1941: the best case for 350+ mph CV fighters?

[wuzak]

The exposed pipe may have been cheap and easy but it can't have been very effective. The surface area is too small to have an appreciable cooling effect. Look at a your car radiator and calculate the surface area of all those fins. In addition it must have had a disastrous effect on the aerodynamics. The P-47 installation is much better aerodynamically it wasn't just moved inside for aesthetics. The typical American practice of hanging the turbocharger in breeze was not a good idea. It may not have been too critical for bombers cruising at 160 mph but for fighters it would affect performance.
The other thing to note is that turbulent flow is what you want for heat transfer but not what you want for drag. I've always been surprised that the leading edge intercooler of the P-38 worked at all.

For the exhaust pipe to turbo you don't actually want heat transfer, but a small amount may have been required in order for the turbine blades to live.

Leaving the exhaust exposed to outside air may have given the required amount.

The P-47 layout also had a longer path to the turbo, so some heat would have been lost.

Temperature difference is the other main factor s heat transfer. In the case of exhausts compared to outside air at altitude, the temperature difference is substantial.

 

[Shortround6]

Shortround, I agree with your 'shifting stuff around to fit turbo inside F4F-3'. I said back on page 6 or 7 that this would have needed to be done probably on the prototype, although I feel pretty sure it would fit, if done at the beginning.

Perhaps it would fit if done at the prototype stage, unfortunately timing is against it.
The XF4F-2 monoplane first flew in Sept 1937. after a few crashes and some other problems the rebuilt XF4F-3 (with a two stage engine) flies in Feb 1939.
The Army has had nothing but trouble with the XP-37 at this time but is persevering with the YP-37 but the first of 13 is not delivered until June of 1939 (after being ordered in Dec 1937).
This was one reason the Army ordered the P-40 in April of 1940(sorry 1939), they wanted turbos but needed reliable aircraft in the squadrons before they estimated the turbo would be ready for squadron service.
It took the army quite a while to sort out the turbo installation. They went through several different models of the turbo itself. They went through several turbo controllers and they went into combat in early 1942 with a system that needed to be replaced as it froze in certain conditions causing overspeeding of the turbo (and sometimes failure of the turbo).

Not sure what the advantage of a turbo Wildcat is if it delays production in 1940/41 and has maintenance/control issues in early/mid 1942. (or later?).

 

[Glider]

Just to throw an odd ball into the equation I think the Macchi 202 could have been the basis of an interesting development. It has the performance, a sturdy undercarriage and was able to carry drop tanks. It lacks firepower and range but that is hardly unique in some of the planes at the time, such as a Seafire and the drop tanks may well help.

It obviously lacks another important requirement, a carrier but the Italians did get close.

 

[Kevin J]

Just to throw an odd ball into the equation I think the Macchi 202 could have been the basis of an interesting development. It has the performance, a sturdy undercarriage and was able to carry drop tanks. It lacks firepower and range but that is hardly unique in some of the planes at the time, such as a Seafire and the drop tanks may well help.

It obviously lacks another important requirement, a carrier but the Italians did get close.

I think the Re 2001 would have been better as it had range, but again its a 1942 service intro fighter just like the Macchi. The only fighter that could have been ready for 1941 is the Seafire Ib, but against it is its lack of robustness.

 

[Glider]

I think the Re 2001 would have been better as it had range, but again its a 1942 service intro fighter just like the Macchi. The only fighter that could have been ready for 1941 is the Seafire Ib, but against it is its lack of robustness.

According to Shores 'Malta The Hurricane Years' the Macchi 202 entered combat over Malta in late September 1941 so it does fit in with the timescale.

I certainly agree that range is the major issue, but its no worse than most and it does have the performance. The Macchi also has a better performance than the Re 2001 and is more robust than the Spitfire, so it stays as my outside contender.

 

[Shortround6]

What is the stalling speed?

or take-off/landing distances?

