’s rudder response seemed somewhat hesitant and ‘lumpy’ in turns, though this effect was less pronounced as the noticeable breeze died away. I kept finding myself ‘co-ordinating’ rudder with ailerons on the tranny sticks to smooth out the turns – though, of course, no ailerons existed! With some practice, the turns smoothed out, but the ‘groovy’ feeling of an aileron model just wasn’t there in the breeze. Juggling the amounts of rudder and elevator in the turns helped a lot, and I found out that up elevator input really tightened the turns once the model was initially banked over by the rudder.

Paradoxically, when fully held over and held on in concert with up elevator, the rudder became very powerful to induce the most unsymmetrical of barrel rolls (despite down elevator input when inverted) and twirls in either direction. Before long, I achieved many crazy height-losing barrel rolls and half loop/half roll combos! These undignified manoeuvres were not exactly of ‘pattern model’ quality, but nevertheless unexpected good fun with this type of apparently ultra-docile model.
Still experimenting with the extreme control surface waggling, the spinning habits were interesting…
At high idle, full rudder and full up elevator deflection produced spiral dives in either direction. The same control surface inputs at higher revs (from about half- to full-throttle) whipped up true spins in either direction. It was exhilarating doing these genuine spins from a great height and then watching the model quickly recover when the controls were centred, and with slight up elevator applied.
The slow-speed handling was generally benign. With the engine at high idle – and even a little lower – the model could be coaxed about the sky with full up elevator held on for a considerable time before it complained. Providing the up elevator input was reduced somewhat every so often, the rudder could still maintain a reasonably accurate directional course, so long as the yaw inputs were kept large and held on only long enough to have an effect. If full up elevator was constantly held on at idle, the model eventually dropped a wing. But simply neutralising the controls, then applying the appropriate yaw/pitch corrections, along with a smidgen more power, rapidly saved the situation.
I purposely allowed the model to go dead-stick on the first flight to test the glide handling. This exercise was drama-free. The aircraft settled into a natural glide-path and I merely guided it home to a gentle landing!
With the still-persistent breeze blowing again, it was important to keep the model moving in the glide with slight forward stick and not allow it far down-wind, otherwise it’d under-shoot badly. The turning response also benefited from largish rudder deflections, briefly held on when needed, then released smartly.
Subsequent flights have shown that the model is best suited to calm conditions as it gets tossed about by low-level turbulence in wind, but it’s largely okay at higher altitudes. In calm conditions, it looks and feels great doing low, slow passes, while the occasional ‘aerobatic outburst’ is a surprising flourish to its otherwise non-threatening flight pattern.

TRADITIONAL HEIR?

This traditional design is a welcome addition within the overwhelming ARTF market. If the frustrating kitting and instruction discrepancies are ironed out, then it would potentially be an ideal way of discovering the lost delights of traditional R/C aeromodelling – and economical flying! And, that’s always a good thing in my view.


DATAFILE

Name: ‘Bushwhacker’
Model Type: Traditional R/C trainer
Designer: Alex Whittaker
Kit manufactured/supplied by: Ben Buckle Models
RRP: £56.99
Wing-span: 55”
Wing area: 412 sq. in./2.86 sq. ft.
Wing loading: 19 oz./sq. ft.
All-up weight (including fuel): 3lbs. 8ozs.
Control functions: Rudder, elevator, throttle
Control throws: Rudder/elevator, +/- ½”
Recommended engines: .15 – .25 cu. in. two-stroke/.30 cu. in. four-stroke or diesel
Engine used: O.S. 15FP
Radio used: Multiplex

Editor's notes 

  • Alex Whittaker's extensive series of build articles covering his Bushwhacker plan can be found in 2007 and 2008 issues of RCM&E and viewed in the digital archive. 
  • The Bushwhacker plan can be purchased at www.myhobbystore.com
  • Check out the 'RCM&E Extra' for links to Alex Whittaker and Colin Buckle's build photos. 

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