I wouldn't worry too much about looking upwards. An aircraft with a large vertical component will be quite close to you and thus the signal strength quite large, compensating for the loss of gain in the antenna. Imagine an aeroplane 5 miles away, 3000ft up. 5 (statute) miles is 26400 ft, so imagine the angle subtended by a triangle 26400ft across by 3000ft up. My school level trigonometry tells me that's about 6.5 degrees from the horizontal.
The further away the aeroplane gets, the more gain you'll need, and the lower angle you'll want to be receiving it.
This is why a colinear works well.
Gain is a concept where you reduce the radiation pattern from one area and add it to another. You don't get anything for free. A half wave dipole has a doughnut sort of radiation pattern. As you start adding on elements, you squash the doughnut. Normally a colinear is end fed, so you basically start with a J-pole - a half wave antenna with a quarter wave matching stub at the bottom. This in itself has a more squashed (and slightly offset) doughnut, but then you start adding on extra half wave sections to the top, with a half wave "hiding" section in between to "hide" the out of phase signal. The more half wave elements you add, the more you squash the doughnut.
Let us know how the QFH compares with a good colinear!
