Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules
Well yes, since the USA formally entered the war days before 1942, you couldn't have 1942 or 1943 as late could you, it is nearer the beginning than the end. For many aspects of aviation the end was coming in mid 1944 with all sorts of people looking to the future.I meant like 1944 late, or 1945 late. Depending on interpretation, either could be considered late.
And horsepower was 1150? Do you have a chart that lists horsepower along with TAS along with Altitude. I'm trying to figure out how much speed would be added with the different altitudes.1. -35 was 11700'-12000' no ram without backfire screens. Critical altitude for the P-39D was 13800' with ram and no backfire screens per wwiiaircraftperformance.org.
And without the screens, I would speculate it'd probably be less?2. -59 was 1100hp at 13800' (coincidence) with screens. Later 9.6 production models without screens was 1125hp at 15500'.
Yes horsepower was 1150 for the -35. I do have charts, but the wwiiaircraftperformance.org site has performance charts for the P-39D that show critical altitude of 13800' with about 370mph of ram. That's your difference in ram and no ram. Also the critical altitude for climb is 12400' and that would be with only about 170mph of ram.And horsepower was 1150? Do you have a chart that lists horsepower along with TAS along with Altitude. I'm trying to figure out how much speed would be added with the different altitudes.
And without the screens, I would speculate it'd probably be less?
The reason the charts can be useful is that the ones on WWII aircraft performance page don't list horsepower for speed/altitude. I was trying to compute what different critical altitude.I do have charts, but the wwiiaircraftperformance.org site has performance charts for the P-39D that show critical altitude of 13800' with about 370mph of ram.
Do you have any idea how much less?The backfire screens meant less power as they reduced manifold pressure, deleting the screens gained manifold pressure.
Curiosity, plus you can always learn something. Shortround's response was pretty solid.Why would you ask me and why do you want to know. What use is a guess anyway?
When were the superchargers you listed developed?
Like 1944 or 1945?
The actual horsepower was listed on the performance memorandums in 5000' increments, but not on the charts. Hope that helps.The reason the charts can be useful is that the ones on WWII aircraft performance page don't list horsepower for speed/altitude. I was trying to compute what different critical altitude.
Do you have any idea how much less?
I should have asked this awhile back, but out of curiosity, what kind of aerodynamic improvements would have been do-able at the time?wuzak said:Lighter weight and better aero.
I did some checking in Warbird Tech Series: Vought F4U Corsair and it says the F4U-3 was to be fitted with a Birman type supercharger as well. From what I read, the goal was to increase the critical altitude a whole lot. They even managed to get up to altitudes of around 50,000 feet (I'm not sure if the cockpit was pressurized, but that seems to be the altitude where it'd be a very good idea!). The problem with the Birman was that it's reliability sucked, MTBF was something like one flight.In White's book about the R-2800 he calls the unit used in the XF4U-3 a Turbo Engineering turbocharger and XF6F-2 as a Birman (Turbo Engineering) turbocharger.
From what it would appear, the closest thing I can find is that Oliver Echols seemed to have a bias against twin-stage supercharging, and allocated all funding to turbochargers.P-39 Expert said:That's the big question, why did it take so long to develop the mechanical two stage supercharger?
This assumes the intake was revised with more spacing to eliminate turbulent airflow, correct?-59 was 1100hp at 13800' (coincidence) with screens. Later 9.6 production models without screens was 1125hp at 15500'.
Regarding the 9.6 design, the engine held together just fine but the actual supercharger gears themselves couldn't take the strain of the step up from 8.8. The actual drive gear had one more tooth and the driven gear had one less tooth to go from 8.8 to 9.6. Same thing in reverse to go from 8.8 to 8.1 (for two stage engines). Allison was hoping to just substitute the 9.6 gears for the 8.8 gears and reap the benefit of more horsepower at higher altitude, but that was not to be without strengthening the gears by widening them which took about a year. Dang. The gear ratio would go all the way up to 11.6 without increasing the diameter of the gears, but Allison never made production engines higher than 9.6.Sometimes I revisit old threads to ask questions I should have asked earlier. I also sometimes actually find answers to some degree that at least help out with the various discussions in the thread.
I should have asked this awhile back, but out of curiosity, what kind of aerodynamic improvements would have been do-able at the time?