You have a wing that is about 75% as big as a Spitfire wing. The flaps look like simple split flaps and they may or may not have intermediate positions or be adjustable unlike the Spitfire which were all or nothing.

It doesn't matter if the plane can hit 350mph or not if you can't operated it off the majority of carriers at the time.

Yes you could "fix" it, (bigger wing?) but what does the "fix" do the performance?

 

[Reluctant Poster]

For the exhaust pipe to turbo you don't actually want heat transfer, but a small amount may have been required in order for the turbine blades to live.

Leaving the exhaust exposed to outside air may have given the required amount.

The P-47 layout also had a longer path to the turbo, so some heat would have been lost.

Temperature difference is the other main factor s heat transfer. In the case of exhausts compared to outside air at altitude, the temperature difference is substantial.

Next time there's a cold winter day (minus 40 where I grew up) take your car for a drive, after the car has warmed up, stop the car, take off your mitts and grab the tailpipe. I think you will get a burn.

 

[Conslaw]

What I gather from all of this is that it would have been exceedingly hard to make the F4F into a 350-MPH aircraft. What if they would have take the XF4U, and split its development into two paths, with one path being the path taken - the path to making it the best plane they could make it, but the other path geared to getting a stopgap 350-MPH carrier into service as soon as possible. This would mean keeping the fuel in the wings, probably unprotected, and with a lighter armorment. Supply of the R-2800 engine would be an issue, limiting production, but even getting one section of proto-corsairs on each carrier could have made things very interesting.

 

[Shortround6]

Post-war Allison was fooling around with a turbo compound engine, exhaust gases routed to a turbine that was connected to the crankshaft.

At high boost pressures the exhaust temperatures exceeded 1750 degrees F going into the turbine and were causing blade failures. The test program resorted to injecting ADI fluid (ater/alcohol) directly into the exhaust piping to lower the exhaust gas temperature. This was with 1945-46 metallurgy not 1940-41 metallurgy.

There may have been a critical temperature of exhaust gas that could not be exceeded without causing problems while just a 100 degrees or so lower would allow the turbine quite a long life?

They didn't want to over cool the exhaust as it will lose power wanted to operate the turbine. a fine balancing act.

You can burn your hand on a exhaust pipe that is under 200 degrees. but 200 degree exhaust gas isn't going to provide hundreds of HP to drive the compressor of a turbocharger.

 

[Reluctant Poster]

Post-war Allison was fooling around with a turbo compound engine, exhaust gases routed to a turbine that was connected to the crankshaft.
View attachment 538593

At high boost pressures the exhaust temperatures exceeded 1750 degrees F going into the turbine and were causing blade failures. The test program resorted to injecting ADI fluid (ater/alcohol) directly into the exhaust piping to lower the exhaust gas temperature. This was with 1945-46 metallurgy not 1940-41 metallurgy.

There may have been a critical temperature of exhaust gas that could not be exceeded without causing problems while just a 100 degrees or so lower would allow the turbine quite a long life?

They didn't want to over cool the exhaust as it will lose power wanted to operate the turbine. a fine balancing act.

You can burn your hand on a exhaust pipe that is under 200 degrees. but 200 degree exhaust gas isn't going to provide hundreds of HP to drive the compressor of a turbocharger.

My answer was a bit too facetious, I apologize to Wuzak. I will say, however, that based on my experience with gas turbines that I wouldn't rely on the cooling effect of that little piece of pipe to protect the turbine blades. It certainly is a very crude way of attempting to control turbine inlet temperature. I would be extremely surprised if the length of pipe dictated solely by the location of the engine vs the turbine could by sheer luck match the temperature drop required to protect the turbine. My guess is that they were routing the piping on the outside to keep the heat away from the superchargers.

 

[Glider]

What is the stalling speed?

or take-off/landing distances?

You have a wing that is about 75% as big as a Spitfire wing. The flaps look like simple split flaps and they may or may not have intermediate positions or be adjustable unlike the Spitfire which were all or nothing.

