Messerschmitt clapped his hands and said, "Philip, that's a great point! I think we should establish a set of aircraft structure design standards as soon as possible, and write these design concepts and design calculation methods into the standards in detail, so that designers can master these methods. Your two design concepts are so good that our business transport aircraft solution is two or three tons less weight than Junckers' transport aircraft, which is amazing, and the airline does not increase its revenue by a little bit. ”

Philip laughed: "Isn't there a very famous saying in the aviation industry that aeronautical engineers have to work hard to reduce every gram of weight. The reduction in the weight of aircraft structures has many beneficial effects. For civil aircraft, the economic benefits it brings have become greater, and for military aircraft, the reduction of structural quality will improve the thrust-to-weight ratio of the whole aircraft, and many indicators such as range and climb rate will be greatly improved, so it is more important to reduce the structural quality of military aircraft design. In addition to these two design approaches, our new aluminium alloy will also play a big role in reducing the weight of the structure, and I believe that we will also be significantly ahead of Junkers in terms of materials. ”

Messerschmitch nodded and said: "Yes, then let's follow the steps, according to the technical requirements of the Romanian side, to determine the main parameters of our commercial transport aircraft program, and then further determine the preliminary shape and size of the tail and fuselage, estimate the performance, draw a three-sided diagram, and arrange the parts." Time is short, let's hurry up. ”

Philip picked up the pen and paper and said, "Okay, let's do the math together." According to the mass balance equation, in the overall design stage, the take-off mass of the aircraft is divided into five major parts, namely structural mass, propulsion system mass, onboard equipment mass, fuel mass and payload mass. Since the total mass of the aircraft is not yet certain, let's assume that the form of the coefficient is the sum of the mass factors of the parts is 1. According to the available information, we can take the values of the five mass coefficients of this commercial transport aircraft in this way, the structural mass coefficient is about 0.32, the propulsion system mass coefficient is about 0.12, the equipment mass coefficient is about 0.15, and the fuel mass coefficient is about 0.15, these four items add up to about 0.74, and the payload coefficient of the aircraft is about 0.26. ”

Philip said as he rustled his pen on the paper.

Messerschmitt thought for a moment and said, "Our 700-horsepower piston engine plus accessories such as the lubricating tank weighs about 300 kilograms, and the two add up to 600 kilograms, which is about the same. I think it's okay, but the structure uses new materials and structural design, and it's not too clear, so let's calculate it first, because we have to review and calculate it later. ”

Messerschmitt is right, the structure of the aircraft is complex, and the accurate calculation of the mass of the aircraft is simply impossible and unnecessary at the stage of the overall scheme design, as long as the approximate coefficients of these classifications are determined. Because the mass of the whole aircraft and the mass of each part of the aircraft are cause and effect of each other, it cannot be calculated directly, and the iterative method of successive approximation can usually only be used to solve the mass of the whole aircraft, and at the same time, in order to save design time, the rough approximation method is always used at the beginning, and then more and more accurate calculation methods are used in the specific design process.

Philip continued: "According to the technical requirements of the Romanian side, the maximum payload weight of the aircraft is 1,500 kilograms, and we can approximate the total mass of the aircraft to be about 6,000 kilograms, the structural mass of 1,920 kilograms, the mass of the propulsion system 720 kilograms, and the mass of the equipment 900 kilograms, which add up to the empty weight of the aircraft, which is 3,540 kilograms and the fuel mass is 960 kilograms. Of course, this is only a preliminary estimate, and it will be adjusted according to the actual situation. ”

Messerschmitt nodded and said, "Well, very good!" Then let's determine the type and parameters of the aircraft. We need to determine the plane shape, relative position, flat tail layout and fuselage structure of the wing, and also calculate parameters such as wing load and thrust-to-weight ratio. ”

Philip continued to write, "Well, okay. I prefer to use a straight wing, preferably a double-girder structure with diagonal struts. The plane shape is rectangular, the relative thickness is about 15%, and the chord length is about 2 meters, so that the integral fuel tank can be arranged in the middle of the wing. The vertical tail adopts a swept trapezoidal wing, and the flat tail is arranged in the middle and upper part of the tail, which is slightly lower than the main wing. What do you think? ”

Messerschmidt was surprised: "Why not choose the lower wing layout, and the rectangular plane shape is the first time I've heard that it can be used on a transport plane." ”

Philip laughs: "A double-girder flat wing with diagonal struts will bring structural weight benefits, and the use of an upper wing has something to do with our landing gear design. You must know that our plan is to use the front three-point landing gear, if we still use the lower wing layout, then the layout of the engine propeller has become a problem, the blades are too close to the ground, and even can be wiped to the ground, unless the landing gear is designed to be very high and long, but then the landing gear structure design has brought problems. So using an upper wing is the best layout. ”

Messerschmidt slapped his thigh and said, "Really, I'm a little confused when I'm old, and I haven't taken into account the impact of the landing gear." Well, let's talk about the design of the cabin! ”

Philip thought for a moment and said, "As a business transport aircraft, the design of the cabin is very important. First of all, I want to design the cockpit with a large windshield and left and right side windows, so that the pilot's vision can be very wide, and the pilot's driving safety and operating comfort can be utilized. The design of the cabin is even more important. In order to make passengers comfortable, there must be plenty of space, for an 18-seater business jet, I think the length of the cabin section should reach about 5 meters, The height and width should reach 1.8 meters, so that 6 rows of seats can be arranged, each row of 3 seats, the aisle is 40 cm wide, and two luggage compartments are designed at the front and rear of the cabin, and the total volume of these two baggage compartments is not less than 3 cubic meters. ”

Messerschmidt exclaimed: "Philip, you have thought it through, this kind of cabin is much better than the current passenger plane." So let's move on to the overall dimensions of the aircraft, as well as the wing area. ”