Groundhog Thread Part Deux - P-39 Fantasy and Fetish - The Never Ending Story (Mods take no responsibility for head against wall injuries sustained)

[buffnut453]

And here we thought the sputtering was just showing off, trying to sound like a WWI fighter to impress everyone!

You mean like this?

 

[DerAdlerIstGelandet]

And here we thought the sputtering was just showing off, trying to sound like a WWI fighter to impress everyone!

That is what I was aiming for. Gotta make that lycoming sound like a Cyclone returning from a long bombing mission over Schweinfurt in a Hollywood movie.

 

[FLYBOYJ]

OK some numbers (I know all of you think this is so exciting!!!!)

Take off, climb to 20,000' go to best cruise for 15 minutes, Max power or War Emergency for 10 minutes, show remaining fuel and remaining range

No wind, standard pressure so DA and PA are equal so for this calculation IAS = TAS

P-39N-0-BE, straight from the Flight Manual

No external fuel tank used

Weight and balance chart show the aircraft with 87 gallons, 7500 pounds.

"Interpolate" the climb chart for 20,000' (Military)

Speed - 155mph, 1900FPM, time to 20K 8.2 minutes, fuel burn 33.8 gallons

I did use a climb gradient calculator to show distance in the climb to 20,000 feet which was 28.2 miles

SM per 1000' = 1.41 x 20 = 28.2

Miscellaneous Aviation Calculations / E6B Emulator

87gallons - 33.8 = 53.2 gallons left after climb.

"Max Range" on Flight Operation Instruction Sheet @ 20,000' shows 35 GPH at 160 MPH indicated.

Fuel used - 8.7 Gallons, miles flown at this leg = 40 miles

53.2 - 8.7cruise fuel used = 44.5 gallons remaining

Enter Combat, I'll just use "military power" fuel flow indicated on the Flight Operation Instruction Sheet NOTE - this setting is shown at 14,500' so it may a little lower at 20K

147 Gallons Per Hour

10 minutes = 24.5 gallons

44.5 - 24.5 gallons = 20 gallons left.

According to the Flight Operation Instruction Sheet, column V "MAX RANGE" 20 gallons get you 125 MILES REMAINING

____________________________________________________________________________________________________________________

Let's do the Corsair!

F4U-1 R2800-8VV

No external fuel tank used

Ref "TAKEOFF CLIMB AND LANDING CHART"

Aircraft gross weight 14,200 pounds 237 Gallons fuel.

Climb to 20,000 feet

130 Knots (150 mph)

1100 Feet Per Minute

13 minutes to 20,000 feet

66 gallons used

Climb gradient calculator, at 150 mph we flew 45.4 miles (2.27 sm/1000' x 20)

237 - 66 = 171 GALLONS REMAINING

CRUISE FOR 15 MINUTES

SPECIFIC ENGINE FLIGHT CHART

At 20,000 feet "Minimum Fuel Consumption" 53 gallon per hour.

Earlier we came up with cruising speeds between 180 and 191 so I'll go with 186 mph.

FUEL USED - 13.2

MILES FLOWN - 46.5

171 - 13.2 = 157.8 GALLONS REMAINING


Enter Combat, ref SPECIFIC ENGINE FLIGHT CHART

War Emergency at Auto Lean at 20,000' = 245 GPH

245/60= 4.08 GPM, 40.83 gallons used in 10 minutes

157.8 - 40.83 = 116.97 gallons left

SPECIFIC ENGINE FLIGHT CHART

At 20,000 feet "Minimum Fuel Consumption" 53 gallon per hour.

Earlier we came up with cruising speeds between 180 and 191 so I'll go with 186 mph.

116.97/ 53 = 2.20 hours range @ 186 mph = 409 MILES REMAINING

Check my math!

 

[SaparotRob]

You forgot to carry the three.

 

[gumbyk]

That P-39 profile looks fairly close to a Soviet one. Not enough range for pilots to defect, but just enough to protect Mother Russia...

 

[P-39 Expert]

WRONG - read the chart!!!!

DOES IT SAY THE 20 MINUTE WARM UP IS INCLUDED?!?!?

no!

I'll blow it up for you

View attachment 624583

"TIME FROM SL" FUEL FROM SL"

SL = SEA LEVEL - IT'S THAT SIMPLE!!!!

