Bungee launched free flight gliders, how hard can it be?
In the depth of winter when all good souls are building next years masterpiece with which to stun the modelling world, Dave Rumball and Paul McMahon came up with the idea of a bungee launched 36" span glider club event with a 1min small field maximum. This was greeted with some enthusiasm by the rank and file and vintage models were dredged from loft, workshop, dusted down and cobbled up from long defunct rubber model surfaces.
An initial bungee specification was agreed consisting of 5m of rubber, 10m of fishing line, pennant at the ring end secured with a dog restraint. Tests are still ongoing as to rubber section and 3/32" , 1/8" and 3/16" are under evaluation. Launch height is not unduly dependent on energy retained in the rubber. The model kites up slowly, balancing model mass against lift. My trim method (and I am sure that there are many others) is to glide check for a dead straight glide and only then to attempt a bungee launch. The model tracks right and left on the line due to turbulence and appears to be mostly directionally stable .I know not why. I am using auto rudder for the glide trim.
Herewith a few models that have appeared on the field
Here are a pair of 32" Mercury Gnomes built by Dave Rumball. One of these achieved the 1 min max at Ferry March 23rd. Surprisingly, neither of these has auto rudder but are super stable on launch and have a modest glide turn.
A pair of the author's bungee launch models. The smaller is a 24" Angel RC discus launch model converted to electric FF and now persuaded to do duty as bungee launch . It is not competitive and only manages 25-30s on the bungee but is great fun. The larger is a 30" bitsa using a retired E30 wing, a DLG tail and a Poundland fishing rod boom. Trim not yet sorted, best so far is 38s.
Pete Gibbons turned up with a 50 year old KK Conquest built when he was a mere 11 years old. It successfully survived a bungee launch and was stable on the line.
Mick Page was observed taking much interest in the proceedings and one looks forward to his interpretation of a competitive model. We are, however, contemplating a handicap for all Nats HLG champions.
Ian Middlemiss March 2012
The more I worked on my long moment arm OD Hi Start glider, the worse it got so I parked it and built an enlarged 36" Mercury Gnome based on observation of the success of Dave Rumballs Gnomes.
The spec is..........
The Big Gnome was flown at Old Warden on an 1/8" rubber Hi Start. Trim ended up at about -4deg on the stab and 48% CG. Flight times average about 40sec much the same as Dave Clark's standard 32" span Gnome. Directional stability is not yet up to the performance of a standard Gnome. The model sometimes piles in right (no damage usually) and I am modifying the fin to increase the side area aft of the CG. Getting the model off the line was initially a problem, resolved by bending the tow hook to an obtuse angle.