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Engine Sag?

R

RV8R999

Well Known Member
So I finally completed (so I thought) the cowling install with 100% skybolt as well as the prop (FP wood) and spinner. Although it all aligned nearly perfectly while the cowl was clecoed, enough slop in the skybolt system has allowed a bit of misalignment at the cowl spinner interface, not to mention the 13" spinner is a little smaller than the cowl anyway.

Not a huge deal so I added some glass and epoxy to the inside radius of both cowl halves and traced the spinner projection onto the cowl face. I've ground the cowling down but so far have left about 1/4" along the bottom half to account for any engine sag and am preparing to grind the top half a little low by an equal amount.

The question is how much sag have you guys experienced as you've broken everything in? Did the sag settle to some value and has stabilized? This will help me adjust this fitting to the likely final engine/spinner position. I am using the VANs aerobatic engine mounts. Thanks!

Ken
 
after 500 hours

I haven't seen any on my '9. So I eventually shimmy out the allowance for it.
I'm not expected any on the '8 (hope I'm not surprised).
 
11 years

I can't remember what mounts I used.

I have gotten no perceptible sag in 11 years. Unfortunately I allowed for it.
 
I didn't allow and do have about 3/16" sag at the spinner. Standard Vans FWF kit mounts.
 
rats...it's the worst when you have some that do and some that don't. I'll go with this criteria...I will take the most pictures and show off the plane the most early in its life so I'll assume no sag and accept any that comes along. Plus, I could always shim and/or replace the mounts when I can't stand it anymore. Thanks guys!

Ken
 
Lord mounts, sag... yes

I went for the more expensive Lord mounts on my O-320, wood prop, dynafocal bird and definitely have saggosis. For a long time it was in the same position, then it went down about 3/16" (+-). I have read a post or two suggesting annual rotation of the mounts but that seems easier said then done. I set my spinner a little high so the sagged position is just fine.
 
Sag

I have the standard Vans FWFwd kit mounts (purchased late 2008) and set my cowling straight initially. I had some early sag (70 hrs, 6 months) and rectified it with some engine mount shimming.

Robert Grigson
RV-8 N215RG
IO-375-M1B 200RV
 
Hi Ken,

As you can see from the posts the results vary.

I made my spinner 3/16th high in anticipation of sag on my 0360/Catto 9a and sure enough, after about 15-25 hrs, it had sagged 3/16th of an inch. Given my experience, my brother built in 3/16th for sag on his IO360/BA CS prop (weighs around 40 lbs more than my combo)7a using the same stock Vans motor mounts and he has seen absolutely NO SAG after a couple of hundred hrs--go figure. If you make it even at construction you can shim up if it does sag.

Cheers,

db
 
simple solution

Since we can't predict sag, don't bother. Build it right where you want it. If it doesn't sag then great, if it does, its a simple deal to shim it back up.
 
I have gotten no perceptible sag in 11 years. Unfortunately I allowed for it.
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Me too. Allowed for it; no sag after almost 4 years.
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Well I guess that makes three of us; I built in an allowance for sag, and got nothing after 3+ years and 650 hours. Oh well...
 
I think if you plotted all the sage data on a graph, you'd end up with a "sneeze plot" - random points all over the page. Gotta be related to different batches and age of mounts or somethign....

My Data: I pretty much ignored sag when I built my cowl, and after 1170 hours, have nothing noticeable.

Paul
 
As a side note, I am getting ready to order my engine mount isolators and Van's now sells Lord brand mounts at $125.00 each. That is less than anyplace I checked. The bolt kit is only $33.00 which is a good deal as well.
 
If you want it to look good on the ground then everything should line up. If you are interested in how it is in flight, then you should consider leaving the spinner slightly lower then the cowling. On the ground the engine is just hanging from the mounts. In the air, that prop is pulling the engine, and the front of the engine does go up relative to the cowling. I allow 1/8"to a 1/4" of sag for flight conditions.
Thus if your engine has sagged, you can now say that you mounted it that way on purpose!
 
