im getting ready to cut out and put the cowl on a older model hangar 9 232 breitling its my first time doing this and im kinda of afraid of screwing it up ! i need a few pointers or do's and donts on getting everything lined up right!

Use cardboard templates.

Cut long strips of cardboard and use them to fine tune the openings that you'll need. Then, with the engine in place, tape the cardboard onto the fuselage with the openings you cut around their corresponding engine parts.

Now, remove the engine but not the cardboard strips. Put the cowl in place and trace the openings in the cardboard onto the cowl.

This will get you close if not dead on. I'm sure somebody out there has some pictures of this.

Cut in small increments and work toward your traced lines. It's easy to remove more material but impossible to put it back.

Be sure to have a good air outlet to keep the engine cool also. I think the general rule is 3 times the outlet opening as the inlet? Someone correct me if I'm wrong on that.

One picture is worth a thousand words. I give credit here to whoever originally wrote this and published it, I found it helpful, so I saved it.

That is exactly the same way I do it but I use construction paper or poster board from the dollar store (dollar stores are a great place to pick up hobby supplies )
I mark the cowl with a sharpie.
I use a dremel with a small and large sanding drum to cut out the cowl and work the holes to size (do this outside or in a garage, there is alot of dust, wear safety glasses)

do you "HAVE TO" remove the engine to do this? and thanks very much for the help!!!!

Not if you don't mind getting fiberglass dust in your engine and taking the chance you may accidently hit the engine with your grinding wheel. Also, if the engine is large enough you won't be able to mount the cowl without removing the engine. Think about it.

That's what I was looking for... couldn't find it for soem reason.

If you don't remove the engine then you can't get the cowl on to transfer the hole locations. This is how I do them too but even doing it this way I can ugly them up. I'm just not very good at cowl opening. [&o]

ok thanks for the info gonna try to do it tonight!

Use your Dremel... and once you have a hole drilled out, use your tube sander not the disk. (Not sure what it's called.) Stay just inside your line and take your time. Don't run your Dremel full blast, just enough so your drum dosen't slow down too much while sanding.

It will give you better control. Once you have it sanded out, use a sanding stick and hand sand it to your line. Use a round Dowel and wrap Med grit Sand Paper tightly around it... and sand your curves with it.

Using you Sanding Drum reduces the chance of your Dremel getting away from you possibly screwing up your Cowel. Also it helps reduces the chance of chiping off your paint.






Luftwaffe Oberst
AMA District II
Radio Aero Modelers Club
Pulaski, NY



Supporter of RedNeck R/C- Fulton, NY

Like he said!!!

DO NOT BE WORRIED ABOUT TAKING YOUR TIME!!!

I can easily spend 3-4 hours cutting a cowl.

BTW: I hold the intake of a shop vacuum tube between my knees angled at the cowl I am working on.

This keeps the fiberglass dust out of the air, though wearing an air mask is a good idea.

If you are cutting a large area out, you can also use a drywall side cutting bit in a dremel to help carve out large areas.

The side cutting bit chops through the fiberglass like butter, so you have to be very careful. You should not use a side cutting bit for your final cuts though... do this as suggested above with a sanding "drum" not a disk.

The sanding drums are round cylindrical bits of sandpaper over a cardboard structure...

Dremel has two sizes, the normally available larger .6" diameter size and the sometimes hard to find .25" size.

The latter is great for cutting out bolt holes and holes for High Speed Needles, etc.

how far back do i need to go with the cowl on the side of the fuse before i start? the cowl will fit over the whole engine easily without doing anything as it is now im just not real sure how to determine where to place the cowl before starting im thinking just back far enough to where it looks right with the shaft coming out

Technique One
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First go ahead and mount the engine in place at the recommended distance. Leave the muffler off.

Sometimes I may also need to remove the HS needle and carb too!

If possible slide the cowl into place.

Then put on your spinner and prop.

Align the cowl to the spinner leaving the proper distance from the cowl to the spinner.

Now mark the position of the cowl on the fuse with a panel line pen ( you can remove the marks it makes with alcohol easily! ).

Remove the cowl and engine and use the alignment lines you drew to make the screw holes.

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Technique Two
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If I cannot slide the cowl over the installed engine...

DO NOT worry about making the cowl screw mount holes at first.

Mount the engine on the plane, and make your cardboard cutouts.

Remove the engine and slide the cowl into a rough position. Put a ruler or other measuring stick in through the front of the cowl to get an approximate distance for cowl mounting.

Make temporary alignment marks on the fuse.

Now start cutting the holes you need to be able to move the engine into it's final position.

Put the engine back on and see if you can get the cowl into place.

Keep working on your cowl holes, e.g. the cylinderhead hole, etc. until you get the cowl to slide in place.

Once done, put the spinner and prop on the engine. Align the cowl to the spinner, and mark the position on the fuse...

Sometimes when I am this far along I tape the cowl to the fuse and go ahead and drill the cowl mounting screw holes, as I now KNOW where it should finally rest...

thank you very very much opjose i think this is not going to be as hard as i thought, your post really explained what i needed to know!!!!

Yep... I've been known to order an extra cowl or maybe two before the plane ever takes to the air.

Here's a trick I like to do on painted cowls. Cover the area you are cutting with masking tape (I prefer blue painter's tape). Then cut and sand your cutout using the tips and techniques listed above. So what's the tape for?? It will help to keep the paint from chipping away as you work with the cutting and sanding tools.

Ken

Yes great point... tape helps a lot and is often overlooked.

Also I typically put on a bit of thin CA around the newly cut openings on the inside of the cowl to help harden the fiberglass fibers and prevent cracking.