Airplane engines vs farm tractor engines

Briar Rabbit

Briar Rabbit

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Rob
I have my airplane in a hangar and try to fly it at least monthly. So why do we need to worry about corrosion more in an airplane engine than farm tractors?

I have owned farm tractors that are almost 50 years old with the original engines. Oil is a lower viscosity than airplane oil so should disappear on upper engine parts and camshafts quicker. Tractor engines run in a far dirtier environment! Granted better filters but still a tough environment. Engine RPM’s are similar at full load and we pull the guts out of them during tillage activities. Some of my tractors sit for entire winters without being run, a combine may sit for 11 months without firing up. If a diesel farm tractor engine doesn’t last 5,000 or more hours it was a terrible engine, most last 8,000 to 10,000 or more. I have a 1973 dozer (original engine) with considerably more hours than that and most years it sat outside and only run in the summer months, always worked hard and definitely in the dirt. Had a 1966 gas farm tractor used for heavy tillage that sat outside it’s whole life and still had an engine that hit 5,000 hours. I bought it in 1985 and used it 20 years. It sat once for 3 years without running, probably not the best for it but put a new battery in and changed the oil - fired right up when I started it.

So why are airplane engines so darn fragile regarding sitting and corrosion? Aluminum cases will contribute less rust into the engine than the cast iron and steel parts of a tractor engine. Oil changes in tractors may be once a year and more than a 100 hours between changes.

Wish John Deere made an io520!
 
Truthfully I think it comes down to oil. These are essentially muscle car engines only in the fact that they have flat tappets.
Back in the day, when flat tappet engines were the norm, you had zinc in the oil. The zinc would put itself into the microscopic pits on the camshaft and essentially make a glass smooth finish.
Even today, if you run a performance engine with flat tappets and you do not run zinc in the oil, you will toast that camshaft lickety split.
Thanks to the EPA, none of the aircraft oil has zinc in it.
I have a friend who ran rotella t4 15w40 in his 520 powered Bonanza for 10 years. At 2,200 hours he finally pulled the engine apart only to find everything looked brand new and was within new tolerances.
I can't help but think that the cam and lifter problems that aircraft engines experience really comes down to oil.
 
Put one in your airplane. Let's see how well it works. ;)
 
mwagg737 said:
Truthfully I think it comes down to oil. These are essentially muscle car engines only in the fact that they have flat tappets.
Back in the day, when flat tappet engines were the norm, you had zinc in the oil. The zinc would put itself into the microscopic pits on the camshaft and essentially make a glass smooth finish.
Even today, if you run a performance engine with flat tappets and you do not run zinc in the oil, you will toast that camshaft lickety split.
Thanks to the EPA, none of the aircraft oil has zinc in it.
I have a friend who ran rotella t4 15w40 in his 520 powered Bonanza for 10 years. At 2,200 hours he finally pulled the engine apart only to find everything looked brand new and was within new tolerances.
I can't help but think that the cam and lifter problems that aircraft engines experience really comes down to oil.
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Interesting theory! Oil would be a lot cheaper too. I pay about the same price for a gallon of Mobil Delvac 15-40 as a quart of Aershell 15-50. I am not aware of any regulation preventing the use of any tractor oil in airplane engines?

I am tempted to retain some used oil from both types of engines, grind the scale off of a steel rod, cut it in half and dip A half in each type of oil, then hang them outside for a while and see which rusts quicker and heavier.
 
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A lot of it is likely water cooled and lots of thermal mass compared to air cooled, and minimal thermal mass. It affects the operable tolerances considerably. And unless you are rolling coal, the diesel is always running LOP. And the real world penalties for a failed tractor engine are nearly never fatal, only financial. So taking the utmost care in service isn’t affecting the odds of a life or limb event like it is when you can unexpectedly turn into a glider.
 
