A look at gyro planes

My columns have said little about gyro planes in the past and there are those who think they are deadly aircraft. 

Truth to tell, with their rotor system in constant autorotation and their light disk loading, they are really quite safe - similar to a high porosity parachute worn by military pilots in many respects. 

However, they are also fairly slow and this motivates operators to fly them low to increase the sensation of speed. Oftentimes this leads to a congruency interface of man, machine, wires and trees. Man always looses.

Flown with respect to the law and safe practices, these aircraft come close to being helicopters without the high cost and maintenance issues. Thus, this month I have chosen to provide a flight evaluation on a gyro that impressed me with its all-around performance to give non-gyro readers an indication of the genre’s capabilities.

I’ll freely admit the Dominator two-place gyro was the one that beckoned the most after my introduction to auto gyros because in a world where form follows function, the Dominator just looked right.

My dreams were not in vain. Neither was my meeting with the designer Ernie Boyette. This is one opinionated man.

With years of successful designs beginning in 1986 when he joined Chuck Beatty in Tampa and 7,000 hours of gyro time, much of it instructing, this is a man worth listening to. Nonetheless, Ernie claims Chuck is the world authority on gyros with a wall full of degrees including that of a physicist.

Boyette claims he is nothing but a shade tree mechanic with building intuition and when he combines his theories with Chuck’s, the results create successful machines.

Numerous crashes of Air Command gyros in the 80’s were eventually attributed to the thrust over drag phenomenon and the Rotor Flight Dynamics (RFD) team set out to solve the problem. Much discussion has dominated the gyro industry concerning centerline thrust as a means of overcoming Pilot Induced Oscillations (PIO) that lead to a bunting action with the resulting negative angle of attack creating flow downwards in the disk and causing the gyro to tumble out of control in 6/10ths of a second.

Various manufacturers have different solutions to this phenomenon. RFD has simply avoided the problem from the beginning with designs that place the horizontal stabilizer directly in line with the center of the prop hub and for that matter, so are the tall vertical rudder/stabilizers where they can maximize the propellers thrust for stability and control.

The tall vertical stabilizer also cancels "P" factor as thrust is equal on both sides of this fin and Ernie claims a take off is possible with one’s feet off the pedals in no cross wind conditions.

When RFD first introduced their revolutionary gyro in 1988, "they just about got laughed off the field," according to Boyette. However, his low passes along the flight line whereby he pumped the cyclic full aft and then full forward without loosing control impressed all assembled. In fact, Dr. Igor Benson, the father of gyros, exclaimed at the time, "I approve."

All of Ernie’s gyros share common design concepts that make a lot of sense, such as big tires and shock absorption systems with nine inches of travel in the mains and five on the nose gear to tame rough paddocks and firm arrivals.

He claims this gear is the answer to the "stop and drop" landings that sometimes occur when pilots try to touch down with inadequate rotor inertia.

This capability is also very handy on emergency landings in rough terrain as the suspension will conform to the topography to reduce the likelihood of roll over. Ernie adds that no one has ever been killed in a Dominator due to a structural error – only through pilot error.

The structure is so strong that one self trained pilot lost control, released his grip and settled in from 250 feet. When bystanders rushed over to the gyro that was no taller than six inches they found the pilot recounting the incident to a police officer! The seat is designed to kick forward on impact rather than compress a pilot’s spine and the surviving pilot is proud of his life extension.

Differential brakes and a castoring nose wheel allow the gyro to be landed in cross winds without risk of careening off the runway with a canted nose wheel.

Additionally they provide sharp manoeuvring in crowded ramp areas with very small turning radii.

Dragon Wings

RFD’s Dragon Wings ™ rotor blades are much in demand with other gyro manufacturers because they are more aerodynamically refined with span-wise twist to reduce drag and increase performance. With more than 1,100 rotor sets sold to companies such as Air Command International, Little Wings Gyros and others, RFD is the leader in production and experimentation with gyro rotors.

After flying only a half dozen training gyros it was obvious the Dominator was superior in performance to the others thanks to the Dragon Wings – and this with less horsepower!

It’s significant that Ernie mounts every set of blades he manufactures on his gyro for testing, balancing and tracking before sending them to a customer.

This greatly aids during troubleshooting when the blades are mounted on the customer’s gyro. A testament to the efficiency of Dragon Wings blades is the world record for gyros under 500 kilograms of 24,463 feet set in central Florida by Dr. Bill Clem with a 914 turbo Rotax. This bettered the previous record by a vertical mile!

His Rotor Flight Dynamics Inc. (RFD) also uses large diameter propeller blades as they provide considerably higher performance in the pusher configuration behind pilot seats. Of course, the intrinsic tandem seating creates far less drag than side by side seating as well to increase acceleration, gliding angles and cruising speed.

