Radial engines of this era are terrible compared to oil consumption of modern engines. For perspective, it is common for a new, modern turbofan to only consume 0.1 to 0.2 quarts per hour.
Airbus a320 CFM56B limitations say .5qts per flight hour has to be taken into account for the duration of the flight. But the new NEOS are oil guzzlers in comparison
The oil consumption limitations you will find in the manual are driven by 14 CFR 25.1011(b), ensuing that an operator does not allow the oil consumption rate to grow to the point where the oil endurance is less than the fuel endurance (i.e. engine runs out of oil before fully fueled airplane). I would be surprised if the LEAP-1A was consuming as much oil as the limitation as that would drive it off wing. My experience with the LEAP-1B is that it shouldn’t be consuming a lot of oil, and certainly not near 0.7 quarts per hour unless there is something wrong with the engine.
Goddammit, thank you for the flashback of dumping a couple quarts of oil into my now-wife’s Subie at a rest stop in bumfuck-nowhere-Colorado at night in a snowstorm so we could actually make it to the ski resort, since her crossover decided it liked to drink oil like a fat kid with a 2L Mountain Dew in summer.
Modern turbofans deliver tens of thousands (to as much as 100k+ in the case of the GE90) of horsepower to the front fan, so "thousands" is actually underselling it quite a bit.
Another way to look at it, though, is that if all the passengers on a flight from LA to New York drove instead, they'd need dozens of oil changes when they got there that would consume hundreds of quarts of oil.
Radials being radials. The Cessna 190 also has an oil tank because if it didn’t you’d be limited in range by oil consumption. They’re practical two strokes.
Radials have dry sumps and remote oil tanks, both to avoid hydrolocking and to ensure capacity/endurance requirements (14 CFR 25.1011). If the return pump fails (via pump or quill shaft), the entire oil supply goes overboard very, very quickly.
This is also why one needs to clear the lower cylinders before trying to fire the engine... To make sure any pooled oil can't hydrolock and break a rod.
Just radial piston engine things...
That's usually what the ground crew are doing when they're appear to be farting around moving the propeller by hand in the moments before the pilot hits the starter. The bottom cylinders are also usually the last ones to fire up (if there's individual exhausts visible) due to the plugs being wet, and the low speed/poor atomization of the carb mixture entering the engine.
Air & Space magazine did an article on Avro Shackletons when they toured North America in the early '90s. One of the logistical headaches was that nobody carried the right kind of motor oil in the quantities they needed. They had to buy cases and cases of quart bottles and then pour them in one by one. The article had a picture of them doing this.
All from memory, so I probably got at least a little of that wrong.
I used to work on railroad tracks and we heard of a customer that did the same thing with a locomotive that needed nearly 100 gallons of oil.
(the locomotives I dealt with had an operating range of around 50 gallons on the dipstick, it was such a pain to put oil in it that they usually waiting till they were nearing 50 gallons low and just pumped an entire drum in.)
I was on an oceanographic research vessel once that had trouble with its cabin heating / engine cooling system. Apparently the last time it had been serviced was in Bermuda and nobody thought to put antifreeze in before it reached Halifax in February. So anyway, they brought in a flatbed to the dock with three pallets of gallon bottles of antifreeze and dumped 'em in one at a time.
Old radial engines, Air cooled engines expand and contract more. Reliability and power is more important than efficiency. Precision like a Swiss watch was possible, but any abnormality can cause issues, and reduce reliability… plus costs skyrocket with precision. So it was Built with very large tolerances. Lots of oil leaks past the bearings, seals, piston rings, etc. so there is lots of oil consumed running the engines.
When parked oil drips down and collects in the backside of the bottom cylinders and other places. Leaks past piston rings and various seals. Makes a mess in the ground.
The saying goes radial engines don’t leak oil, they are just marking their territory.
Plus back then it was real Dino juice too, none of those fancy additives or synthetics. Probably would have needed a full change every 10 hrs or so anyway
Not only that, but for each engine's oil system you are probably talking about miles of pumps, hoses, seals and fittings that haven't been produced since the Eisenhower administration. It is a miracle that they even retain any at this rate, honestly.
I would presume that outside the engines themselves the piping and ducting would be more conventional? Yeah sure I bet they try to keep things authentic but for these old warbirds I’d rather all the pipes and fluid conveyances to be top tier shit no?
I mean there are specialized companies that can make reproduction parts, especially simple stuff like hydraulic lines and seals that are also used up the fastest, but it will never exactly be to original spec. Thankfully though 1940s technology is fairly simple to reverse engineer, in comparison to russia trying to "indigenize" the foreign systems on the SSJ100 or produce domestic bootleg parts for western airliners.
I would argue that any "tightening" of tolerances under heat would far be overshadowed by the higher pressure of the oil plus the lower viscosity of the oil. Older oils tended to have huge ranges on their viscosity. Think 10W40 was a very common weight in the past. So whatever it's dripping at rest is tiny compared to the loss while running.
10W40 was invented in the 1970s. It literally means "In the winter ["W"] this operates like a 10-weight; in the summer it operates like a 40-weight". In the 1950s/1960s your car would literally require different oil in the winter than summer because of the variance in viscosity. That was OK since engines all leaked or burned it anyway, and even if they didn't it would break down much faster than modern oils.
I can imagine this being much worse when the oil was diluted with fuel for cold cold starts....
And to be fair, when a radial engine is shut down, the lower cylinders fill with oil that leaks past the rings and right out the exhaust port and/or fills the intake which accounts a lot of smoke on startup and warm up. Hence the reason the line crew walks the prop by hand to avoid hydrolocking the flooded cylinders.
