Messerschmitt Bf 109

Development history

Messerschmitt had already designed much of the Bf 109 by this point. Like the Bf 108, the new design was based on Messerschmitt's "lightweight construction", which essentially aimed to reduce the total number of strong parts in the aircraft as much as possible. One of the more notable examples of this was the mounting of all structural points to a strong firewall at the front of the cockpit, including the wing spars, engine mounts and landing gear. In more conventional designs these would be mounted to different points on the aircraft, with a framework distributing the load among them.

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Another aspect of this construction technique was the use of a single box-spar in the wing, mounted near the leading edge. Most planes of the era used two spars, near the front and rear, but the box was much stiffer torsionally, and eliminated the need for the rear spar.

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Another major difference was the much higher wing loading than the other designs. While the R-IV contract called for a wing loading of v100 kg/m², Messerschmitt felt that this was unreasonable; with the engines available to them, the fighter would end up slower than the bombers it was tasked with catching.

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A wing generates two forms of drag, parasitic drag due to its form, and induced drag which is a side effect of generating lift. The former dominates at high speeds, when the airflow hitting the wing causes drag that rises with the square of the aircraft's speed. The latter dominates at lower speeds, where the lack of airflow requires the wing to be angled into the airflow at a higher angle of attack. Since the fighter was being designed primarily for high speed flight, a smaller wing would be optimized for high speed use.

Related Topics:
Parasitic drag - Induced drag - Angle of attack

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The downside of such a trade-off is that low speed flight would suffer, the smaller wing would require more airflow to generate enough lift to stay flying. In order to address this, the Bf 109 included advanced high-lift devices on the wings, including automatically opening slats on the leading edge, and fairly large camber-changing flaps on the trailing edge. When deployed, these devices effectively increase the size of the wing, making it better at low speeds and high angles of attack.

Related Topics:
Slats - Flaps

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Another drawback of the high wing-loading is that the plane would require more energy to maneuver. Given the limited amount of power available, this effectively meant that the Bf 109 would not be able to turn as tightly as other designs with larger wings. The high lift devices would offset this to some degree, but they also increased drag and so slowed the plane further. Given that maneuverability was last on the RLM's wish-list, Messerschmitt was certain the benefits outweighed the drawbacks.

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