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

[buffnut453]

When I did those calculations I tried to be as conservative as possible to show minimal fuel consumption so we can determine range, especially for the P-39 but the charts from the flight manual speak for themselves. I wanted to show the source instead of flapping numbers without a mention of fuel consumption. As I was doing the calculations it became apparent that a mission to 25,000' was not the best profile for the P-39

Heyyy....wait a minute!!! I've just figured out the primary role for the YB-40. It was to escort the P-39. The YB-40 as heavily armed, and could fly at higher altitude to protect the P-39 from being bounced from above. It also had longer operating range so it could loiter over the entirety of the P-39 mission.

Sounds like a war-winner to me!!!

 

[GregP]

So, now we know the YB-40 was a Foo Fighter escort of unparalleled capability. I KNEW it was good for SOMETHING. The Flying Fortress is shown below:

The YB-40 is shown below:

Cool!

Some period observations above ...

 

[P-39 Expert]

Several things - The P-39N manual I have shows best fuel consumption climb to 25K at 31.2 GPH at 30 minutes
View attachment 624415

Then there is no data for a 25K cruising altitude if that was your intention?? And nowhere do show GPH.

View attachment 624418

And you didn't include the 20 gallons for warm up, you use 16 gallons reserve for the P-39 and 20 for the F4U, so I'm not going any further with the P-39

F4U

Way high cruising speed and fuel consumption. Greg beat me to the punch. Try around 200 MPH indicated at around 42 GHP at 5000' for the F4U's best cruise fuel consumption.

Sticking with your initial numbers (which are very wrong)

79 gal @ 42 GPH = 1.88 hrs in the air at 200 mph = 376 miles.

Sorry, but my numbers are not wrong. I did use 16 gallons for warm up and climb instead of 20, I was looking at the P-39Q chart. So deduct 4 gallons if you want. You don't use both the 20gal reserve for warm up AND the fuel from sea level (31.2gal in your example) from the climb data chart. Just the warmup/takeoff/climb to 5000ft. Range includes climb but not descent. Since the pilot is climbing in the direction of the target at 170mph IAS he is effectively cruising at that speed until desired altitude is reached, about 10 minutes. The difference in climb speed and cruising speed for 10 minutes is negligible. Total fuel less allowance for warmup/takeoff/climb less combat reserve less landing reserve gives net fuel. Divide by gallons per hour to get cruising time and multiply by TAS (IAS converted) and that equals range. Everything is on the Flight Operation Instruction Chart you posted. I'm using the 120gal P-39.

If the P-39 and the F4U are used for the same mission then they have to use the same formula and mission profile. Takeoff and climb to 25000ft, cruise at maximum cruise, 20 minutes of combat and cruise back at maximum cruise with a 20 minute reserve for landing. The Navy used a cruise out at 15000ft at V max for max range (182mph) and then cruise back at 1500ft at V max range. That works fine for over water flights where the chance of encountering the enemy is small, but that won't work at all for escort or interception missions over land as the AAF did. Cruising out at 15000ft or cruising back at 1500ft would be suicidal.

 

[P-39 Expert]

I felt like doing some math...

So this is what I come up with, using those 2 charts posted and I used very conservative numbers except for take off weight, I used the fully loaded 8000 pounds, no wind condition to assume IAS will equal ground speed (for simplicity).

Start with 120 gallons (per the expert). Take away 20 gallons for warm up per the chart and you start with 100 gallons.

Take off at S/L, climb to 25,000 feet - 140 mph indicated, 31.2 gallons used, 29.9 minutes in the air at 140 mph so we traveled 70 miles.

68.8 gallons left.

In the cruise chart there is no data for 25,000' so we'll use 20,000'

Cruise 15 minutes, 160 MPH, 8.75 gallons used - 39 miles

60.1 gallons left.

Combat! 15 minutes. 10 minutes full power, 5 minutes WEP

34.75 gallons used. We'll also assume this was a traveling fight at 300mph - 75 miles

25.35 gallons left

Fight is over, descend down to 3000' (good cruising altitude) descend 1000' per minute at 160 mph 22 minutes, 12. 8 gallons used, 58 miles

12.6 gallons left.

10 gallons reserve, 2.55 gallons left. At 160 mph you'll burn that up in about 5 minutes, 40 miles

Total mission miles with 10 gallons reserve - 282 miles

I didn't account for blower setting, auto rich or lean or density altitude, just read the data straight off the charts. Also did not account for flying a pattern and landing. OK folks, check my math!

