Why still no dive acceleration difference?

[MadBlaster]

Sorry, I need more information because the example keeps changing. What is the speed of the two planes before they go into the dive? Is the one at 100% throttle already at Vmax? Or are they both at Vmax because the the one at 60% dove down from higher altitude previously? Honestly, this example doesn't seem good one. The information is sketchy. Are you trying to trick me?

[BlackBerry]

Originally Posted by MadBlaster

Sorry, I need more information because the example keeps changing. What is the speed of the two planes before they go into the dive? Is the one at 100% throttle already at Vmax? Or are they both at Vmax because the the one at 60% dove down from higher altitude previously? Honestly, this example doesn't seem good one. The information is sketchy. Are you trying to trick me?

Imagine there are two tempestMKV named 'X' and 'Y' respectively.

X is equipped with a good CSP, while Y is equipped with a bad CSP. Everything else being equal. both a/c weight equal. drag coefficient equal, engine is equal ......

Within the envelop, within Vmax, both good propeller and bad propeller share same efficiency, they performs identically. good prop=bad prop=85% efficiency

But when dive into 0.6-0.7Mach which is out of a/c envelop, good propeller=80% efficiency, bad propeller=60% efficiency.

At first, both X and Y use 100% throttle in level flight SIDE BY SIDE, because they share same efficiency within evelop, both speeds are Vmax.

Then, both begin to dive at 45 angle, and after a while, both speed are entering 0.6-0.7 Mach, suddenly, "Y" CSP lose efficiency to 60%, while "X" efficiency is still 80%. That is to say, "X" engine could provide more thrust.

Question: Will "X" begin to pull away from "Y" from now?

[MadBlaster]

doesn't make sense. the props can not be identical. the curves would have to be different slopes. "suddenly"...is this realistic if they are identical? no.

But assuming it is realistic, i say tenatively 'yes', Y falls behind from this 'sudden' loss of thrust on the bad prop and gravity has not completely taken over yet, so I guess there is an excess reverse thrust. but I have to think about it some more.

[BlackBerry]

Originally Posted by MadBlaster

doesn't make sense. the props can not be identical. the curves would have to be different slopes. "suddenly"...is this realistic if they are identical? no.

But assuming it is realistic, i say tenatively 'yes', Y falls behind from this 'sudden' loss of thrust on the bad prop and gravity has not completely taken over yet, so I guess there is an excess reverse thrust. but I have to think about it some more.

You are beginning to understand me.

"X" vs "Y" ,Everything ELSE being euqal, propellers are different: good prop vs bad prop.

During TAS 0.2-0.6 Mach, good prop=bad prop=85%

During TAS 0.6 -0.8 Mach, good prop> bad prop; ie 80%>60%.

"Y" has no more gravity for help because both dive in same angle=45 degree, and both weight=5 tons.

"Y" has no reinforcement.

[MadBlaster]

the example works better for me if you assume the 'sudden' drop in efficiency for the bad prop happens at the margin of the csp peak envelope at/near Vmax/level. And to make it even more emphasis, the efficiency drops from .85 peak to 0 no thrust when 1 more kph is added above Vmax/level in 1 second, as soon as you enter the 45 dive. also, drag force just kicked you back into the peak envelope. okay, yes the bad prop now has excess negative thrust. because in that 1 second you went from max thrust to no thrust from the prop and drag force pushed you back and not enough time has elapsed for excess thrust from 45 weight vector to overcome the momentary loss from the prop. I'm probably missing something.


Now, we know there are no 'sudden' drops in these curves. they have slopes and they are a functions of TAS, RPM, reduction ratio, blade diameters...etc. this example, rigged.

[BlackBerry]

Originally Posted by MadBlaster

the example works better for me if you assume the 'sudden' drop in efficiency for the bad prop happens at the margin of the csp peak envelope at/near Vmax/level. And to make it even more emphasis, the efficiency drops from .85 peak to 0 no thrust when 1 more kph is added above Vmax/level in 1 second, as soon as you enter the 45 dive. also, drag force just kicked you back into the peak envelope. okay, yes the bad prop now has excess negative thrust. because in that 1 second you went from max thrust to no thrust from the prop and drag force pushed you back and not enough time has elapsed for excess thrust from 45 weight vector to overcome the momentary loss from the prop. I'm probably missing something.


Now, we know there are no 'sudden' drops in these curves. they have slopes and they are a functions of TAS, RPM, reduction ratio, blade diameters...etc. this example, rigged.

Good prop and bad prop share same diameter, same rpm, same advance ratio@same TAS. Their DIFFERENCE IS THE SHAPE OF AIRFOIL SECTION.

TAS Mach / good CSP / bad CSP
0.6 85% 85%
0.61 84% 83%
0.62 83% 80%
0.63 82% 77%
0.64 82% 73%
0.65 81% 70%
0.66 81% 67%
0.67 81% 64%
0.68 80% 60%
0.69 80% 56%
0.70 80% 52%

//////////////////////

Your TempestMKV equipped with bad propeller, my Tempest with good propeller.

If I drag you into a high speed dive, around 0.7 Mach TAS for 40 seconds, what is your energy loses?

To simulate this sharply efficiency drops for bad propeller, you can simply use il2 4.11m, quick mission, spawn @ 5000 m with Tempest mkv, you intently decrease your throttle to 60% during 0.6-0.7 Mach 45 degree dive and 45 degree zoom.

You will feel the energy loss.

[MadBlaster]

putting the weight vector/dive angle to the side for a bit, I think what is missing here in the discussion is the drag vector. Now, beyond peak/vmax. what is happening is the drag vector is slowly overwhelming the thrust of the propeller as it gets more and more inefficient until efficiency is at zero and advance ratio reaches some high number at some given high TAS. So, it is negative excess thrust between those two vectors because drag force is becoming greater than the prop thrust vector (still ignoring the weight vector for now). So, the question is how is the interplay between these two vectors modeled in IL-2. Maybe it is already accounted for in the modeling of the drag force? Like an effectiveness factor or something that is attached to the drag coefficient as the thrust begins to degrade beyond Vmax? I really have no idea, only speculate.


edit:
of course, the only way to get beyond vmax is to dive, and its the sum of all forces...etc. so this interplay between opposing thrust and drag vectors gets masked over by weight/dive vector. am i on the right track?