Why still no dive acceleration difference?

[BlackBerry]

Why 400mph IAS ? Why not any other number?

It's very common to dive to 400-450MPH IAS for WWII late aircrafts such as P51, P47,Tempest, fw190, etc.

Prop planes can't break sonic barrier so it's not that important for Il2 to have highly detailed Mach model.

Prop planes can't break sonic barrier, but Prop planes' propeller CAN often break sonic barrier in a dive, it's an unfortunate fact for il2.

As early as 1904 when Wright brothers made the first a/c, they knew both airscrew and wing are "same thing".

The twisted airfoil (aerofoil) shape of modern aircraft propellers was pioneered by the Wright brothers. They realised that a propeller is essentially the same as a wing, and were able to use data from their earlier wind tunnel experiments on wings. They also realised that the angle of attack of the blades needed to vary along the length of the blade, thus it was necessary to introduce a twist along the length of the blades. Their original propeller blades were only about 5% less efficient than the modern equivalent, some 100 years later.[2]

http://en.wikipedia.org/wiki/Propeller_(aircraft)

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.

It does? Maybe, depends which models you take for comparison .

Tempest MKV 9lbs boost outdives P51B(Mustang III) 18lbs boost.

Dive
For the same reasons as the zoom climb, the Tempest pulls ahead. As the speed is increased it does so more rapidly. The fact is it has the best acceleration in the dive yet seen at this Unit.

http://www.hawkertempest.se/TacticalTrials.htm

Speed and acceleration in the dive is an essential quality to a successful fighter, but a decisive conclusion on the order of superiority is largely dependant on throttle settings, and the maximum speed in straight and level flight of the individual aircraft. Here again, however, by carrying out a number of tests under different conditions, it is reasonable to assume that the Meteor is well ahead of its rivals, followed by the Tempest, Thunderbolt, Mustang and Spitfire in that order.

http://www.wwiiaircraftperformance.org/sl-wade.html

[MadBlaster]

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.

[BlackBerry]

Crumpp, your very good information.

Especially this one, P47d4 vs fw190a5? a6?

I bet that il2 4.11m can't simulate this.

111.JPG

(C)

(1) 10000 fett 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.

There are some interesting records:

1) bf109g6as initially outdives spitfire IX LF, but spitfire overtakes 109 as speed building up.

2)fw190a5 initially outdives p47d, but p47d overtakes fw190a5 as speed building up.

3)Tempest and 109G's initial dive acceleration are roughly same, but Tempest outdives 109G easily as speed building up.


When speed building up, what happens to P47/P51/Tempest? There airscrew tips reach/break sonic barrier??? howabout 109/190's airscrew?

If Daidalos Team solve this "supersonic" issue, we''ll appreciate that.

[MadBlaster]

Doesn't changing the blade angle keep the prop from going sonic in a dive?

[BlackBerry]

Originally Posted by MadBlaster

Doesn't changing the blade angle keep the prop from going sonic in a dive?

That doesn't make sense because airscrew tip's speed is irrelevant to blade angle.

Airscrew aerodynamics is quite complex, one need to read a whole book to master that.

[MadBlaster]

I'm not an engineer or a pilot. I understand that tip speed means velocity at the tip of the prop and it's faster at the tip then near the center. Theres some formula that describes rotational velocity.

my point is when they built these planes, I imagine the didn't want the tip to be breaking the sound barrier all the time, so they put governors on the engines and design the props to keep it from doing that. if your in a dive and ram air is pushing your prop to rpm limits, I'm pretty sure the operators manual is going to tell you that isn't so good and you need to change the pitch angle and slow the rpms/reduce the tip speeds or something might break or do damage when you get near your never exceed speeds.

Going back to your tempest example, will the pilot not try to do something to mitigate the effects of sonic tip speeds? Or simply, the prop design specs try to engineer that out of the equation as much as possible? It seems in your analysis, you assume not, that it is simply a function of prop length, max rpms of the engine and forward velocity. I just don't know if that is realistic. To me, it seems that tips speed breaking the sound barrier would be a rare event. So, not sure why it needs detailed modeling.

