BASIC DESIGN / ASSEMBLY PARAMETERS
Throughout the aviation community, opinions concerning the best design approaches are often widely divergent. There is no disagreement about the pre-eminence of safety, and safety most certainly characterizes Sport Copter designs. For instance, our airframes are completely triangulated horizontally, vertically, and longitudinally with large diameter-tubing and high-tensile clevises. This makes them the strongest gyrocopters in production. Our horizontal/vertical tail assemblies are big because that makes our machines stable and controllable. Likewise, our landing gear is wide-stance and our suspension systems are specially crafted and combined with the lowest-possible center of gravity for maximum stability and controllability. In fact, the vast majority of what you are going to be reading is about what we've done to make our machines the most stable, most controllable, most predictable, and therefore the safest in the industry, both on the ground and in the air.
Recently, there has been a great deal of discussion concerning high-profile versus low-profile gyrocopter designs, specifically, the difference between the engine thrust-line and the aircraft's center of gravity, and the effect this has upon stability under certain flight conditions. Having built gyrocopters since the mid-fifties, and having tested them exhaustively in virtually every parameter, we at Sport Copter are truly proud of the handling characteristics of our machines. We know from long experience that our copters are stable and forgiving, and they exhibit no penchant for nasty surprises, such as the problem addressed by the high/low profile controversy. We simply have the best ground and flight characteristics available on any production gyrocopter.
We also know beyond doubt that a low center of gravity is essential for safety and stability on the ground, especially when it is obviously not creating any problems in flight, so that's how we designed our machines: low to the ground, with wide, beefed-up gear suspension. . . That's just plain good engineering sense, and it's a big help when entering and exiting a gyrocopter. These factors are described in more detail further along in this document.
There is another trait that distinguishes Sport Copter designs: There is no attempt to remain "married" to any one material or construction practice. Whatever configuration or material is deemed best for the job is what is selected. For example, the tail assembly is a riveted aluminum monocoque structure, while the basic fuselage members are large-diameter aluminum tubing, the cabin enclosure is molded composite and the fuel tank is one-piece high impact rotor-mold, specially built for us. By contrast, there are many other aircraft in production that use the same material and construction methods for every one of those components, just for the sake of simplicity. Again, whereas on many gyros you will often find comparatively primitive construction and less-than-optimum materials used for critical control and rotor assemblies, Sport Copter components are precisely machined from the finest alloys. It is no exaggeration to say that the engineering, materials, machining and finish of our components would do justice for any military aircraft.
While there is no question that the new Sport Copter series is more sophisticated than any gyrocopters now in existence, an essential part of the sophistication is the fact that they are designed for total "bolt-together" assembly. This means two things: 1) The time and tools required for assembly are reduced to absolute minimums. 2) The possibility for errors during kits assembly is reduced to absolute minimums.
STABILIZED MASS-LOADING AND ROTORHEAD GEOMETRY
Our airframes are superior to any other gyrocopters flying today. They're highly versatile and they can accept a variety of engines. Their geometry allows better flight control, preventing the "rocking" motion commonly associated with gyrocopters in low-speed flight. The solution to this problem was actually conceived back in the late 1950's by Chuck Vanek. He redistributed the geometry and mass-loading of his airframes, and this company was the first to market this innovative design.
Here is how it works: The main axle is moved further rearward from the center of gravity and the pilot's position is moved farther forward from the center of gravity. During take-off, as the main rotor is winding up and approaching lift speed, the re-distributed mass-loading stabilizes the main keel of the aircraft, preventing rocking back and forth. This eliminates the "porpoising" tendency so often exhibited by ordinary gyrocopters during take-offs, landings and slow-flight operations. The improved geometry also greatly diminishes pilot work-load by requiring far fewer vertical corrections.
There's yet another very effective geometric refinement to be found on all new Sport Copter rotorheads: The rearward limit of rotorhead tilt has been increased by several degrees, meaning that the pilot can tilt the rotor disc farther aft to achieve a more level touch-down attitude at a complete stop.
