2016 was an interesting year for a number of reasons. The US decided to put an Orange Man in charge of things and Britain decided that the EU could sod off. It was a curious time for FPV, too. Quad racing was finally moving away from the snobbery of the model airfield and into the gritty urban ghetto that the likes of Mr Steele enjoy today.
Change was in the air. With ‘Stretch X’ still a mere twinkle in the eye of many a designer, people argued about what an optimal racer should look like. Battery mounted below or above the frame? Does the camera need to be servo-mounted? And will wind resistance be reduced by a 3d-printed scrotum?
Amongst this discussion, some innovators talked of adding a 5th motor-not as a lift generator, but for forward thrust. The principle seems like common sense. Stick an obscenely powerful motor on the back of your machine and you unlock the door to great stuff.
The most obvious advantage is speed. The Screamer 250, one of the only pentacopter designs to be mass produced, could blitz to 80 mph, which was virtually unheard of for a BNF at the time. Acceleration benefited, too. With no need to tilt forward to get moving, you could reach 60 mph in about 3 seconds.
That was just the start. Pentacopters could go pure vertical, and allowed more experienced pilots to try knife-edge flight by performing a quarter-roll from horizontal, yawing upwards to the sky and giving that rear motor the beans. You could even hover on the rear prop for a short amount of time, if you were one of those people who is comfortable living their entire life according to guesswork. Configuring the ESC for reversible thrust expanded your options out further, and there’s probably some grainy account of a mid-air quick stop, as if the aircraft's hit an invisible wall, lurking somewhere within a 2 minute YouTube clip.
The configuration’s third blessing was on your camera. With no tilt necessary for forward flight, you were no longer stuck with a lens that was either cloud watching on the ground or staring at grass and cowpats mid-flight. You could rocket around the sky with a perfectly horizontal cam with absolutely no vegetation perversions whatsoever. So far, so thrusty.
But don’t just go shoving an overpowered motor into the rear end of your favourite quad/loved one. The system came with significant disadvantages which go some way to explaining why it wasn't more widely adopted. To start with, all that rear weight was a literal drawback, meaning you were flying tail-heavy whether you liked it or not. The flight controller would do its best to correct for this, but the rear pair of (lift-generating) motors still had to work significantly harder than the front ones to keep things level.
And the thrust, which was great in straight lines, was little more than a party trick in the rough world of racing. Not only did the extra weight make for dodgy cornering, but having the motor active in turns resulted in an effect similar to understeer in a car. The aircraft just wanted to keep on going forwards, which in racing terms, usually means ‘into the nearest spectator’s groin’. And of course, hammering the thruster even a little too enthusiastically would heavily cut into your flight time.
The final nail in the coffin came from the design. The clearance needed for the rear prop demanded an awkward rear configuration, with the arms tilted upwards in a partial ‘V’ to admit their feisty neighbour. Not to mention that the prop actually contacted the floor until you got airborne, so activating the rear motor at the wrong time could mash the ground, the prop and possibly the airframe into an acrid-smelling metallic-plastic stew.
With all these setbacks, it’s probably not surprising that the pentacopter is a design rarely seen today. But I miss it. As a freestyle idea, or for pure giggles, it’s just too good an idea to pass up. The stunts on offer are pure crowd pleasers, and the feeling of high-speed, horizontal-cam flight is something that cannot be overstated.
With a little DIY, a pentacopter conversion is a great way to get a new lease of life out of any old 250-size frames you have lying around. And a few funny looks at the park. Probably not in that order.