SHOULD the P39 have been able to handle the Zero? Was it training or performance?

[P-39 Expert]

View attachment 487461

A good rule of thumb is combat range is ~ 1/3 range.

Using that rule, a P-39Q had a combat range of 175mi.

Okay, lets see what a P-39N would do. 120 gals internal plus a drop tank of 110 gals = 230 gals. Takeoff and climb to 5000' reserve is 20 gals so now we're down to 210 gals available. A P-39N burned 62gph at 25000' at 2600rpm max continuous power so we have a theoretical 3.4 hours to escort those bombers. Reduce that by 15 minutes combat and a 20 minute landing reserve so now we have 2.8 hours of actual escort time. We're flying faster than the bombers (230mph) so we're weaving to keep from getting ahead of them. So really we're covering the same ground as the bombers but flying faster. The bombers will cover 640 miles in that 2.8 hours and we're going out AND back so our roughly estimated combat radius is about 320 miles. About 50 miles less than a Thunderbolt with drop tanks. If we can cruise at less than 2600rpm maximum cruise (not recommended over Europe) then we can go farther. All hail the mighty Thunderbolt.

 

[drgondog]

View attachment 487461

A good rule of thumb is combat range is ~ 1/3 range.

Using that rule, a P-39Q had a combat range of 175mi.

Milosh - where did you find that particular Chart? Is has several errors but the format is one I will put in my new book about the P-51B

 

[P-39 Expert]

You continually use words like "superior" well 1,300 is superior to 1,200HP but in late 1942 early 43 the USA was introducing the P--47 and the UK the Typhoon and Griffon Spitfire, the game had moved up to 1600-2000BHP for top line fighters.

I'm saying the N and Q were "superior" to the earlier P-39 models. Compare the N to the Typhoon. About the same speed but N climbs a lot faster.

 

[Milosh]

Bill, ww2 fighter range - Bing images

 

[pbehn]

I'm saying the N and Q were "superior" to the earlier P-39 models. Compare the N to the Typhoon. About the same speed but N climbs a lot faster.

The Typhoon dropped 1000kg bombs on Normandy, carrying 4 x 20mm cannon there and back with extensive armour.

 

[pbehn]

Bill, ww2 fighter range - Bing images

Can you put a Spitfire Mk IX on the ground protecting all the allied equipment pls

 

[Peter Gunn]

Okay, lets see what a P-39N would do. 120 gals internal plus a drop tank of 110 gals = 230 gals. Takeoff and climb to 5000' reserve is 20 gals so now we're down to 210 gals available. A P-39N burned 62gph at 25000' at 2600rpm max continuous power so we have a theoretical 3.4 hours to escort those bombers. Reduce that by 15 minutes combat and a 20 minute landing reserve so now we have 2.8 hours of actual escort time. We're flying faster than the bombers (230mph) so we're weaving to keep from getting ahead of them. So really we're covering the same ground as the bombers but flying faster. The bombers will cover 640 miles in that 2.8 hours and we're going out AND back so our roughly estimated combat radius is about 320 miles. About 50 miles less than a Thunderbolt with drop tanks. If we can cruise at less than 2600rpm maximum cruise (not recommended over Europe) then we can go farther. All hail the mighty Thunderbolt.

Are you seriously contending that the P-39 could do the job of the Thunderbolt in the ETO?



Well all hail the mighty Airacobra...

In one of the older threads, I believe drgondog has a post or two on escort range ( for the Mustang, but you can extrapolate ) and planning of same, none of it theoretical.

