Stringalong (oz16997)

About this Plan

Stringalong. Radio control sport aerobatic model. Wingspan 54 in.

Direct submission to Outerzone.

Quote: "Please find attached plans for Frank Knowles' Stringalong biplane. This was a Radio Modeller plan (RM5) from the late 60s, and I remember seeing Frank Knowles flying his in the aerobatics contest at the British Nationals around 1967/8.

My copy of the plans had degraded too much in storage to be of much use, but I was approached by Robert Thompson at the recent Pontefract Retro meet, where he lent me his unused, and excellent condition, plans. Stan Yeo at Phoenix Models scanned them for me, and both Stan and Robert are happy for me to offer them to you.

Hopefully I will be able to get my damaged Stringalong back in the air again now!
Best Wishes,"

Update 13/9/2026: Added article, thanks to RFJ.

Quote: "Multi Biplane. Stringalong, by Frank Knowles.

Like most aviation enthusiasts, I have always had a yearning to build a biplane. I have watched Jack Morton's Tiger Moth zoom around the sky at competitions and have been full of envy, but just couldn't face up to sparing the time from competition flying to build one. However, during the winter I thought why not build a sport biplane anyway? One that would look about right, but not take too much time to build.

I drew up a specification calling for the aircraft to be not more than 4ft long (1 had to get it into a Ford Anglia), the area about 900 sq in, an old fashioned two-wheeled undercarriage, struts to the top wing, open cockpit, tail skid - the lot! Not, maybe, a very efficient layout, but then for efficiency I would build a low winged monoplane anyway! To look well proportioned, the wing span was to be a maximum of 54 in and for simplicity, ailerons would be on the lower wing only.

Span originally was to be equal on each wing, but when I looked into my wood stock, I found I had some 4 ft lengths of material. One main spar for a span of 54 in less tips, came out at 25 in long. Cut 25 in from a 48 in length of wood and you are left with 23in. So, for economy, that was to be the length of the lower wing half, 23 in plus 2 in of tip equals 25 in! Chord was decided as 9 in so the total area came to 920 sq in. I was told, too, that the gap between the wings needed to be at least one chord.

Bearing all the points in mind, I made the first drawings. The wing stagger I arranged by drawing it so that it looked right. Tailplane area was made a little less than 20 per cent, and the thrust line was arranged a little higher than normal, to allow for the drag of the top wing. Maybe I could think of an aerodynamic formula that would justify choosing these dimensions, but I can't!

A radial mount was decided upon as I am a great believer in that system and, for simplicity, I decided to use the same fuselage section as I had used years ago on the Galahad (oz5551). It took just a month of spare time to build Stringalong from beginning to end, and I had her ready for testing in January.

There was intermittent snow the day I flew the model for the first time. As there was about an inch of it on the grass strip, the first flight was made from a hand launch, and she climbed straight out of the launcher's hand and held a 45° climb right up to about 250 ft where I levelled her out, Handling was very good, except that there was a ten-dency to keep going into a steep climb, involving the application of a lot of down trim. On throttling back, the glide was quite gentle, so I brought her in for a landing. As the model approached the ground, I applied more and more up elevator, until it was flying along in a perfect three point attitude and touched lightly down in the snow.

At this point, someone said, I wonder if it would take off from the snow? So I immediately opened the throttle and applied a little up elevator, expecting to get bogged down as the soft snow came right up to the axles. Instead, Stringalong roared into the air after a run of only about 15 feet.

When I got home I checked the CG position and came to the dismal conclusion that I would have to put some ballast in the nose to stop the climbing tendency. I concealed a 6 oz chunk of steel in the nose and tried again. Flying was much better, but still Stringalong wanted to point to the sky. Then, after a word with Norman Butcher about the trimming of his Fokker D VII, I applied about 1 deg. cf incidence on the tailplane. This made a vast difference and I have flown Stringalong like that ever since. There is still a slight tendency to climb, but this can be handled easily enough.

However, on the drawing, I have shown the tail unit as detachable, and I would strongly recommend that it be retained with rubber bands hooked around the tailskid for the initial flights, until the correct trim has been found, and then cemented firmly in place. By fiddling wth the incidence in this way, I feel that the CG could quite safely be allowed to go back again..."

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