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Cowl Trimming Question

Mark Dickens

Mark Dickens

Well Known Member
Patron
On page 45-05, you are instructed to "Trim the top cowl and bottom cowl to the scribe lines around the air inlets and spinner cutout as shown.".

My first question concerns the scribe lines referenced by step 7. The scribe line for the outer air intake (see photo below) is about 5/8-3/4" down, but the drawing seems to indicate a much smaller trim area. So, am I to trim that area down all the way to the scribe line? I know that seems a stupid question, but the drawing indicates a much smaller area. Making a mistake here would be very very bad.

IMG_2396.png

My second question involves the trimming the left air intake (drawing inconveniently left out by Vans). The scribe line accommodates the air intake for the engine and so the scribe lines are different from the right side of the cowl. Before I cut all that out, I just wanted to check that that is intended for removal at this point in the instructions. See below

IMG_2397.png
 
Ah, I had the EXP119 bottom cowl, so could comment on that one, but there could be some mold differences. And I did go just before the scribe line, so basically sanded to it as I got through test fitting.

From my builder log for section 45-05
"I trimmed the oil door and nose gear scribe lines.
I then placed both top and bottom to check on the horizontal scribe lines, looks ok and the MT spinner is basically the same diameter, so I'm proceeding with cutting step 5.
For step 3, I've done the top cowl to the scribe lines, but the bottom cowl, I've done the spinner area to the scribe lines, but nothing more. Want to see more fitting before I do more cutting in that area."

eaabuilderslog.org

EAABuildersLog.org - Free aircraft builders log website.

EAABuildersLog.org is a airplane builders log website to store your projects on the web for free. The EAA (Experimental Aircraft Association, Inc.) provides this website for it's members for free..
eaabuilderslog.org eaabuilderslog.org
 
I wouldn't trust the scribe lines at all. Based on most of the fiberglass in my kit, I found the scribe lines to be more of a hindrance than a benefit. I learned on the very first piece that using the scribe line will cost you time and possibly a replacement part. That proved to be the case on the majority of the fiberglass parts.

I'm not sure why they even bother with scribe lines. That being said, trimming to the scribe lines will teach you to scarf properly!
 
Reflex said:
I wouldn't trust the scribe lines at all. Based on most of the fiberglass in my kit, I found the scribe lines to be more of a hindrance than a benefit. I learned on the very first piece that using the scribe line will cost you time and possibly a replacement part. That proved to be the case on the majority of the fiberglass parts.

I'm not sure why they even bother with scribe lines. That being said, trimming to the scribe lines will teach you to scarf properly!
Click to expand...
Yeah, I'll trim it but not as aggressively as the trim lines would indicate.
 
lipper03 said:
Ah, I had the EXP119 bottom cowl, so could comment on that one, but there could be some mold differences. And I did go just before the scribe line, so basically sanded to it as I got through test fitting.

From my builder log for section 45-05
"I trimmed the oil door and nose gear scribe lines.
I then placed both top and bottom to check on the horizontal scribe lines, looks ok and the MT spinner is basically the same diameter, so I'm proceeding with cutting step 5.
For step 3, I've done the top cowl to the scribe lines, but the bottom cowl, I've done the spinner area to the scribe lines, but nothing more. Want to see more fitting before I do more cutting in that area."

eaabuilderslog.org

EAABuildersLog.org - Free aircraft builders log website.

EAABuildersLog.org is a airplane builders log website to store your projects on the web for free. The EAA (Experimental Aircraft Association, Inc.) provides this website for it's members for free..
eaabuilderslog.org eaabuilderslog.org
Click to expand...
OK, so can you comment on the EXP-119 for those of us at that step? I’m about to start cutting.
 
lipper03 said:
What else are you interested in? Happy to help.
Click to expand...
I don’t know, you said you could comment on the EXP-119. What would you tell someone cutting the cowls for a -119? Should I follow all the scribe lines closely? Is there anywhere I should keep the lines intact? Places to go beyond the lines?
 
stigaro said:
I don’t know, you said you could comment on the EXP-119. What would you tell someone cutting the cowls for a -119? Should I follow all the scribe lines closely? Is there anywhere I should keep the lines intact? Places to go beyond the lines?
Click to expand...
Did you even read my post or check out my log? I wrote what I did and I have lots of pictures, so the attitude needs to get checked sir. Folks here are happy to help, including me, but the tone of your message is not coming across well.
 
lipper03 said:
Did you even read my post or check out my log? I wrote what I did and I have lots of pictures, so the attitude needs to get checked sir. Folks here are happy to help, including me, but the tone of your message is not coming across well.
Click to expand...
Yeah, not sure what to ask and I apologize if it sounded flippant. Thought you had some general advice to give as you suggested such. Did not check out your log, but will do so.
 
