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Closing the throttle in flight - nicely (shock cooling)

Yes exactly. No mention of any C182, so I must have made that up. And it was glider towing, not parachutist lifting. The rest I had mostly right

Last Edited by huv at 25 Feb 10:29
huv
EKRK, Denmark

Peter wrote:

It may be in the same temp range eventually but heating rate (dT/dt) during climb is a lot slower, no doubt partly because you have the airflow stealing a lot of the heat generated.

I assume that is a common misconception that is caused by the Position of the CHT probes that are located more on the outside of the cylinder than on the inside.

As the heating is done from the insight to the outside, there is a “one Inch thick aluminum heatspreader” between the heat source and the CHT probe that slows down the rise at the probe while the cooling is done from the outside and therefore happens much faster at the Position of the CHT probe.

If we had two CHT probes, one at the inside of the cylinder and one at the outside, we would again see a symmetric behaviour for heating and cooling.

Germany

I don’t think so, because

  • during flight, after a sudden power-off, you get a dT/dt based on just the cooling airflow, since there is no heat being generated
  • during climb, you get a dT/dt based on heat being generated minus heat loss to the airflow

Aluminium conducts heat pretty fast.

It is a fair assumption that the heat which the engine can generate is comparable to the heat loss to the airflow, otherwise our engines would always overheat That in turn means that the dT/dt (rate of change of temperature over time) during climb should be about 50% compared to a sudden power-off in-flight event.

Administrator
Shoreham EGKA, United Kingdom

Need to do a back of the envelope calculation on the Weekend.
Agree, that the net heat energy while warming is lower – but need to think about the question if it’s not even more stress to the case if it is heated from inside while cooled at the outside (as during take off) than while only being cooled from outside and not heated.
The temp gradient in the material during “shock heating” is in any case much higher than during “shock cooling”.

But even if I take your 50%: My local runnway is also by far not long enough to add power only by 4’’/min during takeoff run (double the proposed shock cooling avoidance Speed).

Germany

My experience with heatsinks in electronics is that half inch thick aluminium conducts heat awesomely fast – equalising the temp within a few degrees in seconds

These are a similar size – say 4″ × 4″

etc

Administrator
Shoreham EGKA, United Kingdom

I like PilotDAR’s approach – moving the engine controls extremely slowly is a very elegant way of paying respect to both the engine and the passengers. I copied this shamelessly from an A&P who was flying my DA40 once for diagnostics and practiced it ever since.
He was so smooth that you did not even realize he was reducing power.

On the take-off run, I try to dilute the initial power application, but sometimes you just have 2-3 seconds to apply full power due to runway length – I think applying full power while standing on the brakes is torture to …everything. You can almost hear the plane protest…

Turbocharged aircraft engines are even more fragile than NA equivalents, and I’d rather stay on the cautious side of cautious despite the water cooling which I absolutely love.

LSGG, LFEY, Switzerland

Flyingfish wrote:

I think applying full power while standing on the brakes is torture to …everything. You can almost hear the plane protest…

Why you think so? up to 2/3 power on breaks is a non-event on breaks and give more time to watch T & P, RPM, Amps, Oil prop… the last bit can go 1, 2, 3

Paris/Essex, France/UK, United Kingdom

Flyingfish wrote:

– I think applying full power while standing on the brakes is torture to …everything. You can almost hear the plane protest…

I very much agree. The only time I ever apply power against the brakes is to do a normal run up. I also don’t apply the power in my car with my other foot on the brake. I never choose to use a flight manual procedure to open the throttle against brakes for takeoff. I know the procedure is available for some planes, though I choose not to use it.

Home runway, in central Ontario, Canada, Canada

@Flyingfish:
Agree to your points – but there is a „slight“ differenc between „2-3 sec from idle to full power“ and the „2‘‘ MP per minute“ proposed in the original post.

The more I think about it, the more I tend to agree to the „implicit“ point of Peter (which was so implicit that he did not make it ;-) ): The „Shock-Heating“ during takeoff is a significantly higher thermo-mechanical stress for the engine (due to the much steeper temp gradient in an engine that is heated from inside and cooled from outside) than any „shock cooling“ (where the cooling from outside is the same but no heating from inside) could ever be.

Therefore I se the urgent need for an emergency AD on any type that the POH needs to be ammendet that a takeoff is prohibited under any circumstances due to unforseeable harm a takeoff puts on the engine. ;-)

Germany

All that mythes and discussion because of an archaic cooling system that’s been solved 50y ago in cars engine by using coolant and thermostatic valves…
I understand that sometimes coolant system are not fail proof, but I bet 50y would have been enough to create a bullet proof system not too heavy. It’s actually nicely done in thielert/conti/diamond engine and I didn’t see many issues in coolant systems.

Last Edited by greg_mp at 25 Feb 13:16
LFMD, France
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