Ju 87: gunsight should be depressed 3°

[Charon]

From BArch RL 1/660 L.Dv. 20/2 Die Ausbildung im Bombenwurf aus dem Sturzflug, Reich's printing office Berlin, Germany 1940, translated (in part) in Stuka, Bergs and Kast.

 

Quote

The diameter of the aiming circle on the reflector sight corresponds to a distance of 10% of the target distance in each case, e.g. 10m at 100m target distance. The distances of the ends of the three crosshair lines from the tip of the aiming post each correspond to 1% of the target distance. Expressed in angular dimensions, the radius of the light circle is 3°.

 

Due to the fact that at dive angles between 50° and 80° the total value of the lead and wind correction angle generally exceeds 3° would result in a calculated dive aiming point that lies outside the circle if the reflex sight is adjusted as for shooting. To remedy this, the reflector sight used for bombing must be adjusted in such a way that when aiming via the aim post, a lead angle corresponding to the average required angle is already used, or an adjustable reflector sight must be used.

 

In practice, it is advisable to base the adjustment for the Ju 87 on a lead angle of 3°. This means that a lead angle of 3°  is always achieved when aiming via the aiming post, and a lead angle of 6° is achieved when aiming at the point where the circle intersects with the vertical axis [aiming post]. The upper intersection point of the vertical axis with the circle results in a sight line parallel to the adjustment axis and thus the sight line for shooting with the machine gun.

 

[Following sentences omitted as they refer to the Ju 88.]*

 

Since we don't have an adjustable gunsight for these planes, the gunsight of the Stuka should be adjusted 3° down when not equipped with the gunpods. Without this adjustment, the Stuka is only able to bomb accurately in very steep dives, preferably vertical (in reality, 70° was considered the most favorable angle).

 

Unfortunately Bergs and Kast don't translate the Ju 88 section, but given its shallower dive profiles I would expect the displacement to be greater; with no fixed armament there is of course little reason not to depress it as much as needed. (As is, I find that even the maximum hold-over of 6° achievable without leaving the reticle is only accurate in dangerously steep dive angles, and at this extreme hold-over it is easy to lose track of the reticle).

 

I've struggled to navigate the Bundesarchive. Perhaps a German speaker would be able to obtain the full document, if it's not too much trouble?

 

*: B&K: "paragraphs and sections referring to the Ju 88 [...] usually only provided a slight adjustment on values given for the Ju 87."

Edited May 25, 2023 by I./JG3_Charon

[ACG_Bussard]

The Ju-87 in IL-2 uses the standard Revi C/12 D gun sight, which does not provide for flexible adjustment of an offset angle by using a dial. In this respect, everything in IL-2 is correctly implemented.

 

https://www.deutscheluftwaffe.de/fl-52095-revi-c12-d-1944-2

 

The compensation of headwind, tailwind and crosswind is done by considering a wind correction angle to the line of sight. It needs to be considered while dive bombing with an offset. Rule of thumb is: for every 10 km/h of wind = 1° offset.

 

I have the LDv 20/2 you are looking for and of course I can send it to you, but I doubt it is usefull for you, because it is written in old German characters.

 

Below are some illustrations from the LDv 20/2 you are looking for. Hope that helps a bit.

 

Edited May 28, 2023 by Bussard*

[Charon]

58 minutes ago, Bussard* said:

The Ju-87 in IL-2 uses the standard Revi C/12 D gun sight, which does not provide for flexible adjustment of an offset angle by using a dial. In this respect, everything in IL-2 is correctly implemented.

Isn't that accounted for by the second paragraph?:

 

On 5/25/2023 at 12:18 AM, I./JG3_Charon said:

To remedy this, the reflector sight used for bombing must be adjusted in such a way that when aiming via the aim post, a lead angle corresponding to the average required angle is already used, or an adjustable reflector sight must be used.

 

The instruction to adjust the gunsight by the average lead angle only applies when an adjustable gunsight is not used. With an adjustable gunsight, of course there is no need and the pilot may dial in exactly the lead they need on a per-dive basis. With our fixed Revi C/12D, the 3° adjustment ought to be baked in.

 

1 hour ago, Bussard* said:

I have the LDv 20/2 you are looking for and of course I can send it to you, but I doubt it is usefull for you, because it is written in old German characters.

 

I'd be grateful if you would. I fully expect it to be a pain to work through, but with Google Translate and with Bergs & Kast's partial translation to cross-reference, I think I can make use of it.

 

[ACG_Bussard]

The only adjustable sight I know of for some late-war Ju-87s is the BZA bomb aiming system, but this only takes tailwind and headwind into account. 

