P3D v4 Engine RPM reading high

Hey all,

My planes Redline on RPM is about 2700, but its reading 7500... !

I guess the new styrofoam, low mass / high inertia pistons paid off...

Anyone know why this might be happening?

Code:
    <Element>
      <Position X="22" Y="95"/>
           <FormattedText X="36" Y="20" Font="Arial Bold" FontSize="18" Adjust="Center" Color="White" Bright="Yes">
         <String>%((A:GENERAL ENG RPM:1, RPM))%!04d!</String>
          </FormattedText>
    </Element>



[GeneralEngineData]
engine_type = 0 //0=Piston, 1=Jet, 2=None, 3=Helo-Turbine, 4=Rocket, 5=Turboprop
Engine.0 = 2.0, 0.0, 0.5 //(feet) longitudinal, lateral, vertical distance from reference datum
fuel_flow_scalar= 0.29 //Fuel flow scalar
min_throttle_limit = 0.0 //Minimum percent throttle. Generally negative for turbine reverser

[piston_engine]
power_scalar = 1.0 //Piston power scalar
cylinder_displacement= 90.3 //Cubic inches per cylinder
compression_ratio= 8.5 //Compression ratio
number_of_cylinders=6 //Number of cylinders
max_rated_rpm= 2700 //Max rated RPM
max_rated_hp= 300 //Max rated HP
fuel_metering_type= 2 //0=Fuel Injected, 1=Gravity Carburetor, 2=Aerobatic Carburetor
cooling_type= 0 //0=Cooling type Air, 1=Cooling type Liquid
normalized_starter_torque= 0.3 //Starter torque factor
turbocharged= 0 //Is it turbocharged? 0=FALSE, 1=TRUE
max_design_mp= 30 //Max design manifold pressure, (inHg)
min_design_mp= 15 //Min design manifold pressure, (inHg)
critical_altitude= 0 //Altitude to which the turbocharger will provide max design manifold pressure (feet)
emergency_boost_type= 0 //0=None, 1=Water Injection, 2=Methanol/Water injection, 3=War Emergency Power
emergency_boost_mp_offset= 0 //Additional manifold pressure supplied by emergency boost
emergency_boost_gain_offset= 0 //Multiplier on manifold pressure due to emergency boost
fuel_air_auto_mixture= 0 //Automixture available? 0=FALSE, 1=TRUE
auto_ignition= 0 //Auto-Ignition available? 0=FALSE, 1=TRUE
max_rpm_mechanical_efficiency_scalar= 1.0 //Scalar on maximum RPM mechanical efficiency
idle_rpm_mechanical_efficiency_scalar= 1.0 //Scalar on idle RPM mechanical efficiency
max_rpm_friction_scalar= 1.0 //Scalar on maximum RPM friction
idle_rpm_friction_scalar= 1.0 //Scalar on idle RPM friction
 
Last edited:
Thanks Tom.

The original template is the stock Extra 300 from FSX. I lowered the prop diameter from 6 to 5, moved that backwards about a foot, and changed it to a 2 bladed prop from a 3. Thrust scaler reduced to .6.

This is the Prop data // BEGIN /////////////////////////////////////////////////

[propeller]
thrust_scalar = 0.6 //Propeller thrust scalar
propeller_type= 1 //0=Constant Speed, 1=Fixed Pitch
propeller_diameter= 5.0 //Propeller Diameter, (feet)
propeller_blades= 2 //Number of propeller blades
propeller_moi= 3.78 //Propeller moment of inertia
beta_max= 0 //Maximum blade pitch angle for constant speed prop, (degrees)
beta_min= 0 //Minimum blade pitch angle for constant speed prop, (degrees)
min_gov_rpm= 0 //Miminum governed RPM
prop_tc= 0.1 //Prop time-constant
gear_reduction_ratio= 1.0 //Propeller gear reduction ratio
fixed_pitch_beta= 30.75 //Fixed pitch angle of fixed pitch prop, (degrees)
low_speed_theory_limit= 80 //Speed at which low speed theory becomes blended in (feet/second)
prop_sync_available= 0 //Prop synchronization available? 0=FALSE, 1=TRUE
prop_deice_available= 0 //Prop de-icing available? 0=FALSE, 1=TRUE
prop_feathering_available= 0 //Prop feathering available? 0=FALSE, 1=TRUE
prop_auto_feathering_available= 0 //Prop auto-feathering available? 0=FALSE, 1=TRUE
min_rpm_for_feather= 0 //Minimum RPM for prop feathering
beta_feather= 0 //Feathering pitch angle (degrees)
power_absorbed_cf= 0 //Coefficient of friction for power absorbed by propeller in feather
defeathering_accumulators_available= 0 //Defeathering accumulators available? 0=FALSE, 1=TRUE
prop_reverse_available= 0 //Prop reverse available? 0=FALSE, 1=TRUE
minimum_on_ground_beta= 0 //Miminum pitch angle on ground, (degrees)
minimum_reverse_beta= 0 //Minimum pitch angle in reverse, (degrees)
 