IT'S CLEARLY SHOWN THAT IF CLIMB FROM SEA LEVEL TO 25000 FEET AT 140 INDICATED, DEPENDING ON CLIMB ANGLE AND POWER USED, YOU'RE GOING TO REACH 25000 FEET IN EITHER 13.9 MINUTES OR 29.9 MINUTES AND BURN EITHER 39.9 GALLONS OR 31.2 GALLONS, CLIMBING 800' PER MINUTE OR 600' PER MINUTE! I USED NUMBERS THAT GAVE THE BEST CLIMB WHILE USING THE LEAST AMOUNT OF FUEL (AND GOD, THE P-39 NEEDED IT)

(AND THIS IN A NO WIND, STANDARD ATMOSPHERIC DAY)




ARE YOU SERIOUS????

WHERE DOES IT SAY THAT?!?!?! YOU'RE STILL BURNING FUEL IN DESCENT OR ARE YOU GOING TO TELL ME YOU TURN THE MOTOR OFF?!?!?




NOW YOU'RE ADDING YOUR OWN INTERPETATION. IS IT VX OR VY OR DO EVEN KNOW WHAT THAT MEANS?


WHERE DOES IT SAY TO DO THAT?!?


AGAIN, THIS SHOWS YOU DON'T KNOW WHAT YOU'RE TALKING ABOUT!!! HOW ARE YOU GOING TO GET TAS??? YOU DON'T KNOW PRESSURE ALTITUDE AND TEMPERATURE IN THIS EXAMPLE!!!!

IT WAS OBVIOUS THIS WAS HYPOTHETICAL SO TEMPS AND PRESSURE ALTITUDE WAS NOT FACTORED IN,




AND THAT WAS CLEARLY DONE BASED ON COMPARING THE TWO AIRCRAFT TO AN AAF INTERCEPT MISSION!!!! I added the 3000' cruise to actually give a nudge to the P-39!!!!


NOW YOU'RE ADDING HYPOTHETICAL SITUATIONS - I POSTED WHAT BOTH AIRCRAFT WILL DO IN THE SAME SITUATION AND SHOWED EXACTLY HOW IS DONE AND EVEN GAVE A "NUDGE" TO THE P-39. NO WHERE DO YOU SHOW FUEL CONSUMPTION BASED ON THE CHART DATA! IT'S QUITE CLEAR BY THE DATA CLEARLY SHOWN HOW THE P-39 WAS OUT-PERFORMED!!!!

ONCE AGAIN, YOU'RE MIS-INTERPERTING THE CHART, JUST LIKE YOU DID THE WEIGHT AND BALANCE CHART!!!

Please allow me to clarify the Flight Operation Instruction Chart (range chart) for you. First of all none of the figures on the Take Off, Climb & Landing chart are used to calculate range. The Fuel From Sea Level numbers have nothing to do with range, unless somehow mission profile called for a climb to cruising altitude while remaining directly over your base before vectoring to target. Highly unlikely. And it takes hardly any time for a squadron to form up. Per Edwards Park in "Angels Twenty" (factual account of combat over and around Port Moresby, NG) they took off two at a time with the first group making a wide swing vectoring to the target. Each of the seven remaining pairs took off and made a slightly narrower vector, so that the eighth (last pair) made a narrow swing to target and had already caught up with the rest of the squadron. Climb to altitude on course to target.

The range chart is all the pilot needed to plan a mission. To compute range for a mission the allowance for warm-up, takeoff and climb to 5000ft (20gal for P-39N) was deducted from total fuel then that net fuel was divided by gallons per hour and multiplied by TAS (not IAS). That's how all the ranges in each column are computed. For example look at column III at 15000ft. 70net gal divided by 67GPH X 300 TAS (242 IAS) = 313miles. The graph shows 300miles but the actual miles were rounded down a little as a safety factor. Same for all the columns at all altitudes (except column I). Gallons divided by GPH X TAS = range. The Fuel from Sea Level on the Take off, Climb and Landing Chart was not used since it already included the 20gal allowance for Warmup, Takeoff and Climb to 5000ft and didn't account for miles gained toward the target during climb.

