Just a few hours ago I saw THIS POST and thought about it, I really haven't seen this kind of information anywhere. Consequently, I armed myself with spreadsheets and a test bench and started having fun.
To begin with, it's worth deciding how we're going to do the measurements in the first place. I made a test bench consisting of a default engine part and fuel tanks and spawned it on the “Bandit Airport” spawn point. There was a label attached to the test bench, which displayed such parameters as RPM and engine thrust (in unknown units, which I'm too lazy to find out).
Below are the default settings of the part, which were always used.On each test only one parameter was changed, which affected the results, all other parameters remained unchanged.
P.S. By Stable thrust and stable RPM, I mean that the engine mode is settled and the parameters do not change for a long time.
Startup
First, some rather interesting behavior of the engine itself was noticed as it gained thrust. At some point, both rpm and thrust are above a stable value, but immediately after the peak they level off. This behavior has been observed in all engines, but I have not measured how exactly these parameters change depending on the engine parameters.
Blades Count
Further measurements were taken with different number of blades and the result is presented below. It can be seen that as the number of blades increases the engine thrust also increases, but with each new blade its effect decreases (Which is shown in the neighboring table). The RPM does not change.
Thickness
The blade thickness also shows a similar pattern, but there is a strange anomaly in the Ratio area as the difference 1.6/1.4 was unexpectedly smaller than 1.8/1.6 and 2.0/1.8. All experiments showed that with increasing parameters the total thrust increase decreased (it looks like either a root function (which is more likely) or a logarithmic function, but more measurements are needed), and it should be a smooth function, but at this point there is a strange anomaly.
Diameter
Let's move on to the most interesting point - the diameter of the blades. In all other measurements, the stable RPM did not change in any way, but here we can observe the dependence of the number of revolutions on the blade diameter (more diameter - more thrust and less revolutions)
Power
Last of the measurements for today. It is very boring, as it did not show anything new. As power increases, so does thrust, blah, blah, blah.
End
I don't have time to pursue this issue further at the moment, perhaps I will continue later.
Below is a list of questions that have been left unanswered, if anyone decides to tackle them, feel free to do so, don't forget to tag me so I can see the results.
Further research questions :
1) How does the steady state output vary with different engine parameters (time, “Peak” height, its location, and whether it will change at all). This question requires a large number of measurements and is quite labor intensive.
2) The logarithmic or root function determines the stable engine thrust index and with what coefficients.
3) What is the reason for the Anomaly in engine thrust measurements as a function of thickness? Is it a bug, my mistake, or is it really like this?
I hope it was informative enough, and worth the time spent.
Link to a table with the collected data so you can see for yourself.
@MonsNotTheMonster that's not true at all.
Alright, read it.
A good start, though speed and engine pitch remain unanswered. Obviously power shouldn’t matter if RPM is the same, so it’s possible that to maintain the same RPM the pitch differs, producing a difference in thrust.
Oh, yeah.
I believe RPM is probably just, well, RPM, but thrust is absolutely in newtons. The smallest jet engine gives 15000 flat, its rated thrust.
Not sure why you’d want that either. Thing would be useless.
@MonsNotTheMonster 0 pitch. That produces no thrust, doesn’t it?
If not, a slight negative pitch would probably do the job. Not sure if XML accepts any value or only in steps, though.
@hpgbproductions
All tests were conducted with automatic propeller pitch control.
It would be interesting to see how the behavior of the engine would change with the use of manual control.
Are you using auto prop pitch? The startup table suggests that the engine goes to 110% stable rpm first, builds up prop pitch (and thrust), and drops to 100% rpm
@MonsNotTheMonster
The magic is that the Cessna's engine idles to create thrust, but the brakes on the wheels keep the airplane from moving.
@Graingy watch how the cessna's engine act in the vid.(The airframe doesn't go forward) And try to replicate it in sp(fixed pitch blades).
@MonsNotTheMonster I’m confused what you’re getting at.
@Graingy fixed pitch, that doesn't produce thrust when idle, in sp, it doesn't happen. I'm talking about this one, this doesn't happen in sp.
I do know about the manual pitch :v
@MonsNotTheMonster I’m confused. You want full RPM with no thrust? That’s manual pitch.
@Graingy fixed pitch propellers do exist, but by the time you increase the throttle, again, that's where it starts to produce thrust. I wanna simulate how a cessna's engine and its propeller blades act(I want them to not produce thrust while on full rpm or on idle)
Propeller engines in SP are super duper poopy goopy butt ass doo doo.
I hope they get a complete overhaul in SP2...
NEERRRRRRRDD!
I’m definitely gonna have to read this later.
@MonsNotTheMonster you know that fixed pitch propellers exist in SP, right?
The thing is, when the propeller pitch blades are moved to a certain degree, that's when it starts to produce thrust. Which is imo, unrealistic. Most propeller blades are fixed, like the cessna and the older warplanes. And I tried to make a funky tree code that simulates a somewhat "realistic" engine(low rpm when engine start), it somehow worked, if the propeller pitch blades are movable(set the input from VTOL to throttle). Check my CT-1C's engine for more info :v
In other words propellers are broken to high hell.
This is known.
@AndrewGarrison this is pertinent
@Graingy
This may be of interest to you.