Lyc Wet Dog Shake

[Jim P]

Any idea how much, in inches, a lyc will shake on shutdown at the outboard edges?

Jim

[gmcjetpilot]

Sorry there was a thread where someone posted a deflection, could not find it. But it depends on engine, prop and brand/type engine vibration isolators. The deflection depends on where you measure it. I think most of the movement is rotational. If you are looking for gap between baffles and cowl, follow the plans. I think there are some clearances in there.

[cytoxin]

Originally Posted by Jim P

Any idea how much, in inches, a lyc will shake on shutdown at the outboard edges?

Jim

about 2 inches total (1up and 1down) could be more probally less. this is my concern for the fuel pump to flow meter hose.. that hose is suppose to be flexible but its not so flexible as to not wiggle the gascolator/fuel flow assy. remember the baffles are only 3/8 from the cowl so it cant be as much as the video shows..i hope.

http://www.youtube.com/watch?v=yoX4KEXVuFo watch at 6.23

[TSwezey]

From what I saw in the video it looked like it hardly deflectedz! The whole plane deflected but I think the engine stayed pretty still in regards to the airframe.

[cytoxin]

Originally Posted by TSwezey

From what I saw in the video it looked like it hardly deflectedz! The whole plane deflected but I think the engine stayed pretty still in regards to the airframe.

full screen the video if you did not and you will see the more than obvious relative motion. it moves, and a good bit at that.just as you hear the implulse coupling click. however i dont know what type of mounts he's using. vip v/s lords ??


edit : the best ground run video ive seen yet and perfect timing BTW for my concerns...like he read my mind.

[Mel]

The heavier the prop, the softer the mounts, the higher the compression, the more the shake.

[AlexPeterson]

The majority of motion on my engine seems to be rotational during startup or shutdown. I have an O360 C/S prop, with non-aerobatic mounts. I would estimate that the valve covers, during this rotational motion, move up and down maybe 1/4 to 3/8" from their rest position. Certainly no more. My baffles have 1/2" clearance, and there is no sign that they've hit the cowl. The center of the engine, just behind the prop, moves up and down perhaps 1/8".

[RVAddict]

Originally Posted by cytoxin

about 2 inches total (1up and 1down) could be more probally less. this is my concern for the fuel pump to flow meter hose.. that hose is suppose to be flexible but its not so flexible as to not wiggle the gascolator/fuel flow assy. remember the baffles are only 3/8 from the cowl so it cant be as much as the video shows..i hope.

http://www.youtube.com/watch?v=yoX4KEXVuFo watch at 6.23

Seriously off topic guys, and I apoligize, but can anyone identify the pickup truck in that video? I can't tell what it is. PM me if you know so the thread does not get hijacked.

Thanks
Josh

[L.Adamson]

Originally Posted by AlexPeterson

The majority of motion on my engine seems to be rotational during startup or shutdown. I have an O360 C/S prop, with non-aerobatic mounts. I would estimate that the valve covers, during this rotational motion, move up and down maybe 1/4 to 3/8" from their rest position. Certainly no more. My baffles have 1/2" clearance, and there is no sign that they've hit the cowl. The center of the engine, just behind the prop, moves up and down perhaps 1/8".

Initially, I, along with another builder, was concerned about the clearance between the two horizontal fiberglass baffles attached to the bottom side of the top cowling & the vertical aluminum baffle pieces that are on each side of the starter gear ring. We wanted to know if we needed a larger gap, along with the rubber seal.

Numerous aircraft that we looked at, only had an 1/8" gap or slightly more/less, and little signs of wear on the fiberglass, which proves it is much more rotational; and almost nothing with side to side motion, considering it's far forward of the mounts.

L.Adamson -- RV6A

[az_gila]

Originally Posted by AlexPeterson

The majority of motion on my engine seems to be rotational during startup or shutdown. I have an O360 C/S prop, with non-aerobatic mounts. I would estimate that the valve covers, during this rotational motion, move up and down maybe 1/4 to 3/8" from their rest position. Certainly no more. My baffles have 1/2" clearance, and there is no sign that they've hit the cowl. The center of the engine, just behind the prop, moves up and down perhaps 1/8".

On my Tiger (O-360 engine, similar mounts...) I installed an indicator on the bottom right engine mount bolt - well, not quite, but the aftermarket PowerFlow exhaust system has a rod that passes through the cowling about 10-12 inches below the mount. This rod is fixed to the engine mount bolt and the exhaust - it moves with the engine.

The cowling hole had to be opened up to allow for the "wet dog shake", and is about 3 inches wide (rotational shake) and less than 1 inch fore and aft (up/down shake).

The rod can be seen in this picture....



Based on this, I would say the biggest movement is rotational, and the biggest physical movement would be an up/down movement at the cylinder heads.

gil A