ROTEC Engineering Pty Ltd
ROTEC is an Australian family company established in 2000 by two engineers Paul and Matthew Chernikeeff with a "goal to produce and develop affordable and dependable radial engines to rival the craftsmanship and authenticity of a bygone era". They developed a seven cylinder radial (R2800) which was followed in 2005 with a nine cylinder R3600, both for the experimental market.
They are one of the few engine manufacturers which have succeeded in building and selling a very fine product for the experimental kit aircraft builder. We are going to take a look at what they have to offer.
Rotec R2800 Radial Engine
A radial engine has its cylinders situated in a circle in one or multiple rows around the crankshaft. All pistons are connected to one large big end and this configuration creates a very short engine. And its perfect for an air cooled design as all cylinders are exposed equally to the incoming air flow. In radials with two or more rows the cylinder are staggered, like with the Pratt & Whitney R-4360 Wasp Major where the R-4360-51VDT had a power output of 4300 bhp (3210 kW).
High torque, big props
Rotec: "For a given capacity, the radial configuration is arguably the most effective for hauling big props at low efficient RPMs. High torque ratings have always been associated with the radial engine. In layman’s terms this is the result of good bore stroke ratio, low master and link rod angles resulting in superior transmission of cylinder pressure to the crankshaft with all rods acting on a single crank journal. The radial crankshaft is also very short and sturdy when compared to its long spindly inline and flat counterparts and, as a result, does not suffer from torsional distortion or excessive friction caused by the accumulation of many plain bearings".
Rotec R2800 and R3600
This design is a single row, seven cylinder air cooled radial engine. It uses a single bing 40 mm altitude compensating carburettor (with an option for a throttle body injector TBI-40), has planetary propeller speed reduction unit (PSRU ratio of 3:2, engine:propeller) which enabled the propeller diameter to increase due to lower prop RPM and the thrust increased proportionally.
The camshaft is situated between the PSRU and the crankshaft, operating pushrods for the two overhead valves per cylinder. The exhaust is either collected in a ring (option) or expelled through short pipes on each cylinder. With the exhaust ring the genuine radial sound really comes alive!
Electronic and Magnetic Ignition
The dual ignition consists of a single self energized magneto and Hall effect 12 volt electronic ignition system with two automotive type spark plugs per cylinder. The electrical system consists of a 12 volt starter motor and a 35 amp alternator with voltage regulator.
Rotec R3600 Radial Engine
We have made a short overview, side by side, of the specifications of both engines:
|Specifications||R2800 - 7 Cylinders||R3600 - 9 Cylinders|
|Power||110 hp||150 hp|
|Total Swept Volume||2800cc (172ci)||3600cc (220ci)|
|Bore Stroke||80 x 80 mm (3.149” x 3.149”)|
|Dry Weight (no acc)||95 kg||118 kg|
|Dry Weight (w/ acc)||102 kg||125 kg|
|Max Propeller RPM (fixed)||2300 - 2400||2400|
|Propeller HUB||SEA #1|
|2 blade Pitch / Diameter||51 inch / 76 inch||76 inch / 84 inch|
|Compression Ratio||8,5 : 1|
|Fuel||97 RON / 100 LL|
|Fuel Consumption @ 75%||22 l/h (5,8 USG/h)||27 l/h (7,1 USG/h)|
|Recommended TBO||1000 hours|
|Warranty||12 months or 200 h|
This engine is bringing back radial technology from the last century for modern experimental aircraft and replicas. It's not anything like a Rotax or Lycoming but the sound of a running radial is just plain music to the aviation ears!
One very nice example of a Rotec R3600 project is the RV-8R, take a look at the next YouTube Video Radial RV-8R: A Poor Man's Hellcat.