[Paul Eastham]

Hey everyone,
I think I may have done a bad thing (well, yet another bad thing) to my cowl.

Probably due to some overly-aggressive duct taping, I have to "pull" my top cowl backwards about 1/4-1/2 inch in order to move it to the proper gap at the forward end of the fuselage skin. It doesn't require a great deal of force, but it is definitely there.

The interference is coming from the overlapped flange around the spinner, which (as others have noticed) doesn't ever seem to want to cause the rest of the nose area to line up. I did do a lot of sanding on the flange (to the point that I added a few new layers of glass because I got it down so thin) and thought I had it resolved, but I guess it was just the duct tape talking

What do you all think, should I try to do massive surgery on that flange, or live with the tension fit? The sad part is that everything lines up just great once I get it all clecoed together :|

The alternative of filling the gaps around the nostrils instead of dealing with the flange, as others have done, I think is also now impossible due to the trimming I have done to the aft edge of the cowl.

Thanks for any thoughts!
Paul

 

[Rene Bubberman]

No tension

Hi Paul,

Do not worry, it will be ok in the end, but cowls just are terrible to tame. Could you post some pictures to give an better insight on the problem? In any case you should try to avoid a tension fit, otherwise you'll get problems later with your hinges or fasteners, also in the long run when you are flying. Better lay up some extra material: if the fit is perfect except for a gap between fuse and cowl, just fill that up with glass and epoxy. If it is any help, my description is on http://websites.expercraft.com/PHVII/index.php?q=log_entry&log_id=8194 and beyond.

 

[Davepar]

Yes, post pictures if you can.

One thing I realized on the top cowl is that no matter how perfect you get the gap at the cowl/firewall, the darn thing is going to move around. If you use hinges, the top pin is undersized. If you use camlocs, they float around quite a bit. If your top cowl wants to pull down, it's going to pull down because of the slop in the fasteners.

 

[Paul Eastham]

Thanks for the replies. I went out to take some photos and realized the problem is not so bad as I originally posted: the gap is exactly 1/4" and the pressure required to pull the cowl into position is about 10 pounds.

Here's the cowl at rest. 1/4" gap at the firewall (part of which could be considered a paint gap), and the nose has a slight overbite. (Yes, I realize this could have been corrected with filler, but I am committed now

When I pull the cowl to meet the firewall, everything looks perfect:

I suppose I could take a little bit of tension out of the system by setting a larger paint gap (there's only about 1/32 right now)

I suppose the main question is: is this going to lead to premature hinge failure? (Is anyone flying with a cowl that needs to be pushed into position like this?)

 

[f1rocket]

Generally speaking, you do what you have to do to get a good fit. Don't worry about the tension because once you fly and heat up your engine (and your cowl), the cowl will change shape slightly and relax. You'll notice this the most when you are initially concerned about how hard it is to ge the cowls on, but after two-three months of flying, the cowls fit much, much better.

 

[sf3543]

cowl fitting

In my opinion, there is a really easy fix.
Just get a new hinge and use half on each side to replace the upper half hinge pieces on the top cowl. If the holes are off enough, just use the same hinge, since you will need to drill extra holes between the rivet holes anyway for the epoxy to grab onto when you epoxy the hinges to the cowl.
You can make sure your alignment is correct and just redrill through the existing rivet holes in the cowl, into the new hinge half. This will allow the cowl to slide back with out any tension for a much better fit. It will also help you fix the over bite at the front, most likely. Hinges are cheap!
I would try to get a fit with out any tension. Your hinges will work much easier that way. Yes, they will loosen up over time after flight, but why wait.
Besides, if there is tension or bending on the fiberglass, you may eventually get cracking of the paint, maybe not, just something to consider. I would use filler at the front if you have to. This is no big deal.
When you install the hinges with epoxy, do not rivet at the same time. Install the cowl with the epoxy on and holding the hinges with clecos. Then, put it all together on the plane to set up. Do the bottom cowl first and the upper cowl the next day if you are worried about doing too much at one time. But, the secret is letting it set up while the entire cowling is installed on the plane. You can go back and countersink and rivet at your liesure. I didn't rivet mine for several months after epoxying everything together and I had it on and off at least 50 times. The hinges go in and out easily, even before I did any flying.

 

[Paul Eastham]

Hmm, now that I look at it some more, it seems that pulling the top cowl into position is merely lifting the bottom cowl due to slop in the bottom side hinge pins.

I've only drilled a few holes in those hinges -- I could try to drill some different holes so that the bottom cowl stays a little higher. Or I could just leave it -- fighting the slop on all the hinges seems like a unwinnable and useless battle...?

 

[Kyle Boatright]

My experience is that there is very little slop in the hinges, so if you have a problem now, it is most likely because something was out of place when you drilled the holes.

I would fix it now and avoid years of "I wish I'd fixed it" syndrome.

The easy fix would seem to be to replace one side of each hinged connection with new hinge and redrill the holes, making sure everything is properly aligned.

If you're having trouble visualizing a fix, get an experienced builder to visit the project and help out or at least point you in the right direction.