Exactly How to Tune Turboprop Propeller 'RPM' Range?

Hello Team Asobo and FlyingRaccoon, I have one more question. Hopefully this
will be the last on Turboprops. How exactly does one adjust Prop RPM top end?
Lets say mine is spiking to a max of 4K RPM. I need it to be at 1200 to 1400
RPM max, (very low). Gear Reduction does very very little. Is this done with
the prop_power_cf table? Many thanks, Bill, (otgebp) Lionheart Creations

Hello @lyonhaart001 What do you mean by “Gear
Reduction does very very little”
? Prop rpm should be in direct relation of
your N2 RPM ( N2 rpm / gear_reduction_ratio ) Regards, Sylvain

Good morning Sylvain, By setting gear Reduction to 400.1, I was still at 2500
RPM, where before it was 4K+. My thoughts are, perhaps I was on the wrong
path, but maybe that is the route. Should I just keep increasing gear
reduction? If that is the route to go, I am very happy with that. The gearbox
on the real-world engine is quite big. Bill LHC

I tried bumping Gear Reduction to 880.1, then to 2020.1 and Prop RPM was still
at roughly 3400 RPM at highest spike. It did lower a bit on idle, but not on
spike, Max Throttle.

shows idle, 50% condition lever. With Gear Reduction at 2020.1, I can get an
idle of 660 prop RPM, but she still spikes up to 3400K RPM on the prop. This
is my present ‘engines’ config. I am using an early Asobo turboprop model. The
new one for KingAir and Caravan couldnt be used as I couldnt increase the
power enough. The old versions are easily tuneable. Bill LHC

Did you monitor the N2 RPM as well and if so, what’s its value? For example,
here’s the TBM 930 at full throttle: Prop rpm is engine rpm / gear ratio

Many thanks Sylvain. Interesting. My N1 RPM was off the charts at full
throttle. Thank you for pointing out these functions in the engine debug
window. I am very grateful. This also shows my ‘spike issue’ better, bronze
colored arc, bottom right. The TBM has this also, but mine for some reason
kicks in at 55% approximately and jumps high. Perhaps a full redo of this
section and start over. :frowning: Thanks again. I hope SU9 is going smoothly. Bill

Man, this is a nightmare. :frowning: It used to be that adjusting power scalers for
either turboprop or propeller increased that section’s output. But not
anymore. Scalers arent working. If I increase the thrust of the prop, nothing.
If I increase the SHP power to the amount that gets the plane to the right
speed, my prop is doing 5,000 RPM instead of 2000, and i need that at 1200
average / 1400 spiked, and also my turbine is into the one million zone,
somehow. I have to adjust SHP to nearly 12K SHP to get 390 knots max. Gear
ratio at that level does nothing. Gear Ratio at 20000.1 does nothing when your
turbine is cooking at 1M+. I tried an older version Asobo Caravan ‘engines’
file, adjusted it to run at 1200 RPM prop revolutions, kept SHP down and went
for thrust scaler on propeller to just get around it that way, and nothing
happened. Scalers do not function anymore. If only there was an easy way to
get my plane to do 390 knots max, prop at 1200 / 1400 RPM.

Propeller thrust scalar do function. Here’s a comparison of Caravan
performance with thrust_scalar = 1.0 vs thrust_scalar = 2.0

You must proceed in order. 1 -
Configure the turbine according to the POH (proper N1, N2, output hp/thrust) 2

  • Configure the propeller the same way (size, beta, thrust, etc…) 3 - Adjust
    aircraft performances. You don’t want to do 3 by completely changing 1 and 2
    if they were correct or you’ll have other problems. If your aircraft
    performance is not matching your expectations, first make sure you’re getting
    correct thrust from 1 and 2. Then, check your aircraft weight, lift and drag
    as this will also impact performance. Regards, Sylvain

Hey Sylvain, I tried your version new version, Caravan SU9, latest Engine
config. I changed SHP from 867 to 2867, rebuilt, and it did 200 knots. I then
tried 4867 SHP, and that too flew 200 knots. I then made it 12867 SHP and it
too flew 200 knots. I verified through Aircraft Editor that it was loading the
data after each build. I then tried the Scaler, advancing it to 6.0 to see if
I got a result, and no. 200 knots.

I just cant seem to get the
speeds I need. :frowning:

This is my Turboprop section; [TURBOPROP_ENGINE] tp_high_idle_throttle_pos=0
power_scalar = 6 ; Scalar on Turboprop power maximum_torque = 2397 ; Maximum
torque available (ft-lbs) torque_automatic_limit=2500 engine_friction_table =
-10:-0.2, 0:0, 10:0.5, 70:0.5, 105:0.5 ; Rpm → Friction torque
n1_to_shaft_torque_table = 0:0, 66:0.05, 100:1.0, 110:1.1 ; Corrected N1 →
Shaft Torque rated_shaft_hp = 12867 PowerSpecificFuelConsumption = 0.66 ; SFC
tp_idle_range = 0.00 ; increase of n1 idle at high mixture (Percent)
free_turbine = 1

With last years version of Caravan engine config (I saved it) I can change SHP
to 12K SHP and I get my 390 knots at max throttle, flat out. But for some
reason, the newest Caravan system doesnt want to fly faster.

I think I am going to stick with my present original Asobo version with the
prop doing over 4K. At least the speeds are working. Perhaps someday I can
find a way to reduce the prop RPM and keep other speeds proper. Thanks anyways
for your help. I hope everything is going well at Asobo. Kind regards, Bill

Bill, You also need to adjust your aircraft aero configuration. Just putting
more thrust through it doesn’t guarantee a particular speed. The current
system is much more grounded in reality, so if you need more speed and you
have the right thrust, then you need to decrease drag. That being said, I’m
curious as to what you are trying to model that would be capable of nearly
400kts on a single PT6. That puts the plane well above even superfast turbine
singles like the TBM and the M50. That would be an extremely small and light
plane for a turbine like that or something far more slippery than has been
demonstrated yet in the real world. And, you’re missing a critical piece of
Sylvain’s advice: you must also configure the prop accordingly. The engine may
be capable of putting out that much horsepower, but it isn’t going to matter
for much if the prop is drag limited anyhow and won’t go any faster or more
efficiently. That’s the reason the old file is working more when you just
crank up the scalar, because the new file also includes the correct prop
settings: shape, thrust, Cd/Cl, twist, etc Again, none of these things should
be adjusted in isolation.

Thanks Matt for your input. The engine I am modelling is the PW127XT, the
100/150 series, slow RPM with about 2600 SHP approximate. The TBM is running
about 650SHP approximate. It ended up that I couldnt even get a power output
‘boost.’ It was showing output 750, and max output 12K, when experimenting
trying to get it to boost up. Something in the formula to get it to rise the
power output is being missed. Scaler (last result), Max SHP, etc, did nothing.
It ‘must’ be there somewhere. I just couldnt find it. Something was locking it
down to 750 SHP output max. A governor or something setting that I missed or
cannot see. Bill

@lyonhaart001 Not sure if this was finalized
but I have found the following works just great take the MAX RATED ENGINE RPM
for example 38100 (for My PT6-45) divide this by your Published MAX PRPM (in
my case 1870) therefore - 38100 / 1870 = 20.374 set Gear_reduction to =20.374
Bingo Bango :slight_smile: