Questions regarding the shape of the Me 262 and Focke-Wulf 187 fuselage.

[ThePolishAviator]

The Me 262 and the FW 187 are 2 German WW2 designs that are both known for their exceptional speed and agility compared to other aircraft in their weight-class. They also share a weird quirk which is their fuselage cross-section. It's a triangle with rounded edges and walls that are somewhat curved.



I heard that such a design helps to provide lift and is easier to produce than round fuselages. also since the fuselage comes to a point at the point at which the wings are attached I figured that interference drag would be decreased.

But if it provided such advantages then we would see it in at least some post-war designs but I never managed to find such a design. Does this design have some aerodynamic drawbacks I am not aware of or are the advantages it provides too negligible to make up for the extra parasite drag?

 

[sienar]

Ludwig Bölkow designed the fuselage for the 262 and said that it was based on DVL research that showed less interference drag.

 

[OliverSedlacek]

I read that the 262 fuselage was triangular to house the main landing gear without adding more than the minimum drag.

 

[ThePolishAviator]

Ludwig Bölkow designed the fuselage for the 262 and said that it was based on DVL research that showed less interference drag.

Isn't a simple expanding radius fairing enough to reduce interference between the wing and the fuselage?

 

[Nicknick]

Alice Aviation (the first two) had a similar shape.

 

[riggerrob]

My guess is that the fuselage cross-section/bulkheads was optimized for vision downwards. compare this with how the canopy on Grumman's F8F Bearcat bulges out from the topsides of the fuselage. By leaning his head to the sides, the pilot can see better downwards and forward.

 

[Scott Kenny]

Isn't a simple expanding radius fairing enough to reduce interference between the wing and the fuselage?

If the wing meets the fuselage at a 90deg angle, that's how you get minimum drag.

===========
The flat panels are definitely easier to fabricate than curved sections. Plus, it looks like at least the bottom corners are a constant diameter for most of the aircraft length, which also makes fabrication easier. You set the rollers to make the right diameter and leave them there. You only have to fight with complex shapes at the very nose and tail, so you can assign your most experienced metal shapers to make those parts.

 

[Nicknick]

Not so sure about that, the triangle shape is a bit more blended wing body like than a rectangular wing. Note that the underside of the wing is almost flush with the bottom and the angle between the wing and the body is less edgy on the upper side as well.

However, I do agree that better vision played a role too, German aircraft designers put more emphasis in this for fighter planes than the Allied. One reason for the A-Design of the German inline aero engines was the improved vision, so it is logic to go even further with this attempt with a jet powered aircraft.

 

[Arjen]

German aircraft designers put more emphasis in this for fighter planes than the Allied.

Bf 109? Bubble-canopies for Whirlwinds, Typhoons, Tempests, late model Spitfires & Mustangs & Thunderbolts, Bearcats...

 

[Nicknick]

it took a while until Germany could produce bubble canopies, the Fw 190 had a bubble canopy.

 

[Scott Kenny]

it took a while until Germany could produce bubble canopies, the Fw 190 had a bubble canopy.

Not like the P-51D or Bearcat.

 

[ThePolishAviator]

However, I do agree that better vision played a role too, German aircraft designers put more emphasis in this for fighter planes than the Allied. One reason for the A-Design of the German inline aero engines was the improved vision, so it is logic to go even further with this attempt with a jet powered aircraft.

While A shaped engines do have the potential do give you better vision the Germans did not take advantage of that fact at all in their aircraft. Due to the way the prop-spinner cannon is installed the engine is mounted very high up reducing vision compared to similar V-engine designs.

One additional argument against that claim is that despite the extremely heavy changes made to the BF-109 during it's production run it never received a better canopy. It was a razorback plane even as it was modified to be almost unrecognizable from its original design. They never used thinner struts nor did they give it a good canopy. They even were willing to cripple any rear-vision by installing a very large armored plate just behind the pilots head (though to their credit in some variants it was replaced by bulletproof glass making the vision the same as before).

 

[Nicknick]

The A-engine configuration surly didn't help looking backwards and also not in looking along the symmetry axis forward. The improvement was in looking slightly downwards and sideways in frontal direction.

Here you find an intresting video on how bullet prooved glas can even enhance the vision:

View: https://www.youtube.com/watch?v=uCGsyjt5ANU&ab_channel=I%2FJG27_Nemesis

 

[Justo Miranda]

The origin of this school of design is in the inverted Vee configuration of German piston engines. Pilots preferred this configuration because it improved visibility during takeoff and in some combat situations. It was also useful for folding the wheels under the fuselage in the Me 262 and being able to use thinner wings. On the Fw 187 the forward visibility was so bad that Kurt Tank installed a window under the nose so that he could see the runway.

 

[tomo pauk]

On the Fw 187 the forward visibility was so bad

Source?

 

[HoHun]

Hi,

But if it provided such advantages then we would see it in at least some post-war designs but I never managed to find such a design. Does this design have some aerodynamic drawbacks I am not aware of or are the advantages it provides too negligible to make up for the extra parasite drag?

