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I believe you are correct, alsoDrgondog would be the expert but my understanding is that the fighter formations did a series of S turns over the bombers to keep their airspeed up while remaining over or near the bombers. Trying to accelerate form bomber cruise speed to combat speed for fighters could take 2 or more minutes, at which time the attackers have come and gone.
Quit bringing up facts, they ruin the thread
HiI believe you are correct, alsodrgondog once told me that every 40-50 minutes the Mustangs would rev up to even higher RPM's for several minutes to keep the plugs from fouling.
Not a "stock" P-39N for the Wright Field test? Of course it was, it was taken straight from the production line. We've been over the test weights many times before, the quoted figure represents the average weight of the plane during a flight accounting for fuel burn. Virtually all the Wright Field tests used this method to compute weights for tests for all AAF fighter types. Their test weights were lower than published gross weights.The 20 gallons you are using is takeoff and climb to 5,000 feet, Expert. Read the chart, for crying out loud. Also, that test was NOT a stock P-39N. It was flown at 7,274 pounds. The pilot's manual for a P-39N, with the ammunition on board and no extra drop tank comes in at 7,517 pounds (again, with ammunition and without drop tank). Without the drop tank, the range is utterly useless.
A stock P-39N has a 1,200 hp engine with takeoff at 50.5 " MAP and 1,125 hp WER at 44.5" MAP. The report is a test using 59.8" MAP and 1,420 hp that was not released for squadron use. So, you are again cherry picking at an advanced level.
Say you were actually flying a stock P-39N, and you take off and climb to 5,000 feet with your 20 gallons of fuel and you allow for 10 minutes combat at 135 gallons per hour. That leaves you just 44.5. minutes of cruising at 255 mph at 6,000 feet (I let you magically climb 1,000 feet with no fuel burn). Counting the distance traveled in climb and the 44.5 minutes at 255 mph, your range is just under 100 miles ... not really of much use. At 7,500 pounds and 25,000 feet, a stock P-39N can climb at about 1,250 feet per minute assuming it is at Emergency Power. It could climb at 1,100 fpm if at normal power.
For comparison, a Spitfire Mk V in 1941, a year earlier than your high horsepower P-39 test you are looking at just in case you aren't looking at dates, was climbing at 1,940 fpm at 23,000 feet. And it didn't have any issues with C of G, nose armor, or car doors that needed to be opened to bail out. Plus it was in widespread use by the British, something the P-39N wasn't.
But, I'm sure you would KNOW this if you read the test report and also looked at the manual for the service airplanes with an unbiased eye.
You certainly do like the airplane. Perhaps not without some justification. It wasn't a BAD fighter until it ran across an enemy fighter at an altitude above 12,000 feet or so that was closer to home than about 170 miles. Then it was less than wonderful. Of course, you really wouldn't be running into an enemy fighter farther away from home than about 170 miles anyway or you'd run out of fuel getting home. A Spitfire Mk Vb was considered a short ranged and it could travel over 1,100 miles, making for a combat range of half that, or about 550 miles. You'd need more than twice the P-39's range just to be considered a "short range fighter!" But, hey, you could intercept low-altitude enemies over London as long as you kept a close eye on the fuel gauge. A great point-defense or short-range attack, low-altitude fighter, and that is a niche that the Russian exploited.
Where do you get your fuel consumption figures from for cruising at 25,000ft with a 110 gal tank? A 75 gal tank knocks 40 MPH off all cruising figures as per the tests. Could a P-39 actually get to and cruise at 25,000ft with all the fuel you want on it?Not a "stock" P-39N for the Wright Field test? Of course it was, it was taken straight from the production line. We've been over the test weights many times before, the quoted figure represents the average weight of the plane during a flight accounting for fuel burn. Virtually all the Wright Field tests used this method to compute weights for tests for all AAF fighter types. Their test weights were lower than published gross weights.
You're comparing takeoff power at SL and WEP at 9500' and it certainly was available for squadron use.
