Yamamoto (oz8956)

 

Yamamoto (oz8956) by Bob Weston from Model Flight Accessories 1975 - plan thumbnail

About this Plan

Yamamoto. Radio control trainer model for .29 to 40 engines.

Note this model was supplied with a ready-made foam wing, so the plan show no layouts or formers for wing contruction.

Quote: "The Yamamoto was designed by Bob Weston as an extremely easy to fly all weather trainer. The model has been kitted only after various prototype models had logged hundreds of flights between them, many of these flights in very windy weather conditions. We are therefore very confident that it will teach the novice to fly in the quickest time, with or without experienced help. Use a good .29 .40 glow engine with silencer e.g. Merco .29 or .35, O.S Max .30 or 40, Enya .35, Fox .29 or 36. Do not use one of the powerful .40 engines designed for pylon racing. The radio should be a three channel proportional (or four channel using three servos)."

Update 27/12/2019: Added kit review from RCM&E, September 1989, thanks to RFJ.

Quote: "Kit Review: MFA Mk2 Yamamoto - built by Paul Cockerill and described by Ian Peacock.

MFA's Yamamoto is hardly a new model, it first saw the light of day back in 1970! Since then it has been the primary (and in some cases secondary also!) trainer on which many model clubs have settled, for its rugged structure, and easy to fly, all weather capacity has put if four square in the front of the long list of available trainers. Since its inception, it has been followed by the New Yamamoto, which, with its glass fibre, more scale like fuselage, makes a much more eye appealing model. Despite that, the old Yamamoto continued to outsell many of its rivals and in 1988, Model Flight Accessories' Chris Baker decided that the traditional structural version could use a bit of an up-date. Consequently we were presented with one of the first pre-production batch of 'Mk 2' models for assessment.

Now regular readers will be conversant with the ideas of having novice modellers build novice models. After all, it is argued that if a beginner can put it all together and make it fly - then anybody can! Well, in this instance we had just such a beginner available at just the right time. That Paul Cockerill managed, without assistance, to complete the Mk 2 Yamamoto and is competently flying it without accruing any major damage to the airframe proves the point.

What's in the box? MFA's packaging is not at all bad, the Box Art is perhaps not quite so impressive as the major orientals, but is a great deal better than many other British kit manufacturers. The box top contains a large colour picture of the finished model and plenty of information about the contents therein. Within the box one is confronted with two excellent obechi veneered foam wings, totally finished bar the wing tip plates. There are no false leading or trailing edges to fit, and the quality of the veneer and accuracy of section are as high as one is likely to encounter elsewhere and better than many. Unlike many manufacturers who sub-contract wing manufacture, MFA 'do-it-themselves' in a custom designed wing construction area. This, they argue quite rightly, gives them ultimate quality control - and believe me - it shows!

Also in the box is a large quantity of pre-cut balsa and, unusually in this day and age, a large sheet of plywood upon which all of the ply parts are printed. Being the 'Top line' version our kit also contained every item needed to finish the model with the exception of the covering and finishing materials and the resin for joining the wings. This complement includes wheels, tank, spinner, a massive goody bag of nuts, bolts, hinges, horns, etc.,and even featured a pot of white glue and the rubber bands to hold the wings on! A short three page instruction sheet and a two piece plan tops off the component count.

Although the instructions are not overly long, they are clear and concise and Paul found no fault with them at all. The two piece plan is an obvious cost saving and it takes only a few seconds to Sellotape the two parts together (check your alignment is right - there are no alignment marks on the sheets!)

Putting the thing together: Assembling the Mk 2 Yamamoto is a bit of an anti-climax for there is little that cannot be confidently tackled by a raw beginner. Cutting out the plywood parts is a somewhat unusual route to go these days, but as Paul said: It didn't take long - I borrowed a mate's Black & Decker jig saw and cut each piece out about 0.5mm oversize, finishing with sandpaper. The end result was that everything fitted OK and there was some degree of additional self satisfaction.

Doubling up two layers of 3mm ply for the engine firewall is not quite as unusual as it seems, it adds strength due to the glue line and produces the rebates for the fuselage sides automatically. Adding the doublers to the fuselage sides revealed that the doublers were some 3-4mm oversize, but as Paul said: better than being too small, it didn't take long to sand them off flush!

Straightforward drawing and instructions were such that the box fuselage went together in less than an evening, the matched quality sides ensuring that the fuselage finished straight and not like a banana. In fact the cut and quality of all of the balsa parts was well up to the standard expected and no real problems occurred.

