Engine sag poll

[Jim Percy]

1. How much engine sag have you experienced (say, at the spinner backplate)?

2. How many hours did it take to show up?

3. Is it progressive or did it just sag to a point and stop?

Feel free to add additional comments- Aerobatcis/ high G's? Airplane /engine type, hours? Etc.

Thanks-

Jim
RV-7A
XP-360
Not flying yet

[N79PT]

I noticed my RV-6A sag at about 10 hours, now it's got about 44 hrs. Seems like about 1/8 of an inch at the back plate/cowl interface. I hope it's stopped!!
Aloha. Greg

[Mel]

Engine sag is common with new mounts. I found good used mounts and I have NO sag after 13 years. All new mounts will sag, usually about 1/4" at the spinner backplate. I usually advise people to either setup your cowling 1/4" low or put slotted washers under the top of the engine mount at the firewall. Then after the sag shows up, remove the washers. If you already have the sag, then you can place the slotted washers under the bottom of the mount. the minor change to thrustline is negligible. Usually the sag is complete within the first 50 hrs.
Mel...DAR

[gmcjetpilot]

Originally Posted by Mel

If you already have the sag, then you can place the slotted washers under the bottom of the mount. The minor change to thrustline is negligible. Mel...DAR

Mel, what is correct thrust line? I mean the engine is going to end up somewhere. My goal is to get the spinner and cowl aligned. I never worried about the thrust line. Should I?

Lets assume new engine mounts, no extra washers. What is the correct thrust line, before sag or after sag? You recommend cowl low or add washers to top mount points first, than remove later after the it sags. What is wrong with adding washers (shims) to the bottom as needed later? Is that less ideal thrust wise. It would put the engine back to Pre-sag position.

I am not sure what Van has in mind. Did Van assume no sag or 1/4" sag for ideal thrust line. I am not making sense, but you mention it does not make a lot of differnce. I never worried about the thrust line. Thanks George

[Mel]

George,
There is no problem with adding the washers to the bottom "post sag". My idea of putting the washers on the top and then remove them is that the end result would be no washers. You would have to change the thurst line at least 1 or 2 degrees to see any change in flight characteristics. Thrust line should not be a concern.
Mel...DAR

[Mustang]

I was told that there is already an offset thrustline built in to the engine mounts sold by Van's. This is why they recommend no offset to the vertical stab as do other aircraft.

Cheers, Pete

[dan]

1. How much engine sag have you experienced (say, at the spinner backplate)?

Now sits 1/8" to 3/16" below the top cowl line, looking at the side profile.

2. How many hours did it take to show up?

Somewhere around 50-100 hours.

3. Is it progressive or did it just sag to a point and stop?

Sagged, then stopped.

Feel free to add additional comments- Aerobatcis/ high G's? Airplane /engine type, hours? Etc.

Originally built 1/8" pre-sag raise into the alignment. That wasn't quite enough. Could have gone with 1/4", but how could I have known exactly? Different people's experiences vary in this regard.

IO-360-A1B6, Hartzell 2-blade alum prop. Standard cheap engine mounts that came with the FWF kit (next time would use Lord mounts, the style w/gel filled sac in the middle). Occasional aerobatics. ~830 hours.

My hangar neighbor just shimmed his engine up by inserting washers between the engine & mount in a couple of spots. If I wanted to reinstate perfect alignment, that's what I'd do.

[Jamie]

Originally Posted by Mustang

I was told that there is already an offset thrustline built in to the engine mounts sold by Van's. This is why they recommend no offset to the vertical stab as do other aircraft.

Cheers, Pete

Pete:

I'm not sure about the older RV's, but the plans/parts for my -7A have the vertical stab mounted with an offset.

[Tony Kirk]

Originally Posted by Jim Percy

1. How much engine sag have you experienced (say, at the spinner backplate)?

About 3/8".

Originally Posted by Jim Percy

2. How many hours did it take to show up?

About 50-60 flight hours.

Originally Posted by Jim Percy

3. Is it progressive or did it just sag to a point and stop?

I don't think it's got any worse in the past 50 flight hours.

Originally Posted by Jim Percy

Feel free to add additional comments- Aerobatcis/ high G's? Airplane /engine type, hours? Etc.

I hung my O-320-H2AD with new mounts from Van's about one month before I fit the cowl. That was about 15 months before the first flight on Sept. 5, 2005 and there was probably 1/8" sag at that time, with another 1/4" or so in the first 50 hours.

That being said, what do you guys think is the best method of shimming to raise the spinner/engine/thrust-line back where it belongs?
1. Shim the two lower engine mounts?
2. Shim the four lower engine mount to firewall attachments?

Maybe it will require shimming both.

[DeltaRomeo]

My observation on this....

Engine sag is a purely cosmetic issue. In flight with the engine making power (and thus forward thrust) this sag is substantially reduced (in comparison to the thrust component). The danger, if there is any, is that correcting it on the ground with shims on the motor mount or at the engine vibration dampeners will only serve to misalign the engine in flight... (the only time the thrust line makes any difference ).

You'll notice on 'over-shimmed' planes that the spinner can actually ride above the cowl in flight.

A little sag is expected in both me and my plane as we age....

B,
D