![]() ![]() Some of the more successful British aircraft with contra-rotating propellers are the Avro Shackleton, powered by the Rolls-Royce Griffon engine, and the Fairey Gannet, which used the Double Mamba Mk.101 engine. United Kingdom Ĭontra-rotating propellers of a Spitfire Mk XIXĪ contra-rotating propeller was patented by F. The first aircraft to be fitted with a contra-rotating propeller to fly was in the US when two inventors from Ft Worth, Texas tested the concept on an aircraft. ![]() While several nations experimented with contra-rotating propellers in aircraft, only the United Kingdom and Soviet Union produced them in large numbers. They are also being examined for use in airliners. Nonetheless, coaxial contra-rotating propellers and rotors have been used in several military aircraft, such as the Tupolev Tu-95 "Bear". The efficiency of a contra-rotating propeller is somewhat offset by its mechanical complexity and the added weight of this gearing that makes the aircraft heavier, thus some performance is sacrificed to carry it. It is also helpful if the tip speed or the loading of the blades is reduced, if the aft propeller has fewer blades or a smaller diameter than the fore propeller, or if the spacing between the aft and fore propellers is increased. One possibility is to enclose the contra-rotating propellers in a shroud. These substantial noise problems limit commercial applications. Most of this extra noise can be found in the higher frequencies. However they can be very noisy, with increases in noise in the axial (forward and aft) direction of up to 30 dB, and tangentially 10 dB. The torque on the aircraft from a pair of contra-rotating propellers effectively cancels out.Ĭontra-rotating propellers have been found to be between 6% and 16% more efficient than normal propellers. Some contra-rotating systems were designed to be used at take off for maximum power and efficiency under such conditions, and allowing one of the propellers to be disabled during cruise to extend flight time. It also serves to counter the asymmetrical torque effect of a conventional propeller (see P-factor). To use this wasted effort, the placement of a second propeller behind the first takes advantage of the disturbed airflow.Ī well designed contra-rotating propeller will have no rotational air flow, pushing a maximum amount of air uniformly through the propeller disk, resulting in high performance and low induced energy loss. ![]() The energy of this tangential air flow is wasted in a single-propeller design, and causes handling problems at low speed as the air strikes the vertical stabilizer, causing the aircraft to yaw left or right, depending on the direction of propeller rotation. Please see attached images for idea of hull type etc.When airspeed is low, the mass of the air flowing through the propeller disk ( thrust) causes a significant amount of tangential or rotational air flow to be created by the spinning blades. The engine height is currently setup with the cavitation plate on line with the bottom. In layman's terms, which types of prop would anyone recommend trying on this for the best top speed with reasonable holeshot, it will also be used at sea and for playing around etc. I've looked at chopper style props but get confused when they go on about boats needing bow lift and this and the other. ![]() What sort of propeller should I be looking at for this setup? It currently has a 17" stock yamaha 3 blade on there and it runs well with that, mid 40's (mph) around 5700 rpm, so a little room for manoeuvre. Naturally I'm wanting to get it to go as fast as possible, I've always had 50mph in my mind as a nice target. The boat is a 1970's seafire, 10'6 Deep V Hull, 16" transom with a 50hp yamaha 3cyl with power trim. Been working on a slightly daft project for a while and finally ready to start trying to fine tune it. ![]()
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