How to: Custom cowl?
03-22-2005, 01:57 AM
#1
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How to: Custom cowl?
I am getting ready to launch into my next project, the BTE Delta Vortex. One of the mods I'd like to make is to create a custom cowl for this bird. I've seen it done here many times on various planes, but my searches turned up very little on how to actually go about it. I saw one method that utilized foam and glass sheeting, but I don't think I'm ready for the glassing world.
Please post any tips, references, or examples you may have. It will really help in my understanding, and serve to (hopefully) make an amazing plane that much better!
Please post any tips, references, or examples you may have. It will really help in my understanding, and serve to (hopefully) make an amazing plane that much better!
03-22-2005, 07:31 AM
#2
RE: How to: Custom cowl?
Like you, I was afraid of the glass world till I got the right stuff. Use blue or pink foam, not the florist stuff or epp as a plug. Simply shape it the way you want. I used .75oz fiberglass from the LHS and ZPoxy finishing resin. It worked like a snap! I also learned a trick from a Combat Models video about using baby powder. Cover your work area with cardboard, lay your FG out and cut it with an xacto knife to shape. Once you are done needing the clean surface sprinkle the baby powder down on the cardboard. I also always wear gloves now too when working with glass. When you start getting a mess on your hands just rub them around in the powder and you have dry stick free hands very quickly and can keep working. The powder won't hurt your workpiece either.
Lay the FG on the plug and using an acid brush apply the resin. I made mine with 3 layers of glass just to be safe. After letting everything cure good I sanded it while still on the foam plug. Once you are happy with the sanding job use some acetone to melt the foam out, keep plenty of paper towels handy and do it outside for the fumes and volitility.[sm=bananahead.gif]
Prime, cut to allow for engine, Paint, and fly.
I will take a pic later.
Lay the FG on the plug and using an acid brush apply the resin. I made mine with 3 layers of glass just to be safe. After letting everything cure good I sanded it while still on the foam plug. Once you are happy with the sanding job use some acetone to melt the foam out, keep plenty of paper towels handy and do it outside for the fumes and volitility.[sm=bananahead.gif]
Prime, cut to allow for engine, Paint, and fly.
I will take a pic later.
03-22-2005, 08:33 AM
#3
RE: How to: Custom cowl?
What I do for a "custom" cowl is:
1. First you need to decide if the cowl is going to be a "flush" mount or over the fuselage mount.
2. Get some blue or pink foam from Home Depot, Lowes, etc. Frequently you can get damaged sheets of 2'x8'x2" thick for 1/2 (or less) price.
3. Cut the block(s) needed for the diameter of the cowl and enough blocks to make the correct length.
4. If there are multiple blocks (usualy there are ) I fasten the blocks together with carpet tape. The plastic tape works great for this.
5. Now carve/sand the block to the shape you want. As you get close to the final shape put it against the plane FREQUENTLY to insure you have the proper conformation.
6. If you decided that the cowl is to be a "flush" mount, you will need to make the cowl ABOUT 3/32" SMALLER all the way around. This is to compensate for the fiberglass.
7. Cover the foam block with LOW TEMP FILM. Towerkote/Econokote are great for this. If you don't cover the foam, the resin WILL EAT THE FOAM.
8. If you plan on making more than one cowl wax the cowl with about 12 coats of paste wax. If you are only going to make one cowl, 1 or 2 coats of wax will do.
9. I use 2oz fiberglass cloth. Cut the cloth into 2" wide strips about 6" - 8" long.
10. LIGHTLY spray the plug with 3M #77 and apply the cloth to the plug. You want your overlap seams to be about 1/2". Depending on the size/shape of the model/cowl you will need a minimum of 2 layers of cloth. 2 layers of cloth is usually fine for up to a 60 size cowl.
11. Get some acid flux brushes (Home Depot, Lowes, etc - about $.25 each) and mix up some resin, NOT EPOXY. You want to mix it so you have a 30 minute WORKING time. Now dilute this 10% BY VOLUME with acetone.
12. Using the flux brush, apply the resin to the cloth. You need to make sure the cloth is COMPLETELY saturated. If there are any "white" spots, the resin did not go all the way through.