 

I have written you a PM about the regulation you are looking for. 

[Charon]

Thanks for that PM; that will be enormously helpful.

 

----

 

Regarding adjustable sights... take care to distinguish those adjustable by the pilot, e.g. Revi with Schwenkplatte SP-2a , from those adjustable only on the ground. Virtually all gunsights have provision for adjustment on the ground, and the Revi C12/D is no exception:

 

 

Google translates this for me as something like this:

Quote

Adjust with the optical sighting device (luminous agreement) according to the adjustment table of the aircraft concerned.

 

a) for height:

 

If the clamping screw (24) is loose, by adjusting the height adjustment screw (20), which becomes accessible after folding down the cover (17) (Fig. 2). Then tighten the clamping screw (24) again.

 

b) to the side: 

 

by simultaneously or alternately adjusting the two side adjustment screws (10) (Figs. 2 and 3)

 

Please correct me if there are errors here.

 

 

So the height adjustment screw is hidden underneath the cover and anchored with a lock-screw. It's not adjustable in flight, but can be set by the ground crew.

Edited May 29, 2023 by I./JG3_Charon

[ACG_Bussard]

S! Charon

 

I´m well aware of this and you have also understood the description correctly. But that doesn't change the fact that there is no flexible adjustment by a dial on the Revi C12/D.

 

Regardless of this, I would like to know whether you have reliably hit a ground target during a high altitude dive bombing run with a wind speed of more then 30 km/h = + 3° offset, especially by tailwind or crosswind.

[Charon]

I feel like we're talking past each other, and I wish I understood the point of misunderstanding.

 

I agree with you that the Ju 87's Revi  should not have a flexible (i.e. pilot) adjustment. But in that case the inflexible adjustment (set by the ground crew) should be adjusted (screwed and locked) at -3°, just as L.Dv. 20/2 says, and just as all of the practical examples for the Ju 87 depict:

 

 

 

 

9 hours ago, Bussard* said:

I would like to know whether you have reliably hit a ground target during a high altitude dive bombing run with a wind speed of more then 30 km/h = + 3° offset, especially by tailwind or crosswind.

 

No, I'm really bad at it, haha. That's what prompted me to buy Bergs and Kast's book, at which point I realized the Revi was configured wrong.

 

To the extent that I can hit anything, it's only really with very steep dives where the lead angle can be almost neglected. I struggle in 70° dives, even though "Under current conditions and according to available experience, the most favorable dive angle is 70°" (LDv20/2, trans B&K, p98). I'm going to keep reading and practicing and maybe one of these days I'll get it.

 

 

Edited May 30, 2023 by I./JG3_Charon

[ACG_Bussard]

I think there isn´t a misunderstanding and of course it was possible at that time to de-adjust the Revi before the flight according to the L.Dv. 20/2 and the Revi C12/D manuals. But why the whole point? 

 

It is very difficult to hit a target in a crosswind or tailwind situation anyway. The practical advice for the most successful dive bombing is with headwind or no wind at all and a according flight plan: 

 

See section wind @  18:22

 

 

This assumption can also be derived from L.Dv. 20/2 page 18/19 which is in your hand.

 

The only thing that comes to my mind for a pre-flight adjustment of the Revi would a modified Pilot Head Centering for the Ju-87. This can be done with the keystrokes for "Move pilot head left", "Move pilot head right", "Move pilot head up", "Move pilot head down" and finally "Save current corrections in head position" (check your own keystrokes at the keymapping options under "Pilot Head Control"). It would be the best to make a backup of the data/luascript directory beforehand.

 

 

Edited May 30, 2023 by Bussard*

[Charon]

19 hours ago, Bussard* said:

it was possible at that time to de-adjust the Revi before the flight according to the L.Dv. 20/2 and the Revi C12/D manuals.  But why the whole point? 

 

Because "at dive angles between 50° and 80° the total value of the lead and wind correction angle generally exceeds 3° would result in a calculated dive aiming point that lies outside the circle if the reflex sight is adjusted as for shooting" (L.Dv. 20/2, p17).

 

The key point here, IMO, is that the reflex sight there is an aid to the pilot in bombing first and shooting second, and that it becomes hard to judge the aiming point accurately when it falls outside the circle, and especially when it falls far outside the circle.