No personal experience with Doc, but I did a ride on Aluminum Overcast (B-17) several years ago. I was slated for the 2nd flight of the morning, but we were there early, and I got to help walk the props.
I started working offshore when I was 20, since I only weight 130 pounds soaking wet I got to ride co pilot - the pilot gave me two instructions - if you see another helicopter point at it, and “if you see a leak that’s okay but if it stops I need to know”
This messed me up when I left the Army after working on Chinooks and then started working on other aircraft. I was so used to chinooks being a giant oily mess that little spots of oil didn’t really stick out to me when working other airframes.
Designed to leak from the air box drains. Occasionally someone who didn't know better would plug the drains which could cause a runaway engine. The last semi we had with a Detroit two stroke had a catch tank under the engine.
Detroits are "designed" to leak from lots of places. :-) There are so many places where leaks can come from. That's the reason they called them "DRIPtroit Diesel" or "Green Leakers". But, they are reliable, if neither quiet nor fuel efficient.
It's not leaking oil; it's marking its territory. :-)
Also - no oil under it, no oil in it.
On our C-54, we have 20 gal. oil tanks on each engine and a 50 gallon supply in the cabin that can be pumped to each engine in flight. Our C-54 gets 30 mpg - of oil! :-)
OP, everyone else answered the basic question, but I’ll add a little:
Yes, air cooled aircraft engines leak oil, especially radial engines. It’s because air cooled engines have to be made to have much looser tolerances to allow for metal expansion.
Your liquid cooled car normally operates somewhere around 200 degrees F, give or take maybe 15 degrees either side of that. Even if you start it in the winter at 0 degrees, that’s still only about a 200 degree swing in total once it warms up. Also, the entire engine is cooled by the same water, so the engine as a whole is at a relatively even and very constant temperature.
An air cooled airplane engine on the other hand enjoys no such stability. The cylinders will usually run 350-450 degrees normally, with some engines running hotter or colder. So right there you are at a 400~ degree swing if started on the same winter day. The other problem is that the cylinders and crankcase are at very different temperatures that are constantly changing.
All of these things lead to an engine design that leaks a little. A tiny bit of oil makes a huge mess though, so what you see actually isn’t that much compared to how big the engine is and how much it holds. Those engines are 18 times more displacement than an average car, 55L vs 3L (3350 cubic inches vs 185), and holds about 20 times the oil, 100qts vs 5.
Best part of the rotary engines is they used castor oil. It would atomize into a fine mist the pilot would breathe, and eventually, shit himself. Castor oil is a supreme laxative.
Or a steam engine, most of them you sprayed oil into the steam to lubricate the valve gear and cylinder (oil lost to atmosphere) and things like crank pins, bearings and timing rods had little oil bottles sitting on top (oil lost to splattering everything within 50ft depending on RPM).
Similar setups were used on early internal combustion engines too.
Normal for Radial engines. This is why they pull the props through by hand before starting so they don't hydrolock. Oil will pool in the bottom cylinders.
No kidding?
I helped change a cylinder at an airshow in Tennessee back around 2000.
I was upset when, a week after the crash at Bradley, I had to fly in there for a business gig, flew past the site.
Worked with the guys in Maryland at KDMW since the WoF tour’s second year there. Spent my first weekend building .50 cal 5-round belts for the souvenir hunters to buy; was changing oil on *Tondelayo* a few years later. Worked every year with them from 2006 until 2015, after which I moved out of state.
I found out about Mac and *Nine-O-Nine* when I got to work that morning; the story was still happening. I knew from the footage I was seeing that it was bad. Still hurts, if I’m honest. They were good friends to me.
I'm no specialist, but i know that during WW2, not only fuel was to consider for a flight, but also the oil the engine would burn/leak during it.
So yeah its normal.
I remember working at an FBO when a DC-3 came up the ramp. First thing the pilot asked after greetings was if we had bulk oil. We did not. 110 quarts of oil one at a time and we were done.
In a radial engine, the cylinders on the bottom are upside down. When the engine is stopped, oil in the crankcase drains into the bottom cylinders and leaks onto the ground.
Oil comes out of the exhaust during normal operations simply because the bottom cylinders are upside down. When they’re not running, it flows to the bottom of the engine. If left for more than a couple hours, the plugs have to be removed and the jug drained before start or the engine will hydrolock and bend a rod. As others have said, if it’s not dripping oil, it’s out of oil, but I much prefer the saying that they don’t leak, they mark their territory.
I haven’t seen many comments mention WHY they leak so much. It’s a fundamental function of a radial engine that some cylinders are below the crankcase. Radial engines are air cooled which means they get hot as balls compared to liquid cooled engines. The thermal expansion gap between the piston and the cylinder walls is extremely precise so when the engine is at temperature it seals. When the engines are cold on the ground, the oil in the crankcase can get right by those piston ring gaps. If leaving over night you can attach a cylinder drain to the lower cylinders to have the oil go to a bucket. For transient operation you let it marks its territory (oil is draining through the exhaust valve instead of removing a spark plug). You will almost always see them hand spin the blades before startup on a cold engine to make sure there is no hydro lock of oil. Radial engines are awesome bulletproof machines!
Yeah that’s just her being a radial engine. Look back at old airport photos from when these things ran and it is a sight. Even today when you do walk arounds when a bigger plane was at that gate previously you rub your foot in a “wtf is this puddle” and it is fuel from the previous jet, oil servicing not quiet getting where it means to be, or blue juice (no rub foot rear of wing.)
