Mike Pirie

My 'Interceptor', built from Gordon Whitehead's plan, certainly Flies Right Off Ground. What's more, it then gives a 20 minute aerobatic flight. The original 'FROG' Interceptor was produced in the 1930s and was probably one of the world's first ARTFs. With a span of 11 inches it came in a small cardboard box and comprised a fuselage, two plug-in wings, removable undercarriage and a gearbox/propeller unit with a rubber motor. After assembly it was wound up by placing the fuselage in its cradle in the bottom half of the box so that the propeller engaged with a ratchet mechanism at the front of the box, then a small handle was inserted into the box from the outside and turned the required number of times. With sufficient winds the model would then rise off a smooth surface to fly for a short time - probably only for a few seconds.

Gordon's stylish model is a four times scaled up version of the original and spans 1180mm (46.5 inches). The prototype was powered by an RX15 motor with Olympus belt drive turning an 11 x 6 prop from six cells. Things have moved on a bit since the time of Gordon's plan (at least a decade ago) and by the elimination of gearbox, receiver battery and heavy radio gear I succeeded in reducing the a.u.w. by a respectable 100g to 1230g (43 oz), giving a wing loading of 54 g/dm² (18 oz/ft²). On my model a Fanfare Powermax 40T up front turns a 10 x 5 APC prop on direct drive, the energy coming from a 3s2p pack of Kokam 2000s. The motor draws 25 amps (static) so I guess the power loading must be in the region of 250 watts/kg or 90 watts/lb - this could explain the stunning performance!

The colour scheme is as per the original Frog model, the silver fuselage being replicated by the use of chrome Fibafilm. The 'FROG' logo

The original rubber-motored 11 inch span Frog 'Interceptor' parked by Mike's scaled-up version was found on the internet and transferred on to transparent inkjet vinyl (from Overlander).

The plane is a sheer delight to fly, and performs aerobatics (limited in my case) with ease. It is difficult to avoid a bounce on the landing however, and disappointingly it is not very willing to taxi in a straight line (it needs a steerable tail wheel). The only deviation from the plan was for the battery access, which is now by removal of the wings (one bolt to unscrew) rather than having an unsightly hatch on the lower fuselage. I also added a fibre-glass bandage at the wing joint as I didn't like the idea of a butt join. Oh yes, and I added a pilot!