Started 10/29/05
My Bearhawk will have a Lycoming O-360 turning the big fan out front. The following describes the construction of an engine mount for the O-360 engine. This is a little different than the O-540 engine. See Russ Erb's CD for how the Lycoming O-540 and other engines (including some auto conversions) are mounted.
Setting up the engine alignment and making the
motor mount for it must be done with great care. Take
your time and get this part right. I spent over 8 hours just getting
the engine set up in the correct position. If you end up with the engine
canted one way or the other, it will affect how the airplane flies.
There are a couple ways to get the alignment correct - Here is how I set
up mine:
To start with, the fuselage must be set up in its correct, flight level position.
As you may recall, we use the bottom longerons between Stations "B"
& "C" to determine if the fuselage is level fore/aft:
The cross tube at Station "O" is used to determine if the fuselage is level
side-to-side:
In the above picture, the magnetic level is attached to the bottom of
the cross tube at Station "O". The camera is tilted a bit in the picture.
Now that the fuselage is in the correct position, the engine must be set up at the correct location. The goal is to have the engine aligned so that the thrust line (centerline) of the fuselage goes right through the middle of the engine crankshaft (see drawing #1 in the plans). The engine must be at the correct height, level fore/aft and side-to-side, and be at the correct distance forward from the firewall.
I was lucky enough to be able to borrow an old Lycoming O-360 engine case from a friend. The engine case should be the same model as the engine you plan to install. This engine case has some holes in it and its "un-serviceable" but the mounts are in great shape, so it serves my purposes well. The nice thing about doing it this way is that I won't risk burning the paint on my newly overhauled engine.
Here is my set-up for getting the engine properly located:
As you can see in the above picture, I ran a string from the tailspring all
the way out past the front of the fuselage several feet. This string
exactly duplicates the thrust line as shown on drawings #1 and #16. If
you do it this way, make sure the string is pulled tight so it doesn't sag
in the middle. A sturdy fishing line works well for this.
Here is how the thrust line string was set up:
The string was attached to the tailspring at the correct height as shown
in drawing 16. It was tied off in a way to center it in line with the centerline
of the tailpost. The string runs through the fuselage and is tied off a few
feet in front of the firewall (I tied it to my bandsaw). The string should
be exactly 18 1/2" inches above the center of the bottom longeron tubes between
stations "B" & "C":
And it was checked for level fore/aft using a bubble level:
It was also centered side-to-side in the fuselage as verified by plumb
bobs:
With the thrust line established, the engine case was assembled around the thrust line. I used a table and some cement blocks along with various size pieces of wood and wedges to prop the engine up into the proper position.
Click here to go to Engine Mount page 2