Installing the engine cowls.

[Steve Sampson]

Hi -4 builders! I wouldn't mind a bit of help. I have been working on the engine cowls over the last few days. I have run into two problems:

i) in the build book it tells you 'trim the lower edge of the upper cowl to the scribe line' or something similar. I didnt get a scribe line, so I have little idea how much to take off. Anyone else have this problem? How much did you actually end up taking off. It looks to me as though 0.5" in the middle and a bit less at the ends might be right, and give me a straight edge, but I know I cant put it back once its removed. In total, between the upper and lower cowl, I have to remove about 5/8" at the spinner and 1 1/8th at the firewall to get the bottom of the lower cowl to the right height.

ii) if you look at the third picture here, you can see the air intake is considerably offset to the right in the picture. Is this normal? (The uncut cowls are just taped one above each other here.)

I would welcome all the input I can get.

Thanks,

 

[pierre smith]

We did too

Hi Steve,
We didn't have a scribe line on our cowl either and ended up taking a lot more off the rear than the front. Be sure to have the cheek cowls on when you draw the line because if the two cowls are too close together (vertically), the radius of the rear won't match the cheeks.

We took equal amounts off each cowl and we cut both cowls at the same time with a thin cutting disc. We clecoed them together on the parting line and with a friend holding them together as I cut, went through both and they fit really well. We had four or five pieces of duct tape holding them together as well and just cut through tape and all.

The offset for the airbox is the same as ours......actually, it's offset to the left because the carb is. Your fresh air box will be turned slightly to align with the inlet of the lower cowl. Incidentally, the lower cowl should be temporarily on when you do this to ensure proper alignment.

Regards,
Pierre

 

[Steve Sampson]

Cutting the engine cowls.

Hi Steve,
.... We clecoed them together on the parting line and with a friend holding them together as I cut, went through both and they fit really well. .....

Pierre, thanks for that. I can see how you could have overlapped them along the sides, but did you cut off the overlap around the front first? Otherwise it would have blocked you from doing this I would have thought?

Thanks,

 

[pierre smith]

HMM.......

Steve,
The front of both cowls seemed to make a concentric circle when we checked the diameter with the back plate of the spinner. I don't recall having to trim the front much, if at all but the amount removed became more and more the further aft we went, around 1 1/2" of overlap. Bear in mind that they all seem to differ somewhat so your mileage may vary. We clecoed the cheek cowls to the airplane with three clecoes, two in the front and one at the rear when we were satisfied of the alignment of all four cowls. We had to trim the top forward flange of the cheeks in order to have the screws of the forward top skin exposed....it's kinda close to accomplish this and also have a nice line from the front to the rear of all the cowls.

After clecoeing the cheeks, we fitted the top and lower cowl, overlapping the top cowl over the bottom one. we made sure that they fit the cheeks well and duct taped everything in place. Then the parting line was marked with a 3' rule and we cut both the top and bottom cowl in one pass with a thin disc.
Most folks cut the top cowl and then put it back on and mark the lower cowl to match the new cut line....your call. One area I don't like is using the hinge to attach the upper firewall area. The sharp radius makes it difficult to engage the hinge pins. I'd use camlocks spaced 4" apart, as we did on my -6, with hinge pins everywhere else, except at the front air intakes. We used two nutplates on each side where the inner air inlets meet, rivetted to a short piece of .026 aluminum that is rivetted to the top cowl. Pictures follow.

Regards,
Pierre

 

[pierre smith]

Pictures

The first picture shows how low the oil cooler has to be and the second the front inner cowl fasteners.

[/URL][/IMG]

[/URL][/IMG]

Regards,
Pierre

 

[Steve Sampson]

Thanks.

Pierre, thanks for the info and pictures. All useful stuff. I am well along now as you can see from the blog and will probably get the engine cowl finished off tomorrow. (That is if I can hear myself think above the sound of the rain!)

I had to take very different amounts off to you, so as you said, no two cowls are quite the same.

The cowl at the sides, is sitting slightly low compared with the quarter cones on the fuselage. Was that the same for you?

Cheers,