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Author Topic: speed/altitude proper adjustement needed  (Read 5478 times)

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greybeard

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Re: speed/altitude proper adjustement needed
« Reply #24 on: March 21, 2015, 09:55:31 AM »

In that equation, "P" stands for the power of the thrust force (equal to drag at top speed) generated by the propeller, rather than engine power.

Absolutely right! But you forget that top speed was reached by that historical horsepower, so, if it requires a much higher one to get same speed, something in flight model must be fixed, and that should not be power output, since also affecting climbing performance. Personally, I start from drag, but may happen it is airscrew, which is badly modeled. For instance, it happened to me that historical propeller of Spitfire XIV (that's to say its historical data put into flight model) didn't afford historical top speed, simply because it couldn't reach powerplant maximum RPM, already at minimum pitch (100% in game). I was forced to "tweak" fitting the Spitfire XII prop, getting historical performance (with real HP).
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Herra Tohtori

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Re: speed/altitude proper adjustement needed
« Reply #25 on: March 21, 2015, 08:12:30 PM »

It honestly doesn't even make much sense to assign a "power" value to something like an aircraft's propeller that produces a linear thrust force.

What's the propeller's power when airspeed is zero?

Quote
But you forget that top speed was reached by that historical horsepower, so, if it requires a much higher one to get same speed, something in flight model must be fixed, and that should not be power output, since also affecting climbing performance.

An aircraft doesn't really care what the shaft power output of the engine is. An aircraft's motion is solely determined by the forces acting upon it - lift, weight, thrust, and drag. Engine power doesn't actually affect stable climb performance either - that, too, is simply dependent on the equilibrium of those four forces.

If we have a plane with a bad propeller that needs 150% of historical engine power to produce 100% historical thrust, and a plane with a historically correct propeller that only needs 100% engine power to produce 100% historical thrust, both planes will fly the same. The absolute engine shaft power shouldn't even enter the flight state calculations. The plane that has "higher" power just has an engine that's doing 50% more of nothing. If the thrust is the same in both planes they fly the same (although the "high power" version may end up having higher fuel consumption, depending on how the engine modeling does its thing). If the engines are turned off, they both fly the same.



Anyway, if your working hypothesis is that the 150% engine power is used to offset 150% drag, there's a fairly simple way to test it - simply turn the engine off and see if the aircraft has excessive drag. This would be apparent as an abysmally bad glide performance. A good comparison point would be a similar aircraft not affected by odd power anomalies - a P-40M could be ideal, due to very similar airframe. If the two aircraft have about the same glide performance, then that would suggest that they don't have substantially different drag.


Since I don't recall anyone complaining that the early P-40 models have the approximate glide performance of the space shuttle, I very much suspect that the reason for the high power requirement is mostly not related to lift, drag or weight, but instead contained in the thrust component of the aircraft - and that practically means the propeller.
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greybeard

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Re: speed/altitude proper adjustement needed
« Reply #26 on: March 22, 2015, 03:24:01 AM »

... I very much suspect that the reason for the high power requirement is mostly not related to lift, drag or weight, but instead contained in the thrust component of the aircraft - and that practically means the propeller.

I see the point and agree.
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yak

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Re: speed/altitude proper adjustement needed
« Reply #27 on: March 22, 2015, 01:12:55 PM »

yesterday i spent pair of hours tweaking p-40. i found info that lend lease kittyhawks had curtiss 3.36m propeller reductor 0.5 angler 24.5-49.5 or 22-54.5. so original settings were correct!
tweaking this affects acceleration and speed, but p-40 refuses to get its historical speed and climb with given power.
at least i was not able to get it. moderate temperature map were used with wind disabled.
i checked bf109 and yaks-they fly nicely!
thank you gentlemen for useful interesting guide!
such a shame to be on SAS~Storebror's troll list. we all do mistakes- i hope he will forgive me one day!
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yak

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Re: speed/altitude proper adjustement needed
« Reply #28 on: March 24, 2015, 11:27:40 AM »

i used p-40f flight model (that simply feels better than original p-40e) with this tweaked allison:

[V-1710-39]
  EngineAcceleration 1.0
  HorsePowers 1150
  BoostFactor 1.0
  CompressorType 1
  CompressorSteps 1
  cCompressor 0
  RPMMin 500
  RPMNom 2600
  RPMMax 3000
  RPMMaxAllowed 3200
  Reductor 0.65
  PropDiameter 3.1
  PropMass 150.0
  PropAnglerType 1
  PropAnglerSpeed 0.06
  PropAnglerMinParam 1500
  PropAnglerMaxParam 3000
  PropAnglerAfterburnerParam 3000
  PropPhiMin 20.0
  PropPhiMax 45.0
  PropAoA0 11.0
  CompressorPMax 1.52
  CompressorAltitude0 4000.0
  CompressorMultiplier0 1.05
  CompressorRPMP0 1500.0
  CompressorRPMPMax 3000.0
  CompressorMaxATARPM 1.52
  CompressorSpeedManifold 0.5
  CompressorRPM0 1500
  CompressorATA0 1.0
  CompressorRPM1 2600
  CompressorATA1 1.4
  DisP0x 3000
  DisP0y 0
  DisP1x 0
  DisP1y 140
  TESPEED 0.01
  TWATERMAXRPM 113
  TOILINMAXRPM 70
  TOILOUTMAXRPM 98
  MAXRPMTIME 280
  MINRPMTIME 999
  TWATERMAX 125
  TWATERMIN 60
  TOILMAX 115
  TOILMIN 40
  FuelConsumptionP0 = 0.23F
  FuelConsumptionP05 = 0.14F
  FuelConsumptionP1 = 0.16F
  FuelConsumptionPMAX = 0.18F

also changed fmd by adjusting this:
  Wingspan 11.38
  Length 9.65
  Empty 2750.5
  TakeOff 3650.0
  Oil 50.0
  Fuel 400.0
...
VmaxAllowed 850.0
Vz_climb 11.0
 V_climb 280.0
 T_turn 21.0
...
lineCyCoeff 0.095
Cy0_0 0.12
CxMin_0 0.015

resulting aircraft has real speed at all altitudes and climb according to this info i found:
http://www.wwiiaircraftperformance.org/P-40/P-40.html
http://www.asisbiz.com/il2/P-40/Kittyhawks.html

feedback is welcome! maybe someone could make more precise simulation of this legendary warrior!?
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