Why still no dive acceleration difference?

[Crumpp]

I have a question for you:
At 1st second, you begin to 45 degree dive,
At 2nd second, your speed increase a little, acceleration is greater than g.
at 3rd second, your speed increase a little more, and acceleration is still greater than g.

.....

at 20th second, you reach the equilibrium point, and acceleration is ZERO. Your speed remains same.
at 21st second, your speed is same as 20th second.
at 22nd second, hour speed is same as 20th second.
......

How about the 19th second? what's your acceleration? It should be smaller than g, but I need more accurate data.

Is the acceleration at 19th second nearly zero or around 0.5*g?

http://philsci-archive.pitt.edu/1197...y_Solution.pdf

[Crumpp]

At the end of dive, P47D had a much greater speed than fw190G, sth. like 50km/h difference is huge enough.

Look at what the aircraft are placarded for in terms of dive speeds.

The aerodynamic forces will tell you the FW-190A can outdive the P47. Just look at the sea level speeds and power required. At sea level, EAS = TAS and EAS is the speed the airplane always feels.

The P47 generates ~272 THP more than the FW-190A8 to travel ~20mph slower. It takes a lot of power to push that big heavy P47 through the air.

However, the relationship of thrust and drag is not the primary limiting factor in a dive for these airplanes. Dynamic pressure limits and mach limits tend to set the speed limits in WWII fighters.

In the case of the FW-190 vs P 47, the FW-190 is limited to ~466mph at low altitude while the P47 is limited to 500 mph at low altitude.

Those placard limits are not set arbitrarily nor is there any wiggle room or safety factor. A Focke Wulf pilot exceeding 466 mph is taking a huge risk he will not survive the dive. There are plenty of incidents of FW-190 pilots diving straight into the dirt barrier because mach effects made the elevator control ineffective. There are also incidents of the pilot turning the aircraft to confetti by aggressive use of the trim to recover.

In a dive to Vne, the P47 will always gain ~34mph over the Focke Wulf FW-190A.

[BlackBerry]

Originally Posted by Crumpp

Look at what the aircraft are placarded for in terms of dive speeds.

In the case of the FW-190 vs P 47, the FW-190 is limited to ~466mph at low altitude while the P47 is limited to 500 mph at low altitude.

In a dive to Vne, the P47 will always gain ~34mph over the Focke Wulf FW-190A.

I am a little disappointed that we havn't known each other's opinion after many posts.


Crumpp, P47 Vne=500mph, Fw190's Vne=466mph, the difference is 34mph, so if both of them dive steeply and pull to level flight at Vne speed, P47 is always 34mph faster than fw190. That' very simple, all of us know it. However, that is "terminal speed difference", not dive acceleration difference.

Although X plane's Vne is more than Y plane's, it is possible that X is outdived by Y WITHIN Y's Vne speed. The test in Italy 1943 between P47D an Fw190G is very useful to demonstrate this.

(C)
(1) 10000 feet to 3000 feet, starting at 250 m.p.h., diving at angle of 65 degree with constant throttle setting. The FW-190 pulled away rapidly at the beginning but the P-47 passed it at 3000 ft with a much greater speed and had a decidedly better angle of pull out.

That is my explanation:

g=9.8 m/s^2=32.2 ft/s^2

When both Fw190G and P47 dive in 65 degree angle, their acceleration along path(65 degree) is calculated in this formular:

Acceleration=g*sin(65)+g*(thrust/weight)-air braking force/weight

Fw190A has better thrust/weight, P47 has less braking force/weight, but at low speed, fw190's advantage is more profound, so P47 was outdived by fw190g INITIALLY, although P47's Vne (500mph)higher than fw190(466mph). This perfectly demonstrates that terminal speed and dive acceleration are totally two different concepts.

In later dive period, P47 passed fw190, both arrived 3000ft but P47 has much greater speed.Both speeds of them are well BELOW 466mph. Furthermore, P47 got higher speed BEFORE reaching 3000ft, isn't it? Don't forget fw190 was ahead of P47 after initial dive.

For example, when fw190 reached 8000ft altitude, P47 was at 8500 ft, so P47 was outdived by fw190 initially.On what altitude did P47 get same speed as fw190? Perpahps at 5000ft, at that time, fw190 was still ahead of P47, so fw190 probably at 4500ft. BEFORE P47 got same speed as fw190, P47's acceleration was better than fw190, otherwise, how could P47 get same speed? Don't forget P47 was slower than fw190 after initial dive. So P47 time line is below:

Altitude
@8500ft, was slower and after fw190
@6500ft, began to get higher acceleration than fw190, but still slower than fw190
@5000ft, get same speed as fw190, but still after fw190
@4000ft, faster than fw190, but still after fw190
@3000ft, passed fw190 with higher speed and higher acceleration. At this time, both P47 and Fw190 speed are BELOW 466mph.

