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Wednesday, April 16, 2014

Engine Overhaul Tools

Aircraft engine crankcases must be separated to allow removal of the crankshaft, camshaft and other internal engine parts. Many Lycoming engines require special tools to push the crankcase halves apart. Until very recently MMS used a quickly improvised set of tools to do this. The old tools protected the engine parts from damage and undue stress, but were inefficient and had become quite worn. New factory-made tools for this operation are very expensive; however, the engine overhaul manual has pictures of the tools and a clear description of how they are used.

Several years ago money to purchase a milling machine was donated and MMS Director of Maintenance Tim Obarow is a skilled machinist. An adequate amount of heavy steel plate and some other material were purchased and Tim went to work. Using that milling machine and a lathe, Tim fabricated the various parts of the new tooling for the engine shop.

After all the parts were made, MMS aircraft maintenance Supervisor Dale Coates ordered a sturdy case to house the new engine tooling along with copies of instructions for its use. All this cost about $3,200 less than the same commercially available tooling.

After all external parts are removed from the crankcase, the plates are installed on both sides. Here Joel puts the plate on the right side of the engine.

The plates push on the long bolts that pass through the crankcase to separate the crankcase halves. As Joel and Dale begin, the case halves are still held together by dowels that align them (as indicated by the arrow in this picture).

As large nuts on the outside of the plates are tightened the crankcase halves separate until the dowels are disengaged after about 3/8" of movement. The plates are removed and the case halves are easily lifted away from the crankshaft that is bolted to the engine stand.

So, how did the new tooling work? To quote Dale, "Great!"


Monday, March 24, 2014

Horizontal Stabilizer Talk

It is said that necessity is the mother of invention. The truth of that saying is seen in the modifications MMS Aviation mechanics make to airplanes used in missionary service. In fact, the Federal Aviation Administration provides a way changes can be made to production aircraft that are approved by the FAA and issued a Supplemental Type Certificate. As in any acronym-ridden system, we simply refer to this approval as an STC.

One STC we have installed several times was developed by a company in Alaska to improve the durability of the horizontal stabilizer on Cessna 206 and 207 airplanes. The stabilizer skins are removed, new skins are installed in a slightly different configuration, and the leading edge skin is held on with screws instead of rivets. This is valuable because, when a plane is operated on unpaved airstrips, stones kicked up by the wheels and propeller blast can beat up the horizontal stabilizer leading edge quite badly.


Phil works on leading edge attachment. The yellow frame in the picture is a fixture to keep the stabilizer straight while giving good access to it for repair.
After the original aluminum sheet skins are removed the horizontal stabilizer structure is cleaned, inspected, and repaired as necessary. Additional pieces are added to hold the "plate nuts" for the leading edge screws. The leading edge material is thicker than the original and is more resistant to damage.


Josh, a LeTourneau University student on spring break, drives rivets while Phil (standing) bucks the rivets. This swells the aluminum rivet to hold the layers of sheet metal together. 
Skins aft of the leading edge skin are riveted in place as they don't need changed as often as the leading edge. With this STC installed, a damaged stabilizer leading edge can be changed with a screwdriver instead of drills, a rivet gun, and bucking bars. Considerable time is saved as well.


Bob bucks a rivet while Phil drives it with the rivet gun. The more skins in place reduces easy access for the bucking bar (a piece of smooth steel). Added concentration is often required to achieve desired results.
Riveting 101: The repeated hammering of the rivet gun on the rivet head (outside the structure) against the bucking bar (inside) swells the rivet and holds the pieces together. The FAA publishes standards the driven rivet must meet.

An FAA Advisory Circular gives guidance.

Friday, February 21, 2014

What Happened Next

After the cylinders of the Lycoming engine for a ministry in Alaska (previous post) were ready, the engine's crankcase with its internal parts was assembled.  Cylinder assemblies were installed and the nuts that hold them were torqued.


Joel (left) and Dale torque thru-bolts that hold cylinders five and six.
 
Cylinder number three goes into place.
Cylinder valve trains were put in place as well as the accessory gears and accessory housing on the back of the engine.


Joel "safeties" oil passage plugs on the accessory section with lock wire.
Engine assembly is nearly complete as Dale does a final visual inspection of a fuel injector line.
Dale explains fuel injector line inspection criteria to Joel.
The engine test cell is being prepared with the engine mount and instrumentation appropriate for this engine's operational test.  When the test runs are done the maintenance record (read paperwork) will be completed.  It will then be crated for shipping and the engine will be on its way.

