Started May 19, 2007
The first step in the engine cowling fabrication process, is to locate and position the nose bowl. You can purchase your nose bowl from Bob Barrows by going to this website:
http://bearhawk-fiberglass.tripod.com/
If you have purchased a nose bowl that is a split, start by assembling the two halves and drilling and clecoing them together. The nose bowl, prop spinner and prop must be installed to get this set up properly.
The nose bowl must be positioned in its final place and then firmly clamped
in position so it can't move during the fabrication process of the engine
cowling. The nose bowl should be spaced to allow a 1/4" to 1/2"
gap between the nose bowl and prop spinner. To space mine at exactly
1/4", I used some wood blocks as shims. The spinner plate is 1/2" deep
so I used some 3/4" thick wood as a spacer between the spinner plate and
the front of the nose bowl as shown here:
Note in the picture above, the nose bowl has been positioned so the top
is slightly low where it meets the spinner. This is to allow for engine settling.
With new motor mount rubber spacers, you can expect the engine to settle
and move down about 1/8" or so after you have flown for a few hours. If
you align the nose bowl to line up with the prop spinner at the top, the
nose bowl will end up being too high after the engine settles.
Here is a picture of the spacer block used on the inside of the nose bowl
to give the "C" clamp something to clamp to:
With the nose bowl properly positioned, and level, its time to start installing
the "C" channels. The "C" channels were made from .032" thick, 2024
T3 aluminum. There are two "C" channels at the top spaced between 12" and
14" apart. In my case I spaced them as wide as possible, but just close enough
together so I'll have access to the top of my brake fluid reservoir (14"
worked well for my airplane). Here they are temporarily installed:
The "C" channels simply slip up under the flange at the firewall and the
flange on the nosebowl. For now they are just drilled and clecoed in
place.
The top "C" channels can be placed under the firewall flange and under the nose bowl flange because there will be a hinge sandwiched between the channels and the top skin. The hinge acts as a spacer and brings the skin flush with the boot cowl and the outside edge of the nose bowl.
Next, the same size "C" channels were made for the sides. These will
be installed low enough to have good access to the engine bottom spark
plugs:
Make sure that you position these side "C" channels to be parallel
with the bottom of the side windows and tops of the cabin doors. This
will give you nice lines that are parallel and flow nicely, especially when
you start laying out your stripes.
In the picture above, the side "C" channels were just temporarily placed
under the flange of the firewall and the nose bowl and clecoed. This
"C" channel actually needs to sit flush with the boot cowl skin and the nose
bowl flange or the skin will not lay right. To accomplish this, the side
"C" channels need to be trimmed to be between the flanges and then attached
using some 1 3/4" x 3" long steel strips (made from .032 4130N steel
sheet):
The channels were cut to just fit between the flange of the firewall and the flange of the nose bowl.
Here is the side channel installed at the nose bowl:
As you can see, the channel sits flush with the outside of the flange. These
are just temporarily attached with some all aluminum pop rivets but will
later be attached with screws and platenuts.
Here is what it looks like on the inside:
Click here to go to Engine Cowling page 2
Click here to go to the Final Assembly Index page