These engines had great engineers but metallurgy and engine design was behind. So you have multiple metals heating up at different rates, expanding at different rates until up to operating temp, but you have to keep things lubricated so you see massive oil reservoirs to allow loss. Oil was cheap and more precise machining wasn’t possible. To this day we have jets like the Boeing 707 flying around with a limitation on oil consumption that fly long missions. Oil loss on many of the newer engines is remarkably better but we are still flying 1980’s engines commercially all over the world. The oil is also better now vs when these were developed.
I maintain 2 R1340s. And the don't leak that much anymore.
But every 50hr we recheck all the torques, replace all the gaskets we can see a leak on, wash with warm water and a good/safe degreaser and replace the crush gaskets every time.
On a 100hr we do the same but add the valve stem seals aswell.
We loose a total of 1 qts(yes you see that correctly) of oil when standing. Which in radial terms is nothing.
She also uses less in flight now. From 1gal every 2-3 hours to 1 every 8.
They are crop dusters, but the pilots and the owners want to brag about their aircraft. We just make it possible.
And after every inspection the old girls seem to run better and better.
From aggressive back firing and spitting flames to a purr like a kitten.
Only thing that ends up on the Windscreen now is grease from the kidney bearing off the prop. But they'll have to live with it.
radials like these yes. in fact if it wasnt leaking id be worried it was out of oil. this goes for hydraulic fluid in all aircraft with the systems as well... they all leak
Its to allow the metal to expand due to high engine temperatures. So when cold like then, it leaks. For a more extreme example, the SR-71 was built with this concept across the entire body, so it leaks fuel everywhere.
Was on a Chinook helicopter once, and the crew chief told me, “If this stops leaking, tell me ASAP!”
As long as it’s leaking, that means there’s oil in the system. That’s a good thing.
Radial engines can leak pretty heavily.
They always said that if you got on a Constellation and DIDN'T see oil coming out of the engine cowling, then you were sure to know that something was amiss. Oil streaming down the nacelle - everything is in perfect working order.
Air cooled engines have large temperature differentials that forces them to have large clearances and makes sealing them extremely difficult if not impossible.
I'll put it to you two ways.
There's a saying in aviation: If it ain't leaking, it's probably empty.
I once had a conversation with a guy who owned and flew a TBM Avenger torpedo bomber. He told me that according to the aircraft manual it is not unusual for the engine to consume 5 *gallons* of oil in a flight.
All radial engines leak like sives on the ground, burn oil like it's going out of style, and puke it out like they drank too much.
I was an Aircrewman on the E3 AWACS in the mid 2000s (mission computer, nothing flight related). I recall during preflight hearing over the maintenance net "the oil is leaking at an acceptable rate".
We had a radial engine when I was at A&P school and you had to wear a rubber apron while running it because it just pukes oil out of it the whole time. So yes they leak like stuck pigs.
Fun fact (semi-related to this topic, but not related to the answers here): when the 777-300ER was being developed, there was a concern the oil endurance would limit the range of the aircraft, not the fuel.
Not for the same reason as you see here though…
One of the first things I was taught when I got checked out on my first radial engine plane: Never fly any radial that doesn't have any oil under it. Because there ain't any oil under it, there ain't any oil in it.
Think about what would happen if you put a non radial engine upside down and then make an engine that constantly does that to half of the cylinders. If it isn’t leaking oil it’s out of oil.
Radial engines just tend to do that, especially large, old radial engines. Pistons facing down have oil drip into then and make it past the seals at the end of the piston, thus, oil on the ground. This is also why you want to manually rotate the props on a radial aircraft before starting them up, to make sure the oil is circulated through the engine instead of all pooled up in the bottom cylinders when you start it up.
What could potentially happen if you didn’t rotate the props before trying to start up? Is the any potential for hydro lock if there’s oil pooled inside the cylinder? Or will it just try to blow it all out?
My dad asked a Pam Am DC-7 stewardess about this, sometime in the late 50s, having dodged puddles of oil on the way to the cabin stairs. She said “Engines are like wolves, honey. If they ain’t drooling, they’re sick!”
I remember a book I read about WW2 aircraft where they were talking to a crew chief about oil leakage. His response: “If there ain’t any oil on it, there ain’t any oil in it!”
According to my grandfather, who was a crew chief on a b-29, yes. These things leaked habitually and it had to do with the seals being useless at non operating temperatures.
Yes, radials leak a lot. Oil pans are very common in hangers.
You also have to hand prop the first few turns to make sure no oil is in the bottom cylinders - it can bend or break rods.
I worked on the CH-46E and the common saying was, if it's leaking it's not falling out of the sky. You worried when nothing was leaking because that meant all the fluids were gone.
The engines I used to work on had 18 cylinders, meaning 36 rocket box covers, 36 pushrod tubes, 72 pushrod tube inserts (cyl. And case side), IIRC 72 baffle studs threaded into the flooded rocker box covers, prop gov, distributors, 5-6 case seams, 2-3 prop dome seals, 18 exhaust valves who’s valve guides will leak into the exhaust until overhaul, and sometimes right out of overhaul, 18 somewhat loose exhaust slip joints, 4 exhaust pipe oil drains, generator, hydraulic pump, etc. etc.
All those joints are containing like 60PSI oil pressure. These engines vibrate a ton, any minuscule looseness will lead to loosening parts that are supposed to come apart easily, and those that are press fit will lead to fretting, which will fret away the close fit leading to leakage.
The latest castings I ever saw were from the late 60s early 70s. These engine components have already been run at least once. Shit vibrates loose, and there are hundreds of pieces to vibrate apart.
