Runner Beans on free draining soil

I have grown Runner Beans this year on a new allotment plot. The soil is free draining and quite light. I planted young plants in early June. I have watered the beans a lot but they still seem to suffer from drought. The leaves have been yellowing on occasion. I have fed with liquid organic food.
The cropping is really only just beginning. The beans are not tough. But they are not particularly flavoursome either.
Can anyone suggest a variety that succeeds on a dry soil. On the other hand, the climbing French Beans have not yellowed but have been slow to get going.