Why do all CFM Engines consume a large quantity of oil.
More importantly what is stopping them to incorporate a Deoiler in The Oil Vent subsystem to reduce consumption?

You are very correct, those little things burn up the oil. Much more so compared to the IAE. I don’t have the hi-limit consumption rate on hand, but I’m sure it’s more than a pint per hour. GE engines have always used more oil than competitors. The reason why is the oil scavenge system. They must think it’s cheaper to burn it than to try to scavenge it. The type of sealing may also play a role.

Golly, you should see PW engines, if you want to see oil consumption.

There was an old story that the CFM56-5 on the A340 would consume more oil than fuel over a long flight. (A joke) but that on a transpacific crossing would drop to about half full on landing (reality)

GalaxyFlyer wrote:

Golly, you should see PW engines, if you want to see oil consumption.

Quite the contrary on the PW GTF. Max oil consumption is as low as 0.22 qts/hr.

CFM LEAP on the other hand max consumption is 0.45 qts/hr.

All above examples are used on the A320.

StereoTechque wrote:

GalaxyFlyer wrote:

Golly, you should see PW engines, if you want to see oil consumption.

Quite the contrary on the PW GTF. Max oil consumption is as low as 0.22 qts/hr.

CFM LEAP on the other hand max consumption is 0.45 qts/hr.

All above examples are used on the A320.

From what I have heard this is why they don't do oil changes on jet engines outside of removing engines etc - in normal service they burn it fast enough that regular top-ups keep it fresh!

StereoTechque wrote:

GalaxyFlyer wrote:

Golly, you should see PW engines, if you want to see oil consumption.

Quite the contrary on the PW GTF. Max oil consumption is as low as 0.22 qts/hr.

CFM LEAP on the other hand max consumption is 0.45 qts/hr.

All above examples are used on the A320.

Probably true enough on the GTF, but JT8s and JT9s dripped oil all the time. First a friend pre-flighted a B747 with JT9s, he told the the instructor #2 had a oil leak, instructor told him, then all of them if you think that’s a leak. TF34 and TF 39 didn’t leak a drop.

JT8s always did leave a puddle of oil at the bottom of the airstairs on the 727.

In my experience, PW4000s use very little oil compared to a GE CF6. We once had a European outstation “service” the oils on a CF6. They wrote 0 pints of oil uplifted in the logbook. It became obvious that they did not service oils to full once the plane got back to base. Both engines ended up using twice the normal amount of oil. We took a delay as the passengers watched us do engine running oil leak inspections at the gate. They could’ve gotten away with it if it was a PW4000, but not a CF6.

DL_Mech wrote:

We once had a European outstation “service” the oils on a CF6. They wrote 0 pints of oil uplifted in the logbook. It became obvious that they did not service oils to full once the plane got back to base.

I'm a bit befuddled. Wouldn't the logbook entry of 0 pints make it obvious, or am I missing a trick here.

Calculating oil consumption is critical to ETOPs. In order to do so properly, you must assume the oil was serviced properly before. If no oil was added for the prior leg, and was entered as serviced when it wasn’t, then at the end of the next leg, oil would be added for both legs, but the flight time used to calculate oil consumption would be only for the inbound leg, therefore the spot rate would be way high. A red flag is raised, and the AMM must be consulted.

^ Spot On!

I get that part, I guess I'm not understanding how an entry of 0 pints added didn't raise any red flags. Or is it possible to service the oil without adding any.

The CF6-50C2 on the DC-10 and the CF6-50E2 on the 747-200's did not use oil at all. So did the CFM56-3B2's on the 737 classics. The JT9D's used oil like crazy.

I guess we drifted too far away with examples.
The question is why no Deoiler on the CFMs?

GalaxyFlyer wrote:

Golly, you should see PW engines, if you want to see oil consumption.

Or an A35K / Trent XWB after a 15-16 hour sector !

AirKevin wrote:

I guess I'm not understanding how an entry of 0 pints added didn't raise any red flags. Or is it possible to service the oil without adding any.

Yes, it is possible for no oil to be required after a flight. We often get A330's / Trent 700's arriving after 8-9 hour sectors that require no oil uplift. We still need to add an entry in the tech log as you cannot leave it blank.

Regards, JetMech

AirKevin wrote:

DL_Mech wrote:

We once had a European outstation “service” the oils on a CF6. They wrote 0 pints of oil uplifted in the logbook. It became obvious that they did not service oils to full once the plane got back to base.

I'm a bit befuddled. Wouldn't the logbook entry of 0 pints make it obvious, or am I missing a trick here.

