WHAT'S IT LIKE TO FLY THE
It's going to take time to answer this question in detail, so we'll give you the short version right up front.
The vast majority of all pilots have a fixed wing rating.. Outside of the military there are comparatively few helicopter pilots. All of the helicopters ever produced, civilian and military combined, probably wouldn't equal 1 years production of Chevy trucks. Is it any wonder that there is so little credible information available to the helicopter pilot/owner, information he needs enable a truly informed purchasing decision? The requirements for producing and flight testing a commercial quality, FAA certificated helicopter are readily available in FAR Part 27. Over my years of reading aviation magazines however, I have come across very few articles that satisfied my curiosity in regard to the actual operation of a particular helicopter. I hope you'll feel like it was worth your time to read through the following evaluation. First, we will discuss four major subjects, which determine how it feels to fly in any helicopter. Following this, we'll evaluate the HELICYCLE's capability in relation to each of these areas.
Someone has commented that a helicopter is like a bowl of jelly, Punch it in one place and it will shake in another. A standard configuration helicopter, (main and tail rotor version) has three sources of vibration, main rotor, power plant and tail rotor.
Main rotor vibes contribute the lowest and probably the most uncomfortable frequency level. Main rotor vibes are caused by:
We won't stop to discuss each in detail, just remember that a 3 combination lock has 999 possibilities and here we have 5 variables that affect helicopter flight. The power plant has the highest frequency, especially a two-cycle engine. The engine mounting and clutch system must thoroughly isolate these vibrations from the controls and pilot seating area, this design task has historically proven to be very difficult. It wasn't until the advent of the turbine engine that helicopters started to mind their manners in this area. The tail rotor adds it's own contribution in the medium frequency range, and a very mild out of balance condition usually causes a buzz in the foot pedals. A large imbalance can disrupt the tail rotor drive shaft and also cause the airframe to feel like the main rotor is dynamically out of balance as well.
When you go for a demo ride in a helicopter, the first thing you do after fastening your seat belt is to put on the headset. If you thought that this was just so you could hear the pilot better, think again. The management provides headsets so customers won't try to sue for hearing impairment, well almost. Between the turbine whine, (12 - 18" away), main rotor slapping and a noisy, very heavily loaded gearbox right over your head, the idea of bare ears is inconceivable. How do we deal with noise in the HELICYCLE, keep reading, please.
III. STABILITY & CONTROL
This subject could easily take up several textbooks. We will give just one example. FAA certificated helicopters worked on by professional stability and control engineering experts must meet the extensive criteria outlined in F.A.R. part 27. The result of this FAA compliance allows a student pilot to readily master helicopter flight in all types of meteorological , performance and loading conditions, with power on or power off.
In about 1975 two F.A.A. representatives made an unsolicited trip from L. A. to Rotorway in Chandler Arizona to convince us to certificate the Scorpion helicopter. This was to us, an unprecedented opportunity. In effect, they were saying that they would do everything in their power to make it easy for us to certificate our little ship. I was aghast, because I knew something that they didn't. I knew what was required in the stability and control section of part 27 and I knew that the Scorpion though safely flyable, did not comply with it. Further, I had no idea how to make the ship comply. It was several years later, with constant redesign and testing before we were able to understand what took so many years and millions of dollars for the Bell helicopter engineers to figure out. By then Frank Robinson had won the certification race with his R-22.
In a fixed wing aircraft, demonstration of static stability requires no more than positive response to trim in the sense of movement of the controls, this requirement is relatively easy with elevators and ailerons. . It is much harder to meet stability requirements in a helicopter with a spinning, overhead wing. If you disagree, I invite you to spend all the years and many dollars experimenting like I did. Another big factor in helicopter stability is control power. There is an old helicopter designer saying: "Well, my helicopter is a Stable Mabel"! He's asserting that cyclic control response is immediate and rock solid. Point the cyclic in any direction for an immediate response or hold it steady and the ship stays over a dime. Not every helicopter meets 100 % of these criteria.