To get combat range simply deduct the 20min combat reserve and 20 minute reserve for landing in addition to the 20gal reserve for takeoff. To get combat radius take half of the combat range. The reserves could vary if you wanted a longer combat or landing reserve.

The range figures for column I (max cont. power/normal power) vary widely depending on what altitude is used. Right above the range figures in column I it says "At 12000ft Only" meaning the range figure is accurate only at 12000ft. This is because the gallons per hour (GPH) vary from about 100GPH up to 15000ft and then reduce steadily to only 62GPH at 25000ft. So range at 25000ft would be 70gallons divided by 62GPH X 350mph TAS (233mph IAS at 25000ft) = 395mi instead of the 210mi shown on the chart. This is the result of lower GPH coupled with higher TAS at 25000ft than at 12000ft. The other columns II through V show what throttle/propeller/altitude settings will result in the range for that column. Column I fixes the power setting at max. continuous (2600rpm) so the GPH and TAS will vary significantly as altitudes increase. Naturally I prefer to use 120gallons internal instead of the 88.

As to whether the P-39N will fight at 25000ft, the cruising speed in column I was 350mph (233 IAS), the top speed was 370mph and the rate of climb (clean) was 1950fpm per the Wright Field performance tests. Climb at 25000ft was better than any P-40, P-38F/G, P-47, P-51A, F4U, F6F, Zero, Ki-43 or Typhoon in 1943. About the same as a Me109G. But not nearly as good as the Spitfire IX. P-39N was certainly competitive in 1943.

 

[GrauGeist]

Please allow me to clarify the Flight Operation Instruction Chart (range chart) for you.

Better take notes, Joe - it might come in handy someday if you ever become a pilot.

Oh...wait...

 

[FLYBOYJ]

Please allow me to clarify the Flight Operation Instruction Chart (range chart) for you. First of all none of the figures on the Take Off, Climb & Landing chart are used to calculate range. The Fuel From Sea Level numbers have nothing to do with range, unless somehow mission profile called for a climb to cruising altitude while remaining directly over your base before vectoring to target. Highly unlikely. And it takes hardly any time for a squadron to form up. Per Edwards Park in "Angels Twenty" (factual account of combat over and around Port Moresby, NG) they took off two at a time with the first group making a wide swing vectoring to the target. Each of the seven remaining pairs took off and made a slightly narrower vector, so that the eighth (last pair) made a narrow swing to target and had already caught up with the rest of the squadron. Climb to altitude on course to target.

The range chart is all the pilot needed to plan a mission. To compute range for a mission the allowance for warm-up, takeoff and climb to 5000ft (20gal for P-39N) was deducted from total fuel then that net fuel was divided by gallons per hour and multiplied by TAS (not IAS). That's how all the ranges in each column are computed. For example look at column III at 15000ft. 70net gal divided by 67GPH X 300 TAS (242 IAS) = 313miles. The graph shows 300miles but the actual miles were rounded down a little as a safety factor. Same for all the columns at all altitudes (except column I). Gallons divided by GPH X TAS = range. The Fuel from Sea Level on the Take off, Climb and Landing Chart was not used since it already included the 20gal allowance for Warmup, Takeoff and Climb to 5000ft and didn't account for miles gained toward the target during climb.

To get combat range simply deduct the 20min combat reserve and 20 minute reserve for landing in addition to the 20gal reserve for takeoff. To get combat radius take half of the combat range. The reserves could vary if you wanted a longer combat or landing reserve.

The range figures for column I (max cont. power/normal power) vary widely depending on what altitude is used. Right above the range figures in column I it says "At 12000ft Only" meaning the range figure is accurate only at 12000ft. This is because the gallons per hour (GPH) vary from about 100GPH up to 15000ft and then reduce steadily to only 62GPH at 25000ft. So range at 25000ft would be 70gallons divided by 62GPH X 350mph TAS (233mph IAS at 25000ft) = 395mi instead of the 210mi shown on the chart. This is the result of lower GPH coupled with higher TAS at 25000ft than at 12000ft. The other columns II through V show what throttle/propeller/altitude settings will result in the range for that column. Column I fixes the power setting at max. continuous (2600rpm) so the GPH and TAS will vary significantly as altitudes increase. Naturally I prefer to use 120gallons internal instead of the 88.

