Why still no dive acceleration difference?

[Crumpp]

And JtD is wrong in what exactly? AFAIK F=mg, g is a constant and is the same for every object in game.

Of course it is Fatcat. This is not the issue and completely irrelevant as to why your FM's would not exhibit any differences in dive acceleration. It does not answer the original poster's question.

Take the force triangle for a dive. A component of weight contributes to thrust based on the angle of dive. The difference between the force on the axis of motion in the dive and the force on the axis of motion for level flight is your initial excess force that will move the aircraft to its new equilibrium point velocity. The derivative between that and equilibrium is your average excess force along that vector....

Then apply the same formula...

Force = Mass x Acceleration

Rearrange it to solve for Acceleration: The acceleration of gravity is considered constant but acceleration is not constant.

Acceleration = Force/Mass

You then have the aircrafts acceleration rate to the equilibrium point.

Now I am not a computer programmer but I am sure there is a way to look at the code to see if it following those principles.

[JtD]

Originally Posted by Crumpp

It does not answer the original poster's question.

But it does. The original poster asked in the topics title why there are no dive acceleration differences. There aren't because gravity is the same for all planes. As soon as you consider anything else, the dive accelerations are different. Had he asked why all the dive accelerations are different, the question would have required a much more complex answer.
The answer was specifically given to the question asked.

[Crumpp]

The amount of excess thrust determines an aircraft dive acceleration.

The acceleration of gravity is constant but that excess thrust is not constant. It is a characteristic of the design and each aircraft will have a different acceleration in a dive.

[K_Freddie]

Probably something to do with engine type/power and propellor type... Just guessing as I know sweet ....all, you know

[Whacker]

Originally Posted by JtD

But it does. The original poster asked in the topics title why there are no dive acceleration differences. There aren't because gravity is the same for all planes. As soon as you consider anything else, the dive accelerations are different. Had he asked why all the dive accelerations are different, the question would have required a much more complex answer.
The answer was specifically given to the question asked.

Dive acceleration is not solely a function of gravity.

One must also account for frictional coefficients and powerplant thrust as they relate to the specific "dive" profile being discussed, as well as each individual aircraft's operational guidelines and parameters. It's not a simple answer by any means.

If anyone has a direct link to that TAIC study report, please post it, I'd be very interested to read it.

[Crumpp]

as well as each individual aircraft's operational guidelines and parameters.

Excellent point.

[JtD]

Originally Posted by Whacker

Dive acceleration is not solely a function of gravity...

I know. So once more: If someone asks why dive accelerations are the _same_, he doesn't want to know about thrust, drag and whatnotelse. Because these are reasons for _different_ dive accelerations.

[FC99]

Originally Posted by Crumpp

Of course it is Fatcat. This is not the issue and completely irrelevant as to why your FM's would not exhibit any differences in dive acceleration. It does not answer the original poster's question.

Who says that there is no difference in dive acceleration. Whole premises in initial question is wrong. There is a difference in dive acceleration.

Take the force triangle for a dive. A component of weight contributes to thrust based on the angle of dive. The difference between the force on the axis of motion in the dive and the force on the axis of motion for level flight is your initial excess force that will move the aircraft to its new equilibrium point velocity. The derivative between that and equilibrium is your average excess force along that vector....

You are missing the point here, people want dive acceleration "fixed" as there is some magical switch that is turned on when plane start to dive but there is no such thing. All you have are Thrust, Lift,Drag and Weight acting on a plane no matter what's the plane attitude.

If you change something you will change plane behavior in all flight regimes not only in dive. If you have plane behavior modeled reasonably well in level flight and climb than there is no reason to believe that dive behavior is wrong.

Where game has its problems are extreme parts of flight envelope but that's not what the thread starter asked.


BTW Long ago I made tests and posted it on CWOS but it's lost now. But anybody can repeat it.It's simple.

1. Start the plane at alt above the initial testing point. Use no cockpit view to get TAS and stabilize the plane at desired TAS.

2. Keep the TAS constant and measure the time required to pass from the start altitude to end altitude.

3. Repeat for all planes you want to test, try it with no power and full power.

4. Compare the results.


As the test measure the time required to get from StartAlt to EndAlt it also measure the distance traveled. Test requirement is that TAS is kept constant so difference in time from let's say 4000m to 2000m will mean that planes passed different distances which in turn means that their diving angle was different.

