The most troubling problem so far has been the engine cooling. Melmoth 2, which had updraft cooling, cools adequately, but when you consider that I'm flying at low weight and moderate OATs, adequately isn't good enough. Melmoth 1, which has a downdraft system, cooled perfectly even under the most adverse conditions of high power, low forward speed and high air temperature. Famously, if it ain't broke you shouldn't fix it; but I thought I could improve a good thing still further. The reasoning behind the redesign of the cooling system is too convoluted to go into here-you can read about it at length, if you wish to, at the website dedicated to the airplane, http://www.melmoth2.com/-but suffice it to say that although I still think the reasoning behind the updraft system is sound, a bunch of little details may collude to undermine it. I will simply have to attack the difficulties one at a time and see whether I can overcome them. Fortunately, I'm beginning the flight test program in late fall, and so can look forward to several months of cool weather in which to experiment.