The wingmen always use more fuel. And if he is a less experienced wingman, he will use even more of it.
Groundhog Thread Part Deux - P-39 Fantasy and Fetish - The Never Ending Story (Mods take no responsibility for head against wall injuries sustained)
- Thread starter greybeard
- Start date
The wingmen always use more fuel. And if he is a less experienced wingman, he will use even more of it.
FLYBOYJ
"THE GREAT GAZOO"
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
special ed
1st Lieutenant
- 7,113
- May 13, 2018
The amazon ads at the bottom of this thread are "The neverending Story II: The Next Chapter" and "The Neverending Story Season 1". Do they know something? Should we be concerned?
FLYBOYJ
"THE GREAT GAZOO"
and along with that
Shortround6
Lieutenant General
At the back of AHT there are several charts for the combat radius of action for the P-38, the P-47 and the P-51.
The conditions are very clearly spelled out. This is a general information chart/s and not to be used for specific mission planning.
A. warm up and take off equivalent to 5 minutes at normal rated power.
B. Climb to 25,000ft at Normal rated power (distance covered in climb is NOT included in radius)
C. cruise out at 25,000ft and 210 I.A.S.
D. Drop external tanks before entering combat.
E. Combat 5 minutes at War Emergency Power and 15 minutes at Military power.
F, Cruise back at 25,000ft and 210 I.A.S.
G. No account is taken of decreased fuel consumption during decent.
H. Allowance is made for 30 minutes reserve at minimum cruise power.
I. No allowance is made for formation flight or for evasive action other than the the 20 minutes combat.
The P-38J with 410 gallons internal is rated at 275 miles radius.
The P-47 with 305 gallons internal is rated at 125 miles radius.
P-47 with 370 gallons internal is rated at 225 miles radius.
P-51 with 184 gallons internal is rated at 150 miles radius.
P-51 with 269 gallons internal is rated at 375 miles radius.
Now the P-39 falls into a rather strange hole. It can meet the 25,000ft and 210I.A.S cruise with a small speed margin if running clean if it runs at near max continuous power.
The P-39Q-1 had about a 15mph margin on the cruise speed.
HOWEVER the P-39 Q-1 fails to meet the desired cruise speed at 25,000ft by around 45mph if carrying a 75 gallon drop tank according to the chart in the Manual.
Without the drop tank the P-39Q (even with 120 gallons ) has a combat radius of about 65 miles.
9 gallons for warm up per the above conditions. Normal rated is the same as max continuous.
25 gallons for Climb to 25,000ft (took out the 9 gallons for warm up)
15 gallons for 30 minute reserve (assumed 30 gallons an hour for minimum, charts show low 30 gallons an hour range for low altitude)
this leaves 71 gallons. I figured 26 gallons for the combat allowance. this was done by estimating that the Military power used about 25-26% more fuel than max continuous.
P-39 supercharger cannot come close to providing enough air at 25,000ft for anything like full military power at the lower altitudes so using those consumption figures is useless.
Which leaves 45 gallons for the range which the chart for a clean P-39Q at 25,000ft is about 130 miles at 25,000ft and 330mph true which does not line up with fuel/speed figures at the bottom. Assuming the 330mph speed needs 62 gallons and hour you get about .75 hours from 45 gallons or 247.5 miles of range or about 125 miles of radius. Backing off just bit in speed will get you a few more miles.
Now the problem is can the P-39N/Q actually fight at 25,000ft and not just fly in a straight line. the engine is lucky to make 770 hp at 25,000ft using military power 3000rpm and full throttle) WEP disappeared below 15,000ft.
The conditions are very clearly spelled out. This is a general information chart/s and not to be used for specific mission planning.
A. warm up and take off equivalent to 5 minutes at normal rated power.
B. Climb to 25,000ft at Normal rated power (distance covered in climb is NOT included in radius)
C. cruise out at 25,000ft and 210 I.A.S.
D. Drop external tanks before entering combat.
E. Combat 5 minutes at War Emergency Power and 15 minutes at Military power.
F, Cruise back at 25,000ft and 210 I.A.S.
G. No account is taken of decreased fuel consumption during decent.
H. Allowance is made for 30 minutes reserve at minimum cruise power.
I. No allowance is made for formation flight or for evasive action other than the the 20 minutes combat.
The P-38J with 410 gallons internal is rated at 275 miles radius.
The P-47 with 305 gallons internal is rated at 125 miles radius.
P-47 with 370 gallons internal is rated at 225 miles radius.
P-51 with 184 gallons internal is rated at 150 miles radius.
P-51 with 269 gallons internal is rated at 375 miles radius.
Now the P-39 falls into a rather strange hole. It can meet the 25,000ft and 210I.A.S cruise with a small speed margin if running clean if it runs at near max continuous power.
The P-39Q-1 had about a 15mph margin on the cruise speed.
HOWEVER the P-39 Q-1 fails to meet the desired cruise speed at 25,000ft by around 45mph if carrying a 75 gallon drop tank according to the chart in the Manual.
Without the drop tank the P-39Q (even with 120 gallons ) has a combat radius of about 65 miles.
9 gallons for warm up per the above conditions. Normal rated is the same as max continuous.
25 gallons for Climb to 25,000ft (took out the 9 gallons for warm up)
15 gallons for 30 minute reserve (assumed 30 gallons an hour for minimum, charts show low 30 gallons an hour range for low altitude)
this leaves 71 gallons. I figured 26 gallons for the combat allowance. this was done by estimating that the Military power used about 25-26% more fuel than max continuous.
P-39 supercharger cannot come close to providing enough air at 25,000ft for anything like full military power at the lower altitudes so using those consumption figures is useless.