 

With the Revi adjusted as for shooting (0° offset), a 70° dive with 1000m release results in a lead angle of 3° (L.Dv. 20/2, table 1). Up to about 50km/h of tailwind can be adjusted for, but any amount of headwind at all will push the aiming point out of the circle. Practically, the pilot only ever uses the bottom half of the Revi, and they're often forced to hold way over:

 

This is sketch 12 reworked for a 0° offset: 70° dive, 700m release, 25km/h headwind, for a wind compensation angle of 3° and a lead angle of 2°. Note that a higher release, shallower dive, or stronger headwind would all force the aim point to depart the Revi's post entirely

 

On the other hand, with a -3° offset, head/tail winds of +/- 25km/h can be accommodated without even leaving the circle. It's a more balanced setting that lets the pilot use the entire Revi for aiming under typical conditions.

 

To turn your question on its head, why wouldn't they adjust the Revi to -3°? It lets the full reticle be used when dive bombing, and "the intersection point of the vertical axis with the circle" can still be used as "the sight line for shooting with the machine gun" (L.Dv. 20/2, p17) -- i.e., they can still strafe. The only advantage to the 0° setting, as far as I can tell, is that deflection shooting with the guns is easier. But the Ju 87 isn't a fighter; optimizing for the use of the forward guns at the expense of bombing accuracy doesn't seem like a reasonable trade-off for them to have made. From my perspective, adjusting the sight down on a dive-bomber is the obvious thing to do, and so I was unsurprised when I went looking and found that the training material said it must be done.

 

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It is very difficult to hit a target in a crosswind or tailwind situation anyway. The practical advice for the most successful dive bombing is with headwind or no wind at all and a according flight plan: 

 

Yes, although: "These disadvantages must be accepted and eliminated already in the training of the pilots by a lot of practice, because a throw with tailwind offers considerable tactical advantages due to the increased ground speed. [...] Although the crosswind throw is the most difficult to perform from the air and requires practice, it will very often be tactically necessary, e.g. for targets which, due to their shape, require an attack in the longitudinal direction or obliquely to the longitudinal direction independent of the wind (ship targets, bridges)" (L.Dv 20/2, p19)

 

Regarding HvB's video: he is extremely skilled and I respect that, but his attacks are not made by the book. He's attacking very low ("I arrive at 700-800m altitude"), he does not seem to use the dive brakes, and he seems to release around 200m. Contrast with L.Dv 20/2: "For the time being, the release altitude of 1000m can be considered as a release altitude that balances accuracy, the effectiveness of the defense, and the safety of the aircraft." (L.Dv 20/2, p40). Note also that the danger zone for both SD 50 and SC 250 is given as 500m in L.Dv 8/5 aka L.Dv 20/3.

 

It appears as though the textbook dive techniques aren't practiced by any players. The tutorials I can find on youtube either use very low release altitudes to minimize the lead angle and drop based on a learned sight picture (HvB) or use 90° dives so that no lead is needed (Requiem, I fly Central). I suspect the fact that the textbook sight pictures (sketches 12-14, L.Dv 20/2 p 22-23) are impossible to achieve is one of the obstacles to a realistic technique. The absence of any advantage to contact-fused bombs is another part of it, but that's a topic for a different thread.

 

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a modified Pilot Head Centering

No, that's not it at all. I use VR and can certainly lift my head so as to see the target below the reticle. It's just that when I do this, the reticle provides nothing to help measure the hold-over. With the recommended -3° adjustment, it would.

Edited May 31, 2023 by I./JG3_Charon

[ACG_Bussard]

[Charon]

@Bussard* sorry if I've been a bother. The reference you shared has been very helpful, as has having you as a foil to help me figure out what points need clarification or details. I'll give it a few more days in case anyone else has anything to add, then write this up as a bug report in the appropriate thread.

[ACG_Bussard]

A few final notes from me, as I assume that the developers won´t change anything regarding the 2014 released Ju 87 even after your bug report based on the mentioned primary and secondary sources:

• The Great Battles Ju-87 includes not only the D3 but also, as a modification, the G1 with 3.7cm on-board guns. The G1 requires a centered revi for anti tank.
• The Cliffs of Dover contains a Ju 87 B, which also doesn´t include an adjustable Revi. There was no discussion about this. See ATAG forum for CloD.
• Based on the physical formulas given in the link, you can calculate yourself whether an an offset adjusted Revi is necessary:    https://www.theairtacticalassaultgroup.com/wiki/doku.php?id=dive#aim_angle#
• Perhaps you could  change only your aim point in the Revi for testing purposes. 
• Therefore I´ve attached you from my collection a short summary about usage of the Revi for bombing with no wind / head wind / tail wind / cross wind

Happy testing and training and now I'm definitely out!

