When Tyldesley MFC club President and RCM&E columnist Andy Ellison asked me if I fancied doing a review of the revised World Models ARTF Super Chipmunk, I was, to begin with, not that exited at the prospect. All I really knew about the Chipmunk was that it was a training aircraft for the RAF and expected therefore that it would be very slow and docile. Generally a little boring if you like.
A quick Google demonstrated just how wrong I'd been. WOW what a pedigree!
I immediately found lots of references to Aerobatic Championships from the late 60's and 70s. Art Scholl, the owner of this particular variant (N1114V) was one of the best aerobatic pilots of his era and the Super Chipmunk was his chosen weapon.
Art himself met with an unfortunate end while filming a flying sequence for the movie "Top Gun" in the mid 80's. Neither he, nor his Pitts Special was found after he failed to recover from a spin somewhere over the Pacific Ocean. With this entire heritage in hand I then most gratefully accepted Andy's kind offer.
So, to the workshop.
Upon opening the box I was presented with a fully covered and pre printed, fairly typical ARTF and the distributors Steve Webb Models had also provided me with two replacement rolls of Toughlon covering. This printed covering is available as a crash kit should you need it. One for the fuselage and one for the wings. Thoughtful, but I don't know why I would ever need it!
I started to build straight away as I had all the gear ready to go. I had decided with the aid of another clubmate, Ex UK IMAC champion Colin Fisher to opt for a Super Tigre .90 two-stroke to give it more that enough power. Colin used to fly the Goldberg Chipmunk when he first started in competition.
Although my model was recommended for .60 two-stroke or .90 4 stroke motors, Colin told me he had flown his Goldberg variant with a .90 two-stroke in various IMAC contests very successfully.
This advice together with a nod from Andy and my need for speed decided it. I realised I would have to "shoe horn" it in somehow but I'll expand on that later.
The instructions book is very clear but I felt it still requires the builder to have some previous experience. Many of the more detailed steps are omitted and you have to think around some of the problems.
Construction starts with the sticky-out bits.
The wing assembly is very straight forward, except that the hardwood joiner didn't fit too well! In fact it was like the proverbial up a shirt sleeve. I decided to cap it 3mm hard balsa to force a reasonable fit.
With plenty of 1 hour epoxy mixed up and with the dihedral already set up on the bench using various 'things' for packing, the left wing met the right wing and will hopefully now never go their separate ways. With the wing taking up most of my bench I had little else to do than read the instructions and play about with the retracts. I did manage to stave my fascination long enough to gather the four servos for the next step.
The wing has 2 servos for the Ailerons, one for the Retracts and final one for the Flaps. I should mention that it would be difficult to substitute a high torque, standard sized servo for the Retracts as the depth of the mounting is too shallow. The required travel probably wouldn't be sufficient either. It's a proper retract servo for this job.
The Aileron servos sit behind Lite-Ply covers which fitted the wing recesses perfectly.
Some time ago I built a World Models Frontier .40 trainer for my son and was very impressed with the little rod connectors I got with the hardware packs, so it was good to see them here too. These little gizmos are a very neat and tidy way of connecting piano wire to your servo horn whilst leaving it adjustable. All the hardware, including the fasteners, are of good quality and I could have no complaints.
The control surfaces all come pre hinged with some very flash metal hinges. No amount of careful but firm tugging could loosen them so I decided that further 'Cocktail Stick' type pinning wasn't necessary.
With the wing looking good to go and my retract playing fetish, I retrieved the shoe horn from the bottom kitchen draw I turned my attention to the fuselage and the engine installation.
The bit that holds the sticky out bits.
The fuselage is again well constructed with a veritable 'concert hall' amount of space for the radio gear. It was all very pleasing to the eye and truly shame to have to do the major surgery necessary for the installation of the big engine. The problem here was the silencer, or moreover the position of it.
With the engine mounted as suggested (90 degrees to 12 o'clock) you end up with the silencer sticking out of the cowl on the side of the model. Ugly, ugly ugly! I decided to mount the engine at 120 degrees to align the silencer with the centreline of the fuselage on the underside. The only way to do this was to cut away the fuel tank bay floor and then rebuild it with a channel for the silencer. (see pics).