But then again, I only learn aviation stuff from playing this game.


Edit:

Relates to what I was thinking about. http://en.wikipedia.org/wiki/Scimitar_propeller

This can be controlled to some degree by adding more blades to the prop, absorbing more power at a lower rotational speed. This is why some WWII fighters started with two-blade props and were using five-blade designs by the end of the war. The only downside to this approach is that adding blades makes the propeller harder to balance and maintain. At some point, though, the forward speed of the plane combined with the rotational speed of the propeller will once again result in wave drag problems. For most aircraft, this will occur at speeds over about 450 mph.

A method of decreasing wave drag was discovered by German researchers in WWII: sweeping the wing backward. Today, almost all aircraft designed to fly much above 450 mph (700 km/h) use a swept wing. In the 1940s, NACA started researching propellers with similar sweep. Since the inside of the prop is moving more slowly than the outside, the blade becomes progressively more swept toward the outside, leading to a curved shape similar to that of a scimitar.

[JtD]

BlackBerry, I think what you're saying about Tempest vs. P-51C is about right, even if your sources are vague and not always the right ones (you're quoting a comparison between Tempest and Typhoon, for instance). A direct test between the P-51C and the Tempest V revealed that the "Tempest tends to pull away" - which is a marginal advantage for the Tempest. You've tested a marginal advantage for the P-51.
Given the average accuracy of the flight models, which was aiming at a 5%, this is something that simply may happen between individual planes, it is no indication that the general algorithm is wrong.
Mach effects are modelled, not extensive enough for accurate high speed performance imho, but they are there.
The differences in initial acceleration between individual planes is there, if you fly them properly. Some of the acceleration differences you see as simple statements "this one is better" has a lot to do with engine management. If say an Fw 190 and a P-47 cruise side by side and then go into a full power dive, the guy in the 190 slams the throttle forward and off he goes, while the guy in the P-47 adjusts mixture, then rpm and then the throttle and then starts to accelerate. Gives the 190 a two second head start. But even without considering this, if you compare a 190A-4FR with a P-47D-22 at medium altitude in 4.11, you'll be getting something similar to the test you quoted.

[BlackBerry]

Originally Posted by JtD

BlackBerry, I think what you're saying about Tempest vs. P-51C is about right, even if your sources are vague and not always the right ones (you're quoting a comparison between Tempest and Typhoon, for instance). A direct test between the P-51C and the Tempest V revealed that the "Tempest tends to pull away" - which is a marginal advantage for the Tempest. You've tested a marginal advantage for the P-51.
Given the average accuracy of the flight models, which was aiming at a 5%, this is something that simply may happen between individual planes, it is no indication that the general algorithm is wrong.
Mach effects are modelled, not extensive enough for accurate high speed performance imho, but they are there.
The differences in initial acceleration between individual planes is there, if you fly them properly. Some of the acceleration differences you see as simple statements "this one is better" has a lot to do with engine management. If say an Fw 190 and a P-47 cruise side by side and then go into a full power dive, the guy in the 190 slams the throttle forward and off he goes, while the guy in the P-47 adjusts mixture, then rpm and then the throttle and then starts to accelerate. Gives the 190 a two second head start. But even without considering this, if you compare a 190A-4FR with a P-47D-22 at medium altitude in 4.11, you'll be getting something similar to the test you quoted.

JTD, I'll make clear that I am not saying the il2 FM is wrong, on the contrary, I believe il2 is the best simulation of WII a/c, especially 4.11m has achieved "structute failure" at high G manoeuver. Well done Daidalos Team! And many of us just hope il2 go further to become PERFECT.