 

[pbehn]

Okay, lets see what a P-39N would do. 120 gals internal plus a drop tank of 110 gals = 230 gals. Takeoff and climb to 5000' reserve is 20 gals so now we're down to 210 gals available. A P-39N burned 62gph at 25000' at 2600rpm max continuous power so we have a theoretical 3.4 hours to escort those bombers. Reduce that by 15 minutes combat and a 20 minute landing reserve so now we have 2.8 hours of actual escort time. We're flying faster than the bombers (230mph) so we're weaving to keep from getting ahead of them. So really we're covering the same ground as the bombers but flying faster. The bombers will cover 640 miles in that 2.8 hours and we're going out AND back so our roughly estimated combat radius is about 320 miles. About 50 miles less than a Thunderbolt with drop tanks. If we can cruise at less than 2600rpm maximum cruise (not recommended over Europe) then we can go farther. All hail the mighty Thunderbolt.

How much fuel is used by a P39 carrying a 110 gal external tank for warm up take off and climb to 25,000ft? What is the cruise speed of a P39 on max continuous at 25,000ft with external tank?

 

[DarrenW]

They had a vested interest in playing down the P-39 accomplishments and overstating their new planes. How would it play to have the AAF saying "We're giving the Russians a great little plane here, but our Lightnings and Thunderbolts are not quite ready yet".

You are definitely a well-educated and learned man who knows a sh--t ton about aviation history.

After hearing your rant about some sort of secret conspiracy against the Airacobra, I'm seriously considering retracting this statement LOL!!!!

 

[Peter Gunn]

*SNIP*
Put another way, you got almost a group of P-39s for every squadron of LIghtnings, or instead of the 9500 lightnings produced you could have had almost 24000 P-39s. Nobody really looks at it this way, but that's the way it was.

But why would you want 24,000 P-39s? I get your passion for the airplane, but the AAF was hardly stupid when they dumped it in favor of capable designs. Also, one squadron of P-38's was worth more than a group of P-39's on operations. George Welch sure didn't think too much of it, but maybe he was wrong as well.

Also, do you think no one here has looked at data since before 2012? Dude, you have authors and historians in here.

 

[Milosh]

P-39 no need for guesstimate calculations for the Flight Operation Instruction Chart can be found here, P-39 manuals, P-39 Airacobra Pilots Flight Operating Instructions

 

[drgondog]

Okay, lets see what a P-39N would do. 120 gals internal plus a drop tank of 110 gals = 230 gals. Takeoff and climb to 5000' reserve is 20 gals so now we're down to 210 gals available. A P-39N burned 62gph at 25000' at 2600rpm max continuous power so we have a theoretical 3.4 hours to escort those bombers. Reduce that by 15 minutes combat and a 20 minute landing reserve so now we have 2.8 hours of actual escort time. We're flying faster than the bombers (230mph) so we're weaving to keep from getting ahead of them. So really we're covering the same ground as the bombers but flying faster. The bombers will cover 640 miles in that 2.8 hours and we're going out AND back so our roughly estimated combat radius is about 320 miles. About 50 miles less than a Thunderbolt with drop tanks. If we can cruise at less than 2600rpm maximum cruise (not recommended over Europe) then we can go farther. All hail the mighty Thunderbolt.

If you want to develop a Kentucky windage scale model please consider the following:
Start and warm up engines, taxi to transient, take off in pairs and orbit as elements build into flights and into squadrons and finally assemble on group leader for climb. All of the preliminary fuel consumption will be near Max continuous power (Normal @ 39-40"Hg) with approximately 1-2 minutes of Take Off Power ~MP. Tanks would be switched to external tank (75 gallon CL) and climb at Max continuous until 25000 feet. The drag on the P-39 is at maximum while the tank is full. Time for warm up, Take Off, assembly and climb to 25000 feet ~ 25 minutes with total fuel consumption of approximately 30-35 gallons (including 10-15 internal, 20 external) leaving 105-110 internal and 55 external. Remove the fuel required for loiter/reserve for let down and landing - another ~ 10 gallons. So, at start of Cruise for R/V point you start with 120-25=95 gallons of internal fuel plus 55 external.

