TAIL HARDWARE

Guest Discussion
1

At OSH I noticed that both the mockup & production planes have round head screws as fasteners on the elevator assembly. In seemed incongruous that on such a sleek aircrafr that they wouldn’t use flust fasteners

2

Check the specs of the hardware. The round head fastners generally have a tensile strength of 125,000 to 145,000 psi (depending on the type). The flush fastners have a tensile strenght of about 55,000 psi. I would presume that this has some effect on their design specs.

At OSH I noticed that both the mockup & production planes have round head screws as fasteners on the elevator assembly. In seemed incongruous that on such a sleek aircrafr that they wouldn’t use flust fasteners

3

This is a typical example of good engineering – the screw heads are in the boundary layer (still air) and basically the small bumps out of contour with the skin are very little or no effect on the drag of the airplane, and not having to counter sink the holes adds strength and provides a more secure joint with less fasteners, and helps keep the cost down.

Bernie

Check the specs of the hardware. The round head fastners generally have a tensile strength of 125,000 to 145,000 psi (depending on the type). The flush fastners have a tensile strenght of about 55,000 psi. I would presume that this has some effect on their design specs.

At OSH I noticed that both the mockup & production planes have round head screws as fasteners on the elevator assembly. In seemed incongruous that on such a sleek aircrafr that they wouldn’t use flust fasteners

4

thanks for the input. I had no idea but am glad to find out it’s the best way to do it.

5

Bernie, Bernie, Bernie…

They may be in the boundary layer but this is certainly not “still air” and things that stick out add up and make a big difference (I won’t waste everyones time with a more detailed explanation of laminar -vs- turbulent since it doesn’t make much difference in this case).

All these “little things” are what give the Cirrus such low drag as compared to say a Piper Archer which is basically the same size aircraft.

As for the tensile strength argument previously given…well I doubt if these locations need even the lower of the two. The real issues here would most likely be cost, cost and cost.