As to whether the P-39N will fight at 25000ft, the cruising speed in column I was 350mph (233 IAS), the top speed was 370mph and the rate of climb (clean) was 1950fpm per the Wright Field performance tests. Climb at 25000ft was better than any P-40, P-38F/G, P-47, P-51A, F4U, F6F, Zero, Ki-43 or Typhoon in 1943. About the same as a Me109G. But not nearly as good as the Spitfire IX. P-39N was certainly competitive in 1943.

You're all over the place as usual - Because this is a simulation and we don't know outside air temp and pressures, you cannot accurately calculate TAS!!!!

Reserve fuel IS NOT part of (or should be part of) the flown mission profile, mentioned by 2 other pilots, one happens to be a former F-15 driver. It's required should you you have an issue, 30 mins for VFR flight 45 mins for instrument flight.

ShortRound spelled it out in his previous post (1525)

"Without the drop tank the P-39Q (even with 120 gallons ) has a combat radius of about 65 miles"

Refer to post 1543 please. I spelled everything out including the basis for my figures, and manual references, something you seem to avoid -

Oh and I'll stand to be corrected if a gross error is found by you or anyone else

 

[buffnut453]

Please allow me to clarify the Flight Operation Instruction Chart (range chart) for you. First of all none of the figures on the Take Off, Climb & Landing chart are used to calculate range. The Fuel From Sea Level numbers have nothing to do with range, unless somehow mission profile called for a climb to cruising altitude while remaining directly over your base before vectoring to target. Highly unlikely. And it takes hardly any time for a squadron to form up. Per Edwards Park in "Angels Twenty" (factual account of combat over and around Port Moresby, NG) they took off two at a time with the first group making a wide swing vectoring to the target. Each of the seven remaining pairs took off and made a slightly narrower vector, so that the eighth (last pair) made a narrow swing to target and had already caught up with the rest of the squadron. Climb to altitude on course to target.

The range chart is all the pilot needed to plan a mission. To compute range for a mission the allowance for warm-up, takeoff and climb to 5000ft (20gal for P-39N) was deducted from total fuel then that net fuel was divided by gallons per hour and multiplied by TAS (not IAS). That's how all the ranges in each column are computed. For example look at column III at 15000ft. 70net gal divided by 67GPH X 300 TAS (242 IAS) = 313miles. The graph shows 300miles but the actual miles were rounded down a little as a safety factor. Same for all the columns at all altitudes (except column I). Gallons divided by GPH X TAS = range. The Fuel from Sea Level on the Take off, Climb and Landing Chart was not used since it already included the 20gal allowance for Warmup, Takeoff and Climb to 5000ft and didn't account for miles gained toward the target during climb.

To get combat range simply deduct the 20min combat reserve and 20 minute reserve for landing in addition to the 20gal reserve for takeoff. To get combat radius take half of the combat range. The reserves could vary if you wanted a longer combat or landing reserve.

The range figures for column I (max cont. power/normal power) vary widely depending on what altitude is used. Right above the range figures in column I it says "At 12000ft Only" meaning the range figure is accurate only at 12000ft. This is because the gallons per hour (GPH) vary from about 100GPH up to 15000ft and then reduce steadily to only 62GPH at 25000ft. So range at 25000ft would be 70gallons divided by 62GPH X 350mph TAS (233mph IAS at 25000ft) = 395mi instead of the 210mi shown on the chart. This is the result of lower GPH coupled with higher TAS at 25000ft than at 12000ft. The other columns II through V show what throttle/propeller/altitude settings will result in the range for that column. Column I fixes the power setting at max. continuous (2600rpm) so the GPH and TAS will vary significantly as altitudes increase. Naturally I prefer to use 120gallons internal instead of the 88.

As to whether the P-39N will fight at 25000ft, the cruising speed in column I was 350mph (233 IAS), the top speed was 370mph and the rate of climb (clean) was 1950fpm per the Wright Field performance tests. Climb at 25000ft was better than any P-40, P-38F/G, P-47, P-51A, F4U, F6F, Zero, Ki-43 or Typhoon in 1943. About the same as a Me109G. But not nearly as good as the Spitfire IX. P-39N was certainly competitive in 1943.

I'd really love to hear what qualifications you have to make these comments given that you're directly contradicting qualified pilots, including a former F-15 driver. Or do you know better than them?

