Osterkamp on Drag Reduction

[HoHun]

Hi everyone,

I'm currently reading "Du oder Ich" bei Theo Osterkamp.

Something I found quite interesting is that he spent a lot of time tinkering with his Albatros D. III in order to reduce drag.

He describes:

- smoothing the fuselage surface with filler and sanding, giving special attention to filling in the depressions around the nail heads,
- replacing all round-head screws with flush-head screws, and
- fairing in all protusions with fairings made from Balsa wood or formed sheet metal.

This resulted in his comrades painting his aircraft with a black tear-drop shape (signifying his pre-occupation with streamlining) when the squadron introduced personal markings. Osterkamp notes that despite his comrades making fun of him, his Albatros was the fastest one in the squadron.

Osterkamp also describes carefully covering each bullet hole in his Albatros with a fabric patch, painting on the Cockade of the enemy and adding the date of the combat. First time ever I read about "reverse victory markings"! :-D

Regards,

Henning (HoHun)

[MASTIFF]

Does anyone know of an English version of the book?

Tony

[piecost]

Very interesting Henning.

This reminds me of Barker adding an external scoop to the air intake on his Camel and McCudden reducing the dihedral on his SE5a in addition to modifying the engine.

I have often wondered why the Germans did not employ streamlined bracing wires. Perhaps it was due to industrial rather than technical reasons.

Tim

[DRBraun]

That is very interesting to hear of his approach at field modifications. It would be interesting to see what type of fairings he used and on what protrusions.

Although his D.III may have been the fastest, it is unlikely that these modifications really had any impact. The aerodynamic drag of screw heads and dents would have been insignificant compared to the overall "dirty" nature of the D.III's shape.

Howard Hughes sweated details like this on his H-1 and the results at 350mph was worthwhile. But with a lower speed biplane with cable bracing, non-retractable landing gear, and exposed cylinder heads, Osterkamp's attention to detail was admirable but ineffective.

David

[HoHun]

Hi Tim,

Originally Posted by piecost

I have often wondered why the Germans did not employ streamlined bracing wires. Perhaps it was due to industrial rather than technical reasons.

I have to admit that I have no idea when streamlined wires were introduced and which nations used them. If you could fill me in, that would be great!

It certainly was much easier to use round wires for rigging on aircraft, though I suppose the gain in speed would have made it worthwhile ... but I'm not sure if we have hard data on just how big the gain was.

Regards,

Henning (HoHun)

[HoHun]

Hi David,

Originally Posted by DRBraun

That is very interesting to hear of his approach at field modifications. It would be interesting to see what type of fairings he used and on what protrusions.

Agreed - unfortuntaly, no photographs at all in the book (except for one of the author in a WW2 style Luftwaffe uniform - copyright date is 1938).

Originally Posted by DRBraun

Although his D.III may have been the fastest, it is unlikely that these modifications really had any impact. The aerodynamic drag of screw heads and dents would have been insignificant compared to the overall "dirty" nature of the D.III's shape.

Well, I admit that I some doubts regarding the magnitude of the gains, but I think the general trend has to be that any reduction of drag leads to an improvement in speed. I could imagine that careful attention to the engine, something which Osterkamp didn't mention but which I think is a given if someone tinkers with his aircraft for endless hours, it was possible to gain more in terms of power available than the aerodynamic clean-up could in terms of power required.

The German aerodynamicist Dr. Hoerner in one of his textbooks has given a detailed drag breakdown for the example of the Me 109, accounting for individual rivet heads etc., and I think it would be interesting to see the drag of an Albatros calculated in the same style.

Regards,

Henning (HoHun)

[Volker_Nemsch]

.
… of those days had three options to improve the performance of their aircraft:

--- more power (engine tuning, different propellers)
--- aerodynamical improvements (that’s what Osterkamp tried)
--- less weight (reduced equipment or fuel)

There were several aces who tried to get the best possible performance from their engines. In this connection Voss comes to my mind because he somehow was, what we are calling a "petrolhead" today.

Ball experimented with a spinner and this was a different aerodynamic approach to the problem as it was tried by Osterkamp.

Well, I have doubt if the last option was ever really tried that pilots tried to lighten their aircraft by flying with less fuel or ammunition or that they tried to reduce the equipment of their machine.

In this connection the headrest of the Albatros D.V was removed (at least that’s what I read), because it limited the view of the pilot. The tiny loss of weight was a welcome side effect...

Just an idea…

.

[HoHun]

Hi Volker,

Originally Posted by Volker_Nemsch

Well, I have doubt if the last option was ever really tried that pilots tried to lighten their aircraft by flying with less fuel or ammunition or that they tried to reduce the equipment of their machine.

The only incident related to flying weight I can think of off the top of my head is mentioned in van Ishofen's "Ernst Udet" biography. On 24 September 1915, Udet and his observer Justinius overloaded an Aviatik two-seater with a full fuel load, bombs, extra radio gear and two machine guns. The aircraft barely managed to get airborne and was struggling to get altitude, and Udet stalled and crashed the machine when he tried to turn a bit too steeply.

So that's a bit of the opposite effect ... aircrew not appreciating the impact of weight. However, that was early in the war, it happened to a still inexperienced pilot, and it happened to Udet, who even as an experienced pilot tended not to care too much about the technical side of flying.

Regards,

Henning (HoHun)

[HoHun]

Hi Tim,

Originally Posted by piecost

I have often wondered why the Germans did not employ streamlined bracing wires. Perhaps it was due to industrial rather than technical reasons.

I have found NACA TN 279, which points out that depending on the cross sectional area of round wire (1.16 mm^2 to 238 mm^2), the drag it presents is 1.5 to 14 N/m:

http://naca.central.cranfield.ac.uk/...aca-tn-279.pdf

Streamlined wire only had 10% to 20% of that at zero angle of attack (and according to another NACA report, didn't increase this all that much for angles within +/-2 to 3 degrees).

I estimate the drag of the Albatros D.III at 100 mph at sea level as 1800 N.

From a quick look at a three-view, the D.III seems to have very roughly 36 m of exposed wire stays on the wings (well, and the aileron control cables). However, I have no idea which kind of wire thickness was used.

Any idea?

Regards,

Henning (HoHun)

[Ransom E. Olds]

It seems to me that a problem with streamlined wire is that it is only streamlined when properly oriented; otherwise it could be a definite drag producer. At least the round wire is round however it ends up when the riggers are through! Ransom