The ornamental design for a lightfixture for a model airplane, as shown and described.
FIG. 1 is a front view of a light fixture for a model airplane;
FIG. 2 is a rear view of the light fixture;
FIG. 3 is a left side view of the light fixture;
FIG. 4 is a right side view of the light fixture;
FIG. 5 is a top view of the light fixture;
FIG. 6 is a bottom view of the light fixture;
FIG. 7 is a front view of a second embodiment of the light fixture;
FIG. 8 is a rear view of the second embodiment of the light fixture, the undisclosed views of the second embodiment form no part of the claimed design; and,
FIG. 9 is a right side and left side view of the light fixture secured to wingtips of the model airplane.
The model airplane is shown in broken lines for illustrative purposes only and forms no part of the claimed design.