1st question, are you an engineer or a scientist?
"I have to say though that bitching about how good things were in the past is a peculiarly British pastime..."
couldn't disagree more. It's an element of human nature. As universal as the fact that we all breathe air and drink water
"I've been wondering about something for a while which was restimulated by your post. What if they didn't put the heaviest heads on, but the lightest possible ones?"
I think you always use the lightest heads available within the class of head you are using at the moment. If I'm shooting light horse I want to use type 7s which are probably a lot lighter than a 9a for example. But I still want the lightest type 9a on my arrows when I'm shooting at heavy horse. There is definitely it seems a "bigger is better" attitude in the development of heads. It would be very interesting to see a detailed analysis of the ballistic properties of all the different head types.
"Now, to my mind, for a galling arrow, the head doesn't need to be heavy, just strong enough to withstand the impact and hard enough to concentrate all the force at a point without deforming so that it has a chance to go through"
Absolutely. Galling arrows are to keep the other guys heads down and piss them off more than anything else. Probably good for irritating the horses too.
"Ascham said that ash was the material of choice because it gives a hell of a whallop (fierce heavy stripe is how I think he put it), which to me indicates that the job of providing weight to the arrow belonged, perhaps predominantly, to the shaft."
See my previous comments about the bigger or heavier is better syndrome. Since Ascham doesn't really talk about heads that much I'm not sure we can draw any conclusions from him on this particular subject.
"We also have an indication that fletches were 'long and low', from a welsh poem..."
I like low cut feathers for my arrows. Usually 1/2 to 5/8 high at the back and at least 8" long. I've done some swallow tails with 9.5" feathers.
"Where all this is going is that the trick might not be to add a heavy arrowhead- it'd be to use heavy wood and control the attitude of the thing in the air so it presents as little as possible of itself for as long as possible, as big aquatic animals do. What about taking the heaviest shaft you can find, put a bodkin head on which is strong enough to do withstand the impact without deforming, but no more, and experiment with 8.5inch fletches in terms both of height and position on the shaft? It'd still weigh in at over 1000grains and might travel a long way."
Interesting experiment, I'd be interested to see it in action. But, if it would have worked I think they would have figured it out, wouldn't they? And aren't you really restating your definition of a galling arrow?
I think there are things about war bows and war arrows that we have forgotten about and
some of them probably can't be rediscovered until we let 500 guys with war bows kill a bunch of knights and horses. As I've said before I'll bet my life if it didn't work they wouldn't have done it. I think a universal principle of archery is that you want the lightest arrow that will do the job. How light is heavy enough for the particular job is the real question.
"I'd be surprised if this hasn't been done - its just that I haven't heard about it and I'm curious."
Me too. Good conversation!