One way to approach this would be to go back to the equations in earlier chapters and iterate among them, trying to find wing areas, weights, and engine sizes that would accomplish our design objectives.

The question with the design of an airplane as with a car or a tire, is how do we arrive at the best compromise that will result in a good all around design while still being better than average in one or two desired areas? Car tires can be designed to have high traction in mud and snow or to give great mileage at highway speeds but any attempt to design an “all weather touring” tire will result in a compromise with less traction than a mud and snow tire and poorer performance at high speeds than the high speed highway tire design. A car can be designed to go really fast or to get really good gas mileage, but probably not both. This isn’t really much different from designing any other product that is capable of more than one task. And its climbing performance may be even worse! If, for example, we went all out to create a plane that could takeoff in a very short distance and then look at its performance in straight and level cruise we would probably find that it isn’t very good. If we want an airplane that only does one thing well we need only look at that one thing. And they may be different still in climb. The only problem is that we would find that their relationships in cruise aren’t necessarily the same as they are in takeoff and landing. We would find, if we looked at the equations we derived for the other types of flight mentioned above that these same three parameters pop up everywhere. Nonetheless, we can see that three parameters thrust, weight, and wing area, are important factors to consider in takeoff. High thrust will minimize the takeoff ground run but once thrust becomes as high as the weight of the plane we might as well take off vertically! And a big wing area gives us high drag along with high lift. Of course there are limits to be considered. To land in a short distance we might want to also design a plane with a large wing and high maximum lift coefficient but now the thrust isn’t as important as the amount of braking friction available unless it is reverse thrust that we are talking about. To takeoff in a short distance we might want a high maximum lift coefficient to get a low takeoff speed, a large wing area to give a lot of lift at low speed, and a lot of thrust to accelerate to takeoff distance in as short a ground run as possible. In other words, if we wanted to design an aircraft that could takeoff and land in a very short distance we can look at the takeoff and landing distance equations and identify the factors that would minimize these distances. If we were to look at the relationships we found for any of these we could see how we might design an airplane to best accomplish the task at hand. These included takeoff and landing, turns, straight and level flight in cruise, and climb. In the proceeding chapters we have looked at many aspects of basic aircraft performance.

Diagram of airplane cockpit