-KLB- said:
A lot of it is likely water cooled and lots of thermal mass compared to air cooled, and minimal thermal mass. It affects the operable tolerances considerably. And unless you are rolling coal, the diesel is always running LOP. And the real world penalties for a failed tractor engine are nearly never fatal, only financial. So taking the utmost care in service isn’t affecting the odds of a life or limb event like it is when you can unexpectedly turn into a glider.
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Granted that and having the extra lubrication from newer diesel fuel could reduce wear. But that does not explain a lack of concern for corrosion during the off season for the months they sit idle.
I can assure you that down time for a failed engine goes beyond the engine expense on farm tractor engines. A downtime during planting season or harvest season can exceed 5 figures for each day a crop is delayed! No good farmer is going to start a season with a questionable piece of equipment unless he is a hobby farmer. Not many tractor engines are used until they die.
 
Water cooled engines are more air tight than air cooled ones. For example ring gaps on car engines are less than .015" where as airplane engines can be over .030". Airplane engines see a lot more temperature fluctuation so everything is a looser fit. Also, cars and tractors typically have cylinders that are oriented more vertically allowing moister to drain from the cylinders and into the crank case. Further more, if your tractor or old muscle car burns a quart of oil every fill up you just add more oil. If your airplane does you overhaul the engine. If your tractor or car is down 10-20 hp you likely will not notice, if your airplane is you will notice and rebuild.

There are very few catastrophic failures due to corrosion. Most of the time it is diminishing performance and oil consumption that lead to overhaul. Things you will live with in your car or tractor aren't worth the risk in an airplane.
 
Grum.Man said:
Water cooled engines are more air tight than air cooled ones. For example ring gaps on car engines are less than .015" where as airplane engines can be over .030". Airplane engines see a lot more temperature fluctuation so everything is a looser fit. Also, cars and tractors typically have cylinders that are oriented more vertically allowing moister to drain from the cylinders and into the crank case. Further more, if your tractor or old muscle car burns a quart of oil every fill up you just add more oil. If your airplane does you overhaul the engine. If your tractor or car is down 10-20 hp you likely will not notice, if your airplane is you will notice and rebuild.

There are very few catastrophic failures due to corrosion. Most of the time it is diminishing performance and oil consumption that lead to overhaul. Things you will live with in your car or tractor aren't worth the risk in an airplane.
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^^^ That. Plus if you remove weight as a constraint, you can make super stout engines with massive safety factors built in, but on our engines weight is key so the safety factor isn't nearly as high and thus it isn't as stout.
 
A man after my own heart. I've had this same thought as I have 70 yo engines that run 2 hours a year and 3yo engines that run 600 hours a year and everything in between.

Another thing I find interesting is that my big tractor has a 530ci engine that puts out a little over 300hp at 2000 rpm on 15 gph. Sounds a lot like an io-540, right?

I think the guys focusing on the difference between air cooled aluminum engines and water cooled iron engines are onto the answer wrt hours. For that matter, Mike Busch has something like 5 or 6 thousand hours on his engines....I think a lot of a/c engines are replaced before they need to be. Busch's experience also tends to show that the bottom ends will last a LONG time if cared for, it's generally just the cylinders that wear out. Considering the stresses the cylinder assemblies are subjected to, it's a wonder they last as long as they do.

Of course now that I've invoked Mike's name, this thread will derail violently.

The sitting issue is another he has addressed. The problem 95%of the time when an a/c engine sits is cam/ lifter corrosion. Most automotive engines have the cam in a place that oil from the head drips down and keeps it oily. Flat aero engines don't. A tiny spec of rust on a flat tappet can will destroy it in short order.

WRT zinc.....ZDDP is an anti-wear agent, I don't think it has anything to do with corrosion prevention. It was removed from auto oil because it, like lead, destroys catalytic converters. I would be shocked if it isn't still used in aero oil.
 
Weight of components has nothing to do with it. Design consideration to achieve high power/weight ratio? That's more correct. Horizontally opposed air cooled aircraft engines have high humidity exposure for cam and lifters. It's the nature of the beast. Rust never sleeps.

To the oil comment? Do some reading on the history of why we use ashless engine oils. Zinc is metallic and that means ash. Interesting topic. Application is everything. Where did the idea that the EPA is involved come from? We are talking about engines that burn leaded gas!
 
There are plenty of youtube videos showing camshaft/lifter failures in big diesel semis, that are driven thousands of miles a month. All engines have issues. Sadly aircraft engines seem to have more.

