Coring?

[JDCAVE]

During a conversation I had with dad's navigator he mentioned that dad had been given the somewhat "derogatory" nickname "Coring Cave". During a recent conversation I had with a colleague, he mentioned a pilot on a 6-Group Halifax squadron had to return early on one occasion because one or more engines had been subject to "Coring", due to extreme icing conditions, and that the intakes of the engines had been caked with ice. Evidently this was a common problem with Halifax IIIs.

So what exactly is "coring"?

Jim

 

[Snautzer01]

During a conversation I had with dad's navigator he mentioned that dad had been given the somewhat "derogatory" nickname "Coring Cave". During a recent conversation I had with a colleague, he mentioned a pilot on a 6-Group Halifax squadron had to return early on one occasion because one or more engines had been subject to "Coring", due to extreme icing conditions, and that the intakes of the engines had been caked with ice.

So what exactly is "coring"?

Jim

Calling E Engineman

 

[Trilisser]

Coring may refer to "oil coring" which is simply that the oil congeals (due to very cold conditions; WW2 motor oils were a far cry from motor oils we have today available) in the radiator/tank causing oil supply failure=lubrication failure=engine failure.

 

[JDCAVE]

Thanks "T". Further to my question, the following came up with a search:

"A phenomenon that occurs in some oil coolers at low atmospheric temperatures when the oil congeals and restricts the flow through the cooler. If this happens, a rise in oil temperature willtake place without a corresponding rise in coolant or cylinder head temperature. In this case, the RPM should be increased and/or the shutters closed."

https://aviation_dictionary.en-academic.com/1723/coring

Jim

 

[JDCAVE]

See also the following:

"…The engines were subject to 'coring'. This could occur when climbing in cold air when the oil pipes cooled in the airflow and the oil flowing through them became cooler and thicker around the inside of the pipe. This left a thinner small core of oil, in its centre, getting ever hotter when it reached the engine. If unchecked, this could lead to loss of oil pressure, and the engine overheating and possible seizure. The drill was to close down the engine, feather the prop and then descend to warmer air and preferably to land. So, great care was needed to monitor the temperatures and pressures, as no-one wanted to suffer coring on both engines! I never experienced coring on the CFS course, but did so later with a student."

An instructor’s viewpoint

INSIGHTS | VICKERS VARSITY A CFS Varsity trio, led by WJ949,...

www.key.aero

Jim

 

[Engineman]

Calling E Engineman

Hi,
Yes, Oil congealing at low temperature in the pipework of an engine installation, particularly in the oil cooler Matrix, is a potential problem. Careful cooler design to match the cooler characteristics to the oil temp/flow can prevent the problem within the required specification, particularly with regard to air temperature. Many coolers will also incorporate a pressure bypass valve to protect the cooler from damage if the cooler becomes restricted by congealed oil, this also allows continued oil circulation but, will likely also allow oil temperature rise which can be detrimental.

Eng

 

[Simon Thomas]

The carburettor air-intake heat control is meant to allow the pilot to clear any carb ice. In practice it is very hard to detect carb icing, as it can form at temperatures above freezing due to the carb venturi dropping the temperature & pressure in the throat. There are charts which show likelihood of carb icing, such as this: https://www.aopa.org/-/media/Images...dent-Reports-Carburetor-what/nyc02fa025_1.jpg.
For airframe ice to form, you need visible moisture and temperatures below freezing. This would include oil coolers.

The Halifax only had an air temperature gauge. If the icing buildup is particularly bad, the carb heat will be incapable of clearing the ice. Once the engine stops, the residual engine heat typically melts the carb ice - but in nasty conditions it may never clear.

From the Halifax manual:

 

[Engineman]

The carburettor air-intake heat control is meant to allow the pilot to clear any carb ice. In practice it is very hard to detect carb icing, as it can form at temperatures above freezing due to the carb venturi dropping the temperature & pressure in the throat. There are charts which show likelihood of carb icing, such as this: https://www.aopa.org/-/media/Images...dent-Reports-Carburetor-what/nyc02fa025_1.jpg.
For airframe ice to form, you need visible moisture and temperatures below freezing. This would include oil coolers.