NOSEWHEEL DESIGN - On most gyros, the nosewheel and rudder are interconnected, which creates an inherent problem for cross-wind take-offs and landings: Exceedingly low take-off and touch-down speeds are true hallmarks of gyrocopter performance; however, in cross-wind situations, a low forward speed makes any cross-wind component potentially destabilizing if the nosewheel is not aligned with the aircraft's actual path when contacting the ground. With an interconnected nosewheel and rudder, the alignment of the nosewheel is dictated solely by the position of the rudder, which means that in typical cross-wind maneuvers (such as forward slips, pilot-induced aerodynamic skids or "crabbed" lift-offs and touch downs) the rudder-and therefore the nosewheel-will not be aligned with the actual ground path, which can result in the classic ground-loop.
We have an independent system: First, our nosewheel is free-castoring, so it aligns itself instantly upon ground contact, eliminating any tendency to ground-loop. Second, our nosewheel features an ingenious high-viscosity shimmy-dampening system which provides unsurpassed stabilization at all speeds. Third, our nosewheel uses double swing-arm suspension with twin-impact compression bosses (which are actually an integral component of the shimmy-dampening system) giving Sport Copter unrivaled stability and controllability-even at high speeds and over very rough terrain. In short, our nosewheel system design is amazingly simple and effective. . . and the only one of its kind.
Finally, there is the matter of steering a Sport Copter on the ground with a free-castoring nose wheel. Traditionally, non-steerable nosewheels have displayed rather demanding taxiing characteristics, but in the case of the Sport Copter series, steering is easy and smooth. There are three primary reasons for this:
1) The high-viscosity anti-shimmy mechanism defeats the "hunting" tendency of a free-castor to amplify or over-steer answers to steering inputs. The viscosity mechanism instantly "brackets" all steering commands.
2) Primary steering input is accomplished by independent toe-operated hydraulic disk brakes, integrally mounted with the rudder pedals (all four pedals in the two place model). These brakes are thoroughly effective and show no propensity to fade.
3) It is axiomatic that for any ground vehicle, a properly-designed steering system will seek to center itself in the absence of any other input. The Sport Copter accomplishes this by a single spring-loaded centering device which effectively maintains whatever steering input has already been "bracketed" by the viscous damper.
The net result is not only authoritative steering, but an aircraft that practically "nails" itself to the runway centerline during take-offs and landings.
MAIN GEAR DESIGN - We designed the most impressive telescoping-tripod main-suspension system ever used on any gyrocopter. It features a unique and ingenious series of high-impact polymer shock-pads in linear configuration. This feature alone enables Sport Copter to negotiate rough terrain with amazing stability. Incoming compression spikes are simultaneously distributed to and absorbed by each polymer unit. The remarkable virtue in this design lies in the fact that dividing what would ordinarily be one large shock pad into several individual units results in an astonishing increase in spike absorption on the magnitude of better than two-to-one, with absolutely no increase in size or weight.
Even the strut-rebound design exhibits great attention to detail and reliability, especially when considered in the light of generally-accepted industry standards. It's completely enclosed within the upper strut (safely removed from the elements) and it comprises Teflon bushings and stainless steel bolts and carriers, where one would normally expect to find ordinary aircraft steel bolts and aluminum bushings. The bottom-line of these design innovations is an aircraft that can sustain realistic, maintenance-free operations from rough fields, and take truly awesome vertical impacts in stride.
We've built special safety features into our aircraft. First, our basic design philosophy favors time-tested materials for all critical flight components. This means that there is no compromise in the selection of alloys for all frame-member tubing. Exotic lighter-weight alloys have inevitably shorter life expectancies and they're more brittle. In the event of a hard vertical impact, brittleness is one of the least desirable characteristics for a frame member, so only "industry-standard" highest-quality aircraft aluminum and steel alloys are used.