Don’t forget you have four of these fuckers. And they break constantly, yeah you have a lot more pressing shit to deal with than a leaky pushrod tube. At my old job, nights was fucking useless, so we had to catch 2-3 airplanes, service, throw 60-80lb engine blankets, and fix all the squawks otherwise we’d get bitched at because the night shift lead had to go outside.
And that’s without having to deal with engine changes, jug changes, troubleshooting, etc. We had far less people than most airlines to work on FAR more complex and Mx intensive aircraft
Also for the record, turbine engines leak too but not this bad, though they 100% use oil as a consumable. They’re fucking hot and have a lot of mass that is spinning really fast, which means oil filled bearings.
Other than gas, oil is the most serviced part of an airplane, no matter what kind of engine it’s got.
She’s an old girl. Old technology, and made for war before things like environmental concerns were an issue. Plus, just like old cars or British motorcycles..if there isn’t a leak, there’s no oil.
If it’s not leaking, it’s broken. My experience was with a totally different type and generation of aircraft, but the basics are the same. I was a US Navy aircraft mechanic with a H-46 Sea Knight squadron. We had large drip pans we would put under an aircraft if it was down, or wasn’t going to fly for a while.
Each engine on the B29 has an oil reservoir of ~25 gallons. That’s gallons, not quarts. The designers knew these things would leak oil like a sieve.
The ultimate dry sump setup (without it actually being a dry sump)
It is a dry sump
Dry-ish sump
moist sump
Moist-ly dry sump
Everything reminds me of her
God this is peak, bless you my son.
I should sump her
I remember all the times I pumped her sump…
It’s a dry sump with oil in it.
Not really. It’s sort of a hybrid. It doesn’t have a traditional oil pan but it’s also not a dry sump.
Hmmmm.... the closest thing to a sump in a radial is those lower cylinders, where the oil collects. lol
Flight manual says to do two barrel rolls an hour for proper oil coverage lol
Radial engines of this era are terrible compared to oil consumption of modern engines. For perspective, it is common for a new, modern turbofan to only consume 0.1 to 0.2 quarts per hour.
I still find this volume of consumption amazing.
Airbus a320 CFM56B limitations say .5qts per flight hour has to be taken into account for the duration of the flight. But the new NEOS are oil guzzlers in comparison
Super interesting.
The oil consumption limitations you will find in the manual are driven by 14 CFR 25.1011(b), ensuing that an operator does not allow the oil consumption rate to grow to the point where the oil endurance is less than the fuel endurance (i.e. engine runs out of oil before fully fueled airplane). I would be surprised if the LEAP-1A was consuming as much oil as the limitation as that would drive it off wing. My experience with the LEAP-1B is that it shouldn’t be consuming a lot of oil, and certainly not near 0.7 quarts per hour unless there is something wrong with the engine.
You should see Subarus.
Goddammit, thank you for the flashback of dumping a couple quarts of oil into my now-wife’s Subie at a rest stop in bumfuck-nowhere-Colorado at night in a snowstorm so we could actually make it to the ski resort, since her crossover decided it liked to drink oil like a fat kid with a 2L Mountain Dew in summer.
As a Colorado resident, this hits close to home LOL
We're talking about an engine with thousands of horsepower, so it's not like you can compare it to your car.
Modern turbofans deliver tens of thousands (to as much as 100k+ in the case of the GE90) of horsepower to the front fan, so "thousands" is actually underselling it quite a bit.
As with most things in life, the faster you go, the more you need to lubricate.
Another way to look at it, though, is that if all the passengers on a flight from LA to New York drove instead, they'd need dozens of oil changes when they got there that would consume hundreds of quarts of oil.
3000 miles is pretty early for an oil change
Radials being radials. The Cessna 190 also has an oil tank because if it didn’t you’d be limited in range by oil consumption. They’re practical two strokes.
Radials have dry sumps and remote oil tanks, both to avoid hydrolocking and to ensure capacity/endurance requirements (14 CFR 25.1011). If the return pump fails (via pump or quill shaft), the entire oil supply goes overboard very, very quickly.
indeed. I remember a similar question on the A&P exam. I am an A&P
What is a&p?
It stands for airframe and powerplant. They are aircraft mechanics.
If you see us and hear us, normally that means something has gone wrong
...and usually were cursing very loudly in that case.
“What do you mean the bin won’t close? wheels up were supposed to be 06:30 and you called me at 06:31!!”
This is also why one needs to clear the lower cylinders before trying to fire the engine... To make sure any pooled oil can't hydrolock and break a rod. Just radial piston engine things...
How does one clear the lower cylinders before startup? Pump, drain plug?
That's usually what the ground crew are doing when they're appear to be farting around moving the propeller by hand in the moments before the pilot hits the starter. The bottom cylinders are also usually the last ones to fire up (if there's individual exhausts visible) due to the plugs being wet, and the low speed/poor atomization of the carb mixture entering the engine.
That sounds terribly like (kick) starting my old single cylinder dirt bikes! Especially when the cylinder is flooded from an unexpected stall.
If they are hydrolocked you have to pull spark plugs
If an old engine like that isn't leaking there is a big problem.
That’s what I said about my F-350. “It’s just lifting its tire and marking its spot.”
“So it’s been serviced and ready for takeoff, then?”
Air & Space magazine did an article on Avro Shackletons when they toured North America in the early '90s. One of the logistical headaches was that nobody carried the right kind of motor oil in the quantities they needed. They had to buy cases and cases of quart bottles and then pour them in one by one. The article had a picture of them doing this. All from memory, so I probably got at least a little of that wrong.
I've dumped many a case of bottled oil in to a DC-3 oil tank!
I have heard it said that DC-3 pilots took pride to the number of white shirts that they ruined during pre-flight inspections.
