Snapper, thanks again for showing us how, now I just have to find some more hours in the day, I’ve already consigned the model making to my retirement.

Originally posted by Dave Homewood
Indeed. Things may change someday I hope, once the wicked witch of the Beehive is gone.

At least the RNZAF Museum has maintained its very high standards. It is the only thing that has progressed since those days in 1987 when all the 50th Anniversary celebrations went on.

Lets hope its sooner rather than later.

Can’t resist posting an other old friend, resting somewhere after a swim.

I just love this aeroplane

Good question. I am not in the privileged (more like green with envy) position of being as knowledgeable about the spitfire as you so I can only quote others or offer an opinion as an engine engineer.

The Griffon was wider so I imagine that length was needed to ensure good streamlining.

Griffon IV is about 72 inches, with a Merlin 20 at 71inches and the 45 at 69inches

The Griffon owes more to the Merlin than to the Buzzard and R. Although development work started from the base of the Buzzard in the early 30’s, the entire engine was redesigned to incorporate experience with the Merlin. In fact the 36 litre Griffon 60 is shorter than a 60 series Merlin. This was one of the design objectives. These objectives would never have been met with the Buzzard or R. The only thing in common with the Buzzard, R and Griffon was a 6 inch bore and a 6.5 inch stroke. The Merlin was 5.4 inches by 6 inches for 27 litres.

The different sound from the Griffon is not so much that it revolves in the opposite direction, but that its maximum revs are less that the Merlin and the Valve overlap is far less aggressive, giving a different sound from the exhaust. The firing order is the same but just in reverse.

If we had a Hornet flying we could listen to the handed engines, and although they revolve in opposite directions they would still sound the same. One of them would not sound like a Griffon. Must be some one out there who can remember the Hornet flying

Been away for a couple of days but it’s on its way to Stringbag who was next on the list after me. He should get Tuesday.

Brilliant to see those displays and some of the personalities involved. One thing I did note was the sedate nature of the display put on by the RNHF Firefly and Seafury, and the BAe Mossie. I’m sure we’ll have a good old natter when more of have seen it have seen it.

The difference between the Merlin and the Allison can be summed up by saying that without the Merlin Britain would have been invaded, but the US without the Allison would have survived. The Allison got no development money until the US was at war. Rolls Royce had all the experience of the R in the S6 to call on to develop the Merlin during the 30’s in readiness for war.

The Merlin III’s and 45’s and their relatives that powered the Mk’s 1 to V spits had simple single stage, single speed superchargers and generally had a rated power @12lbs boost of 1300hp at 12,000 feet. The Allison V1710 was not too far from these ratings. Were the Merlin was different is that Rolls produced a range of Merlin’s within the 45,46,50 and 55 model range with different supercharger speeds and supercharger sizes that gave the engine a wide rage of available power options at different altitudes.

For example some of the low attitude engines produced 1500 plus hp @18lbs boost at 3000 feet. These powered the clipped, cropped and clapped series of Mk5’s. They were unmatched below 5.000 feet but totally out of it at 15000 or 20000 feet. Others were rated to produce 1000 plus hp at 20,000 feet but were sitting ducks at lower levels.

Enter the 2 stage supercharger designed by Stanley Hooker. This allowed the Merlin 61 to combine the best of both worlds. Take off power was only 1200 hp, but at 30,000 feet the pilot still had 1000hp available. It was this more consistent performance that was the critical factor.

A period of mechanical improvement resulted in engines that could produce more power for longer periods. Merlin 24’s for the Lancaster, 25’s for the Mossie and the 66 (266) for the spit IX (XVI)

The Merlin 66 that is often quoted as the MkIX engine did not enter service in significant numbers until 1944 and had a much lower rated attitude than most people realise. It could produce 1750hp at 5000 feet at plus18lbs in low blower or 1625hp in high blower at 12,500 feet. These figures are for 100/130 fuel

If 100/150 fuel was used 25lb boost could be used and 200hp added to the ratings, but the low blower attitude went down to 3000 feet and the high blower rating to down to 11,000 feet.

The above figures suited the environment that the spitfire found itself fighting in during the latter part of the war.

As for the Americans, the US air force wanted to use turbo supercharges, and as the Allison was primarily an Airforce engine no money was expended on a decent mechanical supercharger. But the Technology did exist and one has only to look to the US Navy and the Wildcat, Hellcat, and especially the Corsair to see some magnificent 2 stage supercharges. The Post war F4U5 Corsair had the most magnificent 2 stage variable speed supercharger for its R2800, its size almost that of the engine.

The Allison’s in the Lightning could produce 1500 hp at 30,000 ft with their Turbo’s, but again not enough money was spent sorting out the controls to stop the engine detonating and destroying itself in the European environment. The intercooler / after coolers were completely inadequate. It was easier to ditch the Lightning and substitute the Mustang.