Bombenabwurf Vorhalt bei Wind.zip

[Charon]

Quote

The classical diving angle was 70°. And by the 70° degrees, the bomb naturally when you had released it didn't go on in this 70°. It fell to the [???] . So therefor we had a lag. And this lag was calculated out by a switch of our sight.

 

Ju 87 Pilot Heinz-Georg Wilhelm Migeod:

https://www.youtube.com/watch?v=XxDkoIVcq6o&t=1010s

[ACG_Bussard]

Because I was just in the mood. 🙂

 

Source: Junkers Ju 87, Peter C. Smith, Crowood Aviation Series

 

Even shallow dive angles from 30° - 45° were used in Summer 1940 against convois in the channel (Flachsturzverfahren according to the battle reports from the StG 1 in the German federal archives RL 10/512). 

[Charon]

The Ju 87 was aerodynamically and structurally capable of bombing in a 90 degree dive, but doing so wasn't generally appropriate or tactically sound in combat conditions. Basically all of the primary sources I can find agree that a steep but not vertical (typically 70°) dive was preferred in most cases (the StG 1 ship attacks you mention being an exception, because they were conducted with such a low release altitude, against a long target, that they could simply drop as the target disappeared beneath the nose).

 

I'll quote from the Bergs and Kast translation of these sources, for convenience:

 

Quote

In present conditions and according to the available experience, the most favorable diving angle is 70°. This angle balances the advantage and disadvantages of the vertical and flat angle.

Bergs and Kast, Stuka: The Doctrine of the German Dive-bomber p54

Translated from TsAMO, F.500 Op 12452 D.239 Aerial Tactics: the Dive Bomber

This passage also appears verbatim in L.Dv 20/2

 

Quote

The best preparation for practical bombing is achieved when the diving angle of 50° or 70° is drilled into the pilot during basic training.

Bergs and Kast, Stuka: The Doctrine of the German Dive-bomber p108

Translated from L.Dv 20/2, Guidelines for Dive-Bombing Training (Ju 87 and Ju 88) April 1940

 

Also note the training exercises given for Ju 87 pilots in this same document: of the 8 preliminary exercises, all are conducted with a 70° dive angle. Of the 6 main exercises, one is at 70°, four are at "over 60°", and one has no dive angle listed ("from low altitude"). No 90° dive exercise is given. (B&K p118-119)

 

Consider also the practical problems with a vertical dive. The pilot must judge the start of their dive precisely. If they should overshoot and find the target is below their point of aim, they'll need to roll the plane 180° while in a dive before they can correct their aim (dives beyond 90° being forbidden by L.Dv 366, Special Guidelines for Diving with the Hs 123 and Ju 87. Trans. in B&K p151). And they will then exit their dive heading opposite the rest of their flight. A pilot aiming for a 70° dive, by contrast, can deal with overshooting their entry simply by steepening the dive a little and compensate by decreasing their hold-over.

 

A pilot who attempts a vertical dive in combat with a tailwind may also find themself pushed beyond the vertical, with all the same problems as an overshoot. Note that a tailwind is tactically favorable, as it increases speed over the ground and hastens egress.

Edited April 23, 2024 by Charon

[ACG_Bussard]

Sorry, no, there was no 70° rule and no classic used angle of 70°. Apart from the training regulation L.Dv. 20/2 quoted by you and the secondary literature you mentioned, there is no further evidence supporting this.

 

The typical dive angle was between 60° up to 90°. So in short this was flexible, depending on the situation of the mission and skill of the pilot.

 

Secondary source in example:

 

Junkers Ju 87 Stuka, Mike Guardia, Osprey Publishing, page 9

 

More primary sources, because you couldn´t find more:

 

a) dive angle up to 80°

 

L.Dv. 576-4, Ju-87 B Bedienungsvorschrift Abwurfwaffe, 12/1938, page 17

 

b) dive angle up to 90° - with tailwind an a lower angle, like you correctly said.

Werkschrift Ju-87 B-1, Betriebsanleitung Flugbetrieb, Hauptabschnitt 10, 4/1939, page 15

 

c) dive angle up to 90° 

Werkschrift Ju-87 B-2, Betriebsanleitung, Hauptabschnitt 10, 6/1940, page 24

 

d) dive angle up to 90° 

L.Dv.T. 2087 Ju 87-R1, Bedienungsvorschrift Fl, Flugbetrieb II, 3/1942, page 10

 

e) dive angle up to 90° 

L.Dv.T. 2087 D-5 Bo, Bedienungsvorschrift Ju 87 D5, 1/1944, page 25

 

Further I disagree that a shallow dive angle up to 45° was the exception, as this wasn´t used only on ships but also as close air support at land in mid/late war too. And finally that a dive angle of more than 90° is inappropriate is hardly worth mentioning, isn´t it?

