[Kevin Horton]

I'm working on a system to minimize the air leakage between the cowl inlets and the plenum chamber on my RV-8, and I need to have some idea of how much engine motion my system needs to accommodate. I've ended with a more complicated concept than I originally hoped, and I am not convinced that I would do it this way again, but I am way past the point of no return. So I press on.

I've got a Lycoming IO-360-A1B6 and a Hartzell prop, using standard hardness engine mounts purchased from Van's. I need a rough idea of how much side to side and rocking motion the engine might make during start up or shut down. The side to side motion can be characterized by seeing how much the spinner moves laterally. The rocking motion can probably only be seen if doing engine runs with the cowling removed - how much do the cylinder heads move up and down?

thanks,

 

[AlexPeterson]

Kevin, it is hard to judge how much the spinner moves, but it is not a lot. The outboard ends of the cylinder move up and down an alarming amount, perhaps a half to 3/4 inch? I think it moves the most when it first starts firing upon startup, as it is trying to accelerate the prop. The main motion seems to be in the roll direction.

What have others observed?

 

[dan]

FWIW, same as you, Alex. Haven't measured, but it shakes a fair amount at shutdown.

The most movement imho is on a hot start if it doesn't just roar to life...it kicks and protests a bit sometimes, and that's when you get some real movement.

 

[RV7Guy]

lighter prop

I have the WW 200RV prop on my 7. The shut down and start up shake is minimal with the lighter prop. The heavier prop is definitely going to cause more shake.

 

[videobobk]

Shake

Darwin is right, the weight of the prop will make a big difference, especially the blades. Hub weight shouldn't make much difference. I also would suspect throttle position at first firing could cause changes. For this reason I try to start at about minimum throttle. To get an idea, I would set a video camera on a tripod pointing at the area to be measured. Crank the engine (better hold on to the camera) and play it back frame-by-frame. You might tape a ruler or marked paper measure to the location. It should be easy to figure from that.

Bob Kelly

 

[DaX]

To get an idea, I would set a video camera on a tripod pointing at the area to be measured. Crank the engine (better hold on to the camera) and play it back frame-by-frame. You might tape a ruler or marked paper measure to the location. It should be easy to figure from that.

Bob Kelly

Mythbusters style!

 

[gmcjetpilot]

Lord Vibration Inc

using standard hardness engine mounts purchased from Van's. I need a rough idea of how much side to side and rocking motion the engine might make during start up or shut down. thanks,

Movement will be significantly less with Lord Corp J-9613-40 mounts. They have the extra silicon filled spacer that handles the big motion during shut down/start. They where made for Mooney's to solve some banging problems (in a tight cowl). It controls motion with out making the rubber stiffer, affecting normal operations. Only Lord Corp makes this type.

Van sells some low cost ones (VPI), but if you want the best get the Lord Corp J-9613-40's. They have better shutdown/start movement control and in my opinion better quality overall. They do cost more; Google you can find the normal suppliers: Spruce Aircraft, Sacramento Sky Ranch, Chief, WagAero.

Van does not sell *"Lord" dynafocal mounts; he sells a lowest bid third brand, VPI, not even Barry Controls.

Regardless if you get the "equivalent" to Lords J-9613-40 in another brand, like Berry Controls it will not be the same. Lord is the only one with a silicon filled damper around the spacer, which dampens large scale motion (see pic below). However in flight it "de-couples" from normal vibration. Not a put down of Berry, but they tried to copy this low motion design, by just increasing the stiffness of the rubber, thus people complain of vibration. Lord has the patent on this.

The down side lord's for about $100, Berry about $77 and what ever Van's cost, like $60 each. So you might pay about $160 more total? No big deal or savings if your fillings are rattling. Also less vibration during start and shut down means less cracked air boxes, oil coolers and fretting hoses and wires. Best price I found was at Sky Geek.

None of the other mounts have that silicon spacer/damper.

Typical spacer with out a damping spacer sleeve.

* Van does sell conical mounts for $99 each. I do believe these are "Lord" J-1552's, which are also awesome, for the conical engine. If you have a conical mounted engine, never use plan bushings, it's horrible set-up. Bushings may only cost $7.50 for each corner but you will not like it. It's a big bullet to spend $400 verses $30 in this case but its worth it. I had a RV-4 with conical mounts and it was NIGHT and DAY with the Lord mounts v bushings.

 

[kentb]

I had to modify my cowl, because of shutdown shake.

My mixture control on the TB for my IO-320 only cleared the cowl by about 1/2 inch. I made a hole in the side of my cowl. I have sense made a bubble on the side to allow for motion. I think that I may have 1.5 inches of clearance now.

My engine doesn't like to such down smoothly and jumps a lot (run-on) as I shut it down. I think that most of the motion at this time is rotational motion. That would be twisting motion opposite the rotation of the engine/prop. On second thought the motion will go opposite and the with the rotation in an oscillating fashion.

I have not measured, it is just what I think that I am seeing.

Kent

 

[Kevin Horton]

Movement will be significantly less with Lord Corp J-9613-40 mounts. They have the extra silicon filled spacer that handles the big motion during shut down/start. They where made for Mooney's to solve some banging problems (in a tight cowl). It controls motion with out making the rubber stiffer, affecting normal operations. Only Lord Corp makes this type.

Thanks for the pointer to these special engine mounts George. They might be a solution if I need to reduce the engine movement on start and shut down. I wonder whether they are designed to handle 6g. They wouldn't need handle nearly that much on a Mooney.

Thanks to the other posters who provided info on how much their engine moved. It looks like my current design might be OK. If I see signs that things are colliding under the cowl, I might try those expensive Lord Corp J-9613-40 mounts, if Lord will tell me how many g they are good for.