Digital CHT gauge with shock cooling alarm?

[Guest TAA GregW]

Can anyone advise the model and supplier of a digital CHT gauge that also provides a shock cooling alert?

 

KSA'a units have been great but it seems they are no longer in operation. I could go to a Grand Rapids EIS 4000 that provides a lot of extra info like EGT, RPM, volts, fuel flow etc but as my new aircraft has full set of analogue gauges already, I really just need CHT and shock cooling alarm.

 

 

[jetjr]

Dynon make small ems with this feature but its like the GR eis

 

What about mgl E3 Or TC1?

 

 

[dutchroll]

Aerospace Logic do, and Electronic International gauges will do that but only on the multi-channel analysers (not the plain garden variety CHT gauges).

 

I don't think I'd get too worried about shock cooling myself. There's some pretty substantial debate over whether it's as big a problem as it's sometimes made out to be, especially for your normal, average, sensible aircraft operation. The greatest shock cooling we generally get is when we switch the engine off at the end of the flight, and that's pretty hard to avoid. My engine monitor is setup to look for standard shock cooling and despite doing spinning and aerobatics where there can be large power changes, and some pretty rapid descents back to the airfield, it hasn't alerted me even once that there's any problem. I read one incident where a guy was told his cylinder cracks may be shock cooling, only to dig through the maintenance documentation and find out that his cylinders had 3000 hours on them including a re-bore!

 

 

[Yenn]

What aero engine is capable of being re bored? The only likely one to me is a Subaru and that is water cooled, so shock cooling les of an issue.

 

Parachute dropping must be one of the most likely candidates for shock cooling and I know some allow for it. I have also seen parachute drop pilots who would no even know or care what shock cooling was

 

 

[Bruce Tuncks]

Quite a few years ago , the glider tug pawnees had frequent cylinder cracks. Of course glider towing followed by a rapid descent is the worst duty cycle you can do, except for parachute dropping as Yenn points out.

 

Two things were changed: keeping the engine revs up on descent, and using new cylinders instead of " zero hour" reconditioned ones. You can zero hour the log book but not the metallurgy.

 

I don't know what they did to the cylinders to recondition them but it turned out to be false economy.

 

 

[Pearo]

Quite a few years ago , the glider tug pawnees had frequent cylinder cracks. Of course glider towing followed by a rapid descent is the worst duty cycle you can do, except for parachute dropping as Yenn points out.Two things were changed: keeping the engine revs up on descent, and using new cylinders instead of " zero hour" reconditioned ones. You can zero hour the log book but not the metallurgy.

I don't know what they did to the cylinders to recondition them but it turned out to be false economy.

I am skeptical about this given my knowledge of metallurgy. Is there any reports on this? I rack my brain on a regular basis on how shock cooling can be an actual thing, especially in all cast engines such as the lycoming's. Whilst not entirely the same, the number of air cooled motorcycles I have driven straight into water over the years (exluding the torrential rainfalls of the sub tropics) and yet I have never experienced any cylinder or head cracking. In this case, the temp differentials are greater than that of an aircraft because I dont have the benefit of a big fan or relative airflow. Anyway, taking the thread off topic, but I think it might be a myth. I would be looking at other issues such as detonation or overheating.

 

 

[Bruce Tuncks]

I too am impressed by motorbikes and how well they cope with non-forced air-cooling at low speeds. And they don't seem to need special "air-cooled motorbike oil". I wonder why not.

 

On those Lycoming cylinders, the tugmaster of the day was a good bloke who tried to save money by using reconditioned cylinders which legally were zero-time. We certainly had quite a few cracking events. I well remember discussions about the cost of them.

 

I always thought these were caused by a combination of fatigue and the hard duty cycle of glider towing, but I have no way of assigning percentages to each of these. Would not rapid cooling cause some uneven temperatures within the metal with subsequent internal expansion stresses? And would not these stresses work to propagate a dislocation into a crack? But fatigue life was I think the main cause.

 

 

[dutchroll]

What aero engine is capable of being re bored? The only likely one to me is a Subaru and that is water cooled, so shock cooling les of an issue.Parachute dropping must be one of the most likely candidates for shock cooling and I know some allow for it. I have also seen parachute drop pilots who would no even know or care what shock cooling was

I meant re-honed, sorry. But anyway, it had significant work done on it to extend its life, then it cracked.

 

 

[facthunter]

When an aircooled cylinder is under high load the "hot " areas will be really hot with a large temp gradient across the heads . Stopping the motor under these conditions will cause rapid equalisation of the temps, PLUS.. If you are at high altitude and speed the cooling rate will be high. The more cycles you subject it to the more likelihood of cracks developing. The bigger the heads the more stress also. Closing the cowl gills is the first thing to do to to reduce the cold gale going through the motor. Turbocharged motors like those fitted to a Chieftain need special care and make descents with some power on as a normal procedure.

 

Radial engines often get a heat transfer to the crankcases if you land after a high power approach and don't allow time for the heads to cool a bit. A bit of just above idle time with plane into wind and cowl gills wide open is the deal after landing in those circumstances. Nev

 

 

[dutchroll]

The M14P radial has a 150 deg C max limit for shutdown. Mind you, on a really hot day it's not always possible to get the CHTs down to 150, but you can get them pretty close (within 10 degrees). You have to shut it down sometime.

 

Unless you are operating your engine regularly in quite an unusual manner, it seems to be very debatable as to whether shock cooling is likely to cause issues for the average pilot observing normal engine limitations. Far more likely are problems caused by not warming the engine up properly before applying high power settings....and I've heard of that happening quite a bit.