Roy Holmes

Resource contributor
Bill,
You have a 300 hp engine driving a prop that probably only needs a 100 hp engine.
And it is a fixed pitch one so there is no mechanism to keep it from revving. Then you reduced the amount of work it has to do by 0.6. That’s why it is over revving like crazy.
Roy
 
Thanks Roy. I could have sworn I used the full prop system from the Extra. I'll go back and redo things. Very much appreciated.
 
So, I copy paste off a new aircraft config and begin my work.. copy in the Mooney engine/prop system, and find that it too is redlining up at 6K RPM.

sigh..
 
Copied out the Cessna 172 Engine/Engine/Prop sections. Same thing. High RPM ranges over 5K RPM. I must have done something to the AIR file to cause this. :S
 
Assuming that " A:GENERAL ENG RPM:1, RPM " is the correct variable and that there is no Recip variable in your SDK's , then
run an analogue to digital comparison .

Grab a circular analogue RPM gauge place it temporarily in your panel or as a pop up window .
Run the analogue RPM at 2,500 , copy your digital readout value , then divide your Digital value by your analogue value to get a Factor value .
Run a series of different analogue RPM's , and check if their value with Factor value applied equals the Digital value in each case .
If the Factor value is accurate at all RPM's then simply apply the Factor value into your Digital readout script .

Cheers
Karol
 
Assuming that " A:GENERAL ENG RPM:1, RPM " is the correct variable and that there is no Recip variable in your SDK's , then
run an analogue to digital comparison .

Grab a circular analogue RPM gauge place it temporarily in your panel or as a pop up window .
Run the analogue RPM at 2,500 , copy your digital readout value , then divide your Digital value by your analogue value to get a Factor value .
Run a series of different analogue RPM's , and check if their value with Factor value applied equals the Digital value in each case .
If the Factor value is accurate at all RPM's then simply apply the Factor value into your Digital readout script .

Cheers
Karol
I JUST THOUGHT THIS IN BED! I JUMPED OUT OF BED TO WRITE THIS VERY THING, lolol.... Thanks Karol. This verifies it.

We had done this years ago with a turboprop. It was too difficult to change something. It was like EGT or something, so we gave it a division value (something like that), and the readout was proper.

Now, how to write that in code....

7400 RPM must equal 3,000 RPM. 3600 RPM would then by 1500 RPM at the gauge readout at 50% power.
 
This might be it. This was the tach code for the Quest Kodiak. We had to change 'something'. I think this might be it. It might have been N1, not sure.

<Value Minimum="0" Maximum="3.8397">(A:GENERAL ENG1 RPM, rpm) 3000 min 0.00128 *</Value>
 

Roy Holmes

Resource contributor
Bill,
I can see why you might need to fudge something like EGT which is not a direct measurable characteristic in the sim, but RPM is dead on.
If you suspect the gauge and it was an analog one, scaling is a likely source of error, but a digital gauge should give an accurate reading if you have the units correct, which you have.
Your Aircraft.cfg data looks to be correct so I suggest you look at Record 509 in the air file. This is engine friction vs RPM. Too low friction will allow the engine to over rev.
The right hand peak number for the Extra is 30 at 2675 RPM but it is 47 at 2575 in the Mooney Bravo. At first sight that would cause the Mooney Bravo to over rev if it had the Extra air file value.
Basically, almost all the piston engine parameters are in the aircraft.cfg but friction is also important so you really should use the correct air file for the model in question.
Roy
 
Hey Roy,

Many thanks for that. That must be where I messed up. I wonder if I change it, if things would completely fall apart on my fuel ranges and top end speeds?

In the mean time, I did get the RPM digital readout to fudge correctly. I do not have to retune my speeds and fuel ranges. The gauge is reading right on. But the dial gauge is not.

Also, and correct me if I am wrong, this is supposed to be Prop RPM if I am correct, not engine RPM. You have a Garmin G1000 that shows Manifold and RPM, and if I am correct, you use the Manifold and Prop RPM with each other to tune your prop RPM. So that is working fine with the digital readout, but not the dial. This is what I have. I tried some variations, but I get no movement.

So, presently this fudge calc gives me the correct Prop RPM;
<String>%((A:pROP1 RPM, RPM) 0.41 *)%!04d!</String>

And this dial hates fudge...