While RFD is aware of unlicensed production of their products in other countries they can only guess at the number of Dominators flying at more than 200.

RFD’s tandem trainer is powered by a Subaru car conversion and produces 105 hp making it one of the smallest engines currently operating on two place gyros.

A hydraulic pre-rotator coupled to this diminutive four cylinder enables spooling up the rotor disk to 50 percent of the normal blade speed.

Hydraulic systems allow more horsepower to be transmitted to the rotor disk and are more durable than friction wheels typically used on other gyros according to Boyette. Although RFD blades are quite long, their lightweight aluminium construction results in operating weights that are less than half the competition. While blade weight is often associated with autorotational inertia, Boyette increases this energy by putting small blade brass weights in the tips where the inertia is multiplied by the lengthy moment arm into more kinetic energy than competitive blades. This author’s numerous power off landings confirmed this excellent autorotational energy.

Another edge of the Dragon Wings rotor blades is a six degree, non linear twist with the outboard section at higher pitch angles. This allows the gyro to fly at higher speeds as it delays the onset of rotating blade stall – a factor that limits cruising speeds of other gyros (and helicopters for that matter). To prove this concept, individuals such as Dr. Clem have exceeded 130 mph in Dominators.

RFD also invented the two bearing rotor head, replacing bushings with needle rollers to relieve the coning stresses that were causing failures in many gyros around 300 hours of flight time.

To minimize potential rotor head damage Boyette employs various techniques including the invention of a slide to allow some fore and aft rotor head motion to relieve stresses on the mast, a teeter bolt to allow some sideways rotor motion and a hydraulic damper that will not allow sudden motions that could harm the systems. Their version of the bifilar "tuned damper" is also found on late model helicopters.

In Boyette’s installation, a fiberglass rod with a slideable weight permitted him to "tune"  the rotor blade to minimize the feed back associated with the natural frequency of the rotor disk.

In Flight Proof

Ernie’s tandem is outfitted with an EIS engine system that confirmed the Subaru’s burst into life and all parameters. Spooling up the rotors as we taxied in the 15 mph crosswind towards his property’s lengthy in-to-wind grass strip we find ground handling proves very precise with the differential breaking and the shock absorption of the gear.

Turning into the flow at the runway’s threshold we once again engage the pre-rotator while applying take off power and are airborne in roughly 500 feet. Directional and pitch control are excellent and we accelerate in ground effect to 60 mph and initiate a steep and sustainable climb that easily exceeds 500 fpm.

Visibility excels up front and even the ground is abundantly evident 800 feet below me as Ernie demonstrates steep banks with extremely high turn rates. These are more aggressive than I have witnessed before in the six two-place gyros previously flown and really capture one’s attention.

Moments later this relative novice assumes control and finds that level flight is easily accomplished as are balanced turns. The natural stability of the Dominator series with the centerline thrust is readily apparent and a joy to some previous gyro flights whereby a pilot needs to constantly make "corrections" in turbulence – often leading to a need to correct for the corrections.

For the many gyro (and helicopter) pilots who have been there, you will know the challenges and fatigue this phenomenon creates.

With the Dominator, pilots can concentrate on the view and let the gyro handle cruising flight in the 75 to 80 mph range with a fuel flow in the 5-6 gph range. She will go a lot faster, but who’s in a rush?

Returning to the close-in circuits, (remember gyros tend to glide like greased crow bars), numerous touch and go landings show just how easy the Dominator is to fly (don’t try it without training though).

Ernie allows me to have my fill of power assisted and simulated engine failure approaches. On one of these, I get a little slow in the flare and drop the Dominator in from about one foot and the shock absorption is so good it makes that landing seem quite reasonable.

During a demo on another gyro a few days earlier, my demo pilot dropped his prototype in when he was de-gusted in a cross wind and it jarred our teeth. Not so with a Dominator.

For that matter, cross winds pose no problems because the nose gear is fully castoring so pilots will never experience that lurch that occurs during touchdown on other gryos when their direct connection to the rudder cants them into the wind.

For further information, contact Rotor Flight Dynamics Inc. at 813-634-3370 or write to 19242 Grange Hall Loop,  Wimauma Fl. 33598

The following specifications are provided by RFD

Model - Tandem Dominator

Engine - Subaru conversion

Power - 105 HP

Rotor diameter - 28 feet

Take off distance - 0-500 feet

Landing distance - 0-20 feet

Rate of climb - up to 900 fpm

Cruise speed - 80 MPH

Fuel capacity - 14 gal

Fuel consumption (cruise) - 5 to 6 gph

Ken is a director on the COPA Board. He lives in Victoria, B.C. and provides services internationally in advanced training, expert witness, flight test and aircraft sales. He has logged more than 15,000 hours on 375 types of fixed wing and rotary aircraft. Soaring his Diamond Xtreme is what he does for pleasure.