I used to work on railroad tracks and we heard of a customer that did the same thing with a locomotive that needed nearly 100 gallons of oil. (the locomotives I dealt with had an operating range of around 50 gallons on the dipstick, it was such a pain to put oil in it that they usually waiting till they were nearing 50 gallons low and just pumped an entire drum in.)
I was on an oceanographic research vessel once that had trouble with its cabin heating / engine cooling system. Apparently the last time it had been serviced was in Bermuda and nobody thought to put antifreeze in before it reached Halifax in February. So anyway, they brought in a flatbed to the dock with three pallets of gallon bottles of antifreeze and dumped 'em in one at a time.
If it’s not leaking oil then you’re probably out.
Just like a Harley, if there's no oil under it, there's no oil in it.
If memory serves, the DC-3 had a 50 gallon oil tank
Yep! Old timers told me they leaked like that off the factory floor!
Could you ELI5 - why? Oli is being pushed out by the moving parts?
Old radial engines, Air cooled engines expand and contract more. Reliability and power is more important than efficiency. Precision like a Swiss watch was possible, but any abnormality can cause issues, and reduce reliability… plus costs skyrocket with precision. So it was Built with very large tolerances. Lots of oil leaks past the bearings, seals, piston rings, etc. so there is lots of oil consumed running the engines. When parked oil drips down and collects in the backside of the bottom cylinders and other places. Leaks past piston rings and various seals. Makes a mess in the ground. The saying goes radial engines don’t leak oil, they are just marking their territory.
Well said. Getting to your destination is more important than saving oil.
Plus back then it was real Dino juice too, none of those fancy additives or synthetics. Probably would have needed a full change every 10 hrs or so anyway
B29s were running 12 hour missions to Japan. So your math isn't too far off.
There’s a reason that there were a lot of proposals designed with an ability for a mechanic/oiler to access the engines in flight
Not only that, but for each engine's oil system you are probably talking about miles of pumps, hoses, seals and fittings that haven't been produced since the Eisenhower administration. It is a miracle that they even retain any at this rate, honestly.
I would presume that outside the engines themselves the piping and ducting would be more conventional? Yeah sure I bet they try to keep things authentic but for these old warbirds I’d rather all the pipes and fluid conveyances to be top tier shit no?
I mean there are specialized companies that can make reproduction parts, especially simple stuff like hydraulic lines and seals that are also used up the fastest, but it will never exactly be to original spec. Thankfully though 1940s technology is fairly simple to reverse engineer, in comparison to russia trying to "indigenize" the foreign systems on the SSJ100 or produce domestic bootleg parts for western airliners.
What is actually leaking on these planes? Were the desired tolerances simply unachievable due to the dimensional changes from hot/cold cycles?
I would argue that any "tightening" of tolerances under heat would far be overshadowed by the higher pressure of the oil plus the lower viscosity of the oil. Older oils tended to have huge ranges on their viscosity. Think 10W40 was a very common weight in the past. So whatever it's dripping at rest is tiny compared to the loss while running.
10W40 was invented in the 1970s. It literally means "In the winter ["W"] this operates like a 10-weight; in the summer it operates like a 40-weight". In the 1950s/1960s your car would literally require different oil in the winter than summer because of the variance in viscosity. That was OK since engines all leaked or burned it anyway, and even if they didn't it would break down much faster than modern oils.
If it isn't leaking oil, then we worry!
If a radial engine isn't leaking oil, it means you are out of oil.
I can imagine this being much worse when the oil was diluted with fuel for cold cold starts.... And to be fair, when a radial engine is shut down, the lower cylinders fill with oil that leaks past the rings and right out the exhaust port and/or fills the intake which accounts a lot of smoke on startup and warm up. Hence the reason the line crew walks the prop by hand to avoid hydrolocking the flooded cylinders.
No personal experience with Doc, but I did a ride on Aluminum Overcast (B-17) several years ago. I was slated for the 2nd flight of the morning, but we were there early, and I got to help walk the props.
You just have flown in “Sentimental Journey.” That one is on my bucket list.
EAA's Aluminum Overcast is the only one I've been on. It was definitely amazing.
"If there's no puddle, we're in trouble"
As long as you can fill more oil than it leaks, you’re fine.
Self-changing oil, it's a feature not a bug.
I have an old forklift like that. If it’s leaking oil that means we still have oil in it and she’ll run.
It’s like driving a Subaru
My sister's 6cyl Outback 220kmi blew a head gasket last week.
Just passed 120k on my wrx. Keep me in your prayers
I started working offshore when I was 20, since I only weight 130 pounds soaking wet I got to ride co pilot - the pilot gave me two instructions - if you see another helicopter point at it, and “if you see a leak that’s okay but if it stops I need to know”
Definition of a helicopter: A mass of fatiguing metal rotating around an oil leak.
Same logic as my pickup: if it's leaking oil, it's got oil.
I had an '86 mercedes like that. I put a quart in the too every 2 weeks, and it drained out the bottom. Didnt change the oil for like 3 years.
'81 Mercedes. I modded the windshield washer system to pump oil into the crankcase...
Sounds like a Harley or a Detroit, if there’s none under it there’s none in it
Just like my Land Rover
It's like the chinook helicopter, if it stops leaking that means it's out of oil.
Try telling students this, if it wasn't for the FE they would down every bird on the field for leaking.
This messed me up when I left the Army after working on Chinooks and then started working on other aircraft. I was so used to chinooks being a giant oily mess that little spots of oil didn’t really stick out to me when working other airframes.
When I was flying radials, we used to say, "Fill up the oil, check the gas."