The Halifax only had an air temperature gauge. If the icing buildup is particularly bad, the carb heat will be incapable of clearing the ice. Once the engine stops, the residual engine heat typically melts the carb ice - but in nasty conditions it may never clear.

From the Halifax manual:
View attachment 762567

Yes, float-type Carburettor icing is possible in air temperatures upto about 30 degrees C, due to the cooling effect of gasoline evaporation freezing water vapour in the air. This problem probably contributed to many aircraft losses. The "Halifax" came in types with Merlin and Hercules engines. Those with float-type carbs would suffer carb icing. Later engines may have had Bendix or RAE-Hobson injection carbs that were very much less likely to get carb icing. However, never say never, some icing in flight can effect the intakes.

Eng

 

[JDCAVE]

Part of my above query, had to do with dad's nickname. The other question in the back of my mind comes from whether the Halifax III and VII aircraft were more susceptible to icing related engine issues as compared with Lancaster X aircraft, either the Merlin 38 equipped or the Merlin 224 aircraft. On the raid to Chemnitz, 5/6-March-1945, 7 Halifax III and VII aircraft crashed with 5 certainly due to icing. Whether this was due to ice on the control surfaces or due to icing of engine ending intakes. The following was reported in the court of Inquiry into these accidents…

F/L McHolm of 420 Squadron described his experience flying [Halifax iii] in the difficult conditions:

"At 1700' I entered cloud and my windscreen iced up as soon as I went into cloud. At 2,000' I used hot air as I thought I could hear ice being thrown off the propellers. I ran in hot air for 30 seconds, changed to cold and the engines still ran normally. After climbing to 4,500' the aircraft became very sluggish and the rate of climb dropped off. I could see heavy rime and clear icing on the wings, cowlings, windscreen and the air intakes which were completely iced over. "On reaching approximately 6,000' the aircraft stalled at 160 mph with the engines all at full power. I checked the stall and continued to climb but the aircraft was still very sluggish and stalled three more times, loosing about 1,000' on each occasion. The last stall was more vicious than the previous ones and the controls were snatched out of my hands and the control column was forced back into my stomach and the aircraft started to spin to the right. I put the nose of the aircraft well down before I was able to apply corrective measures. On recovering from this temporary loss of control I had gained sufficient air speed to assist me in climbing again and I reached 9,500' where I broke cloud. I could then see that the aircraft was loaded with ice and it took full power to maintain this height. I continued to the French coast at approximately 9,500' but considered I had used too much petrol so I returned to Base, landing approximately five hours after take-off, and after landing the air intakes were still frozen. "During the vicious stall, had I given the order I consider that all my crew and myself could have abandoned the aircraft without difficulty."

Comments concerning engines are highlighted in bold.

BTW, dad disliked the Merlin equipped Halifax II and V aircraft, which he flew at HCU.

Jim

 

[JDCAVE]

Yes, float-type Carburettor icing is possible in air temperatures upto about 30 degrees C, due to the cooling effect of gasoline evaporation freezing water vapour in the air. This problem probably contributed to many aircraft losses. The "Halifax" came in types with Merlin and Hercules engines. Those with float-type carbs would suffer carb icing. Later engines may have had Bendix or RAE-Hobson injection carbs that were very much less likely to get carb icing. However, never say never, some icing in flight can effect the intakes.

Eng

This is interesting as dad had considerable difficulties with the aircraft equipped with the Merlin 38 engines during his operations in February 1945. On his operation to Dresden, all engines gave trouble and he was constantly feathering and restarting engines in sequence throughout a very long trip. His Base reported difficulties with lead-fouling of spark plugs, but these had supposedly been resolved by this time.

Jim

 

[Trilisser]

This is interesting as dad had considerable difficulties with the aircraft equipped with the Merlin 38 engines during his operations in February 1945. On his operation to Dresden, all engines gave trouble and he was constantly feathering and restarting engines in sequence throughout a very long trip. His Base reported difficulties with lead-fouling of spark plugs, but these had supposedly been resolved by this time.

Jimt

To avoid lead fouling, the engines should have been run at high power for a few minutes every now and then.