I think the 0 pints implies "we checked it, it was full, so we didn't add any," versus "we didn't check it and added 0." When the plane got home, they found 2x the normal burn and concluded that the outstation didn't check it at all.

Regarding the CFM56-5C, there was a thread a while back where it got brought up: viewtopic.php?p=23286961

I think all of the engines have a scavenging system, and some of the oil vapors don't get separated out. Some are probably more effective than others, and there are likely design tradeoffs associated with the systems like simplicity vs oil burn.

LH707330 wrote:

.

Regarding the CFM56-5C, there was a thread a while back where it got brought up: viewtopic.php?p=23286961
.

I tried continuing in the same thread, but then admin locked it.

CFM56 engines have deoiler as well, it is integrated inside low pressure spool and air goes out by vent tube in the tailpipe. From my experience engines installed on A321 have bigger oil consumption than those on A318/9, so deoiler configuration is not main cause probably. But oil consuption diference between this and V2500 is huge, CFM56 requires serving each daily check usually 2-5 cans. V2500 requires servicing each weekly check and just 1-3 cans.

Is there not also something about the turbine bearing seals not fully pressurizing at low RPM and thus aircraft that tend to have longer than normal taxiing can end up with higher oil consumption?

77west wrote:

Is there not also something about the turbine bearing seals not fully pressurizing at low RPM and thus aircraft that tend to have longer than normal taxiing can end up with higher oil consumption?

Correct. But this holds true for Labyrinth seals. Almost all modern engines use Carbon seals which have better sealing then labyrinth.

77west wrote:

Is there not also something about the turbine bearing seals not fully pressurizing at low RPM and thus aircraft that tend to have longer than normal taxiing can end up with higher oil consumption?

In addition, at low engine RPM, air-oil separators are less effective as they rely on centrifugal forces to separate the oil from the air.

Regards, JetMech

Just a practical question: In the case of tri-jets, in particular the DC-10 and MD-11, the engine nr. 2 is mounted some 10m above ground.
How is the oil level control and top-up performed? Logically, a cherry picker or similar device would be required to access the engine. Or is there a possibility to pump the oil to the engine from a ground-accessible location?

Best regards,
Hendric

* I know the Douglas jets don't us the CFM-56, but I think the question is still relevant for the topic.

hitower3 wrote:

Just a practical question: In the case of tri-jets, in particular the DC-10 and MD-11, the engine nr. 2 is mounted some 10m above ground.
How is the oil level control and top-up performed? Logically, a cherry picker or similar device would be required to access the engine. Or is there a possibility to pump the oil to the engine from a ground-accessible location?

There are a few lift trucks designed for #2 engine. We would mostly service using one of these:



If the truck was not available, you could climb inside the tailcone and open up the “patio.”



There were remote servicing points inside the tailcone, but these were not used at my airline.

I wish there was a "like" button on A.net!

DL_Mech wrote:

hitower3 wrote:

Just a practical question: In the case of tri-jets, in particular the DC-10 and MD-11, the engine nr. 2 is mounted some 10m above ground.
How is the oil level control and top-up performed? Logically, a cherry picker or similar device would be required to access the engine. Or is there a possibility to pump the oil to the engine from a ground-accessible location?

There are a few lift trucks designed for #2 engine. We would mostly service using one of these:

If the truck was not available, you could climb inside the tailcone and open up the “patio.”



There were remote servicing points inside the tailcone, but these were not used at my airline.

DL_Mech wrote:

If the truck was not available, you could climb inside the tailcone and open up the “patio.”

That looks really falloffable.

AirKevin wrote:

DL_Mech wrote:

If the truck was not available, you could climb inside the tailcone and open up the “patio.”

That looks really falloffable.

It was loads of fun. Slippery Skydrol everywhere, one slip and you fall to your death (at least AA put up one of the safety rails). But the view up there was fantastic.

DL_Mech wrote:

There were remote servicing points inside the tailcone, but these were not used at my airline.

FedEx must have added them to the MD-11 they acquired from Delta.

LMP737 wrote:

DL_Mech wrote:

There were remote servicing points inside the tailcone, but these were not used at my airline.

FedEx must have added them to the MD-11 they acquired from Delta.

They were there, just airline policy not to use them (don’t know why).

DL_Mech wrote:

They were there, just airline policy not to use them (don’t know why).

Wow, that's just mean.

Seriously though, I'm guessing this was done to lessen the chances with over servicing the number two. If you're not careful that's exactly what will happen, especially with the IDG. Always a good idea to leave the drain bottle hooked up for about ten to fifteen minutes after you service it. As for the number two engine, I figure out how many quarts are needed and add just that amount.