Engine sag question

[cjensen]

My engine has been hanging for almost a year now, and I started the cowl work tonight...

I've heard that the engine sags on the mounts the most in the first year. So my question would be...do I allow for any more significant sag when fitting up the cowl, or is the year's worth of sag about as bad as it will get for several years?

[roadrunner20]

Originally Posted by cjensen

My engine has been hanging for almost a year now, and I started the cowl work tonight...

I've heard that the engine sags on the mounts the most in the first year. So my question would be...do I allow for any more significant sag when fitting up the cowl, or is the year's worth of sag about as bad as it will get for several years?

IMHO, I would not allow much.
I did & did not see the sag as others have mentioned.
Maybe others can chime in, but it's should not be too much. 1/4"?

[L.Adamson]

My engine hung on the mount for four years. It's now been flying for nearly a year. The spinner is almost level to the top of the cowl for sag. So far, it's still where I mounted it..............at least as well as the eye can tell.

L.Adamson --- RV6A

[rvbuilder2002]

Originally Posted by DanLandry

IMHO, I would not allow much.
I did & did not see the sag as others have mentioned.
Maybe others can chime in, but it's should not be too much. 1/4"?

I usually plan for (and see) about an 1/8" sag, but that is on cowl installations that are done right after the engine is mounted. I have never seen a change occur with it just sitting static. I think the engine running and the airplane flying is what makes it occur during the first 100 hours or so.

[carguy614]

At 74 hours I have yet to notice any appreciable sag in the installation. Needless to say, I am really not expecting any to show up at this point. That being said, I do no aerobatics (9A), so I would expect that aircraft exposed to more stress on the mounts may be more likely to experience a little sag. Best to plan for a little in your installation, as it would be much more difficult to allow for clearance later.

Just a thought,
Chris

[RV8Squaz]

I have 350 hours on my -8. I initially installed mine with the spinner about 1/4- 1/2" above the cowl. Why so aggressive?.... I used to fly the AF T-6A. When we picked them up at the factory the spinner was even or just slightly above the cowl, after 1000 hrs, the spinners were about a solid inch or more below! I fly a lot of aerobatics in mine, I started 1/4-1/2" above and now I'm at least a 1/4" below!

Jerry
RV-8 N84JE IO-360

350 hrs 2 1/2 years

Originally Posted by cjensen

My engine has been hanging for almost a year now, and I started the cowl work tonight...

I've heard that the engine sags on the mounts the most in the first year. So my question would be...do I allow for any more significant sag when fitting up the cowl, or is the year's worth of sag about as bad as it will get for several years?

[terry.mortimore]

Hi gang:

One thing I've always wondered about in regard to mounting the cowling to allow for sag, is this not just cosmetic for us looking at it on the ground?

What I mean is won't the engine pull itself forward on its mounts when its under power and center itself in it's dynafocal mount? Therefore would you not want to mount your cowl for this and not worry about what it looks like on the ground?

If this is true, I believe the best approach would be to hang the engine with a fresh set of mounts and mount the cowl as soon as possible before they have a chance to sag down.

Like I said, just something I've wondered about so don't yell at me.


tailwinds, terry

[roee]

So here's a question for y'all. I assume that the amount of sag that everyone is describing is as observed on the ground, with the engine off. I wonder then, with the engine on, in flight, if the engine assumes a slightly different position? After all, the rubber mounts still have a lot of give, and in the first scenario we only have the force of gravity, whereas in the second scenario we have additional forces created by the engine/prop (forward thrust, as well as various turning effects).

If there is a significant difference in the engine's position, then it seems to me that one would want to set up the cowl so it lines up with the spinner as best as possible under normal cruise conditions, to minimize drag. This may not necessarily be the same position that makes it line up to look pretty on the ramp with the engine off.

I have no experience with this (yet). Just thinking out loud.

[roee]

He he, Terry, great minds think alike! You beat me to it by one minute!

[LifeofReiley]

engine sag... set-up right initially, you'll see about none to nothing at all.