Ju-86P-2 Range and Cruise Speed

[Lurberri]

I’ve been cross-referencing the Ju-86P-2’s in-game performance in WitE2 with the official manual ''D. (Luft) T. 2322/1 - Junkers Ju 86 P-1/P-2 Bedienvorschrift-Fl'', dated March 1941, and the Jumo 207A-1 engine performance charts. While the Fuel Capacity (4,074 lbs) and Endurance (390 min) in Game are well-modeled, the Cruise Speed is incorrectly set to 149 mph, which artificially cripples the aircraft’s reach, the resulting Total Range (968 miles) is mathematically inconsistent with the aircraft's high-altitude mission profile and the efficiency of its diesel engines.

Technical Breakdown based on official Manual Specifications:
Fuel Consumption: 315 liters/hour (Total for both engines).
The Indicated Airspeed (Va) above 6 km is 300 km/h (186 mph), as per manual p. 29. The game currently uses a incorrect Cruise Speed of 239 km/h (149 mph). However, at the Ju-86P-2's operational ceiling of 11,000m, an Indicated Airspeed (Va) of 300 km/h translates to a True Airspeed (TAS) of approximately 345 km/h (214 mph) due to low air density. By using a cruise speed of 149 mph, the game treats the aircraft as if it were flying at sea level, ignoring the high-altitude efficiency of the diesel engines. Correcting the speed to reflect historical high-altitude TAS would increase the operational radius.

My only doubt is whether the speed listed in the manual is actually IAS or TAS. Even if it were TAS, 300 km/h is higher than the 239 km/h the plane has in the game, thus increasing the total range.

1- Climb Phase (to 11,000m): According to historical flight plans, the Ju-86P-2 required a 45-minute climb to reach its operational ceiling. At max continuous power, this phase consumes approximately 595 lbs (approx. 314 liters) of diesel, covering roughly 90 miles at a reduced average ascent speed.
2- Mission Cruise at Altitude (11,000m): a) Available Cruise Fuel after the climb, 3,479 lbs remain for the mission transit. b) Fuel Efficiency (Fuel Flow): According to performance charts, the Jumo 207A-1 turbocharged diesel engines were extremely efficient at high altitudes due to reduced air density, allowing for a much higher cruise speed. The specific fuel consumption at 11,000m was approximately 230 kg/h (approx. 507 lbs/h) for both engines combined. c) Historical Cruise Speed (Marschgeschwindigkeit): If the manual speed is IAS, then it would probably be a mission cruise speed (TAS) of 214 mph (345 km/h) at 11,000m. d) Remaining Endurance (Gesamtflugzeit) subtracting the 45-minute climb from the in-game 390-minute endurance leaves 345 minutes (5.75 hours) for the cruise phase. e) Given the 507 lbs/h fuel flow, the remaining 3,479 lbs of fuel easily support the 5.75 hours of cruise time remaining in the aircraft's endurance (3,479÷507 hours potential, validating the in-game 6.5h endurance as a conservative/safe value).
3- Calculated Total Range: 90 miles (Climb) + 1,230 miles (Cruise at 214 mph) = ~1,320 miles vs 968 miles Current In-game Range.

The discrepancy is caused by the in-game Cruise Speed (149 mph), which likely reflects low-altitude, fog or landing patterns (page II10 of the flight manual: "Höchstgeschwindigkeit in Bodennähe bei schlechter Sicht und Nebel 240km/h", Maximum speed near the ground in poor visibility and fog is 240 km/h). For comparison, the Ju-88D-2 (2,778 lbs fuel / 240 min endurance / 233 mph Cruise Speed) achieves 932 miles. It is illogical for the Ju-86P-2—carrying 46% more fuel and staying airborne 62% longer with more efficient high-altitude diesel engines—to only gain 36 miles of additional range over the Ju-88.

The TAS speed at 11,000 meters behaves very differently than at other altitudes; it increases dramatically, resulting in a significant overall increase in range. I've been very conservative; the actual range at those altitudes is probably much greater than what I've stated.

It can be verified that the Ju-86P carried out missions at a much greater distance than is possible in the game, considering that the Ju-86P that was forced to land by the Soviets due to an engine failure in the Rovno region on April 15, 1941, had the mission of carrying out a reconnaissance over Zhitomir from its base on the outskirts of Krakow, in Poland (a total of 42 hexes in the game, something unrealizable with the data we currently have in WitE2). But even so, that's a relatively short flight; the Ju-86Ps covered considerably longer distances on some missions.

