P-38 with Roll-Royce Merlins

[helmitsmit]

More like 1941-1942 performance.

FW-190s were doing 390mph + in 1941 in combat, so were Hawker Typhoons. The 109F4 was doing a few mph short of 400 in late 1941, as was the Mig 3. The Spitfire, 190A and 109G all exceeded 400mph in level flight in 1942. The P-38 was doing over 400mph as well.

One of the great 'mightofbeens' was the improved Spitfire proposed by Supermarine in 1939. Supermarine significantly reworked a Spitfire II into a "Mk III" with a two speed Merlin XX in 1940 and recorded a level speed of 400mph at 21,000 feet. They clipped the wings, added 14 Imp Gal (17 US gal) to the fuel tanks, strengthened the engine mounting, made the tail wheel retractable, re-arranged the landing gear and undercarriage and added more armour protection.

However, the RAF decided that the Hurricane was in more dire need of a performance increase and the new Merlins went to them. The other consideration of the RAF was that production numbers were more important than the extra performance at the time, the Spitfire being considered superior to the 109 by the RAF. So, instead of the large step foward with the Mk III, the RAF decided to go with the incremental Mk V, which required far less changes in the production line and had an engine more readily available in the Merlin 45.

In essence, the amount of significant changes to the Spitfire design emboldened in the Mk III meant that, even despite the very real improvements in speed, roll rate and rate of climb, there were too many changes in the airframe for it to be put into production quickly.

The RAF ended up paying for that decision over France in 1941, where a faster, stronger and more agile Spitfire could of blunted the technical advantage that the LuftWaffe enjoyed when the FW 190 appeared. Considering that the Mk III enjoyed almost identical advantages over the Mk V that the 190A did ( i.e a +20-30 mph speed advantage at most heights, better roll, better climb, better dive), a 190A vs a Spitfire Mk III would of been a far more even fight.

I've got a thread on the Mk 3 if you want to join and chat? The mk 3 would have been a beautiful sight over England and France.

 

[Twitch]

Ok everybody, how come the P-63 had decent performance? A supercharged Allison. The P-63C used a V-1710-117 of 1,325 HP that raised to 1,800 HP with water injection. Its max speed was 410 MPH @ 25,000 feet.

The P-63A used the V-1710-93 with 1,500 HP war emergencey power. It had same top speed at 25K feet and could get ther in 7.3 minutes plus had a range of 2,575 miles! It also had a service ceiling of 43,000 feet! Plans to install a V-1650-5 Packard-Merlin were abandoned as there was no need!

The Allison produced performance with a supercharger an no turbocharger.

 

[helmitsmit]

Maybe it was that Rolls Royce were better at supercharging their engine because they had more experience then Alison?

 

[chris mcmillin]

Twitch,
The aux supercharger on the P-63C engine was a fluid-coupling driven additional blower that fed compressed air to the engine blower at high altitude. It was a good set-up and is almost comparable to the Merlin performance. The thing about the Merlin is that the twospeed/twoSTAGE blower with intercooler/aftercooler just did such a good job it was hard to beat.
In hydroplane racing, there was a guy that made Allisons that had Merlin blowers grafted onto the rear case. They ran but didn't get a lot of testing and development before the team disappeared. An interesting idea that was to be copied by Dave Zueschel, a SoCal airplane engine guy on Mike Carroll's Airacobra racer that crashed on it's first flight. Too bad, another team that never had a chance to develop an Allison with a two stage blower.

Allison G6 (used in the F-82) rods are used in the competitive Merlin racing engines in air racing today. These are big, smooth and well suited to racing. They require a custom bearing be made, but the stroke is the same on both the Allison and the Merlin. The Allison is a pretty well built and capable engine, there are some Yak-3's racing at Reno, and I love to hear them at 80 inches and 3200, the Yaks go about 380 mph. The super Merlins are making 140 in hg with their custom blower gears and turn 3400 rpm, the caps staying on their Allison G6 rods. Those Mustangs have gone 511mph (Dago Red, N5410V, race#4, Reno Saturday Gold Heat, 2003) around the pylon course.

Those old Rolls rods would stretch the rod bolts at the 3600 to 3800 rpm that it took to get big MP before the era of custom blower gears, and throw the caps off, hole the crankcase, then 125 inches of manifold pressure would run down the cylinder with the missing piston, pressurize the crankcase and blow all of the oil out of the hole in the case, evacuating the oil system and destroying everything else rotating. All of the oil would be deposited over the airplane, and cover the windshield with oil. The prop would go to high rpm, flat pitch because of the engine oil is no longer operating the governor, so the poor guy has a huge 11 foot four bladed air brake out there, so about 40 seconds to get it up, configured to land, and down on a runway before the thing slows from 400 kts to 100 kts. What a sight!

Cool Packard. (A guy in Chicago had one similar parked next to his Hispano HA-1112 I was negotiating for my father to purchase, right before Carl Icahn bought TWA. Dad retreated from the deal after ole' Carl came to town. The airplane had a 15 hour old Merlin 500 with the real four bladed propeller. It was in perfect shape, in Battle of Britain movie paint, stored in his expansive garage with the wings on tires right next to it. If only.)

Chris...