Try not to have too many runs as these will need to be removed later. This will need about 48 - 72 hours to dry, depending on temperature and humidity.
13. After the initial coat of resin is dry, mix up some more epoxy, again with a 30 minute work time, but do not dilute this batch. Using another flux brush, put a coat of resin over everything, again, being careful of runs.
14. When this is dry (24 - 48 hours) sand the cowl starting with 60/80 grit and work down to 150 grit. Any dips/low spot fill with spot putty (Red stuff in a tube in the automotive section ). after sanding this down, put a thin coat of primer (I use automotive "high build" primer) on the whole thing and sand again to show anything you may have missed. Repeat the above as needed until you are satisfied with the results.
15. Trim any excess fiberglass from the back of the plug. You do not want any fiberglass hanging over the edge to block removal of the plug. If you decided to save the plug (12 coats of wax) put the plug in a bucket of water and CAREFULLY flex the cowl on the plug to allow water to get between the cowl and the plug. You should be able to get the plug to pop free from the fiberglass cowl. If this is a one time deal, take the cowl outside, make an X in the back of the cowl (through the film covering), peel the covering back and pour some gasoline onto the foam. You will only need a couple of ounces for a 60 size cowl. Go have a cup of coffee and come back in 20 - 30 minutes. Peel the film and the "sludge off the inside of the cowl and dispose of properly. Now wash the cowl with soap and water.
16. The cowl is going to be very soft and flexable at this point. Shape the cowl as you need it (primarily to fit the fuselage ) and put it aside for 3 or 4 days to harden up.
17. Now you can trim the cowl to length, cut any holes needed and do a final prep for painting.
This sounds complicated and like it is a lot of work, but it really isn't. The hardest parts of the whole thing is carving/sanding the foam block and waiting for everything to cure/dry.
1. First you need to decide if the cowl is going to be a "flush" mount or over the fuselage mount.
2. Get some blue or pink foam from Home Depot, Lowes, etc. Frequently you can get damaged sheets of 2'x8'x2" thick for 1/2 (or less) price.
3. Cut the block(s) needed for the diameter of the cowl and enough blocks to make the correct length.
4. If there are multiple blocks (usualy there are ) I fasten the blocks together with carpet tape. The plastic tape works great for this.
5. Now carve/sand the block to the shape you want. As you get close to the final shape put it against the plane FREQUENTLY to insure you have the proper conformation.
6. If you decided that the cowl is to be a "flush" mount, you will need to make the cowl ABOUT 3/32" SMALLER all the way around. This is to compensate for the fiberglass.
7. Cover the foam block with LOW TEMP FILM. Towerkote/Econokote are great for this. If you don't cover the foam, the resin WILL EAT THE FOAM.
8. If you plan on making more than one cowl wax the cowl with about 12 coats of paste wax. If you are only going to make one cowl, 1 or 2 coats of wax will do.
9. I use 2oz fiberglass cloth. Cut the cloth into 2" wide strips about 6" - 8" long.
10. LIGHTLY spray the plug with 3M #77 and apply the cloth to the plug. You want your overlap seams to be about 1/2". Depending on the size/shape of the model/cowl you will need a minimum of 2 layers of cloth. 2 layers of cloth is usually fine for up to a 60 size cowl.
11. Get some acid flux brushes (Home Depot, Lowes, etc - about $.25 each) and mix up some resin, NOT EPOXY. You want to mix it so you have a 30 minute WORKING time. Now dilute this 10% BY VOLUME with acetone.
12. Using the flux brush, apply the resin to the cloth. You need to make sure the cloth is COMPLETELY saturated. If there are any "white" spots, the resin did not go all the way through.
Try not to have too many runs as these will need to be removed later. This will need about 48 - 72 hours to dry, depending on temperature and humidity.
13. After the initial coat of resin is dry, mix up some more epoxy, again with a 30 minute work time, but do not dilute this batch. Using another flux brush, put a coat of resin over everything, again, being careful of runs.