 

I´ll hope that I could helped you a bit. 😉

 

Edited April 23, 2024 by Bussard*

[Charon]

On 4/23/2024 at 2:47 AM, Bussard* said:

Sorry, no, there was no 70° rule and no classic used angle of 70°

I've already linked to a timestamp of a stuka pilot saying "The classical diving angle was 70°". That seems indisputable.

 

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And finally that a dive angle of more than 90° is inappropriate is hardly worth mentioning, isn´t it?

 

Multiple printings of the Betriebsanleitungs and Bedienungsvorschrifts think it's worth mentioning. "Es darf nicht über 90° gestürzt werden".

 

I think you're misinterpreting these manuals. These give the limit; the Ju 87 can indeed dive up to 90°, but they never tell the pilot he should dive at 90. The point is to give the pilot the confidence that he won't overspeed or fail to pull out if he needs to dive a little steeper than he planned. That does not mean a pilot should plan for his dive to be right at that limit. That would leave no margin to correct it. Thus the training curriculum emphasizes the 70° dive, not the 90° dive.

 

L.Dv.T. 2087 tells the pilot what he can do; L.Dv 20/2 tells him how he should do it.

 

I also note that Rudel gives an account of one 90° dive. And just as I've suggest above, it was not planned as a 90° degree dive. It was a steep (70°-80°) dive that he was forced to steepen:

 

Quote

Our diving angle must be between seventy and eighty degrees. I have already picked up the Marat in my sights. We race down towards her; slowly she grows to a gigantic size. All their A.A. guns are now directed at us. Now nothing matters but our target, our objective; if we achieve our task it will save our brothers in arms on the ground much bloodshed. But what is happening? Steen's aircraft suddenly leaves mine far behind. He is traveling much faster. Has he after all again retracted his diving brakes in order to get down more quickly? So I do the same. I race after his aircraft going all out. I am right on his tail, traveling much too fast and unable to check my speed. Straight ahead of me I see the horrified face of W.O. Lehmann, Steen's rear-gunner. He expects every second that I
shall cut off his tail unit with my propeller and ram him. I increase my diving angle with all the strength I have got—-it must surely be 90 degrees—sit tight as if I were sitting on a powder keg. Shall I graze Steen's aircraft which is right on me or shall I get safely past and down? I streak past him within a hair's breadth

Stuka Pilot, Rudel, p15

[ACG_Bussard]

Well, I think you simply got a bit lost in this 70° dive angle thing. Even the co-author of the book you purchased and quoted several times from mentions the differences between crew training (namely the L.Dv 20/2 Ausbildung im Bombenwurf aus dem Sturzflug, 1940) and the combat practice.  The co-author's comments that theoretical training did not influence combat practice, as you suggest, but that combat practice at the Stuka-Squads was simply different from training lessons.

 

For your convenience I have linked the video from the co-author, the relevant starts from 46:23 until 50:47:

 

 

He talked in this Q&A about the following dive angles:

 

Crew Training 70° up to 90°
Shallow dive angle for Convoys / Merchant ships 40° to 50 °
Steep dive angle for Warships 70° to 90°

 

This in combat used dive angles are confirmed by the books by the authors Paul C. Smith (Junkers JU 87 STUKA, Crowood Aviation Series, 1998), Mike Guardia (JUNKERS Ju 87 STUKA, Osprey Publishing, 2014) and Georg Brütting (Das waren die deutschen Stuka-Asse 1939 - 1945, German Motorbuchverlag, 1976). The primary source in the German Federal Archives, BArch RL 10/512, for deployment in England and the Mediterranean in 1940/41 I have already mentioned. It can be downloaded there, if you want to.

 

And with regard to the Stuka operating manuals (LDv.576/4 and L.Dv.T 2087) and factory documents from Junkers that I have cited numerous times, the screenshots are not only the technical documentation what the JU-87 is capable of but rather part of the pilot's operating instructions (on allied side, the so-called UK pilot notes or US pilots operating instructions) with notes how to take-off, landing, dive, emergency, etc. Your assumption are therefore plain wrong, probably a language issue on your side, which I don´t have as German is my mother tongue.

 

To clarify: I'm not saying that the 70° dive angle was a bad one, it just exceeds the viewable angle of the Revi gun sight because of the necessary offset angle. And I never said 90° that the dive angle is the way to go, because you can also dive between 70°+ up to 90° and this works well in IL-2 too (and as well in real combat practice by the "old hands" back then).  

Edited April 25, 2024 by Bussard*