Engine Mount Installation

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Before proceeding further with the Belly Panel project, I decided to move on to the Engine Mount installation.

There are certain welds on the airframe that deserve more attention and respect. These include the wing spar brackets, wing strut brackets, spar crossover tubes,  landing gear brackets, tail feather attachments and the Engine Mount Brackets.  Every weld is important but a a bad weld on the engine mount can ruin your day. 

This project starts by first taking the fuse off the rotisserie to expose the front end of the airframe.  The four airframe connection points must be accurately welded to agree with the chosen engine mount holes and the engine mount must agree with the engine you plan to use. My future plan was to use a Lycoming or Superior 180HP Engine and for now all I needed to do was decide on which type of Engine Mount to use.  There are basically two types of mounts – conical or Dynafocal.  The Dynafocal Mount is said to reduce noise and vibration inside the cockpit and the swing out feature sounded good in theory. The installation needed for the swing out feature will require careful alignment of the top and bottom brackets on each side so that the hinges will not bind and stay in alignment. There is no means of adjustment for a misaligned hole so careful tack welding and trial fitting is necessary to assure proper fit of the Engine Mount. 

In later years I would discover that the swing out Engine Mount is not as practical for servicing the engine as it sounds.   As you can imagine, the throttle cable, mixture cable, carb heat cable, magneto cables, oil lines and numerous electrical connections disallow any means of hinging the engine away from the firewall without first disconnecting everything.  Only during a major service event will the swing out Engine Mount feature be utilized.

Floorboards and Re-Welded Seats

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While my main effort was to complete all the welding on the fuselage I had to re-focus my attention to the wood floorboards and seating attachment issues.  That’s because metal tabs and seat mounts had to be welded on the fuse to hold them down.  I chose 5/16″ exterior grade plywood and carefully cut it out to fit around tube joints and around the control sticks.  This was not to be the final finished floorboard.  In fact I ended up fabricating three different floorboard patterns until I ended up with a suitable design that evolved with other changes I made along the way.

During this early phase of construction I was reminded of the labor intensive method used for annual inspections for my Cessna Skyhawk.  My A&P (Airframe & Powerplant) Mechanic at the time had the complete cockpit interior removed including the seats and carpeting and all the floorboard inspection panels were also off.  This close up inspection is to check for airframe corrosion, control cable integrity, pass through wiring integrity, fuel line integrity, etc. But my mechanic also found a large mouse nest which certainly did not belong there!

This led me to think how easy or difficult it would be to inspect my homebuilt when it was finished. The plans specified that all interior sidewall sheet metal panels have a lip or 90 degree edge to be used to attach to the wood floorboards.  This would require me to completely remove all the metal sidewalls just to get to the floorboard removal and that would be incredibly difficult and time consuming.  The plans also specified a fabric belly and Yes, I could have added several removable inspection rings but they are very small and difficult to get into. Thus I decided in the months ahead to design a system of easily removable full width belly panels and omit the fabric belly altogether.

During this phase of building was the time I also purchased and modified a pair of Cessna 172 seats and removed the upholstery and removed 3 inches of metal frame width and re-welded them back together.

Welding the Elevators, Trim Tab, Stabilizers, and Rudder

Welding Tail partsMaking the tail parts require accurate welding fixtures.  Plywood panels were purchased and painted flat white.  Then a 2″ pencil grid was drawn on the entire face of the panels.  I then transposed the full size shape of the stabilizer, elevator and rudder on the plywood panels and located  each rib location, hinge knuckle, cross brace etc. per the plan. The tubing was bent using a spring and soft rubber hammer and plenty of hand persuasion.  Gradually I got the metal to agree with my curvy drawing.  The horizontal stabilizer had a tricky leading edge taper that required spliting the last outboard length a few inches from the end and then removing sufficient material and then squeezing the ends together and re-welding the seam back together.  The seam was then ground smooth.

The metal tubes and ribs were cut to size and fitted tightly together on top of the plywood pattern. Wood blocks were used to keep everything in their place during welding.  Only tack welds were used to temporarily hold parts together.  The assembly was then removed and finish welded on a welding table.

Welding the thick hinge knuckles and bushings was the most difficult due to the differental thickness of the knuckle and the parent tube.  It was important to keep the heat directed to the heavier wall tubing and avoid burning through the adjoining thinner parent tube.  Also keeping the hinge knuckles aligned  was done with sacrificial bolts that sometimes became unknowingly welded to the finished assembly.

The plans also called for small 1/8″ rods in certain end locations.  This was used as a anti bending brace to avoid end deformation during the later fabric cover and shrinking process.

Finishing the Turtledeck

Fabricating the Turledeck 3 of 3After the metal fabrication and system testing of the lift and lock mechanism was complete it was time to finish and protect the metal.  A backyard sandblasting set up was used to clean and prepare the metal for paint.  This set up was used for all smaller parts like tail pieces, rudder, landing gear legs, etc.  I found out that sandblasting is very messy and its impossible to recover used blasting material when you do it outside. All future sandblasting was done by Southwest Sandblasting in Grand Rapids who do an outstanding job.

After the turtledeck was sandblasted it was cleaned with MEK and hand brushed with a 2 part epoxy primer from Randolph Coatings quickly followed by a 2 part epoxy J-3 yellow finish color.  The 2 part epoxy paint protects the metal from corrosion and is impervious to MEK and all other Poly Fiber chemicals used for fabric attachment and finishing.

Because the inside fabric of the turtledeck can be seen when it is raised I used untinted Poly Brush to avoid having pink brush marks visible.

Learning to Weld

Welding ProjectsWith the fuselage securely attached to the rotisserie it was time to learn to weld the 4130 steel tubing.  Using a oxygen/acetylene gas rig and jewelers torch I test welded several scrap pieces together but it was’nt until I got expert instruction from Chuck & Craig Garret from my local EAA Chapter 145 that I finally gained some confidence.

I started welding on the fuselage lift handles and then the wing spar brackets, elevator bell crank assembly, floorboard mounts, rudder pedal mounts, engine mounts and landing gear and wing strut brackets.  They say the best way to test a weld is to try to tear or break it apart.  Unfortunately that destroys your weld.  Sadly, a few years later I put some of my welding to a real world test during a bad landing/ground loop event.  The good news is, the welds survived – the bad news is, the landing gear did not.

I will post more about that event in a future post including photos of the damage and the repairs made to the aircraft.

The Starting Point

Trip To Orillia, OntarioEvery Project has a starting point and N728DC started with a trip to  Orillia, Ontario to inspect a Sportsman 2+2 fuselage that was for sale.  In November of 1995 we packed up the family, rented a trailer and headed to Canada to inspect and possibly buy a former builders uncompleted project.  A set of color coded plans were used to inspect tube diameters and a thorough set of measurements were also taken to confirm if the fuselage fabrication was done correctly.

It turned out that everything was spot on.  The frame was square and true, the welds looked good, and there was no corrosion.  In fact it also turned out that the fuselage was actually fabricated by Wag-Aero and sold as a kit in their catalog for a much higher price.

There was still a lot of welding to complete but this fuselage would provide a huge head start to a long and complicated project.