Groundhog Thread Part Deux - P-39 Fantasy and Fetish - The Never Ending Story (Mods take no responsibility for head against wall injuries sustained) (9 Viewers)

[FLYBOYJ]

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.

In my years in aviation you usually weed out the BS'ers when they get basic terms and definitions wrong. I'm always willing to educate and at the same time learn but all hope is lost when one is shown they are wrong but are not willing to accept their errors. "Legends in their own minds."

 

[GregP]

Thank you Bill Marshall for post 2,854. I'm pretty sure we have beaten the P-39 to death and our P-39 Enthusiast (maybe not quite Expert) still won't see the light of day.

One often-quoted definition of insanity is doing the same thing over and over and expecting a different result. I believe we're have arrived there. We have met the enemy and he is now us. At least most of us know how to use a pilot's operating handbook and the charts therein, so it hasn't been all for naught.

The P-63 was a pretty decent airplane, but also wasn't going to be used for escort work. The P-39 got better with time, but wasn't what was needed and never was a high-altitude airplane, but it wasn't too bad if you stayed under 12,000 feet and kept pretty close to home. Outside of that narrow mission, it was out of its element.

 

[wuzak]

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.

Did the fuel pumps run at constant flow?

If so, wouldn't the take-off/climb allowance be the fuel actually used, not the fuel flowing from the tank? Bearing in mind that take-off is performed at near maximum power and fuel flow rate.

 

[Shortround6]

The engine in the P-39 used 109 gallons an hour to make 1000hp at 2600 rpm. Or 9.17 hp/hr/ gal

At military power of 1125hp/3000rpm it used 138 gallons an hour or 8.15 hp/hr/ gal.

You don't get to use the lower fuel consumption of max continuous when figuring military power.

 

[XBe02Drvr]

Yeeeaaaaah...

I still don't think you get the whole "range" and "mission planning" thing let alone the mission profile for deep penetration escort.

Like trying to teach a tortoise to fly.

 

[P-39 Expert]

The engine in the P-39 used 109 gallons an hour to make 1000hp at 2600 rpm. Or 9.17 hp/hr/ gal

At military power of 1125hp/3000rpm it used 138 gallons an hour or 8.15 hp/hr/ gal.

You don't get to use the lower fuel consumption of max continuous when figuring military power.

You need to use the fuel consumption at 25000' or 62gph at normal power (2600rpm). You must estimate military power consumption at that height, it is not quoted anywhere in the manual.

 

[GrauGeist]

I looked at all the charts and simply could not find the figures for "Ludicrous Speed".
Shouldn't it be found by the "Combat Speed" portion of the chart?

 

[pbehn]

I also doubt and air force would routinely switch fuel source as its pilots lifted off and raised undercarriage, eventually there will be a problem with a valve or an air lock and a pilot will die.

 

[XBe02Drvr]

In the tests mentioned they quote different design numbers, diameter and even the blade angle range in one case. There is absolutely no way a test pilot knows what the implication of this is unless he is told by someone who does.

Actually, a trained test pilot knows a lot more of this stuff than you give him credit for. Many, if not most of them are engineers by training and very few are your stereotypical "Joe Pilot" who just happened to fly a test hop.
A member of our flying club was a Navy Test Pilot School graduate, had a masters in aero engineering from Purdue, combat experience in Korea, had worked in engineering test at Edwards, instructed at the NTPS at Pax River, and would be the first to tell you that the young ones coming up were way better educated than he was.

 

[pbehn]

You need to use the fuel consumption at 25000' or 62gph at normal power (2600rpm). You must estimate military power consumption at that height, it is not quoted anywhere in the manual.

I have asked you 3 times where you get this from. WHERE DO YOU GET IT FROM?

 

[buffnut453]

I wish you chaps would stop groundhogging this thread with all this boring talk about aircraft performance. I'm still waiting for an answer to my post #2746 about the gas heater. Now there's a KEY question that needs answering!!!

 

[buffnut453]

LET THE GROUNDHOGGERY BEGIN!

Dude, the groundhoggery has been going on for over a year. I really, REALLY don't want it to start all over again!

 

[buffnut453]

My God man, have you learned NOTHING in this thread?

If so, he's not the only one!

 

[P-39 Expert]

No. Test weights stated are Always GW before takeoff.

Conditions including taped gun ports, removal of sway braces, external tank/no tank. The Test weights Were mostly conducted Under combat weights - and as such Optimistic'. Major Price was the Wright Field Bell project officer and notorious for producing 'optimistic' reports. I draw your attention to comparisons of RAF test results to Wright and Bell tests.

P-39 Performance Tests

Looking at Op manual for P-39Q and 75 gal external tank, a couple of entries stand out, beginning on pg 24:

GW for stated FERRY combat load (full internal load of fuel plus 75 gal tank but ZERO 50 cal ammo) = 8,100 (of which the wt of tank/fuel & sway brace =800). Not stated but with full ammo, 330 pounds (1000 rnd), The P-39Q could only take off with 75gal external if 55 less gallons of fuel (or ammo) carried - in which case - leave the 75 gal tank at home.
All Ranges stated are Ferry type profiles, with Maximum range =1000 miles for P-39Q-1 at 8100 GW.
Data above 15000 feet are left 'blank', save Condition II -->20K cruise settings of 30"MP, 2600rpm and IAS of 179mph/TAS and 76 gpm for Cruise.
The Optimal Cruise for distance is at 14,000 feet at 32"MP, 2280RPM and 74mpg (Clean)

There are no service ceilings published for 75 gal tank, nor is any data provided above 20K. Any proof that escort of any type was possible at 25K??

Note also that the fuel allowance for warm up, takeoff and climb to 20K consumes 42 gal.

