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Andrews Web Site
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Date: 4-20-2019
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Number of Hours: 0.50
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Manual Reference:
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Brief Description: Received Wing Spar Fittings
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Received a set of wing spar fittings from Mustang Aero. These are very important structural parts. I would expect a high degree of precision in their manufacture. Here are my observations of the parts as received:
1. I was expecting the 1/4 holes to come as D size. In reality, they vary. 7 of the 8 fittings were either D size or C size.
2. One of the fittings was much larger than D size to the point where a bolt would not be a tight fit. If you insert a bolt in the fitting, it feels tight, however the hole has a lip on the bottom causing the tight fit, the majority of the hole is quite loose. This fitting is unacceptable and will not be used.
3. If you read the original Mustang II plans, it recommends against having matched holes in the front and back fittings. Instead, it recommends drilling the holes through the spar using the front fitting as a guide, then drilling through the bottom blank fitting. This technique would then allow some misallignment of the drill, but still insure a tight fit. (If you have a hole in both steel parts, the bottom hole might try to pull the drill bit into position and enlarge the hole in the aluminum.)
As a result of all this, I orderd a set of blank fittings from Mustang Aero. This is a super expensive thing to do for what you get (no price break for no holes) but I could not find a local heat treat shop willing to do a small batch to make my own.
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Wing spar fittings as received
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