Aircraft speed at altitude

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OldCrow

Charter Member
Does anyone know the easiest way to modify an engine to make it slower at low altitude and faster at higher ones.

Example:
I have a Ta 152H...

[piston_engine]
power_scalar = 1
cylinder_displacement = 178
compression_ratio = 6.5
number_of_cylinders = 12
max_rated_rpm = 3250
max_rated_hp = 2050
fuel_metering_type = 0
cooling_type = 1
normalized_starter_torque = 0.034
turbocharged = 1
max_design_mp = 52
min_design_mp = 9
critical_altitude = 41000
emergency_boost_type = 2
emergency_boost_mp_offset=4.118
emergency_boost_gain_offset=0.715
fuel_air_auto_mixture = 0
auto_ignition = 0
max_rpm_mechanical_efficiency_scalar = 1
idle_rpm_mechanical_efficiency_scalar = 1
max_rpm_friction_scalar = 1
idle_rpm_friction_scalar = 1
fuel_flow_scalar = 1
emergency_boost_duration = 2000

I need it to go about 20 mph slower at sea level and about 10 mph faster at both 30,000ft. and 41,000ft.

What's the best way to acheive this?
I just need a push in the right direction please.
 
Propeller reduction gear ratio is probably the easiest one, found in the propeller section. Smaller values will give the result you want. The climb rate will also be reduced.
 
Prop ratio will affect the overall performance of the a/c.

Sorry to say it, but (depending on what you call easy) the settings your looking for, to affect given speeds at given altitudes, I believe will be in the 'prop' settings themselves.

In the airfile, there are two main entries for the prop, that control the (what's the right word) 'pull' through the air, at given power settings, prop pitch, altitude(?), and so on.

What your basicly talking about is, the prop has too much 'pull' at the lower altitudes, if your speed there is too high. It just needs to be re-adjusted.

The easiest way...would be to use Airfile Manager, if you have a working copy. It would take alot of testing though, to correctly finalize the results, with any degree of accuracy.

Realisticly, there's too much involved in the airfiles, to correctly adjust something like the prop, without re-adjusting any related entries. Especially CFS3 airfiles.

(Assuming it's the FP model, since the numbers are different than my own Beta H1. Lol, I only have three months into that FM.)
 
Old Crow,

You may already be aware of this but CFS 3 has modeled in the "altitude effect" on speed. The ASI in aircraft register a higher air speed at lower altitudes than they do at higher altitudes. Most modern ASI have an outside ring to adjust for alt/temp to give you TAS. Temp and air density will produce large errors in an ASI with regard to TAS.

IAS = Indicated Air Speed
TAS = True Air Speed
CAS = Calibrated Air Speed

At 25,000 the ME-262 will indicate 300 mph IAS but the actual TAS is 433 mph.


The next time you are in QC take a B-17 up to 25,000 ft, press the Z key and compare the TAS to the IAS in your aircraft. The TAS will be higher. The TAS is the actual speed you are moving across the ground in a no wind situation.

The effect on mixture is also modeled in, You will not notice it on the models with fuel injection but it is very obvious on others. There are a few things that are not correct and accurate for engine operation however as you have most likely discovered.

O-1
 
Thank You guys. I assumed I might have to dig into the prop settings but was hoping I wouldn't have too, especially in the AIR file.

>Crossram, it is the TA 152s from Firepower. I hate those flight models.
>O-1 driver, I was working with TAS using the Z key.

I posted this in hope their was some magical solution in the Engine Config I was missing. I guess not.
 
greycap.raf said:
Propeller reduction gear ratio is probably the easiest one, found in the propeller section. Smaller values will give the result you want. The climb rate will also be reduced.
Click to expand...
Thank You again greycap. This did the trick. I've got it close enough now, good call!
 
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