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about to make first cowling cut - seems extreme?

IowaRV9Dreamer

Well Known Member
I'm finally going to start work on this cowl from 2010. The first step is apparently to get the front and back to mate and form a 13" circle. The manual provides some high level guidance - basically trim it till it works.

This is how it looks to start (left side):
TMmkTLaI3I4wSZA3dX0pfG9V7knINkP4C9AMBd-Mcwm03_3RCjgg7YX60dEessPu_GJIJP6ysR22fYgn1ifyDTTyWLDO0OH441aCLzQCCf0AMh3VDs4mbm0CrvMnZqGufKeHwUIIGyv5rWfX0mIXRAX-Eaw4JnaALN4y0e3MxYS-nToRAXtWz6ZYkg9b1sEGS2N19MFIulw-_RvHjuEvpWtqgxQ42krVTwigcSCEvCRjwXW9b4LLnF3DqMD78oZG3_bzUeTyJw2ouK07btjAED7tqhi8WcJO5X3L3xc6Cvlo9oZ1T6IrmI8hLHyY_8SMJGOrm8gFnLxeyh_MebtYpqXgQFeVkUO8gbCxtaS84nIw2tTetu37yukpHxevlpnLEwR-3FgNOHOObaRBo8Z4DSV0ufHA9FDTt1ErKXXKL3v1ySJIwFjG7AR9738k4CzAusa8Uc1KmHrwy0184iWUOC7TmgoyS1B4ezvO_zfi6W-Xv9nsyA26XohCYxkJtUOCoYE-SSrnHjygHuLXKFvh5CvbSV5Cuz-xzP-LRdq3n-xlKFb6bqOJtVVc2djVF4HRBi3tXzq3nG75Phdlle5_l0L0k0f6TwF4Cqf98i1wLLt8IJGHDV4dmaM3S3ur3FN7zJPuoVIoszIWbPsTZofIjeJC6pnMQCwy=w600-no


The right side is similar, but the outboard edges are reversed:
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I put a straightedge across the lower cowl molded lip (on the inboard sections, where the upper cowl is supposed to sit) and you can see that there is a lot of extra material above line where top and bottom cowl should meet.
7uD_u98AsCeRkzNBJpwGWi6VdsZ3gTf2w57nb4AmP7mUnK9LAsbtkC9Tk0vcfeuxcKdOlCoP7tGHippKfKZYuG8xZP3tnzjtnKPSt--JolvaBs0xGjIDDpSTEoaPT35TDgOBwB_GDVMOFEos5iuE8UcDl0zpTEfjPNP3sPFVESNOyjRSy-lqNK3Ad6PpzxL2l2RG5pNjPsUAkTdI8DwU7I13gf8B17wWcgrsf1z3eS05ICJmnhlzHcUan1mNkdUSkahc0gChXw0PRVj0dB89_44nbywwbLZx6KSNifRdXI45qgLvksdiDtA2xhsuXLacJhynoTszGNLO-zCp5NarCbaeuCkrAu8Q8ivECe3WvJt4Jiin2MGV6jQze-TLqB264CjEgkB58Iqbf3IIc0xcNRZNGMswXjHYH8yblEWUPc2MeaNcWlWszj07XktL4UJMFUI1KrrPiDRAPuedWcLx5kM5RupSi_Um_0XDSoxHzwgzhFiRxOE6RzJwyTZTBB9owxmvF6aAZXieU0R2iLCZc25xu6E5MV0u3GZULRFXUh01eszG8q2LdZi-siTjLrwqYHheEpw1PmrZ-lbsONeoEUb5PNqOhe5IcDXQS3jHxLsrGnXHSUiyyE8j7RE9GfTHNxuXJUO3joWR7IC6CyLPpdJlADSIWaMQ=w600-no


