Harry, According to my Alon parts manual the main wing attach bolts, nuts and washers are as follows:
AN10-24 Wing Attach Bolt - Main Spar (or "beam", as they call it) AN960-1016 Washer AN310-10 Nut The AN10-24 Bolt is a standard AN bolt, 5/8 inch diameter. The heads of the bolts on my plane, which are original equipment are not marked with the triangle and X which designates a close tolerance bolt. They are the AN10-24 designated in the factory parts manual. I don't know what bolts any of the other models of Coupes are supposed to have. Below is the text of what my friend wrote to me some time ago concerning shear loading vs tension loading. When dealing with bolted connections in shear, it is often thought that the bolts themselves bear the shear load. This is actually not the case. As you stated, the bolts, when torqued, are in tension. This tension imparts frictional loads between the mating parts. When the torque is high enough, the resulting bolt tension imparts enough friction between the mating parts that the bolts carry no shear load. (I'm not making this up... see the attached excerpt from one of my textbooks!) Therefore, proper torque is very important. If the joint consists of multiple bolts, equal torquing is also very important since the design analysis assumes the bolts behave as one fastener acting at a specific location called the bolting "centroid." Undertorque of a single fastener results in an offset of the resistive load that may cause the load to shift from bolt to bolt as the loading changes. Plated connections do not use close tolerance bolts for the reason stated above as long as the plates being joined can take the resulting compressive load and corresponding frictional load. Close tolerance bolts are used, however, when it is undesirable to impart a compressive or frictional load on the bolted member... such as our propellors! The "drive lugs" on the close tolerance propellor bolts simply increase the bearing area of the high strength bolts on the much lower strength aluminum propellor hub. For what it's worth............ Good Flying, Wayne DelRossi
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