CRASHMISTER

My Feedback: (31)

Hey gang What is the best way to cut the openings needed in a cowl??// problem is its to flimsey to cut strait any advice would be appreciated Pat D.

Nathan

My Feedback: (12)

Dremel.

RCKen

My Feedback: (9)

As Plane Insane said, use your dremel. Take a look at the attached pic to see how to mark your holes. Use thin cardboard to mark where the holes should be, and then transfer that to you cowl. When you start cutting the cowl, don't get in a hurry. Use your dremel and work slow, with the bit turning just what you need to cut. If you get the bit too fast any slip will eat up a lot of material at once

Campy

My Feedback: (1)

What I do for marking/cutting the cowl is:

1. Mount the engine and muffler in the plane.

2. Take some cardboard that comes inside new shirts (and some times from the dry cleaners) and cut several strips long enough to go the full length of the engine PLUS 2" - 3" (For instance, the distance from the firewall to the thrust washer is 4", the strip would be 7" long.). Depending on the size of the plane will determine how wide to make the strip(s). On a 40 size plane I usually make 2 strips about 3" - 4" wide and 1 strip about 1" - 2" wide. I prefer to use 3M brand BLUE masking tape. I highly recommend the "60 Day Safe Release" type. The 60 day will not pull up any underlying paint, comes off of film/fabric coverings leaving little, if any, residue. It has a "paper like" appearance, NOT TEXTURED, and the side of package will have 2 DOTS in the adhesive level.

3. Mark the fuselage about 2" - 3" back from the firewall with a soft lead pencil. Now temporarily tape a strip of cardboard in place on the mark and draw a line around the cylinder head.

4. Remove the cardboard strip and cut out the hole. Test fit the strip and hole over the cylinder head and modify as needed until the hole is ABOUT 1/4" larger than the cylinder head all the way around.

5. Take this strip and tape it in position on the fuselage.

6. Repeat steps 4 and 5 for the muffler and needle valve. For the needle valve I usually make the hole slightly larger than the diameter of the needle valve head.

7. After all the strips are FIRMLY taped in position, CAREFULLY FOLD them back and remove the engine and muffler.

8. Mount your cowl and SECURELY fasten it in position.

9. Now fold the cardboard strips down over the cowl and draw the outlines of the openings onto the cowl.

10. Remove the cowl and strips of cardboard and remount the engine and muffler.

11. I use a dremel to cut out the openings in the cowl. I have a pointed, trianglular shapped cutter about 1/4" in diameter I use to start the openings with and open them up to about 5/8" diameter. Then I use a sanding drum (cut off wheel for straight lines ) and go to within 1/16" of my marked line.

12. At this point I trial fit the cowl to the plane/engine and make any minor adjustments to the cowl. I usually switch over to 220 paper (and sand by hand ) for the minor adjustments and do any finish sanding with 320 or 400. Rubbing alcohol will remove any tape residue and the pencil marks without damaging any finish you have on the plane.

By using the cardboard strips I am rarely off when trial fitting the cowl.


Hope this answers your questions.

khodges

My Feedback: (1)

I place masking tape on the cowl in the area of my cuts, and use the template idea as in above posts. Then use the Dremel, and take my time making the cuts. The tape will help prevent splitting and flaking of the gelcoat, or tearing if the fiberglass is really thin. Most .40 -.90 size cowls, I usually add another layer of 'glass inside to strengthen them. The weight gain is negligible compared to the extra strength and longevity you'll get. Just beware of the thickness where the cowl fits over the front of the plane, you might have to sand either one a bit to make the fit

ballgunner

My Feedback: (1)

The problem with Dremel is that it turns so fast it doesn't cut plastic, it melts it, even at it's lowest speed setting. I have a Black & Decker cordless screwdriver that turns slow enough to cut. Problem is that only hex shanks will fit. Micro Mark has a shaft with a chuck the same size as a Dremel chuck. Costs about $9.95 and will take any Dremel tool. Turns a few hundred RPM and does the same work at slower speeds. I still have two Dremels but the B&D gets a good work out on plastics.

MinnFlyer

My Feedback: (4)

If your dremel is melting plastic, you're using the wrong bit.

Ilike the 9011

http://www.dremel.com/html/products/...tage_bits.html

CRASHMISTER

My Feedback: (31)

WOW THANKS GUY'S It worked Perfect , after all your advice I went back and re layed out my openings as explained in post #4 found the motor was off almost 1/2 inch. I still got some tape bubbles in the ultracoat . Can I smooth these out with an iron?????

MinnFlyer

My Feedback: (4)

Yup

Campy

My Feedback: (1)

Yep. If they are over a SOLID SURFACE ( balsa, etc ), take a pin and put a hole in one end of the bubble. Then heat the area with your iron and QUICKLY, using a soft dry cloth, firmly wipe it down moving towards the hole. This forces the air out of the bubble and reseals the covering to the balsa.