Dad's Allis 8030 busted a crankshaft once.

That being said, I just flew a 52 year old Lycoming O320 with three original cylinders, new mags, plugs, carb, harness and it ran great. I borescoped the cam lobes last year through the front of the crankshaft and found nothing. The oil filter cuttings are far cleaner than the O470 we have that was overhauled in 1995 which has less than half the hours on it. Like an old tractor this O320 uses oil... Curiously, three out of the 4 cylinders have oil wet bottom plugs every time I pull the plugs, except this year, now 2 out of the 4 have oil wet the plugs.
 
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I think the biggest difference is airplane engines have lots of aluminum. That, and if the tractor engine breaks you don't fall out of the sky and die.
 
Briar Rabbit said:
So why are airplane engines so darn fragile regarding sitting and corrosion?
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The reasons I've been told over the years centers around the engine design/ops and the materials used to achieve those 2 requirements. Since an aircraft engine is designed for light-weight, air-cooling, and continuous operations at a high percentages of max power, the materials used to produce this engine have a higher instance of corroding when not operated. It's also the reason different lubricants were designed for these engines. If you were to change the tractor design closer to the aircraft design, or operate it similarly, then you would start to see the same issues in your tractor as you do in your aircraft.
 
Might want to compare to VW and Porsche, rather than tractors. Horizontally opposed, wet sump, oil cooled engines. Weight a priority and some sit for quite some time. There was a Porsche engine option for Mooney for a short time. I had an older 911, think the main structural difference was overhead cam vs in the case. You could change cams without splitting the case. Hard core home mechanics would spend a lot of time searching for high zinc oils for the older engines.
 
Aircraft engines ARE 1930s tractor engines for the most part. Tractor engines we learned things and moved on. Aircraft engines, for various valid and invalid reasons, we didn’t.

Chuckling at those saying the “materials” are different without naming any of them, though. Not seeing any particularly extra sensitive to corrosion “materials” in either my airplane engine or my tractor engine.

Seen a lot of crappy camshafts on airplane engines online over the years though. Seems like that’s been an industry problem for a long time now. That said air cooled engines aren’t particularly nice to valves and valve guides, so camshafts sometimes take abuse they shouldn’t have.

Bottom ends tend to last equally as long on anything, generally.

There’s a reason we have screw on and off cylinders too. Farm kids used to pop one off the tractor or the airplane and replace by lunchtime before pulling a jug was considered a “Big Deal”(TM) in the modern world.
 
When you mix aluminum and iron and add moisture from blowby, you get lots of corrosion caused by electrolysis. Tractor engine have little aluminum and closer tolerances so there's less crankcase moisture and less electrolytic corrosion. Old tractors even had cast iron pistons, not aluminum.

And, as some of us keep pointing out, ground-running that aircooled engine puts moisture into the case that doesn't get driven out by elevated temps over time. You wreck that engine. I don't think too many tractors get that treatment; they're left alone as they should be.
 
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My tractor engine has common-rail EFI (at over 20K psi!), and a catalytic converter. And it weighs something like 18 lbs. per horsepower.
Oil for a lead-fuel-burning engine is generally different, oil for an air cooled engine is generally different, and oil for diesel vs. petrol engines are very slightly different.
Plus, most airplane engines are pure rubbish.
 
denverpilot said:
Chuckling at those saying the “materials” are different without naming any of them, though. Not seeing any particularly extra sensitive to corrosion “materials” in either my airplane engine or my tractor engine.
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There you go thinking again. Didn't actually think we had to spell it out, but there's always someone who didn't get the memo. :rolleyes: The materials*, i.e., the specific chemical make-up, mfg process (cast vs forged), heat-treatment, etc., that are used in air-cooled aircraft engines are different than the materials (see prior note) used in the manufacture of liquid-cooled tractor engines. For example, did you know the amount of carbon and other alloys in steel affect its corrosion resistance? Add in the use of dissimilar materials, i.e., steel vs aluminum vs magnesium, in aircraft engines and you multiply the corrosive effect by creating an environment ideal for a 2nd type of corrosion called galvanic which is basically non-existent on tractors. So, yes Virginia, it's all about the materials used.
*is a substance or mixture of substances that constitutes an object.
 