I did some checking in Warbird Tech Series: Vought F4U Corsair and it says the F4U-3 was to be fitted with a Birman type supercharger as well. From what I read, the goal was to increase the critical altitude a whole lot. They even managed to get up to altitudes of around 50,000 feet (I'm not sure if the cockpit was pressurized, but that seems to be the altitude where it'd be a very good idea!). The problem with the Birman was that it's reliability sucked, MTBF was something like one flight.
From what it would appear, the closest thing I can find is that Oliver Echols seemed to have a bias against twin-stage supercharging, and allocated all funding to turbochargers.
Often, from what I remember: There was a tendency to see the turbochargers designed in ways that reduced efficiency quite a bit. When Hooker came around, he actually identified numerous problems in the formulas that gave rise to the supercharger design. One thing that I remember being told was that (at least with twin-staged designs), the two stages were the same diameter (later on, it would be found that having the first stage larger and the second stage smaller would give better performance).
Interestingly, I'm not sure if there was enough money to have developed turbos for mass-production and twin-stage supercharging.
This assumes the intake was revised with more spacing to eliminate turbulent airflow, correct?
From what it appears, the problems with the 9.6 designs was that they seem to have miscalculated the amount of structural strength needed for the engine to hold together while driving a larger supercharger.
So, they kind of were suffering a bit of wishful thinking, combined with miscalculation?Regarding the 9.6 design, the engine held together just fine but the actual supercharger gears themselves couldn't take the strain of the step up from 8.8.
I don't know exactly, but you have to think that they weren't expecting the gears to wear that quickly. Cost them a year to redesign the accessories case to accommodate the wider gears. Could have had the new engine in early '42 instead of late '42. Of course they still had to deal with the backfire screens etc until mid '42 when they adopted the aluminum intake manifold and deleted the backfire screens. And raised the military power limit from 5 minutes to 15 minutes.So, they kind of were suffering a bit of wishful thinking, combined with miscalculation?
I should have asked this awhile back, but out of curiosity, what kind of aerodynamic improvements would have been do-able at the time?
From what it appears, the problems with the 9.6 designs was that they seem to have miscalculated the amount of structural strength needed for the engine to hold together while driving a larger supercharger.
Ironically, had they done more work early on, they'd have saved themselves a lot of trouble later.I don't know exactly, but you have to think that they weren't expecting the gears to wear that quickly.
That would have had a significant effect on their usefulness in the war. As for the differences of ram compression by using a redesigned intake, as seen on the P-63 seems to increase critical altitude by around 900 feet over the P-39D (2000 vs 2900)Could have had the new engine in early '42 instead of late '42.
Sorry about that.You quoted me without a link to the original post so the question lacks context.
I remember this discussion coming up regarding the amount of power related to the square of the supercharger RPM. I figure, this was already known prior to the decision to redesign the gear, so I figure the culprits would be...The engine would hold together, the supercharger gears would not.
I should have asked this awhile back, but out of curiosity, what kind of aerodynamic improvements would have been do-able at the time?
Sorry about that.
- Lighter weight and improved Aerodynamics: Page 2, Post 32
- Use of the Birman supercharger: Page 5, Post 88
But it seems that it took them a lot quicker to overcome their problems than Allison did with their higher geared superchargers...I would note the British ran into a somewhat related problem with the Merlin once higher boost levels were being put into use. The original supercharger drive (exact parts I don't know but I think it was a quill shaft?) was good for up to 15lbs of boost (perhaps 16lbs depending on gear ratio/altitude?) but had to modified for 18lb of boost, this is for the singel stage engines.
I'm pretty sure it didn't make production either. I'm curious what variables caused such a short service life. I'm curious where would one even look to find information on the Birman supercharger?In terms of the of the Birman turbocharger, I don't think it ever made it into production and may not have been available for flight testing at the time of the XP-39.
Do you have any examples?In terms of aerodynamics there are many improvements that could have been made with the XP-39 given time and effort.
That makes sense. There was this book I got recently which showed a bunch of aircraft designs, including proposals for the P-39. Interestingly, it actually showed one design with the turbo lying flat in the wing. It was a very unusual configuration.However, the turbo was not reliable at the time of the XP-39 (with issues on the XP-37 and YP-37) and reworking the aerodynamics was easier without the turbo.