Meanwhile, a great deal of attention has been focused on seat installation, to ensure maximum vertical impact protection. The seat bottom is secured by four stanchions located well along the open spans of the two upper frame members, providing yet another opportunity for impact-absorption.
The rotor mast is multi-member-triangulated, affording the strongest frame/mast assembly in the industry. This means, for example, that the mast can sustain a rotor strike without catastrophic failure, an event which is typically far more structurally traumatic than a roll-over.
All Sport Copter seats are provided with 4-point restraint belt attachments for maximum survivability.
The combination of a generous wheelbase (thanks in part to the Stabilized Geometry described earlier) a full-beam tripod main suspension system and massive frame/mast assembly results in roll-over integrity that far surpasses other gyrocopters, or indeed, almost any low-wing aircraft.
Despite the fact that we are still discussing safety features, the new Cyber Seat calls for a separate heading, since it represents as much a quantum leap in pilot comfort as it does in pilot protection. Designed by Jim Vanek, it is made of composite material and lined with a new high-impact cushion. We have been working together with another company that developed this new cushion material. It has been jet-sled tested to 14 G's, and is already in operational use in seats for long-range military transport and in ejection seats for fighter aircraft.
This remarkable cushioning material actually reconfigures itself to the shape of the occupant without appreciably varying local pressures against the occupant. To appreciate this characteristic, picture lying on your side upon a conventional high-quality foam cushion: You would of course feel much more cushion-pressure against your shoulders and your hips than against your waist, because the shoulders and hips represent considerably more weight and sink much deeper into the foam, which in turn exerts more pressure against the shoulders and hips than against the waist. Now if you were to try the same experiment on this new high-impact material, you would discover after a few moments that the cushion pressure against your body feels everywhere the same.
As you can well imagine, this uniform-pressure characteristic translates into unmatched comfort for extended periods, but even more impressive is its ability to provide very high-impact cushioning without rebound. Under impact, the microscopically small individual foam cells exhibit much the same ideal crash behavior as solid-state rigid styrofoam cells, requiring very high local pressures before collapsing without rebound. Of course, the beauty of this new foam is that after a few moments, it does rebound.
The Cyber Seat is now standard equipment on all SPORT COPTER models, encapsulating the pilot with full support all the way to the top of the helmet, and providing unmatched comfort and impact protection.
Many small aircraft have been designed and built utilizing pilot seats that double as fuel cells. We at SPORT COPTER believe that although a one-piece seat/fuel cell offers attractive simplicity and considerably lower manufacturing costs, the concept of combining two components that ought be as far apart as possible is unacceptably hazardous. Moreover, there are situations where it is actually desirable for a pilot seat to partially fail upon impact, while this is certainly never the case for a fuel cell! Apart from the obvious safety considerations is the fact that routine spills during filling result in stained upholstery and intractable fume-odor inside the cabin. Consequently, our seats are completely separate from the fuel cells, which are the finest high-impact aircraft quality roto-molded units available.
The "LIGHTNING" is powered by the Rotax 503, with single-carb, 2.58-to-1 gear reduction box, and B-gear drive, producing 47 horsepower from a highly reliable, easily maintained engine.
The "VORTEX" accepts a wide variety of engines, such as the Rotax 582, the Rotax 618 or the Subaru four-cylinder Legacy series, to name a few.
The "SPORT COPTER 2" will be powered by the Lycoming IO-360. A special, purpose built engine for experimental delivers 225HP. We changed from the Suburu 2.5 for various reasons.
Given the critical role of the rotorhead, incorporating refinements into rotorhead designs is typically an evolutionary process, unlike the occasional flashes of brilliance that characterize the development of most other components. The term "evolutionary" implies the subtle nature of these refinements, often leaving the designer/manufacturer eager to display them to the public but reluctant to reveal them to the competition. So please bear with us for the relative brevity of this section.
