Flight Test: Autogyro Cavalon
PUBLISHED: 12:57 07 December 2016 | UPDATED: 13:49 07 December 2016
If you fancy the look and feel of a Robinson R22 but at a fraction of the price — and running costs — try the Cavalon
Words: Nick Bloom; Photos: Keith Wilson
A Robinson R22 helicopter costs around £203,000. For just over a third of that − £78,000 for the basic model − UK agent RotorSport will sell you a Cavalon, an autogyro with side-by-side seating in a comfortable, fully-enclosed cabin.
Sitting in one in flight is not unlike sitting in a two-seat helicopter, with joystick and pedal controls, rotor blades whirling overhead and a splendid view out, particularly down. The cruise speed of around seventy knots is considerably slower than the R22’s 95, but then running costs for the Cavalon, particularly maintenance, will be considerably cheaper. Replacement rotor blades cost around £3,000 each and they are ‘lifed’ at 2,500 hours.
Both Cavalon and R22 require a significant outlay in training − a minimum of 35 hours to convert a standard PPL for ‘gyroplanes’ (as the CAA now calls them), 39 hours for helicopters. Perhaps the major difference is the Cavalon needs a runway of at least 300 metres for takeoff, whereas the R22 doesn’t. (In theory the Cavalon can land ‘on the spot’, but in practice it usually needs a short runway for landing as well as for takeoff.)
You can’t hover a Cavalon just above the ground and there’s no collective, the lever in helicopters controlling lift. This makes it easier to fly, but inevitably robs the autogyro of some of the helicopter’s versatility.
The Cavalon has some superficial similarity to the old RAF 2000, but with two major additions that make the aircraft far safer. The first is a tail boom with horizontal tail surfaces, which improves stability; the second is raising the rotor higher above the fuselage.
Essentially, autogyros achieve their pitch and roll control in the same manner as weightshift microlights, by altering the centre of gravity in relation to the ‘wing’. So the greater the distance between ‘wing’ and centre of gravity, the greater the control and stability.
There is a built-in pitch/power coupling in most autogyros: the engine has to be mounted high to give clearance to the propeller blades. Increasing power tends to pitch the aircraft nose-down and any suggestion of negative G is anathema to a lifting surface dependent on airflow from below. (which is what keeps the autogyro’s blades turning). You can get away with having the thrust line on the fuselage axis, but only if the rotors are considerably higher still, as they are in the Cavalon.
The Cavalon is a most striking-looking aircraft. With its egg-shaped pod, sharply pointed at front and rear, it has a sci-fi look, the kind of thing Frank Hampson might have pictured us all using instead of cars in the future in his illustrations in Eagle comic in the 1950s.
Andrea Banks and Kevin O’Neill, co-owners at Elstree, had only just had their Cavalon delivered when I first saw it. They run a microlight school, Fly By Light, and have plans to offer instruction in the Cavalon.
A week later, photographer Keith Wilson and cameraship pilot Claudio (provided by MAK Aviation) are with me in Fly By Light’s clubroom, briefing for a flight test. I won’t be able to take the controls for takeoff and landing as Kevin, an experienced instructor on microlights, isn’t yet able to instruct on ‘gyrocopters’.
He agrees the handling in flight is similar to that of a fixed-wing aircraft, but since I won’t be flying a takeoff, I ask him to talk me through the procedure. “Start the engine with the propeller set to fine,” he says. “After the usual pre-takeoff checks, pre-rotate the rotor to 200rpm with the aircraft held on its brakes. Release brakes, hold the stick fully back and slowly power up. Check the rotor rpm is increasing. You’ll need right rudder to counteract spiral airflow. Adjust attitude in pitch so that the nosewheel is six inches off the ground and wait for the aircraft to fly itself off. Once it does, lower the nose and hold the aircraft just off the ground until it accelerates to 70mph, then climb away.”
He adds, “For safety reasons, we keep to 70mph below 300ft.” I ask what the lift-off speed is and he estimates it’s around 45mph. I can see the logic in staying low after takeoff in order to add energy to the spinning rotor blades in case of engine failure.
Above 300ft, there would be room to dive and maintain rotor speed and lift, but there would be too much risk of rotor speed decaying and loss of control below that. However, Kevin assures me the undercarriage, which certainly looks sturdy, is strong enough to withstand a steep descent from below 300ft.
