Ed Sweeney Superbird
Whilst the whirlybird proved successful as far as the design could go it was not a great circuit machine and so in 1972 it was developed by Ed Sweeny (not by Du-bro) into a single rotor machine. The last two issues of American Aircraft Modeller (Dec1973) included the conversion article written by Ed Sweeney that showed you how to convert the 505 to a belt driven helicopter using a clutch, a new rotor head made from a flat turnbuckle, a nylon aircraft nose gear mounts as bearings plus hand-made rotor blades.
Superbird - Build and flying article from American Aircraft modeller
If you compare this picture to that of the original 505, you'll see that the top-mounted K&B 40 is gone, that metal fuel tank is gone, as are the stock rotor blades and head. The new head is made from a turnbuckle and a couple of nylon aircraft nose gear mounts. Hand laminated and carved main rotor blades with a flat-bottom airfoil (paddles, too) replaced the 1/4 inch balsa slabs of the original 505. The tail rotor blades have also been replaced. The flat 1/32 inch ply TR blades have been swapped out for some hand carved TR blades having an airfoil.
The motor is a Supertiger 23 and it has a Kavan muffler mounted on it. Visible on the bottom is the large centrifugal clutch, the drive belt, and the hand made pinion/fan assembly on the motor. The pinion was turned from a piece of aluminium, and looked like a metal sewing thread bobbin. Holes were drilled into the hub so it looked like a cylinder from a "six shooter" pistol. Short bits of something like 3/32 inch or 1/8th music wire were inserted into the holes, making the grooves to drive the toothed timing belt.
The fan "blades" were short pieces of aluminium, filed so they had an airfoil shape, bent to an "L" shape, and then screwed onto the fan hub. You can see several of the fan blades on the hub. The start mechanism was a cone (seen as the bottom of the fan hub) and a standard airplane starter cone was used to turn it over.
This was a fixed-pitch heli, and the flybar weights are seen to be nothing more than a few large diameter steel washers.
As I recall, the radio I used was a Cannon Electronics 4-channel "Econoflite" system, built entirely from a kit. Servos were Cannon's equivalent of the then popular Kraft KPS-10 servo. It was an AM system, and was flown on 75.640 MHz, "green/white" frequency flags and all.
As an aside, Bill Cannon was a pioneer in what today is considered small or micro RC systems, and one of the last US-based RC equipment manufacturers, outlasting Kraft, Orbit, Bonner, Citizen-Ship, EK-Logictrol, ACE R/C, and many others.
Photoshop did a remarkable job of restoring colour and detail to this photo. It was originally shot onto a 35 mm negative by one of my then RC mentors, Chuck Curtis, an RF Engineer who spent a lot of time designing and building his own RC gear. I believe he is still an active flyer, flying with the Gallatin Eagles, in Bozeman, Montana. I took the negative to a local photo processing shop and had it printed as a 3 x 5 print having a textured finish that looks remarkably like silk, weave and all. The original photo is a bit overexposed and faded. I clicked the "one button" photo fix button and after about 30 minutes, this picture was rendered as shown. I remember very vividly that dirty old yellow "flying cap", that light blue jacket, and even that old table at our local flying site which was about 15 acres of empty farm land adjacent to what was then Summit Engineering Company in Bozeman, Montana.
This picture was taken shortly before this highly modified 505's maiden flight as the "Superbird". Shortly after this heli got airborne for the first time, the setscrew in that "Y-shaped" swashplate follower came loose, and the Superbird was no more. That was probably the most memorable 30-second flight I've ever known in a helicopter.
There is a lot of nostalgia in this picture and it certainly stirs up a lot of fond memories, not only of the early RC helicopter days, but of some of the guys who taught me to fly planks, and who encouraged (and scoffed, though in good humour) me in this new extension of RC -- the RC helicopter.
I was all of about 21 years old in this picture, in College working towards my BSEE degree, and enjoying RC as much then, as I do now.
A salutary lesson to use Loctite however, apart from the build article article I have no 'positive' flying info on this helicopter only reports of failures; this could of course have more to do with the quality of the build than the quality of the design.