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  #11  
Old 11-06-2018, 08:19 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by Walt View Post
Seen this issue before, Lord says no big deal. The fact that most other mounts don't even have this damper I can't imagine its that important, and not worth changing the mounts for.
The gel "footballs" appear to be viscous dampers, without any load capacity of their own. As such they would limit startup engine shake, largely a torsional reaction around the crank which displaces the mount in shear. They would also damp significant disturbance like roughness when finding the limits of lean mixture. They don't appear to do anything when the mount is loaded in tension or compression, and I doubt they have any effect in steady-state operation at small vibratory amplitudes.

The load carrying molded rubber assemblies have sagged in shear after 8 years/830 hours and probably exceed the limits published by Lord. I've spoken with a VIP representative and have some questions out with Lord; more later.
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  #12  
Old 11-06-2018, 09:18 AM
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Just a data point.

Conical mount engines are magnitudes more rigidly attached to the airframe. Startup and low RPM idling are definitely not as smooth, but in cruise there's hardly any difference.

Seems to be a reasonable tradeoff. I've flown hundreds of hours in RVs with conical mount engines swinging Hartzells and found the vibration difference to be minor.

Many Continental-powered airplanes use conical mounts, and I don't find those airplanes to vibrate excessively either.

That said machining some adapters to use off-the-shelf isolators, such as the ones below, might be something worth looking into.

https://www.energysuspensionparts.com/9.4101

Not the right sizes but you get the idea.
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  #13  
Old 11-06-2018, 09:52 AM
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Been there, done that:

http://www.vansairforce.com/communit...t=Polyurethane
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  #14  
Old 11-06-2018, 10:00 AM
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Did you try a softer durometer than 85? What you observed was what I expected with large, machined polyurethane mounts.
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N9187P PA-24-260B Comanche, flying
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N244BJ RV-6 "victim of SNF tornado" 1200+ hrs, rebuilding
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Not a thing I own is stock.

Last edited by rocketbob : 11-06-2018 at 10:05 AM.
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  #15  
Old 11-06-2018, 10:17 AM
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Nope. Have not made it back to experimenting with different formulations yet.
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  #16  
Old 11-06-2018, 11:34 AM
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Yes I think there is more room for experimentation here, especially if we can talk Dan into doing it .

I would love to have a $25.00 set of mounts that can be replaced every few years. $400+ is just getting out of hand.

These particular mounts are really the worst design of all isolators you see on GA airplanes, being hollow in the middle since they were originally designed to have the silicone-filled part. This makes them more sag-prone, and ultimately what caused this failure I suspect. In your case Mike since you did some simple lathe turning, this area was filled with 85 durometer polyurethane and that adds additional rigidity.

In my opinion, some machined cups to interface with smaller off-the-shelf polyurethane isolators probably would work very well.

I've had pretty good luck retrofitting poly mounts in cars.
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N9187P PA-24-260B Comanche, flying
N678X F1 Rocket, under const.
N244BJ RV-6 "victim of SNF tornado" 1200+ hrs, rebuilding
N8155F C150 flying
N7925P PA-24-250 Comanche, restoring
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  #17  
Old 11-06-2018, 08:52 PM
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If you want min vibrations go back with LORD.... Berry is cheaper and less engineered....

I have had the gel vibration dampers go 1000's of hours and keep on going. You have to
be careful not to pinch them or nick them with a tools. In fact I've never seen a Lord mount leak.
May be they had a bad batch?
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  #18  
Old 11-06-2018, 10:48 PM
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I was flying (and maintaining) a buddy's Cardinal earlier in my flying days and discovered the silicone goop on the engine mount durring an oil change. These had a bunch of time on them without being disturbed. They were good one day; then not good the next.
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  #19  
Old 11-07-2018, 08:52 AM
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I know the Lord are supposed to be the best, but I may eventually switch back to the VIP I purchased from Vans when building my airplane many years ago. I installed new Lord mounts a couple of years ago when I had to remove my engine for a repair. To be honest, I really haven't noticed any change in vibration levels. What I have noticed, is I think my engine is moving around more.

When I first got my airplane flying, I had to go with a shorter alternator belt because the pulley was rubbing on the cowl. That solved the problem. I have an IO-360 with a B&C alternator. Flew it for 10 years like that without any rubbing.

Now, since I reinstalled the engine with the Lord mounts a couple of years ago, the pulley is rubbing against the cowl again. I have already put a washer between the isolators and the engine on the bottom to correct for a little sagging, but the pulley is still rubbing. Granted, I'm doing a lot of aerobatics at higher g loading since starting this IAC competition stuff. But I've always done a lot of aerobatics and didn't have rubbing for the first 10 years. I may need to switch back to the VIP or find stiffer mounts designed for aerobatics.
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  #20  
Old 11-09-2018, 04:00 PM
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Quick follow up...

The gel-filled inserts probably failed due to overload, a case of excessive deflection of the mounts due to load and age. Sag in shear allows the middle of the gel bag to get pinched against the ID of the inboard steel rings molded into the doughnuts, and when that happens, compression or tension displacement would tend to peel back the ends of the rubber bag.

I suspect the Lord J-9613-40 mounts seen here are just too soft for a 390 with a metal Hartzell on a sport plane, the result being a lot of sag in only 800 hours. Examine application listings which include Vans, and you'll see the same isolator spec'ed for a 320 with a Catto, and a 360 angle valve with a metal BA. The engine difference is as much as 50 lbs, and the prop difference might add 50 more. The prop center of mass is roughly 28 inches forward of a set of mounts spaced 10 vertically inches apart, so there is a force multiplier too.

The fun starts when trying to select an isolator with slightly increased capacity. None of the three aviation isolator manufacturers publish aviation mount catalogs with technical data, notably shear and compression ratings (lbs per inch). They do publish good data catalogs for hundreds and hundreds of industrial isolators, for every imaginable application except aviation mounts. Go figure.

Lord has the data, but the only way to get it is to identify a particular isolator part number, then ask someone in product support. They won't recommend a specific mount, but will shotgun a few suggestions and state the stiffness values when asked. There is no practical way for a customer to simply select an isolator from a list, based on engineering values.

Barry was somewhat less forthcoming than Lord. No catalog listing, just a "For what part number?" response.

For Vibration Isolation Products (VIP), aircraft isolators are a legacy product acquired when the current owners bought the company. There may be engineering data somewhere in the files, but no one seems to know where. Best they can do is cross reference Barry and Lord parts numbers, and of course they know they supply Vans with their part # 50011-20.

For now, what I've done is order a set of VIP 50016-08 isolators, which they identify as an aerobatic mount. "Aerobatic" means it has the same high stiffness rubber assembly on both sides of the mount ring. A standard mount (like the VIP 50011-20) is a stiff assembly paired with a soft assembly. Using two stiff assemblies means the mount has a higher shear rating (the sum of the two), and the same compression rating as the standard isolator when either inverted or upright. The higher shear rating should help limit torsional engine movement at startup, i.e. less cowl banging, as well as offer more sag resistance. The downside will probably be more vibes in the cabin. We'll see...more later.
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