My general advice is to double check your fit, and then trim when you have confidence.

My experience is that the scribe lines are close, but I was careful and took my time checking overlap and left an out. The first cut to a scribe line for me was only the top cowl, and only the front and bottom, rear was to a different mark I made, but in the end it looks like I could have used the scribe line there too, but it was close, so do some test fits.

I had both top and bottom on and off many many times. Yes that was a pain, and yes I did cut too much on the right rear vertical of the lower cowl and did have to fiberglass that edge ( my marking tool I made to feel an underneath edge and allow a marker on top must have caught a wrong edge, so cut off too much). So another general advise is that you can’t really do something you can’t fix.
 
Mark Dickens said:
On page 45-05, you are instructed to "Trim the top cowl and bottom cowl to the scribe lines around the air inlets and spinner cutout as shown.".

My first question concerns the scribe lines referenced by step 7. The scribe line for the outer air intake (see photo below) is about 5/8-3/4" down, but the drawing seems to indicate a much smaller trim area. So, am I to trim that area down all the way to the scribe line? I know that seems a stupid question, but the drawing indicates a much smaller area. Making a mistake here would be very very bad.

View attachment 120649

My second question involves the trimming the left air intake (drawing inconveniently left out by Vans). The scribe line accommodates the air intake for the engine and so the scribe lines are different from the right side of the cowl. Before I cut all that out, I just wanted to check that that is intended for removal at this point in the instructions. See below

View attachment 120648
Click to expand...

Mark Dickens said:
On page 45-05, you are instructed to "Trim the top cowl and bottom cowl to the scribe lines around the air inlets and spinner cutout as shown.".

My first question concerns the scribe lines referenced by step 7. The scribe line for the outer air intake (see photo below) is about 5/8-3/4" down, but the drawing seems to indicate a much smaller trim area. So, am I to trim that area down all the way to the scribe line? I know that seems a stupid question, but the drawing indicates a much smaller area. Making a mistake here would be very very bad.

View attachment 120649

My second question involves the trimming the left air intake (drawing inconveniently left out by Vans). The scribe line accommodates the air intake for the engine and so the scribe lines are different from the right side of the cowl. Before I cut all that out, I just wanted to check that that is intended for removal at this point in the instructions. See below

View attachment 120648
Click to expand...
Not a 14 builder but have 6, 7 and 8 epoxy cowl experience. They all seem to have the same fitment issues. The greatest advice I would pass on is not to get too happy with the die grinder, it takes a tremendous amount of time to get the two halves to fit just right. The one area that is and should be the focal point is the interface of the flanges behind the spinner bulkhead. I don't trim anything along the sides until I can get the front cowl halves to NEST together correctly. Obviously this is easier said than done. When done correctly the spinner and bulkhead will match that of the cowl, the outer inlet cheeks will mate together perfectly and the side skins just overlap until everything is fitted to the aircraft. The reference line I use for the very first cuts is a horizontal line off the molded flanges on the bottom cowl as you have in the photo. Establish the lines on the lower cowl that you trust, make them perfect, then leave them alone! Just trim the upper to match the lower , Don't chase both upper and lower at the same time. Make yourself various sanding blocks to get a true mating surface. Taking your time here will pay huge dividends!

I didn't mean to oversimplify a very difficult process. Until you can get the forward cowl halves to literally FALL together, don't even bother with the sides. You shouldn't have to force anything together. Hope this helps. Happy Sanding! Ray
 
I completed trimming the cowl this morning and even though I left an extra 16th above the scribe line, I ended up taking it off to get the top and bottom cowl to fit properly, so it looks like (at least in my case), the scribe lines were accurate. A lot of sand, fit, sand, fit, sand, fit, etc.
 
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