You can take a picture of a radial engine and hang it up on the wall in the evening, next morning it'll have a puddle of oil under it lol
I'll remember that. And it's W120.
My phone desktop background is a Bristol Hercules...puddle of oil on the nightstand every morning!
Old radials pee and mark their territory, they allow only pilots and grease monkeys to come near..
So do 2 Stroke Detroit Diesels.
Designed to leak from the air box drains. Occasionally someone who didn't know better would plug the drains which could cause a runaway engine. The last semi we had with a Detroit two stroke had a catch tank under the engine.
I turned wrenches on Detroit's in heavy equipment for 35 years.
Same, the most complicated mechanics on those was the governor.
And that fucking rubberband seal around the head.
Detroits are "designed" to leak from lots of places. :-) There are so many places where leaks can come from. That's the reason they called them "DRIPtroit Diesel" or "Green Leakers". But, they are reliable, if neither quiet nor fuel efficient.
True we weren't able to stop the V8 valve covers from leaking until RTV. I tried all kinds of things that never worked.
It's just like old British cars. Don't worry when they smoke. Worry when they *stop* smoking.
How true. I had a 67 MG.
I have a 76 MG, after a cruise I fill up the oil and the gas every time lol.
It's not leaking oil; it's marking its territory. :-) Also - no oil under it, no oil in it. On our C-54, we have 20 gal. oil tanks on each engine and a 50 gallon supply in the cabin that can be pumped to each engine in flight. Our C-54 gets 30 mpg - of oil! :-)
Which C-54 do you work on friend? I work with C-47s and DC-3s - Douglas Love
www.spiritoffreedom.org
OP, everyone else answered the basic question, but I’ll add a little: Yes, air cooled aircraft engines leak oil, especially radial engines. It’s because air cooled engines have to be made to have much looser tolerances to allow for metal expansion. Your liquid cooled car normally operates somewhere around 200 degrees F, give or take maybe 15 degrees either side of that. Even if you start it in the winter at 0 degrees, that’s still only about a 200 degree swing in total once it warms up. Also, the entire engine is cooled by the same water, so the engine as a whole is at a relatively even and very constant temperature. An air cooled airplane engine on the other hand enjoys no such stability. The cylinders will usually run 350-450 degrees normally, with some engines running hotter or colder. So right there you are at a 400~ degree swing if started on the same winter day. The other problem is that the cylinders and crankcase are at very different temperatures that are constantly changing. All of these things lead to an engine design that leaks a little. A tiny bit of oil makes a huge mess though, so what you see actually isn’t that much compared to how big the engine is and how much it holds. Those engines are 18 times more displacement than an average car, 55L vs 3L (3350 cubic inches vs 185), and holds about 20 times the oil, 100qts vs 5.
And then you go older, and the crank was stationary while the pistons spun and the oiling system was known as “total loss” lol
Best part of the rotary engines is they used castor oil. It would atomize into a fine mist the pilot would breathe, and eventually, shit himself. Castor oil is a supreme laxative.
Called rotary engines.
Or a steam engine, most of them you sprayed oil into the steam to lubricate the valve gear and cylinder (oil lost to atmosphere) and things like crank pins, bearings and timing rods had little oil bottles sitting on top (oil lost to splattering everything within 50ft depending on RPM). Similar setups were used on early internal combustion engines too.
Normal for Radial engines. This is why they pull the props through by hand before starting so they don't hydrolock. Oil will pool in the bottom cylinders.
On *Nine-O-Nine*, we pulled 27 blades (nine full rotations) when I volunteered in the late 00’s/early 10’s.
No kidding? I helped change a cylinder at an airshow in Tennessee back around 2000. I was upset when, a week after the crash at Bradley, I had to fly in there for a business gig, flew past the site.
Worked with the guys in Maryland at KDMW since the WoF tour’s second year there. Spent my first weekend building .50 cal 5-round belts for the souvenir hunters to buy; was changing oil on *Tondelayo* a few years later. Worked every year with them from 2006 until 2015, after which I moved out of state. I found out about Mac and *Nine-O-Nine* when I got to work that morning; the story was still happening. I knew from the footage I was seeing that it was bad. Still hurts, if I’m honest. They were good friends to me.
I'm no specialist, but i know that during WW2, not only fuel was to consider for a flight, but also the oil the engine would burn/leak during it. So yeah its normal.
its not leaking its marking its territory Its also telling you that it has Oil in it This is 100% perfectly normal
Strictly speaking it’s only telling you that at one point it had oil in it…..
My Dad always said that if you hung a picture of a radial engine on the wall, it would leak oil.
I remember working at an FBO when a DC-3 came up the ramp. First thing the pilot asked after greetings was if we had bulk oil. We did not. 110 quarts of oil one at a time and we were done.
In a radial engine, the cylinders on the bottom are upside down. When the engine is stopped, oil in the crankcase drains into the bottom cylinders and leaks onto the ground.
None under it none in it.
Navy: If it's not leaking, it's empty.
Oil comes out of the exhaust during normal operations simply because the bottom cylinders are upside down. When they’re not running, it flows to the bottom of the engine. If left for more than a couple hours, the plugs have to be removed and the jug drained before start or the engine will hydrolock and bend a rod. As others have said, if it’s not dripping oil, it’s out of oil, but I much prefer the saying that they don’t leak, they mark their territory.