Kevin continues: “For landings, you fly a normal approach at 60-65mph and round out twice in what instructors describe as a wedge − first the thick end, then the thin. The approach power setting is 3,000rpm. You touch down at 2,700rpm and only fully close the throttle when you’re on the ground. It’s most important − and the opposite of fixed-wing practice − to push the stick fully forward as soon as all three wheels are down. The rotor is still spinning and the downdraught has to be directed to the rear. In extreme cases, back stick at this point can actually cause the aircraft to go backwards!”
I ask about loading. The maximum useful load (fuel, occupants and baggage) is 244kg. By comparison, the Eurostar EV-97 SL microlight has a useful load of 185kg and the Cessna 152, 267kg. Luggage space is limited − just room for two slim backpacks, one behind each seat, and each of these is limited to 10kg. Two adults, plus 20kg luggage, leaves 70kg for fuel. Fuel capacity is 100 litres (72kg) so the Cavalon will actually carry two adults, full fuel and luggage. Fuel consumption is seventeen lph, giving an endurance of 5.5 hours, and a range of around 360nm.
The Cavalon is a tall aircraft (2.8m), so Kevin asks me to keep an eye on the tip of the rear rotor blade in case it fouls the doorway as he pushes it onto the apron. He pushes it easily by the rudder, linked to the nosewheel, and of course there are no wings to worry about.
There is a lot to admire in this machine, immaculately finished and perfect in every detail. Vorsprung durch technik!
There isn’t an internal steel tube structure: it’s a fully monocoque carbon fibre composite shell, except for the steel tube on which the three fins, tailplane and rudder are mounted (there’s no elevator). This tube is kinked and has a rubber ‘tail bumper’ on it. Kevin points out that, instead of the usual inverted-T, keel-and-mast structure, which transmits noise and vibration from the rotor, the Cavalon has a separate mast, one of many hidden design features.
The rotor blades are aluminium. You cannot get a autogyro with a C of A and the Cavalon is currently on a CAA Permit to Fly, although it should be transferred on to an LAA Permit fairly soon. I have operated aerobatic aircraft on a CAA Permit and in practice it makes little difference to operation or maintenance.
The fully enclosed pusher engine is fan cooled. In this Cavalon, it’s a 115hp Rotax 914 turbo driving a three-blade variable-pitch propeller. Pitch control is electric, and there is a manifold pressure gauge as well as a rev counter in the cockpit. For this flight we’ll just leave the propeller in fine pitch, says Kevin.
With such a high thrust-to-weight ratio, I would expect this aircraft to be a sprightly performer, even when its lift is provided by relatively inefficient rotor blades, compared with most fixed wings. As I understand it, the idea of fitting a rotor in place of a wing came to Juan de la Cierva in the early 1920s because so many pilots were being killed by allowing their aeroplanes to get too slow, resulting in a stall and spin. Rotor blades could be turning and providing lift regardless of how slowly the aircraft was flying.
The blades in an autogyro are made to turn by airflow from below, either because the aircraft is descending (gliding) or because the rotor cone is tilted at an angle of attack relative to flight. Autogyros cannot stall, but if the blades aren’t rotating fast enough the aircraft will still fall rapidly, at least until upward airflow restores lift and control.
Continuing my initial impressions of the Cavalon, I notice an external oil cooler and a fairly wide undercarriage that looks good for self-righting and containing unwanted roll inputs. Everything is carefully streamlined and the sleek finish is good enough for a luxury sports car.
There are strobe lights on either side of the fuselage behind the doors and some smart ‘headlamps’ on the nose, presumably not for use when landing but to enhance visibility to other aircraft, because not having wings can make you harder to see. The doors are hinged at the top and have ingenious fittings to facilitate removal − you can fly without them. They are held up by gas struts.
One complication with autogyros is the advancing blades on one side generate more lift than the retreating blades on the other. Juan de la Cierva had a ‘Eureka moment’ in his development of these aircraft when he came up with a simple automatic system for correcting this − flapping hinges. However, this does make autogyros with conventional anti-clockwise rotation more efficient for single occupancy if the pilot sits in the right-hand seat, so that’s the one that Kevin will be taking today.
The seats in the Cavalon are adjustable, as are the rudder pedals. The pedals on the left are already set fully aft, but as I have rather short legs I opt for the seat fully-forward adjustment as well. (Actually it’s just the seatback that’s adjustable, via a strut at the top rear.) Climbing in proves unusually easy for such a small aircraft as the floor is quite near the ground, enabling me to lift a foot past the left-hand control stick (the Cavalon has full dual controls) and onto the floor.