For mission planning the Combat Radius must account for a.) drop tanks for combat leaving only internal fuel, b.) 5 minutes of Combat Power, c.) 15 minutes of Military Power at an average of ~2.5 to 3X Cruise Power consumption. That translates to burning 20+ gallons of your remaining (120-15-25) for takeoff/formation assy) - leaving you with 60 gallons to get home and land with reserve.

Before going back to your escort cruise scenario, let's pause:

AT optimal cruise power setting with low RPM/MP the Allison at 10K was ~ 60+ gallons per hour and the cruise speed with external tank was 20-30mph less than in clean mode. If the optimal cruise speed of the P-39 was the same as the turbo/supercharged P-38 at 25000 feet (doubtful) then 250mph TAS less 30mph=220 mph TAS for external 75 gallon tank (with 55 remaining internally) --------> less than 1 hour and approximately 220 miles from start of escort cruise at 25000 feet (optimistic) before dropping empty tanks.

If combat occurs under above scenario, then the 60 gallons at 250 mph (now clean) gets you back over the channel in the 1 hour of optimal fuel consumption.

The Brequet equations will yield a more optimistic range based on ratio of L/D and the fact that Induced Drag will decline as the weight fraction of fuel decreases over time.

Two points - I have never seen equivalent Range tests performed at Eglin for P-39 (as exist for P-51 and P-47) but I know that the Power/Thrust available per pound of fuel consumed for the P-39 Allison at 25K is much less than the P-51. The Mustang Packard consumed about the same fuel per hour but the cruise speed for max mileage at both 10,000 and 25,000 feet were so much higher because of the superior L/D of the Mustang. The cruise speed of the P-51B/D was about 290-305 mph TAS at 25000 feet for optimal range - a FAR better combat state than either P-39 or P-38.

Second point - I am Not positive about the aggregate estimates of internal fuel consumption for the narrative for P-39 and substituted a P-51B narrative. Would be delighted of you can point me to a source that clarifies operational data for the P-39 for warm up, take off, climb and cruise (clean and w/external 75 gallon tank) at 25K

 

[pbehn]

Are you seriously contending that the P-39 could do the job of the Thunderbolt in the ETO?

This is what "whataboutery" results in. Whatever the strengths and weaknesses of the P-47 were it wasn't up to the job at the time. Neither was the P-38 though both together provided numbers for missions to be made, things to be learned and progress made. The answer was the P51 which was not only more powerful and aerodynamic than the P 39 it carried more fuel with a total of 489 US gal for the P-51D, it is purely academic whether the P39 was better than the P47, the Spitfires range was also increased and it was used on long range missions, they required huge numbers acting in waves escorting the bomber group AND additional planes to escort individual bombers who couldn't keep with the group.

 

[drgondog]

Bill, ww2 fighter range - Bing images

Thank you !

I haven't seen one yet that accurately depicts Combat Radius for the P-38H to P-38 J w/o LE tanks to P-38J with either LE 55 gallon tanks installed as kits or production. Ditto on differentiating the P-51B w/o 85 gallon tank to P-51B/C with 85 gallon tank to Radius with 75 gallon vs 110 gallon external tanks.

The Lockheed P-38 55 Gallon LE kits started arriving in UK in late November (Ditto P-51B 85 gallon Fuselage tank kits) but neither were capable of Berlin missions until Big Week and March 1944 when enough per FG were finally installed. .

 

[DarrenW]

Please read the official performance tests for the P-39 at wwiiaircraftperformance that were made available in late 2012

The actual documents may have been mostly unavailable to the general public, but the data from them could most certainly be found in period books of the time. For instance, here is the performance figures for the P-39N that I gleaned from Combat Aircraft of the World (W.R. Taylor) which was published way back in 1969. See any similarities with your oft-quoted document?

 

[P-39 Expert]

How much fuel is used by a P39 carrying a 110 gal external tank for warm up take off and climb to 25,000ft? What is the cruise speed of a P39 on max continuous at 25,000ft with external tank?