The whole reason we keep going round and round on this ridiculous topic is because you steadfastly refuse to accept anyone else's inputs. You either ignore them (e.g. the reference to "useless" 30 cal machine guns) so you can repeat your false claims later, or, as per this latest post, you entirely misinterpret aircraft performance documentation.

The members of this forum include a great many qualified pilots, aeronautical engineers, warbird restorers, published historians, and a great many other inter-related fields.

So...please enlighten us. What, exactly, are your qualifications and experience levels? From my perspective, you're talking nonsense. For the record, I have a MS in aerospace systems, 20 years air force service, have been a qualified pilot, a published author on aviation history, and now am a systems engineer...and I'm far less qualified than many on this forum. They teach me new things every day. In order to be taught, one has to be willing to listen and learn. You seem unwilling to exercise those two traits.

 

[pbehn]

Actual combat radius is approx. 1/3 of range. Doesn't matter what a/c.

Errr, I don't know, that's subjective. Many major missions were planned and flown right to the edge of performance limits. Gotta be bit more specific

It is approximately true for planes on internal fuel, simply because the amount of fuel you have to allow as a worst case for start up, take off and climb followed by form up of the fighter squadron and form up with the bomber group. Even the internal fuel of the original P-51 doesnt change that hugely. On the Schweinfurt raid Spitfires took the bombers to the coast and P-47 as far as the Belgian border. Now the Spitfire was short ranged but not THAT short. The P-51 had about 80 US gallons more, so 40 gallons there and 40 gallons back doesnt get you far into Germany from the Belgian coast. When you add the extra fuselage tank and external tanks things change dramatically, ut then it became a complicated mix of distances at cruising speed, time "on station" weaving or circling with the bombers, an allowance for combat and then getting back home. There are two "contingencies" that as far as I can see were never built into calculations. One was the carb. overflow system draining back to the main tank. The other is they didnt actually have to get "home" to their home base in UK, there were emergency landing strips on the coast at Manston and Woodbridge.

 

[Greg Boeser]

Nobody climbed directly toward the target when taking off. And just what the hell are you doing flying off with out the rest of your formation? Standard practice was to take off, circle the field while the rest of your flight formed up, then when all elements of the formation were in place, climb to cruise altitude. If you are escorting bombers you need to throttle back to avoid separating from your charges.

 

[FLYBOYJ]

Nobody climbed directly toward the target when taking off. And just what the hell are you doing flying off with out the rest of your formation? Standard practice was to take off, circle the field while the rest of your flight formed up, then when all elements of the formation were in place, climb to cruise altitude. If you are escorting bombers you need to throttle back to avoid separating from your charges.

Actually I calculated that just to show performance numbers, but I totally hear you. And in the Real world we would have calculated for atmospheric conditions to include "density altitude and true airspeed"

 

[Shortround6]

The range chart is all the pilot needed to plan a mission. To compute range for a mission the allowance for warm-up, takeoff and climb to 5000ft (20gal for P-39N) was deducted from total fuel then that net fuel was divided by gallons per hour and multiplied by TAS (not IAS). That's how all the ranges in each column are computed. For example look at column III at 15000ft. 70net gal divided by 67GPH X 300 TAS (242 IAS) = 313miles. The graph shows 300miles but the actual miles were rounded down a little as a safety factor. Same for all the columns at all altitudes (except column I). Gallons divided by GPH X TAS = range. The Fuel from Sea Level on the Take off, Climb and Landing Chart was not used since it already included the 20gal allowance for Warmup, Takeoff and Climb to 5000ft and didn't account for miles gained toward the target during climb.

Ok, from the take-off, climb and landing chart.
at 7500lbs, 35.3 gallons to get 25,000ft this includes warm up and take according to fine print at the bottom of that section of the chart. More on this later.

