Some prop engine sounds not changing with RPM?

  • Is there a reason why the engine sounds on some prop planes like the P38 do not change pitch with revs? P47s another one.

    The sound of the engine is determined by the engine rotation speed and with the constant speed propellers of the P38 that rotation speed is kept constant by changing the angle of the propeller blades. If the rotation speed is too high the governor adjusts the blade angle to a more coarse setting which increases the blade angle and the blades bite into the air more strongly. Then if the speed decreases the blade pitch is reduced to reduce the load on the engine. The blades are adjusted so quickly that the rotation speed is pretty much constant throughout the entire flight, unless you fly very slow and with low power.

    This means the propellers spin at a constant speed all the time and therefor the sound is very monotonous, just like in the real aircraft.

  • Ok thank you.


    So the plane's speed is changed by changing the prop blade pitch and this is what the levers on the left of the cockpit are doing?


    The thing is I see or hear no drop in engine RPM when the throttle/ levers are dropped back to zero when in flight.

  • Hard to believe the sounds are exactly the same from the start of a takeoff roll to full power climb out and also exactly the same when going from cruise power to idle power when starting a descent. Those big old Wasp engines are louder than a freight train and these are nowhere close to sounding like the real world versions.


    My first type rating was in a DC-3 with similar engines and similar CS prop systems and I can tell you for an fact, the sound changes are very noticeable from low end to high end and back again. Most especially on the take off roll when going from idle to military power.


    Regards,

    Rau

  • The aircraft speed is controlled with the throttle levers which are the ones with the orange balls at the end. That controls how much power the engines produce, just like a gas pedal in your car.

    The black levers to the left of the throttles control how fast the propellers should spin. You could imaging this being the gear shift of the car or of your bicycle.

  • The real world engine may sound different under load than at idle, that is true but the rotation speed is still constant unless you fly slow enough for the governor to hit the full fine pitch. However, most of the engine's sound is caused by just the rotation and ignition and the frequency of the rotations and explosions in the engine's cylinder is still the same if the rotation speed is held constant. So there just isn't much difference in sound between roughly 30% load and say 80% load.
    The real world engines of the P38 also have turbo chargers I think, so these would certainly change the sound...

  • A bit of drama on opening the throttles would not do any harm, there is more exhaust noise, higher vibration ... a bit of a simulation problem alright .... and the unforgetable semi-deafening loud beating from full throttle, full fine pitch unsynchronised propellors at maximum rpm. Talking about powerful twins, not the fixed pitch Aerofly Cessna 172 single though it is a 180, I never flew one but the PA-28 180 is very different from a 140 or 160. The Baron sounds a bit more throttled back and propellor pitch lever (you only move one) adjusted.

  • I'm sorry, I still don't understand how an engine with zero throttle can sound the same as it does with full throttle, but as strange as it is you have confirmed it's not a bug it's intentional.

    Awesome graphics though! 😊

  • I'm sorry, I still don't understand how an engine with zero throttle can sound the same as it does with full throttle, but as strange as it is you have confirmed it's not a bug it's intentional.

    Awesome graphics though! 😊

    I found some old videos of the real deal from WWII training films when searching on youTube. Just search for Corsair. The range of sounds is very evident in the dives and climbs but more noticeable in the take offs. Crank up the volume and hold on.


    Regards,

    Ray

  • Same on the Pitts, I have many hours on S2B and I can say : when you cut the throttle the sound change a lot ! yes the prop "rpm" rest stable above a certain speed , and the sound of the prop rest constant and it is dominant, but not the engine sound !

    It is like in a car if you stay in 4th gear with throttle at 5000 rpm on a flat road and if after in a descent with no throttle you maintain the same 5000 rpm still in 4th gear but with only the brakes ! You have the same engine rotation but not the same sound because of no or little combustion in the engine !

    So we have 2 sounds for the engine : the rotation sound (in some way merge with the prop) and the combustion sound .

    Regards,

    Alain

  • Same on the Pitts, I have many hours on S2B and I can say : when you cut the throttle the sound change a lot ! yes the prop "rpm" rest stable above a certain speed , and the sound of the prop rest constant and it is dominant, but not the engine sound !

    It is like in a car if you stay in 4th gear with throttle at 5000 rpm on a flat road and if after in a descent with no throttle you maintain the same 5000 rpm still in 4th gear but with only the brakes ! You have the same engine rotation but not the same sound because of no or little combustion in the engine !

    So we have 2 sounds for the engine : the rotation sound (in some way merge with the prop) and the combustion sound .

    Regards,

    Alain

    Exactly.. Zero throttle surely means zero (or idle) combustion. It seems like little or no percentage of the the engine sound is caused by combustion or more significantly exhaust?

    The IL-2 series are about to introduce a P38 so it will be interesting to see their take on it with their record of attention to detail and accuracy.