The Wasp R985 engine was a commonly used engine as a single prop motor for the World War II Allied Force. It is currently in use today on planes that have been retrofitted for aerial advertising and banner display as well as aerial fertilizer applications (crop dusting).
With aged service equipment, the requirement for inspections can be specific to airworthiness directives (ADs) as defined by the Federal Aviation Administration or by Service Bulletins (SB).
ADs are defined by safety protocol as administered by the FAA from reports and investigations from regular required maintenance and scheduled repairs. SBs can also be discovered from the regular maintenance checks but is typically related to the comfort/function of the plane rather than the safe operation.
Old Service Bulletin Header
As written from the Service Bulletin:
“Service experience indicates that some R-985 Wasp Jr. cylinder heads, which due to rebarreling or cylinder barrel chromium plating have operated for longer than normal expected usage, can develop a circumferential root crack in the inner first or second blind threads which contact the end of the cylinder barrel. This crack can propagate in fatigue around the cylinder head and radially outward until a major of head fails in tension and is liberated. It is estimated that 1 to 2 percent of high time cylinder heads contain a crack and that, through use of this special inspection procedure, they may be identified and removed from service before failure can result. The critical area, or crack origin, is almost always primarily located approximately 30 degrees from the rear spark plug toward the exhaust or left side of the cylinder assembly. Inspections should be more concentrated in this area. It is the intent of this bulletin to:
- Provide instructions for ultrasonic inspection of the inner cylinder head threads, at each overhaul.
- Provide instruction for visual inspection, at each periodic maintenance interval.
In short, this service bulletin / airworthiness directive provides for an ultrasonic testing (UT) procedure for crack detection closer to the bottom section of the head itself.
The written procedure defines two specific items which are critical to the inspection.
UT Transducer
To get UT transducer over the reduced access of the cylinder head, it needs to be custom built for the proper access to the area of interest. With this special transducer, it is also required to perform a specific calibration with a defined custom calibration block as defined in the Service Bulletin / Airworthiness directive.
UT Standard
To calibrate the equipment to a proper sensitivity level, a special standard was produced by Pratt & Whitney for this specific procedure and are hard to come-by as this engine has not been produced since for a few years.
Below is a picture of the special transducer on the Pratt & Whitney standard for this inspection.
Special Standard and Special Transducer
With these two very specific items, QCL is able to fulfill this airworthiness directive / service bulletin for these aerospace parts directly with 100% quality control assurance.
Tabletop Inspection Setup for Wasp R985 Cylinder Head
QC Labs has a long history of performing routine and specialized inspections for the aerospace and aviation industries. By investing in our equipment and our people, we provide high quality inspections to maintain the safety of your assets.
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Image Sources: – https://en.wikipedia.org/wiki/Pratt_%26_Whitney_R-985_Wasp_Junior (right header image); https://en.wikipedia.org/wiki/Boeing-Stearman_Model_75 (left header image)