Which leaves 45 gallons for the range which the chart for a clean P-39Q at 25,000ft is about 130 miles at 25,000ft and 330mph true which does not line up with fuel/speed figures at the bottom. Assuming the 330mph speed needs 62 gallons and hour you get about .75 hours from 45 gallons or 247.5 miles of range or about 125 miles of radius. Backing off just bit in speed will get you a few more miles.
Now the problem is can the P-39N/Q actually fight at 25,000ft and not just fly in a straight line. the engine is lucky to make 770 hp at 25,000ft using military power 3000rpm and full throttle) WEP disappeared below 15,000ft.
FLYBOYJ
"THE GREAT GAZOO"
SR - a lot of this coincides (or comes close to) my numbers taken from the manual with no temp or DA adjustment.
Example - you show:
9 gallons for warm up per the above conditions. Normal rated is the same as max continuous.
25 gallons for Climb to 25,000ft (took out the 9 gallons for warm up)
34 gallons.
from the chart;
Fuel includes warm up and take off allowance
Of course we have variance with a Vx or Vy climb
FLYBOYJ
"THE GREAT GAZOO"
Noticed that as well
Thus the reason for no cruise data in the flight manual at 25,000'
FLYBOYJ
"THE GREAT GAZOO"
P-39 Expert
Non-Expert
wwiiaircraftperformance.org, F4U-1 Airplane Characteristics and Performance. Same for the F6F. Makes sense, pilot is climbing in the direction of the target as he is gaining altitude. Doesn't include descent since there is a reserve for landing included in calculations.
Shortround6
Lieutenant General
I low balled it a bit.
For the combat allowance I figured that the Military power at 25,000ft would be in proportion to the max continuous power.
I used 104 gallons per hour compared to 140 gallons an hour for an average between take-off and power at 15,500ft.
Then I multiplied that factor times the 62 gallons per hour of the max continuous at 25,000ft. A bit rough perhaps.
One does have to interpret these pilots manual charts sometimes. The one you are listing for the N seems to missing a line. Or has some confusing terminology.
The line that is labeled Maximum emergency power is actually military power as the note at the bottom corrects.
The chart from the P-39Q manual has the correct lines in the chart but then stops at "max cruise" which is identical to the economical maximum line in the chart for the N with both planes using the V-1710-85 engine.
We can fudge figures a gallon or two here and there but nothing is going to make the P-39 even a medium range fighter.
Our expert took the 62 gph figure at 25,000ft and ran with it.
Why does the P-39 burn 57% of the fuel at 25,000ft that it does at 15,000ft with the same rpm (2600) and throttle setting ( full throttle) ?
Because it's supercharger cannot deliver enough air at that altitude and rpm to burn any more fuel. Not because the P-39 was some marvel of fuel efficiency.
A 7000lb airplane trying to fight at 25,000ft with 800 hp is going to be at a real disadvantage no matter how fast it can fly in a straight line.
The P-39 has by far the worst power to weight ratio of any of the possible American fighters at those altitudes.
The F4U-1 even at 12,000lbs has a power to weight ratio of 1 hp for every 7.74 lbs (assuming 1550hp at 15,000ft since it has 1650 at 23,000ft with ram)
Shortround6
Lieutenant General
Great idea if you have 1-3 fighters going to meet up with 1-4 bombers.
Horrible idea if you have an entire fighter group meeting up with a bomber group under real life conditions.
You have to get the fighters off the ground in sequence, form up your flight, squadron and group formations, then fly to the rendezvous location where the bombers may be on time, or early or late depending on how their take-off and forming up operations went.
Counting on flying to the direction of the target as soon as you are wheels up means your fighter group is strung out for miles in very small clusters as you enter enemy airspace. First aircraft off the ground may be 10 or more minutes ahead of the last planes.
FLYBOYJ
"THE GREAT GAZOO"
But he is still climbing and burning fuel!!!! This is NOT the same as a cruise setting! Reserve fuel IS NOT used for descent and landing!
FLYBOYJ
"THE GREAT GAZOO"
Agree with all -
Later today I'm going to do some calculations straight out of the flight manual for the P-39N. Take off at S/L and climb immediately to 20,000 feet. For the climb chart I'm going to "interpulate" a climb to 20,000' (because the climb chart goes from 15K to 25K). I'll then plug in a 15 minute cruise at 20K followed by "combat" at max power for 10 minutes. After that I'll show at 20,000' what fuel is left and the maximum range that is left.
No wind, standard pressure so DA and PA are equal so we are perfectly clear!
buffnut453
Captain
No, no, NO. The reserve is NOT to cover descent and landing. The reserve is there in case the pilot needs to go around or find an alternate airfield. No pilot should be relying on his/her reserve as the means to get into their primary airfield.
FLYBOYJ
"THE GREAT GAZOO"
"Pilot 101". Reserves usually 30 minutes VFR and 45 minutes IFR, used today in GA and I think this was a norm during WW2
"Reserve fuel" is not a reserve of fuel if you are planning on using it to accomplish your mission. If everything goes as planned it should still be in the tanks at engine shutdown.
You mean I have been doing it all wrong? I thought the sputtering of my engine made me sound cooler when I go for my $100 burgers.
Peter Gunn
Master Sergeant
Wait... a P-39 fighting at 25,000 feet...
...
BWAHAHAHAHAHAHHAHAHA
You're kidding right? Right?
...
BWAHAHAHAHAHAHHAHAHA
You're kidding right? Right?
Thumpalumpacus
Colonel
Fighting for breath, maybe?
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
And here we thought the sputtering was just showing off, trying to sound like a WWI fighter to impress everyone!
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