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Fitting cowling troubles

A

alpinelakespilot2000

Well Known Member
Like many before, I'm unsure about how to get my upper cowling and lower cowling to fit each other around the spinner.

Vans indicates that the spinner area should be fit so that the spinner opening is circular, then drill holes at point "B" (shown in picture below). However, the front of the already-fitted upper cowl currently overlaps the uncut lower cowl the at the outboard locations (points "C"), preventing the top cowl from sitting down on the bottom cowl at points "A" or "B". This suggests that I'm going to have to first trim down the cowl at points "C". However, how do I how much to trim here until the top and bottom cowls are on the fuselage at the same time? I definitely don't want to do this until I know how much needs be cut off. It seems like a chicken-egg scenario.

Any suggestions on how to proceed would be much appreciated.

 
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cowling

You want to have your spinner handy during this process. Get your 13" spinner out and set it on top of the cowling every now and then during this fitting process. What your are doing here will determine the centricity of the cowling face to the spinner. Put the two halves together like you have in the picture. You should be able to dissect the half line at the two cowling halves buy taking a quick measure from the apex at the top of the cowling and then measuring down to the half point. You can make a half circle also and have a tick mark on the top of the cowling ad tick mark at the top of yout template to reference. The straight bottom of the half circle should transfer over to the sides of the cowling to give you an idea where it needs to be trimmed at. Do the same for the bottom of the cowling as well. Make sure your reference point is at the very top and very bottom of the spinner face and is straight up and down with the cowling. You don't want to look from the front and see that your lines are crooked. I made some cut lines with a sharpie and then carefully trimmed the cowling. I would usually cut on the upper part of the mark and then sand down to the mark. THe bottom cowl-will determine more of the shape since it has the joggle for the nutplates to be installed are the inlet area. Take a little off each time until your spinner is aligned with the circle on the face of the cowling. Don't worry about getting the outter areas of the inlets cut to shape at this point. You will get that done when get the cowling fitted on the plane.
Once the spinner is fitted and the front area is determined to be circular. Mount the prop and spinner assembly to the engine. Make a spacer plate ( I used a piece of plywood 5/16" thick. It taped this to the backiside of the spinner back plate. This will give you your spinner/cowling gap. It will also keep the spinner and cowling lines parallel with each other. Make sure the spacer is smaller than the 13" so your can align the cowling halves to spinner closely. I had a Jerry Harold spinner so your Van's spinner might need a bigger spacer plate if it sets down inside the backing plate. BUT WHATEVER IT IS YOUR WANT YOUR GAP TO BE ABOUT 5/16-3/8 of an inch. Any closer and a pain to get the cowling off. If it's aA-model and there are no gearlegs to interfer with, this gap can be closer.
Once the spinner is mounted and your plywood plate is attached to the backside of the spinner, mount the bottom cowling. Getting it to line up with the back of the spinner is easy and the make it square to the palte. I temp drilled holes into the cowling and into the plywood to hold the front in place. This then determines where the cowling needs to be trimmer to mate up with skins on the firewall flanges. Get the cowling trimmed up and into place so the cowling drops down onto of the paino hinges. I trimmed carefully and used a sanding block to finalize the cut so I got a tight fit. Once the cowling is drilled and clecoed to the hinges you can get the halve line cut for the halves to meet up on the sides. I leveled up the plane and used a laser line that was self levling to project a line onto the cowling where is was going to be trimmed at. It was on a tripod with a up/down screw jack. I got the front of the laser line to line up with the front joggle on the bottom of the cowling at the spinner and where it landed at the back of the cowling at the firewall.
I would then trim this line on both sides. taking care to make it straight. Then get the top cowling and do the same as the bottom was done to get it to line up with spinner. Once the front in determined, trim the back to drop it into place and drill and cleco it down. When you get to the halve you trim the top to fit the bottom cowling. I started at the back the then worked my up to the inlet. You may have to do a little more sanding to get the inlet lines together and some of the inlets don't line up. I have to build up one side of mide because it was off about 1/4". Just do whatever it takes with sanding and fiberglass floc to make it all line up and fit. Once this is done, I then dtilled the hinges for the sides making sure the cowling was sucked together very well so when you installed the hinges the don't seperate too much. THE COWLING IS A BASH TO FIT, PAINT TO MATCH AFFAIR. It took me about a month to get it all right.
 
alpinelakespilot2000 said:
Like many before, I'm unsure about how to get my upper cowling and lower cowling to fit each other around the spinner.