The Tail Feathers: The tail parts are all cut and joined from 6mm balsa and present no real problems. The anti warp keys - (tail plane tips part no.T4) are cut from the left overs when the tail plane leading edge sweep back is produced. Radiusing the edges and chamfering the rudder and elevators as shown on the plan takes only a short while and the whole fuselage and tail assembly can with care, be accomplished in as little as an evening.

Wings: If the fuselage and tail is quick and simple then the wings are an absolute doddle! Only the two balsa wing tip plates are needed to complete each panel, just glue on and sand round the edges! 5-minute epoxy joins the wing halves at the pre-determined, chamfered, angle to produce the correct dihedral. Six inch wide glass tape is provided for joint reinforcement but no resin. Ordinary glassfibre resin is recommended - ie polyester and this was, in fact, used despite the fact that we have had wings dissolve recently where the polyester has soaked through the veneer and eaten the foam inside. M.F.A. are obviously confident that their wing skinning system is unlikely to show up any problem in this area and in practise, no troubles were encountered, everything coming out "just like the book says". Whilst the resin was still wet, left-avers were applied to the inside of the fuel tank bay, as per instructions, to provide a tough, fuel proof finish.

Finishing: MFA recommend traditional paint finish. In fact they give quite a detailed list of the products needed and how to do it. They also say that Solarfilm can be used as an alternative, thereby safely hedging their bets! In practise, we did, in fact film cover. Solarspan was actually chosen for its greater opacity and Solartrim used for all of the decorative finish. Balsa lac was employed on areas of ply, glass fibre and anywhere else where it might benefit the adhesion of the 'span. Final fitting out of engine, tank, radio, etc, followed the instructions to the letter - well almost!

Fitting the servos to the ply tray as shown gave just a little bother with the output arms fouling on the fuselage sides so we installed the servos crossways rather than in line. Rigid pushrods are used and because of the pre-cut pushrod exit holes in the fuselage, small dog legs are needed at the rear end of both rods. These are not massive bends as on some models and have caused no trouble, however, with just a little thought and the repositioning of these exit-holes, straight pushrods can be used, a much more satisfactory operation. all up weight was about 5-1/4 lb, approaching the top of the recommended range, and the balance point was spot on. In fact the whole assembly, finish and installation had been so painless, the anti-climax was deafening!

Paul summed it up quite well I feel by saying: It's a long time since I last built a model - a wind-up rubber band job when I was a child. The Yamamoto was so much easier - no small fiddly bits, everything figured out for you and no special tools needed. In fact, after raiding Ian's loft for the Solarspan, I even used the wife's steam iron to put it all on with! I can't see how anyone with even an inkling of savvy couldn't come up with a reasonably well finished model in no more than a couple of weeks of spare time! Amen to that - of all the basic trainers that we have had through our hands over the years, MFA do seem to have got it right (again!).

So - what about its flight? Well, if the assembly had been an anti-climax, then the flying was nothing if not exciting! Paul had just acquired a second hand set of radio, but, at the stage of test flying, had yet to acquire a suitable motor - so - what did Peacock do? I lent him one!

In fact I had just received a sample from MacGregor Industries of the new Chinese ASP 40 which, according to MFA is the upper limit for a two stroke for the Yamamoto (.29-.40 quoted on the plan!). Now, what was not overly apparent was that this Chinese device was some motor! It was incredibly tight at top dead centre and seemed as if it might need forever to run in. Therefore it seemed a 'good idea at the time' to run it in aboard the Yamamoto! Well, everything turned out right on the day (despite what you often read in magazines!) a gentle, predictable breeze blowing straight down the strip and a cloudless sky. A thorough pre-flight check showed up no problems (I'd already discovered that Paul had both throttle and elevator control 'backwards' and had rectified this), we fired up the ASP 40, leaned it out a bit for running in, and found it holding a screaming 14,000 rpm right from new without any sign of overheating or tightening up. Releasing the Yamamoto saw it leap off the ground in some 3 feet or so and head heavenwards like the proverbial homesick angel. Quite obviously we had some motor here. Reducing the throttle by some 75% brought the whole thing back into the realms of normality, and we were able to assess the flight performance of the model.

No real vices, nice clean stall upon applying full up at the tickover, yet capable of some quite exciting flying when on "full song" and a handful of down trim fed in. In fact, says Paul, I was somewhat concerned at (a) my ability to handle such a fast and apparently aerobatic model and (b) whether my building skills were such that the whole airframe would stay together under the conditions that Ian was flying it! However, when throttled down sensibly I found it smooth and responsive and I even managed to land it myself on the second flight and take it away from the hand launch to complete my third flight solo..."

Supplementary file notes

Instructions, thanks to hlast.
Review.

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Yamamoto (oz8956) by Bob Weston from Model Flight Accessories 1975 - model pic

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