It doesn't matter if the plane can hit 350mph or not if you can't operated it off the majority of carriers at the time.

Yes you could "fix" it, (bigger wing?) but what does the "fix" do the performance?

I don't pretend to know some of the details you are asking and its obvious that any alterations would inevitably increase weight and impact performance. However, you are starting with a 370+ mph aircraft and can take some hit on the performance and still meet the 350+ target the thread is aiming at. This is I suggest a more realistic approach than trying to find ways of making a slower aircraft faster.

As for take off distance I don't know. However I do know that the Macchi 202 had a very impressive climb. Time to 1,000 meters 39 seconds, 2,000 meters 1 min 28 sec, 3,000 meters 2 min 28 seconds, 4,000 meters 3 min 32 seconds so I don't think getting off the deck would be a problem. These figures are considerably better than a Spit V and there were few fighters that could outclimb a Spit at that time.

 

[Shortround6]

"I will say, however, that based on my experience with gas turbines that I wouldn't rely on the cooling effect of that little piece of pipe to protect the turbine blades. It certainly is a very crude way of attempting to control turbine inlet temperature. I would be extremely surprised if the length of pipe dictated solely by the location of the engine vs the turbine could by sheer luck match the temperature drop required to protect the turbine. My guess is that they were routing the piping on the outside to keep the heat away from the superchargers."

You could be right, but the B-17s, B-24s, P-43s and to a lesser extent the P-38s all used the exposed pipe and the exposed turbocharger. After the P-39 fiasco they had to know that there was some drag penalty.
On the XP/YP-37 the turbo had been located right under the engine with more or less exposed exhaust piping.

but this was never repeated.

heat issue?
maintenance issue? Easier to check for leaks without having to take off exhaust shrouds?

 

[GrauGeist]

The Japanese had an exposed turbo-supercharger on the Nakajima KI-87 prototype

 

[wuzak]

Next time there's a cold winter day (minus 40 where I grew up) take your car for a drive, after the car has warmed up, stop the car, take off your mitts and grab the tailpipe. I think you will get a burn.

I doubt the exhaust pipe is the same temperature at the tailpipe as it is near the engine. Temperature having been lost on the way.

Also, I'd suggest that the tailpipe would be warmer on a hot summer's day (+40C) than on a cold winter's day (-40C). Maybe not a lot of difference, but a difference nonetheless.

 

[wuzak]

My answer was a bit too facetious, I apologize to Wuzak. I will say, however, that based on my experience with gas turbines that I wouldn't rely on the cooling effect of that little piece of pipe to protect the turbine blades. It certainly is a very crude way of attempting to control turbine inlet temperature. I would be extremely surprised if the length of pipe dictated solely by the location of the engine vs the turbine could by sheer luck match the temperature drop required to protect the turbine. My guess is that they were routing the piping on the outside to keep the heat away from the superchargers.

It would probably not be to reduce the temperature to within the limits, but rather to increase the margin.

The routing of the exhaust pipe would be away from equipment.

 

[fliger747]

As long as no one else had 350 mph fighters it didn't matter as much. The Navy experimented with a turbocharged Corsair but in the event did not pursue. For much of the early war (maybe later also) much Pacific combat took place at medium and low altitudes. The Supercharger is probably a lighter and simpler avenue here for the mission. The engine was already maxed out at low alt MP wise.

Especially at sea (or some place like Munda) dispatch reliability was an important concern.

 

[tomo pauk]

As long as no one else had 350 mph fighters it didn't matter as much. The Navy experimented with a turbocharged Corsair but in the event did not pursue. For much of the early war (maybe later also) much Pacific combat took place at medium and low altitudes. The Supercharger is probably a lighter and simpler avenue here for the mission. The engine was already maxed out at low alt MP wise.

Especially at sea (or some place like Munda) dispatch reliability was an important concern.