Vans indicates that the spinner area should be fit so that the spinner opening is circular, then drill holes at point "B" (shown in picture below). However, the front of the already-fitted upper cowl currently overlaps the uncut lower cowl the at the outboard locations (points "C"), preventing the top cowl from sitting down on the bottom cowl at points "A" or "B". This suggests that I'm going to have to first trim down the cowl at points "C". However, how do I how much to trim here until the top and bottom cowls are on the fuselage at the same time? I definitely don't want to do this until I know how much needs be cut off. It seems like a chicken-egg scenario.

Any suggestions on how to proceed would be much appreciated.

Click to expand...

You will want to fit the cowling to the fuse and straight line the top half first. Then fit the bottom half. You will deal with the front end and spinner are last. Milled fibers will be your friend at this point. There will be some cutting and grinding... and some trimming up front too. Just take it slow. Don't be to concerned about the fuse fit to be perfect in the beginning. Adding a few lay ups for final fit is easy to do. Lots of sanding will now really come into play. A paint stick gap at the spinner works very well, just tape one on top and bottom to start with. And... have fun!
 
LifeofReiley said:
You will want to fit the cowling to the fuse and straight line the top half first.
Click to expand...
Thanks for the help guys. Yes, I did this already and it fits fantastically. I was pleased with how it came out. It's been fitting the two halves together that have been most challenging because I don't want to trim too much off those outside front corners to make the spinner area fit until I know what the top-bottom side seams are going to look like at the front. I'm paranoid about having the side seems fit great back near the firewall only to find out that I had trimmed too much from the front corners side seams in an attempt to get the spinner area to fit. Sounds just like I need to take it slow and do what it takes to make it fit.
 
trim the front first, around the spinner

You want to get the spinner diameter area fitted FIRST. This will determine where your sides with end up. Frankly, I've seen too many cowling with the cowling sticking up 1/2 over the top over spinner because they fit the sides first and it set the spinner diameter forever. Set your spinner first and then get the sides to fit. Do the bottom cowling after this and then fit the top to that. It's too hard to try and fit the bottom to the top since it a lot bigger and has more area around the firewall to fit too.
 
Aden Rich said:
You want to get the spinner diameter area fitted FIRST. This will determine where your sides with end up. Frankly, I've seen too many cowling with the cowling sticking up 1/2 over the top over spinner because they fit the sides first and it set the spinner diameter forever. Set your spinner first and then get the sides to fit. Do the bottom cowling after this and then fit the top to that. It's too hard to try and fit the bottom to the top since it a lot bigger and has more area around the firewall to fit too.
Click to expand...
Thanks Aden. You're method sounds like a good way to do it. The only problem is that I've basically followed Van's advice and fitted the top half first. I've got it to fit great around the spinner (both fore-aft and have allowed for future sag). I've also got it drilled to the fuse, so the top is pretty much locked in place. I'll have to fit the bottom to what remains.
 
alpinelakespilot2000 said:
Thanks for the help guys. Yes, I did this already and it fits fantastically. I was pleased with how it came out. It's been fitting the two halves together that have been most challenging because I don't want to trim too much off those outside front corners to make the spinner area fit until I know what the top-bottom side seams are going to look like at the front. I'm paranoid about having the side seems fit great back near the firewall only to find out that I had trimmed too much from the front corners side seams in an attempt to get the spinner area to fit. Sounds just like I need to take it slow and do what it takes to make it fit.
Click to expand...

Looks like you're on the right track. You can tape on tongue depressors off the top of the spinner to set that angle, just have the paint sticks between the top half and the spinner backing plate too. You will add material to the front bottom at the spinner guaranteed.
 
Also, if you elect to use the hinge pin method for the top and bottom halves, I recommend a combination P3 and P4 hinge. This will allow you to hide the hinge part.
 
LifeofReiley said:
Also, if you elect to use the hinge pin method for the top and bottom halves, I recommend a combination P3 and P4 hinge. This will allow you to hide the hinge part.
Click to expand...
I'm using hinge only on the lower cowl at the firewall sides. The entire top cowl uses milspec camlocs and the bottom will either use camolocs or, just as likely, #8 screws and tinnermans, as I've seen lots of posts indicating the hinge eyes breaking off when used on the bottom. Thanks again for the help.
 
Don't let it sag

alpinelakespilot2000 said:
Thanks Aden. You're method sounds like a good way to do it. The only problem is that I've basically followed Van's advice and fitted the top half first. I've got it to fit great around the spinner (both fore-aft and have allowed for future sag). I've also got it drilled to the fuse, so the top is pretty much locked in place. I'll have to fit the bottom to what remains.
Click to expand...

When your engine isolators start to sag, shim them back up to original position. When you first started, your crankshaft flange should be perpendicular to the the datum plane of the fuselage. I had to shim mine up into place and only had to add one small shim on the bottom of the mounts once it was broke in. This gives you a square thrust line.
 
