reenforcing lower cowl

[Dorsal]

On my list of "once I retire" things I have for my plane is to chase down some of the vibrations (small but noticeable) I feel at various flight attitudes. One that I am fairly confident of is the lower cowl which strikes me as a little flimsy along the back edge. Have others strengthened this? put a reenforcing strip across or made an attach strap to the firewall?

[Esser]

My kit has a large reinforcement that doubles up as a damn for the air just below the rad. I find mine quite sturdy. Does yours not have this?

[Dave S]

Dorsal,


Similar issue up here. Back when I started testing the plane, one of my hangar neighbors observed that the lower rear part of the cowl where the air exits the cowl behind the radiator was vibrating up and down quite visibly.



With the nose gear, some material is cut out of the rear of the cowl bottom and I originally though the cutout was in part responsible for weaking this part of the cowl and exacerbating the vibration problem - not so sure now.



To reinforce the cowl in this area, I riveted an aluminum bar across the bottom of the cowl in this area with the bar on the inside surface of the cowl. That seems to have solved the issue. I don't have the precise dimension of the aluminum bar right off hand, but I believe it was approximately 1/8" thick.


The other thing I did on the cowl bottom was to rivet in a fabricated aluminum "U" shaped edge for the NACA duct - this won't help the vibration at the back issue but I wanted something a bit more solid than the simple fiberglass edge. Photo attached; but, photo included to show approximately where the rear lip reinforcing bar went in later - the bar was riveted in just a bit forward from the notch in the rear of the cowl for the nose gear, on the flat part of the cowl, so it would not be near the radiator bottom.



If I recall, the vintage of your kit and mine is about the same.

[Dorsal]

Esser, No it does not, do you have a pic? I like the idea of closing the gap under the radiator, any challenges getting the cowl on and off?

Dave, that is kind of what I was thinking, how wide is your bar (was thinking 1.5" or 2")?

[Dave S]

Dorsal,


I'll get an exact measurement tomorrow and get back to you.

[Dorsal]

My solution, noticeably less vibration in climb out, seems less in cruise too.

[Esser]

Not sure how well you can see it

[Dorsal]

Thanks, seems the same idea though I don't think anything will bond to the bottom of my cowl now, has become kinda oily over the years.

[Esser]

Some alcohol and a scrub brush should fix that up fairly easily

[efwd]

How would one be able to tell they need to reinforce this area. The builder manual advised to reinforce the NACA opening but nothing of this much wider surface. Then again its not facing into the relative wind. What was the experience you had in flight that led you to reinforce?
Eddie

[Dave S]

Dorsal,


I see you got a start on your reinforcement. I didn't get to the 'port yesterday - grunty weather. Today I measured what I put in - it was a 1/8" by 1" aluminum bar 22.5" long with the center of the bar 4" forward of the firewall.



I like you idea of using the angles.

[Esser]

Yours will be fine Eddie. It’s an older thing

[Dorsal]

efwd, On my craft it was pretty flexible and I expected it was flapping in the breeze (confirmed with a go-pro mounted on the landing gear). If your ship is the same vintage as Esser then I agree this should not be a problem.

Dave S, Thanks for checking, mine is a 4' X 1/2" angle stock cut in half and riveted together. It is mounted 3.5" from the back edge of the cowl to the center of the brace, so just about the same. Significantly more rigid and simple to install. I will have to watch if I spill any oil that it does not pool up behind the brace.

[efwd]

But Josh has reinforced his.

[Esser]

Nope Eddie, mine came like that. Sorry if I made it seem otherwise

[Wheels]

I used some styrofoam reinforcement and covered it with fiberglass. It still flexed enough to craze the paint on the sides of the cowl. It's just a really thin piece of fiberglass and kinda needs to be for weight and aerodynamic properties. however, I too would like less paint cracking from removing and replacing during inspections.

[efwd]

no Josh, I went back and noticed that you had stated it came that way. Mine is far newer than yours and mine is not reinforced. I'll have to look. I feel like mine is in contact with the bottom of radiator but I could be wrong.
Eddie

[airlina]

This is a photo of my lower cowl support . This is on an IO-240 cowl and is a necessary mod . On a few occasions over the years that bottom screw has fallen out during flight and I can tell immediately because of the flopping that occurs at the bottom of the cowl. I have learned a drop threadlocker solves that problem. Bruce N199CL

[Dorsal]

Nice Bruce, that was my other plan though a little more complicated with a nose gear. I agree, you can definitely feel the difference. I like all your access holes under there (and the nice clean edges).