DH Chipmunk (oz13683)

About this Plan

DH Chipmunk. Radio control sport-scale model. Wingspan 51 in, for .35 to .40 2-stroke engine or .45 to .50 4-stroke.

Direct submission to Outerzone.

Update 13/3/2022: Added article, thanks to RFJ & Al.

Quote: "I must confess that although I have admired the looks of the 'Chipmunk' I have never built a model of one, so when I was
asked to design one for R/C Scale Aircraft I didn't hesitate. I did hesitate when told that completion was required in seven weeks time - yes seven weeks! About the same time editors give you to do a kit review, let alone design and build a scale model from scratch... oh well, too late to say no now so let's get on with it.

The brief: Shock horror, no .40 cu in 2-stroke size Chipmunk in the Nexus plans handbook to call upon for the 50th Anniversary, So my brief from Nexus was to design a .40 size scale 'Chippy' about 52 inch wing span, for 4 -5 function radio control.

Fortunately a similar size free-flight design the Chipmunk (oz1670) by John Greenland is still available in the plans handbook. It has quite an accurate outline thankfully. Our ed's question was could this be converted to R/C? The answer was a 'Definitely not!'. The outline and dimensions are basically the same as our model but the similarity ends there.

Let's analyse our task: The fuselage, sculptured at the front to cover that lovely inverted 'Gipsy' engine, faired over the wings and conical in shape to it's tail tip, not forgetting the large greenhouse canopy.

The wings, thin in section and tapering on both leading and trailing edge. Reasonably proportioned ailerons and large flaps, good tailplane area and large fin/rudder, in short some good goings and some difficult ones too. My main concern is going to be wing loading at 52 in wingspan, and a flying weight of about 4.5 lbs would be absolute maximum - it's not going to be easy. If it was 1/4 scale I'd give it 99% chance of success. but I have heard of other small 'Chippie' lookalikes that were tricky to fly, ours would only get one chance to prove itself.

Small models can be made to be easy to fly and stable so we must plan our campaign carefully at the outset.

Let's start with the wings: I like to build the wings first then fit the fuselage to it, that way you get the wing seating spot-on and more importantly the wing incidence right. It's relatively easy to build strength in a deep rib, wide cord wing but far more difficult to build strength into a thin taper wing. Take a look at the exotic composite wings that pylon racers build and you'll see exactly what I mean. My method is quite conventional.

Study the plans of the wing and your first impression would be that it's over engineered, not a bit of it. It must be rock solid with spruce spars all round, even the leading edge. I find this is great for resisting those hanger rashes you get with a balsa leading edge.

Build port and starboard separately, assemble ribs and lower spars over the plan then position the hardwood leading edge leaving about 1/8 in projecting. Then glue together the 1/16 x 4 inch bottom sheet with plenty of sheet spare especially on the leading edge. Glue on the trailing edge, aileron bottom spars and flap bottom spars if you decide to include these.

Now to build-in the washout. Pin all the trailing edge firmly to the building board including the tip rib along its length, place a 3/8 packing under front of R1 at the full depth section..."

Supplementary file notes

Article.

Corrections?

Did we get something wrong with these details about this plan (especially the datafile)? That happens sometimes. You can help us fix it.
Add a correction