Martin Baker MB-5 (oz9705)

About this Plan

Martin Baker MB-5. Profile semi-scale CL stunter for 1-1.5cc engines.

Quote: "THIS MODEL was built for a purpose - aren't they all? The purpose behind this one was a school fete six or seven years ago, in which the school model club (which I ran at the time) was expected to perform. So in addition to Goodyear racing we decided to do some scale/semi-scale combat plus balloon bursting. I persuaded two boys to either build or re-paint models of suitable type and then cast around for inspiration.

The then current issue of Aero Modeller provided this in the form of scale drawings for the MB5 which looked in plan view to be just right. A quick check on the dimensions showed that scaling up the 1/72 scale drawings by a factor of four would give me a reasonable sized model for a 1.5 cc motor. Plans were duly drawn up and construction details filled in, the wing chord being increased slightly but no other altera-tions to the outline were made.

The original model was powered by an Oliver Tiger Cub MkII, fitted with a 7x6 prop, and flown on 42 foot lines. The first flight proved something of a disappointment as the looping radius was excessive and overall control response poor. The weight of the Oliver motor coupled with the long nose was a major factor, but how to improve the situation?

The answer I settled for was flaps. These were then fitted and the model tried once more - the difference was astonishing, the model now being capable of all the acrobatic manoeuvres I was able to put it through. Triangular and square loops were both within its capabilities.

The version drawn here is fitted with a removable undercarriage as per radio control practice, and has more refined flap connectors than my original. The flight performance with an OS 10 plus silencer is quite adequate for a model of this type, all basic aerobatics being within its compass, plus a fair turn of speed.

The fuselage outline has now been flattened slightly to allow cutting the basic shape from 4in wide balsa sheet.

For those who are put off by the complexity of coupled flaps and elevators, don't connect them up! Glue the flaps onto the rear of the top and bottom 1in x 1/16in TE and take the push rod directly from the bellcrank to the elevator horn. With the additional length of push rod it may be necessary to add a support/guide halfway along to retain positive control. With a light engine such as a PAW 1.49 the lack of flaps should not prevent most basic aerobatics from being performed - in fact without flaps the ME5 would make a good stunt trainer..."

Martin Baker, Aeromodeller, December 1975.

Direct submission to Outerzone.

Supplementary file notes

Article pages, thanks to RFJ.

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