Tom that is a great point! Next time you fly would you mind taking some precise measurements for me? :))

Ken
 
Paul what motor mounts do you have? And is it worth going to aerobatic mounts if I plan to occasionally do aerobatics. (See RV-8 aerobatic mount post in forums)
 
Tom Martin said:
If you want it to look good on the ground then everything should line up. If you are interested in how it is in flight, then you should consider leaving the spinner slightly lower then the cowling. On the ground the engine is just hanging from the mounts. In the air, that prop is pulling the engine, and the front of the engine does go up relative to the cowling. I allow 1/8"to a 1/4" of sag for flight conditions.
Thus if your engine has sagged, you can now say that you mounted it that way on purpose!
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Tom, that is great info! Now I can leave mine slightly low and be happy.
 
Tom,
Good info, but I have to ask why the engine lifts up in flight? Does it actually lift the front of the engine up in flight? I’m not disputing you, but it doesn’t make sense to me. Gravity doesn’t go away. Does the crankshaft have a positive angle of attack? Maybe it does, but that implies that our engine mounts have a built in angle relative to our builder installed longerons that accounts for this. If that is the case then shimming the engine mount after an engine sag, relative to what we are seeing on the ground should correct this.
I have done this on one of my three RV builds (the only one to exhibit any sag) - put a shim (washer) between the engine mount and firewall to correct a little sag, and it made everything line up. I can’t say that I’ve noticed any difference in flight, looking at the cowling/spinner relationship.
 
I suspect that the amount of sag over time can depend on a number of factors including the type of elastomeric engine mount. I have Lord mounts and they have a silicone filled void in them. It’s a superior design to the Barry Mounts and they will transmit less vibration from the engine into the airframe. However I have a feeling that the Lord mounts might be more prone to a bit of sag over time. My engine sagged 3/16” over 500 hours and I shimmed it back up using the lower mount washer trick....worked fine.

The Barry mounts might sag less because they are stiffer. The aerobatic mounts might sag even less because they are even more stiff.

And of course sag over time can be a direct result of stresses induced in the mounts due to flying characteristics and G forces.....read aerobatics.
 
Captain Avgas said:
I suspect that the amount of sag over time can depend on a number of factors including the type of elastomeric engine mount. I have Lord mounts and they have a silicone filled void in them. It’s a superior design to the Barry Mounts and they will transmit less vibration from the engine into the airframe. However I have a feeling that the Lord mounts might be more prone to a bit of sag over time. My engine sagged 3/16” over 500 hours and I shimmed it back up using the lower mount washer trick....worked fine.

The Barry mounts might sag less because they are stiffer. The aerobatic mounts might sag even less because they are even more stiff.

And of course sag over time can be a direct result of stresses induced in the mounts due to flying characteristics and G forces.....read aerobatics.
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If I read this correct the Barry's mounts are stiffer than the Lord mounts. I believe the stock Van's mounts are Lord mounts. If that is the case then I probably need to swap mine out for Barry's mounts. Can you clarify this if you have any info on the stiffness of each? Thanks
 
BluSkyRidr said:
If I read this correct the Barry's mounts are stiffer than the Lord mounts. I believe the stock Van's mounts are Lord mounts. If that is the case then I probably need to swap mine out for Barry's mounts. Can you clarify this if you have any info on the stiffness of each? Thanks
Click to expand...

This is a tricky subject and you can get as many opinions as there are posters. The anecdotal evidence on VansAirforce and my own personal experience is that Lord Mounts tend to sag a little over time (about 3/16” at the spinner). However they are undoubtedly superior at isolating vibration and that should always be the prime consideration. Vibrations transmitting from the engine to the airframe are bad for your instruments/wiring, bad for airframe cracking, and unpleasant for the occupants.

Mind you, builders with Barry Mounts have also reported engine sag in the past.

For general flying including occasional gentleman’s aerobatics I’d steer clear of aerobatic mounts.

Vans Aircraft will buy whatever engine mounts they can get at the cheapest price on the day...that’s how they operate. Usually that’s the Barry Mount. I checked their store today and they say they are supplying Barry Mounts. But some builders have reported that they have received Lord Mounts from Vans in the past in their FWF kits. When I purchased my FWF kit it came with Barry Mounts and so I deleted them and purchased more expensive Lord Mounts from another supplier.

Personally I’d go with the Lord Mounts. Either allow for a bit of sag or simply shim the engine at a later date (it’s no big deal). The Lord Mounts are a more sophisticated design and should give you a smoother ride. Lots in the archives on this.
 