Generally, postwar fighters tended to have their engines embedded in the fuselage, so you generally ended up with fuselage cross sections that circumscribed one or two circles.

With regard to the Me 262, Ludwig Bölkow actually wrote about that in his "Erinnerungen" (p. 62 ff).

Bölkow had performed wind tunnel tests in Götting on an instrumented model, which showed excessive flow velocities in the wingroot area. After enlarging the fuselage to the well-known triangular shape, the results were clearly better.

Since the Me 262 aerodynamic design team expected resistance on part of Willy Messerschmitt to the suggestion to change the fuselage state, they decided to ask Seitz, the head of the overall design team, whether he had use for more fuselage space for tankage, and since that had indeed been a concern for Seitz, Bölkow presented the new fuselage shape as a response to Seitz' requirement for more fuel.

Messerschmitt was a bit skeptical at first, but let Bölkow (who was only a junior engineer at the time) explain, and after having a look at Bölkow's wind tunnel data, he gave the go-ahead for the new fuselage shape right away. As a final thought, after Messerschmitt had already given the green light, Bölkow pointed that as a bonus, the new shape also provided more space for gear retraction.

Regards,

Henning (HoHun)

 

[Justo Miranda]

Source?

-Le fanatique de l’Aviation Nº 6, 498 and 515 (monografie).

-Flugzeug Classic 11/2013.

- “Focke-Wulf Fw 187 der vergessene Hochleistungsjäger” by Ditmar Hermann and Peter Petrick. Aviatic Verlag, ISBN 3-925505-66-0.

 

[Justo Miranda]

The last concept

 

[tomo pauk]

-Le fanatique de l’Aviation Nº 6, 498 and 515 (monografie).

-Flugzeug Classic 11/2013.

- “Focke-Wulf Fw 187 der vergessene Hochleistungsjäger” by Ditmar Hermann and Peter Petrick. Aviatic Verlag, ISBN 3-925505-66-0.

I know that the 'belly' window was installed.
I was asking for a source that confirms the notion that 'on the Fw 187 the forward visibility was so bad'. Also - 'so bad' when compared to what fighter types?

 

[fabulousfour]

- “Focke-Wulf Fw 187 der vergessene Hochleistungsjäger” by Ditmar Hermann and Peter Petrick. Aviatic Verlag, ISBN 3-925505-66-0.

I don't want to hijack this thread, but I disagree that Dietmar Hermann writes anything about bad visibilty in the Fw 187 in his book. The opposite is true.

The translation of the caption of the relevant photo in the book is:

„To further improve visibility for the pilot, a large window was installed in the floor of the fuselage.
This gave the pilot of the Fw 187 excellent visibility.“

"Further" implies that the visibility was already good before the installation of the window in the floor.

And on another page:

„As this photo clearly shows, the Fw 187 offered an excellent all-round view. The built-in window in the floor even gave the pilot a view downwards. With this design, Focke-Wulf was a leader at the time. The successful design principle of the Fw 187 was incomprehensibly not implemented in the next twin-engined Focke-Wulf development, the Ta 154. The Ta 154 offered much poorer visibility for pilots.“

 

[Scott Kenny]

I don't want to hijack this thread, but I disagree that Dietmar Hermann writes anything about bad visibilty in the Fw 187 in his book. The opposite is true.

The translation of the caption of the relevant photo in the book is:

„To further improve visibility for the pilot, a large window was installed in the floor of the fuselage.
This gave the pilot of the Fw 187 excellent visibility.“

"Further" implies that the visibility was already good before the installation of the window in the floor.

No, it just implies that there had been modifications to improve pilot visibility before putting the window in the floor.

 

[Arjen]

The German caption of the image posted by @fabulousfour says
"Damit hatte der Pilot der Fw 187 hervorragende Sichtverhältnisse".
This translates to
"With that [the floor window] the pilot of the Fw 187 had excellent visibility".

Excellent, not better.

From Kurt Tank - Konstrukteur und Testpilot bei Focke-Wulf, volume 1 in Die deutsche Luftfahrt, by Wolfgang Wagner, Bernard & Graefe 1991, about the first Fw 187 V1, the first prototype:

Sie hatte für den Piloten bei Start, Flug und Landung nach allen Seiten eine ausgezeichnete Sicht, auch nach unten, weil sie ein großes Fenster im Rumpfboden besaß.

This translates to

She had at take-off, in flight and landing, excellent visibility for the pilot in all directions, even down, because she had a big window in the fuselage floor.

Remarks by test pilot Hans Sander, who flew the Fw 187 V1 after Kurt Tank.
All Fw 187 aircraft, prototypes and other, had the floor window.

 

[Nicknick]

Honestly, I can't see a reason why the visibility could have been bad. The pilot sits quite high at the front of an aircraft which has a declining nose and a slim triangle shaped fuselage.

 

[sienar]

A floor window was considered for the 109 during its early development. I wonder if this was something the RLM fancied.