20 minute combat allowance, computed by me of 29.5 gallons using the percentage difference in fuel consumption between max continuous at 15,000ft and military power at 15,000.
take the percentage difference an multiply times 62 gph and then divide by 3 for 20 minutes. about 29 gallons

the 30 minute reserve. 16 gallons according to column V of the chart at sea level.

total is 81 gallons rounding down.

congratulations you have 39 gallons of fuel for cruising.
According to column I of the chart that should be good for 220 miles at a speed of 350mph which is higher than needed. Radius 110 miles.
Running at 310-315mph could extend range somewhat and take the engine out of the max continuous power setting which is warned against in Note (A) in the instructions.
"Avoid continuous cruising in column I except in emergency"

a couple of points,
1, I used an online calculator to go from IAS to true airspeed so result is a bit generic.
2, the speed numbers in Column I may be a bit optimistic?
AS a check I converted the IAS at 15,000ft to true MPH and got 375.7mph. Plane test at Aircraft Performance has top speed at 16,100ft as 389.5mph using 3000rpm and 46.7in of MAP.
Engine running 400rpm slower and lower manifold pressure only goes 14mph slower?

BTW (from 1st paragraph) there may be one or more errors in the Take-off, climb and landing chart. At 8000lbs doing a ferry climb to 25,000ft the P-39N was supposed to use 31.2 gallons of fuel.
unfortunately it used 38.1 getting to 15,000ft and 34.6 gallons getting to 10,000ft according to the chart. Is this the secret to the P-39N's performance? It made fuel as it climbed?
Also the times to altitude vs fuel burn seem a little off. As in it takes 5.8 minutes to go from 10,000ft to 15,000ft during the Ferry climb (2300rpm/31in MAP) but the plane only uses 3.5 gallons of fuel?

 

[GregP]

Good job SR6.

I surely hope so, but I'm betting it won't be enough ...

 

[FLYBOYJ]

Appreciate you looking at this - just a few questions

Ok, from the take-off, climb and landing chart.
at 7500lbs, 35.3 gallons to get 25,000ft this includes warm up and take according to fine print at the bottom of that section of the chart. More on this later.

20 minute combat allowance, computed by me of 29.5 gallons using the percentage difference in fuel consumption between max continuous at 15,000ft and military power at 15,000.
take the percentage difference an multiply times 62 gph and then divide by 3 for 20 minutes. about 29 gallons

I computed a 10 minute combat at max power (147 GPH) in my calculations assuming a quick powerful encounter, this was a subjective choice. Why are you splitting the "combat allowance" between max continuous and military power? Is this subjective or do you have a reason for this?

According to column I of the chart that should be good for 220 miles at a speed of 350mph which is higher than needed. Radius 110 miles.
Running at 310-315mph could extend range somewhat and take the engine out of the max continuous power setting which is warned against in Note (A) in the instructions.
"Avoid continuous cruising in column I except in emergency"

If this is being used for a cruise, unless you're time pressed, why not use Column V for Maximum range? I mean, isn't the purpose of this exercise is to squeeze every mile we can out of this dog?

a couple of points,
1, I used an online calculator to go from IAS to true airspeed so result is a bit generic.
2, the speed numbers in Column I may be a bit optimistic?
AS a check I converted the IAS at 15,000ft to true MPH and got 375.7mph. Plane test at Aircraft Performance has top speed at 16,100ft as 389.5mph using 3000rpm and 46.7in of MAP.
Engine running 400rpm slower and lower manifold pressure only goes 14mph slower?

Using a IAS to TAS calculator - how are you calculating this without OAT? Are you using a standard lapse rate in the calculator or a 0.02 estimation correction? If we are doing a model with no real world conditions (actual temp, atmospheric pressure winds) you can almost plug in any number you want.

 

[Greg Boeser]

Stop interjecting real world considerations into our totally theoretical calculations!
By the way, since we climbed to 25000' and the P-39 has a combat ceiling of 35000', we should get up there and catch the jet stream for an even better boost in range. Assuming that we are attacking in the most favorable conditions. Then after combat we duck back down and use a nice shallow dive, power off, to get back home.

 

[P-39 Expert]

Ok, from the take-off, climb and landing chart.
at 7500lbs, 35.3 gallons to get 25,000ft this includes warm up and take according to fine print at the bottom of that section of the chart. More on this later. Again, figures from the take off, climb and landing chart have nothing to do with range. The takeoff allowance for range calculation is 20gallons for this particular plane in clean condition.

