On the one hand, a retractable landing gear eliminates the drag of the legs and wheels, which can be rather high (in fact several times larger that the drag of the tailplane). But on the other hand, the installation of a retractable landing gear also adds weight to the model, which has to be compensated by a larger lifting force, which causes more induced drag. The following figure compares the required power for a model with a fixed landing gear with a second model, having a retractable landing gear. This is done assuming different values for the additional installation weight and four different flight conditions:

1. level flight at 100 km/h,
2. level flight at 200 km/h (cruising from pylon to pylon),
3. a tight turn at 100 km/h pulling 10 g, corresponding to the maximum lift available and,
4. a turn at 200 km/h, pulling 20g.

Required power of a model with a fixed undercarriage, compared with models having a retractable landing gear. A ratio below 1.0 means that a fixed landing gear is better.

The results show, that at high speed, the retractable landing gear always reduces the required power by 2% to 3%, even if the installation would add 200 grams to the mass of the model. Only at uninterestingly low speeds and high loads the lighter fixed undercarriage model has an advantage. Pilots often say, that a model with a retracted landing gear has smoother handling characteristics, but this might be the result of the sleek optical impression.

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