The bare wood of the modification was given several coats of Aerokote fuel proofer to make sure it lasted as long as the rest of the model. With this dry overnight I installed the Super Tigre .90 in the kits supplied engine mount and double lock nutted all the bolts. A silicon elbow was fitted to the end of the silencer to direct the muck away from the fuselage and save on the cleaning a little and knock a bit of the noise off.
I usually do the first couple of flights on aerobatic models without the cowl to permit some adjustment of the thrust lines without slotting the cowl fixing holes. However with time pressing on and a deadline to meet, this time I chose to fit it and bite the bullet. There is plenty of side thrust already installed on the bulkhead and I just assume that someone at World Models had put it there for a good reason.
The cowl is a thing of beauty being fibreglass-cloth and the paint work is excellent and a perfect match for the covering. The supplied 'blank' cowl to help judge the cut-outs now seems to be the norm for ARTF's.
Screwing cowls to models has always been a bug bear of mine and now I think I've perfected my technique. After drilling suitable holes into the fuselage I screw in a short piece of large (M8) nylon bolt smeared with 5 min epoxy until it's flush with the sides. This stays in place and provides the perfect reinforcement for the supplied self tapping screws. What you end up with is a very strong self locking, fastening system that has never let me down.
I proceeded with fitting the supplied tank into its pre cut bearers and the associated plumbing required. The tank is held in place with a ¼" balsa bar which I screwed in place rather than glue as the instructions suggest to allow me to remove it should problems arise. I glued in the servo tray using foaming polyurethane wood glue to fill any gaps. The tail plane was epoxied in after a few dry fits and the checking of the wing alignment.
The Fin and Rudder required several adjustments to get the fit and alignment correct but likewise were epoxied into place when square. This just left the radio and ancillaries.
Packing foam for the receiver and battery is supplied so I used it. As we've already established, there is tons of space in this fuselage so the servos look lost in their tray. After fitting the rudder linkage I couldn't help wondering if I'd missed something. It was in a bag that fell off the bench. The tail-wheel. This turns directly with the Rudder and takes quite a bit of fitting. My advice would be to take your time and get it right. I thought that a collet was missing from the assembly but I couldn't find a good enough picture in the instruction book to clarify this. The only thing stopping the whole tail assembly coming loose from the rudder is the cyano required to fix the wire into the control surface. Well we all have to trust glue I suppose!!
All the servos fitted were standard JR 591's and Futaba 3003's except for the retract servo, a Hitec HS 75BB. After looking into various ways of multipin connecting the wing, the desire to fly took precedence and I opted to connect them directly into the receiver. I set all the movements as suggested in the instructions and mixed the flaps to down elevator in two stages on my JR 9X transmitter. The receiver aerial was routed out of the top of the fuselage to the moving part of the rudder and secured with a rubber band. I spent an unusual and worringly long period of time playing with the retracts once again and showing them to various members of the Royle household. Nobody was even the slightest bit impressed except for my 2 year old Boxer dog who barked at them then tried to eat them. Oh well it must be just me that's impressed with mechanical simplicity.
The retract speed was just right, not too slow as to warrant dropping the wheels two circuits before landing, and not so fast that they'll they punch there way through the top of the wing to make inverted landings possible.
With the CG checked and the model ready to go, the British winter weather lived up to expectations and did its worst for a week. Nothing to do but I put the model on a shoebox in the conservatory and play with the wheels again. Well, at least until the rain stopped!
Lift off
With the ST .90 whipping the APC 14" x 8" and aluminium spinner (not the plastic one that comes with the kit) at a fair old rate, I leaned her out in the pits at Tyldesley MFC HQ and carried her to the runway. After gunning the engine to around half throttle the whole thing tipped nose over in a very undignified manner on the clubs wintered (and long) grass strip. Not even full up elevator could stop the inevitable from happening. It was with a little embarrassment I returned to the pits for a brew before enlisting the help of one of our beginners to hold the tail and provide her with a gentle push. All part of the training I told him!
