Model IV Smooth Cowling Help

[Hoenshell]

I've had a lot of problems with the top smooth cowling to my model IV and was hoping I could find a direction to go before I pull engine and start building the firewall. My top cowling did not fit properly to the bottom cowling and I had to cut the top forward with a slit to move the area behind the prop flange back for clearance. While fitting the cowling I noticed that I have to bow in the top cowling to meet the bottom cowling. Now that I have clecoed the top to the bottom it causes the passenger side area around the front door post to bow out quite a ways, over an inch. It also takes quite a bit of pressure for me to hold it in. I have had two ideas on how to fix this issues, I would be most appreciative to hear yours?

This shows the gap on the pilots side...
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Here is the pilot's side that is pretty good...
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My best thought is to again, cut the cowling and try to get it to relax into properly place and then fiberglass the cut back together in a slightly new location causing the gap to close. For example, cutting along this line or somewhere in this general area. I haven't give enough thought of exactly where this should be cut yet.
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I have another idea that I don't like too much and that would be to weld some tabs that will hold that gap closed under pressure that the cowling could slip underneath. What do you think? Thanks for the help in advance.

[HighWing]

As I remember, the early round cowls did somewhat the same. But on both sides a little less dramatic. Having experienced a Lancair IV build, I tried some techniques I learned there - the Piano hinge joint between top and bottom cowls. To correct the point in discussion, I made two attachments that were Hysoled around the forward door posts and when inserting the pin into the piano hinge it first goes through the hole in the attachment to secure it firmly to the door post22888.2288922890

[Hoenshell]

Not sure that I want to change directions and go with the piano hinge; although, it might be the best idea. Anyone have any other thoughts, experience or ideas on how to fix this problem? What issues will this cause when trying to close the door?

[rawheels]

Shawn (or anyone else with insight),

I'm to the point in my install where I'm fitting the smooth cowl on my IV, and having the same issues you describe. Got any pointers?

Here are the items I notice so far:
* Looks like I'm going to have to trim off 5"+ from the back end. Sound about right? That puts the prop flange in the right spot, but just seems odd to have to trim off that much and it would cut through where the scribe line for a NACA vent is indicated on the cowl.
* The top cowl doesn't fit onto the bottom cowl at the front around the inlets. Seems like the material is too thick. Did you end up sanding down the thickness or something?
* Going to need to trim off at least an inch off the bottom of the top cowl in order for the prop opening to be circular. It would be cutting off the bottom of the cowl where the finish seems rough. Maybe that is supposed to be a guideline for cutting. Did you have a similar fit?
* It takes a lot of pressure to bend the top cowl down the sides. I think this is what you are describing above, so I'm assuming this is your experience too, right?
* Instructions say to use camlocks p/n 92000/92005/92015, but my kit came with p/n 98010/98011. I assume they are interchangeable, but instructions say to use qty 28 and only 27 come with the kit. How did you work with that?
* Similar issue at the prop opening. Figure D-1, pg 21 shows 3x 91204 nutplates (and assoc hardware) being used, but only 2 sets came as part of the kit.


Appreciate all the help form those who have gone before.

Ryan

[GWright6970]

Ryan,
I am of the opinion that something happened to the mold that the factory uses to make the smooth cowl for Model IV'S.
"Mr bill" here on the forum installed one it appears, with few issues. The rest of us had nothing but problems.

The fit between the top half and the bottom half is frustrating and not correct. Yes, the top cowling half literally "pulls" the front of the bottom cowl aft, requiring far more FORCE than appropriate.

The top cowling has an "overbite" on the front corners where it mates with the bottom cowling half. Some builders have added to the corners of the bottom half Bondo or Fiberfill to make them mate on the same plain.

Mr Bill said he removed his fuel pump from his 912Ul, mated the two cowling halves and slide it aft over the engine, and centered it behind the engine prop flange. He had no issues. I did this, and found that the cowling nose was at an unacceptable angle. In order to correct this, I cut out a wedge of fiberglass in the top cowling behind the prop so that the face would be parallel to the prop face. The description and photograph are here:

https://teamkitfox.com/Forums/threads/5383-Smooth-cowl-Rotax-912-IV-1200-fit-HELP!

I hope this helps. I will try to add more when I can get to my computer. Doing this on my phone is a challenge!

[rawheels]

Thanks Grover, I appreciate the link. It is helpful to know that I'm not the only one with the issue. I've only made 4 cuts, but I instantly think they were wrong...guess we'll see. Keep those tips and hints coming.

On a related note; I decided to install the oil cooler before I made any "major" cuts to make sure it would align with the opening in the cowl. The front of the cowl hits the mounting brackets and they prevent it from moving back into place. The cowl ends up sitting about about an inch in front of the prop flange. Did you run into this too?

1st pic is dark, but in the top-right corner you can see that with the cooler hitting the cowl the prop flange is inside the cowl.

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2nd pic show the oil cooler install. Brackets do not allow for adjustment.
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3rd pic shows the rub mark from either the cooler or the mounting bracket on the inside of the cowl.
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[Hoenshell]

Ryan;

I sent you over to my Facebook page that has a bunch more pictures, but your experience sounds about like mine. I ignored the NACA vent indicated on the cowl and I had to cut right through it I believe. The top corners needed some thinning of material and it still doesn't fit right. I heard a suggestion to pack the back side of the corner with glass and micro and then sand the front to make flush. I did not cut off an inch to the bottom of the top cowling. My prop flange opening is not perfectly circular yet, but I think that can be easily fixed. Yes, the natural way the top cowling lays is a problem and causes fitting problems. I can't wait to get this piece finished. I'm not using my camlocs and may have some available. Not sure what my kit came with or is calling for.