I never knew we had so many engine “experts” here. If everyone knows what the problem is, why hasn’t a solution been proposed? And why isn’t every post in this thread the same and everyone agreeing?
 
mondtster said:
I never knew we had so many engine “experts” here. If everyone knows what the problem is, why hasn’t a solution been proposed? And why isn’t every post in this thread the same and everyone agreeing?
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Because there is a really easy solution. Fly your damn airplane. Airplanes that are regularly flown don't tend to have issues like corrosion.
 
mondtster said:
I never knew we had so many engine “experts” here. If everyone knows what the problem is, why hasn’t a solution been proposed? And why isn’t every post in this thread the same and everyone agreeing?
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Ok. So we build an all-steel engine that weighs twice as much per hp. Or we make it all-aluminum, which presents difficulties with crankshaft strength and resistance to galling, and aluminum cylinders have never pleased anyone. Aluminum valves would last about 30 seconds. Or we somehow come up with a fuel that doesn't generate water as a byproduct of combustion, meaning that it either has no hydrogen in it or we don't use the oxygen from the air. Good luck with that. Or we build it as a liquid-cooled engine, which the Continental Voyager was, and it didn't sell. Expensive and heavier.
So do you have any ideas what we could do? People who complain that our technology is archaic are of two types: those who invent something better and those who complain without finding out why things are the way they are.
 
Dan Thomas said:
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So do you have any ideas what we could do? People who complain that our technology is archaic are of two types: those who invent something better and those who complain without finding out why things are the way they are.
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Quite frankly, The reason our engines are archaic is the FAA. Add to that the litigious society that we live in, and you just have a recipe for nothing new in certified aviation.
There are quite a few new and innovative designs out there in the experimental world, that we'll probably never see in the certified world Because of the FAA.
 
For those that don’t buy the difference in newer technology and air cooled vs water cooled look no further than the Rotax 9 series. Those guys don’t face the same issues traditional aircraft engines do. Their cylinder are similar to chrome cylinders.
 
mwagg737 said:
The reason our engines are archaic is the FAA.
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Not necessarily. The Feds have been streamlining the certification processes in recent times and have fast tracked others. Just look at the Part 23 rewrite. The main issue is the market in which to sell it. No one is willing to bet major $$$ on a new engine if there is no market to return their investment. Just look at the limited engine conversion market and they're using existing engines. So it's more a supply and demand issue than certification issue as Rotax did with several of their models.
 
If Rotax brings out a 180-200 hp engine that’s competitive price and weight to a LyCon they will steal the market.
 
Bell206 said:
There you go thinking again. Didn't actually think we had to spell it out, but there's always someone who didn't get the memo. :rolleyes: The materials*, i.e., the specific chemical make-up, mfg process (cast vs forged), heat-treatment, etc., that are used in air-cooled aircraft engines are different than the materials (see prior note) used in the manufacture of liquid-cooled tractor engines. For example, did you know the amount of carbon and other alloys in steel affect its corrosion resistance? Add in the use of dissimilar materials, i.e., steel vs aluminum vs magnesium, in aircraft engines and you multiply the corrosive effect by creating an environment ideal for a 2nd type of corrosion called galvanic which is basically non-existent on tractors. So, yes Virginia, it's all about the materials used.
*is a substance or mixture of substances that constitutes an object.
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All true but folks are pretending those things are the reason for the two most common failures... valves breaking, and crankshaft damage.

It’s pretty rare to see other things affecting aircraft engines before other parts wear out from use. Occasional cracked cylinders in third place.