It would be better represented if it were adjusted the Cruise Speed to 214 mph (345 km/h) (and the Total Range accordingly to 1,320 miles) or to 186 mph (300 km/h) to would correctly reflect the Ju-86P-2's historical role as a strategic deep-reconnaissance asset.

I have attached the relevant page 29 from the ''Bedienungsvorschrift-Fl'' for your review.

[Denniss]

Höchstzulässige angezeigte Geschwindigkeit bei Bahnneigungsflug = Maximum permissible indicated air speed during a shallow dive.
I'll look if I can find solid data for the Ju 86.

[Lurberri]

Höchstzulässige angezeigte Geschwindigkeit bei Bahnneigungsflug = Maximum permissible indicated air speed during a shallow dive.

I've checked, and you're absolutely right about that. But in other respects, I think I'm on the right track. The Ju-86P is an absolutely special machine, very different from the others when making comparisons. The data on range (and cruising speed) that appear in most encyclopedias about this aircraft are clearly incorrect. It's based on speeds that don't take altitude into account. The TAS Speed changes everything above 10,000 meters... and consequently, the range increases dramatically.

At 12,000 meters, the density is approximately one-fourth of that at sea level, which drastically reduces aerodynamic drag and allows the true airspeed (TAS) to be much higher than the indicated airspeed (IAS) for the same amount of thrust. At that altitude, the air density is so low that a standard Indicated Air Speed of 300 km/h results in a True Air Speed (TAS) of ~550 km/h.

6.5 hours of flight at high-altitude TAS (discounting the time it would take to climb to high altitude, about 45-50 min.) results in a much greater ferry/recon range (even if the IAS were 149 mph).

The Jumo 207A-1 diesel engines are extremely efficient at altitude. The current range of 1575 km is based on low-altitude, non-pressurized variants, the Ju 86P-2 is a completely different aircraft. The game is as if it were using the fuel consumption of the gasoline-powered "D" version.

Manual ''D.(Luft) T. 2322/1)'':
The official manual (page II a) specifies a total flight time of 6.5 hours with 2150 liters of fuel (and therefore indicates a fuel consumption of 315 liters per hour, the calculation shows that it actually takes 6.8 hours with that consumption). On page 30 of the manual it even states that the P-2 reconnaissance version could carry up to 2300 liters of fuel. But the BIG DIFFERENCE is the speed at 12,000 meters!

[Lurberri]

At typical aircraft cruising altitudes of 11,000 m (approx. 36,000 ft) and 12,000 m (approx. 39,400 ft), the relationship between Indicated Airspeed (IAS) and True Airspeed (TAS) changes dramatically compared to sea level.

At 11,000 meters, air density is roughly 25% of its sea-level value. Since the airspeed indicator (IAS) depends on air molecules hitting the pitot tube, a much higher actual speed (TAS) is required to produce the same "feel" of air on the wings.

As a standard rule of thumb, at these altitudes, your TAS is approximately double your IAS.
Example: If your instrument shows 250 knots (IAS) at 12,000 m, your actual speed through the air (TAS) will be roughly 500 knots. This is why long-haul aircraft fly at these levels. Because the air is so thin, aerodynamic drag is significantly lower. This allows the aircraft to achieve very high TAS with the same amount of thrust that would only produce a low speed at sea level.

The "leap" in performance is due to the exponential drop in air density. As density decreases, aerodynamic drag (which is proportional to density) drops significantly, allowing the aircraft to achieve a much higher True Airspeed (TAS) for the same Indicated Airspeed (IAS).

Below 10,000m the air is still relatively dense. You gain speed, but you are still fighting significant resistance.

Above 10,000m you enter the "sweet spot" for aircraft travel. The air density is so low that the TAS multiplier becomes very high, often exceeding 1.8x to 2.0x your indicated speed.

[Lurberri]

Another clear example of the distances at which the Ju-86P routinely operated (and which would be absolutely impossible to simulate with the current game scope) are the reconnaissance missions carried out from the Kastelli base (located about 30 km south of Heraklion, Crete) over Egypt.

Cairo (a city over which the Ju-86Ps also flew from this Greek base), and the Suez Canal, are more than 500 miles (in real-world terms) from Kastelli, and were frequent targets of its high-altitude missions (in the game it would be even worse because on the map Cairo is located about 60 hexes from said airfield). Obviously, the game doesn't accurately simulate the range of this aircraft.

[Lurberri]

The data one can find, both online and in numerous books, is very confusing and clearly contradictory. Many sources clearly fail to consider the effect of high altitude on fuel consumption, cruising speed, and range.

