WHY IS THE HELICYCLE© TURBINE POWERED?
In this article we will address the following:
I. The extensive research conducted by Eagle R & D into 2-stroke, 4-stroke and turbine engines; and the pros and cons of each.
II. The reason for choosing the turbine and how it's configured.
III. The factors which made it possible for Eagle R & D to offer the The turbine package for such a reasonable price.
IV. The long term commitment Eagle R & D is making to bring Sport Helicopters into the turbine era.
I. The prototype HELICYCLE© was powered by a Rotax 618 2-stroke engine, however by the time Eagle R & D succeeded in getting into full production Rotax stopped producing this power plant. The most promising type of engine for the HELICYCLE© was still thought to be a two-stroke so work was begun to convert 700 & 800cc Rotax snowmobile engines for the ship. The first obstacle was availability. To prevent air craft use, Rotax sells only crank and block assemblies. The rest of the parts must be purchased individually. This created the second obstacle. The price of the individual pieces added up to such an unreasonable amount that Eagle was forced to look for their own ignition, carburation and exhaust systems. This meant a full blown dynamometer engine test program had to be conducted to confirm this equipment. The dyno work was completed; however it proved difficult and time consuming (i.e. costly)! The results however were very positive. An all up engine weight of 100 lbs produced an honest 85 h.p. at 6300 rpm which enabled the HELICYCLE© to fly at Leadville, Colorado (9,500 ft.) with a light fuel load. This was pretty heady stuff, but still far too many of our builders wanted something more reliable like a 4-stroke or even a turbine. Eagle R & D's major goals are safety first and customer satisfaction second, thus we made the decision to install a Rotax 912 and to demonstrate it at the 2002 Arlington EAA Air show. This was accomplished with about 400 hours of effort after the HELICYCLE© returned from the Sun N' Fun Air show. The installation performed well at sea level, but it turned out to be very costly (way over 50% of the airframe cost), very heavy, and very time consuming for the builders to install.
Just prior to flight testing the 912 installation, one of our most experienced builders completed a T-62-T32 Solar Turbine engine installation in his ship. We had been in close contact with this builder during the process and were awaiting the opportunity to flight test this very creative adaptation of the T-62. The update and flight test results on this installation are noted in the factory update portion of the HELICYCLE© web site. The bottom line is that although the T-62 as designed, is very heavy (180 lbs) and very cumbersome looking, it has fantastic potential from performance and ease of flight standpoints. (More to come).
While in attendance at Sun N' Fun 2002 we also made an interesting discovery. Hirth Motors (respected long time manufacturer of light aircraft engines), introduced a brand new electronically fuel injected, three cylinder two-stroke helicopter engine that looked like it had been designed specifically for the HELICYCLE©. Eagle R & D promptly ordered an engine. The promise of this power plant really won't be known for at least two years from this writing. The installation in the HELICYCLE© is not too extensive, however logging at least 100 hours to prove it's reliability is a minimum 12 to 18 month task.
As you can see, arriving at the correct choice of power plant, while considering performance, cost and reliability is no task for the faint hearted.
II. A. The choice of a turbine to power the HELICYCLE© was really instigated by our builders. A straw poll of eleven builders at the Arlington Air show voted 10 to 1 in favor of the turbine. Subsequent phone calls showed that 95% of the builders wanted a turbine.
Prior to flight testing the T-62 installation Eagle had two serious concerns regarding this type of power plant.
1.High fuel burn.
2.Turbine response time with a single spool rather than a conventional two spool engine. In a 2 spool set up the gas generator spins at a constant rpm and can instantly provide the proper amount of hot gasses to drive the power turbine regardless of how abruptly the helicopter is being maneuvered.
The fuel question was resolved serendipitously. Flight testing has proven the HELICYCLE© rotor lifts almost 12 pounds per horse power. The prototype lifted only 10.5 lbs. This is over 100 lbs of lift improvement. 50 lbs. was used up in added weight to increase the seat load to 220 lbs. This left us with the ability to increase power plant weight and carry four to five more gallons of fuel. The turbine burns 3.5 more g.p.h. than the 2-stroke so with the addition of the 5 gallon auxiliary tank we can achieve a flight duration close to our original target. The turbine burns JP-4, kerosene or diesel fuel. Today most gas stations carry diesel so it is easy to fill up on a cross country flight.
The single spool response time was found not to be a problem. Low level 55 mph full stop quick stops with instant recovery before touch down are no problem. Rotor rpm varies plus or minus 20 rpm and this is fine for the HELICYCLE's© low 2 P.S.F. disc loading.
