Engine cowls

[trackdom]

Hi,
I am aligning top and bottom cowls . Plans say to place cowls 1/8*” below the spinner due to engine sag . For my former RV8 O-320 engine I didn’t misalign the cowls and engine didn’t move . For the second RV8 engine is a O-360 .
As anyone experienced this sag issue ? I am afraid that this misalignement could stay for ever , that would be a pity .
Thanks to share .
Dominique

 

[Marc Bourget]

What's your real goal?

Work of Art statically depicting an aircraft or a real live, flying airplane?

Spinner best serves its true purpose and function in flight.

On the ground, it may sag, but it's ready to assume its proper position when under power.

FWIW

 

[trackdom]

My goal is to fly for real for sure . But doing things as accuratly as I can is a pleasure too.

 

[Carl Froehlich]

Just bias the cowl during fit-up so the top of the spinner is even with the top of the cowl.

Carl

 

[rv8ch]

...

On the ground, it may sag, but it's ready to assume its proper position when under power.

...

Indeed - this is what I tell people to explain why my spinner is slightly below my cowl - it's to allow it to get into the right position when flying. "I did it on purpose!"

 

[trackdom]

Indeed - this is what I tell people to explain why my spinner is slightly below my cowl - it's to allow it to get into the right position when flying. "I did it on purpose!"

So you didn’t position the cowls 1/8 " below the top of the spinner before cuting the cowls? And now spinner is below? So plans are correct .
Thanks

 

[trackdom]

Just bias the cowl during fit-up so the top of the spinner is even with the top of the cowl.

Carl

Thanks for that information .

 

[Scott Hersha]

I’ve always fit mine as Carl suggests and on one of them, my first RV8, I got some engine sag eventually. I just put a thick washer under the bottom engine mount fittings at the firewall. That fixed it, and it stayed there. Also, before you do this, make sure your shock mount bolts are fully torqued.

 

[rv8ch]

So you didn’t position the cowls 1/8 " below the top of the spinner before cuting the cowls? And now spinner is below? So plans are correct .
Thanks

Actually, I tried to make it so that the cowl and the spinner would be perfectly aligned on the ground, but I failed. The spinner is a couple of millimeters below the cowl. I learned afterwards that when the engine is pulling, the engine (and spinner) will go up a little bit. I do not have any evidence of this beyond what I've read, and it does seem to make sense. Perhaps one day I'll see if someone can get a zoomed in photo during a formation flight to see where my spinner sits in relation to the top of the cowl.