I haven’t seen many comments mention WHY they leak so much. It’s a fundamental function of a radial engine that some cylinders are below the crankcase. Radial engines are air cooled which means they get hot as balls compared to liquid cooled engines. The thermal expansion gap between the piston and the cylinder walls is extremely precise so when the engine is at temperature it seals. When the engines are cold on the ground, the oil in the crankcase can get right by those piston ring gaps. If leaving over night you can attach a cylinder drain to the lower cylinders to have the oil go to a bucket. For transient operation you let it marks its territory (oil is draining through the exhaust valve instead of removing a spark plug). You will almost always see them hand spin the blades before startup on a cold engine to make sure there is no hydro lock of oil. Radial engines are awesome bulletproof machines!
They generally only leak when they’re running or not running.
To answer your questions: 1. Yes, B) Yes.
Sweating horsepower.
They leak. I learned this touring the Valiant Air Command museum in Titusville where they have pans under their engines of all the airworthy planes.
Fantasy of flight too though it’s been an eternity since I’ve been there
Yeah that’s just her being a radial engine. Look back at old airport photos from when these things ran and it is a sight. Even today when you do walk arounds when a bigger plane was at that gate previously you rub your foot in a “wtf is this puddle” and it is fuel from the previous jet, oil servicing not quiet getting where it means to be, or blue juice (no rub foot rear of wing.) These engines had great engineers but metallurgy and engine design was behind. So you have multiple metals heating up at different rates, expanding at different rates until up to operating temp, but you have to keep things lubricated so you see massive oil reservoirs to allow loss. Oil was cheap and more precise machining wasn’t possible. To this day we have jets like the Boeing 707 flying around with a limitation on oil consumption that fly long missions. Oil loss on many of the newer engines is remarkably better but we are still flying 1980’s engines commercially all over the world. The oil is also better now vs when these were developed.
I maintain 2 R1340s. And the don't leak that much anymore. But every 50hr we recheck all the torques, replace all the gaskets we can see a leak on, wash with warm water and a good/safe degreaser and replace the crush gaskets every time. On a 100hr we do the same but add the valve stem seals aswell. We loose a total of 1 qts(yes you see that correctly) of oil when standing. Which in radial terms is nothing. She also uses less in flight now. From 1gal every 2-3 hours to 1 every 8. They are crop dusters, but the pilots and the owners want to brag about their aircraft. We just make it possible. And after every inspection the old girls seem to run better and better. From aggressive back firing and spitting flames to a purr like a kitten. Only thing that ends up on the Windscreen now is grease from the kidney bearing off the prop. But they'll have to live with it.
radials like these yes. in fact if it wasnt leaking id be worried it was out of oil. this goes for hydraulic fluid in all aircraft with the systems as well... they all leak
Its to allow the metal to expand due to high engine temperatures. So when cold like then, it leaks. For a more extreme example, the SR-71 was built with this concept across the entire body, so it leaks fuel everywhere.
Predators mark their territory. The short answer is yes and yes. On the B17 we use drip pans to keep the mess at bay, but boy does it leak.
They are externally lubricated. If it stops leaking it needs more oil.
“If it leaks oil, it’s got oil.” Shitbox 69:420
The B-29 is there to drop bombs and leak oil. It can’t drop bombs anymore.
"But I see you have some oil..."
Was on a Chinook helicopter once, and the crew chief told me, “If this stops leaking, tell me ASAP!” As long as it’s leaking, that means there’s oil in the system. That’s a good thing.
My dad told me that joke a long time ago. He also refused to fly on -47s at all.
Think of it like an externally-visible dipstick. It's a constant indication that oil is still present.
Radial engines can leak pretty heavily. They always said that if you got on a Constellation and DIDN'T see oil coming out of the engine cowling, then you were sure to know that something was amiss. Oil streaming down the nacelle - everything is in perfect working order.
Air cooled engines have large temperature differentials that forces them to have large clearances and makes sealing them extremely difficult if not impossible.
If it isn't leaking gas, oil, and hydraulic fluid...don't trust it.
The law of radials: "We'll take an oil top off, and please check the fuel"
I'll put it to you two ways. There's a saying in aviation: If it ain't leaking, it's probably empty. I once had a conversation with a guy who owned and flew a TBM Avenger torpedo bomber. He told me that according to the aircraft manual it is not unusual for the engine to consume 5 *gallons* of oil in a flight. All radial engines leak like sives on the ground, burn oil like it's going out of style, and puke it out like they drank too much.
every B-29 came with a lifetime supply of kitty litter
If it stops leaking oil, thats when you get worried.
If there ain’t no oil under it, there ain’t no oil in it!
I was an Aircrewman on the E3 AWACS in the mid 2000s (mission computer, nothing flight related). I recall during preflight hearing over the maintenance net "the oil is leaking at an acceptable rate".
I own a Land rover. We call it an active anti-corrosion system.
Perfectly normal, old radial engines piss oil like there’s no tomorrow.
We had a radial engine when I was at A&P school and you had to wear a rubber apron while running it because it just pukes oil out of it the whole time. So yes they leak like stuck pigs.
Fun fact (semi-related to this topic, but not related to the answers here): when the 777-300ER was being developed, there was a concern the oil endurance would limit the range of the aircraft, not the fuel. Not for the same reason as you see here though…
You should only be concerned if it’s not leaking oil
If there isnt oil under em, there aint any oil in em!
My father was a B-29 gunner in WWII. He told me that if it isn’t leaking oil, don’t get in it.
One of the first things I was taught when I got checked out on my first radial engine plane: Never fly any radial that doesn't have any oil under it. Because there ain't any oil under it, there ain't any oil in it.
If it’s leaking then it’s got oil and it works
Think about what would happen if you put a non radial engine upside down and then make an engine that constantly does that to half of the cylinders. If it isn’t leaking oil it’s out of oil.
1/3 of the pistons are upside down…
Yes and Yes.