@1000ft(if don't pull to level), ahead of fw190, faster than fw190, higher acceleration than fw190 and the distance between them are enlargening.

@-5000ft(deep valley! Air density =SL), P47 still has a little acceleration, while fw190 reaches equilibium point at 1200km/h (if firm enough). Distance between them is big.

@-7000ft (deeper valley, air density=SL), p47 reaches equilirium point with 1400km/h(if firm enough)and fw190 is still 1200km/h, distance between them is bigger.

@-10000ft(deepest valley,air density=SL), p47 is still 1400km/h, fw190 is still 1200km/h, distance between them is even bigger and increasing for ever.


if @1000ft level flight(pull his stick to avoid loss), ahead of fw190, faster than fw190, and LOWER SLOW DOWN RATE than fw190, distance between them are enlargening.


The most interesting is the level flight out of envelop, above Vmax. When both P47 and Fw190 fly at Vmax at sea level, P47's 7ton weight couldn't himself at all, and P47 has a bigger wing area while same 2000HP engine with fw190, so P47's Vmax is less than fw190.

But if both of them level fly above Vmax, the 7 tons weight helps P47 a lot because the heavier, the more ability to retain high speed above Vmax.

Acceleration=g*(thrust/weight)-air braking force/weight

Acceleration is always negative when you are slow down from 800km/h to 600km/h on the deck, and it usually takes a whole minute/60 seconds to slow down to 600km/h(Vmax).

Thus if P47's big 4-blade propeller efficiency is 20% higher than fw190's small 3-blade at the speed range from 680 to 800km/h IAS(out of envelop), fw190 will suffer a lot of ENERGY BLEEDING.

We all know bf109k4 has a excellent climb rate over La7, it usually takes k4 a whole minute to establish 500 m altitude advantage if both have same energy in the beginning. P47/P51/Tempest could also establish 500 m higher altitude if they use high speed boom and zoom tactics-----their own method! AS EFFECTIVE AS BF109K4.

It is obvious for all il2 players if 109K4' s climb rate is degraded to la7 level. People will shout:"Sh*t, where is 109K4's climb advantage? how can I do a energy fighting?" Unfortunately, if il2 neglects the propeller efficiency difference/sharp drops between various aircrafts at high speed(680-800km/h), P51P47Tempest will lose half of their energy fight tactics effect------energy-saving high speed boom and zoom, and not many players will notice it, many players don't know that P51P47Tempest are tigers WITHOUT teeth in il2. The teeth had been taken by someone who, for some reason, didn't pay enough attention to high Mach number/compressibility effect which leads to efficiency decrease of a CSP.

[MadBlaster]

Blackberry, it's complex calculus algorithm. But in computer, this is handled/simulated by optimizing the algorithm every few milliseconds. He already said, he doesn't have access to the flight model. What exactly to you expect him to do? His formula describe at a moment in time when forces are max. He would have to expand the formula from Tzero to Tn when terminal velocity is reached.

Really, I shouldn't talk about math or physics. I had to copy off my buddy's papers to get through high school. Just a heads up.

[MadBlaster]

Ah, what the hell.

T=time. If you take your formula below and integrate it over T(intial) until T(terminal), where T(terminal) is time when terminal velocity is reached and T(initial) is when forces are at maximum, I think that gives you your answer. But I make no promises.

Acceleration=g*sin(65)+g*(thrust/weight)-air braking force/weight

[BlackBerry]

Originally Posted by MadBlaster

Blackberry, it's complex calculus algorithm. But in computer, this is handled/simulated by optimizing the algorithm every few milliseconds. He already said, he doesn't have access to the flight model. What exactly to you expect him to do? His formula describe at a moment in time when forces are max. He would have to expand the formula from Tzero to Tn when terminal velocity is reached.

Really, I shouldn't talk about math or physics. I had to copy off my buddy's papers to get through high school. Just a heads up.

Accurate calculation should be performed by Computer. As il2 players, we just need to know on what speed will we dive with better acceleratin than opponents.

In the example of P47 vs Fw190G, the P47 did three steps to overtake Fw190.

1) to get better dive acceleration

And after some time,

2) to get a higher speed

And after some time,

3) to over take fw190G

Therefore, P47 acquired better dive acceleration firstly. So we can estimate roughly:

A)From 400km/h to 500km/h IAS, fw190A has better 65 degree dive acceleration.

B)from 500km/h to 750km/h and above, P47 dives faster.

It's important for P47 to keep high speed in battle field. If a fw190a rides on you at 3000m altitude, with same altitude and IAS, he is ready for shooting at you because there is 350 meters distance between you. THE SPEED OF YOU IS VERY IMPORTANT. If both of you are 500km/h, your P47d could outdive fw190a immediately in a 65degree dive, when you dive to 900m altitude, you could pull around 150m away from him, thus you are out of his shooting range(500m) when both of you begin to level fly near the sea level.

