Groundhog Thread Part Deux - P-39 Fantasy and Fetish - The Never Ending Story (Mods take no responsibility for head against wall injuries sustained) (1 Viewer)

FLYBOYJ · May 23, 2021

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!

pbehn · May 23, 2021

FLYBOYJ said:
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. OK folks, check my math!

That is why it was used for a couple of missions by 4 aircraft across the channel.

Greg Boeser · May 23, 2021

I'm assuming that if there is no figure for a certain altitude for a certain cruise condition, it's because that throttle setting would not permit sustained operation there?

FLYBOYJ · May 23, 2021

Greg Boeser said:
I'm assuming that if there is no figure for a certain altitude for a certain cruise condition, it's because that throttle setting would not permit sustained operation there?

Yes - the data stops at 20,000 feet so I used those cruise numbers although one page of the manual gives climb data to 25,000'

Greg Boeser · May 23, 2021

Because you can operate at that altitude at max continuous.

pbehn · May 23, 2021

When the P-39 was introduced into Europe what target could it hit? If you damage or destroy French and Belgian infrastructure the Germans just tell the local population to repair it, at their cost. The only important targets are the ports which you yourself need or must pretend you need to keep attention from Normandy, but that was in 1944.

FLYBOYJ · May 23, 2021

Greg Boeser said:
Because you can operate at that altitude at max continuous.

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

GregP · May 23, 2021

It's like trying to get more pregnant. Tough to do.

GregP · May 23, 2021

Just more fuel for the bonfire ...

FLYBOYJ · May 23, 2021

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

Thumpalumpacus · May 23, 2021

FLYBOYJ said:
OK folks, check my math!

That's too much arithmetickin' for this Texan to manage at 9:30 pm. You best find a 7-Eleven to stop at before entering the fray, right? Gas up, and grab an energy-drink while you're at it.

buffnut453 · May 24, 2021

FLYBOYJ said:
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

That's all well and good, Joe....but we all know that, in a couple more pages of this thread, the P-39 will magically be comparable to the F4U Corsair again thanks to P-39Expert's calculations and/or considered opinion.

It's kinda sad that some of us, self included, hope for a different result. Methinks I'm gusting perilously close to the definition of insanity.

ThomasP · May 24, 2021

To be fair, the first ~160 production P-39N-1 were still fitted with the normal P-39 fuel tankage for 120 USgal.

Thumpalumpacus · May 24, 2021

buffnut453 said:
Methinks I'm gusting perilously close to the definition of insanity.

Or at least the Internet definition of it.

Greg Boeser · May 24, 2021

Those charts are full of data. How is a layman supposed to interpret them? Be nice if someone could start a new thread with a tutorial.
Otherwise a layman may just take the most impressive number from whatever convenient column to prop up his argument.
For example, what is the difference between a combat climb and a ferry climb?

FLYBOYJ · May 24, 2021

buffnut453 said:
That's all well and good, Joe....but we all know that, in a couple more pages of this thread, the P-39 will magically be comparable to the F4U Corsair again thanks to P-39Expert's calculations and/or considered opinion.

It's kinda sad that some of us, self included, hope for a different result. Methinks I'm gusting perilously close to the definition of insanity.

Or total debauchery of chart usage. The record goes round and round

FLYBOYJ · May 24, 2021

Greg Boeser said:
Those charts are full of data. How is a layman supposed to interpret them? Be nice if someone could start a new thread with a tutorial.
Otherwise a layman may just take the most impressive number from whatever convenient column to prop up his argument.
For example, what is the difference between a combat climb and a ferry climb?

You have a point but those presented are pretty easy although some data is hidden and is in small type. I think some people take half the data from the chart and then try to use their own formula to make calculations

Airframes · May 24, 2021

When it came to my opinion on the P-39, I used to be indecisive. Now, I'm not sure ...................................

Glider · May 24, 2021

ThomasP said:
To be fair, the first ~160 production P-39N-1 were still fitted with the normal P-39 fuel tankage for 120 USgal.

And there would have been a reason for reducing it in the rest. Then P39 needs to be clear if the performance figures are with the 120 or 90 US Gal, and prove it of course

FLYBOYJ · May 24, 2021

Glider said:
And there would have been a reason for reducing it in the rest. Then P39 needs to be clear if the performance figures are with the 120 or 90 US Gal, and prove it of course

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

Groundhog Thread Part Deux - P-39 Fantasy and Fetish - The Never Ending Story (Mods take no responsibility for head against wall injuries sustained) (1 Viewer)

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