Scott Hersha said:
Good info, but I have to ask why the engine lifts up in flight? Does it actually lift the front of the engine up in flight?
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The engine is supported at four points at the rear of the engine. The center of gravity of the engine is ahead of those points, and on the ground at rest the weight of the engine causes it to rotate and rest it's weight against the front of the upper mounts, and the rear of the lower mounts. The flexibility of the mounts allows this, and over time allows it more as the mounts wear in. When the engine is pulling, instead of just hanging, it pulls the engine forward, loading the front of the lower mounts instead of the rear. The upper mount hasn't changed its loading, so the engine rotates up by an amount allowed by the flex in the lower mount.
 
Captain Avgas said:
Lord Mounts tend to sag a little over time (about 3/16” at the spinner). However they are undoubtedly superior at isolating vibration and that should always be the prime consideration. Vibrations transmitting from the engine to the airframe are bad for your instruments/wiring, bad for airframe cracking, and unpleasant for the occupants.
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“Undoubtedly superior” and you know this because you’ve done extensive testing on both mounts?

“Airframe cracking”, wow, that sounds pretty serious. Where exactly on the airframe have you found cracking?

Captain Avgas said:
Vans Aircraft will buy whatever engine mounts they can get at the cheapest price on the day...that’s how they operate. Usually that’s the Barry Mount. I checked their store today and they say they are supplying Barry Mounts. But some builders have reported that they have received Lord Mounts from Vans in the past in their FWF kits. When I purchased my FWF kit it came with Barry Mounts and so I deleted them and purchased more expensive Lord Mounts from another supplier.
Click to expand...

More expensive mounts DOES NOT mean they are better but knock yourself out if you want to spend more $$$$. I’ve got some nice waterfront property to sell you if you’re interested :D

I’m happy to report that I’ve got Barry mounts on my IO360, routinely perform aerobatics and can report zero sag, zero vibration or “airframe cracking”, and zero issues over the last 5 years and 420+ hours. Install the prop, zero out the tracking, balance as needed and I dare say it won’t matter what mounts you use.
As always, your mileage may vary.
 
Snowflake said:
The engine is supported at four points at the rear of the engine. The center of gravity of the engine is ahead of those points, and on the ground at rest the weight of the engine causes it to rotate and rest it's weight against the front of the upper mounts, and the rear of the lower mounts. The flexibility of the mounts allows this, and over time allows it more as the mounts wear in. When the engine is pulling, instead of just hanging, it pulls the engine forward, loading the front of the lower mounts instead of the rear. The upper mount hasn't changed its loading, so the engine rotates up by an amount allowed by the flex in the lower mount.
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That makes sense Rob. I’m wondering if the engine/prop lifts enough in flight for you to see the top edge of the spinner back plate from the cockpit. I’m pretty sure on my RV4 I would be able to see that, but not sure. I’ll try looking for it next time up. Everything lines up nice on the ground, and I’ve pulled enough G’s for my new B&C alternator to leave score marks on the bottom cowl. I gouged out some of the honeycomb material in that area, and reinforced with some cloth/epoxy to give it some room - which has worked out fine. After this, everything still lines up nice on the ground, so the engine is definitely moving around a little.
 
Carlos151 said:
More expensive mounts DOES NOT mean they are better but knock yourself out if you want to spend more $$$$. I’ve got some nice waterfront property to sell you if you’re interested.
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I highly recommend you do a bit of searching through the VansAirforce archives....plenty of informed comments there over virtually 2 decades about the superiority of Lord mounts. That’s the reason so many builders pay extra to have them. As with most purchases in life you get what you pay for.

You’ve obviously opted for the cheapest product you could lay your hands on...and that’s fair enough...many builders are on a tight budget. It’s OK to admit you bought on price.
 
Captain Avgas said:
You’ve obviously opted for the cheapest product you could lay your hands on...and that’s fair enough...many builders are on a tight budget. It’s OK to admit you bought on price.
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:D:D:D:D:D:D:D:rolleyes: You're a funny guy Bob. My bank account would beg to differ with your analysis.

Captain Avgas said:
my own personal experience is that Lord Mounts tend to sag a little over time (about 3/16” at the spinner).
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May your "undoubtedly superior" expensive saggy mounts give you many hours of happy flying.

Captain Avgas said:
bad for airframe cracking
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Still waiting to hear where this "airframe cracking" is happening. Sounds pretty serious.
 
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I'm running VIP mounts on the Rocket. Nice and stiff - no sag (yet), inexpensive and plenty smooth in flight. Big improvement over the Lord units that were on the airplane when purchased.
 
great point!

