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No, the AAF just insisted on six .50calMGs AND a 37mm cannon, a much larger wing etc. until they got it up to 8900lbs.
Just put the damn thing into a regular P-39.
The XP-39E bore the same armament as the P-39D but featured a new wing with square-cut tips.
Bell P-39D AiracobraThe P-39D differed from the P-39C primarily in having a heavier armament. It had four wing-mounted 0.30-inch machine guns with 1000 rpg, two fuselage-mounted 0.50-inch machine guns with 200 rounds per gun, plus the 37-mm cannon (with increased ammunition capacity of 30 rounds).
They put one in the XP-39E and flew it in April 1942. Unfortunately they also put a new wing and tail on it and in their own inimitable AAF style they made it weigh 8900lbs. It was decently fast up to 25000', but would barely outclimb a regular P-39D. It never got the four blade propeller it needed.
If they had just put that aux. stage into a regular P-39D it would have only weighed 7900lbs including 4 blade propeller. At 1000lbs less than the E it would have been a rocket.
Where's that midwife? Contractions have started already!
They were in the wooden mockups.No, the six .50 cal guns were Larry Bell's idea when he realized the P-38E was never going to be an interceptor. He was trying to pitch it as a ground attack plane.
They did plan on using an intercooler but eventually gave up on it. Should have discarded it earlier and moved the carburetor forward to the normal position on the engine stage supercharger for the additional critical altitude. Intercooler/water injection only needed for WEP. At military power the extra 400hp at 25000' would have been plenty.What is more than a bit strange about this saga of the P-39 holding the two stage engine is that the original XP-39 had a lot trouble with the intercooler (proper airflow for cooling).
Allison was planning on using an intercooler with the two stage engine, Perhaps Bell was too for the P-76 and P-63, but the subcontractor never delivered a suitable intercooler matrix forcing Bell to use large amount of water injection for the two stage engine. Did simplify the air scoop problem though.
Without a good intercooler high altitude performance is going to crap or short lived until the ADD fluid runs out.
got pictures?They were in the wooden mockups.
Hello P-39 Expert,
ASSUMING that the Aux Stage Supercharger actually fit into the engine compartment, there are still a bunch of problems that need to be addressed. Apparently it did fit.
First of all, regarding "it would have been a rocket", the benefit of the second stage is mostly increased altitude performance. Yep.
Low level performance would not have changed much especially with the increased weight. Low level performance already pretty good.
The increased altitude capability also brings a greater requirement for cooling capacity which was somewhat lacking even with the engines that were already installed in the P-39. Only at military power, then only for the max 15 minutes. Tolerated just like on regular P-39s.
The new ASB also sits at the aft end of the engine and would make a aft CoG problem even worse. Perhaps this could be counterbalanced by a significantly heavier 4 blade propeller, but would any steps be taken to bring the CoG in empty condition further forward to address handling problems? Remember the aux. stage took the space that the coolant tank had occupied, so the small increase in weight in the rear would have been offset by the heavier 4 blade propeller. Balance maintained.
The new P-39 Rocket would still have a relatively low internal fuel capacity. What mission would it be suited for? Remove the .30s in the wing and put in fuel tanks.
- Ivan.
Photos in "Cobra" by Birch Matthews.got pictures?
They made a mock up of the Spitifre withe six 20mm cannon too, that didn't get far.
No photo of the actual P-39E shows any wing guns or even cowl guns.
AAF wanted it to fly nonstop from San Francisco to Hawaii. Thank goodness they gave up on that.
Only at military power, then only for the max 15 minutes. Tolerated just like on regular P-39s.
Remember the aux. stage took the space that the coolant tank had occupied, so the small increase in weight in the rear would have been offset by the heavier 4 blade propeller. Balance maintained.
Remove the .30s in the wing and put in fuel tanks.
Hello P-39 Expert,
The problem here is that with the ASB and operating at higher altitudes, it ISN'T like on regular P-39s.
The power delivered to the propeller isn't the determining factor for cooling requirements. The extra power required by the ASB also requires extra cooling. The higher altitude and lower air density decreases the effectiveness of radiators as well.
Don't know for sure until you try it.
I would be very interested in seeing how much this "small increase" in weight actually affects that balance.
As was mentioned earlier, the P-39 had a tendency to be very near its aft CoG limit even without any changes.
To correct the handling problems, there needs to be more than just maintaining balance and I am not convinced that a propeller change would do it.
Stop trying to invent CG problems. P-39 didn't have any real CG problems. Not like a P-51 with a full fuselage tank.
There are a couple problems with this idea.
First of all, the outboard sections of the wings where the guns are located are a rather small and flat volume.
Second, without the wing guns, the firepower becomes somewhat inadequate by US if not Soviet standards.
All that was needed was 30 extra gallons, 15 in each wing. Then it would have 150 gallons internal, just like the P-38 and P-40. The two outside tanks on the P-39 held over 8 gallons each. You couldn't fit the equivalent two more of those in each outer wing?
The plane had a 37mm cannon. It could not possibly be under armed.
You keep inventing imaginary problems for the P-39. It was in balance, heavily armed and a very good fighter plane with the -85 engine. Only real problem was excessive weight in the models with the -39 and -63 engines.
- Ivan.