To most folks, performance means how fast, how far and how high. To the designer it means gross weight, power to weight ratio and C.G. tolerance. To comply with F.A.R. Part 27 it means all of the above at all weights from minimum to maximum and at both extremes of C.G. and from sea level to 7,000 feet or higher. Sounds pretty complicated, but its not! It's easy to understand because it's all directly related to power. Power to weight ratios get better when the power density of the engine and the empty weight of the airframe are are optimized per the available dollars and the laws of physics allow.
The difficulty of reducing weight for a designer is really measured in dollars. Weight reduction takes place one ounce at a time. If a pound of weight could be saved on any one part, it wasn't very well designed to start with. I have been appalled in the past, to watch two second-generation owners of kit plane companies add the equivalent empty weight of a small 3rd passenger to their 2 passenger designs. Of course, this was all done with the lofty goal of improving the design. We'll let you guess how this affected their performance, cost and fatigue life.
Now lets pull pitch in the HELICYCLE and see how it feels and sounds!
Main rotor vibration and cyclic feed back are low in the HELICYCLE, of it's "fully harmonized" rotor system. The previously mentioned five factors have all been dealt with in such a manner, that each is balanced with respect to the others. This kind of relationship is normally achieved during the F.A.A. certification program, by an "In-flight strain gauge testing program". Geometry adjustments are made until all the stress load null points are achieved. The result is a happy rotor system that maintains it's smoothness in "G" loads and turbulence and does not shake itself out of adjustment during every other flight. A rotor which is not harmonized, needs constant fine-tuning to maintain its smoothness. This constant maintenance of the rotor system can take all the fun out of flying your helicopter
The second major reason the HELICYCLE rotor system is so smooth has to do with its elastomeric feathering bearings. "Two-per-rev" cyclic feed back can be a rude shock to the kit helo builder/pilot the first time he gets his machine up to full R.P.M. Why does this cyclic control move in a circle and vibrate so badly, he asks himself as he mentally recalls how much he paid for his kit! "Two-per-rev" has to be experienced to be understood. You won't experience much, if any, rotor feedback in the HELICYCLE because of it's cutting edge design.
Power plant vibes in the HELICYCLE are not noticeable in the controls or the pilot seat. I well remember the early days when the "Scorpion Two" was powered by a V-4 Evinrude two-cycle. The collective stick vibrated so badly that my hand hurt unbearably after a 15 to 20 minute flight and I don't recall making any flights over 25 minutes in that machine. We finally designed our own scratch built four-stroke power plant mostly just to get away from the vibration. We have succeeded with the HELICYCLE however. You can fly off a load of fuel and never feel any discomfort from power plant vibes.
Tail rotor vibration is normally corrected by proper dynamic balancing, with one exception. Tail rotor flapping during cross wind flight can be a nuisance and it can be extremely dangerous, even to the point of loss of the tail rotor. Tail rotor flapping is minimized by proper hinge design. An angle called Delta 3 is built into the HELICYCLE tail rotor yoke to control flapping. The Helicycle tail rotor is flight tested to verify proper function and you can forget about this problem in your HELICYCLE. In addition, the tail rotor is tuned for correct pitch in cruise flight. If pitch control was ever lost, you could continue in flight or perform a run-on landing.
The HELICYCLE is a very quiet helicopter by design, both to the people on the ground and to the pilot. Rotor noise is low because the swept area is small, and the rpm is optimized. The tail rotor runs at a low enough RPM so that it doesn't whine. You can land in a field right behind a convenience store/gas station and unless someone inside sees you, it's very doubtful that they will know you are there. The HELICYCLE uses a large set of spiral bevel gears in the transmission. The spiral angle of the gears is designed to keep noise low and the gearbox is behind the pilot, not overhead. Gearbox noise in the HELICYCLE is minimal. (A video on the transmission is available for $10.00 from Eagle R & D).
Here are the reasons for low engine noise. The power plant is well behind the pilot. Liquid cooling helps reduce noise. The exhaust extraction unit is ported at mid-chamber and a hi-tech after muffler quiets things further. The exhaust outlet is almost 7 feet behind the pilot and it's pointed up so ground noise is minimized. You can easily fly the HELICYCLE in comfort without a headset. I prefer this method, because with a headset you can't really hear what's going on with the machine. We believe the HELICYCLE is the quietest helicopter ever built outside of the Cal-Poly pedal powered helicopter.
