Brian Jackson
02-27-2005, 01:22 PM
Hi Folks.
Please pardon me because this will probably be a big question, but I’ll be as concise as possible. Here goes:
Last night I finished the preliminary drilling of my GyroBee Mast. It is a redundant mast with two 1x2 tubes, typical of many gyros. To ensure all holes were thru-drilled to precisely line up, I inserted zero-tolerance dowel rods through all existing thru-holes and clamped both tubes together. I took every conceivable precaution before and during drilling. I spent days doing “dry runs” just to make sure nothing was left to chance.
So last night I thru-pinned and clamped the cluster plate holes, side-clamped and compression-clamped the rotorhead area and, after triple-checking every facet, proceeded to drill the finest 16 holes of my life (4 holes X 4 walls.) The results were pure poetry. Tolerance pins could be inserted and removed with light, smooth, uniform force.
The next morning I double-checked the uniformity of the 2 mast halves and noticed something alarming… when one end was pinned the other end was a thou or two off and the opposing pins could not be passed, and vice versa.
Question 1: With such tight tolerances, does thermal expansion come into play? .002” over six feet seems like it would.
Question 2: Could the bending moments of a toleranced redundant tube impose excessive loads? (See Attached Image). Since the bolt is so much stronger than the aluminum surrounding it, would it not make sense that cyclic fatigue is being introduced in a no-tolerance situation?
Lastly, I’m not aware of any failures due to this directly. But is it not conceivable that some mast breaks could have been attributed to weakening of material by metal fatigue? Redundant mast, crystallized metallurgy via fatigue and “no room” tolerances, the brittle nature of metals under those loads, the propagation of cracks under those loads, and a sudden load from any direction.
I’m not an aeronautical engineer, just some guy building a gyro myself. I’m not an idiot though.
Please pardon me because this will probably be a big question, but I’ll be as concise as possible. Here goes:
Last night I finished the preliminary drilling of my GyroBee Mast. It is a redundant mast with two 1x2 tubes, typical of many gyros. To ensure all holes were thru-drilled to precisely line up, I inserted zero-tolerance dowel rods through all existing thru-holes and clamped both tubes together. I took every conceivable precaution before and during drilling. I spent days doing “dry runs” just to make sure nothing was left to chance.
So last night I thru-pinned and clamped the cluster plate holes, side-clamped and compression-clamped the rotorhead area and, after triple-checking every facet, proceeded to drill the finest 16 holes of my life (4 holes X 4 walls.) The results were pure poetry. Tolerance pins could be inserted and removed with light, smooth, uniform force.
The next morning I double-checked the uniformity of the 2 mast halves and noticed something alarming… when one end was pinned the other end was a thou or two off and the opposing pins could not be passed, and vice versa.
Question 1: With such tight tolerances, does thermal expansion come into play? .002” over six feet seems like it would.
Question 2: Could the bending moments of a toleranced redundant tube impose excessive loads? (See Attached Image). Since the bolt is so much stronger than the aluminum surrounding it, would it not make sense that cyclic fatigue is being introduced in a no-tolerance situation?
Lastly, I’m not aware of any failures due to this directly. But is it not conceivable that some mast breaks could have been attributed to weakening of material by metal fatigue? Redundant mast, crystallized metallurgy via fatigue and “no room” tolerances, the brittle nature of metals under those loads, the propagation of cracks under those loads, and a sudden load from any direction.
I’m not an aeronautical engineer, just some guy building a gyro myself. I’m not an idiot though.