Interconnected Propeller Drive
Gevers Aircraft, Inc. * GENESIS *
The wing mounted props are belt driven from fuselage mounted engines.
Safety is greatly improved with the Genesis. The twin engine twin propeller arrangement has both engines connected together to both propellers in such a way that during an engine failure both propellers are still powered equally by the remaining engine. As a result no action is required by the pilot to maintain directional control during an engine failure because there is no asymmetric thrust only a decrease in total power. In normal operation the propellers will be coupled together and are driven at the same RPM. However, they can be coupled and decoupled in flight from the cockpit at the pilot's discretion. Engine out rate of climb is also significantly improved with this design.
This interconnected propeller system gives the Genesis the operational ease of a single engine design with twin engine performance and greater safety than both. This is a very simple mechanical fail-safe system. Two engines are mounted facing each other in the fuselage directly above the main landing gear. They both drive into a common, simple gearbox through overrunning clutches. The gearbox drives two constant speed props through a triple set of redundant timing belts and pulleys. The 3 parallel belts in each set are separated by partitions preventing a failed belt from becoming entangled with the others. Belt drives are becoming common in new production helicopters along with experimental and FAR part 23 aircraft. This belt system is lighter and more reliable than a gearbox system because there are three belts in parallel providing a triple redundant fail safe advantage that a conventional gearbox system does not have. No power is transmitted through the gearbox unless one engine is shut down.
The high reliability of timing belts is well known. Failures of these components occur from misalignment, contamination, and shock loads. Alignment and lack of contamination are guaranteed by this design. And if shock loads occur (prop striking an object), we want the belt to fail rather than the engine. Belts in a properly designed system will last longer than the engine overhaul time (and will be replaced at overhaul).
Overrunning clutches provide single engine simplicity with multi-engine reliability.
During normal operation both engines produce nearly the same power, and are geared together so they run at exactly the same RPM. The engines power a common gearbox, which in turn drives both propellers and provides automatic synchronization. There are two instances in which the engines would not operate as one.
In the first case, one engine produces so little power that it can't maintain the RPM at which the other engine is running. For example, during a catastrophic engine failure or even when one engine is at 75% power and the other is at idle. Here the overrunning clutch on the dead or idling engine allows it to "drop out" so it doesn't contribute any detrimental drag on the other engine. In fact, it can even be shut off and re-started while the other engine powers the gearbox and both propellers. One engine can suddenly loose power (and even come to a stop) and the other engine automatically assumes the load of both propellers - no asymmetric thrust. The "dead" engine does not load down the running engine.
It should be noted that one engine driving both props is more efficient (and much safer) than the conventional situation of one engine driving one propeller. Two props running at half power produce more thrust than one prop at full power. This design also avoids the asymmetric thrust which causes the aircraft to assume a dangerous high drag producing configuration.
A second situation in which the engines would not run at the same RPM is produced when the pilot elects to de-couple the props. This is done with a cockpit control which separates two gears in the gearbox. Each engine drives its respective propeller as in conventional designs. The overrunning clutches are still in the drive system.
Decoupling is required in the unlikely event of a propeller failure, in which the offending prop must be shut down. Note that in the case of a runaway prop (pitch goes to low - RPM goes out of control) the overspeeding prop cannot damage the engine by forcing it to a higher RPM. In fact the propeller speed governor located on the engine prevents engine overspeed even when the load is suddenly removed.
Internal fuselage mounted engines.
Hinged side panels in the fuselage allow for easy access to both engines for maintenance.
Locating the engines above the center main landing gear is structurally beneficial because the landing forces from the engines are transmitted directly to the main gear without passing through the wing structure.
The majority of aircraft noise comes from engine exhaust and the propellers. Noise levels in the Genesis cabin are decreased because the exhaust and propellers are well behind the passengers and sound baffling can be used in the engine compartment similar to a car. Whereas a typical single engine aircraft has the prop directly infront of the cabin and the exhaust below the pilot's feet and a typical twin has both the exhaust and props right next to the passengers on both sides. So the Genesis is much quieter than conventional twin or single engine aircraft.
Eliminating the engine nacelles from the wing reduces drag and returns that section of wing to a smooth lift generating surface.
With the engines internally mounted better temperature control for the engines is possible over the range of flight conditions from ground operation to cruise. Forced airflow through the engine compartment gives the pilot direct control of cooling when hot as well as heating in cold environments.