Please see my post #1503.

 

[P-39 Expert]

At 7500 pounds - It now matches the 2nd chart

Start with 120 gallons (per the expert). Take away 20 gallons for warm up per the chart and you start with 100 gallons.

Take off at S/L, climb to 25,000 feet - 150 mph indicated, 35.3 gallons used, 10.8 minutes in the air at 150 mph so we traveled 27 miles.

64.7 gallons left.

In the cruise chart there is no data for 25,000' so we'll use 20,000'

Cruise 15 minutes, 160 MPH, 8.75 gallons used - 39 miles

55.95.1 gallons left.

Combat! 15 minutes. 10 minutes full power, 5 minutes WEP

34.75 gallons used. We'll also assume this was a traveling fight at 300mph - 75 miles

21.2 gallons left

Fight is over, descend down to 3000' (good cruising altitude) descend 1000' per minute at 160 mph 22 minutes, 12. 8 gallons used, 58 miles

8.4 gallons left.

About 5 minutes of fuel remaining - 13 miles

212 miles

Please see my post #1503.

 

[P-39 Expert]

LET'S DO THE CORSAIR!!!

237 Gallons

Using max weight per the flight manual 14,200 pounds

Warm up and take off fuel consumption included per the flight manual chart.

Take off at S/L, climb to 25,000 feet - *125 knots indicated, 83 gallons used, 19 minutes in the air at *143.8 mph = 45 miles

159 Gallons left

Cruise 15 minutes, 14.5 gallons at *191mph ( *based on Report No. 6195 April 1, 1943 from Chance Vought. NAVAIR bases charts on endurance) = 47.7 miles

144.5 Gallons left

Combat! 15 minutes. 10 minutes full power, 5 minutes WEP 88 gallons at 380 mph = 94 miles NOTE: Military power used 275 GPH low blower per my manual (numbers were shown)

56.5 Gallons left

Fight is over, descend down to 3000' (good cruising altitude) descend 1000' per minute at 191 mph 22 minutes, 15.9 gallons used, 70 miles

40.6 Gallons left

Minus 10 gallons reserve -

30.6 Gallons left

40 minutes left in the air at 191 mph = 127 miles

384 miles

View attachment 624443

View attachment 624444

Please see my post #1503.

 

[GregP]

In Post 1503, you say cruising out and returning at 15,000 feet would be suicidal. That's EXACTLY why USN and USAAF airplanes are different ... they have differing requirements and different missions. So, there is no real point in comparing them for missions since they do different things. Hence, two different services.

You made the point perfectly. Navy/Marine and Air Corps airplanes were not going to do the same missions very often, so there is no point in comparing the two.

So don't. Compare instead against aircraft that would be flying the same missions.

 

[P-39 Expert]

In Post 1503, you say cruising out and returning at 15,000 feet would be suicidal. That's EXACTLY why USN and USAAF airplanes are different ... they have differing requirements and different missions. So, there is no real point in comparing them for missions since they do different things. Hence, two different services.

You made the point perfectly. Navy/Marine and Air Corps airplanes were not going to do the same missions very often, so there is no point in comparing the two.

So don't. Compare instead against aircraft that would be flying the same missions.

I said cruising back at 1500ft, not 15000ft.

It's the only way to compare a land based AAF plane to a land based Navy carrier plane if they were flying the same missions.

 

[GregP]

There is really no point in comparing Naval and non-Naval aircraft for mission range.

The only time they are likely to tangle is if land planes attack a carrier task force. If that DOES happen, the range is immaterial since the carrier planes are essentially operating very close to home and the land planes have to have whatever range is required to attack the carriers and get back. The only performance characteristics that matter in that case are performance numbers such as turn. climb, speed, and armament, not range.

 

[fubar57]

GregP Until a month ago I was unaware that there was a B-24 trialled as a gunship as well, the XB-41

PUBLIC DOMAIN​

 

[FLYBOYJ]

Sorry, but my numbers are not wrong. I did use 16 gallons for warm up and climb instead of 20, I was looking at the P-39Q chart. So deduct 4 gallons if you want. You don't use both the 20gal reserve for warm up AND the fuel from sea level (31.2gal in your example) from the climb data chart.

