Anyway, I started searching Vic Smeed designs since the model just had 'that look' about it. It didn't take long on OZ to identify the mystery model as VS's Cherub. First 'mystery' solved!!
Second 'mystery' was to identify the extent of Bernie's departures from the original F/F design.
- Rudder & elevator control surfaces were obvious. But as built, the rudder in particular, was huge, being >50% of the fin area. Probably not so bad for full propo & adjustable travel but far too big for bang-bang S/C . Not surprising that Bernie said it had been a "bit of a handful". Fortunately, my Mule II.4 tx with Martin's terrific encoder has adjustable throws.
- Another control problem was the default control surface throw of +/- 45 degs. Moving the connections at the servo to the innermost holes and to the outermost holes on the control surface horns significantly reduced the rudder & elevator deflections, but the throws are still excessive for S/C. Adjustable throws will have to handle any further reduction, as I don't have any longer control horns and home-made horns would need to be of a length that they would be prone to breakage
- the wing incidence had been reduced by a 6mm packer at the trailing edge. I removed that straight away.
- Since the Cherub uses an under-cambered profile and a lifting tail plane, the original CG is >50% MAC. I've had some not so good experiences with similar F/F configurations when converted to R/C without any changes to the CG & rigging angles - the worst being a violent nose dive if the glider exceeded a certain (relatively slow) flying speed. My research at the time indicated movement of the Centre of lift to behind the CG as the speed increased. Once in the nose dive, the recovery was down to good luck rather than good management. Consequently, my strategy is to increase the longitudinal dihedral by packing up the tail plane TE, and moving the CG forward to about 30% to get a more R/C friendly configuration
- Before I could pack up the tail plane TE, I had to un-glue the tail plane . Thereafter, I think I'll use dowels and rubber-bands, to accommodate fine trimming and transportability.
- As received, the nose had been changed to try and get the motor, and hence the CG forward. Bernie had even turned up a heavy brass prop nut, about 2-3 times larger than the normal ali spinner-nut.
a) Convert to GG instead? Or,
b) Make another fin & tail plane with smaller control surfaces? Or
c) ???
After much deliberation (aka procrastination), I settled on:
- A probiscorectomy - a longer nose to get as much gear, hence mass, as far forward as possible while making the rear end as light as possible.
- Fin + rudder surgery to increase the fixed fin area by reducing the rudder size
- Return wing incidence to original design
- Make tailplane removable and pack up tailplane TE 3mm initially