Care must be taken to have the seats located at the correct height from the floor so that the legs will not become cramped. In the majority of machines, the vertical rudder is operated by the feet. Unless the seat is at the proper height, the pilot will be in a strained position as he cannot shift around nor take his feet from the rudder bar. Either the rudder bar or the seat should be adjustable for different lengths of legs. Usually the adjustment is made in the rudder bar since it is not usually advisable to shift the seats owing to the necessity of having the pilot's weight in a fixed position. In some old types of monoplanes, the pilot sat on a small pad placed on the floor of the fuselage. Needless to say, this was a horribly uncomfortable position to be in, but as the flights of that time were of short duration it did not matter much. If the feet could be removed occasionally from the rudder bar the matter of seat position would not be of so much importance, but to sit flat on the floor, with the legs straight out, for a couple of hours is a terrible strain and has undoubtedly caused many accidents through cramps.
As both the passenger and the fuel are varying weights, the fuel tank seat idea is good. This allows both of these items to be placed at the center of gravity of the machine where weight variation will have no effect on the balance of the plane. In this position, however, the fuel must be pumped up to a higher auxiliary tank since the main tank would be too far below the carbureter for gravity feed.
The flooring of the cockpits can be either of veneer, or can be built up of small spruce slats about 1/2" x 1/2", the slats being spaced about 1/2" apart. The latter floor is specified by the government for seaplane use, and is very light and desirable. The floor is placed only at points where it will be stepped on. Observation holes are cut in the floor on a line with the edge of the seats so that the occupants can view the ground without looking over the edge of the fuselage. The observation port holes are about 9 inches in diameter. Glass should never be used in the cockpits except for the instrument covers, unless it is of the non-splintering "triplex" laminated type of glass. The use of inflammable celluloid should also be avoided as being even more dangerous than the glass. The triplex glass is built up of two or more layers of glass, which are cemented together with a celluloid film applied under heavy pressure. This form of construction is very strong, and while it can be broken, it will not fly apart in the form of splinters.
All instruments should be placed directly in front of the pilot so that he can take observations without turning his head. Usually all of the instruments, with the exception of the compass, are mounted on a single "instrument board" placed in front of the pilot and directly under the forward edge of the cockpit opening. The compass can be placed on the floor as in American machines, or inserted in the upper wing as in some European machines. The motor control apparatus is placed where it can be reached conveniently from the seat. Oil gages, gasoline gages, and revolution counters are generally placed on the instrument board where they can be easily observed. If a wireless set is carried, the switches are placed on, or near, the instrument board. Owing to the uses to which the different machines are put it is impossible to give a list of instruments that would be suitable for every machine. The simplest machine should have the following instruments:
Altimeter
for measuring altitude.
of special aeroplane type.
Incidence indicator.
Air speed indicators
for measuring the speed of the machine relative to the air.