Aerodynamic Tail Cones and Challenges With Vibrations Causing Failure

Prior to retirement I was in the truck washing industry, and before that I was in the aviation sector. Interestingly enough, when you are clean aircraft or trucks, you notice things that other people perhaps do not see, unless they are mechanics. Often I saw corrosion, and cracks in the fiberglass of tail cones on aircraft and on over the road trucks. As the fuel prices increased, there were more and more modifications to the aerodynamic body configurations of truck trailers, truck tractors, and aircraft.

Okay so, let’s talk about some of the challenges which go along with increasing the airflow across such surfaces.

Now then, it’s not too hard to design a very nifty tail cone for the back of a tractor-trailer truck rig. Of course, if it goes over length, the Department of Transportation, or DOT will have a tizzy, so everything has to be approved. One interesting approval came with an exemption for car carriers which had an extra fiberglass piece on the back which was rounded, and increase the aerodynamic efficiency, lowering the coefficient of drag, thus increasing the fuel mileage.

The trucking industry was able to get this approved, because it was at a time when our president was concerned with overcoming our addiction to foreign oil. Good, and this is a time when the regulatory process worked, and exemptions were made, and rightfully so in my opinion. However, the roads are quite bumpy, and in the air when you’re flying an airplane there are wind shears and bumpy air as well.

What tends to happen is those vibrations cause cracks where the fasteners couple on to the superstructure or body of the fuselage, or truck trailer. As cracks get bigger they must be repaired, but each time the tail cone structure gets weaker, until it has to be replaced rather than repaired. In the future, hopefully we will have stronger materials, preventing these things from happening.

Still, we will be challenged by some laws of material science which have to with brittleness, hardness, strength, vibration, UV damage, and going from one type of material to another. For instance in this case either aluminum to fiberglass or carbon composite, or steal onto fiberglass or carbon composite by way of special fasteners and hardware. Interestingly enough, there was a problem with the Boeing 787 Tail cones, just as there were problems with the aerodynamic tail cones that went on the car carriers which received the waiver from DOT regulations.

You see, there are always challenges with new designs which are put forth, or on modifications which are made on existing designs. Structural integrity is very important, even if the extra piece is cosmetic, or put forth for an aerodynamic purpose, even if it won’t be holding any weight. Indeed I hope you will please consider all this and think on it.

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