Shawn

[jmodguy]

Ryan
I see what you are up against. I can stop by this weekend and take a look. Does yours bow out on the right like the other pic?

[GWright6970]

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Ryan, DO NOT CUT the bottom inch off the top cowling. That will not do! Please don't! No one has had to do that. My top and bottom prop openings were also screwed, out of round. I addressed that last. Please see the photo above. You are correct, the oil cooler and it's mounting not only hit the back of that oil cooler scoop, they penetrate it it by a few inches as seen in this photo.

BACKGROUND
At the very start of realizing that this cowling was a serious problem, I made an "artificial baseline point" being an invisible vertical plane behind the engine's prop flange. With the fuel pump removed from my 912UL, I centered the mated cowlings and found that the oil cooler hit the cowling, the top cowling half was well into the propeller. To fix this two major things were done.
1) I cut out a wedge in the top cowling behind the leading edge, and re-fiber glassed it closed. 2) I removed the oil cooler scoop completely and enlarged the opening enough to let the oil cooler and the mount extend forward out of the cowl as depicted in the photo. I never intended to leave it like this and at some point knew I would place a better air entry into the oil cooler. I was unable to find a suitable pre-made fiberglass scoop on the internet, so I made my own. This is for another thread, if anyone wants to see details.
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23316This is how I cut the top cowling to pull back the nose out of the propeller's arc. (I obviously fiberglassed from the underside for structural integrity, and to keep it nice and smooth on top.)
23317Glassed in.

Please note: The new Rotax 912UL fuel pump is quite a bit larger than it's predecessors. The fuel pump opening is larger than is seen in these photos. I am placing a fastener through the face, instead of the side of the cowling in front of the fuel pump, to connect the top and bottom cowling.

After you correct the top cowlings nose, adjust the cowling for the oil cooler, and set your camlocks that anchor it all to the fuselage and the two halves together, etc., you can mate the two halves together on the engine, and then inscribe/cut a more centered opening on the cowling halves behind the prop.

I hope this helps.

[rawheels]

Oil cooler hole has been cut. Obviously will need to open it up, but these are the minimum cuts to allow the bottom cowl to fit in place. Top cowl actually fits pretty nice (without the windshield). I know the instructions indicate that you should have 5/8" clearance between the prop flange and the cowl all around the opening, but I may just leave the bad angle on the top cowl alone. I'll still have a good amount of clearance to the prop. Will definitely be making a custom glare shield at some point as the curve of the windshield will need to be very different to fit the new cowl.

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[jmodguy]

You might want to set the windshield before you cut the aft edge of the cowl.

[rawheels]

Installed the camlocks on the lower cowl. The forward most fasteners on both sides are on the raised portion of the cowling and will cave in the fiberglass when tightened. Will probably have to build up some filler behind it to make up the void, but otherwise it seemed to go on just fine. Only took me about 100 times of fitting the cowl on and off before I got brave enough to drill the first few holes!
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*Oh, and I did reinstall the windshield without the glare shield and I think it will work fine. I'll just need to make to new glare shield to fit the new curve profile.

[bbs428]

Wow! that's really starting to take shape nicely.
Seems a lot of airplane building is removing and re-installing the components multiple, multiple times.
I know that pain well enough. Here's to the end result being worth it! :D

[rawheels]

I found this kind of interesting. The black line was drawn on the part when I received it. Matches pretty closely to the one I removed from the original 582 installation. The brown line is from the template I made for the smooth cowl. Mine will be a little shorter than others (because I cut the bottom off of the top cowl), but interesting to see how much lower the smooth cowl sits on the frame vs the previous round cowl.

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[rawheels]

Started on the form for the oil cooler inlet and cut the wedge for the top cowl. Need to order my fiberglass supplies next...

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[avidflyer]

I went through this same thing about 2 months ago, fitting a smooth cowl to my Kitfox 4 rebuild. I built my panel and cowl to be as low as possible, and so the cowl lip didn't match the windshield, but I fiberglassed the cowl to the windshield and now have a perfect fit. Redid the oil cooler opening as well. Time consuming, but I'm pretty happy with the result. Been struggling with the getting the engine to run smooth, otherwise it would be flying by now. JImChuk

[Hoenshell]

Did everyone putting on a smooth cowling on a Model IV trim the firewall prior to installing the windshield? I'm curious if the windshield causes and flexing in the cowling that would change the firewall shape?

[Av8r3400]

That looks really nice, Jim!!

[rawheels]

Yes, I finished the firewall and cowl before installing the windshield, I didn't notice the windshield changing the cowl at all. However, the cowl does form the shape of the windshield until the glare shield is in place. Even with leaving the paper on, I got scratches in the windshield from pressing the center of it back to get the top cowl in place (over and over). If I would do it again, I'd try to create the glare shield based on the cowl shape before installing the windshield.

BTW, I got mine in the air for the first time last weekend. Need to take some pitch out of the prop, but otherwise it went great.

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[Iowa 67]

Looks great! I like the looks of the smooth cowl, thought maybe i would put one on mine someday. After reading this thread and seeing the issues you dealt with making it fit, I've decided my round cowl looks good.