Fig. 9 is an older form of Nieuport monoplane chassis, a steel cross spring being used in place of the usual rubber bands. This is simple, but comparatively heavy, and is subject to frequent spring breakage. To guard against spring failure, a long ash skid is placed under the axle. The spring system is connected with the body by three sets of oval steel struts. An old type of Curtiss chassis is given by Fig. 11. This has been widely used by amateurs and exhibition flyers, but requires a fairly smooth landing ground as there are no shock absorbers. The only shock absorption is that due to the deflection of the tires. The extreme forward position of the front wheel effectually prevents any tendency toward nosing over when landing.
Fig. 11. An Old Type of Curtiss Exhibition Chassis With Three Wheels.
Fig. 12 (Left). Standard H-3 Shock Absorber. Fig. 13. (Right). Rubber Cord on Axle.
A Standard H-3 shock absorbing system is given by Fig. 12. This has a bracket or hanger attached to the axle over which the elastic cord is wrapped. The cord is wrapped in continuous turns between the axle hanger and the bottom of the Vee support members. As shown, the upper streamlined bar is the axle, while the lower is the cross bar brace which serves to hold the lower ends of the U's. I am indebted to "Aerial Age" for this cut. In order to guide the axle in a straight line in its up and down movement, two radius links are attached between the axle and the front vertical strut. One decided advantage of the "Standard construction" is that the cords are wound without crossing the strands, thus reducing cutting and wear between the cord turns. Fig. 13 is a variation of Fig. 12, the cord being wound directly around spools on the axle and the lower stationary cross tube. The axle is guided by a slot in the guide plate at the right, while end motion is controlled by a radius link. Fig. 14 is the double wheel arrangement of a large "Twin" bombing plane. Two wheels are placed directly under each of the motor units so that a portion of the load is communicated to the chassis by tubes. Diagonal tubes transmit the body load to the chassis.
Fig. 14. Chassis for Twin Motored Biplane of Bombing Type.
Folding Chassis. Owing to the great relative resistance of the chassis it has been suggested by many designers to provide a folding frame which will automatically fold up into the body after the machine has left the ground. This would be a decided advantage but the gear is complicated and probably not altogether reliable.
Height of Chassis. The height of the chassis is made as small as possible with a sufficient clearance for the propeller tips. It is usual to have the tips of the propeller blades clear the ground by from 10 to 12 inches when the aeroplane is standing with the body in a horizontal position. Any smaller clearance is almost certain to result in broken blades when landing at a sharp angle or when running through high grass. If the chassis is excessively high the resistance will be high and the machine is also likely to be top heavy.