Yes, the sound, Lizzie!
I didn't realise today was the Trooping, but when I was sitting quietly at my emails here, I heard this sound and immediately thought "That's a Lancaster: what on earth is that doing here!"
Nothing else sounds like it nor flies as slowly or low, and to hear one flying for real fully laden, as you said, must have been magical.
Another sight/sound that impresses me is when a steam locomotive JUST starts off: no revving and farting, just a sigh of steam and it moves away with panache and dignity, no matter how many carriages it has behind it.
Ron.
Ah, now for me I love the sound of a light footed Merchant Navy or West Country loco pulling away with a heavy train and slipping on damp rails, then regaining it's grip with the power of the engine, and skill of the foot plate crew, at their best. Other loco's are also impressive when briefly slipping, and there is a great recording of the ex-LMS pacific Princess Elizabeth "suffering" from this whilst coming back with very obvious blasts from her exhaust. Wonderful!!

You see I just love loud, powerful engines! 
Its just a pity those dam Southern region Locos were are so dam inefficient!
Ah, you mean those Bulleid's original "Spam Can" Pacific's. Built during the war and after they were designed for multi-traffic use so as to gain governmental approval. Bulleid actually designed and built these engines with maximum power output, but light-weight in structure. The boiler was (and still is) a magnificent steamer, with a design 280 psi, the highest of any British loco. The Nominal Tractive Effort of the Merchant Navy's (introduced from 1941) at 37,500 lb's, and with Tractive effort per ton of engine weight at a splendid 396 lb's, was better than any of the other Pacific's of both the LNER and LMS, although the LMS Duchess did produce 40,000 lb total tractive effort. The total tonnage at 94.75 tons was the lightest out of the A3's, A4's and Duchess classes.
No, I suspect Mark the "inefficiencies" that you refer to was the massive enclosed 40 gallon oil bath that contained the chain driven valve gear, along with central crankshaft big end, which often spilt oil everywhere, created fires, and was in the way if the running gear in the bath broke and needed urgent repairs. Engines could break down, and there is on record instances of the big end failing, unheard by the footplate crew due to the oil bath silencing it, and suddenly breaking through the bottom of the latter. One failure also occurred right in the centre of the level crossing at Brockenhurst which led to hours of traffic delays, both on the railway and on the highway, until a breakdown crew from Eastleigh arrived and cut away the offending parts!
No, Bulleid was way ahead of his time, and was a maverick in the mould of Brunel, but the oil bath etc., was one step too far and it was only when all but 50 of the Merchant Navy's and West Country's were rebuilt from 1956 that the real worth of these engines could be witnessed, although by then it was too late. However, many were recorded doing 100 mph+ right up to final withdrawal in 1967.
Great engines, but originally with big flaws.
