After decades of searching, I finally had a late night revelation. Let’s get rid of linkages altogether!
They are clumsy, expensive, and heavy. I turned on the lights (in more ways than one) and set the idea to paper. At the time
I had a Dave Patrick Ultimate, so I modified the bipe to completely eliminate linkages. I mounted the flight controls directly
to the servos. The plane is a modern 3D capable design, so it could use the high control throws a Direct Drive setup would
give me. The modern computer radios have sub trim and end limit adjustments to make up for the lack of a linkage adjustment.
All the essentials were there - and no sloppy links, rods or cables.
The maiden flight was pretty exciting. I was violating the laws of linkages that were set down by the Wright
brothers and had not been challenged in almost a hundred years. The plane tracked solidly. Imagine taking off a new plane
and not having to add any aileron trim whatsoever! It had none of the “mushy” feel that we have unknowingly learned
to live with. It did not dance around like most planes when upset by a little turbulence. The flight was a revelation. Direct
The outside loop (my nemesis from childhood) was precise and tracked absolutely straight. With linkages, when
you push on the stick, the variable slop in the ailerons allow them to be deflected different amounts by the reverse in air
loads. Direct Drive does not have variable slop…..or any at all for that matter…….so outside loops track
as straight as inside loops.
I flew that Ultimate for more than a year with Direct Drive. After a thousand flights, it had no more control
slop than it did on the first flight…none! It never required trim changes for the first flight of the day. On the few
occasions when the trim did change, it was the result of broken flying wires, which attests to how hard I wrung it out. The
Ultimate died a sad death when I ran it out of gas while torque rolling (the absent minded professor).
Local club members were interested in the Direct Drive bipe, so I put together several scratch designed 28%
Ultimate kits, which improved on the original ARF aerodynamic limitations, and were designed around the Direct Drive system.
That’s when I decided to expand the Direct Drive concept to larger planes and see how far I could take
it. I built a 50% Ultimate that weighed 60 pounds as a test bed. The 3W200 was anemic, but the Direct Drive system slung the
monster around like it was the little 28%. The plane flew so well that I used it as the basis to develop a laser cut 42% Ultimate.
The weight savings of using Direct Drive and several other unique design features resulted in a 41 pound plane with a 3W212
engine (21 pounds of that is the engine, pipes, and electronic gear). This 100” wingspan bipe flies the IMAC Unlimited
sequences at less than ½ throttle. It tested the drive system under the extremes of performance, and the Direct Drive has
yet to hiccup. It is impressive to see this big bipe hit a full throttle 3D snap roll into a hover. The stress on the controls
and airframe have got to be phenomenal……but they take it. Pull-pull setups on my old 42% Aeroworks Ultimate would
stretch like putty when I attempted full control deflection snaps, and the plane just wallowed around. With Direct Drive it
looks like the plane hits a wall. Meanwhile, the precision is incredible. It’s like having a direct connection to the
aircraft. The plane never requires a trim change, ever! My next step will be to install a more typical DA150 on the 42%, which
should create a 37 pound killer bipe.
I helped John Braziel install Direct Drive on his 39% Aeroworks Extra. It uses triple servos on each aileron
and rudder. He waited until right before covering to install the drive system, and it went without a hitch. John flies a climbing
upright flat spin using 60 degrees of elevator and rudder deflection. His waterfalls are so tight he can’t keep a wing
tube in the plane.
Jeff Fisher assembled a 35% Carden Extra to use in IMAC competition. He insisted on using Direct Drive before
he ever chose which plane to build. Once again the installation went flawlessly in a single evening. In one contest with the
new plane Jeff went from middle of the pack to second place in sportsman.
On the larger planes the system often goes unnoticed. It is fun to watch people when they finally realize
what they are looking at. The usual response is to wonder why nobody came up with the idea before now.