The official Bedienungsvorschrift-Fl D.(Luft) T.2322/1 of March, 1941 (which would obviously be the definitive reference) doesn't mention cruising speeds at altitude, which complicates matters, although it does state on pages 41-42:

"Fuel consumption figures (see also Betriebsdatentafel, operating data sheet) can be found in the flight distance table for the Ju 86 P-1, P-2, compiled by the Rechlin test center."

However, I don't have any Rechlin report available. The official manual uses 2150 liters in its table on page 29, but that doesn't mean it's the maximum fuel capacity of the aircraft, although it's very close. The next two pages show that the fuel tanks (of both the Ju-86P-1 and P-2) have a capacity of up to 2,200 and 2,300 liters, respectively. However, there is an operational filling restriction of 1,100 liters per tank (there are two, located inside the fuselage), which leaves the actual fuel capacity at a maximum of 2,200 liters for standard missions (pages 7 and 18 of the manual).





Fliegerweb.com (https://fliegerweb.com/de/lexicon/Gesch ... u+86+P-584) indicates a cruising speed for the Ju-86P-1 bomber version of 320 km/h at 10,000 m, its endurance as 390 minutes (6.5 hours), and its fuel capacity as 2,420 liters. It then indicates a range of 1,120 km and a maximum range with additional tanks of 2,090 km (since the aircraft cannot carry external fuel tanks, this most likely refers to filling the existing internal tanks to capacity). The climb time to 10,000 m is 54 minutes. It is reasonable to assume that both the cruising speed and range of the P-2 version, without the 1,000 kg bomb load, are greater. The text indicates (without reference to which of the two models it refers to, but it is reasonable to assume it was version P-2, since the table containing the data for P-1 clearly shows that these are different):

"Die Maschine erreichte nach den Start in cirka 45 Minuten 11,000 m, dabei wurden 265 km zurückgelegt. Die Marschgeschwindigkeit in 11,000 m betrug 375 km/h". (The aircraft reached an altitude of 11,000 meters in approximately 45 minutes after takeoff, covering a distance of 265 kilometers. Its cruising speed at 11,000 meters was 375 km/h).

[Lurberri]

In William Green's book "The warplanes of the Third Reich" (1972, 1st ed.), London, UK. Doubleday & Company. ISBN 0385057822, can be read on page 425: "The proposed method of operation was to climb to an altitude of 36,090 ft. from take-off, this altitude being attained in 45 min. and a distance of 165 miles being covered during the course of the climb. The pilot would then maintain this altitude, cruising at 215 m.p.h., to within 125 miles of the target, whereupon a slow climb would be commenced to a maximum altitude of 39,370 ft., this being reached at a distance of 60 miles from the target. Thirty miles from the target the pilot would throttle back the engines and make a steep gliding approach to arrive over the target silently and presumably undetected at an altitude of 32,000-33,000 ft. After releasing the bombs the pilot would then open up the engines and climb back to 36,090 ft. for the return flight. No defensive armament was provided as it was assumed that the Ju 86P would perform its entire mission well above the attainable ceilings of existing fighters. Normal fuel capacity was some 220 Imp. gal., this corresponding to an endurance of some four hours".

Part of the confusion surrounding the performance of this aircraft may stem from the fact that the Ju-86P-1 bomber typically operated with approximately 1,000 liters of fuel, or 220 Imperial gallons (I've read 1,040 liters in other sources) and had an endurance of about 4 hours. This results in a performance that is quite different from that of the P-2 version without bombs, further contributing to the confusion in many works that conflate the two versions.

I found another interesting source, although I don't know the origin of its data, in Janusz Ledwoch's book (in Polish) "Junkers 86," Wydawnictwo Militaria 142, Warsaw (2001). On page 61, we find this table (which only refers to the P-1 bomber version, but indicates a cruising speed at 10,000 meters of 375 km/h, 1,040 liters of fuel, and a combat range with maximum bomb load of 745 km. The climbing speed is 54 minutes at 10,000 meters). It should be added again that the P-1 version with the maximum 1,000 kg bomb load has significantly lower performance in all these parameters than the reconnaissance version. I've included the original page and the English translation.

[Lurberri]

By the way, I have a question. Given that the Ju-86P began operational use by the Aufklärungsgruppe OBdL in mid-1940, and was used extensively during reconnaissance missions over the Soviet Union prior to Operation Barbarossa... why is this aircraft withdrawn in the game until it returns as reinforcement for western europe as late as January 10, 1943 (turn 82)? I know of specific missions in which this aircraft operated on the Eastern Front well before that date.

And where are these planes until that specific date of their "reappearance"? Because I don't see them in Western Europe or North Africa, and they should be somewhere, these aircraft operated extensively in the west after temporarily withdrawing from the eastern front in mid-June 1941.