SPORT COPTER has somewhat larger rotorheads than other comparable machines because they were designed for substantially higher loads. The large size is fairly obvious when you are standing next to one of our machines. But when you have the opportunity, you might care to get on a step-ladder and check out one of our rivals' rotorheads. If you do, you won't find any of the features described here:
First, all SPORT COPTER rotorhead components have built-in, replaceable bumper-stops (made of a new broad-temperature polymer) which protect all moving parts from each other as they reach the limits of their respective movement-arcs. The components of other rotorheads simply mash into one another when they reach their arc-limits, leaving dents, scoring and an occasional crack.
Second, the rotorhead itself is actually shock-isolated from the aircraft by a compression-type shock-mount for the longitudinal pivot. This isolation is achieved within the longitudinal carry-through by means of specially-formed polymer and Teflon bushings, compressed and mounted with machined stainless steel retainers, caps and bolts. This results in a significant reduction in shock and vibration transfer between the rotor and the rest of the aircraft. Both the bumper/limit-stops and the rotorhead isolation are intelligently engineered features found in no other gyrocopters, but in time they will almost certainly become accepted design standards throughout the industry.
Our semi-enclosed composite body enhances both appearance and performance. The one-piece windshield protects the pilot from adverse weather and provides much better visibility in rain. Pilot fatigue from pounding wind forces is eliminated, and cross-country flights are faster, safer and much more enjoyable.
The fully enclosed heated cabin provides complete all-weather utility and comfort, along with maximum aerodynamic efficiency and elegant good looks.
FLIGHT CONTROL SYSTEM
In view of the host of innovative features designed into the new SPORT COPTER series aircraft, it may be surprising to learn that we consider the flight control system to be the single most important advancement. To appreciate the assertion, one needs to have a reasonable understanding of typical rotary-wing control response:
If there is any unbecoming trait that distinguishes rotary-wing aircraft behavior from that of most fixed-wing machines, it is control response. Apart from various "fixes" designed into large, sophisticated helicopters, gyrocopters and helicopters usually are quite "touchy on the controls", which is an almost universal complaint of experienced fixed-wing pilots transitioning to rotary-wing operations. This "over-responsiveness" has generally been considered to be the "nature of the beast", but it is not.
The root cause of this "over-responsiveness" lies in the geometry of the linkage between the control stick and the rotorhead. Virtually all gyrocopters (and small helicopters) use conventional push-rods and standard aircraft rod-ends for this purpose. A standard aircraft rod-end provides a very strong and stable free-gimbal connection, similar to the human shoulder joint, but unlike a shoulder, it has a very limited range-of-motion. Even the special High-Range rod-ends have inadequate movement for this purpose. Owing to this limited range-of-motion, the over-all distance of any control command must likewise be limited, since long movements of the push-rods call for correspondingly large changes in the connector angles, and even the best aircraft rod-ends simply cannot accommodate such large angle variations.
The upshot of this mechanical limitation is that since rod-end angle variation must be kept to a minimum, a little movement has to go a long way. In other words, small movements at the rotorhead have to translate into fairly large movements at the control stick, in order to have sufficient range-of-motion to go around. Consequently, small control stick movements mean big rotorhead movements, resulting in a touchy copter . . . and rapid linkage wear, to boot!
What SPORT COPTER conceived to deal with this classic rotary-wing nemesis may well be its finest achievement to date: The Roto-Control. The Roto-Control somewhat resembles a human shoulder because that is basically how it acts. Comprised of a finely-machined, bearing-mounted aluminum cylinder specially built to accept a standard aircraft rod-end fitting at either end, the Roto-Control enables those two rod-ends to act like a pair of real shoulders, with more than enough range of motion to accommodate any control/response ratio a designer might wish to select.
So while other gyrocopters (and most helicopters) continue struggling with over-sensitive controls, SPORT COPTER now has a control system that provides the response and feel of a high-performance fixed-wing aircraft, without having added a single pound of weight! Moreover, the Roto-Control means a SPORT COPTER is more obedient and forgiving, dramatically easier to master and a joy to fly.