Like I said in my post, reserve for warm up, take off and climb to 5000' is 20 gal. Climbing the remaining 20000' to 25000' took about 10 minutes but remember while you are climbing you should be headed toward your target so you are not losing this 10 minutes. P-39Q Pilot's Manual shows 267mph at 25000' with drop tank. Q had the wing guns so you can probably add about 15mph to that for the N since it didn't have the drag of those guns, so around 283mph.

 

[P-39 Expert]

If you want to develop a Kentucky windage scale model please consider the following:
Start and warm up engines, taxi to transient, take off in pairs and orbit as elements build into flights and into squadrons and finally assemble on group leader for climb. All of the preliminary fuel consumption will be near Max continuous power (Normal @ 39-40"Hg) with approximately 1-2 minutes of Take Off Power ~MP. Tanks would be switched to external tank (75 gallon CL) and climb at Max continuous until 25000 feet. The drag on the P-39 is at maximum while the tank is full. Time for warm up, Take Off, assembly and climb to 25000 feet ~ 25 minutes with total fuel consumption of approximately 30-35 gallons (including 10-15 internal, 20 external) leaving 105-110 internal and 55 external. Remove the fuel required for loiter/reserve for let down and landing - another ~ 10 gallons. So, at start of Cruise for R/V point you start with 120-25=95 gallons of internal fuel plus 55 external.

For mission planning the Combat Radius must account for a.) drop tanks for combat leaving only internal fuel, b.) 5 minutes of Combat Power, c.) 15 minutes of Military Power at an average of ~2.5 to 3X Cruise Power consumption. That translates to burning 20+ gallons of your remaining (120-15-25) for takeoff/formation assy) - leaving you with 60 gallons to get home and land with reserve.

Before going back to your escort cruise scenario, let's pause:

AT optimal cruise power setting with low RPM/MP the Allison at 10K was ~ 60+ gallons per hour and the cruise speed with external tank was 20-30mph less than in clean mode. If the optimal cruise speed of the P-39 was the same as the turbo/supercharged P-38 at 25000 feet (doubtful) then 250mph TAS less 30mph=220 mph TAS for external 75 gallon tank (with 55 remaining internally) --------> less than 1 hour and approximately 220 miles from start of escort cruise at 25000 feet (optimistic) before dropping empty tanks.

If combat occurs under above scenario, then the 60 gallons at 250 mph (now clean) gets you back over the channel in the 1 hour of optimal fuel consumption.

The Brequet equations will yield a more optimistic range based on ratio of L/D and the fact that Induced Drag will decline as the weight fraction of fuel decreases over time.

Two points - I have never seen equivalent Range tests performed at Eglin for P-39 (as exist for P-51 and P-47) but I know that the Power/Thrust available per pound of fuel consumed for the P-39 Allison at 25K is much less than the P-51. The Mustang Packard consumed about the same fuel per hour but the cruise speed for max mileage at both 10,000 and 25,000 feet were so much higher because of the superior L/D of the Mustang. The cruise speed of the P-51B/D was about 290-305 mph TAS at 25000 feet for optimal range - a FAR better combat state than either P-39 or P-38.

Second point - I am Not positive about the aggregate estimates of internal fuel consumption for the narrative for P-39 and substituted a P-51B narrative. Would be delighted of you can point me to a source that clarifies operational data for the P-39 for warm up, take off, climb and cruise (clean and w/external 75 gallon tank) at 25K

My source is the P-39Q Pilots Manual, google it. At 25000' the P-39Q burned 62 gallons per hour at 2600rpm (maximum cruise power aka maximum continuous power), the highest cruising power available at that altitude. Full power at 25000' would cost you about 71gph. My estimate was prepared just like the manual says to plan a mission. I stand by those figures.

