JU88 Dive Bombing

[II/JG53_Felix]

Presuming there is a bug with JU88 dive bombing.
JU88 manual indicates that max speed in a dive with the air brakes deployed is 575kmh.
My own testing is showing max dive is around 340kmh! This is with the standard dive setting of airbrake deployed, engines idling, radiator closed and aircraft trimmed nose heavy - with 4 x SC250, dive bomb fuse .8 sec delay.

[Torric270]

Presuming there is a bug with JU88 dive bombing.
JU88 manual indicates that max speed in a dive with the air brakes deployed is 575kmh.
My own testing is showing max dive is around 340kmh! This is with the standard dive setting of airbrake deployed, engines idling, radiator closed and aircraft trimmed nose heavy - with 4 x SC250, dive bomb fuse .8 sec delay.

I have always read the number to be: Don't deploy dive brakes above 575 km, as in you are in a glide bomb dive and want to use them to slow down. Or, don't exceed 575km in a dive with the dive brakes deployed for the added stress on the airframe.

As for if you want to go faster in the dive, just add some throttle back, but I don't know how many more g's you would pull in the pull out.

[II/JG53_Felix]

Hi Torric,

Thanks for your reply. I picked up the following article from somewhere. It indicates that a JU88 diving from 3050m, in standard configuration, lasts about 15 sec and the airspeed at the end of the dive was about 580 kmh. This makes sense to me, the aircraft would accelerate in the dive. The game does not correctly model this acceleration. (Appreciate that not all things in the game are as IRL for the purpose of playability). Then again perhaps it does but the airspeed does not indicate correctly! Have not timed a dive from 3050m. Should try the JU87 and see if it has the same issue.

article
The Dive Attack in a Ju 88

The Junkers Ju 88 was a fast maneuverable bomber, designed to deliver either horizontal or dive-bombing attacks. It was the largest bomber able to perform the latter, giving it a lethal capability against fast moving targets like ships, and pin-point targets such as bridges or fortified positions. Until the advent of the guided missile, the steep dive attack was the most accurate practical means of delivering bombs on defended targets.

For the diving attack the Ju 88 flew a programmed maneuver. The bomber ran in at an altitude between 3.000 and 5,000 m (10,000 and 17,000 ft), depending on the strength of the AA gun defences at the target. In the floor of the bomber was a small window through which the pilot could observe the target and align the aircraft on it. He then leveled the aircraft precisely, using the artificial horizon. Etched on the floor window was a series of the parallel lines perpendicular to the line of flight, to enable him to judge his distance to the target. Before entering the dive it was important to gauge the strength and direction of the wind, so the bombers navigator would look out for smoke coming from a ship or rising from fires on the ground that indicated this. If the wind blew strongly from either side, the pilot needed to aim his dive at a position on the upwind side of the target.

Before entering the dive the navigator called out the final checks: throttles back and propellers in coarse pitch, to prevent the engines over-speeding during the dive; the BZA dive-bombing sight, with a reflector glass in front of the pilot's head, was switched on; the target's altitude above sea-level was then set on the audio altimeter. Now all was ready to begin the attack.

As the target slid under the last of the horizontal lines on the floor window, the pilot pulled the knob to extend the under-wing dive brakes. This caused a large nose-down trim change, which lifted the bomber's tail and tilted it into its 60 degree dive. That bunting maneuver imposed a negative G loading on the crew and was uncomfortable, though during their training, crews had quickly became accustomed to it.

With the bomber established in its 60-degree dive, the target now appeared on the reflector glass of the dive-bombing sight in front of the pilot's eyes. His task was to fly the aircraft so as to place the illuminated aiming circle over the target, and hold it there throughout the dive. As anyone who has been in a 60-degrcc dive in an aircraft will testify, such a dive is disconcertingly steep and it feels as if one is going down vertically. To assist in judging the angle the Ju 88 had a series of lines of inclination etched into the cockpit side glass to the left of the pilots head. Yet with some training, pilots found they were able to judge the correct dive angle to within quite narrow limits by eye.

Throughout the dive, the targets defenders would react as violently as they could, and strings of bright tracer usually flashed past the cockpit. This made this form of attack seem more dangerous than it was LT Horst von Riesen, who flew Ju 88s with KG 30, told this writer: "At first it seemed that they could not miss us. But in fact we were closing the range very rapidly, and we did not present an easy target. After two or three sorties we learnt the truth of it."

Unless the gunners were actually on the target (for example a warship) they had a difficult deflection shot on the rapidly falling aircraft. If commenced from 3.050 m (10,000 feet), the diving phase of the attack lasted about 15 seconds. By the end of it the bomber had attained a speed of around 580 km/h (360 mph). When the altimeter indicated 1,500 m (4.9(H) ft) above the previously set target altitude, a warning horn sounded in the cockpit to prepare for bomb release. Four seconds later, the bomber reached 1,000 m (3,300 ft) and the horns blast ceased. That was the signal for bomb release, and the pilot pressed the release button on the control column. As the bombs left the aircraft, an automatic mechanism placed the elevators in the up position. That brought the bombers nose up and pulled it firmly out of the dive. At the end of the maneuver the aircraft was in a slight climb. The pilot now retracted the dive brakes, selected fine pitch on the propellers, and pushed open the throttles.

As the Ju 88 was recovering from the dive, it was at its most vulnerable to return fire. When attacking well-defended targets, crews would often continue at low altitude to make their escape on the deck', weaving from side to side as they made their getaway.

end article

[Torric270]

Great write-up, thanks.

