Grumman Bearcat (oz15415)

About this Plan

Grumman Bearcat. Radio control sport scale model. Wingspan 36-1/2 in, for .20 -.29 engines and 4 functions.

Scale is 1/12.

Quote: "Build a Bearcat, by John Rutter.

The Bearcat has one of those shapes that you either love or hate; it looks like a flying barrel but it has always held a certain fascination for me as a possible model subject. The full-size was supposed to be the smallest machine that could be fitted around the largest available engine and a pilot, a combination which gave superb performance even if the lines lack the grace of a Spitfire. To give a measure of the performance there was, apparently, a test in the USA where the Bearcat and a Mustang were lined up on a runway and took off together on a signal. The Bearcat had made two 'firing' passes before the Mustang had tucked its wheels up!

The model presented here is of similar high performance when fitted with a Super Tigre 29 but it also performs more than adequately with a 20 and my first attempt at a Bearcat used a Veco 19. Although the model is not especially difficult to fly, it is a little unstable laterally and, especially when fitted with a big motor, becomes very small very quickly so I really would not recommend it to an inexperienced modeller.

Making a start: The outlines of the model are pretty accurate, depending on which drawings you look at, but where I cheated (if you like to call it that), was in the sections used. For instance, the fuselage has flat sides where the full-size is all curves and the wings have a fully symmetrical 'model' section. The tail feathers are simple flat plates.

I started construction by cutting the tail pieces out of fairly soft and light 3/16 sheet. These were then covered with film and put aside. The elevators are joined with 16g wire and a 16g brass horn is silver soldered to the centre of the joiner giving a hidden internal elevator horn. They were top hinged to the tail with the covering film. The rudder used a similar horn arrangement but was centre hinged with mylar strips. The fin strake is added after the top skinning of the fuselage, so leave the joint area flat.

Wings: The wings on the prototype are foam veneer with balsa leading and trailing edges but we've given you built-up wing details on the plan if you prefer these. Please note that there is a generous amount of washout incorporated. This is quite deliberate and it cost me the original model to find out that a small amount of washout is just not good enough. The original version had a very nasty tip stall (dropping its left wing without warning - just like the real thing, but that is taking realism too far!) but this second attempt is viceless in that regard. Because of the large amount of washout you will have to carve the trailing edge out of solid sheet being careful not to lose the section. The ailerons are cut away later leaving a 1/4 in wide strip on the wing. I stopped the ailerons well short of the tip as a further safeguard against tip stalling. The leading edge is also a balsa strip cut from the sheet. I didn't bother with modelling the oil cooler intake at the wing root but you might want to.

The ailerons on my model are top-hinged with the covering film and actuated by a 14g torque rod; err on the thicker side if you can't get this size. Scale dihedral. is about 2 in under each tip and the centre section is reinforced with thin glass cloth and resin; I glassed the wing locating dowel in place too. The aileron servo sits on its side on a pair of pine bearers that are epoxied into the wing. This, again, is my personal preference and you might prefer to cut a box out of the wing and put the servo upright but please don't use servo tape on its own. What with fuel and vibration the possibility of a loose servo would be very real and not worth contemplating if you imagine the possible results on a fast model like this. One last point - keep the leading edge well rounded to further safeguard against tip stalls.

Fuselage: The fuselage is fairly straightforward in its construction, though I know that planking is not everyone's cup of tea. My 'Mk 1' version used a lot of thick sheet and block with planking only on the top of the fuselage. After the crash, the block had disintegrated and was totally unrepairable whilst the planking merely had a longitudinal split. There's a moral in there somewhere! Anyway, planking is lighter.

I won't give a blow by blow account of the construction because, if you find it difficult to build, you probably couldn't fly it either (standard excuse but with a basis in fact)! Points to note are that I left the bottom section of all the formers off until after the tail had been pulled in and the rear formers added so that the whole assembly could be easily built over a straight line marked on the board. The top of the fuselage can be planked at this stage too..."

Bearcat from Radio Modeller September 1988.

Direct submission to Outerzone.

Supplementary file notes

Article pages, thanks to RFJ.

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