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The reason interference fit rapairs or fasteners improve fatigue life is by providing a residual tension field around the hole which causes the hysteresis loop of stress-strain caused by the load to become biased toward tension dominance, reducing the accumulated damage from each load cycle; all...

Multiple heat treats of these alloys drive the metallurgical precipitates out and change the grain size. I never heard of anyone heat treating AD rivets, but anything is possible. If you know the design loads, you ought to choose a fastener with the appropriate strength level and diameter to...

I used Marvel in my C-170, precisely to prevent valve problems from 100LL; which it took care nicely. I added about half a quart at each oil change and a capful or so when topping off the oil. The airplane had a can under the rear seat when I bought it, and I ignored the hint. After having 2...

richsad Please email me if you have found a method for calculating the end loads - I found your thread in a search for the same method. These other guys are all wet - there are defintely external shear loads on the end of a flexible hydraulic hose, all you need to do to prove it to yourself is...

If the holes are not drilled through, don't do anything but a little clean up and polish of any burrs or sharp edges. The reason the part has lasted for so long is because there are no holes and the stress concentrations are nearly non-existent, maybe Kt of 1.1 or 1.2; i.e., the stress field is...

It's all about the mass of air being moved, and about your perception of the noise. In fact, perception of noise is the major hurdle in regulating and controlling noise - this is why there are so many dB scales in use, in an attempt to capture a means of mathmatically describing a nuisance that...

The best approach to this problem is to scrap the analysis and go directly to the lab - you will never accurately predict structural response and failure to real bird strikes. There are more variables in the joint design, backup structure stiffness, and so on to ever hope to model. You will get...

It's all about the design of the joint and the load transfer in the fasteners, not just the overall stress level. In fact, if you were to assume 15 ksi to develop loads for developing joint loads, your guess would be sadly undersized. On the other hand, adding a repair that would lower the...

Installing a first or second oversize fastener is only useful for obtaining a good fit in a hole where the original fastener had to be drilled out or otherwise removed such that the hole was slightly damaged, without going up to the next size fastener which might incurr net section tension...

Use class 2 holes for basic installation of hi-lok fasteners. Use class 1 holes where specified for fatigue critical installations - pay attention to the repair manual in this case. Ease the hole fit to one between class 2 and 3 for installation in composites. "Hi-tigue" hi-loks...

Good Luck - get your order in early, because this is the dilemma of the entire industry. This is a fall out of "just in time" supply, which in the aerospace industry translates to "just too late". No one uses titanium nuts in conventional airplanes, they use steel; Ph13-8Mo...

Hello - it's been a couple of years since I looked around here. I am a senior strength engineer at a major manufacturer of fighters and I have a few comments and suggestions. Removing hi-loks - if conventional collars are installed, grap the collar with a pair of vice grips and an allen wrench...

6061 is probably the best choice accounting for availabilty, cost, machinability, and corrosion resistance, especially for small production runs. Strength is moderate (for aluminum alloys). I hate to recommend shops because it's hard enough to get work scheduled, but Danner Machine in Seattle...

Get your hands on a Peery or Bruhn aircraft structures textbook, or an Advanced Mechanics of Materials textbook by Den Hartog or Boresi and Sidebottom. All of these cover this topic very well. This is a fundamental problem that any aircraft structures engineer worth the title must be able to...

You will need to refer to design charts from one of the major aircraft companies, or possibly an old structures text book (they are the best ones) to answer this question. ESDU may have design charts, or look around for the Royal Aeronautical Society charts that preceded ESDU. The bulb...

7050 rivets are the modern replacement for "ice box" rivets. I have specified this rivet type many times where the strength of AD rivets was not quite enough. They are a little harder to drive, and less tolerant of excessive hits with the rivet gun; i.e., the buck tails will split...