Page 16 - Nov 2015 Volume 9, Number 11

Ask the Expert
Answers to a Variety of Good
Questions from Readers
by Tom Clements
Ialways appreciate when readers of our magazine take the time to contact Kim Blonigen, our editor, with operational questions they would like me to address. I try to reply as rapidly as possible to the person who is posing the question. Sometimes, ideas for an entire article or two are prompted by the question(s), whereas at other times a brief personal response is all that is necessary.
This month I will present the questions and my answers to a variety of topics that have been received in 2015. To all who wrote to us, thank you for your input!
The first question comes from Ray Orr, Chief Pilot for Air Charter Coordinators of Brisbane, Australia. Ray wrote, “In the King Air magazine, the photo in a Raisbeck advertisement of the belly of a King Air 200 while in flight shows that a wing strap has been fitted. Could Tom explain the strap history? We don’t see many straps here in Australia and the industry experts are mostly too young to know the real history.”
Oh boy! Now here’s a meaty topic upon which I could spend a lot of ink! I will give a rather abbreviated version of the story here and suggest a Google® search for those who want to read even more about wing spar straps.
David Saunders of Camarillo, California, president and owner of Aviadesign, came out with a Spar Strap for the Twin Beech 18 after there had been seven wing separations and the FAA mandated a strap modification, yet Beech offered no strap kit. A few years later, in 1974 and 1975, two relatively low-time model 99s (19-passenger, unpressurized, PT6-powered, commuter planes) showed up with lower main spar problems and Allegheny Airlines commissioned Saunders to develop a failsafe strap for the 99 that would extend the wing spar life past the low 10,000-hour life that Beech had mandated in response to the problems’ appearance. Beech’s fix was to come up with the “Super Spar” in which the bolt’s bathtub fittings were integral with the lower spar cap. (This design was also used on the first 1,000-plus 200s, as well as on F90s.) To change from the old to the new spar was a huge job that only a few Beechcraft facilities could accomplish, and it was very expensive with a lot of downtime. But Mr. Saunders’ strap provided a “secondary load path” by connecting the left and right outboard wing sections to each other
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via a strap that ran through the wheel wells and under the fuselage. The outboard wings were modified with two doublers – one running almost to the tip, and a second one terminating near the tie-down ring. The strap was bolted to the doubler just outboard of the wheel well. Before the holes were drilled and the strap bolted on, 1,000 pounds of sand bags were placed on each wing tip to flex the wings down so that the strap would always be carrying some of the lifting loads.
There was concern about “galvanic corrosion” between the steel strap and the aluminum wing and spar structure, and the spar cap was insulated from the strap in the wheel well.
Beech, of course, thought that Mr. Saunders was Satan himself, succumbing to the NIH (Not Invented Here) syndrome and cutting a great deal into their sales of super spars. The strap did not eliminate the requirement for bolt and bathtub fitting inspections and one drawback was that the strap needed to be removed for that inspection. Later, Saunders made a revised strap that was widened around the bolt location and had a hole in the center that allowed inspection while still installed.
Some of those 99s that should have been parted out when they hit 10,000 hours are still going strong with the strap with over 50,000 hours. Saunders went on to develop and sell straps for almost all King Air models. In the late 1970s, two King Airs – one was an E90 and the other a 200 – had the lower forward wing bolt break in flight. The 200 (after the crew heard a “snap” and observed the outboard wing making small movements
DECEMBER 2015