P-47 Engine damage tests

[PL_Harpoon]

I performed some tests to see how the engine damage is modeled.

 

The premise was simple:

start at 8000 ft, go full boost (60" MP at 8k), full RPM (2700), no water injection and see how long it takes for the engine to die.

 

I was expecting the engine to die at somewhere between 5 and 15 minutes as this settings is somewhere between Mil (52" MP) and WEP (64" MP).

 

Here are the results:

SETTINGS	TIME OF DEATH (min)
radiators neutral	~9
radiators neutral	~8:40
radiators neutral	~2
radiators neutral	~2:20
radiators neutral	~1:30
radiators neutral	~26
radiators full	~14
radiators full	~4
radiators full	~6:20
radiators full	~6

 

First thing that surprised me was how inconsistent results are. One time I was able to fly for 26 minutes while at other times the engine died after less that 3 minutes.

Those shorter times are troublesome.

 

Also, there was no warning before the engine died. Every time the CHT was within limit (around 190), the carb air was below 50 deg, and engine oil was around 90.

 

Another thing, setting radiators to full also didn't change anything. Or at least didn't prevent the engine from blowing up within the first 5 minutes.

 

Lastly, the summary screen showed two types of damage (seemingly at random): "engine overheat" or "engine degraded".

 

 

Am I missing something or does the engine damage model need some further tweaking?

 

Here are track of some of the attempts.

 

PS. Random system damage was off during most of those tests (meaning turning it off didn't improve the results).

 

P-47 engine test_rad-neut_overheat@2_no water.trk P-47 engine test_rad-neut_overheat@2.20_no water.trk P-47 engine test_rad-neut_overheat@1.30_no water.trk P-47 engine test_rad-neut_overheat@26.40_no water.trk P-47 engine test_rad-neut_overheat@9.trk P-47 engine test_rad-full_overheat@4_no water.trk

[grafspee]

In every single track i noticed excessive cockpit shake this is indication of detonations. About random time to failures, hmm just RL randomness ?? 

If you have time and desire i would perform better tests.

52" 2700 is max take off power.

I would perform test at 53 54 55 56 57 59 60" and find out at witch engine is getting detonations?

Edited January 1, 2021 by grafspee

[PL_Harpoon]

That was easier than expected to be honest: 55 without water injection. Just ran 5 tests, in all the engine held for 30 min.

With water injection 64 is quite safe - at least within 5 minutes. Out of 5 tests one resulted in damage after 6 mins. In the others water ran out before anything else happened.

 

I guess the engine limitations (5 min for WEP, 15 for MIL) are mainly to increase the lifetime of the engine.

[grafspee]

34 minutes ago, PL_Harpoon said:

 

 

I guess the engine limitations (5 min for WEP, 15 for MIL) are mainly to increase the lifetime of the engine.

This is very important conclusion,  this time limits are set that brand new engine as well as engine which has lots of hours hold it to this limitations.

jus imagine what would happen if those numbers was set at the edge of brand new engine strengths, so for engine which did 100- 200 hours would give up before those time stamps.

[GUMAR]

5 hours ago, grafspee said:

This is very important conclusion,  this time limits are set that brand new engine as well as engine which has lots of hours hold it to this limitations.

jus imagine what would happen if those numbers was set at the edge of brand new engine strengths, so for engine which did 100- 200 hours would give up before those time stamps.

I tried similar WEP tests for max speed. Without detonation engine seemed to be in good condition after all water was used. In all test flight reports Ive seen, IC shutters were neutral, and carb temp. was well. below 50. Unfortunately there is no data for 100/130 gasoline, but with NO water injection on 150 octane fuel at 65” MP in level flight there is no detonation with shutters is neutral.

http://www.wwiiaircraftperformance.org/p-47/p47-26167.html

[PL_Harpoon]

So, the conclusion here is:

be carefull of the throttle position at low-medium altitudes.

 

Don't exceed MP of 55" without water injection and 64" with water injection.

 

Also, don't run on WEP at more than 5 minutes.

 

If you follow those rules you should be safe from detonations.

[GUMAR]

On 1/2/2021 at 2:13 PM, PL_Harpoon said:

So, the conclusion here is:

be carefull of the throttle position at low-medium altitudes.

 

Don't exceed MP of 55" without water injection and 64" with water injection.

 

Also, don't run on WEP at more than 5 minutes.

 

If you follow those rules you should be safe from detonations.

And keep carb. temp below 50