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Does DCS model the electrical load on the aircraft and the corrisponding load that places on the engine?


Angel_Scott

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In an automobile engine, you can optionally upgrade your alternators like if you had a couple thousand watts worth of stereo in the back. The consequence is the magnetic feedback in the coils places a load on the engine, robbing power (just like your AC)

 

So my question is, does DCS model this effect, such that, if I need best possible speed out of my aircraft, turning off everything gives me just a little bit more, or is the electrical load on a modern aircraft so small compared to the thrust that this isn't really worth the time/money to model? Thanks.

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Aircraft do not work that way. Turning something off will not give you an increase in engine performance because there is technically no on/off switch that directly effects anything on the engine other than fuel flow or air flow. Aircraft that use an electrical starter will draw power from the aircrafts batteries like in a car or using an APU, however the electric generators on aircraft are designed to provide more than enough power to keep everything on permanently that is needed to operate the aircraft without causing additional mechanical work load on the engines.

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There will probably be some kind of loading, but the difference is probably close to nothing when you compare how powerful these engines are.

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On 12/15/2020 at 8:13 AM, Angel_Scott said:

So my question is, does DCS model this effect, such that, if I need best possible speed out of my aircraft, turning off everything gives me just a little bit more, or is the electrical load on a modern aircraft so small compared to the thrust that this isn't really worth the time/money to model? Thanks.

 

Don't quote me on the exact numbers, but, if you consider the radar system on an F-15 alone, that's approximately a 14-15kW system when operating at peak power.  Let's say the rest of the jet eats enough electrical power (ignoring hydraulics here) for 30kW, thus making our radar the largest single consumer of electrical energy (we still have a jammer and a couple other high-powered items so doubling the electrical cost isn't out of this world).

 

The engines on an eagle produce high double digits MW of work at peak power.  So, think about how much more power you'll get out of them if you shut everything down - not that I think you can, since the generator gearboxes will be turning constantly anyway.


Edited by GGTharos

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  • 3 weeks later...
On 12/17/2020 at 6:13 PM, Repth said:

Aircraft do not work that way. Turning something off will not give you an increase in engine performance because there is technically no on/off switch that directly effects anything on the engine other than fuel flow or air flow. Aircraft that use an electrical starter will draw power from the aircrafts batteries like in a car or using an APU, however the electric generators on aircraft are designed to provide more than enough power to keep everything on permanently that is needed to operate the aircraft without causing additional mechanical work load on the engines.

 

Aircraft work exactly that way.

 

Even on a jet engine a generator will not spin by magic, so it will have an effect on power output and it will load even a jet engine. The mechnical load on the engine is directly dependent on the electrical load of the generator and thus directly dependent on what is switched on in the aircraft. For AC, there is not even a battery in the line, for DC, the system is very like in a car. Will you notice this effect? In a jet, most of the time not, however this gets relevant if you draw really large amounts of power, like for example an AWACS does. My guess is, it is not modelled in the aircraft we have in DCS. If I think about it, even on the Yak-52, the mechanical load of the generator should not greatly exceed 6kW as a maximum and thus be less than 2% of TOP, not that I can think of any way of actually drawing 100A with the eletrical equiptment of that aircraft.

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On 12/15/2020 at 1:13 PM, Angel_Scott said:

In an automobile engine, you can optionally upgrade your alternators like if you had a couple thousand watts worth of stereo in the back. The consequence is the magnetic feedback in the coils places a load on the engine, robbing power (just like your AC)

 

So my question is, does DCS model this effect, such that, if I need best possible speed out of my aircraft, turning off everything gives me just a little bit more, or is the electrical load on a modern aircraft so small compared to the thrust that this isn't really worth the time/money to model? Thanks.

The biggest drain on thrust from engines BY FAR is the bleed (vs the electric generator).

 

The bleed is literally bleeding (who'd have guessed) thrust from 1 (or more) of the stages in the engines. Typically this is used to pressurize anything (cabin/suit etc) as well as provide options for window defog, crossbreed ignition, anti ice for engine cowl and/or LE parts of the wings. Not all aircraft are going to have all these, but going off memory, I know for sure the F18 have bleed switches/dials/levers and i'm almost sure the F16 does. The F14 has some VERY LOUD bleed air in the cockpit (that i like to turn off).