Tom Martin said:
If you want it to look good on the ground then everything should line up. If you are interested in how it is in flight, then you should consider leaving the spinner slightly lower then the cowling. On the ground the engine is just hanging from the mounts. In the air, that prop is pulling the engine, and the front of the engine does go up relative to the cowling. I allow 1/8"to a 1/4" of sag for flight conditions.
Thus if your engine has sagged, you can now say that you mounted it that way on purpose!
Click to expand...
Outstanding Tom! I don't have any sag, but even after lots and lots of careful positioning of my cowl, it's sitting about 1/16" - 1/8" proud of the spinner. No one has called me out on yet, but when they do, I have a great response! :D
 
Flew behind both Lords and Barrys on my Mooney. Both installed as new sets. The Lords were better in every category except price. That is only one data point.

Unfortunately, neither brand seems to last as long as their old stuff with identical part numbers. That observation is shared by many.
 
Carlos151 said:
Still waiting to hear where this "airframe cracking" is happening. Sounds pretty serious.
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Engine mounts (isolators) perform a very important function, particularly on aircraft with reciprocating engines. They are designed to serve the purpose of damping vibrations from the engine and prop to minimise their affect on the airframe. Engine and prop vibrations can be described as multiple impacts as in taking a hammer to the structure...and they can certainly do serious damage including cracking major structural components, loosening rivets, fatiguing metal, and damaging instruments.

There are dozens of Service Bulletins in force for the Vans RV aircraft range pertaining to airframe cracking. Some of those SBs may be attributable to airframe vibrations. In other cases the cracking may be primarily attributable to other stresses, but exacerbated by airframe vibrations.

At any rate I personally feel compelled to pay a small premium for a product that many claim provides superior damping. I have inspected both the Barry and Lord mounts and the differences in their construction are certainly considerable.

It would be a shame if this excellent thread simply descended into a defence-of-product-choice argument.
 
Captain Avgas said:
I have inspected both the Barry and Lord mounts and the differences in their construction are certainly considerable.
Click to expand...

How does this visual and tactile observation translate into performance differences. I would think that a vibration analysis would be required to show that one or the other was transmitting more or less of numerous different harmonics into the airframe.
 
cut them in half

lr172 said:
How does this visual and tactile observation translate into performance differences. I would think that a vibration analysis would be required to show that one or the other was transmitting more or less of numerous different harmonics into the airframe.
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We need someone with a deep freezer, a waterjet cutter, some spare time, and some spare cash to cut them both in half and take some pictures. I'd chip in $10 to see that!

Not to say that would clarify which is "better", but it would show how they are built.
 
Captain Avgas said:
There are dozens of Service Bulletins in force for the Vans RV aircraft range pertaining to airframe cracking. Some of those SBs may be attributable to airframe vibrations. In other cases the cracking may be primarily attributable to other stresses, but exacerbated by airframe vibrations.
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Actually Bob there are a total of three SB's relating to cracking, NOT dozens. Here you go:
  • SB 16-03-28 Cracking of wing aft spar web at the inboard aileron hinge bracket attach rivets.
  • SB 14-02-05 Cracks in Elevator Spar
  • SB 14-01-31 Horizontal Stabilizer Cracks

NONE of these Vans issued SB's relate to issues with engine mounts. I will grant you that excessive vibration might exacerbate these issues further back in the airframe but I dare say if you're getting that kind of vibration, something is seriously wrong. Engine mounts, regardless of brand name, are designed to reduce engine induced vibration, not eliminate it. There are literally hundreds of issues that could cause vibration from an improperly tracked prop, improperly balanced prop, miss-timed or miss-firing engine, spinner, spinner back plate, exhaust harmonics, etc, etc, etc. Like Larry mentioned, a "visual and tactile observation" does not translate into actual performance numbers. Just like you can have the exact same motor mounts in two different aircraft, one may sag, the other may not, one may vibrate, the other may not. Too many variables to arbitrarily discount one manufacturer over another.

dedgemon said:
Since we can't predict sag, don't bother. Build it right where you want it. If it doesn't sag then great, if it does, its a simple deal to shim it back up.
Click to expand...

David called it right, IMHO.
 
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Carlos151 said:
Actually Bob there are a total of three SB's relating to cracking, NOT dozens.
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Here are the numbers of Service Bulletins and Notifications from Vans Aircraft pertaining to airframe cracks in each specific RV model. Anyone can check this on Vans site.