The seats are comfortable and the cabin has a reasonably high roof and roomy feel. There are no toe brakes and no differential braking. Instead there’s a brake lever rather cleverly combined with the centre console-mounted throttle lever, allowing one-handed operation of both.
At first glance, there seem to be rather more controls and instruments than I’d have expected in a simple two-seat aircraft. Each control stick has a ‘cooliehat’ electric trim for pitch and roll, the latter to allow for single-occupant flight. It has a trigger for radio transmission and − most important − a pre-rotator button. Without a pre-rotator, you need a long takeoff run to get the rotor up to speed, just using airflow.
I am pleased to find a duplicate throttle on the left of my seat, meaning I’ll be able to fly formation with my right hand on the stick. This is not standard in the Cavalon, but can be fitted as an extra.
In addition to the usual engine instruments, including water temperature, there are a propeller pitch control, a choke on the centre console and switches for two electric fuel pumps, the second used for landing. There is a pneumatic pressure instrument and control − the elevator trim and the pre-rotator engagement are operated by compressed air − and rows of circuit breakers on the instrument panel.
For comfort, there is a cabin heat lever, two air intakes on each door for keeping cool and (currently folded away) a sun screen at the rear of the roof transparency. A GPS, Mode S transponder, intercom and radio are fitted, as you would expect.
Then there are the additional controls and instruments for the rotor: a rotor rpm gauge, a rotor brake control marked Flight/Brake, and the already mentioned button on each stick for using engine power to start the rotor turning. There are the usual analogue flight instruments for altitude, airspeed, direction, and climb-and-descent, and a rudder trim indicator. But there is no slip ball, instead a strand of wool is taped on the outside of the windscreen.
Kevin joins me in the cockpit and we lower our doors. These have a nice, solid feel to them, as do the catches securing them. I am delighted with the view downwards, and the view ahead is better than in most fixed-wing aircraft. My view to the right is good, even though there is a diagonal door pillar in the way. Kevin and I do up our seat belts, which include a shoulder harness, and don noise-cancelling headsets. One control I failed to spot turns out to be behind us, between the seats − a fuel tap, with a red guard over it.
The cabin with two inside and the doors closed still feels fairly roomy, which is a tribute to good design. There isn’t actually a lot of spare space and the only place to stow maps, sandwiches and other loose objects is behind the seats − adequate, but not over-generous.
Kevin produces a check-list and starts to run through it. He confirms prop fully fine, starts the engine (using choke) and waits for the temperatures to rise, then checks mags and pressures, hatches and harnesses. Taxying appears to be exceptionally easy with the wide track main wheels, steerable nosewheel, great visibility, and, of course, no wings to worry about, the rotor at this stage still being parked and aligned with the fuselage.
There are more pre-takeoff checks at the hold, including one to confirm we have roll control. You can see the tip of one (still locked) rotor blade alter its incidence angle as the control stick is moved sideways − an indication that the whole rotor disc is tilting relative to the rest of the aircraft. It is not deemed necessary to check the electric propeller pitch control.
Once we’re lined up on the runway, Kevin locks the wheel brakes, throttles up to between 2,000 and 3,000 rpm, unlocks the rotor and engages the pre-rotate clutch. The rotor hesitates then slowly begins to turn, gradually gathering speed. When 200rpm shows on the rotor speed dial, he releases the wheel brakes and, holding the stick back, allows the aircraft to begin moving forwards.
As we start to gather speed, he gradually opens the throttle to full rpm. The nosewheel lifts early in the run and I feel Kevin checking its rise by a slight forward movement of the stick. I can feel the aircraft wanting to lift, which it does after a run of perhaps eighty metres, but rather than climb away, Kevin gives increasing forward stick to hold the Cavalon just above the runway.
I sense Kevin struggling a little to hold it steady. I wonder if it’s necessary to keep quite this close to the runway and for quite so long, because from the way the aircraft seems to be oscillating minutely in all three axes (mainly pitch), this part of the takeoff doesn’t look easy. However, well before we reach the end of the runway, after a run of perhaps 400 metres from the start, the ASI reaches the required 70mph. At last he eases back on the stick and we climb away.
Initial climb rate once speed settles at 65mph seems to be a healthy 800fpm. He throttles back to bring the turbocharger off-line. Kevin flew helicopters in the Army Air Corps before becoming a microlight instructor, but he tells me it took him 45 hours of training − ten over the minimum − to get his Gyroplane licence (as a pilot, not an instructor).
