Hi there
Im currently building a seagull spacewalker 2. I have previous flight experience but this is my first build. I was just wondering if anyone had any tips on cutting the fibreglass cowl i dont want to risk cracking it or making the holes for the engine head and muffler too big
any help or build tips to do with this plane would be great thanks
Calum

well i take a clear piece of plastic pick up the cowl mounting holes trace out the engine head cut it out in the clear plastic. install the cowl with the plastic over it trace out the hole on the cowl and cut. i use a dremell with a cutting wheel for straight lines and sanding wheel for the corners.
make sure that you have enough space around the engine head or exhaust to allow airflow, or you will over heat the engine.
thats how a full scale cools and heats recip engines, with cowl flaps that close or open the back of the cowl for airflow around the cylinder heads

What I have done is similar, I use paper templates mark the Engine cut outs. I then trace them onto the cowl. I then drill around the inside of the markings, pop the plastic out and clean it up with the dremel.

Take a piece of cardboard about 8" long and 3" wide. Trace around the head of th engine on one end of the strip and cut this out. Place the strip on the fuselage so the hole is over the cylinder on the engine and tape the cardboard in place.

Repeat this for the needle valve and the exhaust (if the exhaust is needed).

Fold the cardboard back abd remove the engine.

Mount the cowl and screw in place.

Now fold the cardboard strips back down on the cowl and trace the hole openings onto the cowl. Lift the cardboard strips back up and put !/2" - 3/4" masking tape over these marks. Now put the cardboard strips back down and trace the hole openings onto the masking tape.

Now you can remove the cardboard strips and the cowl and remount the engine.

Next, cut the holes SLIGHTLY UNDERSIZE from the marks on the tape and trial fit the cowl. Enlarge the holes A LITTLE AT A TIME, trial fitting after each enlargement. Continue doing this until you get the openings to the size you need for a perfect fit. You will most likely have the cowl on and off at least 5 times for trial fittings before you get what you want for opening size.

The masking tape will minimize/eliminate any chipping of the gel coat on fiberglass or painted cowls.

After you have made the initial openings in the cowl, I suggest switching to a Dremel TAPERED stone for the adjustments/enlargements of the hole size.

The tape will most likely clog the stone, however careful use of a flat piece of metal will clean the stone. Secure the metal in a vise and LIGHTLY run the stone on the edge of the metal to remove the gunk.

IF you have a Dremel or other high speed drill use this fitted with a 1/16th drill bit pushed in so that only the flutes are showing.

This works well as a cutting tool using the side of the drill. [ My engineering teacher is spinning in his grave]

Mark it out with a waterbased pen then cut and tidy up.

Dremel

Great ideas on creating a template not going to add anything there. When you start cutting though the key is to not push on the cowling with the tool when you are drilling or cutting. Let the tool do the work because too much pressure and you're bound to crunch the fiberglass. This is especially important when you're using a drill bit or other piercing object.

All good advice.

Side cutting bits fly through the fiberglass like a hot knife in butter, so they can easily get away from you... but they are wonderful when removing large areas.

Dremels with sanding drums & wheels permit finer control.

Always work slowly. Refit and test, then cut, rinse, lather, and repeat...

It's taken me as long as 3-4 hours to do a more complex cowl, but the end result is that people often ask me how I get everything cut so close and neatly.


A minor tip...

Once you've started an opening or hole, and are nearing the final sanding, apply thin CA to the inside of the cowl around the area that you are working on.

This will prevent cracking and help to strengthen the areas you are cutting into. It will also eliminate fiberglass "hairs" in the cut out areas.

after I drill out the access holes for the needle valve,EZ fueler,etc... I will enlarge them with a fine round file so I don't burn too much of the cowl with my dremmel even at low speeds the motor tool can open up holes fast with the file you can tweek the hole if its a little off center and there alot more control.
I will then use Blue tape too cover the holes on the outside of the cowl and re-enforce the holes with epoxy on the inside,trimming away the exess with the file after its hardened.
epoxy sticks well to the interior of the cowl and stifens the holes

Yup Epoxy does it too.

Excellent tip! I will have to add this one to the note book.

thanks everyone for your great advice thats been a great help

One other "might do" is with every hold you drill in the cowl for screws. Sand the back and apply a CA hinge which helps keep it from widening and cracking