In the escort role, there is no provision for forming up, nor consideration that when the P-39 actually reached 20K, that the TAS per the tables with 75 gal tank is 179IAS/270mph TAS was adequate to support US Heavies at 20K. - Well above FTH and Extremely sluggish to throttle up airspeed to deflect attacks. About the same speed as a fully loaded B-24 at 20,000 feet (cruise =170 to 180mph IAS).

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

Test weights were average weight for that flight, starting with full fuel and landing with a small reserve. British used 95% of published gross weight as the noted weight in their tests. None of the official Wright Field tests were noted at the published gross weight of the plane. None in wwiiaircraftperformance.org anyway.

So the test was bad because of a Major Price? A Wright Field performance test?

Weight of a 75gal drop tank with fuel is only 500lbs (450lbs fuel and 50lbs tank), not 800.

You are on the wrong chart if you are figuring range. Everything you need for range is on the Flight Operation Instruction Chart, nothing on the Takeoff, Climb and Landing Chart will help you with range or radius. Don't use the "Fuel From S.L" figures for range, that's all factored in on the Flight Operation Instruction Chart.

Please, I have never said that a P-39 was a "Super Escort". The question was could it escort bombers in Europe. I have proven that many times by using information from the pilot's manual.

 

[pbehn]

Actually, a trained test pilot knows a lot more of this stuff than you give him credit for. Many, if not most of them are engineers by training and very few are your stereotypical "Joe Pilot" who just happened to fly a test hop.
A member of our flying club was a Navy Test Pilot School graduate, had a masters in aero engineering from Purdue, combat experience in Korea, had worked in engineering test at Edwards, instructed at the NTPS at Pax River, and would be the first to tell you that the young ones coming up were way better educated than he was.

I have no doubt about that at all, even in WW2 pilots had instruction on how planes worked, but when it comes to the actual prop in front of him, without starting to measure diameter chord and profile then check all the workings of the pitch mechanism he can just note the manufacturer's product number.

In the test reports I linked one stated the blade angle range and the other didnt, I presume that is because he was asked to, because it had become significant.

 

[pbehn]

I wish you chaps would stop groundhogging this thread with all this boring talk about aircraft performance. I'm still waiting for an answer to my post #2746 about the gas heater. Now there's a KEY question that needs answering!!!

Have you noticed how we have leapt from proving a Bf 109 couldnt get a bomb to 25,000ft onto proving that a P-39 could haul a 110gallon tank to the same height and cruise effortlessly, economically and with eternal grace?

 

[Clayton Magnet]

Forgive my ignorance, but how could a single stage Allison haul a 110 gallon tank to 25000 feet, when it started gasping for air about 10000 feet lower?

 

[GrauGeist]

I have proven that many times by using information from the pilot's manual.

Then why didn't they?

 

[XBe02Drvr]

Test weights were average weight for that flight, starting with full fuel and landing with a small reserve. British used 95% of published gross weight as the noted weight in their tests. None of the official Wright Field tests were noted at the published gross weight of the plane. None in wwiiaircraftperformance.org anyway.

So the test was bad because of a Major Price? A Wright Field performance test?

Weight of a 75gal drop tank with fuel is only 500lbs (450lbs fuel and 50lbs tank), not 800.

You are on the wrong chart if you are figuring range. Everything you need for range is on the Flight Operation Instruction Chart, nothing on the Takeoff, Climb and Landing Chart will help you with range or radius. Don't use the "Fuel From S.L" figures for range, that's all factored in on the Flight Operation Instruction Chart.

Please, I have never said that a P-39 was a "Super Escort". The question was could it escort bombers in Europe. I have proven that many times by using information from the pilot's manual.

UN-EFFING-BELIEVABLE!! A tortoise lecturing an eagle on flight performance! I can die now, content that I've seen everything. Thank god for the 1st amendment. Everybody is entitled to express their opinion, and the entertainment value is priceless!

 

[DerAdlerIstGelandet]

No. Test weights stated are Always GW before takeoff.

Conditions including taped gun ports, removal of sway braces, external tank/no tank. The Test weights Were mostly conducted Under combat weights - and as such Optimistic'. Major Price was the Wright Field Bell project officer and notorious for producing 'optimistic' reports. I draw your attention to comparisons of RAF test results to Wright and Bell tests.

P-39 Performance Tests

Looking at Op manual for P-39Q and 75 gal external tank, a couple of entries stand out, beginning on pg 24:

GW for stated FERRY combat load (full internal load of fuel plus 75 gal tank but ZERO 50 cal ammo) = 8,100 (of which the wt of tank/fuel & sway brace =800). Not stated but with full ammo, 330 pounds (1000 rnd), The P-39Q could only take off with 75gal external if 55 less gallons of fuel (or ammo) carried - in which case - leave the 75 gal tank at home.
All Ranges stated are Ferry type profiles, with Maximum range =1000 miles for P-39Q-1 at 8100 GW.
Data above 15000 feet are left 'blank', save Condition II -->20K cruise settings of 30"MP, 2600rpm and IAS of 179mph/TAS and 76 gpm for Cruise.
The Optimal Cruise for distance is at 14,000 feet at 32"MP, 2280RPM and 74mpg (Clean)

There are no service ceilings published for 75 gal tank, nor is any data provided above 20K. Any proof that escort of any type was possible at 25K??

Note also that the fuel allowance for warm up, takeoff and climb to 20K consumes 42 gal.

In the escort role, there is no provision for forming up, nor consideration that when the P-39 actually reached 20K, that the TAS per the tables with 75 gal tank is 179IAS/270mph TAS was adequate to support US Heavies at 20K. - Well above FTH and Extremely sluggish to throttle up airspeed to deflect attacks. About the same speed as a fully loaded B-24 at 20,000 feet (cruise =170 to 180mph IAS).

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