 

Does DCS model extra thrust if you intentionally disable these switches? I don't care how powerful anyone claims these engines to be, if you take out the thrust produced in 1 or 2 stages then you're looking at ~5% - depending on how many stages these engines have.

 

edit: i dont think DCS models anything like the depth here required. there's just too much going on in a multiplayer setting with SAMs and AI aircraft etc, with over a hundred missile types all interacting, for hardware to have time to compute these sorts of depths.


Edited by FoxxyTrotty
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4 hours ago, FoxxyTrotty said:

 

The bleed is literally bleeding (who'd have guessed) thrust from 1 (or more) of the stages in the engines. Typically this is used to pressurize anything (cabin/suit etc) as well as provide options for window defog, crossbreed ignition, anti ice for engine cowl and/or LE parts of the wings. Not all aircraft are going to have all these, but going off memory, I know for sure the F18 have bleed switches/dials/levers and i'm almost sure the F16 does. The F14 has some VERY LOUD bleed air in the cockpit (that i like to turn off).

 

Does DCS model extra thrust if you intentionally disable these switches? I don't care how powerful anyone claims these engines to be, if you take out the thrust produced in 1 or 2 stages then you're looking at ~5% - depending on how many stages these engines have.

This is not how it works and espacially not how it is calculated. The bleed air taken from the engines is indeed reducing thrust, but you do not reroute an entire stage. There are typically two controlled bleed air valves after two different compressor stages which will take some (very varying) amount of compressed air for auxiliary purposes. And again, you are not bleeding thrust, as the compressors do actually not generate any, but air flow. Thrust is generated in the nozzle.

 

For the different aircraft we have in DCS, bleed air usage is very different. Most common usage across fighters is for cabin pressurization, however to a much lesser extend and thus required power than in an airliner. Than there is different stuff, like cooling of electronic bays, or even lift generation in form of blown flaps in the MiG-21. Now for the performance impact, there is not alot of material on this site for fighters, as they have nearly no stuff which is only optionally used powered by bleed air, thus the manuals don't contain any references. The influence of packs on airliners, which requrie by far the most bleed air, is somewhere in the region of 2% at take off, so it is safe to assume the influence of all the bleed air powered stuff on fighters is significantly lower and thus in a region were it can safely be neglected. You would probably not notice the difference anyway.

 

On a site note, there are engine operating points where unused air is bled from the compressors intentionally to prevent compressor stalls.

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  • 8 months later...
On 1/7/2021 at 9:48 AM, Jonne said:

 

Aircraft work exactly that way.

 

Even on a jet engine a generator will not spin by magic, so it will have an effect on power output and it will load even a jet engine. The mechnical load on the engine is directly dependent on the electrical load of the generator and thus directly dependent on what is switched on in the aircraft. For AC, there is not even a battery in the line, for DC, the system is very like in a car. Will you notice this effect? In a jet, most of the time not, however this gets relevant if you draw really large amounts of power, like for example an AWACS does. My guess is, it is not modelled in the aircraft we have in DCS. If I think about it, even on the Yak-52, the mechanical load of the generator should not greatly exceed 6kW as a maximum and thus be less than 2% of TOP, not that I can think of any way of actually drawing 100A with the eletrical equiptment of that aircraft.

Most jets have a CSD or Constant Speed Drive that drives the generator, surprise surprise at same constant speed through idle to max rated thrust and above. It is connected to the accessory gearbox or similar. I have never seen any ITT/EGT/TIT changes or loss of jet engine performance IRL or in a manual due to generator running at max capacity. Systems are designed in such a way that you are able to load these and use everything you need. Certainly true on modern combat aircraft as well as civilian equipment.

However what does have a huge performance penalty is using bleed air for anti/de-ice purposes and or if pneumatics are used to run hydraulics in addition to electrics and pumps connected to the gearbox.

To add to that, some older soviet types might and western piston general aviation aircraft do suffer from loss of engine power with excessive electrical demands. Some IRL have automatic shedding of generators in case of exceeding or approaching engine limits such as the Mil-8/17. This is well simulated and quite accurate in DCS.


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you’ve seen the effects you just don’t recognize them. the accessory gearbox is usually on the N2 section of the engine. the more load on the N2 section the more fuel is required for it to operate the N1 section for a given N1/EPR rating. The impact of electrical load (and hydraulic load) is to fuel consumption. In a nutshell more sparks = less range

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