[NO BUG?] VSTOL issue with the new patch?

[Eldur]

On 5/29/2021 at 12:21 AM, lukeXIII said:

The engine thrust is much less than 23800 lbf at 105% rpm. Also, thrust does not increase linearly with rpm.

 

Is there a chart somewhere that shows the actual thrust at different rpms? Would be easier to understand things with that. I'm aware though of the thrust not being linear with rpms. But it's hard to imagine 109% being 23800lbf while 105% would just be somewhere around 16500lbf. But I might be wrong with the assumption of 23800lbf being max. dry thrust. Which is why I'd like to see a power chart.

 

Nevertheless...

 

On 5/29/2021 at 12:21 AM, lukeXIII said:

It looks like you are using the chart incorrectly. Using the charts with standard conditions (15°C and 29.92 inHg) you do not have to make any corrections to hover weight or fan speed. Basically all the lines you follow are horizontal and vertical.

 

... I now think you got me. I was following the parallel lines at the bottom section down to the scale, beginning on the 15°C line. Guess that was wrong and might have been the error RAZBAM had in there as well before the change, because...

 

On 5/29/2021 at 12:21 AM, lukeXIII said:

The lowest fan speed on the chart for the 408 engine is 98%, which indicates that you are using the wrong chart (the 406 engine chart).

 

... I was using the 408 chart, but prolonged the rpm scale to the left outside of the drawn area. And with what probably was my error, following the parallel (diagonal) lines down to the scale from the 15°C line on, I ended up at roughly 92-93%. By just going straight down, I indeed see the ~105% there. So basically, it must be a total coincidence that the error I assumed Herby made brought about the same error in there as the one I made at the other end

 

Supposedly I have to relearn things now... I always kept the thing below 640°C JPT because it instantly starts to deteriorate power with more than that after just a few seconds. Well, RAZBAM probably should revisit their engine stress damage modeling. It's basically raising the JPT depending on how far you're over the max continous temp which is 645°C. With that, the limit comes down which results in a loss of thrust basically. There's an "Engine Life Count" chart right after the limits table they probably should realize in the module and determine possible damage based on that.

 

Also, I couldn't make out any difference with the LIDS and/or having dumped all the water. I guess that should be noticable.

[Aernov]

Max thrust is, probably, reached at max engine rating, which is short lift wet (and a lot of takeoff-related charts use SLW or Dry as requirement). And engine damage or power limiting shouldn't start until allowed time for particular engine rating is exceeded (i.e. you can keep 113.5% RPM and 780 JPT dry for 14 seconds or 111% 750 degrees combat thrust for 9 minutes 50 seconds  without consequences aside from life count dissipation). And after VTO (slooow one) and hovering with roughly 18 000 lbs GWT (no armament, just fuel and water) at 107-109 RPM dry I have checked the chart and it was pretty much spot on (with default DCS 29.92 inHg, +20 degrees at 33 ft ASL). So, at this mass (there were over 3000 lbs of fuel) I could have been hovering for 10-15 minutes continuously (fuel flow was around 220 PPM though) with power to spare (to 113.5 RPM, plus wet datum to 120% RPM). There's a lot to relearn and come to terms with, but it is a great change to realism.

Life count dissipation and overtemp time recording on ENG page would be great, and can be used in-game for gauging expected engine performance. Life count IRL doesn't necessarily mean engine damage, it's just engine "life expectancy" until next maintenance/change (as far as I know).

Edited June 2, 2021 by Aernov

[Eldur]

14 hours ago, Aernov said:

Life count dissipation and overtemp time recording on ENG page would be great, and can be used in-game for gauging expected engine performance. Life count IRL doesn't necessarily mean engine damage, it's just engine "life expectancy" until next maintenance/change (as far as I know).

 

You're absolutely right here. It's basically a countdown to take the engine out of the airframe for maintenance. And one thing many sims "like" to do is instantly start damaging the engine or at least reducing its performance as soon as you're past the clock at a given power rating. So basically if the manual says 5 minutes is allowed at a given setting, you'll damage the engine for sure if you run that for just one second longer. And that's certainly not realistic at all. It's a guideline (or restriction) to keep the engine in shape for a while, but exceeding it (if not excessively) should not inflict damage at all, but you'd get some nice words from your mechanics after a sortie, and probably your boss as well...

 

As for the relearning, a lot is done now by switching water injection to TO. At a certain point it kicks in and lowers the JPT significantly so it's possible to output more thrust even within the 640° safe margin. I guess it's actually worth now keeping the water for that instead of trying to lighten the thing up. I usually didn't use the injection at all if it was not needed (basically with total weight somewhere below 20-21k lb) prior to the change.

[lukeXIII]

On 6/2/2021 at 10:58 PM, Eldur said:

Is there a chart somewhere that shows the actual thrust at different rpms? Would be easier to understand things with that. I'm aware though of the thrust not being linear with rpms. But it's hard to imagine 109% being 23800lbf while 105% would just be somewhere around 16500lbf. But I might be wrong with the assumption of 23800lbf being max. dry thrust. Which is why I'd like to see a power chart.

 

Those charts are basically already showing engine thrust (hover thrust is equivalent to the hover weight in lbf). For a 0 datum engine in standard conditions, max hover thrust wet is around 21,000 lbf at 116.8% rpm and dry is around 20,000 lbf at 113.5%.

[Eldur]

1 hour ago, lukeXIII said:

 

Those charts are basically already showing engine thrust (hover thrust is equivalent to the hover weight in lbf). For a 0 datum engine in standard conditions, max hover thrust wet is around 21,000 lbf at 116.8% rpm and dry is around 20,000 lbf at 113.5%.

 

This is exactly what made me raise the question since every info I can find on the 408 is that it has 23500-23800lbf of thrust, but the chart basically has it limited to 21000lbf just like you said. Something's clearly weird here.

[AlphaJuliet]

Hey,

Should be fixed, give me a heads up if not.

Cheers,

Alpha