No one has ever seen such a petal-shaped engine! You've all flown on a variety of civil aviation aircraft, and even one or two business jets are on standby at home. But turboprop turbofan engines are everywhere, this kind of beautiful and charming engine is really rare, because there are very few aircraft in the world, the most famous is the Almost no future of the An-70, which is the advantages of the turboprop fan engine, generally referred to as the propeller fan engine.
Strange and good-looking paddle fan engine
Civil aviation passenger aircraft generally use a large bypass than turbofan engine, simply put, the diameter of the first stage blade is very large, the air flow is divided into two bypasses inside and outside, and the thrust is provided by the compressed air of the gas and the outer bypass, so the thrust of the large bypass than the turbofan engine is often amazing, such as the performance of garbage but the total thrust is larger than the Transport 20 Japanese C2 transport aircraft.
The C2 is a shame for transport aircraft
So what is the principle of another common turboprop engine for military transport aircraft? The body of the turboprop engine is generally called a gas turbine, which is the same thing as the turboshaft engine commonly referred to on helicopters and the gas turbine on ships and tanks, and the core engine is the same as the jet engine. What's so different? The tank's gas turbine and the helicopter's turboshaft engine are all generated by the core machine to generate mechanical energy, and then driven by the transmission or reducer rotor or tracked active wheel and propeller.
Now the so-called paddle fan engine is not particularly clearly defined in the world, for a simple understanding, we believe that the structure is similar to the cancellation of the turbofan shell while using an advanced large-diameter propeller engine can be called a paddle fan engine, rather than judging by the presence or absence of transmissions. If the blade diameter of the turboprop engine is particularly large, the blade shape is larger and more efficient, then it can also be considered a paddle fan engine, and the propeller fan is turboprop plus, Pro, max and so on.
The early paddle fan engine is the above definition, GE once had the Underutted Fan concept, further radical design on the basis of the NASA concept, not even a transmission gear, directly behind the spindle installed two large diameter and blades are very curved and thin blades of the advanced blade type co-shaft reversing propeller, which is equivalent to simplifying the structure and reducing the weight. From the outside it looks a lot like a turbofan engine with two propellers, and wikipedia defines it as well, which is that there are no transmission gears.
The GE36 is a product of the above concept, developed in the 1980s, the test aircraft is a rear-engined Boeing 727 aircraft. The engine body is the famous F404, the maximum diameter of the housing part is 1.94 meters, the rear of the two propellers front and rear diameters are 3.35 and 3.25 meters, respectively, the front paddle 10 blades, the rear paddle is 8. The dry weight of the entire engine is 2.7 tons and is capable of generating a maximum thrust of 110 kN, while the improved model can increase the thrust to 133 kN, which is much more powerful than the prototype F404.
Its blades are made of composite materials, very thin and with a large swept angle, and the weight of a single blade is about 10 kg. When working, the rotation speed of the blade is 1393 revolutions per minute, and when tested on the 727, it can maintain a cruising speed of Mach 0.83, while the fuel consumption is lower than that of similar engines, which is equivalent to saying that the GE36 has both high thrust and high cruising speed, while the economy and maintenance are also good.
At that time, the oil price was very high, and Boeing planned to develop a short-haul narrow-body airliner code-named 7J7, which was equipped with GE36 with economy as a selling point. However, aside from the problems with the aircraft itself, the fuel economy caused by the decline in oil prices is not so important, and the use of new types of engines can lead to potential cost increases. Therefore, with the collapse of the 7J7 plan, the enthusiasm of Europe and the United States for paddle fan engines has also cooled down, fuel-saving turboprops, low-end pistons, and high-end turbofans.
We have mentioned before that the Boeing 747, the most well-known of the 747 family is the 400, in fact, the 747 also has the concept of the 500X, Boeing plans to replace the 747 with a newer wing, and in order to economically replace the large paddle fan engine, the maximum take-off weight of the 500X has reached 450 tons, more than the C5 and the An-124, the longer range carrying capacity is also higher, but the inherent problems of such engines and the decline in the attractiveness of giant airliners have led to Boeing's lack of interest in developing new aircraft.
There were no 747-500 aircraft
The problem of the paddle fan engine has also emerged, mainly in three aspects, the new things are not mature enough, the paddle design is difficult, and the noise is extremely large, resulting in civil aircraft basically not getting involved. So the question comes, how many uncertain problems have been successfully overcome by the Soviets, civilian restrictions, the use of military aircraft is not finished, new things can become mature old things, high design difficulty can also be overcome, noise that is not simpler?
The An-70 is the only aircraft in mass production that uses paddle fan engines
The Soviet Union began to design the An-70 transport aircraft in the 1980s, and in order to improve the performance of the aircraft, it used the D27 paddle fan engine, which was also the only mass-produced paddle fan engine in the world. The prototype of the D27 is the D36 turbofan engine, the installation object is mainly the An-72 and the An-74, which is a small and medium-sized turbofan engine, after changing to the paddle fan engine, two large-diameter thin-blade propellers are installed in the front, the model is SV27, the diameter reaches 4.5 meters, and it can produce 13800 horsepower, which is very suitable for the use of the An-70. The aircraft tested was the Il-76, which can clearly see its huge blade diameter, compared to the D30 engine is very different, to know that the fuselage diameter of the general airliner is not so large. The core part of the D27 is basically the same as that of the D36, but it is equipped with planetary reduction gears, the front propeller of the 8 blades receives more than half of the power, the rear propeller is 6 blades, only a small half of the power, the weight of the propeller reaches 1.1 tons, and the dry weight of the entire engine is only 1.65 tons.
At take-off, the speed is 1000 rpm, which can produce considerable lift in combination with the flaps of the An-70, which is also a major reason for the strong carrying capacity of the An-70, and in the cruising state, the speed is reduced to 850 rpm. The noise problem mentioned earlier has also been solved, and the distance between the two propellers has increased from the original 0.6 meters to 0.9 meters.
The An-70 fully demonstrates the superiority of the propeller fan engine, and the traditional impression of the image of Soviet aircraft fuel-intensive violence does not exist here in the An-70, and all performances are better than the A400M. If Russia and Ukraine do not have contradictions to continue to be brothers, then many Russian aircraft will use this propeller fan engine, there is no such thing as what paddle fan engine is not good enough so no one uses it.
The diameter of the engine blades is almost the same as the diameter of the fuselage
Back to the beginning, the D27 is a paddle fan engine, but it is very close to the turboprop, even the shape is similar, so the paddle fan should be called a super turboprop engine, which solves some of the problems of the turbofan and turboprop, and is indeed an engine worth promoting. It's just that the An-70 has no way forward, and various aircraft companies lack enthusiasm for paddle fan engines, and paddle fan engines basically have no future.