Friday, February 7, 2014

Sizing-up Progress in the Engine Shop

The engine shop at MMS Aviation has been a busy place lately.  Dale is supervising the assembly and test of a Lycoming engine for a ministry in Alaska.  Today cylinders and pistons were measured to assure proper clearance between them. 


Tim gave a mini refresher course about how to set up and use the cylinder bore gauge.  Dale, right, observes.


Dale measures each cylinder, checking dimensions in several places of the cylinder bore.


Joel records the dimensions on the engine build-up sheet as Dale gives him the gauge's reading.

Thursday, December 19, 2013

Refurbish or Restore

The dictionary says refurbish means to repair and make improvements, or to brighten or freshen up.  Restore is to return (something) to an earlier or original condition by repairing it, cleaning it, etc.  At MMS Aviation we do a lot of heavy-duty maintenance on airplanes so I wanted to know which word best described our work.  My conclusion is that both terms pretty well captures what goes on at MMS, but rather than just writing about it, here are a few pictures to illustrate it.


Work began in the upper forward cabin of this Cessna U206F.  Chuck cleans the wing support structure so it can be properly inspected.  Disassembly was accomplished by removing rivets that held the various pieces together. 
Airworthy parts were cleaned and painted before reassembly.  Parts that were damaged were replaced with new parts.

Work progressed from the upper forward cabin to the tail cone.

When the tail cone repair was complete the fuselage was rotated onto its left side to work on the belly and landing gear support structure.  The last two skins to be replaced have been removed.
 

Chuck and Jake use floor support structure to check rivet hole patterns because sometimes there are more holes in the old skin than need to be in the new one.  New aluminum sheet is below the original skin that is the pattern for the new skin.

The airplane being refurbished/restored was used most recently in Indonesia and may have been in Africa before that.  It will next be used in Suriname and based in a costal city so corrosion prevention is a priority.
 
This plane is a 1976 model and it's important to remember that it has been well maintained and safely operated by missionary aviators for nearly 37 years.  With the work MMS Aviation mechanics are doing, who knows, we may see it serve another 37 years in missionary aviation. 

Tuesday, September 3, 2013

A Look Back at April 2013

Before I summarize a very busy summer in the next blog, April at MMS Aviation needs mentioned.  Major aircraft maintenance events begin and finish throughout the year at MMS.  Typically this heavy maintenance involves repair following accidents and incidents, engine overhauls, or complete restorations.  Many times significant work on an airframe is combined with an engine overhaul.
 
To have three of these projects completed within a week of each other is rather rare and a bit exciting.


The top snapshot above is of a Cessna 206 that was completely restored after many years of use in four different countries by Mission Aviation Fellowship.  The Cessna Cardinal in the center picture is owned by two ministries in Wisconsin and received an annual inspection and some airframe repair along with an engine overhaul.  The Piper Lance in the lower photo is owned and operated by LAMP in Canada and had its engine overhauled.  The Lance also got new carpet installed in the cabin, several windows replaced, and repair and repainting of external fiberglass parts.

April was a fun month.

Tuesday, May 28, 2013

Prayers for The Hoblits, MMS Aviation, and MAG

Brad and Crystal Hoblit successfully completed their application/evaluation process last week and were accepted as MMS' newest apprentice family. The Hoblits intend to complete maintenance training with MMS before making the move to Burlington, NC where they'll pursue the additional flight training component offered through our partnership with Missionary Air Group (MAG).

Speaking of MAG, several members of MAG's operational staff were in the hangar last Monday for meetings, aviation maintenance strategy sessions, and to participate in the Hoblit's candidate evaluation: Sean Donnelly, President & CEO; Scott Grote, Director of Aviation Maintenance; Keith Dodson, Director of Operations; and Paul Jones, Guatemala Program Director. Paul just returned from a year of language school in Costa Rica and will make the move to Guatemala later this summer. Both Scott and Paul are graduates of MMS apprenticeship.

Scott, Paul, and Sean utilize the MMS Supervisor's Office.

Brad drills holes in the front spar of a horizontal stabilizer...

...and squeezes rivets on a bulkhead frame as part of his technical evaluation conducted by MMS Staff.

He also underwent a consultation flight with Paul Jones, 
MAG's Guatemala Program Director.

Paul and Brad debrief after the flight.

Brad, Crystal, and Lillia Hoblit

The Hoblits have returned home to the Dayton, Ohio area to raise the financial and prayer support necessary to begin service. Please pray for Brad, Crystal, and Lillia as they embark on this new adventure to join us in Coshocton, OH.

And please pray for MMS and MAG as we continue refining roles and responsibilities related to our growing operational relationship and training partnership.