So I have to cut this much off the bottom cowl, on both the outboard fronts and sides? It seems like a lot, but I think that is why the cowl won't nest together in the front.
7wQIOsu8OezG8XUuFHkgIl9ceWjeXsNc_jEn-huuHyinhs_8z_DQUK8h5eYr3VBeM0rHYLB5DEicOhsJhNOxw6wT0ijT2_oZZPkjvZ-5BNzwQOoKOLKmWRzHhNU0cShbDFtlv1nfl7oWOv0MZJ2z-IEucbpDI_Cihp2MvkSc5icyt91F7kU3x4qFM3b11VMHUTbX7tBKHYhaM0EgdbuyevYG4iAqtzRJ1nHp1gSTKZvOtbwzuWT40ljLh3-WZC6FbDG-m9M_y8KiIt0U2qkHNLNXrrpQTX34Sb09QALr2IyoYYF2w2Xu_cOMQGzZjlMYNdw3uExlHVCESUYUg4Rf6PuiC2RjKz7_vRTNCogZbaMSoHip3eGrYZzFSOIH-Wz6AuVdxInX1OM5mYedDvCRArmo3iR5N4ZxDLjpl2vS8dnou4ASy6YtAKZq-kk9N-h1z8QTSoxU-y8yXfBeLsfdPuaIBKq2T1JwR4muWldi-CtQUO1OTmiZWUtRaoRR_PykVEgLuGCCTypGZUvAOUq4K78LZzwowQEqS-O5cXxyUElYNTNndbUUlET4g_n6D1JbYgcWvILST0uW2tLyCQE-ncbLdvMbrP2IS9Dnnm8m28RmJxyI6dfpa7fUTzcmtM_agLjZjJP-I0jzp0z9Shf_zubIEddm9bb2=w600-no


Am I even close to the right path?
 
That's about how much I had to trim, Dave. But follow Dan Horton's advice. He's the man. Trim the top cowl first, and then the bottom cowl to match. I trimmed mine about that much, but went just a bit too far. I had to fill the gap later. If I were doing it again, do it a bit at a time. Cut half that amount, then check. Then half the amount again, and so on. You'll get it.
 
That's about how much I had to trim, Dave. But follow Dan Horton's advice. He's the man. Trim the top cowl first, and then the bottom cowl to match. I trimmed mine about that much, but went just a bit too far. I had to fill the gap later. If I were doing it again, do it a bit at a time. Cut half that amount, then check. Then half the amount again, and so on. You'll get it.

Great advice. I’m currently fixing my cowl that a P.O. trimmed too far. Much easier to sand a little at a time than having to build up an edge.
 
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Look on 3rd page

Look on the third page of this fiberglass area. Near the bottom, look for my post Cowl tool. I fit the bottom first, and trim a little off again and again till the top lays down to fit
 
Thanks to all of you for your help. It is funny how I get stuck so badly on simple things.

After a small amount of trimming of the bottom cowl at the outboard corners, and about 3 hours of sanding / filing / dremeling, I have a top and bottom cowl that actually mate together:
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It is a better fit than it looks in the picture; when I clamp it together and drill it I'm sure it will be OK for now. I think it will get bettter when the sides are trimmed to allow them to touch rather than nest. At least the spinner base is round.

I was surprised to see that the right inlet is about an inch "deeper" than the left one, especially since the right cylinder is closer to the front of the engine. I'm sure it will all work out.
 
I was surprised to see that the right inlet is about an inch "deeper" than the left one, especially since the right cylinder is closer to the front of the engine. I'm sure it will all work out.

The depth of the inlets, as delivered, is no indication of finished depth. It's just excess glass, like the overlaps you've trimmed. The reality is that you want them short, as that moves the upper inlet ramp forward, and flattens the lower ramp:

Inlet%20Flange%20Trim.JPG


Inlet%20Pinch.JPG


I've updated the photos in the referenced thread.
 
Thanks Dan. I was trying to lay out the screw pattern on the inner side of the inlets and noticed the difference. Your pics really help, they way you draw them is very intuitive. Its probably not accurate but it seems intuitive to provide more "room" for the incoming high speed air to slow down / increase pressure.

And, HUGE thanks to you for updating the photos in the thread. I had seem them years ago but when they disappeared I was having trouble following the discussion. Thanks SO much!
 
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Perhaps you could expand on why you think it's "probably not accurate".
LOL Sorry Dan. This is a great example of why I'm a better engineer than writer. I was referring to the inaccuracy of my understanding of fluid dynamics, not any inaccuracy in your drawings or explanations.

I have no idea if a larger volume inside the cowl is better to slow down the incoming air... but it feels right to this EE. I imagine the shape of the transitions really matter too, especially the upper one which would probably create a lot of turbulence without those extra pieces.

I should have been more clear.
 
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