B. The second reason for the turbine choice is cost. The turbine and it's installation package, clutch, pulleys and belts, etc. is very little more than the price of the Hirth 2-stroke and it includes a fuel control governor which dramatically simplifies flight operation. If the throttle is manually controlled, it adds a level of concentration (for the novice) that doubles pilot work load.
C. The third reason is mechanical simplicity. The turbine uses no cooling system and it can be installed or removed from the ship in a just a few minutes. There is little to do to monitor or service it. It is also vibration free and much easier on the HELICYCLE's© main transmission.
D. The fourth reason is the higher perceived reliability. This is also enhanced by the complete overhaul that Eagle is conducting on every power plant shipped. The engine is completely disassembled right down to separating the turbine wheel from the compressor. The high speed bearings are replaced. All appropriate components are dye-penetrant and magnaflux checked for cracks. The turbine assembly is re-balanced on special equipment to original manufacturers specs.
The turbine assembly is carefully re-assembled with new gear box castings designed and manufactured by Eagle specially for installation in the HELICYCLE©. The electronic and manual fuel flow components are dynamometer calibrated for every engine. The builder need only connect the wiring to be ready for first start up. The alternator is built into the engine drive pulley. It weighs almost nothing and puts out 15 amps. The light weight starter (1/2 of the original) is 24 volts and capable of 3 h.p. at 125 cranking amps. This allows a battery weight of only 9 lbs.. Two small 12 volt gel cell batteries are utilized so the instrumentation still runs on 12 volts.
The engine mounts are installed and the engagement clutch with a fool proof 300 lb. pressure adjustment is included. The oil sump, oil cooler and oil filter with a special canister are ready for the builder to install.
III. Three critical factors came together simultaneously to enable Eagle R & D to offer this power plant for a very reasonable price:
A. Availability. To our knowledge the only adaptable turbine for the HELICYCLE©, for which a several year supply is available, is the Solar T62-T32. As a manufacturer, we cannot count on just picking up an individual engine here and there.
B. Successful Contractual Negotiations for Continued Power Plant Supply. Eagle R & D could not risk beginning a costly program like this one without assurance that the next several years supply would be forth coming. In addition, a volume purchase contract makes it mutually beneficial for our contact to provide us with a fair price.
C. Critical Mass Even if you know the way from point "A" to point "B", you'll never get there if you can't get started. The opportunity for Eagle to produce a large volume of engines makes lots of wheels turn. Tooling amortization, volume purchases and the opportunity to gain production efficiency because of the volume, all combine to help lower costs. Manufacturing is always a chicken or the egg question. How do you lower costs without volume, and how do you achieve volume without lower costs. Fortunately for Eagle, our customers provided the solution and they will benefit from it.
IV. Modifying the T62-T32 for use in the HELICYCLE© by providing our own gear box, is only the first step for Eagle R & D. What happens when a customer needs a hot section overhaul? He certainly won't want to pay as much for a replacement turbine wheel as he did for his whole engine & Eagle is going to make sure he won't have to.
We plan to invest in the tooling to produce our own wheels in the very near future. We already posses the CNC grinding and machining capability. In addition, we will be making the replacement wheels out of a much improved alloy than what was used in the past. The turbine wheel runs up to 11000 F. and the material tensile strength needs to achieve 180,000 P.S.I., at this temperature, a formidable task. The turbine and compressor wheels are of course only the first step for Eagle. There are a lot of other fancy burner can stampings and furnace brazed parts.
Years ago, when we began building our own 4-stroke piston engines at Rotorway (Circa 1975) we had to first learn how to build crankshafts and cylinder heads. Once we accomplished that, the rest of the process went pretty quickly. We believe the same can be true for the turbine and like we've said before we're not counting on our own strength, we have a powerful friend who helps us.
The turbine powered adventure is a whole new hall game, but it's about time for something new and exciting to power the next generation of sport aircraft.
We believe that the previous cost barrier can be overcome with some out-of-the-box thinking coupled with some good old fashioned hard work.
Every normal person gets tired of the same old thing. It's no wonder that the Amateur Built market is starting to languish. If we still had to make do with a 1985 Apple computer, guess what the computer market would be like today. The clunky recip power plant has been around forever by comparison, so it’s no wonder the wind is starting to blow in another direction.
An inexpensive turbine could be just the ticket to jump start Sport Aviation all over again!