RV3 3
RV4 2
RV6 4
RV7 4
RV8 3
RV9 2
RV10 4
RV12 8
RV14 2

That’s a total of 32 instances of airframe cracks across 9 models....sounds like dozens to me. And still counting of course. I don’t think it serves any purpose to downplay the role that we’ll designed engine mounts can play in minimising airframe cracks.

I think the problem here is that there are builders using Barry and VIP mounts who don’t really know what a Lord mount actually looks like and therefore cannot appreciate the differences in the design principles. I have therefore provided a URL to an image on the Chief Aircraft website for a Lord J-9613-40 Mount typically used on an RV7 with an IO-360. The image shows the internal gel cell that acts as an additional damping device.

https://www.chiefaircraft.com/ld-j9613-40.html
 
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Captain Avgas said:
Here are the numbers of Service Bulletins and Notifications from Vans Aircraft pertaining to airframe cracks in each specific RV model. Anyone can check this on Vans site.

RV3 3
RV4 2
RV6 4
RV7 4
RV8 3
RV9 2
RV10 4
RV12 8
RV14 2

That’s a total of 32 instances of airframe cracks across 9 models....sounds like dozens to me. And still counting of course
Click to expand...

You’re counting the same SB multiple times! :confused: :confused:
So you’re taking 3 SB’s and turning them into 27 SB’s. That sounds a little saggy to me :eek:

SB 16-03-28 RV3, 4, 6/6A, 7/7A, 8/8A, 9/9A, 10, 14/14A
SB 14-02-05 RV3, 4, 6/6A, 7/7A, 8/8A
SB 14-01-31 RV6/6A, 7/7A, 8/8A
 
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The gel sack is not used in ALL Lord mounts, nor is it even used in all applications of the same engine. In some cases, Lord specifies mix and matching their off the shelf products to meet customer requirements. Some aerobatic applications use the "compression" pucks on both sides of the mount to stiffen it up, as one example.

Yes, Lord has been in the isolation mount game for a long time, but that does not mean they have a monopoly on dampening out harmfull vibration.
 
Carlos151 said:
You’re counting the same SB multiple times! :confused: :confused:
So you’re taking 3 SB’s and turning them into 27 SB’s. That sounds a little saggy to me :eek:

SB 16-03-28 RV3, 4, 6/6A, 7/7A, 8/8A, 9/9A, 10, 14/14A
SB 14-02-05 RV3, 4, 6/6A, 7/7A, 8/8A
SB 14-01-31 RV6/6A, 7/7A, 8/8A
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Karl, You would gain greater credibility if you did some serious research before posting.

Let’s take SB 16-03-28 as an example. This SB describes cracking of the wing aft spar web at the inboard aileron hinge bracket attach rivets on 8 different models. It’s a massive 14 page document because each model is designed differently and therefore the fix is different for each model...and the parts required to affect the fix are different for each model. The parts required to repair each model are actually covered by seperate SBs as follows:

RV3. SB 16-03-28-3
RV4/6. SB 16-03-28-46
RV7/8. SB 16-03-28-78
RV9. SB 16-03-28-9
RV10/14. SB 16-03-28-1014

So saying that this is one SB is totally disingenuous...it’s many SBs for many different models with different wing aft spar designs and different fixes with different parts. But let’s cut through the cr@p. Whether it’s one SB or 8 SBs doesn’t change the fact that it pertains to a serious and extensive spate of airframe cracks across 8 different RV models. And claiming that it is only one SB is just a pathetic ploy to downplay the extent of the problem.

Builders defending their purchase decisions on VansAirforce is commonplace. We’ve all been guilty of it. But I do tend to find that posters on VansAirforce who buy the cheapest product available are often the most vociferous (and tedious) in defence of their choice. Perhaps that’s natural....no one wants to admit that they were poorly researched in their decision....or even worse, stingy.
 
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Captain Avgas said:
So saying that this is one SB is totally disingenuous...it’s many SBs for many different models with different wing aft spar designs and different fixes with different parts. But let’s cut through the cr@p.
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Bob, the only disingenuous post is your math interpretation of single SB's issued by Vans.

If we used your new math thesis for these "massive 14 page documents", why not go a step further and issue an SB for each RV built since they're all technically different, so that would be 10,844 at last count. Shear and utter nonsense and you don't need an engineering degree to figure that one out!!