In il2 FM, the wing drag coeffiecent is a constant, since most a/c fly below 0.8 Mach, the result is very accurate. However, there is small flaw in high speed diving. See picture below:

1.JPG
Even the best prop diver---Tempest MKV can hardly reach 0.8 Mach in diving----maximum permissible airspeeds 540m.p.h. IAS below 10000 ft, but the airsrew==a twisted and rotating "wing" could exceed 0.8 Mach with its "tip" in a high speed dive.

As long as we could simulate "the balance of propeller power", il2 will be nearly perfect. Don't forget those exhaust tubes just behind airscrew! Exhaust boost!

IMG_0830.jpg

In WWII, US had NACA-16 series airfoil(eg. 4-blade Hamilton), UK had ARA-D airfoil, German had Gottingen airfoil.

I just suspect that those engineers of Hamilton or Rotol intently designed very big 4-blade airscrews in order to optimise high mach performance at high speed.


P51D----Hamilton Standard, four-blade, hydraulic, constant speed, 11 feet 2 inches, non-feathering

Bf109----The propeller is a V.D.M.9 - 12087. Three bladed metal constant-speed with electric pitch change, hand controlled or automatic. Diam. 9' 10" Max. blade width 11 5/8".

Tempest MKV----All versions of the Sabre drove four-bladed, 14 ft (4.267 m) diameter de Havilland Hydromatic or Rotol propellers.

Fw190A9----Three types of propeller were authorised for use on the A-9: the VDM 9-112176A wooden propeller, 3.5 m (11 ft 6 in) in diameter, was the preferred option, however, many A-9s were fitted with the standard VDM 9-12067A metal propeller and some had a VDM 9-12153A metal propeller with external, bolt on balance weights.

P47D----The P-47D-16, D-20, D-22 and D-23 were similar to the P-47D-15 with minor improvements in the fuel system, engine subsystems, a jettisonable canopy, and a bulletproof windshield. Beginning with the block 22 aircraft, the original narrow-chorded Curtiss propeller was replaced by propellers with larger blades, the Evansville plant switching to a new Curtiss propeller with a diameter of 13 ft (3.96 m) and the Long Island plant using a Hamilton Standard propeller with a diameter of 13 ft 2 in (4.01 m). With the bigger propellers having barely 6 in (152 mm) of ground clearance, Thunderbolt pilots had to learn to be careful on takeoffs to keep the tail down until they obtained adequate ground clearance, and on landings to flare the aircraft properly.

Last but not least, I believe the high-speed dive and zoom advantage of P51P47Tempest is their most important tactic in combat, and is the most amazing aspect of their flight characters.

If they can outzoom from high-speed against opponent for 300 metres higher; if they can outdive rival for more kinetic energy(sth. equals to 300 metres Potential Energy ). What will happen?

As we all known, Bf109s are very good at climbing(low speed,max climb), usually, in low-medium altitude, Bf109 has 1000ft/minute climbing advantage to their opponents.

Bf109's Energy fight: When finding enemy at rear, same energy, 700-800m away , 109 will probably climb, after 2 minutes(Be patient! Be careful about the 3rd one!), 109 will establish 600 meters higher advantage over the opponent who follows the 109. And then, 109 will fight back by using this 600 meters "extra" energy. This kind of story takes place again and again and again in most il2 servers.

P51P47Tempest could also "E-fight" in different style: diving and zooming. If a P51 find a 109 at rear, same energy, 700-800m away, P51 can dive to 650km/h IAS ( by split S), if 109 follows, he will find P51 is gaining on him, that is, P51 is quite faster than him, and the distant between them has been enlarged to 1000 m, and then, P51 will zoom at 60 degree (Be patient! Be careful about the 3rd one!), of course 109 will cut the coner, but P51 has zoom advantage so that 109 could not get close to shooting range during zooming period. Roughly P51 will find himself 600 m higher than 109, and this is the time to fight back.


1v1 is quite funny, teamwork of E-fighting will be more attractive, believe it or not. If you have some advantage, be good at using it, don't waste it, don't spoil it, be patient.