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lyonhaart001 avatar image
lyonhaart001 asked lyonhaart001 commented

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





flightmodel
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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

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lyonhaart001 avatar image lyonhaart001 FlyingRaccoon ♦♦ ·

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

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lyonhaart001 avatar image lyonhaart001 FlyingRaccoon ♦♦ ·

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.


screenshot-2022-04-25-103514.jpg

Photo 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



engines.zip


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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
1650959644802.png

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1650959644802.png (506.7 KiB)
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lyonhaart001 avatar image
lyonhaart001 answered lyonhaart001 commented

Man, this is a nightmare. :( 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.

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Propeller thrust scalar do function.

Here's a comparison of Caravan performance with thrust_scalar = 1.0 vs thrust_scalar = 2.0

1651138948567.png


1651138963686.png


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


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1651138948567.png (225.0 KiB)
1651138963686.png (239.4 KiB)
lyonhaart001 avatar image lyonhaart001 FlyingRaccoon ♦♦ ·

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.

screenshot-2022-04-28-172439.jpg

screenshot-2022-04-28-172238.jpg


screenshot-2022-04-28-172127.jpg

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





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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

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