I know a 14 page SB might be a lot for some folks to read but if you take the time to do so you will find out that NOT A SINGLE ONE talks about engine sag caused by engine mounts. NOT A SINGLE ONE talks about "airframe cracking" caused by engine mounts. Like I posted earlier, engine mounts in essence mask the underlying problem, they don't solve it

Carlos151 said:
Engine mounts, regardless of brand name, are designed to reduce engine induced vibration, not eliminate it. There are literally hundreds of issues that could cause vibration from an improperly tracked prop, improperly balanced prop, miss-timed or miss-firing engine, spinner, spinner back plate, exhaust harmonics, etc, etc, etc..
Click to expand...

So indeed, lets cut the cr@p, building RV's is about making choices. You seem to think that YOUR choices are the only correct ones but I guess I'm the first one to tell you that is NOT the case. I know it's hard to accept, but taking shots at builders choices proves that you have done zero credible research into viable options and will discount anything that may not be YOUR idea. You would certainly gain greater credibility before posting based on "anecdotal evidence" as you put it.

Perhaps you need to heed your own words:

Captain Avgas said:
no one wants to admit that they were poorly researched in their decision....or even worse, stingy.
Click to expand...

It's OK to try different choices, you should try it sometime.

Toobuilder said:
Yes, Lord has been in the isolation mount game for a long time, but that does not mean they have a monopoly on dampening out harmfull vibration.
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BTW, my engine hasn't sagged yet :D

Captain Avgas said:
The anecdotal evidence on VansAirforce and my own personal experience is that Lord Mounts tend to sag a little over time (about 3/16” at the spinner).
Click to expand...
 
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Carlos151 said:
BTW, my engine hasn't sagged yet :D
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It's interesting. I used lord mounts on the 6 and the engine sagged almost a 1/4" over 500 hours (most of it in the first 100 hous). On the 10, I used whatever Van's supplied. Unsure, but think VIP, but could be Barry - no name on the box. I left the prop up almost 3/16" to account for sag. At 150 hours, it hasn't sagged even 1/16" Obviously this doesn't mean one is better than the other, just different chemistry in the rubber. I would expect that the latter isolator doesn't provide as much dampening. However, that doesn't directly translate to problems or cracking. I suspect that harmonics and frequency are much more import than raw vibration. I do fly it with confidence that it won't shake it into pieces. Maybe that's smart, maybe foolish. I trust in the long term Van's reliability numbers and they seem to ship way more VIP/Barry than Lord.

Larry
 
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lr172 said:
I do fly it with confidence that it won't shake it into pieces. Maybe that's smart, maybe foolish. I trust in the long term Van's reliability numbers and they seem to ship way more VIP/Barry than Lord.
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Totally agree Larry. There seems to be no common denominator with engine sag; some do, some don't regardless of engine mount selection.

IMHO Vans has provided us with some really nice machines to fly with an infinite choice of customizing options, some better than others but none right or wrong. In the myriad of engine and prop combinations if the vibration were to get bad enough, most of the time your aircraft will let you know ahead of time. I trust my ride as much as you do yours. They are indeed magic carpets.
Cheers.
 
magic carpet

Carlos151 said:
... They are indeed magic carpets. ...
Click to expand...
That's for sure! I was just doing some required climb tests a few days ago - still climbing at just under 1000 fpm at over 13,000 ft, @2500 rpm. I could have gotten more with a better leaning technique - I'm still learning.
 
rv8ch said:
That's for sure! I was just doing some required climb tests a few days ago - still climbing at just under 1000 fpm at over 13,000 ft, @2500 rpm. I could have gotten more with a better leaning technique - I'm still learning.
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That's great Mickey, you must be getting those numbers since your engine didn't sag :D:D:D

Beautiful paint job!!! Rock on.
 
FWF Temperatures

I wonder if engine temperature and FWF temperature has anything to do with engine sag. I.E. are those when engines that tend to run hot likely to see more sag over time than those who's engines generally run at lower temperatures?

Skylor
 
skylor said:
I wonder if engine temperature and FWF temperature has anything to do with engine sag. I.E. are those when engines that tend to run hot likely to see more sag over time than those who's engines generally run at lower temperatures?

Skylor
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I think you might be onto something Skylor. High temperatures will definitely impact any rubber compounds and definitely gel compounds. Makes sense. This may narrow down the scatter plot of those engines that sag and those that do not.
 
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