14. When this is dry (24 - 48 hours) sand the cowl starting with 60/80 grit and work down to 150 grit. Any dips/low spot fill with spot putty (Red stuff in a tube in the automotive section ). after sanding this down, put a thin coat of primer (I use automotive "high build" primer) on the whole thing and sand again to show anything you may have missed. Repeat the above as needed until you are satisfied with the results.
15. Trim any excess fiberglass from the back of the plug. You do not want any fiberglass hanging over the edge to block removal of the plug. If you decided to save the plug (12 coats of wax) put the plug in a bucket of water and CAREFULLY flex the cowl on the plug to allow water to get between the cowl and the plug. You should be able to get the plug to pop free from the fiberglass cowl. If this is a one time deal, take the cowl outside, make an X in the back of the cowl (through the film covering), peel the covering back and pour some gasoline onto the foam. You will only need a couple of ounces for a 60 size cowl. Go have a cup of coffee and come back in 20 - 30 minutes. Peel the film and the "sludge off the inside of the cowl and dispose of properly. Now wash the cowl with soap and water.
16. The cowl is going to be very soft and flexable at this point. Shape the cowl as you need it (primarily to fit the fuselage ) and put it aside for 3 or 4 days to harden up.
17. Now you can trim the cowl to length, cut any holes needed and do a final prep for painting.
This sounds complicated and like it is a lot of work, but it really isn't. The hardest parts of the whole thing is carving/sanding the foam block and waiting for everything to cure/dry.
03-22-2005, 09:32 AM
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RE: How to: Custom cowl?
Hmm very interesting. Thank you for the info and such a detailed description guys!
A couple of questions:
-Is glassing the preferred method, over balsa sheeting? If so, why would that be?
-How do you attach a flush mount cowl it to the plane? Is it a permanent fixturing?
-If it is germinate, how to you work on the engine if the need should arise?
-How do you "cut" the fiberglass? The only experience I've got with glass is with my trainer. The kit called for a piece to be wrapped and glued around the center of the wing. I used an exacto knife and the stuff frayed like crazy.
-To get the dimensions needed for the cowl, I assume you mount the engine to the firewall and derive the info you need that way?
A couple of questions:
-Is glassing the preferred method, over balsa sheeting? If so, why would that be?
-How do you attach a flush mount cowl it to the plane? Is it a permanent fixturing?
-If it is germinate, how to you work on the engine if the need should arise?
-How do you "cut" the fiberglass? The only experience I've got with glass is with my trainer. The kit called for a piece to be wrapped and glued around the center of the wing. I used an exacto knife and the stuff frayed like crazy.
-To get the dimensions needed for the cowl, I assume you mount the engine to the firewall and derive the info you need that way?
03-22-2005, 02:25 PM
#5
RE: How to: Custom cowl?
ORIGINAL: JasonWilliam
Hmm very interesting. Thank you for the info and such a detailed description guys!
A couple of questions:
-Is glassing the preferred method, over balsa sheeting? If so, why would that be?
>A plastic film covering or glassing is used over balsa sheeting. The
>films provide a nice finish, are relatively easy to apply and are a lot
>lighter than paint, but are not resistant to dings and dents.
>
>Glassing a plane is typically done one of 2 ways. You can apply the
>fiberglass cloth (usually 1/2 oz OR 3/4 oz) with either resin or water base
>polyurethane. The resin method is heavier and harder to sand, but is
>about 40% stronger than the poly method. While the poly method has
>only about 60% of the strength of the resin, it is only about 1/2 the
>weight. Both ways provide a very nice surface to paint on and both
>help the plane resist dings and dents.
>
>If you are just glassing the center section of a wing, I suggest staying
>with the resin method of applying the fiberglass and use 2 oz - 4 oz
>fiberglass cloth. It will provide added strength to the joint.
-How do you attach a flush mount cowl it to the plane? Is it a permanent fixturing?
>A flush mount cowl is accomplished by epoxying hardwood blocks to
>the firewall. The cowl slides over the blocks and is screwed into the blocks.
>The outside surface of the cowl is flush/even with the fuselage.
>It is not a permanent fixture, just the blocks which are hidden by the
>cowl. It is a matter of preference (in most cases) on which type you
>use.
-If it is germinate, how to you work on the engine if the need should arise?