Does it mention what version of 88 was in this write-up as the difference in 580 and a limit for the A-1 to 575 may indicate a later version. If memory serves, with the wing extensions and other fixes the ju88 was to reach it's full potential with the a4, so I believe they had stricter limits on the a-1.

[II/JG53_Felix]

Hi Torric,

Yes, a correct observation.

Die Ausbildung in Bombenwurf aus dem Sturzflug (JU87 JU88) - April 1940 (The training in bomb-throwing from a dive)
- indicates 575kmh should not be exceeded with the dive brake extended.

In notes particular for the JU88 it often mentions 50 degrees.

p. 79 (note: my very rough "Google Translation"!)

JU88 - nosedive
The JU88 aircraft may be toppled both bound and unbound methods. It should be noted that the dive always occurs with extended brake.

The dropping of the bombs may be made only with automatic interception. The speedometer of 575kmh, with extended brake must not be exceeded. The inclination angle of 50 degrees shall not be exceeded temporarily, over the dive with a larger angle than 50 degrees to endure change of intercept other non-automatic lines. ... end

Bit confusing at times. The bound and unbound refers to the use of the automatic or manual release.

Interesting note on p. 77 about this.

quote
This is at a dive angle of 50 degrees, a release from 1000 m and release speed of 550 kmh - 0.9 sec.

The examples show that the target method of the bound shedding process is easier than that of the unbound. However, the bound method suffers from the well-known tactical and technical weaknesses. Measured with 350 compared throws carried out by several squadrons, a clear superiority of the unbound method with respect to impact location, training and tactical expediency was revealed. ... end

[Torric270]

Hi Torric,

Yes, a correct observation.

Die Ausbildung in Bombenwurf aus dem Sturzflug (JU87 JU88) - April 1940 (The training in bomb-throwing from a dive)
- indicates 575kmh should not be exceeded with the dive brake extended.

In notes particular for the JU88 it often mentions 50 degrees.

p. 79 (note: my very rough "Google Translation"!)

JU88 - nosedive
The JU88 aircraft may be toppled both bound and unbound methods. It should be noted that the dive always occurs with extended brake.

The dropping of the bombs may be made only with automatic interception. The speedometer of 575kmh, with extended brake must not be exceeded. The inclination angle of 50 degrees shall not be exceeded temporarily, over the dive with a larger angle than 50 degrees to endure change of intercept other non-automatic lines. ... end

Bit confusing at times. The bound and unbound refers to the use of the automatic or manual release.

Interesting note on p. 77 about this.

quote
This is at a dive angle of 50 degrees, a release from 1000 m and release speed of 550 kmh - 0.9 sec.

The examples show that the target method of the bound shedding process is easier than that of the unbound. However, the bound method suffers from the well-known tactical and technical weaknesses. Measured with 350 compared throws carried out by several squadrons, a clear superiority of the unbound method with respect to impact location, training and tactical expediency was revealed. ... end

I did some tests and I can get up to 410 km/h diving from 4500 m with leaving the throttle at 100% and adjusting pitch on the way down to keep it within limits.
This may be a quick fix as they could probably increase the dive speed but to somehow limit the plane to a 50 deg angle with dive brakes would be a lot of work, especially when you can glide bomb at ~30 deg angle and run it up to 650 km/h :-)

This would go along with what a real pilot stated in a documentary I watched where he said they removed the dive brakes and the 20 mm cannon to increase speed.

[Kodoss]

Manual says Prop pitch to 9:15 and idle.


d. Height loss at flare out
1)At Glide bomb (up to 20°) with a flare out acceleration of 2g
Va=675 km/h height loss h=~300m (up to 2000m height)
Va= 600 km/h height loss h=~300m (above 2000m height)
2)At dive with automatic and dive brakes with a flare out acceleration of 3g and Va= 575 km/h
height loss h=~700m at 60° dive
height loss h=~900m at 70° dive
At dive with automatic, without dive brakes with a flare out acceleration of 3g and Va= 500 km/h
height loss h=~550m at 60° dive
height loss h=~700m at 70° dive

Early A-1 had a restriction, not to dive with a bigger angle as 50°(march 1940 manual)

11. At dive with automatic [and dive brakes]
(flight weight of 9500 kg = 2-4 250 kg bombs, full wing tanks)
Va= 575 km/h
out of 50° flight = 450 m [height loss]
At flare out by hand increases the height loss up to 800 m.
That reminds me I have still to finish the Ju 87 manual...:doh:

[II/JG53_Felix]

Manual says Prop pitch to 9:15 and idle.

Early A-1 had a restriction, not to dive with a bigger angle as 50°(march 1940 manual)



Thanks for confirming that Kodoss. That was my impression.

Have fun with the JU87 manual! Do you know what the expected speed is for the JU87 at the end of its dive-bomb attack? I suspect the game will not model it correctly.

[Kodoss]

From Betriebsdatentafel Ju 87 B-2

Dive and glide flight:
max. RPM = 2400
Vw max. = 600 km/h (TAS)

Highest IAS at flare-out:
Height = Va (IAS)
0 km = 600 km/h
2 km = 550 km/h
4 km = 490 km/h
6 km = 440 km/h

As a side note, the dive training starts for:
80° at 5500m height
70° at 2750m height
60° at 1750m height
for all 3 angles the point of begin for the dive is in a distance of 1000m horizontal from the target.