I'll disagree with 1st sentence - it did matter. A 350 mph fighter will have much better chances to do multiple passes against a 300 mph inbound strike. The 320 mph fighters might struggle to make even one pass against a 300 mph inbound strike, resulting in a 'scratch a flattop' message.
Real-world examples might include inability of F4F-4s to catch torpedo-armed 'Kates' at Santa Cruz, that resulted in Lex being torpedoed and sunk. That is despite having a radar support, imperfect as it was back in 1941. Or, inability of Zeroes CAP to reliably intercept four B-26s at Midway.
Granted, those are examples from 1942, but we can think of a scenario that involves Ju-88s, G3Ms or Pe-2s in 1941 and see how the seaborne interceptors stack against those.

With that said, I tend to favor a R-2800 powered fighter for the USN in this thread - offered a lot of power under 20000 ft.

 

[pinsog]

I'll disagree with 1st sentence - it did matter. A 350 mph fighter will have much better chances to do multiple passes against a 300 mph inbound strike. The 320 mph fighters might struggle to make even one pass against a 300 mph inbound strike, resulting in a 'scratch a flattop' message.
Real-world examples might include inability of F4F-4s to catch torpedo-armed 'Kates' at Santa Cruz, that resulted in Lex being torpedoed and sunk. That is despite having a radar support, imperfect as it was back in 1941. Or, inability of Zeroes CAP to reliably intercept four B-26s at Midway.
Granted, those are examples from 1942, but we can think of a scenario that involves Ju-88s, G3Ms or Pe-2s in 1941 and see how the seaborne interceptors stack against those.

With that said, I tend to favor a R-2800 powered fighter for the USN in this thread - offered a lot of power under 20000 ft.

Agree 100% with this. Also, the Zero wasn't a 350 mph fighter at this time, but you really needed a 350 mph fighter to effectively combat it, or at least an altitude advantage so you can make a diving pass and breakaway, gain separation and climb back up for another pass.

Also fliger747, the P&W 1830 in the F4F-3 was doing 1100 hp at SL, at 5,500 feet was already down to 1050 hp, and was down to 1,000 hp at 12,200. A turbocharged P&W 1830 or even a turbocharged Wright 1820 was rated at 1,200 hp from SL up to 25,000 feet. That is 10% more hp at SL, 15% more hp at 5,500 feet and 20% more hp at 12,200. All of those altitudes are right where Japanese torpedo and dive bombers operated when going after US carriers.
10% more hp is significant.
15% more hp is really significant
20% more hp is freakin' huge

Whats the difference in performance between a 2,000 hp Thunderbolt and a 2,400 hp Thunderbolt? A lot.
Whats the difference in performance between a 2,000 hp Corsair and a 2,400 hp Corsair? A lot.
Whats the difference in performance between a 1,500 hp Spitfire and an 1,800 hp Spitfire? A lot.

20% is a huge jump.

Tomo pauk, we would all prefer an R2800 powered fighter in 1941-42 but the engine timeline doesn't work out. A turbocharged F4F-3 is at least possible.

 

[pinsog]

Shortround, will a turbocharger heat the intake air more than a supercharger at low altitude? If an F4F-3 and a turbocharged F4F-3 are both running at 1100 hp, side by side at 1000 feet, could they use the same intercooler? Or does a turbocharger produce more heat for a given hp than a supercharger?

My reason for asking is, instead of installing a larger intercooler like you would need at 25,000 feet, just use the original intercooler and you would still gain 100 hp down low. Or maybe slightly increase the size of the intercooler to get 1,200 hp up to 20,000 feet instead of 25,000 feet.

 

[tomo pauk]

Tomo pauk, we would all prefer an R2800 powered fighter in 1941-42 but the engine timeline doesn't work out. A turbocharged F4F-3 is at least possible.

P&W delivered nine R-2800s from Jan-Nov 1940 (those can go in the prototypes), another eight in Dec 1940, another hundred before end of the March of 1941.