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Reduced thrust at low RPM?


DarkFire
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Before I consider reporting this as a bug & do hours of testing to provide data, has anyone else noticed that engine thrust at under 90% RPM has significantly reduced since 2.5 was introduced? It used to be the case that 85% RPM was cruise throttle at pretty much any altitude, but now anything under 90% RPM cannot sustain constant airspeed at pretty much any altitude.

 

This may be entirely realistic, I don't know, but I do remember reading that real Russian pilots use 85% - 87% RPM as a cruise setting.

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Yes, temperature, altitude, and pressure affect the thrust.

 

Could you please tell me the atmospheric conditions of your mission? And map as well.

 

Caucasus, standard DCS day.

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Personal wish list: DCS: Su-27SM & DCS: Avro Vulcan.

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We've noticed this too. We used to cruise at 85% but have bumped it up to 90% now since they changed the thrust to be dependant on temperature.

 

Thanks, not just me then. This has made things rather awkward. Doing things like achieving an accurate TOT has become somewhat difficult because the changes have left the Su-27 with only 2 effective speeds: ~0.9M (from 90% - 95% RPM you get roughly between 09.M & 0.95M) or AB.

 

I'm glad that engines now take in to account temperature, pressure etc. when calculating generated thrust, but it appears that maybe the Su-27 engines need a little bit of tweaking because I distinctly remember reading that real pilots use 85-87% RPM for a cruise setting, suggesting that for a reasonably wide range of operating conditions this engine RPM range generates sufficient thrust to maintain level speed at cruise altitudes, which at present in DCS, it doesn't.

System Spec: Cooler Master Cosmos C700P Black Edition case. | AMD 5950X CPU | MSI RTX-3090 GPU | 32GB HyperX Predator PC4000 RAM | | TM Warthog stick & throttle | TrackIR 5 | Samsung 980 Pro NVMe 4 SSD 1TB (boot) | Samsung 870 QVO SSD 4TB (games) | Windows 10 Pro 64-bit.

 

Personal wish list: DCS: Su-27SM & DCS: Avro Vulcan.

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That cruise setting would likely be based on profiles in Russia, and even then would vary.

 

Sukhois in Afghanistan required a 50% longer takeoff run to get airborne, and were prone to bursting tires on landing. Temperature matters. A *lot*. A few percent variance does not 'require tweaking because you don't *feel* it's right'.

 

What conditions are you testing under? What conditions was your reference under? If you cannot answer definitively those two questions then what you *feel* or how it *appears* is entirely subjective and irrelevant. ''caucasus day'' is not very specific.

 

Hard data or move on, basically. Need temperatures and atmo conditions of both yourself and your half remembered reference. This sort of thing comes up regularly. It can only be determined with hard data.

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That cruise setting would likely be based on profiles in Russia, and even then would vary.

 

Sukhois in Afghanistan required a 50% longer takeoff run to get airborne, and were prone to bursting tires on landing. Temperature matters. A *lot*. A few percent variance does not 'require tweaking because you don't *feel* it's right'.

 

What conditions are you testing under? What conditions was your reference under? If you cannot answer definitively those two questions then what you *feel* or how it *appears* is entirely subjective and irrelevant. ''caucasus day'' is not very specific.

 

Hard data or move on, basically. Need temperatures and atmo conditions of both yourself and your half remembered reference. This sort of thing comes up regularly. It can only be determined with hard data.

 

Standard DCS day is the same every time you load up the mission editor. +20°C, Standard pressure at sea level, 0 wind. Unless that was changed very recently.

 

Secondly a standard cruise setting would be used throughout the altitude envelope. Otherwise it would not be called a standrad cruise power setting. Climbing high enough will show close to if not exactly the same temperature as ISA in general, so at, say 8-10 kilometers the conditions are close enough for a comparison. Not hard data, no, but sufficient in my mind to spot a power setting difference of 5-10%. We would need to have the IRL cruise speed at said setting to compare though.

 

Regards,

MikeMikeJuliet

DCS Finland | SF squadron

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Thanks, not just me then. This has made things rather awkward. Doing things like achieving an accurate TOT has become somewhat difficult because the changes have left the Su-27 with only 2 effective speeds: ~0.9M (from 90% - 95% RPM you get roughly between 09.M & 0.95M) or AB.

 

I'm glad that engines now take in to account temperature, pressure etc. when calculating generated thrust, but it appears that maybe the Su-27 engines need a little bit of tweaking because I distinctly remember reading that real pilots use 85-87% RPM for a cruise setting, suggesting that for a reasonably wide range of operating conditions this engine RPM range generates sufficient thrust to maintain level speed at cruise altitudes, which at present in DCS, it doesn't.

