Model Forum / Radio Controlled / Air Models / February 2004

A number 1 don't get in a big hurry. First you need to measure the
length from the engine's thrust washer (the part where the spinner
backplate fits against)  to the firewall minus what ever clearance you
want between the spinner and the cowl (1/16 to 1/8"). Then measure the
height of the cowl from end to end. Subtract this from your first
calculation and mark the fuse sides this distance back from the
firewall. Now make some rough "guesses where the cut-outs need to be and
start cutting the cowl a little at a time until you can get it on and
lined up with the marks on the fuse sides OR if you want to use the card
stock routine - Mount the engine and then  tape card stock on as
directed - mark the approx. location of the cut outs required for the
cowl then take the motor off and cut out the card stock to these marks -
fit the cowl back on and lined up the with marks derived by your
measuring and calculations and mark the cowl. What ever you do don't  
try to cut the cowl all in one step. Cut inside the marks and slowly
open the cuts up till your happy with the fit. You need to leave a
little clearance (1/16-1/8") all around the head and muffler. I just did
one of these today on a 30% Ultimate the whole process took about 2 hrs.
DON'T get in a big rush - take your time and enjoy the best hobby there is.

Search rec.models.rc.air
for 'cowl gords'  The first hit is one I wrote telling how to do this.
Gord Schindler
MAAC6694

On 2/23/2004 4:56 PM Ted shuffled out of his cave and grunted these
great (and sometimes not so great) words of knowledge:

An easy solution for your problem.  Take a piece of scrap 3/32 or 1/8"
lite ply and cut it the same width as the engine.  The length you will
want is from the front of the mounting lugs to the furthermost rear
point.  Measure and mark where the holes in the mounting lugs need to
go.  Now laminate a piece up some scrap balsa to make something about
3/8" square and measure from the front of the mounting lugs to the front
of the drive washer.  Add 3/4" to this measurement.  The 3/4" you want
to overlap the lite ply.  MAKE SURE THE WOOD IS CENTERED ON THE PLY AND
EQUAL ON BOTH SIDES OF THE PLY and CA in place.  Bolt this into your
motor mount and center/align your cowl.

It sounds complicated, but it isn't.  Takes about 5 - 10 minutes to do.

I am probably out of step with those who know all the right way to do
things, but this is what I use to accomplish the same goal.

First I mount the engine where I want it to be.  Second I use a water
soluble pen to mark the centerline of the crankshaft (side AND top) along
the fuselage for about 6 inches.  Then I measure back from the spinner some
distance and put a mark on both of the previous lines and write down the
distance - less 1/8 inch for spinner clearance.  Usually I get 4 to 8 inches
back depending on the size of the engine.  What is important is marking a
known distance on the centerline.  I also measure back from the spinner to
the center of the 'jug' and write that value down.

The next step is to remove the engine and mount the cowl making sure that
the front of the cowl is not more than the distance written down on the
center lines.  This sets the cowl depth and does not require that the cowl
be hard mounted, but it does help.  Then I use a more permanent marker to
extend those lines onto the cowl and mark them.  Now I transfer the written
'jug' measurement to the line where it will penetrate the cowl.  Remove the
cowl and start cutting.

To do what you need, reverse the process.  Measure the jug to spinner
distance and shorten it 1/8 for clearance.  Cut your jug hole and go from
there.

Hope this has helped and not confused you.  It confused me for a few years!

Good luck.

Easy fix.  Cowls fit under fuse tape-mounted ruler(s)!  Tape metal flexible
cork backed rules (office supply - cheep) to the fuse stretching into the
engine cowl area.  Make marks to relocate rulers (dry erase or permanent
markers with denatured alcohol to remove works great).  If you find need to
remove rules for access or bump these taped rules the marks let you return
without repeating all remounting.

Look at your problem and decide sequence systematic, issue-by-issue.

My sequence is:

Mount the Cowl without Engine reference positions to cowl on rules.  Then
mount the engine without Cowl reference positions of engine clearances and
access routes on rules.  Then use the marks to cut cowl close then trim and
fit trim and fit, trim and fit, etc until together.

Detailed:

First screws mount the cowl. (I add rubber hole grommets from the hardware
to save the cowl from vibration.)

Then tape rulers in place on the fuse lying rules across the cowl.
Reference the cowl by marks on the ruler aligning a rule edge with engine
shaft or airplane center and exit either the cowl opening or spinner back
plate distance.  PS. Don't forget screw accesses and choke pin locations
need to be defined either this marking or the next remount.

Remove cowl, mount engine under same ruler locations to ruler mark for
distance and center.

Mark clearance hole limits.   I sometimes tape or reference mark its corners
on mono-coat another rule over the motor head to be exposed and make marks.

Remove the motor, mount the Cowl and start marking from the rules then
remove rules and remount the engine.

Now it is just keep fitting and cutting the cowl in bits until you have the
fit you want.

If you want to adjust engine angles actively after that I use washers added
to the mount.

For my Quarter scale building, I add a set a caliper measurements to assist
and verify this procedure.

This I learned from a master builder, Mike B.  Thanks again, Mike; I owe you
ten other thank you's that improved my building and enjoyment of the hobby.

First I mount the engine.  Then I tape a block to the fuse that is higher
than the engine head.  Then I tape a 12" long (or to suit) piece of  1/8 x
3/8 spruce (or something like that) on the block so that the end of the wood
is directly centered over the glow plug.  Then I dismount the engine and
mount the Cowl.  Then I cut the hole and we are in business.