What you could do is measure the vertical speed with power idle prop windmilling versus prop feathered. On the TBM you’ll end up with the exact same vertical speed when maintaining glide speed which means there is no propeller drag. The Kingair can even keep flying indefinitely with power idle…
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I tested that in Caravan… exactly the same speed.
Thanks! So can we conclude the prop drag is not modeled in MSFS?
No we can’t. I determined there is beta_range for DA-62, which is a small propellor aircraft, no turbo.
Could it be the case, that beta_range (or feathering, things with blade angle) are have only minor influence on turboprops ? I found something about airflow in these engines…
I only investigated the SDK airplane DA-62. For DA-62 - no turbo - there is some drag effect when lowering the beta_range_min value, which becomes the blade angle when throttle is lowered and propellor starts windmilling. When I put higher values in beta_range_min I have less drag while landing, I see more airspeed. The default for this parameter is 11 degrees. When I lower it further, at first the aircraft overall speed will be slower (between 8 and 11) and when I put values below 8, the aircraft can’t take off properly. So I think they implemented something, but not all. When throttle goes up, the blade angle should increase… and not stay on the beta_min value ! (@anon50268670 correct me if I’m wrong please… when this analysis is correct we may have a Zendesk ticket for this)
As mentioned before, simply experimenting with the blade angle in the cfg file has not much to do with FDM design/analysis.
The blade angle not increasing with increasing throttle is a classic case when altering the blade angle without working on prop curves. That’s not a case for the zendesk.
Btw. A ‘turbo’ is a super/turbocharged piston engine, not a turboprop.
I used the SDK aircraft DA-62. The only analysis you have put here sofar on this forum is #3 which is not a proper test, let alone “FDM” or whatevery you call a good analysis.
I don’t know how many flight models you have designed and/or analyzed in the last few decades, but if you can’t agree that my #3 post is a proper test, you don’t know much about flight model design.
There’s nothing about the propellor model you describe in #3, you just expect result (drag) and you did not vary any input… you just expect your aircraft to have a significantly lower airspeed while landing without flaps… you’re right with that expectation, but you have no idea how much drag there actually is, because you did no relative measurement varying inputs. I “simply experimented” with blade angle range and looked at the effect for various values. So before criticizing me, it would be appropriate you show some actual results. The notion “it does not break” is simply not sufficient for any valid conclusion.
It’s not my fault If you are unable to comprehend the performance section of a POH/AFM and hence to draw the correct conclusions!
Honestly, you don’t know what you are talking about.
What missing actual results are you talking about?
What else do you suggest besides comparing aircraft performance in the sim and IRL.
edit: I did search, but I couldn’t find the part where I wrote “it does not break” (whatwever this means)
On turboprops that is correct, the single engine aircraft I’ve tested are fairly accurately modelled.
The link you posted is about turbofans, not props. On turboprops the drag effect on a windmilling prop is much higher actually compared to piston engines, at least on the turboprops I flew. There is a reason why every multi-engine turboprop has an autofeather system or at least a drag reducing device installed.
@anon50268670 that is what I found as well, for DA-62 it does seem to work… but I’m not sure it it is correct. I can’t put things lower than 8 degrees… why is that… beta is supposed to be a range ? and not a single setting ?
And now let’s end this rant, mister alpha insider… I know little of aircraft, but I’ve been building simulators with parameters for 20 years or so. I do know how to test. This interesting thread went off topic on two fronts now… It’s not about XPlane and also not about your qualifications toward me. If you really want to proceed this debate, put a PM please.
A contradiction IMO. Anyway, no PMs necessary. I’m out.
Let’s proceed… for TBM-930 Turboprop I see these inputs, I leave out the (many) feathering settings,
Beta range
beta_max = 60 ; Maximum blade pitch angle for constant speed prop, (degrees)
beta_cruise = 45; usual beta in cruise (full torque) used to setup prop Cx (degrees)
beta_min = 25 ; Minimum blade pitch angle for constant speed prop, (degrees)
minimum_on_ground_beta = 25.0 ; Miminum pitch angle on ground, (degrees)
Reverse prop
prop_reverse_available = 1 ; Prop reverse available? 0=FALSE, 1=TRUE
minimum_reverse_beta = -15 ; Minimum pitch angle in reverse, (degrees)
Also available beta related stuff, but Greek for me…
power_absorbed_cf = 1.3 ; Coefficient of friction for power absorbed by propeller
prop_cx_min = 0.30; Value of the propeller Cx when beta = 0
prop_cx_at_cruise_beta = 1.0; Value of the propeller Cx when beta = beta_max
advance_ratio_on_effective_beta = 0.2; Factor of the advance ratio on the effective beta
prop_cx_parabol = 1; 0 = use old interpolation, 1 use parabol equation for Cx
Any suggestions ? (I won’t dare to go speculate any further about these things 
)
The blade angles are completely off, I did compare them with the EASA TC some time ago, unless they changed something in the meanwhile they are off by a considerable amount. Especially the ground idle setting of 25 degrees is completely wrong, should be around zero or even slightly negative.
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The blade angle in the cfg file doesn’t mean anything without knowing the associated prop curves.
That’s why I mentioned that this value is basically just for fine tuning.
Modifying the prop curves, a blade angle of 2.5° can have the same effect like a blade angle of 25°.
Ah ok, yeah I don’t really know how any of that works.
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