Code:
         <Rotate>
                 <Value Minimum="3000" Maximum="7500">(A:PROP1 RPM, rpm) 3000 min 0.41 *</Value>
            <Nonlinearity>
                <Item Value="2000" X="13" Y="162"/>
                <Item Value="3500" X="52" Y="95"/>
                <Item Value="7000" X="95" Y="151"/>
            </Nonlinearity>
            <Delay DegreesPerSecond="45"/>
        </Rotate>

I tried varying the Values, 1500-2500-3000 is what its supposed to be, with 1500 as 0 point.
 

Roy Holmes

Resource contributor
Bill,
"max_rated_rpm= 2700 //Max rated RPM is engine RPM".
Prop RPM would be engine RPM times "gear_reduction_ratio= 1.0 //Propeller gear reduction ratio"
Since that is 1.0 your Prop RPM should be the same as engine RPM
Typical for Piston engine.
Turbo props have a substantial gear reduction, 17.6 for the King Air so Engine and Prop RPM are not the same.
You absolutely should not have such high RPM from a piston, unless it is a racing engine!

PM me with the air and aircraft.cfg files if you like and I'll see if I can fix it.
Roy
 
Thanks Roy. Let me see if I can fix it first. Frustrating that I cannot seem to figure out what it is.

I have done several transplants of the engine/engine/prop sections of the Cessna 172, Maule, Mooney, and Extra. I have studied them, gone through them. Its very odd that the other planes operate fine in the sim, but when I put their data into my plane, my plane acts totally different.

When I checked Section 509 last night, modified it to identical settings, and it did nothing, I was surprised. It should have made a slight change in things.

Anyways... A bummer. Would be nice if its a very small 'thing' that is messing all this up and if I could just figure out what it was, I wouldnt have to re-engineer the entire airfiles. The plane was handling so well, the cruise speeds were right on, the flaps down speeds, angle of attack at final, fuel ranges, all well tuned....

I would love to fudge this, as its all running beautifully, all except the Manifold and Tach... and fuel flow...
 

Roy Holmes

Resource contributor
Bill,
When you have a fixed pitch prop, RPM varies with HP, prop diameter, number of blades, pitch angle and airspeed.
I assume you are only getting over revving at full throttle and that there is a throttle setting where you are at your max RPM.
BTW on the ground static you should only get about 85% of the redline so around 2300 for 2700 redline. 2300 would be your max static RPM
This is because once in the air and flying faster the RPM will increase.
If you find you are at max static RPM and about 50% throttle, write down the data and reduce the engine HP to 50% of its original value.
You should then get the max static at a higher throttle setting.
Keep adjusting the HP until max throttle gives you max static RPM. That will be the correct HP for that propeller diameter, number of blades and pitch angle.
Then you will no doubt find your performance is less than you want. Now look at the data you wrote down during the test and decide on a test matrix of increased diameter, increased blade number and 2 values of prop pitch at three values of engine HP
Flight test each test point and note speeds at max throttle. Once you get a good solution for max speed, you can begin any other optimization you want such as cruise fuel consumption, though the fuel flow scalar is the best way to do that within reason.
That is the approach I take when developing flight dynamics, plan, test, write down your results, then analyse what you have and keep iterating until you are satisfied.
Roy
 
Ok Roy... I did a ton of work. Soul searching was mixed in with it. Lots of grit added to my spirit as well. Dang....

While on this 'journey', I learned how to do copy/pasting sections via Text via your advice on using that program 'Air Update'. Brilliant program. I think I found an issue though in it. I tend to find bugs, unfortunately, as it started doing strange things. I can only think I needed to perhaps turn it off each time to clear it, etc, etc, as I was trying change this and that and experiment with sections.

Very glad I learned about that program and its capabilities.

I ended up changing the readings quantities. I just couldnt get things to work. Sadly, my prop RPM isnt lowering nor speed lowering when I pull back on the blue prop lever. I'll ask on that in another post in the FD section. But happy that I got all the rest working well. Took a few days (A WEEK????) to get it all working. But its working nicely now. Thankful.

Thanks also Karol for your advice on the dial. Worked a charm.


Bill
 
I had a whim (at nearly 1AM) and tried it out. Some more splicing with Air Update. This time, I had good results. Happy...
 

Roy Holmes

Resource contributor
Bill,
I answered you in the Flight Dynamics forum but look at what you wrote at the beginning of this thread:
"This is the Prop data // BEGIN /////////////////////////////////////////////////

[propeller]
thrust_scalar = 0.6 //Propeller thrust scalar
propeller_type= 1 //0=Constant Speed, 1=Fixed Pitch" ====== FIXED PITCH no RPM control,
Roy
 
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