Placing both engines near the C.G. greatly reduces the rotational moment of inertia of the aircraft, which improves spin control and safety. The C.G. is also kept low in this arrangement improving high-speed taxi maneuvering in the water and on land.
Movable propeller arms.
Mounting the engines internally and driving the propellers through timing belts allows for the propellers to be mounted on arms that can be rotated clear of the ground and water spray. This also eliminates the possibility of passengers and ground personnel from coming into contact with a running propeller. For cruise, the props are positioned so the thrust line matches the drag line. This eliminates the inefficiencies of a typical amphibian where the high thrust line creates a large nose down pitching moment in cruise. The propellers are mounted on the upper end of the outrigger landing gear leg. When the landing gear is extended the props automatically raise.
The overrunning clutches and central power gearbox allow for improvements in engine controls. The pilot no longer has to look at instruments inside the cockpit to synchronize engines during the critical takeoff period when he needs to be looking outside. There is one lever for engaging and disengaging the gearbox to connect the propellers. When engaged, both throttle and both "Prop" levers act together so operation is similar to a single engine aircraft. Power changes can be done without the need to match engines by referring to the manifold pressure gages and tachometers. When the gearbox is disengaged, the controls are identical to a conventional twin engine aircraft.
The propeller arms are part of the landing gear outriggers so they move automatically when the gear extends or retracts and the pilot does not need to actuate or monitor them separately.
- No asymmetric thrust from engine failure to cause extra drag and asymmetric lift.
- Little pilot action required at engine failure and no tasks required inside the cockpit - greatly enhances safety.
- More available thrust than conventional aircraft with an engine failure.
- An overspeeding propeller will not damage an engine.
- Greatly improved engine out rate of climb.
- The pilot has a greatly reduced workload during normal takeoff. He is not required to look in the cockpit for power reductions or to synchronize engines.
- Identical engines facing each other allow for counter rotating props which minimizes engine costs.
- Mounting the engines internally also provides better temperature control (cooling & heating). Forced airflow through the engine compartment can be directly controlled by the pilot in flight and on the ground. This is especially advantageous for preflight heating and post flight cooling in both hot and cold environments.
- The location of the propellers and engine exhaust behind the passengers reduces noise levels in the cabin.
- The use of timing belts and the central gear box ensure that both propellers remain at exactly the same RPM - no pilot action required to synchronize the props which allows more time for scanning of instruments or traffic.
- Pulley diameter ratios give speed reduction without using much more expensive geared engines (reduces overhaul cost).
- The engines and mounts are protected from propeller imbalance forces, which reduces wear and improves reliability.
- The propellers are protected from engine power pulses, which reduces blade fatigue & improves reliability of the props.
- The engine crankshaft is not stressed from propeller gyroscopic forces.
- Forces from a propeller striking an object do not damage the engine crankshaft.
- The sudden loss of a prop blade will not try to tear the engine off of the airframe or compromise the structure.
- Hard landings are more tolerable because landing forces due to engine weight are transferred to the main landing gear directly beneath the engines without passing through the wing structure.
- Drag reduction from absence of engine nacelles improves speed and efficiency.
- The low center of gravity due to engine location makes high speed taxiing safer on water and land.
- Since the engines are not attached to the wing, engine vibrations and landing shocks do not compromise the strength of the wing structure.
- Placing both engines near the C.G. greatly reduces the rotational moment of inertia of the aircraft, which improves spin control and safety.
- During a takeoff or landing on water, the props are fully shielded from water spray (and damage) by the wing.
- Retracting the landing gear lowers the props to the center of drag eliminating the nose down trim drag of a high thrust line.
- On the ground, passengers and ground personnel are afforded greater safety since the props are above the wing.
- In the unlikely event of a prop failure simply extending the gear puts the prop thrust lines close to the centerline of the aircraft, minimizing yaw from asymmetric thrust.
- In the unlikely event of a prop blade separation, the resulting damage from vibrations will be limited to the prop arm above the wing pivot and not affect the engines, landing gear, or C.G.
- With the landing gear retracted, the outriggers fill in the hull aft of the step, forming an aerodynamically clean fuselage.
- This patented system allows the C.G. of the engines to remain low while the propellers are mounted in a manner to give protection from water spray and are clear of passengers while operating on the ground.
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