I don’t know any source of solid stats on the above but would be interested to see if folks see other common failures more prevalent than those without turbocharging being involved.
 
denverpilot said:
I don’t know any source of solid stats on the above...
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FWIW: There's quite a bit of statistics on recip engine failure modes out there. The FAA publishes analysis reports (FMEA) on recip engine failure modes on occasion which are also discussed in an AC. Plus there are various other in depth reports out there as well. I couldn't get my FAA FMEA report to link but linked another similar type report (except higher Hp/Turbo) below from the ATSB if you wish to read. I also pasted a table from another report that I don't have permission to link but it shows a different view on how failure modes are classified.

https://www.atsb.gov.au/media/29980/b20070191.pdf

upload_2020-2-20_17-0-53.png
 
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Matthew Rogers said:
Or.......Rotax? Liquid cooled, lighter, cheaper.
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Apples to oranges. The Rotax is geared, Lycs and Conts are direct drive except for a very few odd models. A smaller engine turning at a higher RPM can generate more power with less weight, but now you have the extra failure point of gearing, though Rotax seems to have that under control.

Homebuilders often use auto engines that were designed to produce their power at high RPMs, so they use redrives---gears, belts, whatever---to let the engine spin up while staying within the limits of the prop. I installed a Subaru 2.2 in a Glastar; it had a timing-belt redrive so the engine could hit redline at 5600 and the prop maxed at around 2500. Flew OK, but if I tried to cruise at the same ratio I would have with a Lyc (2700 redline, 2500 cruise, about .93 ratio) I'd have to run the engine at nearly 5200, and it hated that. It used a lot of fuel, even leaned, and the noise was awesome. So I cruised at 4600 and acepted a 110 MPH cruise instead of the 135 a Lyc O-235 would have given me. About the same HP.
 
Bell206 said:
FWIW: There's quite a bit of statistics on recip engine failure modes out there. The FAA publishes analysis reports (FMEA) on recip engine failure modes on occasion which are also discussed in an AC. Plus there are various other in depth reports out there as well. I couldn't get my FAA FMEA report to link but linked another similar type report (except higher Hp/Turbo) below from the ATSB if you wish to read. I also pasted a table from another report that I don't have permission to link but it shows a different view on how failure modes are classified.

https://www.atsb.gov.au/media/29980/b20070191.pdf

View attachment 82918
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Timing belt?
Battery causing power loss?

This table doesn’t look sane for the light GA aircraft we’re talking about???
 
Question about tractor controls... Is it true that closed throttle is full forward and full throttle is full back? Zero actual tractor time (beyond sitting on Grandpa's lap as a kid) but it seems every student I have had that grew up driving tractors has an ingrained muscle memory to pull back on the throttle at the EXACT wrong time... Makes go-arounds very interesting. :(
 
smv said:
Question about tractor controls... Is it true that closed throttle is full forward and full throttle is full back? Zero actual tractor time (beyond sitting on Grandpa's lap as a kid) but it seems every student I have had that grew up driving tractors has an ingrained muscle memory to pull back on the throttle at the EXACT wrong time... Makes go-arounds very interesting. :(
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Not on mine, but couldn’t tell ya if it’s normal.

There’s a throttle pedal and it’s linked to a lever that forward is full throttle. Pedal returns to wherever the lever is set at when you release it.
 
I’ve not driven many tractors but the ones I have driven full power is full forward on the throttle lever
 
denverpilot said:
This table doesn’t look sane for the light GA aircraft we’re talking about???
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Table is for recip GA aircraft less than 12,500lbs. You can add "coolant system" to your improbable list as it covered all types of recip aircraft regardless of category. And as an FYI, if the battery faults it can cause a voltage drop in the electrical system, which can/will cause a voltage drop to the ignition system, which can/will cause the less than ideal spark, which can/will cause a power reduction due to improper fuel/air ignition in the cylinders................;)
 
smv said:
Is it true that closed throttle is full forward and full throttle is full back?
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Specific to tractor, especially when operating older tractors.
 
schmookeeg said:
I assumed that table was in regards to auto conversions for E-AB or STC
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Sure what it looks like. Thought we were talking standard certified engines and the typical spamcan...?

Bell206 said:
Table is for recip GA aircraft less than 12,500lbs. You can add "coolant system" to your improbable list as it covered all types of recip aircraft regardless of category. And as an FYI, if the battery faults it can cause a voltage drop in the electrical system, which can/will cause a voltage drop to the ignition system, which can/will cause the less than ideal spark, which can/will cause a power reduction due to improper fuel/air ignition in the cylinders................;)
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My ignition system works just fine without a battery. :)
 
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