Airplanes power: kW -> kN problem?

[Milko]

Hello

I'm doing the concorde. I'm sensing a strange anomaly. Setting a power 33810kW (Airbus A321) I get a power of 294kN. Setting a power 68200kW (concorde) I get a power of 226kN (then minor).

Giuseppe

[jamespetts]

Giuseppe,

do you specify tractive_effort=[some number] in the .dat file? The extrapolation of tractive effort from power is intended only as a makeshift solution in a case where the .dat file creator has not specified it in the .dat file.

[Milko]

Hello James

I did not know!  , I always set the power to achieve the desired Tractive effort. Planes do not have the power but the thrust (similar to Tractive effort). Ok ... I'll try to get files loaded to set the Tractive effort instead of power. 

Giuseppe

[jamespetts]

Giuseppe,

really, you should set both the power and tractive effort, as it is very difficult to guess one from the other accurately.

[ӔO]

don't airplanes only really need thrust, which is kN?

[Milko]

Hello

The problem is that the power for jet aircraft does not exist. The characteristics of the motors specify only the thrust. If no problem, I would specify in ".dat" the only thrust and then leave power in automatic calculations, I would not know what a power set ..

Giuseppe

[jamespetts]

Hmm, as a matter of physics, aircraft engines must necessarily actually have power (which is just energy divided by time): it is necessarily true that aircraft engines use a certain amount of energy for any given amount of time. It might be that, like steam locomotives, their power is not generally measured, but they must have a particular amount of power. As with the steam locomotives, the only way to do it, I think, is to deduce the correct level of power by working out how the aircraft should perform (how fast that they go when fully loaded principally).

[ӔO]

Hmm, one problem with the various types of engines is the power rating. Turbofans are usually given in thrust (kN), while turboprop and piston prop are usually given in power (kW).

If wiki is to believed, then...

GE CF6-80C2 produces around 44,700 kW of power and 244kN of thrust.
The numbers are actually pretty close, when looked at in imperial units.
59,900 hp of power and 55,640 lbf of thrust.

You have four of these on a 747-300, so you get a total of 178800 kW of power and 976 kN of thrust.


At the lower end, you have something like an ATR-72, which has 2x 1,846 kW turboprop engines, but no thrust given.

[Milko]

Hello

This link http://en.wikipedia.org/wiki/Thrust shows how thrust and power are convertible passing through speed. At constant thrust the power thus varies at different speeds.
I would say: we all agree a conversion factor and apply it to all the planes, what do you think? Starting from what was said to set the AEO factor = 1800 (ie 1kN = 1800kW)?

Giuseppe

[jamespetts]

That seems to be a sensible idea - and that starting point can be modified if in-game behaviour is not found to be realistic.

[ӔO]

I did some research, and I think the reason you don't find thrust for turboprop and reciprocating propeller are due to this: http://en.wikipedia.org/wiki/Constant-speed_propeller and this: http://en.wikipedia.org/wiki/Propeller_%28aircraft%29

I did some calculations, and 1800kW = 1kN is what I would use for turbofan airplanes.
For propeller airplanes, I would use something else.

I compared the weight to thrust ratio for 747-300, it has significantly more than an ATR72 would if went with 3700kW = 2kN.

747-300: 377,000kg/244kN = 1545kg/kN
ATR-72: 22,500kg/2kN = 11250kg/kN

It doesn't look right. 14kN would put the ATR-72 into a similar area.
22,500kg/14kN = 1607kg/kN
Since the ATR-72 is designed to fly at slower speeds, it will have wings that have more lift and require less thrust. 14kN of thrust from the two 1850kW engines would be my best guess. or around 265kW = 1kN

[Bernd Gabriel]

The physics code does not require an explicit power figure. Vehikel_besch_t::loaded() calculates force and power from what ever is given. Of course at least one of them must be given.

[Milko]

Hello

So:
Jet:  1kN -> 1800kW
Propellers: 265kW -> 1kN

As soon as possible I will upload the fixes in github.

Giuseppe

[Milko]

Hello

Excuse me, I made ​​a mistake. The factor to be applied to Jet is not 1kN = 1800kW but 1kN = 180kW .... in making the division I added a zero.

Giuseppe

[Milko]

Hello James

I placed the files of the aircraft by adjusting power and thrust.
I also removed all "increase_maintenance_after_years = 30".
I do not have access to your PC with github at this time, James can you please upload it?
The name of each zip file is the name of the destination folder of files.
I also added the characters "----" to end of file.

Giuseppe

[jamespetts]

Giuseppe,

thank you for that. I think that it's probably better to wait until you have Github access before adding these, however, as there might be differences on the Experimental versions of these aircraft from your original source files from which I presume that you have modified these, which differences need to be preserved. Without using Github, that would mean manually copying the relevant changes from each file, which would become rather tedious, as there are a great many of them. There is no hurry in any event, as there are quite a few things that I need to do to the pakset before I can release the next version.

Thank you again for your tireless work on the aviation side of things!

[Milko]

Hello James

I modify the files after download directly from your repository, I downloaded this morning.

Giuseppe

[jamespetts]

Ahh, in that case, things are much easier. Done!

[Milko]

Hello James

Thanks

A curiosity:
You think you make a new release of pak128brit short?

Giuseppe

[jamespetts]

It's difficult to predict actual timings, but the plan is as follows: I am waiting for Bernd to fix some bugs related to aircraft interacting with the braking physics system in the latest version of -devel. I then plan to put out a release candidate of the executable, and let that be tested for a few weeks before the main executable is ready for a full release.

Whilst all that is going on, I plan to finish some fairly significant works that I have started on the pakset. These include:

(1) filling in gaps in the timeline of rail vehicles, especially in the early era, and especially relating to railway carriages;
(2) recalibrate comfort, as the current calibration has anomalies;
(3) recalibrate the different types of railway track and make sure that each type has its own unique graphics;
(4) properly merge the latest bridges from Standard with existing bridge types;
(5) implement the factory boost system; and
(6) remove obvious anomalies in the price/maintenance cost of vehicles.

If anyone would like to help with any of these things (particularly no. 5), this would help to accelerate the release.