A fixed-wing pilot now has to repeat the full PPL training syllabus, including cross-countries, before gaining this licence, with just a ten-hour credit for existing skills. Ab initio students don’t have the ten-hour credit and have to fly a minimum of 45 hours. Kevin says he would have liked more training time.
What does this tell us? Are autogyros really that different from fixed-wing aircraft? I think partly it’s a reflection on the autogyro’s unfortunate history, particularly dating from the period when Bensen-type autogyros first began to be able to fly out of ground effect and kept crashing. When the tandem-seat, long-keel and high rotor formula began to appear, the type became a lot safer, but there were still pilots coming to grief in Bensen-style autogyros (including the RAF 2000).
The CAA has perhaps understandably responded by increasing the number of hours of dual training required. You can, however, have too much training and make flying overcomplicated. Students becomes so aware of all the things that can go wrong and so crammed with theory they fly in a fog of fear and confusion. Instead of gaining confidence early on, thereby being open to learning, they get stuck.
There is another possible reason why, even with 45 hours training, an ex-helicopter pilot like Kevin should feel only just ready to fly the Cavalon − the aircraft is difficult to fly and, despite all the improvements, still has ‘dark corners’.
Maybe this is because autogyros will always have them. Certainly this is true of twins, vintage biplanes, advanced aerobatic aircraft, floatplanes and helicopters. All are safe, but only providing you keep your wits about you, don’t become complacent and know their ‘gotchas’.
Back to the flight test. We are clear of Elstree now so Kevin allows me to take control. The Cavalon in cruise seems to handle like any other aircraft, fairly steady and responsive with the controls well harmonised. Perhaps there’s a little bit less manoeuvrability, but I wouldn’t swear to it. The aircraft seems stable and Kevin says it will fly itself while you fold your map (unlike a helicopter!).
One difference is the vibrating control stick, which I’ve noticed in other autogyros. I’m sure you get used to it. Kevin says there’s a modification, a loose clamp you fit to the control cables, which the factory thinks will reduce the vibration by seventy per cent. It’s not, as I imagined, that the blades need balancing, it’s a purely aerodynamic effect of the advancing and retreating blades changing angles.
While I’m on the subject of cruising, as with all rotary-wing craft, autogyros give a steadier ride in turbulence than aeroplanes. Kevin seems slightly nervous as I draw steadily closer to the Cessna for the photoshoot. I try to keep in mind that the Cavalon has an 8.4 metre ‘wingspan’, equivalent to a four-seat Jodel, and maintain an appropriate separation.
The principal hazard in autogyros is unloading the rotors with negative G. We are a long way short of doing that, though, and I think to myself, all that training can make you over-cautious. Nothing happens to alter my feeling that this is like any aircraft, rotor or not.
Incidentally, one virtue of autogyros is they can cope with relatively high crosswinds. I can confirm from flying with crossed controls that side-slipping into wind should be an option.
On the way back I ask him about ‘loitering’ − slow flight and steep turns. “You can make tight orbits quite safely at 20mph,” Kevin says, “providing you stay above 500ft.”
It only remains for me to observe Kevin make a landing, and it all looks straightforward. There are two fixed-wing aircraft in the circuit behind us, so he keeps the speed up during our descent. I don’t see a wedge or even a two-stage roundout. We head towards the runway from a higher position than normal, make a steeper descent (a bit like coming in with full flap) and, as the runway approaches, arrest the descent in the usual way. That is to say, Kevin eases back on the stick and we go from a diving attitude to one parallel with the ground.
Kevin brings back the power then, as the aircraft slows down, pitches up slightly to a climbing attitude. There is a lot of drag from the rotor at this point and we slow rapidly, shortly afterwards touching down on the main wheels. Kevin closes the throttle. The nosewheel comes down and the instant it does, Kevin gives full forward stick. We come to a stop and he is able to steer off the runway. The rotor is slowing and soon runs down, whereupon Kevin applies the rotor brake, parking the blades.
It was a short landing, perhaps fifty metres, but nothing too unconventional, except that full forward stick once the nosewheel came down. Kevin says there are more dramatic ways to land the Cavalon. At 15-20mph indicated from 1,000ft, the nose pointing at the numbers in a very nose-down attitude, for example (but only down to 500ft; below that height, airspeed must be kept above 60mph).
Hopefully some of the training does involve exploiting the versatility that is such an important feature of autogyros, and not just alerting students to the ‘dark corners’. The Cavalon is versatile, beautiful to look at, a pleasure to fly and certain to turn heads wherever you go. It makes a very acceptable substitute for a Robinson R22.
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