Slender-nosed Dornier Do 317A

[Wurger]

Browsing through NASM`s captured German aviation technical documents, Reel 2084, Frame 1111, I found this Dornier Werke "versuchsbericht", dated from 11/11/1941. In it I have sorted these three pages, showing that, besides the location of aircraft gun turrets at cabin`s top (B-Stand), most of the test models were of an hitherto unknown to me "Schlanken" cabin, without steps as in the well-known Do 317 "Kampfkanzel".

 

[HoHun]

Hi Wurger,

Browsing through NASM`s captured German aviation technical documents, Reel 2084, Frame 1111, I found this Dornier Werke "versuchsbericht", dated from 11/11/1941. In it I have sorted these three pages, showing that, besides the location of aircraft gun turrets at cabin`s top (B-Stand), most of the test models were of an hitherto unknown to me "Schlanken" cabin, without steps as in the well-known Do 317 "Kampzkanzel".

It seems the goal was to evaluate the lean cabin vs. the fat cabin with regard to zero-lift drag, and to find a low-drag turret shape by elongating it in several steps (while also trying versions with a squared off rear, probably because flat planes are optically superior for sighting the guns).

Is that reel available online? I just tried to google it, and though I found some Smithsonian archive interface, I'm not sure what its purpose might be since the most coherent almost-on-topic find I was able to locate was a four-pager on a German circuit meant to support infrared viewing devices. The rest of my finds was essentially random noise (though that Hell's Angel guy on the magazine cover was wearing a chromed Wehrmacht helmet as well as an Iron Cross medal, now that I think about it), and though I requested digital content, there are a lot of collections that have a single page available digitally, probably to spoof the search engine or somthing.

And Dutch forum members should brace for the realization that Fokker is a German manufacturer according to the Smithsonian! :-D I did actually stumble upon an interesting looking "Fokker D.23 Brochure", but unfortunately, the the title page is all that's available. Or I don't understand how that site works, which is just as likely.

Regards,

Henning (HoHun)

 

[Wurger]

Hello HoHun,

I have bought it from NASM. They hold a tremendous ammount of German WW2 reports, but to get them you have to order and pay paper copies, which is quite primitive these days.

 

[HoHun]

Hi Wurger,

I have bought it from NASM. They hold a tremendous ammount of German WW2 reports, but to get them you have to order and pay paper copies, which is quite primitive these days.

Thanks a lot for the explanation, and kudos for sharing going through the expense and sharing your finds with us!

Upon a closer look, the drawing does actually show the gun position in several differently elongated variants, in addition to the original circular one.

The photograph is not entirely sharp, but I now realized that it does indeed show the gun position no. 3, which according to the drawing has a length of 1.5 times its diameter.

Not entirely clear how they would have mounted a gun in that elongated bubble, but I guess they were doing preliminary research to see which gun position shapes it would make sense to go for.

("Schlanker Rumpfbug" literally translates to "lean fuselage bow", by the way. "Schlank" is etymologically closely related to the English "lank".)

Regards,

Henning (HoHun)

 

[Wurger]

Please find attached some more images from the report. The main goal was to trace the best A-Stand location taking aerodynamic resistance in account.

 

[HoHun]

Hi Wurger,

Please find attached some more images from the report.

Awesome, thanks a lot!

The aircraft with the lean nose had 7.5% less drag than that with a fat nose, which I'd consider a quite significant diffence.

The main goal was to trace the best A-Stand location taking aerodynamic resistance in account.

As I understand it, it wasn't strictly speaking the location, but the length of the A position that was investigated. The rear end of the position moves back, but the front end stays where it is, with the position becoming an elongated bubble as the result.

Note that the text states than only when the A position was increased in length to twice the width or more, a reduction in drag was achieved, while the bubble with 1.5 length-to-width ratio actually increased the drag of the entire aircraft by 0.4%.

While the cut-off rear of the A position didn't make much of a different with regard to drag with the short (ratio 1 to 1.5) bubbles, cutting off the rear did incrase the drag of the longer bubbles noticably.

Regards,

Henning (HoHun)