[ACE-OF-ACES]

I guess in my head, i'm thinking the steeper you climb the less the wing helps in lifting the aircraft against gravity.

So the steeper you climb the more thrust is required to achieve the same height as you might at a shallower angle. I don't think displacement is the same.

But in a zoom climb your not using your thrust as much as you are converting your speed to height

I think in the context of the test, the optimum angle of climb does not change much from 1500ft to 10,000ft.

Well that depends

One mans big angle is another mans small angle

I will say this

That 'I think' the angle changes alot between 1500ft and 10,000ft during a standard roc test

So with that said

Help me calibrate your statment

How much angle change do you consder to be 'not much'?

The reason it is so close to a constant is that the best climb speed tends to be slightly above the stall speed.

Actually, Ace this speed is determined more out of engine efficiency than anything else. The plane may infact climb steeper at 140IAS but would not be an efficient use of fuel or power. Furthermore, it may not actually increase the rate of climb at all, so climbing steeper would waste fuel and engine life with out any gain.

There are several German tests on the 109 for determining the appropriate angle of climb and much of the discussion involved airspeed because it helped keep the engine cooler.

Note I did't say how they determined the best climb speed

Only that it is for all intents and purposes constant from SL to 30kft

Unlike the best climb angle which changes alot from SL to 30kft (ie not constant)