In comparison with a Spitfire V the normal P-39 held 20% more internal fuel. There is no way on this earth that a Spitfire V had a combat radius of 550mi. Escort fighter bases in England were only 520mi from Berlin. Most escort range charts credit the Spitfire V with a combat radius of 175mi. Barely across the English Channel.
Somebody certainly is "cherry picking" and it's not me.
Roger Freeman did well on the narrative regarding the P-51B in general, but incorrect on several points:Hi
The plugs were one of several problems that arose with the introduction of the P-51B, it appears to have been 'solved' by using British RC5/5 plugs instead of the original ones. There is a good summary of the various problems, and 'solutions', in 'The Mighty Eighth War Manual' by Freeman, pages 195-196, extracts below:
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Mike
Switch to drop tank is a lot earlier, right after gear and flaps up and climb speed has been established. Most of the fuel used on the ground and during takeoff will drain back into the main internal tanks. Most of the 20gal takeoff/climb allowance is used climbing toward the target and is therefore used in the range calculations.That gets you to 5000ft, switch to drop tank is probably a bit earlier.
actually about 40 gallons would be a better estimate.
Going to loose a lot planes looking for airfields, an extra 5 gallons might be to your advantage.
Doesn't work that way unless you want an lot of planes running out of gas.
Drop tank does not count for combat (especially a 110 gallon tank) and does not count for return flight.
You have 60 gallons or less internal fuel for the trip back.
Every other escort fighter was figured as internal fuel minus take-off allowance, minus reserve for "landing/finding field" and combat allowance.
only reason the P-39 looks good for fuel consumption is because it isn't making enough power.
You estimate wrong. You have been told this before.
going from 2600rpm to 3000rpm is a about a 15% increase in RPM. Since internal friction goes up with the square of the speed (RPM) that is a 33% increase in power lost to internal friction. Guess what? the power to turn the supercharger impeller goes up with the square of the speed, another 33% increase in power required just to turn 3000rpm.
Where does this power come from?
Pixie dust?
Unicorn Poop?
Satanic rituals?
Groundhog mystical incantations?
Try more fuel burned in the cylinders to get the power at the Propshaft measured in lbs/hp/hr.
A much closer estimate would be the amount of fuel needed at 15,500ft for military power divided by the fuel burned for that power,(1125hp divided by 138 gallons equals 8.15 hp per hour per gallon). then find the power at 25,000ft and divide by 8.15. (770 hp divided by 8.15 equals 94.47 gallons and hour) or 31.17 gallons for 20 minutes.
However that is ONLY if the P-39 can remain at 25,000ft. If it is forced to trade altitude for speed at any point and descends to 20,000ft the with the engine still doing 3000rpm and the throttle still wide open it will make about 910 hp and the fuel burn will go to 111.65 gallons per hour (or 1.86 gallons per minute.)
The phenomenal performance actually looks pretty crappy compared to P-38G or a Spitfire VIII or even a Spitfire IX.
Or even a MK IX Spit with a 30 imp gallon tank still attached.
Sorry, 370mph or so at 25,000ft just isn't good enough.
Nope,Where do you get your fuel consumption figures from for cruising at 25,000ft with a 110 gal tank? A 75 gal tank knocks 40 MPH off all cruising figures as per the tests. Could a P-39 actually get to and cruise at 25,000ft with all the fuel you want on it?
This works ONLY if your escort fighters arrive over the bomber stream and in enemy territory strung out in a line in the order they took off. If you actually want to form up into flights or squadrons it does not work. The AAC planners did not count the climb for range calculations, you have been told this many times.Most of the 20gal takeoff/climb allowance is used climbing toward the target and is therefore used in the range calculations.
Which really sucks if you are the fighter pilot/s you just had their radius decreased in mid flight. That translates into POW.Naturally if combat is encountered before the fuel was exhausted in the drop tank then the tank would be jettisoned and combat radius would be decreased.
It's wrong unless you can repeal the laws of physics.That's the increase in fuel burn that I used for my estimate.
