As a former Liaison Engineer, now a Stress Analyst (for the past two years), I am surprised no one mentioned the Boeing Structural Repair course for Engineers. I took it later in my career, after I'd learned most of the precepts through the school of hard knocks, but I believe it would be very...
Typically, the aircraft SRM is the best reference for fastener installation, since many of the aircraft manufacturers use their own hole tolerances, etc. I normally work primarily in the military world and a good general reference is T.O. 1-1A-8 "Structural Hardware". It includes rivets...
On the subject of knife edge countersinks,everyone agrees they're poor practice but the actual criteria vary. I know a Boeing standard is 66% sheet thickness for max allowable countersink depth (with Briles being 75%). I was wondering what other criteria are out there (other companies...
Lcubed is correct about the heat affected zone. Picking up a spotweld location with a fastener requires complete removal of the zone or you can see cracking of the annealed material. Birdstruck is also dead on about the dangers of knife edge countersinks. For my part, I will add that the...
The staggered pattern gives better results in a fluid tight application as the clamp up regions around each fastener overlap more efficiently, minimizing a leak path. I've seen this pattern in shear webs of integral fuselage and wing fuel tanks.
Alex:
A key issue for Liaison Engineering is equivalent strength. Your methodology for fasteners is correct, but you must look at the cross sectional area lost, determine the equivalent load it could have carried (normally tensile ultimate depending on the load condition), and determine your...
Calvin:
I am not familiar with what Boeing did on this 60's era aircraft (hot vs. cold). You're right that 0.040 stackups could probably use cold dimpling. However, with a harder 7075-T6 stringer underneath, they may have had to hot dimple. As far as replacement of the skin: if replacing the top...
CDR:
My experience is on older aircraft where quite a few of the skin lap joints are dimpled. The skin stack up is usually two 0.040 sheets of 2024-T3 and a 0.040 7075-T6 stringer for MS20426D6 rivets. In this case the dimple goes through all layers, including the stringer. The problem I have...
They exist simultaneously and are related by Young's modulus, at least in the linearly elastic region. Plasticity makes for a bit of difference, but permanent set (i.e. strain) will have some amount of residual stress associated with it.
Wil:
Forgot to mention that I was at Tinker for an extended TDY in the summer of 98 with OC-ALC/LCRA. Those were in my young and foolish Lieutenant days. We probably know quite a few of the same folks.
Russ
Wil:
Your name doesn't ring a bell with me, but in looking at your bio I'm amazed it doesn't. I do know the current Kadena engineer (Dustin C.) fairly well from his time at Tinker. I'm sure you know Joe R. at Boeing in Midwest City. Since you're no longer in civil service are you with one of the...
I would agree with Wil, that the FTI cold expanded bushing system does look beneficial. We had a tech rep come out about a month ago to demonstrate. It seemed to address the issues of freeze plugging (is that a verb?) separate layers - i.e. installation of multiple freeze plugs and aligning them...
A point I would also make, which you may already be aware of - the absolute necessity to plug each layer independently, so that the plug does not act as a fastener itself.
A problem we have had even beyond the X oversizes, the complete lack of Z (3/64) oversize fasteners.
Bravo, wktaylor. Outstanding posts. I also spent some time as an Air Force engineer in fighters and tankers. Presently work on -135 variants in the liaison/PDM role. I wholeheartedly agree with your comments on blinds in inlets - solids would most certainly be preferable, but often the lips and...
