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1,4701 hp, 380 mph @ 22,500 ft for the Mk Vb.
1,720 hp, 408 mph @ 22,000 ft where, with the cube root of the power increase rule, we'd expect 400 mph. So, the new nose, 4-bladed prop, and whatever "cleanup" was done added 8 mph to the expected top speed. Not bad, but not great, either. Still, it WAS a useful jump in performance.
At 22500 ft, the Merlin 45 or 50 on the Mk.V will be making about 1000 HP with ram, not 1470. Not even the Merlin 46 or 47 (the ones with big S/C) will do more than 1100 at 22500 ft. See your chart.
The pilot of Spitfire VB will be very happy if it can fly at 360 mph at 22500 ft straight and level.
The Merlin 66 will do perhaps 1550 HP at 22500 ft with ram. FWIW: data sheet
As I understand it a single stage Merlin could produce the same power as a two stage Merlin if it had the fuel and uprated parts and maybe bigger radiator(s), but why would you do that, a lot of time and effort to make a sows ear out of a sows ear?Those must be sea level speeds.
Hi Tomo.
The formula is: New Speed = (cube root [new power / old power]) * old speed for estimate of speed increase due to power alone.
It may surprise you that I have spreadsheets with the Merlins, Griffons, and Allisons, etc. in them, but not all of them report power at the same altitudes. I don't mind doing a power chart at all, but I sort of flinch when someone wants me to go to the trouble of doing power charts for all models of two separate engine designs. It isn't that important since we basically KNOW what these airplanes will do.
For the purposes of estimating a change in performance due to power increase alone, knowing the power of one of them at some altitude does nothing unless we know the power of the other one at the same altitude. Since I see and work on warbirds almost every week, I'm not that interested in spending time digging around for no good reason, and there isn't in this case. 80%+ of the increase in performance of the MK. IX over the Mk. V was from the increased engine power. I wouldn't be surprised at all if it turned out to be 90%+. Take a MK. IX and put in a Merlin 45 and you'd have almost an exact clone of a Mk. V.
And there's nothing new to either you or me in the above at all.
You have lost me here, you only have to look at Reno racers to see the effect all the little improvements make.Having small improvements add up to a total speed increase is not my experience with warbirds at all, and it also doesn't work very well with civil aircraft, either, say a Mooney 201. I have a good friend who has one. There are lots of mods out there and each has a speed increase associated with it. Adding them all will NOT give you an additive speed increase.
He was not a very liked man, too many times he had Spitfires endlessly circling until he was happy everyone formed up under him before attacking while the Betty's flew off into the distance. No aircraft could catch a Betty with a 10 mile head start in that situation.There was a tactical aspect too. The commander, an Australian Ace named Clive Caldwell,
So is everyone else considering how blindingly obvious it wasI'm surprised they never added aft fuel to that design then...
So was every other aircraft when loaded with drop tanks or bombs, the much vaunted P51 would stall and pancake if not flown straight and level when fueled up, I remember reading once about a red tail pilot that would take off with the canopy unlocked so he had a chance to get out at low level if his plane stalled. The MkXIV could fight with the 90G combat tank fitted and outperform the Me109 and FW190 with it attached.When carrying the 90 or 175 gal tank the aircraft was restricted, once airborne and at cruising altitude, to straight and level flight.
You have lost me here, you only have to look at Reno racers to see the effect all the little improvements make.
A simple "yes, I'm wrong, Merlin 45 was not near 1470 HP at 22500 ft" would've been just fine.Hi Tomo.
80%+ of the increase in performance of the MK. IX over the Mk. V was from the increased engine power. I wouldn't be surprised at all if it turned out to be 90%+.
Take a MK. IX and put in a Merlin 45 and you'd have almost an exact clone of a Mk. V.
As I understand it a single stage Merlin could produce the same power as a two stage Merlin if it had the fuel and uprated parts and maybe bigger radiator(s), but why would you do that, a lot of time and effort to make a sows ear out of a sows ear?
A single-stage Merlin could produce about the same power at sea level and, likely be decently close up to it's critical altitude. The single-stage engine might even make a few more hp down low since it is not driving the same supercharger and therefore uses less power than the 2-stage engine supercharger.
After that critical altitude for the single-stage, the single and two -stage engine will stay decently close until the altitude where the pilot changes supercharger gears in the 2-stage aircraft. Then, the 2-stage guy will pull away dramatically and continue to perform quite well until his critical altitude, after which he will gradually lose performance like a normal engine does until he reaches the altitude where the max power he can make is just the power required for level flight.
The single stage Merlins topped out at 18lb of boost.
You might be able to get more low down without a boost limiter.
The two stage engines started out at 12lbs of boost and worked their way up to 25lbs of boost.
There were a few things that limited power at times. The single stage engines didn't get to use 18lb of boost until the supercharger drive system was beefed up. Somewhere between 14lbs and over 16lbs it was possible to start breaking the drive shaft and or clutches. The up graded drive system didn't arrive until after the 2 stage supercharger showed up.
A two stage system actually makes things a bit easier on the engine. A two stage supercharger will actually take less power to drive for the same manifold pressure and heat the intake charge less. And that is without the intercooler. The 2 stage engine is flowing more air ( it is denser) that a single stage engine using the same manifold pressure.
Two of fittings can actually make a difference in power. I have never really seen any charts or much talk about the difference in thrust between exhaust manifolds. We are told that one style had less drag than another but believing that both had the same amount of thrust is a bit harder to swallow. But since exhaust thrust varies with both altitude and speed of the aircraft even with the engine burning the same amount of air it gets simplified in most explanations.
The "snow guard" is another piece that has some different effects. We are told it was worth about 6mph.
But what it did was disrupt the airflow going into the intake and lower the ram effect. This lowered the critical altitude (FTH) of the engine. So the engine is making less power at a given height than a plane without the snow guard, this is somewhat altitude dependent.
Mosquito Merlin 25 (normal Ø10.25" impeller and 8.15/9.49:1 S/C ratios) 1-stage 2-speed low & high gear was rated at +25 lb boost with 150 grade
Spitfire Merlin 66 2-stage 2-speed low & high gear was rated at +25 lb boost with 150 grade
A simple "yes, I'm wrong, Merlin 45 was not near 1470 HP at 22500 ft" would've been just fine.
Bingo.
A Mk.IX with Merlin 45 would've been faster than the Mk.V, featuring less draggy exhausts, less draggy BP glass layout, no ice guard, and a bit better fit & finish.
1600+ HP for the latest 1-stage Merlins, 2000+ HP for the latest 2-stage Merlins (both for the cases with latest fuel and no water-alcohol injection, and at low altitude).
The pilot of an aircraft with a 2-stage engine already has the advantage down low.
There is such a thing as an 1-stage 2-speed supercharged engine, too.
Just looked at the report and the model dimensions - Several model table dimensions are 'off' from 0.3 scale Model dimensions in Fig 1, and off from actual dimensions.
I would have my doubts about the single stage two speed engines making 25lbs of boost.Mosquito Merlin 25 (normal Ø10.25" impeller and 8.15/9.49:1 S/C ratios) 1-stage 2-speed low & high gear was rated at +25 lb boost with 150 grade
Spitfire Merlin 66 2-stage 2-speed low & high gear was rated at +25 lb boost with 150 grade