As you pile on internal and external fuel and go higher, this mythical beast becomes more economical and faster, even my dear old grandmother would raise an eye brow at the proposition, it sounds like perpetual motion.It's wrong unless you can repeal the laws of physics.
At 25,000ft there is no difference between the different types of power, because the engine could not develop enough power to trouble the bearings or any other component. This can be seen in the tests.Regarding my estimate for fuel burn at combat power vs normal power,
No. Test weights stated are Always GW before takeoff.Not a "stock" P-39N for the Wright Field test? Of course it was, it was taken straight from the production line. We've been over the test weights many times before, the quoted figure represents the average weight of the plane during a flight accounting for fuel burn. Virtually all the Wright Field tests used this method to compute weights for tests for all AAF fighter types. Their test weights were lower than published gross weights.
Are you sure it isn't GROUNDHUGGERY? We are talking P-39 here...*SNIP*
LET THE GROUNDHOGGERY BEGIN!
There are a few problems with this statement. First of all, we KNOW that the evil Brits were conspiring to kill the P-39 what with their demands to add weight to it for no apparent reason (just for starters), so data from RAF not trustworthy.*SNIP*
The worst part of this ad-nauseum rendition of the 'super escort' P-39 (any production version) is that you never think to compare Wright Field/Bell test data with RAF test data - folks that REALLY needed a suitable fighter
Yeeeaaaaah...Switch to drop tank is a lot earlier, right after gear and flaps up and climb speed has been established. Most of the fuel used on the ground and during takeoff will drain back into the main internal tanks. Most of the 20gal takeoff/climb allowance is used climbing toward the target and is therefore used in the range calculations.
Of course drop tank does not count for combat, the reserve for combat has already been deducted from the fuel total. Calculation is based on using the drop tank during climb and the outbound leg of the mission. The range calculation assumes that the tank remains in place on the return leg while internal fuel is being burned since cruising speed was not increased when the tank was dropped. Pilots were encouraged to bring the tank back if possible if no combat had been encountered. Otherwise pilots would have simply dropped the tank when the fuel was exhausted and the tank could not have been reused. Naturally if combat is encountered before the fuel was exhausted in the drop tank then the tank would be jettisoned and combat radius would be decreased. This is true of any plane carrying drop tanks, not just the P-39. Remember the P-39N cruising speed at 25000' without the drop tank was 350mph at the same power setting (2600rpm normal power) instead of 276mph with the tank. If combat is encountered the drop tank is dropped and the combat reserve (24gal) and the landing reserve (10gal) would be deducted from the 120gal internal fuel leaving 86gal to get home. 86gal divided by 62gph = 1.4hr x 350mph = 485mi, well over the combat radius quoted in the calculation.
Regarding my estimate for fuel burn at combat power vs normal power, you are correct that going from 2600rpm to 3000rpm is about a 15% increase. That's the increase in fuel burn that I used for my estimate. Throttle setting was the same (full), mixture setting was the same (auto rich), plane was well above critical altitude. Only difference was rpm. You are entitled to your estimate, but that doesn't make it correct. Let's say that your estimate is correct at 31gal. vs my estimate of 24gal. Those 7 gallons represent 7 minutes less flying time (7 divided by 62gph) and 31mi at cruising speed (7 min x 276mph). That reduced combat radius by 16 whole miles. Hardly relevant at all.
Compared to a P-38G the P-39N climbed a good bit better up to 25000' and was about the same speed up to 20000'. P-39N was well matched with contemporary 109s and 190s they would have encountered in early 1943. And nothing climbed with a Spitfire IX. Nothing.
In flight test reports here P-39 Performance Tests there is Normal rated power, Military power and War emergency power and the critical altitudes these were at, for level speeds and climb, this sort of stuff isnt my "bag" which is why I was asking where he got his info. I am pleased to see from other posts the laws of physics also apply to the P-39.Hmmm - "combat power vs normal power"
Word search no such thing...
"Military Power/ Takeoff Power" found in manual.
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