Yeah, that had been a big surprise from the British, Kelly Johnson thought as he reflected on the events of this past September. As Johnson and his design team went over the RAFs' new specifications for their "Lightning Mark 1" as the British had referred to it in a recent communication they had calculated the RAFs' modifications would add about 600 pounds to the empty weight. Though as one of his engineers pointed out they didn't know exactly what the empty weight would be as they didn't know what 4 20mm cannons weighed. "Well, whatever it would be add at least 600 pounds more."
Just as bad as the weight gain was the loss of fuel capacity. The rubber lining of the fuel tanks would reduce their volume by about 15% to 20%. This would leave the P-38 with a useable fuel capacity of about 310 gallons. A decrease of 80 gallons. They wouldn't know the exact numbers until they starting building them. Another delaying disruption to Lockheeds' attempts to increase production. The only bright side to all this was the Air Corps' decision to follow the RAF's lead and put armour and self sealing fuel tanks in their planes. Simplifying production greatly. The only substantial difference between their planes and the RAFs' now being the Air Corps' had guns. Kelly Johnson thought he could perceive the hand of Major Ben Kelsey in this. "They oughta make him a colonel for that."
The guns were becoming another headache too. Really the Air Corps' problem but Johnson knew any changes needed would mean another slowdown in production. The 37mm cannons were unreliable and would frequently jam. The ammunition load out was inadequate plus the shells trajectory didn't match the .50 HMGs. Funnily enough the Browning .50 caliber HMGs, usually very dependable, would frequently jam too. Usually when the pilot was pulling a little bit of G to line up on the towed sleeve target. It was looking as though that Air Corps' final choice of armament wasn't.
Then there was the new report from Langley they'd received about a week ago. NACA had conducted extensive wind tunnel testing of many types of Navy and Army planes including the P-38 with the goal of reducing drag thereby increasing the planes airspeed. Looking at the results of the wind tunnel testing NACA had done on the P-38 it was shown the guns were the single biggest source of drag on the P-38. Followed closely by the turbocharger and its associated piping. NACA had developed some recommendations on how to reduce the drag produced by these two items. As Kelly Johnson read the report he thought, "Any way of improving the performance after my Atalanta's weight increase is worth closely considering."
The first of two recommendations from NACA for the P-38 describing methods on how reduce the drag concerned the gun barrels. It suggested locating the length of the barrels as much as possible within the gun bay. And keeping the gun ports as closely fitting to the barrel and/or muzzles as was feasible without hindering the recoil. How to do that with the two 37mm cannons Johnson could only guess. What the Air Corps would do about their gun problems was anybody guess.
The second recommendation was about reducing the turbocharger drag. Not too much could be done about the scoops needed to direct cooling air onto the exhaust piping and the turbocharger other then suggesting the use of more smaller scoops located at key hot spots rather then using a few larger scoops which should then allow covering the exposed exhaust piping instead of leaving it exposed to the slipstream. What was of more interest to Kelly Johnson was the shroud NACA has designed to cover the front 2/3rds of the turbochargers' turbine well. (Similar to what the future P-47 would have.) According to NACA not only would the shroud reduce drag but the airflow over the rear of the shroud would by drafting eliminate back pressure by lowering the air pressure over the turbine wheel by a small amount compared to the ambient air pressure. Depending on airspeed and altitude. This claim interested Kelly Johnson. Struggling as he was to offset the reduction in performance the increase in weight the new armour and fuel tank protection would bring. Plus it looked like an easy modification to carry out.
Next on Kelly Johnsons' list of headaches was the report received a week ago from the Air Corps about their first semi-operational P-38 squadron recently established at Selfridge Field near Detroit, Michigan. Located as they were not far from Lake Huron and Lake Erie the pilots were experiencing problems with carburetor icing while flying in the often cool and damp conditions. So far it had been handled by the expedient method of running the fuel mixture lean and gunning the engines while in the landing pattern. But this had caused one near crash when a pilot had been forced to make a go-around and in his haste throttling up had forgotten to switch to rich mixture. The resulting detonation had destroyed one engine and damaged the other. Forcing the pilot to make an emergency landing on the taxiway paralleling the second runway. Followed by running off the taxiway and tearing off the nose gear. Not too bad considering. And there had been a few other incidents of carburetor icing mentioned in the report.
"Hall, we have to do something about this low carburetor air temperature problem." Kelly Johnson had said while talking with Hall Hibbard two days ago. "We are busy preparing to ship to the British Isles planes that have no effective carburetor heat when throttled back for landing. It's bad enough here but consider what the English climate will do to these planes. What are our options here?"
"Kelly, I just learned this morning from General Electric that they've finally put their new B-2 turbocharger into production. I think we'll be getting the first of them toward the end of October. The higher compression will require more cooling then what we can do now." Hall Hibbard said. "Remember the box intercoolers you were telling me about two months ago? Will they be be able to cool the higher boosted hot air from the new turbochargers? Will they be able to prevent carburetor icing due to low carburetor air temperature?"
"I would say so Hall. The airflow through the box type intercoolers, placed in their location in the centre wing leading edge will be controlled by the exit shutters. We can design these shutters to close completely. That will keep the CAT from dropping too low."
"Alright then Kelly. Work up the design specifications for our new intercoolers. Give then to me and I'll get in touch with the company that's making Boeings intercoolers and I'll see about arranging for them to start building new intercoolers designed for our P-38s. We're going to need them soon for the new B-2 turbochargers. Looks like we can solve two problems at once" Hall Hibbard said.
"Hall," Kelly Johnson had replied, "those new intercoolers just might solve 4 problems at once."
A 1000 P-38s on order by mid 1940!? That's their financing right there! IOTL they ran over the R&D Cost of the XP-38 by a good $500,000 but the initial YPs and the British/French orders were for just under $150k/unit irrc. By 1944 unit cost as delivered was something like $92k. So, if Lockheed can build these first 1000 for $100k/ea. and they have contracted sale prices of say $140k, then they are sitting on $40,000,000 of future profits. They should be able to get a loan against those contracts.