The standard DCS day was fine before the engine thrust was revised to take temp, etc into effect. The standard temp is 15° C. What happens if the temp is set to that in the mission? Do you recover the lost thrust? Just don't have the time to check myself. Just passing thru. Sorry.

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The standard DCS day was fine before the engine thrust was revised to take temp, etc into effect. The standard temp is 15° C. What happens if the temp is set to that in the mission? Do you recover the lost thrust? Just don't have the time to check myself. Just passing thru. Sorry.

 

No worries.

 

Tried 15 degrees C. 87% RPM fails to maintain constant velocity in a 10,000m altitude cruise.

 

I'll test this fully, probably in a couple of weeks when I have a bit more spare time than I do at the moment.

 

For now, all the conclusions I reached in these threads are (obviously) now obsolete.

 

https://forums.eagle.ru/showthread.php?t=147556

 

https://forums.eagle.ru/showthread.php?t=151731

System Spec: Cooler Master Cosmos C700P Black Edition case. | AMD 5950X CPU | MSI RTX-3090 GPU | 32GB HyperX Predator PC4000 RAM | | TM Warthog stick & throttle | TrackIR 5 | Samsung 980 Pro NVMe 4 SSD 1TB (boot) | Samsung 870 QVO SSD 4TB (games) | Windows 10 Pro 64-bit.

 

Personal wish list: DCS: Su-27SM & DCS: Avro Vulcan.

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No worries.

 

Tried 15 degrees C. 87% RPM fails to maintain constant velocity in a 10,000m altitude cruise.

 

I'll test this fully, probably in a couple of weeks when I have a bit more spare time than I do at the moment.

 

For now, all the conclusions I reached in these threads are (obviously) now obsolete.

 

https://forums.eagle.ru/showthread.php?t=147556

 

https://forums.eagle.ru/showthread.php?t=151731

It'll dpend, too, on fuel/AAM configuration as well. I just tried with a Vaziani takeoff, fuel 80% and 4 AAMS. Performed a standard full mil power takeoff and and full mil intercept climb (maintain 860 TAS during the climb) to 11,000 m. At 88% RPM, I settled in at 10,100m for the cruise with a TAS of around 700. Reducing throttle one more percent to 87% started causing issues. By the time the phugoid oscillations stopped and the airspeed was dialed in, I was down to around 7000 meters (or somewhere around there).

YouTube Channel: https://www.youtube.com/channel/UCU1...CR6IZ7crfdZxDg

 

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It'll dpend, too, on fuel/AAM configuration as well. I just tried with a Vaziani takeoff, fuel 80% and 4 AAMS. Performed a standard full mil power takeoff and and full mil intercept climb (maintain 860 TAS during the climb) to 11,000 m. At 88% RPM, I settled in at 10,100m for the cruise with a TAS of around 700. Reducing throttle one more percent to 87% started causing issues. By the time the phugoid oscillations stopped and the airspeed was dialed in, I was down to around 7000 meters (or somewhere around there).

 

Sounds about right, that's pretty much what I'm seeing. I tried a similar thing with the heaviest load I could find (max FAB-500's, 2x R-73's & ECM, works out at roughly 31,000Kg with max fuel) and with that sort of load even 90% RPM was really marginal.

System Spec: Cooler Master Cosmos C700P Black Edition case. | AMD 5950X CPU | MSI RTX-3090 GPU | 32GB HyperX Predator PC4000 RAM | | TM Warthog stick & throttle | TrackIR 5 | Samsung 980 Pro NVMe 4 SSD 1TB (boot) | Samsung 870 QVO SSD 4TB (games) | Windows 10 Pro 64-bit.

 

Personal wish list: DCS: Su-27SM & DCS: Avro Vulcan.

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It's also worth noting that at relatively low altitudes any RPM setting that will allow for steady speed will result in a speed that's too high to allow for neutral manual pitch trim. I say manual because both the radar & barometric altitude hold modes of the ACS will allow for neutral pitch trim at these speeds.

System Spec: Cooler Master Cosmos C700P Black Edition case. | AMD 5950X CPU | MSI RTX-3090 GPU | 32GB HyperX Predator PC4000 RAM | | TM Warthog stick & throttle | TrackIR 5 | Samsung 980 Pro NVMe 4 SSD 1TB (boot) | Samsung 870 QVO SSD 4TB (games) | Windows 10 Pro 64-bit.

 

Personal wish list: DCS: Su-27SM & DCS: Avro Vulcan.

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