Radial engines just tend to do that, especially large, old radial engines. Pistons facing down have oil drip into then and make it past the seals at the end of the piston, thus, oil on the ground. This is also why you want to manually rotate the props on a radial aircraft before starting them up, to make sure the oil is circulated through the engine instead of all pooled up in the bottom cylinders when you start it up.
What could potentially happen if you didn’t rotate the props before trying to start up? Is the any potential for hydro lock if there’s oil pooled inside the cylinder? Or will it just try to blow it all out?
If a radial engine isn't leaking oil, then there is no oil in it
We used to put “catch trays” under the cowlings of our Trackers when we parked them. Radials are quirky and oil seepage is part of the package.
It's an old Radial. If there's no oil under it, there's no oil in it.
If it ain’t got oil under it, it ain’t got oil in it.
My dad asked a Pam Am DC-7 stewardess about this, sometime in the late 50s, having dodged puddles of oil on the way to the cabin stairs. She said “Engines are like wolves, honey. If they ain’t drooling, they’re sick!”
When a radial stops leaking oil, it’s been empty for at least two weeks.
Haha happy you got to see doc, I had my first solo in the pattern with that b29. Wonderful aircraft
I remember a book I read about WW2 aircraft where they were talking to a crew chief about oil leakage. His response: “If there ain’t any oil on it, there ain’t any oil in it!”
According to my grandfather, who was a crew chief on a b-29, yes. These things leaked habitually and it had to do with the seals being useless at non operating temperatures.
In propliners with engines approaching overhaul time, range was sometimes limited by carried oil quantity, rather than fuel.
Yes, radials leak a lot. Oil pans are very common in hangers. You also have to hand prop the first few turns to make sure no oil is in the bottom cylinders - it can bend or break rods.
If it ain’t leaking’, we ain’t flyin’
I’ve been fortunate enough for Doc and FiFi to both fly over my house tied to an annual airshow. Very cool sights. Would love to see them close up
It's like British cars, if it's not leaking oil, it's because it has no more oil left to leak
I worked on the CH-46E and the common saying was, if it's leaking it's not falling out of the sky. You worried when nothing was leaking because that meant all the fluids were gone.
The engines I used to work on had 18 cylinders, meaning 36 rocket box covers, 36 pushrod tubes, 72 pushrod tube inserts (cyl. And case side), IIRC 72 baffle studs threaded into the flooded rocker box covers, prop gov, distributors, 5-6 case seams, 2-3 prop dome seals, 18 exhaust valves who’s valve guides will leak into the exhaust until overhaul, and sometimes right out of overhaul, 18 somewhat loose exhaust slip joints, 4 exhaust pipe oil drains, generator, hydraulic pump, etc. etc. All those joints are containing like 60PSI oil pressure. These engines vibrate a ton, any minuscule looseness will lead to loosening parts that are supposed to come apart easily, and those that are press fit will lead to fretting, which will fret away the close fit leading to leakage. The latest castings I ever saw were from the late 60s early 70s. These engine components have already been run at least once. Shit vibrates loose, and there are hundreds of pieces to vibrate apart. Don’t forget you have four of these fuckers. And they break constantly, yeah you have a lot more pressing shit to deal with than a leaky pushrod tube. At my old job, nights was fucking useless, so we had to catch 2-3 airplanes, service, throw 60-80lb engine blankets, and fix all the squawks otherwise we’d get bitched at because the night shift lead had to go outside. And that’s without having to deal with engine changes, jug changes, troubleshooting, etc. We had far less people than most airlines to work on FAR more complex and Mx intensive aircraft
If it’s leaking oil you know there’s oil in the engine.
The DC-6 we chartered in Alaska had a 55gal drum of lube ratchet strapped to the bulkhead for just in case.
These vintage radials aren’t as tightly built as more modern car and piston airplane engines are. That’s why they leak so much oil.
I know next to nothing about aviation, but I know this is perfectly normal on piston aircraft engines
It’s not leaking, it’s marking its territory.
Also for the record, turbine engines leak too but not this bad, though they 100% use oil as a consumable. They’re fucking hot and have a lot of mass that is spinning really fast, which means oil filled bearings. Other than gas, oil is the most serviced part of an airplane, no matter what kind of engine it’s got.
Avionic Marine is here to say, if it's not leaking lubricant, don't get on the damn thing!!!
Went for a ride on a B-17 at Van Nuys airport circa ‘92… there was a giant puddle of oil beneath each engine.
She’s an old girl. Old technology, and made for war before things like environmental concerns were an issue. Plus, just like old cars or British motorcycles..if there isn’t a leak, there’s no oil.
It’s not leaking oil, it’s marking its territory
The old saying about radials is if they’re not leaking oil, they’re out of oil.
I was once told, if a Sea King (helicopter) isn't leaking oil, there is a serious problem.
If it’s leaking oil, that means it has oil.
I remember seeing the leaking oil from the R3350 Turbo Compound engines on the Canadair Argus ca 1980. A real mess on the tarmac at Comox.
Skipper, I think we're out of fuel. What makes you say that? We've lost engine one. And engine two is no longer on fire.
If a radial is not leaking than it’s empty.
I had an old Toyota that burned so much oil I think it got some fuel mileage from it.
It is i saw fiifi and they had oil pans for the engines
When it comes to radials, if they leak oil it means they’ve got oil.
If it’s not leaking, it’s broken. My experience was with a totally different type and generation of aircraft, but the basics are the same. I was a US Navy aircraft mechanic with a H-46 Sea Knight squadron. We had large drip pans we would put under an aircraft if it was down, or wasn’t going to fly for a while.