3. STABILITY AND CONTROL
Building stability into a powered rotor system may well be the ultimate of all black arts. Making the HELICYCLE feel as stable as the twice-heavier R-22 in windy conditions, has not been an easy task. It has taken me many years and a number of prototypes to fully understand all the factors involved in helicopter stability. A big part of the stability equation is in control power.
The time between cyclic input and rotor response just feels right in the HELICYCLE. It's immediate, just like a fixed wing aileron response. The roll rate is about 120° per second from the start of full step input, yet in a hover there is no problem holding things rock steady. Cyclic movements are not so small or precise that extra technique to hold a point is required.
The collective control is modulated. This affords the pilot the appropriate ratio of movement between collective position and main rotor pitch, throughout its travel. The novice pilot won't know what's going on, but the motion will feel just right.
The throttle on the HELICYCLE using the turbine power plant is automatically correlated. That is, as you raise collective, power is automatically added and vice-versa to maintain the proper rotor RPM.
Cyclic control travel in pitch and roll is harmonized and speed response is quite linear. A trimmed condition at high cruise is not a hands off thing, but its not hard to maintain airspeed within 3-5 mph. Directional control is a no brainer in hover, cruise & autorotation. Lots of tail rotor thrust from the large diameter tail rotor give you control authority that make flying the Helicycle a pleasure.
Power off performance should be evaluated in three areas. The entry, the steady state descent and the flare-to-touch-down. The solidity ratio on the HELICYCLE rotor contributes to improve the entry, which would otherwise be somewhat abrupt. The airflow reversal drop, which takes place on any autorotative entry, has a less dramatic effect on a larger rotor so this is one area where its tough for a small diameter rotor to shine. The steady state descent is not as slow as a Bell Jet Ranger, but neither is the R-22. The flare builds rpm quickly and the flare angle is nominally greater, however the blade tip weights provide plenty of inertia to achieve a soft touch down. The flare needs to be entered at the correct airspeed and altitude. This is pretty much true for all helicopters, but there is usually less tolerance for error on small diameter rotors. Its not a question of safety, its just that a little more precision is required to achieve a "no-crow-hop" touchdown.
In about 1976 I started trying to build what we then called the "Super Single Helicopter". It was to be a 400-lb. empty weight machine with scalded cat performance. It proved to be an impossible task at the time. We made several tries over several years, with no success. The 400-lb. empty weight seemed to be impossible to achieve with the then available power plants. We finally gave up and redesigned the 2 place Scorpion into a more streamlined machine we called the EXEC. That was doable because the power plant made by us, already existed. I never really gave up on the "Super Single" idea so you might say the HELICYCLE was an underground idea for almost 20 years. When Rotax finally came out with honest 65 hp for 85 - 90 lbs. I really began to believe it could be done. It's gotten so much better though, because now, 100 lb. 800 c.c. two cylinder two strokes can put out almost 100 hp at the low cruise rpm of 6200/6300. At 65% power, which is all we need for cruise speed in the HELICYCLE, we can finally close in on the LYCOMING reliability we've been searching for. The power to weight ratio (gross weight/h.p.) now gets pretty close to 7 to 1 which is the same as the hot rod of helo's, the Hughes 500. With this kind of power things really start to get interesting. First, a 220-lb. pilot can still fly with dispatch. Second, you can now land and take off at turbine helicopter altitudes. Third, you can depart an area like a scalded cat. If you're a helicopter pilot already, you know what available power means, if you are not, and you build a kit helicopter with a lesser ratio, you will surely find out. The turbine power plant has an equal or better power to weight ratio than the 2-stroke.
All right, it's time, welcome aboard. Pre-flight completed, clutch engaged, ready to spool up. First raise collective about 3 1/2 inches from bottom then slowly roll on the throttle to 605 rotor rpm. Position cyclic about 1" left of center and add collective to get to a light position on the skids. (Adjust heading as ship gets light) Correct to exact rpm and engage automatic throttle (if optional electronic throttle is installed.) water temperature in green. NOTE: We only "split needles" (check overrunning clutch) every second or 3rd flight. Now we're ready to pull pitch. As we add about 1" of collective we square up with the cyclic. Now we're in a steady 3-foot hover. We hold a moment, feel the controls for proper smoothness and function, listen to the transmission and engine, take a quick look at the blade track and we're ready to depart. We've decided to depart to the rear, so a 180 is in order.
