Yes and I don't think the differences will be worth the effort or necessarily more accurate. The current assumptions already give good agreement with in flight behaviors.

Propellers design is based on measured data. That is why you cannot work propeller theory accurately without it. That is also the reason why n=.8-.85 is a valid assumption. The design is reworked until it does achieve that level.

That was the biggest lesson of the NACA 16 series and subsequent airfoils derived from calculations. What you think on paper often does not give good agreement at that level due to compressibility.

Propellers spend most of their time in the transonic realm. Even today, the largest potential for error and the most difficult aerodynamic problems are rooted in our ability to mathematically model compressibility effects. Airfoils are designed around coefficients of pressure and our limitations for compressibility modeling hamper our ability to predict behaviors.

With the advent of CFD we are getting better but there are no CFD analysis of WWII era propeller designs.

Drag coefficient is wrong.
In level flight drag = thrust.
D=0.5*density*speed^2*drag_coefficient*reference_a rea
From the above equation calculate drag coefficient and use it to calculate drag at different speeds and altitudes. What you called as "drag coefficient" ans used throughout the different examples is not correct.

Yes, i just simplified the calculation.

For a certain aircraft, wing area is a constant, my compare/data is on the deck, so air density is also a constant(1.29kg/m^3). Therefore, my "drag coefficient"=real "drag coefficient"*constant. The final result will not be different if you use real drag coefficient in the formular.

Of course, but his approximation is not wrong and is based on the relationship of velocity.

There is nothing wrong with doing that as a ballpark of expected behaviors.

I was actually impressed that he did that. It shows an understanding of the relationships indicative of someone with formal education in aerodynamics or at least intelligent enough to work the relationships to conclusion.

Actually they already made the decision in WW1
 

Thanks again for this interesting topic.

I just want to remind that 4-blade propeller fighter aircraft were used before WW2, so perhaps it is not really something as revolutionary as we may think?

Some german design (not produced in great series or prototypes) using 4 blade prop in the 30ies are for instance DO C1 nightfighter (1931) , or Arado 64 experimental (1931).

The oldest fighter design i know using a 4-blade propeller is the german WW1 fighter Siemens Schuckert SSW DIII series (1917-1918 ), that was considered as a very capable fighter at the time, once its cooling problem solved.

The key is airfoil. IMO, at high speed above Vmax:

3-blade Gottingen=3-blade RAF=3-blade ClarkY=3-blade NACA16=4-blade Gottingen/RAF/ClarkY


However, 4-blade NACA16 is an exception. NACA16 was developed after 1939. There are three disadvantages of German propeller edficiency in late WWII AT HIGH SPEED ABOVE Vmax,ie 0.7Mach.

1)smaller diameter with same rpm as allied, so bigger advance ratio, less efficiency(maybe 10-15%). This is confirmed easily.

2) late period wide chord airfoil gives better performance within Vmax, but worse above Vmax(maybe 10%). This is also comformed.

3)allied 4-blade Naca16 outperforms 3-blade naca16 above Vmax. This has NOT been confirmed yet, but probably. maybe 7-10% efficiency improvement.


The third issue is very important, if it is confirmed, allied may have 30% efficiency advantage over German/Russia when above Vmax. If not, or 4-blade naca16 even worse than 3-blade naca16 at high speed. The allied advantage will not be profound.

30% efficiency advantage is around 500-600 HP in late WWII, hugh difference, key role in high speed dive/flight, vital for P47P51 high speed tactics.

Yeah I don't understand the fixation on 4 blades. It is not some magical performance enhancement or brand new technology. For some reason, people like to think that because some of the late war allied fighters went to a 4 bladed propeller that there was something wrong or obselete about a 3 bladed propeller.

You are making a tradeoff between power absorbtion and efficiency. It does not make any difference if you load more power but lose efficiency to convert it to thrust. It also does not make any difference if you increase power absorbtion by adding a fourth blade or widening the chord of the existing three.

WWII really reached the limits of piston engine technology and there is not much to choose or accurately depict in propeller designs. There is a reason n=.85 is valid.

Problem is the NACA 16 series did not realize it's predicted performance. According to the NACA, the Clark Y and Gottingen were equal or better.

Whether 4-blade Naca16 outperforms 3-blade Naca16 above Vmax is NOT confirmed, the confirmed fact is that 3-blade naca16=3-blade ClarkY and 4-blade ClarkY=3-blade ClarkY.

Even assume 4-blade naca16 has no advantage above Vmax at all, that is to say, P47P51 is equipped with German old narrow chord Gottingen airfoil, P47 still has around 20% efficiency advantage(300-400HP) above Vmax, ie 0.7Mach.

So simply assuming 85% for all CSP when above Vmax is totally unacceptable for high speed tactic il2 players.

Not anything outstanding about the propeller and everything to do with the engine.....


This condition is key. Of course, above Vmax we are outside of the aircrafts design envelope and our efficiency curve no longer approximates a slope of zero. Instead it takes on a negative slope.

Just though as it is a good assumption to have a slope of zero in the envelope, it is also a good assumption that all CSP designs will have a similar negative slope outside that envelope.

See:


Now, that is not to say it would not be very cool to add the minor differences outside the envelope and some very basic assumptions could be made based on general propeller characteristics. A generic curve could be the thing that fixes the "supersonic dives" that are possible in the game.

I also think that individual and specific characteristic's are way more trouble than it is worth for dubious accuracy without the actual data. It would also open up a huge can of worms for your developers and people having to decide what data is applicable.

Look at all the arguments over such very well documented performance parameters as climb rates or Vmax. Now you want to add in propeller design?

The whining would never stop, not that it does now.

My suggestion would be to concentrate on accurately modeling the limits and behaviors found in the Operating Instructions.

I think it would be more realistic and easier to model the consequences of exceeding the dynamic pressure and mach limits of the aircraft than trying to find a generic braking point. You don't think, "my efficiency curve will drop off and drag rise due to compressibility will keep me safe" when you point an aircrafts nose down in a steep dive. You think, "don't exceed Vne...don't exceed Vne" as your butt cheeks suck up the seat.

For example, our FW190 tries to dive away from a P47. At ~466mphTAS, the FW encounters compressibility, and loses elevator control. The FW now happily sails to the dirt barrier or the pilot very very carefully uses the elevator trim to recover without overloading the airframe.

At 466 mph TAS, the P47 is in full control. He either:

1. Watches the FW hit the dirt barrier from the comfort of altitude.

2. Catches the FW on its straight path to the dirt barrier and shoots it down. His top speed is ~40 mph faster...

2. Follows the FW on its rather helpless recovery and shoots it down.


Diving away is a very bad option for the FW190 if the limits are accurately modeled.