>You remove the cowl to get at the engine.
-How do you "cut" the fiberglass? The only experience I've got with glass is with my trainer. The kit called for a piece to be wrapped and glued around the center of the wing. I used an exacto knife and the stuff frayed like crazy.
>To cut fiberglass you need a NEW #ll blade and a piece of glass.
>I suggest using an old mirror or get a piece of "double strength"
>glass. Lay the fiberglass on the piece of glass and use a straight
>edge to guide your cutting. You can also apply a line of thin CA
>to where you need it cut and then cut in the CA area. Some 150
>or 220 grit sandpaper will remove any edges that are left.
>After you have applied fiberglass with resin or poly, I suggest
>using a Dremel with a cut off wheel.
-To get the dimensions needed for the cowl, I assume you mount the engine to the firewall and derive the info you need that way?
>Yep. Mount the engine and find out the distance from the
>firewall to the front of the thrust washer on the engine.
>To this number I suggest adding an additional 3/4" for the
>overall length. Remember, you can trim off the excess,
>but the fiberglass isn't going to stretch. I also like
>to put 3 or 4 2/56 screws near the edge of the firewall.
>Before I start "carving", I press the foam block against
>the firewall so the screw heads indent the foam. It makes
>it easier to insure proper alignment by setting the foam
>block over the screw heads.
Hmm very interesting. Thank you for the info and such a detailed description guys!
A couple of questions:
-Is glassing the preferred method, over balsa sheeting? If so, why would that be?
>A plastic film covering or glassing is used over balsa sheeting. The
>films provide a nice finish, are relatively easy to apply and are a lot
>lighter than paint, but are not resistant to dings and dents.
>
>Glassing a plane is typically done one of 2 ways. You can apply the
>fiberglass cloth (usually 1/2 oz OR 3/4 oz) with either resin or water base
>polyurethane. The resin method is heavier and harder to sand, but is
>about 40% stronger than the poly method. While the poly method has
>only about 60% of the strength of the resin, it is only about 1/2 the
>weight. Both ways provide a very nice surface to paint on and both
>help the plane resist dings and dents.
>
>If you are just glassing the center section of a wing, I suggest staying
>with the resin method of applying the fiberglass and use 2 oz - 4 oz
>fiberglass cloth. It will provide added strength to the joint.
-How do you attach a flush mount cowl it to the plane? Is it a permanent fixturing?
>A flush mount cowl is accomplished by epoxying hardwood blocks to
>the firewall. The cowl slides over the blocks and is screwed into the blocks.
>The outside surface of the cowl is flush/even with the fuselage.
>It is not a permanent fixture, just the blocks which are hidden by the
>cowl. It is a matter of preference (in most cases) on which type you
>use.
-If it is germinate, how to you work on the engine if the need should arise?
>You remove the cowl to get at the engine.
-How do you "cut" the fiberglass? The only experience I've got with glass is with my trainer. The kit called for a piece to be wrapped and glued around the center of the wing. I used an exacto knife and the stuff frayed like crazy.
>To cut fiberglass you need a NEW #ll blade and a piece of glass.
>I suggest using an old mirror or get a piece of "double strength"
>glass. Lay the fiberglass on the piece of glass and use a straight
>edge to guide your cutting. You can also apply a line of thin CA
>to where you need it cut and then cut in the CA area. Some 150
>or 220 grit sandpaper will remove any edges that are left.
>After you have applied fiberglass with resin or poly, I suggest
>using a Dremel with a cut off wheel.
-To get the dimensions needed for the cowl, I assume you mount the engine to the firewall and derive the info you need that way?
>Yep. Mount the engine and find out the distance from the
>firewall to the front of the thrust washer on the engine.
>To this number I suggest adding an additional 3/4" for the
>overall length. Remember, you can trim off the excess,
>but the fiberglass isn't going to stretch.
I also like>to put 3 or 4 2/56 screws near the edge of the firewall.
>Before I start "carving", I press the foam block against
>the firewall so the screw heads indent the foam. It makes
>it easier to insure proper alignment by setting the foam
>block over the screw heads.
Hope this answers your questions.