Oh Yeah, the poor old Kingcobra had the same wing layout as the Airacobra. Those guys couldn't get more gas in the wing because of the trike gear wheel well. The way a Mustang is made it is dang near perfect, big, huge square behind the gear well, they used huge stressed doors (like they did the B-25) to hold the wing together over such a big area, and the thing held enough fuel internal to go that much farther than everything else, so the old King was done. Bummer, I love the Bells.

 

[helmitsmit]

that is good stuff out of interest what is the hp of the 3400rpm merlins?

 

[Bullockracing]

OK, this is all very interesting, but how about one of the artists from here giving us a picture of how well a P-38 would look with some late-model Merlins in it, and the air scoops associated with that type of engine (a la Spiteful?). I would love to see one, perhaps with a thinner wing to eliminate the compressibility factor...

 

[helmitsmit]

Yeah I see what you mean the wing might have made a bigger difference.

 

[Twitch]

The Merlin supercharger was crap until Sir Stanley Hooker improved it too.

 

[wmaxt]

OK, this is all very interesting, but how about one of the artists from here giving us a picture of how well a P-38 would look with some late-model Merlins in it, and the air scoops associated with that type of engine (a la Spiteful?). I would love to see one, perhaps with a thinner wing to eliminate the compressibility factor...

Of course the wing is a compromise, the original wing was designed with two criteria in mind first a high climb rate. Second ability to carry extra fuel. A thinner wing, maybe laminar flow, would hurt both those criteria but would have made it faster.

wmaxt

 

[wmaxt]

Maybe it was that Rolls Royce were better at supercharging their engine because they had more experience then Alison?

The Army Air Corps settled on Turbo's in the early 20's (1922 I think) and allowed only Turbocharging research to proceed as the prime supercharger system. Elsewhere in the world mechanical supercharging was more popular.

wmaxt

 

[Twitch]

The one thing about turbocharging in any engine application is that it is free, in that it take no power away from the engine in order to produce additional power. It all comes from exhaust. All the time a supercharger is not switched on it pulls power from the engine.

 

[wmaxt]

The one thing about turbocharging in any engine application is that it is free, in that it take no power away from the engine in order to produce additional power. It all comes from exhaust. All the time a supercharger is not switched on it pulls power from the engine.

Thats true, another aspect of turbo's is that they are not dependant on engine speed and can give full boost from SL to 30,000ft seamlessly (depending on air quality).

wmaxt

 

[Hop]

The one thing about turbocharging in any engine application is that it is free, in that it take no power away from the engine in order to produce additional power. It all comes from exhaust.

The turbo uses exhaust thrust which in a non turbo engine can be used to augment the thrust of the propeller.

At lower speeds exhaust thrust isn't very important, but at high speeds it is, often comprising a sizeable proportion of total thrust, because prop thrust drops off with speed.

 

[Jabberwocky]

On the Spitfire Mk I the exhaust from the engine was worth around 70lbs of thrust, which equated to around 70hp at 300mph. Doesn't sound like that much, but after the ejector exhausts were fitted, Spitfire Mk I performance rose from the 348-9 mph of the test machine, to 360-2 mph, despite the increase in drag from the new exhaust fairings. Thats around 20-24 mph improvement that you wouldn't necessarily see with a turbocharger.

On later marks the more streamlined 'multi-ejector' exhaust was installed, adding around another 7 mph in top speed.

 

[syscom3]

The one drawback to the P38's turbo system was it took up space in the boom, and it had a complex ducting system that gave mechanics fits.

In one Lockheed study looking at a Merlin install, they figured they could add a couple more fuel cells into the booms with attendent gains in range.

 

[syscom3]

Heres a thread that was started back in October about turbocharging and supercharging. Loads of information in it.

http://www.ww2aircraft.net/forum/2355-supercharger-vs-turbocharger.html

 

[helmitsmit]

Why not use a turbo-supercharger?

About the wing the Spitfire eliptical wing had a very low drag/lift ratio and alowed for high angles of attack. Why not use a similar wing on the P38???

 

[FLYBOYJ]

About the wing the Spitfire eliptical wing had a very low drag/lift ratio and alowed for high angles of attack. Why not use a similar wing on the P38???

Becuase the elliptical wing is hard to manufacture....

 

[wmaxt]

Why not use a turbo-supercharger?

About the wing the Spitfire eliptical wing had a very low drag/lift ratio and alowed for high angles of attack. Why not use a similar wing on the P38???

The P-38 had a high aspect ratio wing - the next best thing to the elliptical wing. The high aspect ratio and the fowler flaps were essential to its turning performance. At maneuver setting the flaps on the P-38 extended and dropped 8deg, increasing lift ~25-30% with almost no drag penalty.

wmaxt

 

[wmaxt]

Stats from a study by Lockheed for a Merlin XX installation.

Allison ------------------- Merlin XX
Rating Military - 1150 @ 20,000ft ----- 1170 @ 21,000ft
Criticle Altitude - 20,000ft ------------- 21,000ft
Rating continous - 1,000hp @ 20,000ft ---875hp @ 20,000ft
Gross weight -----13,500# ------------ 14,500#
Speed Criticle Alt - 425mph ------------ 431mph
Time to Climb -----5.94 to 20,000ft ---- 5min to 15,000ft

The P-38 would have been faster but climb would have dropped.

wmaxt