Deadeye

Hey guys. I have this bird on my workbench right now, and want to implement the use of a cowl ring to avoid ugly exterior screws. Normally, I would use 4 screws that screw into blind nuts, but the cowl is so long on the Extra, I can't see a way to get to the top screws. Bottom screws would be easily accessed through the half round cowl cut out on the bottom. So what kind of latch system could I use that would retain the top of the cowl? I can't move the cowl up and down, so a tab/slot system can't work from what I can see.

Thanks.

Devo

I used the cowl ring mounting method on my GP 60 size 300s. It makes for a much cleaner installation. It also is the easiest cowl I own to remove and re-install. I basically stole the idea from captain232. My cowl does lock in at the top aft end and therefore has to be raised about 1/4 inch to clear the lock, then pulled straight forward. If you absolutely cannot raise the cowl, I believe you could live without the upper lock, if you had to, because the cowl becomes pretty rigid when you attach it to the ring. The simple fix? I drilled two holes, fore to aft, one on each side of the ring and into former 6. I then just use two phillips head wood screws that I access through the intake at the front of the cowl using a long screwdriver. I should also mention my engine is Saito 120 mounted inverted. I'm also using a Slimline pitts style smoke muffler.

Deadeye

Would you be so kind as to post some pictures? If possible, I would like to see a close up of the top latch you speak of. Is it a wedge type shape that pulls tight when the bottom screws are in? Because I think I can move the top 1/4 inch or so up. Also,
Did you make a sub type firewall to mount the OS inverted? I was going to go inverted on my Saito 125, but I would've had to build a firewall adapter with the Dubro iso mount I used. I really appreciate the feedback.

Devo

Yes a picture is worth a thousand...

First I made my cowl ring, making sure that it would clear everything when it was pulled straight forward and that the periphery was just slightly smaller than the sum of formers 6 and 25. This allowed the cowl to fair in with the fuselage when installed.

Then I epoxied the two blocks in place using a piece of material the same thickness of the ring to space the blocks away from former 25. When the epoxy had cured on the blocks, the two screw holes were located and drilled, being mindful of obstructions to the screws through the cowl opening. I found that I didn't need to taper the blocks because the srews keep the cowl firmly in place.

Next the cowl has to be trimmed to the right length, this is a tricky and critical step. If the cowl isn't trimmed properly now it won't fit right when it it glued to the ring. Thinking I would use it, I set up the stock cowl first. After adding the ring and filling the cowl to make the lines flow with the fuselage, it became too heavy. I purchased a fibergass cowl from Stan's and used it instead. The fiberglass cowl was easier to trim because it was somewhat transparent. At this time I also added any other clearance holes that were needed. Which, in my case, there were only the two holes for the rocker covers.

When everything fit right I epoxied the cowl to the ring. When it cured I went back and added light weight fiberglass cloth all around the inside of the cowl where it met the ring.

The pictures are an attempt to show how the cowl fairs in when installed, the blocks installed and the shape of the cowl ring mated to the cowl.

It was a little more work than the usual method of mounting a cowl, but I think the end justifies the means.

Good luck!

Devo

Sorry, I missed your last question. I built the engine box per the plan and use the stock mount, except I had to notch out the firewall to clear the smoke muffler. I have a spare Dubro isolation mount that I looked at using, but couldn't find a way to make it work. The mount was just too bulky. I highly recommend mounting the engine inverted in this plane and using remote glow. With the cowl installed you can only see the rocker covers. Plus, it balances very nicely.

Also, I have a 125 Saito now. If I had it when I built this plane, I would have used it. My Extra is pretty fast with the Saito 120 and smoke system. If you subtracted the difference in weight between the 120 & 125 and the weight of the smoke system you'd have a real screamer.

Again good luck, you'll love this plane.

Deadeye

Devo, Imagine my surprise to come in from building last night to find your reply. The surprising part? My top front holders are put exactly like yours! I really appreciate your help here, and your Extra looks great. Did you use black dope to fuel proof the firewall area? Or did you color epoxy somehow? Thanks again, and "Whip it good" (Devo song of the 80's for you youngsters).

Devo

The black in the engine compartment is Lustercote. Deadeye, are you planning to invert your engine? Also keep in mind that not only the aft of the cowl has to raise, but the cowl as a whole raises prior to removal.

Deadeye

Devo,
Engine is installed sideways. I wanted the Dubro iso mount, and that was the only way to make it fit. I've got the ring made, now just trying to figure out how to secure the bottom. It would be nice to find a really long 6/32 ball wrench, but haven't found one yet.

Devo

Deadeye, it's your turn to post pictures. I'm curious to see how your cowl works with the engine mounted sideways. When you get it worked out. Are you using the stock cowl or a fiberglass cowl?