Aden Rich said:
When your engine isolators start to sag, shim them back up to original position. When you first started, your crankshaft flange should be perpendicular to the the datum plane of the fuselage. I had to shim mine up into place and only had to add one small shim on the bottom of the mounts once it was broke in. This gives you a square thrust line.
Click to expand...
Hi Aden-
You're not the first person I've ever heard suggest that one should not adjust for future sag, but Van's clearly indicates you should do so, as do most of the posts I've found in the archives. I'd be interested in hearing more discussion about this,but I think it depends on the quality of the mounts, whether they are dynafocal or conical, as well as how long the engine has been on the airframe before working on the cowl.

Now, that said, I thought I had planned for more sag than I ended up with when I finally got both halves together. It's probably going to end up pretty close to centered around the spinner. In the future, I may have to end up adding an additional washer to the lower engine mounts as you suggest. I have seen that suggested before as one way to solve the problem.

As a follow up to my earlier posts, I finally went ahead and hacked away at the outboard portion of the inlets and it is finally starting to fit pretty good. You just have to take it slow. It's also very helpful to get both halves of the cowling up on the plane as soon as possible so that you can get a good idea of about how much will have to come off. I still have a little bit of an "overbite" on the outboard portions, but have almost none around the summer. I THINK this means that I'll have to add some fiberglass to the lower cowl at those locations, but we'll see.

Thanks again to all for the (on-going) help.
 
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Steve,

No Sag unless you're conical... You will be adding milled fibers to the bottom cowl at the spinner location and will also be cutting off some of the inside of the inlets too.
 
LifeofReiley said:
Steve,

No Sag unless you're conical... You will be adding milled fibers to the bottom cowl at the spinner location and will also be cutting off some of the inside of the inlets too.
Click to expand...
Darrell-I've got Lord dynafocal mounts, so I'm not anticipating much, if any sag.

Just by chance, is this where you think I might have to add some milled fibers to the bottom cowl? I've pretty much got a round spinner opening, but still seem to have some excess flange showing. I can raise the bottom cowl up a little, maybe, but not much unless I want an oval opening.

 
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Steve,

Yes, you will need a little there but... you must have taken a load of material out of the back side of the cowl spinner face to get the fit you have now. I was speaking more about building up the spinner face on the bottom cowl half. How thin did you go?
 
LifeofReiley said:
Steve,

Yes, you will need a little there but... you must have taken a load of material out of the back side of the cowl spinner face to get the fit you have now. I was speaking more about building up the spinner face on the bottom cowl half. How thin did you go?
Click to expand...
Actually all I did was take off some big blobs of flox or epoxy on both the front of the bottom cowl flange and the aft part of the top cowl spinner ring. The spinner face and lower cowl flange are still about as thick as the rest of the cowl. I don't think I'll need to build up the inside (or aft side) of the bottom cowl face or flange but I'll watch as I fit it further. Also, the picture makes it look like the top and bottom fit closer (fore and aft ) than they really do. Whatever the case, based on the randomness of those "blobs" that I had sand off, I suspect everyone's canopy is slightly different in terms of out it comes from Van's.
 
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alpinelakespilot2000 said:
Actually all I did was take off some big blobs of flox or epoxy on both the front of the bottom cowl flange and the aft part of the top cowl spinner ring. The spinner face and lower cowl flange are still about as thick as the rest of the cowl. I don't think I'll need to build up the inside (or aft side) of the bottom cowl face or flange but I'll watch as I fit it further. Also, the picture makes it look like the top and bottom fit closer (fore and aft ) than they really do. Whatever the case, based on the randomness of those "blobs" that I had sand off, I suspect everyone's canopy is slightly different in terms of out it comes from Van's.
Click to expand...

It's looking Great!! Onward thru the Fog... :D
 
Garland Edwards said:
Darrell, Can you describe how you use the P3 and P4 hinges in combination?

Thanks,
Garland.
RV7 ( in the works)
Click to expand...

Hi Garland,

Okay... the idea is to hide the hinge part of the piano hinge and also provide a surface for paint to adhere to for a more seamless cowl look and finish. If you use the P3 that Van's supplies you the hinge ends up in the middle of the cowl halves as the top and bottom come together. If you will remove one half of the hinge and swap it for a P4 (wider mounting area) you can offset the hinge part to be hidden. Now you have a flat surface for paint and a cleaner look for sure. One other thing this does for you... It keeps the hinge cleaner and the pins seem to slide much easier. Here someone will buy a P4 and share half with another builder and split the cost of the hinge. Or, Team Rocket sells the hinge set-up and ready to go.
 
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