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Cowlingfront/spinner clearance

E. D. Eliot

Well Known Member
I'm interested to know what you have found the measurement between the front of the cowl and the rear of the spinner to be. I suppose that this will be self evident when I get there in the cowl assembly but I am just curious. I'll be there tomorrow.

By the way, I am blown away by the fit that is produced by exactly following the instructions for cutting and sanding the edges of the cowl down to the scribe lines in the instructions. Wish that the scribe lines were a little more prominent though.

I believe that the cowl can be trimmed - fit in place and anchored to the piano hinges in the span of about 6 hours. Just amazing. Takes two people to do it easily.

Thanks for answering
 
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Have you hung the engine yet? I had to do a lot more trimming than that suggested by the scribe lines to get a good fit. At one stage I even wondered if the engine was misaligned on the mounts, but it worked out fine in the end. My cowl to spinner clearance is about 3/16", but 1/8" would be OK.
 
I used a long piece of 1/8" thick aluminum bar stock as a spacer taped so it was tight to the prop backing plate and adjusted the fit of the cowls accordingly. Also waited until the engine was hung rather than relying on blind faith that the clearances would be correct. The links below have photos of what I did .... the second link has a photo that shows how the final gap turned out.

http://www.dogaviation.com/2016/05/bottom-cowling-tweaked-for-better-fit.html

http://www.dogaviation.com/2016/05/more-progress-on-rv-12s-cowling.html

Happy building,
 
Thank you

Many thanks to both of you who took the time to answer my question. Yes, we really go 'all in' when we trim the fiberglass to the scribe lines! I have the bottom one half cut and sanded to the scribe lines and the fit to the fuselage is amazingly good, Haven't measured to the back plate yet this morning and your answers are very helpful.

Now, I have to make a guess as to how much of a 'gap' to allow between the fuselage sides and the fiberglass edges - for paint. I'm guessing that 1/16" is about right?

Thanks again - Ed Eliot
 
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If the gap is too small, won't it create a nightmare for installing and removing the cowling without scratching it? I have not got to that part of my construction yet, so I would defer to those who are flying for advice. Certainly a small gap looks great and it is good for drag, but if you end up gouging the paint everytime you remove the cowling it will look awful before long.
 
If the gap is too small, won't it create a nightmare for installing and removing the cowling without scratching it? I have not got to that part of my construction yet, so I would defer to those who are flying for advice. Certainly a small gap looks great and it is good for drag, but if you end up gouging the paint everytime you remove the cowling it will look awful before long.

Can't consider all RV's the same....
On the RV-12, the cowl to spinner gap has no influence in cowl removal / installation difficulty.
 
Is is safe to assume that cutting to the scribe line will not remove too much material. In other words, does a builder typically cut to the scribe lines, then remove additional fiberglass to fine-tune the fit?

Jerre
 
Is is safe to assume that cutting to the scribe line will not remove too much material. In other words, does a builder typically cut to the scribe lines, then remove additional fiberglass to fine-tune the fit?

Jerre

I would NOT cut exactly to the scribe line and I would NOT even consider anything more than a very rough trial fit before you install the engine. For my 12 for the first cuts I was always about 1/4" outside the line first and then trimmed, filed or sanded to fit. I used 1/8" cowling to spinner gap and to center the cowl to the spinner I needed about an extra 3/16" on the left side. If I cut to the line the cowling would have been off center with a 1/4" or so gap. It could just have been my cowl but why risk trashing any parts by cutting too close.
 
I cut and fitted my circa-2012 RV-12 cowl before mounting the engine. By following Van's molded-in trim lines I ended up with a very nicely fitting cowl. My cowl-to-spinner clearance is @ 3/32" with no rubbing. That being said, I think having the engine in place would alleviate some builders' cowl fitting concerns.

As rvbuilder2002 noted, this cowl-spinner clearance is not a significant factor for cowl removal. The significant factors are 1) providing an appropriate shape around the exhaust pipe-cowling exit hole and 2) ensuring that the long thin longitudinal slot along the bottom of the cowling is sufficiently wide to readily clear the nose strut with nose strut fairing installed. With these clearances, the lower cowling can be easily removed by slightly lowering it vertically and then sliding it aft and off.
 
Blake has a nifty tool that is useful for installing the cowling. Rent or buy it here.

The tool mounts to the face of the crankshaft/flywheel on commonly used Lycoming and Continental engines. It has an adjustable disc that simulates the spinner position. The cowling can be clamped, or clecoed, to the disc while you trim, fit, drill it to the airframe, or other cowl half. This allows the cowling to be positioned very accurately and solidly while working on it.

You could even install the cowling before you buy your prop. Of course, you need to know the dimension from the flywheel face to the back of whatever spinner you plan to use. Planning and common sense required!

Anyway, it's a very handy tool that eliminates the need for you to cobble together a homemade tool, or actually work around an expensive prop/spinner.

Obviously, you need to have the engine hung to use this tool! Doh... I hate to have to point that out, but someone will ask!

YMMV, but many of you may find a tool like this very useful and time-saving.
 
Increasing Cowl To Spinner Clearance

After dry fitting my spinner, I appear to only have only about a 1/16 inch of clearance between the spinner bulkhead and cowl. On the other hand I have good clearance for the exhaust pipes and oil lines :).

So I pulled the lower plugs and used cleco clamps to position the spinner on the bulkhead, centering the spinner.

After speaking to the folks at the mother ship, I purposefully "tried" to place the holes in the spinner bulkhead slightly forward of the midline to allow a little sanding of the bulkhead if needed. Most of the holes ended pretty much in the midline and at least none were aft of the midline. I also ordered the S-1210 spacer which moves the entire spinner assembly forward a tiny bit. Hopefully the combination of sanding the spinner bulkhead and installing the S-1210 spacer will give me the magic 1/8 inch clearance.

Jeff
 
My clearance is 5/16" which to me seems just right and nice when comparing to other aircrafts. I aimed for a larger gap than stated in the KAI. I also installed the engine first prior cutting the cowl and never regret it.
Just my 2 cents
 
Need to remove spinner to remove cowling?

F/U... Just a heads up and a ?. When I installed the top cowling this pulled back the lower cowling so that I now have 3/16 inches of clearance from my spinner using the optional S-1210 spacer.

Now for my ?. I do not see how I can set the most medial screw holding the top and bottom sections of the cowling together without removing the spinner. This would seem to imply that I must remove the spinner every time that I wish to remove the cowling. Is this correct?

Jeff
 
No, it is not necessary to remove the spinner to remove the cowl. Something is wrong. Do you have a picture?
 
No, it is not necessary to remove the spinner to remove the cowl. Something is wrong. Do you have a picture?

OK So there are six screws holding the top and bottom of the canopy. I placed the two most medial screws behind the spinner. My bad. Happily this is fiberglass and I can move the nut plates.

Jeff
 
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