 

[pbehn]

Like I said in my post, reserve for warm up, take off and climb to 5000' is 20 gal. Climbing the remaining 20000' to 25000' took about 10 minutes but remember while you are climbing you should be headed toward your target so you are not losing this 10 minutes. P-39Q Pilot's Manual shows 267mph at 25000' with drop tank. Q had the wing guns so you can probably add about 15mph to that for the N since it didn't have the drag of those guns, so around 283mph.

Please refer to and answer Drgondog's post on a similar subject. Prior to logging on to this forum I couldn't have asked the question I did, it is from reading posts like his that I have learned something.

There is much more to it than just taking off. One escort plane was part of squadron and a group of circa 600 that need to form up and rendezvous first with each other and then with the bomb group.

 

[Shortround6]

9500 or so P-39s produced between January 1941 and August '44. About half went to Russia. Most of those were the superior N and Q models produced from Dec '42 which comprised about 7000 of the total 9500. N and Q differed only in wing armament (4 .30s vs 2 .50s) and since the Russians removed the wing guns the Russian N and Q were pretty much the same plane. Earlier D, F, K and L had the 12000' engines, the M, N and Q had the 15000' engines that were about 100hp better at all altitudes.

The K and L had engines rated at 1325hp for take-off NOT WEP although they were down to 1150hp at 12,000ft.
The 1200hp engines in the M, N and Q did NOT have 100hp more at all altitudes. They didn't have at the lower altitudes.

They had around 50hp more than the old engines in the Ds and Fs. below 12,000ft.

They had 125hp less than the K and L below a few thousand feet an NO, use of WEP does not make up for that.
The old engines were allowed to use 1490hp up to 4300ft
The K & L engines could make 1580hp up to 2500ft.
Both engines then tapered off to 1150hp at 12,000ft.
The "super" engine was allowed 1410hp up to 9600ft.

I have no idea how you get 100hp better at all altitudes out of that.

yes they were better at higher altitudes.

I did a little number crunching and taking a P-39Q with 87 gallon tanks and taking out the wing .50s and replacing them the four .30 cal armament gives you a take-off weight of 7411lbs with full fuel, oil, ammo and pilot. Getting down under 7300lbs is going to take some effort.

AS far as the P-39 vs early P-47 as an escort fighter, ROFLMAO.

 

[P-39 Expert]

But why would you want 24,000 P-39s? I get your passion for the airplane, but the AAF was hardly stupid when they dumped it in favor of capable designs. Also, one squadron of P-38's was worth more than a group of P-39's on operations. George Welch sure didn't think too much of it, but maybe he was wrong as well.

Also, do you think no one here has looked at data since before 2012? Dude, you have authors and historians in here.

I'm just making a point about the dollar cost of the two planes. Those Lightnings were expensive. Not saying Welch was wrong, wasn't he the guy who was crashing his P-39s so he could get P-38s? Also the first man to break the sound barrier (F-86 diving). Sorry Chuck Yeager. And I believe he actually got airborne at Pearl Harbor (had him mixed up with Buzz Wagner). Depends on the model of the P-39. Older ones (D,F,K,L) not as capable as later models (M, N and Q). N actually the better of the three. If he had an old one he was probably crashing them on purpose.

I'm neither an author nor historian. But if you haven't looked at the P-39 in wwiiaircraftperformance.org then you don't have the latest information. And I can tell that a whole lot of you authors and historians haven't.

And by the way, am I a moron? I have a masters degree and I read pretty good. Am I not capable of reading a page of information and commenting on it?

Look, I have read everything I could find on WWII and before late 2012 I thought exactly the same as you. The P-39 was a turd based on all the hearsay and stat books that don't agree with each other. But now you can compare all the planes (except Russian) straight up and compare them accurately. PLEASE GO TO THE SITE. I'm no shill for them, it's free. Or just keep on repeating what William Green and the rest say about the P-39.

BTW, you guys are dead meat, I have finally figured out how to post a photo that is already open. So you'll soon be seeing the graphs already open.