A new engine project, officially presented by the Italian engine designer RME at the AHS Annual Forum in Virginia Beach, held in May 2015, is a different approach to a more reliable and highly redundant piston engine. The new engine is using existing design methods, technologies, and engine parts but is combining them in an unusual way creating a surprising result with unprecedented combustion piston engine redundancy. The hulking acronym T.E.P.S. means Twin Engine Pack System and actually means two engines in one. Our European correspondent visited the engine designer and discovered surprising features and brand new project details.
A detailed, virtual, multibody model of the T.E.P.S. engine unit was developed at Politecnico di Milano (Milan Technical University) using the multibody/multidisciplinary software MBDyn. The multibody model provided the possibility of identifying the time history of transmitted torques and angular speeds, starting from pressure in cylinders in function of the throttle position. This allowed for predicting the stress levels on the engine components like pistons, connecting rods, crankshafts, and other components of transmission like belts, pulleys, mast, and rotor. The software even allowed simulation of some flight maneuvers like pull-out, flat, and coordinated turns.
Current Market Situation
Today’s rotorcraft are powered by a single piston engine, single turbine, or by a twin turbine - defining with its powerplant the helicopter category. Powerplant redundancy can be found only in twin turbine helicopters which usually weigh more than 2,000 kg/5,000 pounds and where each turbine delivers more than 400 SHP. The result is high operating cost due to the high fuel consumption and complexity.
Starting from this market evaluation, where the entry market is dominated by light, single-engine powered devices, RME CEO, Roberto Papetti identified a problem and designed the possible remedy. Light piston, twin-engine powered helicopters are missing because suitable twin-engine solutions are not available. RME wants to leverage this dilemma and offers the T.E.P.S. engine as a problem solver.
The Problem
The lack of usable powerplants is limiting the use of light helicopters and only a twin engine is according to RME able to ensure the possibility to certify the aircraft as a Class-A, VTOL aircraft and to fly over densely populated areas.
T.E.P.S., Twin Engine Pack System Solution
The T.E.P.S. engine project is based on the RME four cylinder, flat, 100-hp engine with 2.5-liter displacement. The RAP 2.5A called engine is already being tested in a fixed wing aircraft and has logged almost 1,000 operating hours on a RME dyno is now is in first industrialization phase
The experience acquired in RAP 2,5 engine testing has allowed to significantly speed-up the T.E.P.S. project, delivering real-life data.
Despite the Twin Engine Pack System is one engine, the manufacturer calls it “Pack” because of the integration of two engines in one single unit. The “Pack” consists of two completely autonomous four cylinder, four stroke, gasoline, inline engines capable of synchronous operation or should the (emergency) situation require, also single operation. Total weight of the package is 285,6 pounds (130kg), and 330 in³ (5.4 liter) displacement engine deliver up to 240 HP.
The T.E.P.S. engine consists of two, four cylinder, inline engines that are attached to each other with their crankcases, creating an eight cylinder, flat engine with two fully independent, separated crankcases. It's like having a Siamese twins attached to each other, back to back, by the skin. To minimize the engine width, RMA designer slightly shifted one engine approx. 3 inches (86 mm) backwards so that the crankpins of one engine are aligned to others engine main bearings. (Image)
Each engine with 2.7 liter displacement is equipped with its own lubrication/cooling system, power supply and a two channel engine controller unit (ECU). In order to ensure highest safety standards two spark-plugs and two fuel injectors per cylinder will be used. Each engine has its own electronic throttle-body controlled by a proprietary ECU. Both ECUs are controlled by a common EEC (Electric Engine Control). This EEC controls the synchronous operation of both engines and in the case of an emergency -when one engine looses power - automatically and instantaneously increases the power of the remaining engine.
Full power with one engine inoperative
Each engine in a pack is designed to deliver continuous 120 hp at 3,400 rpm; in a normal operation mode the pack could deliver up to 240 hp – all depending on the installation. In the case the engine is installed in a two-seat Class-A VTOL helicopter, certified for flying over densely populated areas, 120-hp output will be assured all time even with one engine inoperative. This is the highlight of the T.E.P.S. engine; in a case of failure of one engine (in a 120 hp, normal operation mode, each engine delivers 50 percent of its nominal power) the EEC opens the throttle of the remain engine so the result is always 100 percent power or 120 hp.
In a common four-seat helicopter, UAV, or fixed wing total power output could be 240 hp (2 x 120 hp) on both engines or 120 hp on one engine.
The cooling of the T.E.P.S. engine is provided by two independent cooling systems and is mainly (by 80 percent) assured by a patented oil to air system (oil cooling with an air-cooled radiator). Cylinders and cylinder heads are fitted with cooling fins which are designed to provide 20 percent of cooling in a case of failure of the oil cooling system. Besides the newly designed crankcase, the T.E.P.S. engine is using “engine top” (cylinder, heads, pistons) components tested in the smaller four-cylinder engine.
RME designed a proprietary helicopter transmission/reduction unit similar to solutions already in use. The RME system is based on a combination of grooved pulleys, reinforced elastomeric trapezoidal belts and with free wheels with multiple clutches. It is able to withstand the high load irregularity of a reciprocating propulsion units. The first rpm reduction step is performed by two parallel belt drive systems that connect each engine shaft pulley to two driven pulleys located on a common output transmission shaft. (Image)
Final comment
First of all we have to say that the T.E.P.S. engine is right now just an engine project, and potential buyers could get it only in several years. Despite this, the information received from RME is saying that the probability that this engine project could be realized soon, have recently, risen considerably. The Italian RME was in December 2015 in final negotiations with “three major, established engine manufacturers” and is expecting that ink on the sale contract might be drying when you read this lines.
The RME engine is opening the way of the technical feasibility of a helicopter to be certified as a Class-A VLR device, powered by an innovative twin piston engine pack. Currently the design of the T.E.P.S. propulsive unit design is completed and the realization of the first prototype is under way. First run-up and beginning of dyno testing is scheduled for first quarter of 2016. This engine could be of interest even for a fixed-wing applications and for UAVs. The idea of a twin engine pack connected to a single propeller is something very appealing and mean highest safety and redundancy level compared to existing solutions.
For more information on Robby Moto Engineering visit www.robbymotoeng.com.
Marino Boric graduated with university degree as aeronautic engineer, acquired degrees in business development/trade and commerce and in journalism. He flew as civil and military pilot. He has built experimental aircraft. As a journalist, he specializes in aviation and propulsion and travels worldwide, flight-testing UL, LSA, Experimental, and certified aircraft. He is writing for U.S., European and Chinese media companies.
