P-51 will overheat at extreme high altitudes on auto radiator.

[FeuerFliegen]

I was testing the P-51B today, and at 11k, I had the water overheating, and then when I switched it to manual mode, I realized that the auto mode was keeping it at 0% (fully closed)

 

Seems like the only reason it should overheat in automatic radiator mode is when auto has the radiators set to 100% open and it still can't keep the engine cool enough.

[[CPT]Crunch]

Might make for a good bug report, sounds wrong, no reason why it shouldn't be full open up there when hot, not much air for drag on it anyway with it full open.

[JtD]

Because the radiator is controlled by a thermostat, which is a constant value over altitude, and the water temperature limit is dependent on ambient pressure, both of which are lower at high altitude.

 

So in theory this is possible, in practice I doubt that it was designed that way. In particular as closed is never really closed, so that with the low power output & heat production at high altitude even a radiator in closed position should provide sufficient airflow to keep the temperatures at bay.

[357th_KW]

On 5/4/2023 at 7:18 PM, SCG_FeuerFliegen said:

I was testing the P-51B today, and at 11k, I had the water overheating, and then when I switched it to manual mode, I realized that the auto mode was keeping it at 0% (fully closed)

 

Seems like the only reason it should overheat in automatic radiator mode is when auto has the radiators set to 100% open and it still can't keep the engine cool enough.

 

I saw your post the other day mentioning how slow the P-51 is at high altitude and tested this a bit myself, and got the exact same results.  It happened with the -3 or -7 engine, 100 or 150 octane, and it happens in the P-51D as well.  Somewhere above 32,000ft the auto radiator control stops working, and the radiator itself seems to stop working.  Manually controlling it still won't allow you to keep the engine from overheating.  None of the P-51's can get anywhere close to their historical service ceilings with this bug.  I couldn't get any of them to climb from 32,000ft to 42,000ft (their historical service ceiling) without the engines failing from overheating well before getting there.

 

Here are a few different historical tests of P-51B's with both engines and a P-51D, all of which were able to climb up in emergency power at those high altitudes without blowing up their engines, with info on coolant shutter position etc.

P-51B-5

P-51B-15

P-51D

 

Edit: I went ahead and posted this info in the bug report section

Edited May 9, 2023 by 357th_KW