Furthermore, you may 60km/h(17m/s) faster than fw190a in the end of dive(750--800km/h), during the slow down level flight of 30 seconds, fw190a speed decreases more quickly than you, roughly you are round 1000 meters ahead of fw190a when both of you become slower than 650km/h.

I've never seen that significant dive advantage in il2, so I suspect the propeller efficiency calculating (700km/h-800km/)in il2 FM.

[MadBlaster]

Originally Posted by BlackBerry

Accurate calculation should be performed by Computer. As il2 players, we just need to know on what speed will we dive with better acceleratin than opponents.

In the example of P47 vs Fw190G, the P47 did three steps to overtake Fw190.

1) to get better dive acceleration

And after some time,

2) to get a higher speed

And after some time,

3) to over take fw190G

Therefore, P47 acquired better dive acceleration firstly. So we can estimate roughly:

A)From 400km/h to 500km/h IAS, fw190A has better 65 degree dive acceleration.

B)from 500km/h to 780km/h and above, P47 dives faster.

It's important for P47 to keep high speed in battle field. If a fw190a rides on you at 3000m altitude, with same altitude and IAS, he is ready for shooting at you because there is 350 meters distance between you. THE SPEED OF YOU IS VERY IMPORTANT. If both of you are 500km/h, your P47d could outdive fw190a immediately in a 65degree dive, when you dive to 900m altitude, you could pull around 200m away from him, thus you are out of his shooting range(550m) when both of you begin to level fly near the sea level.

Furthermore, you may 60km/h(17m/s) faster than fw190a in the end of dive, during the slow down level flight of 30 seconds, fw190a speed decreases more quickly than you, roughly you are round 1000meters ahead of fw190a when both of you reach Vmax.

I've never seen that significant dive advantage in il2, so I suspect the propeller efficiency calculating in il2 FM.

I just got a flashback of chasing p47 in a steep dive in 109 g-10. I got some light hits with machine gun and he was getting away, then he pulled hard g and the wings flew off. No EAD, but it was pretty funny. All he had to do was fly straight.

[BlackBerry]

You know the 4.11m simulates the G effect on airplane structure, if you pull your stick too hard at high speed, you may lose your wings or get damaged.

I think the 4.11m is lack of pilots strength simulation. Before 4.11m, we had a "super" airplane structure and "super man" pilot with great strength.

"super" plus "super" is "ordinary" result: aircraft is quite firm at high speed maneuver.

However, in 4.11m, we have a "ordinary" plane structure and "super" pilot.

"ordinary" plus "super" is "oddness": aircrafts are too fragile. At high speed, the stick should be very heavy, so heavy that a pilot could not pull out 8-11g even with his full strength. So we need "ordinary" plane structure and "ordinary" pilots, the result should be "ordinary": aircrafts are not so fragile at high speed.

[MadBlaster]

I see you were still writing.

Originally Posted by BlackBerry

The teeth had been taken by someone who, for some reason, didn't pay enough attention to high Mach number/compressibility effect which leads to efficiency decrease of a CSP.[/B]

You have to audit the numbers coming out of the sim using devicelink tool. That is the only way you could prove it. I tend to think that would be rather difficult. There's probably some stuff you need visibility on that devicelink numbers don't tell you. Maybe some randomness. For example, rudder yaw. But you have the input parameters show in this thread a few posts back, so you could do reasonableness approximation to get comfortable with it. You could build your own algorithm in C++, put in those input parameters, and run it with output to a file. then check that output to devicelink numbers from the sim. if the numbers are close, then it is accounted for. if not, then your statement could be true. otherwise, it is speculation. Crumpp says he thinks it is accounted for in standard formulation and generated some output that does not disprove his conjecture.

[BlackBerry]

Originally Posted by Crumpp

http://philsci-archive.pitt.edu/1197...y_Solution.pdf

Come on, Achilles and the Tortoise story is very simple.

Sum of time=1+0.5+0.25+0.125+........ is limited, will never bigger than 2.
of course, Achilles can't over take tortoise WITHIN 2 seconds because tortoise is some distance ahead of Achilles in the beginning.

In ancient time, people didn't know the property of "infinite series", so they were puzzled. They drew the conclusion that Achilles would never overtake tortoise because there are infinite numbers of time series in the sum, We modern people will laugh at them because the sum of infinite numbers is limited to "2".

My story, is totally different, from 1st to 20th seconds, a 45 degree diving a/c acceleration changes from g(usually higher) to 0. During the dive process, a/c moves to equilibium point. The acceleration is always decreasing. If you treat it as a constant acceleration motion, you'll make a mistake.