#101
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Probably something to do with engine type/power and propellor type... Just guessing as I know sweet ....all, you know
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#102
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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. |
#103
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#104
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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.
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#105
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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.
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#106
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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. |
#107
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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? Quote:
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. Last edited by BlackBerry; 05-10-2012 at 04:13 PM. |
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#109
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As early as 1904 when Wright brothers made the first a/c, they knew both airscrew and wing are "same thing". Quote:
Their original propeller blades were only about 5% less efficient than the modern equivalent, some 100 years later......... That conclusion is based on low Mach data, for supersonic airscrew, the story is totally diefferent. In my opinion, the airscrew theory/simulation is the weakness of il2's FM. Quote:
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Last edited by BlackBerry; 05-11-2012 at 12:38 AM. |
#110
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if you simply want to test 'drag' without digging into the code, I think it better to do it with the engine off (i.e., no thrust test).
- go into fmb and set your spawn kph to zero and start a track in cockpit view. - spawn your plane say 5000 meters and leave the engine off. - close your rads, neutral your trims, set you prop pitch to 100%. -push nose into 90 degree vertical. -end the track when your plane hits the beach at zero alt. -go back and look at track. look at speedometer at say 20 second mark per track time. (e.g., speed says 400 kph at 20 seconds for this plane) -repeat with another plane and compare results. - For the thrust piece, you can use devicelink to get an idea. There is an acceleration parameter that can be graphed/logged. You can see the effect of adjusting throttle and prop pitch. Prop pitch changes and its effect on acceleration is modeled. The csp may be slower to change blade angle than the vdms. At least, that's how it feels like to me. The fw vdm has a torque limiter. I think p factor is also modeled. You can produce de-celeration by adjusting blade angle, according to devicelink. |
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