Plane that needed longest to get to EndAlt is the best diving among the tested planes because it needed smallest help from gravity to keep its speed. Consequently it will dive fastest in a dive that is performed at same diving angle.

[BlackBerry]

Originally Posted by FC99

Who says that there is no difference in dive acceleration. Whole premises in initial question is wrong. There is a difference in dive acceleration.

You are missing the point here, people want dive acceleration "fixed" as there is some magical switch that is turned on when plane start to dive but there is no such thing. All you have are Thrust, Lift,Drag and Weight acting on a plane no matter what's the plane attitude.

If you change something you will change plane behavior in all flight regimes not only in dive. If you have plane behavior modeled reasonably well in level flight and climb than there is no reason to believe that dive behavior is wrong.

Where game has its problems are extreme parts of flight envelope but that's not what the thread starter asked.


BTW Long ago I made tests and posted it on CWOS but it's lost now. But anybody can repeat it.It's simple.

1. Start the plane at alt above the initial testing point. Use no cockpit view to get TAS and stabilize the plane at desired TAS.

2. Keep the TAS constant and measure the time required to pass from the start altitude to end altitude.

3. Repeat for all planes you want to test, try it with no power and full power.

4. Compare the results.


As the test measure the time required to get from StartAlt to EndAlt it also measure the distance traveled. Test requirement is that TAS is kept constant so difference in time from let's say 4000m to 2000m will mean that planes passed different distances which in turn means that their diving angle was different.

Plane that needed longest to get to EndAlt is the best diving among the tested planes because it needed smallest help from gravity to keep its speed. Consequently it will dive fastest in a dive that is performed at same diving angle.

I tried：4.11m Tempest mkv vs p51c engine overheat off, radiator closed

From 3000m altitude to 2000m, keeping speed=700TAS

2minutes and 2 second for tempest mkv
2minute and 30 second for p51c

So, p51c outdives tempest? No. Tempest mkv definitely outdives p51c!

BTW, this kind of "dive" is very shallow, smaller than 10 degree.

[BlackBerry]

When P51 dives to 4500 m=15000ft altitude, and reaches 640km/h=400 mph IAS, that is 1.25*640=800 km/h=222m/s TAS, the mach number is equal to 222/322=0.69. That's fuselage speed.

However, the speed of tip of airscrew is far more 0.69 mach.

4-blade hamilton airscrew,10.5 feet diametre, the reduction ratio of airscrew rotating to engine is 0.477. 3000rpm engine, 1431rpm=23.85r/s airscrew, the rotating speed of tip is：3.14*10.5*0.303*23.85=238m/s

So the combination speed is: (238^2+222^2)^0.5=325 m/s.

Unfotunatly, sonic speed at 4500m altitude is 322m/s, that is to say, the tip of airscew is 1 mach. There is no mach number "concept" in il2's model at all, how can I believe that il2 simulates 1 Mach aerodynamics very well?

http://en.wikipedia.org/wiki/Indicated_airspeed

In aneroid instruments the indicated airspeed drops-off with increasing altitude as air density decreases. This leads to an apparent falling-off of airspeed at higher altitudes. For this and other reasons never exceed speeds (abbreviated VNE) are often given at several differing altitudes in some aircraft's operating manuals, the VNE IAS figure falling as height is increased, as shown in the sample table below.
Diving below mph IAS
30,000*ft 370
25,000*ft 410
20,000*ft 450
15,000*ft 490
10,000*ft 540

Ref: Pilot's Notes for Tempest V Sabre IIA Engine - Air Ministry A.P.2458C-PN

Tempest could dive to 450 mph IAS below 20000ft, aha, tempest's big rotol 14-ft airscrew, 3800rpm, 450mph IAS, the tip of rotol must be supersonic, so is P51's hamilton, thus the efficiency curves of their airscrews play an important role when they dive to high speed.

Why tempest outdives p51? For more efficiency airscew @ supersonic? Maybe. For much more heavier fuselage? Probably.

All in all, il2's model is lack of supersonic simulation, that's why we couldn't experience what tempest/p51 should be. That's why tempest couldn't outdive dora easily in game.