I am mounting a cowl on a Kyosho Su-31 with a Saito 72 and have run into a chicken vs the egg kind of problem. To to locate and mount the cowl centered on the spinner requires the engine to be mounted; and the cowl will need some cutting to fit over the engine valve covers to do this. To accurately cut the valve cover openings in the cowl (using the paper template on the fuselage method) requires the cowl to be mounted in its final location first.
I can't be the only person to have encountered this, but all my searches turn up solutions to cowl/engine mounting that assume the cowl fits over the engine.
Any other ideas out there? Yeah, yeah, I know, get a smaller engine....:)
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!
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.
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