Shoestring (oz14208)

About this Plan

Shoestring. Radio control scale model racer.

Direct submission to Outerzone.

Update 22/11/2022: Added article, thanks to RFJ.

Quote: "This Shoestring handles well at all speeds; slow, fast and in between. It will even fly well with a .19 engine! But it was designed to go fast with a hot racing .40; the limit in NMPRA rules.

The wing is a flat-bottom section with a six percent airfoil. This type of section was selected for its construction ease and its excellent lift-drag ratio. No tip washout is incorporated in the wing and apparently none was needed as the model has never shown any unwanted tendencies. All flying and control surfaces are scale with no detrimental controlling effects. Small movements of the large control surfaces simply reduce the induced drag during maneuvering, yet are plenty effective at landing speed. The landing speed approximates the run-of-the-mill multi in a normal, not a slow, landing.

The fuselage, when drawn to scale, was just too fat and pudgy looking. The real Shoestring really had a racy look. So the total fuselage cross-sections of the model were reduced to barely exceed the mini-mum NMPRA cross-section rules. The nose and tall moments were retained in true scale. Now the model looked as racy as did its larger counterpart! The wing, stab and thrust line were all set at zero incidence. Two degrees of right thrust were used in the engine mount. The two degrees right thrust will cause a loss of less than one tenth of one percent of total thrust output and it proves to be a real benefit on take-offs.

It was decided to mount the engine on maple engine bearers well tied into the fuselage structure rather than use the radial type mount. This type of mounting provides a solid mount for the transfer of thrust and minimizes the vibration that can sometimes be troublesome with the radial type of engine mount. The prototype model had the engine sidemounted with the cylinder in the right cowl. This arrangement made the entire fuselage structure difficult to construct unless building jigs were used. The inverted engine configuration solved most of the construction problems of the fuselage and has not proved detrimental in any respect. The small amount of added drag caused by the slightly exposed cylinder head is certainly not noticeable!

The construction methods used are fairly common and well detailed on the plans. The only departure from normal is in the fuselage structure that requires the doweling together of the engine mount section and the main pars of the fuselage. This is due to the fact that the two sections are built separately and on the top view of the fuselage plan for overall building ease and accuracy. White glue or slow drying epoxy, such as Formula Two Hobbypoxy, should be used for this critical joint.

This Shoestring was designed as a scale project for the NMPRA racing event and for maximum realization of the model's potential, it should be built as such. This model is hard to pass in a race and getting off first can just about assure a win! For racing the big 'uns, the pilots and owners usually remove all instruments except the airspeed indicator, tachometer and oil pressure gauge. So leave some unfilled instrument holes in the model's instrument panel.

Take some time on the cockpit and carburetor air scoop to get good details that can further add to the handicap points. The airscoop can even be made removable for all flying other than official qualifications and racing! I even use a 'chicken-gear' to replace the official racing Landing gearl The finish and attention to scale details is very important for maximum handicap points..."

Supplementary file notes

Article.

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