20 minute combat allowance, computed by me of 29.5 gallons using the percentage difference in fuel consumption between max continuous at 15,000ft and military power at 15,000.
take the percentage difference an multiply times 62 gph and then divide by 3 for 20 minutes. about 29 gallons That's for combat at 15000ft. Are we cruising at 25000ft? Then combat should be at 25000ft. I figure combat GPH in column I by converting normal power to combat power by dividing the GPH by 2600 (max cont. RPM) and multiplying that by 3000 (combat RPM). At 25000ft GPH is 62 divided by 2600 X 3000 = 72GPH. 20 minutes at 72GPH = 24gallons.

the 30 minute reserve. 16 gallons according to column V of the chart at sea level. Correct, 32GPH for 30 minutes.

total is 81 gallons rounding down. 20gal takeoff, 24gal combat and 16gal reserve for landing = 60gal total reserves.

congratulations you have 39 gallons of fuel for cruising. 120 less 60 = 60gallons for cruising.
According to column I of the chart that should be good for 220 miles at a speed of 350mph which is higher than needed. Radius 110 miles. 60 net gallons at 25000ft burns 62GPH (.97hrs) times 350mph = 338mi. Radius is half that or 169mi. Remember per the chart the range in column I is only accurate at 12000ft. At 25000ft you are only burning 62GPH where at 12000ft you are burning 105GPH due to the thinner air.
Running at 310-315mph could extend range somewhat and take the engine out of the max continuous power setting which is warned against in Note (A) in the instructions.
"Avoid continuous cruising in column I except in emergency"

a couple of points,
1, I used an online calculator to go from IAS to true airspeed so result is a bit generic. There is a IAS-TAS conversion chart in the P-39Q manual that curiously is not in this P-39N manual. That's what I used.
2, the speed numbers in Column I may be a bit optimistic?
AS a check I converted the IAS at 15,000ft to true MPH and got 375.7mph. Plane test at Aircraft Performance has top speed at 16,100ft as 389.5mph using 3000rpm and 46.7in of MAP.
Engine running 400rpm slower and lower manifold pressure only goes 14mph slower? The chart derived from that test shows 392mph at 15000ft. 375 max cruise vs 392 top speed.

BTW (from 1st paragraph) there may be one or more errors in the Take-off, climb and landing chart. At 8000lbs doing a ferry climb to 25,000ft the P-39N was supposed to use 31.2 gallons of fuel.
unfortunately it used 38.1 getting to 15,000ft and 34.6 gallons getting to 10,000ft according to the chart. Is this the secret to the P-39N's performance? It made fuel as it climbed?
Also the times to altitude vs fuel burn seem a little off. As in it takes 5.8 minutes to go from 10,000ft to 15,000ft during the Ferry climb (2300rpm/31in MAP) but the plane only uses 3.5 gallons of fuel? That chart does seem to be a little off in the 8000lb section on the "Ferry" line. Looks to me like the 25000ft column the fuel from sea level is too low. But the rest of the chart looks pretty normal. Again, you don't use any figures from the Takeoff, Climb and Landing Chart in computing range. Everything you need to compute range is on the next page on the Flight Operation Instruction Chart (range chart).

Please expand above.

 

[P-39 Expert]

Nobody climbed directly toward the target when taking off. And just what the hell are you doing flying off with out the rest of your formation? Standard practice was to take off, circle the field while the rest of your flight formed up, then when all elements of the formation were in place, climb to cruise altitude. If you are escorting bombers you need to throttle back to avoid separating from your charges.

See my post #1546. first paragraph.

 

[P-39 Expert]

Stop interjecting real world considerations into our totally theoretical calculations!
By the way, since we climbed to 25000' and the P-39 has a combat ceiling of 35000', we should get up there and catch the jet stream for an even better boost in range. Assuming that we are attacking in the most favorable conditions. Then after combat we duck back down and use a nice shallow dive, power off, to get back home.

Actually for the P-39N service ceiling was 38500ft, combat ceiling was 31000ft (climb at 1000fpm) and the Flight Operation Instruction Chart (range chart) says it will cruise at 30000ft.

 

[pbehn]

Stop interjecting real world considerations into our totally theoretical calculations!
.

Like clouds? With heavy cloud a formation has to head into it well separated but on the same rate of climb and direction. This is to hopefully get through the cloud without collisions and in roughly the same place. I have read of collisions and pilots emerging above but not able to find each other. Shouting "I am over here" doesnt help, I am told.