We do three things at once; pull about 1" of collective, ease off power pedal and move the cyclic slightly to the rear. As the ship rotates to the right we follow with the cyclic and stop rotation at 180º with the pedals. The cyclic is now forward and we're climbing through 50' at about 55 mph. We ease off the collective slightly, and roll the nose over with about 1/2" more forward cyclic.
Speed builds rapidly as we level off momentarily. As soon as we're at 75 mph we come back about 1/2" on the cyclic and again begin to climb. We're climbing out at 8 - 900 fpm and are quickly at 500', at which point we move the cyclic forward slightly to pick up our cruise speed of 90 - 95-mph. It surprises us, but our collective position is now only slightly higher than it was in a hover. Boy, that was fast, we turn left briefly to spot the people on the ground where we took off. We're already 3/4 of a mile away and can hardly make them out. If we could hear them talking though, they would be saying, "boy, that little thing is fast." Their previous idea that the HELICYCLE was just a cute toy has been completely forgotten.
The real fun flying in a helicopter is in flying reasonably close to terrain features. In the mountains it includes flying along a vertical rock face, while in a climb. As you top out, you'll get the sensation of shooting up and over. Being in an 800 fpm climb is not that noticeable when there are no close features, but the sensation is awesome when a huge mountain is right next to you and you can levitate right over it. It's also a lot of fun to fly low over the Snake River here in Idaho. At 8' and 40 mph, the ducks and geese take off and fly right under you. As they flap their wings and look up at you to maintain their distance, it's easy to believe that you're a bird yourself.
Now it's time to practice an autorotation. We're climbing out to 500'. At 500' ease off on collective and come back on the cyclic to 65 mph. Switch off the automatic throttle and adjust for proper rpm. (605). When we have our touch down point selected, we're ready. We roll off the throttle, bottom the collective and push in a little right pedal all at once. As the airflow over the rotor reverses from coming in over the top of the rotor to flowing up from the underside of the rotor, we get the sensation of starting down in a high-speed elevator. It's okay though, the sensation only lasts for a second or so and we are now in a steady state descent. During the entry, we didn't notice any tendency for the nose to pitch up or down. This makes autorotative entry really nice in the HELICYCLE.
Now in our descent, we maintain 65 mph and we may adjust the rpm with the collective if it goes over 610 - 615 rpm. This is easy to do in the HELICYCLE because of the "modulated collective". Okay, we are now at flare height of 30 ft., so we come back on the cyclic about 1 1/2" to 2" to build the flare. The nose pitches up, the airspeed drops to 10 mph, the ship descends to the point where we know the tail rotor is within a few feet of touching the ground, so we better do something quickly. We do --- level the ship with forward cyclic and find ourselves moving forward about the speed of a slow jogger while settling to the ground. Touch down is imminent, so we pull up collective about 6" to arrest the descent. We have to time this pull just right, because right now, our rotor has lots of stored inertia; it's spinning at least 10% over normal. If we pull too hard or too soon we could find ourselves up at 20', all out of ideas. If we wait too long, we could land hard enough to bend the rear landing gear. Well, we did it right and touched down smoothly. The ship slides forward about one skid length and comes to a stop. The rotors are still turning at about 80% rpm, so we spool back up, engage the auto throttle and we're off.
By now if you've never flown a helicopter you may be thinking, "boy this is really pretty easy." Don't be fooled.
The HELICYCLE is the culmination of 35 years of design evolution. None of my past designs, with exception of the 4-place Windstar, even come close. Building R-22 equivalent or better handling qualities, stability and performance into the HELICYCLE for 1/5 the price is the crowning achievement of this old codgers career.
Eagle RnD 2512 Caldwell Blvd. Nampa, Idaho USA 208-461-2567 Fax 208-454-3752