The engine was run up to full throttle and with my head nod the brave helper released. The "Chippy" (We nickname everything at our club) had only travelled about 10 feet before she leapt into the air and I quickly realised that the power to weight was just what I'd hoped for!
There was loads of power available. At just about half throttle I only had to give her a couple of dabs of down elevator and a touch of left aileron and she was flying like a dream.
Just basic circuits were the orders for this flight but I did try a couple of slow and low passes, more for the small crowds and the camera's benefit than anything else. The slow speed handling was superb and I put the wheels up for effect. It did seem to me that the flying was much smoother with the wheels away and I was surprised at the difference. With the wheels back down for a 'dirty' pass up the strip I added the first stage of flap. She did nose up a little but I did think I was going a little fast. A slower engine speed and everything was well, so I added the second stage of flap. Now I was flying at a ludicrously slow speed which surprised me as the flaps aren't really that big, but she began to show her disapproval of the tight turns I was asking her to do although nothing to nasty manifested itself.
After a few approaches and overshoots she landed well but just as she stopped the bloody thing nosed over again.
On the second flight after avoiding the nose over I decided to try a few Rolls and with just aileron she lost no noticeable height at all. Loops were as big as you would like and Stall Turns could be done as high as you want as the model just went up forever. The power was awesome and much to my approval.
Back in the workshop at the end of the day, I rechecked everything especially the c of g but it was bang on with the instructions. I had noticed in the dive she was pulling herself out a little so I moved the c of g back with a few small chunks of lead on the tail.
I waited around two weeks to get a decent flying day again and this brought on a new problem. Just at the beginning of a take off run the wheels decided to put themselves away. Upon investigation I found that the retract servo had fried and stopped driving one way. The wheel would go up but never come down. So I disconnected the retract servo and locked the toggle over with a plastic cable tie. The servo positioning meant that only another slim servo would do the job, so borrowing one at the field was out of the question. (Hence the many wheel down pics).
I'd come to fly her so with my usual helper she was airborne again. I did manage to release some up elevator this time and she made a reasonable length along the strip before she got off. After a few circuits Andy Ellison appeared and promptly tried to rip the wings off in an effort to show me that I needn't be scared. Not sure Art Scholl's cockpit Voodoo doll thought that though!
With flicks, spins and rolls at every opportunity he obviously liked it but made a few observations about the unbalanced controls meaning the up and down elevator felt different.
His flying urged me to be a little more adventurous and so inverted flight was tried and now I saw what Andy meant. It was a little heavy on the down elevator compared to the crisp response of up elevator. This could easily be sorted out on my JR9X with the ATV's and differential Dual rate settings. The landing this time was almost perfect save for the eventual nose over just as she stopped again. We really must get the grass cut!
Anyway with a few more flights under my belt now I feel I can draw a conclusion.
If you're looking for an aerobatic "scalie" that is a change from the all too common Extras and Caps then I think you can't go far wrong with this model. The flying characteristics would suit someone like me practising for "B" certificate or a more experienced modeller looking for an addition to his stable.
The retracts are interesting and to be fair I'll try her again when our strip is its usual bowling green texture to see if the nosing over problem is any better. The more I moved the C of G back the flickier the whole thing got but that may suit a more experienced flyer. The World Models Super Chipmunk R90S is a revised, cheaper version of the older model (the 90S) but the specification is virtually the same.
With a price tag of £149.99 it is a lot of plane for your money. I would probably have gone for a four stroke motor if I had one but in the end the shoe horn did me proud yet again. The replacement rolls of Toughlon covering in the crash kits are around a fiver each and all are available via distributors Steve Webb Models at http://www.stevewebb.co.uk/. Check your local good model shop and they should be able to hook you up.
The full specification is as follows:
Wing Span : 64.0 in / 1620 mm
Wing Area : 682 sq in / 44.0 sq dm
Flying Weight : 7 lb / 3300g
Fuselage Length : 53.0 in / 1340 mm
Engine Required : 2C 0.60 cu and 4C .70 cu / 0.90 cu
Radio Required : 6 Channels . 7 servo's ( optional inboard flaps)