WRONG - read the chart!!!!

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

no!

I'll blow it up for you

"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)

Just the warmup/takeoff/climb to 5000ft. Range includes climb but not descent.

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?!?!?

Since the pilot is climbing in the direction of the target at 170mph IAS he is effectively cruising at that speed until desired altitude is reached, about 10 minutes.

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

The difference in climb speed and cruising speed for 10 minutes is negligible. Total fuel less allowance for warmup/takeoff/climb less combat reserve less landing reserve gives net fuel.

WHERE DOES IT SAY TO DO THAT?!?

Divide by gallons per hour to get cruising time and multiply by TAS (IAS converted) and that equals range. Everything is on the Flight Operation Instruction Chart you posted. I'm using the 120gal P-39.

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,

If the P-39 and the F4U are used for the same mission then they have to use the same formula and mission profile.

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!!!!

Takeoff and climb to 25000ft, cruise at maximum cruise, 20 minutes of combat and cruise back at maximum cruise with a 20 minute reserve for landing. The Navy used a cruise out at 15000ft at V max for max range (182mph) and then cruise back at 1500ft at V max range. That works fine for over water flights where the chance of encountering the enemy is small, but that won't work at all for escort or interception missions over land as the AAF did. Cruising out at 15000ft or cruising back at 1500ft would be suicidal.

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!!!

 

[wuzak]

Takeoff and climb to 25000ft, cruise at maximum cruise, 20 minutes of combat and cruise back at maximum cruise with a 20 minute reserve for landing.

Is that because there was no other cruise setting that worked at 25,000ft?

 

[FLYBOYJ]

Is that because there was no other cruise setting that worked at 25,000ft?

Or the test data wasn't done or wasn't available to put in the flight manual.

 

[FLYBOYJ]

"Range includes climb but not descent"

Has anyone else ever heard of that?

 

[FLYBOYJ]

F4U Manual, take off, climb and landing chart -

YOU DO WHAT THE CHART TELLS YOU!

 

[GregP]

Hey Fubar57,

There was also a B-24 with a B-17 nose grafted on:

You just never know what they will come up with, such as:

The Leduc 0.10 is certainly a strange bird. Ask the erstwhile pilot above!. If someone was attacking you from the rear, how would you know it was anything but an engine failure? Certainly not by turning around and looking over the tail!

Then we have a Russian candidate:

This adds fuel to the adage that, "If it is weird, it is British; if it is ugly, it is French; if it is weird AND ugly, it is Russian." Talk about a flying tank!

 

[FLYBOYJ]

You don't use both the 20gal reserve for warm up AND the fuel from sea level (31.2gal in your example) from the climb data chart. Just the warmup/takeoff/climb to 5000ft.

Gee - lookie here...

and smack in the middle of the cruise charts it says...

Why is that???

EDIT!

Because on the climb chart it says this:

So I'll stand to be correct but let's look at numbers;

90 gallons internal, climb to 25K 31.2 gallons 20 for warm up and take off, 11.2 for climb

90 - 31.2 = 58.8 gallons fuel left at 25K

You made a claim that internal fuel was 120 gallons, ok...

120 - 31.2 = 88.8 gallons.

I'll give you the benefit of the doubt, that gives an extra 20 gallons. Where do you want to use it?

Suppose we put it in the cruise home at 3000' - according to the cruise chart that buys you up to 120 miles @ 217mph cruise, so now the mission profile I completed goes to 402 miles with no reserve

BUT

If the internal fuel is 90 gallons, you lose 10 gallons which puts you at 342 miles with no reserve.

EDIT - The flight manual that I have for the P-39N shows 90 gallons in the W&B 87 useable.

 

[BiffF15]

Interesting. Also remember you are doing a single ship. Add more aircraft, use more fuel for ground ops, takeoff, and rejoin. The more you add, the more fuel you use, and the shorter the range.

 

[FLYBOYJ]

Interesting. Also remember you are doing a single ship. Add more aircraft, use more fuel for ground ops, takeoff, and rejoin. The more you add, the more fuel you use, and the shorter the range.

From our resident fighter pilot, thank you Biff!

BTW - I went back and looked at the numbers and in the descent for the P-39 coming down from 25K down to 3000' I could have used a best fuel consumption of 32 GPH at 215 mph indicated. Would have added an extra 20 miles but used less than a half gallon more.

 

[Milosh]

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