SHOULD the P39 have been able to handle the Zero? Was it training or performance? (5 Viewers)

[Glider]

If you read the pilots manual this is how they tell pilots to plan a mission. The consumption rate at 25000' is 62gph at max continuous power from the manual. It is constant throughout the mission, same power setting, same altitude. After reserves you have 2.8hrs to escort. You must use the bomber speed because although you fly faster than them, because of weaving you never pass them. If the escort speed is used, then 2.8hrs x 281mph = 787mi or a radius of 393mi, which is even farther (71mi) than using bomber speed.

Your consumption is constant at 62gph. The only variable is bomber speed or escort speed. Your forward progress with weaving is the bomber speed.

A small point but for the few long range daylight heavy bomber missions the RAF did from May 1944, the favoured UK built escort aircraft was the Tempest. It had a decent range of 740 miles or 1,500 with drop tanks and did escort RAF bombers to the Rhur which is respectable.

Note that the 1,500 range was with two x 45 gallon drop tanks. They rarely but sometimes did use 2 x 90 gallon drop tanks on long range missions but I don't know the range,

Your call P39N or a Tempest

 

[pbehn]

Your call P39N or a Tempest

P39, it is purely a box art issue, they look cute under attack, with their long range tanks strapped underneath.

 

[DarrenW]

Pretend we got one of the kits and put the 33gal tanks back in the wings, or that we had one of the first ones with 120 gallons internal.

If we did that performance would suffer in an escort role so why would anyone do such a thing? I hope you realize that removing a quarter of the internal fuel wasn't done to reduce range (at least I hope you don't think this was the reason). The engineers were trying to keep the Airacobra's speed and climb competitive and range wasn't a primary concern at the time so they cut the fuel load accordingly.

Like everyone has been telling you up to this point, you can't have the extra fuel AND the figures quoted from the army tests as well. It's one or the other so please pick one and be done with it.

 

[pbehn]

Like everyone has been telling you up to this point, you can't have the extra fuel AND the figures quoted from the army tests as well. It's one or the other so please pick one and be done with it.

I believe I read somewhere that sometime in 1941 Bell received a special delivery of solid and liquid anti-gravitum. It is little known in todays world but features a lot in WW2 aircraft discussions.

 

[Shortround6]

If the bombers are doing 230mph true per hour then and you have two hours of fuel after climb to altitude and allowing for reserve then you have a radius of 230 miles or a bit more, doesn't matter what distance your fighter actually flies in that hour.

However this is NOT the way escort Missions were planned or flown. Please listen to Drgondog, His father Flew P-51s during the war, I beleive he was a squadron commander (?) . He, himself has flown P-51s, He is an aeronautical engineer and and has written at least one book pertaining to the bombing campaign over Germany and is working on another.

Basically it doesn't matter how big a drop tank you can strap on a plane, what matters is what happens after you have to drop said tank/s. How much internal fuel you have to fight for 15-20 minutes and how fast do you have to fly to get back to the channel where you can start to let down/slow down. and then cross the channel. Always keeping that 20-30 minute reserve so you can find an airfield, any airfield in sunny England.

P-39s problem is that it is NOT going to stay at 25,000ft for long in combat. Once you start turning/maneuvering you will lose altitude.
don'r short change yourself, If you drop 5,000ft your fuel consumption goes up 20 gallons and hour or more, dropping to 15,000ft makes it go up another 20 gallons or more, over a 50% increase in gallons per minute.
P-47s often found themselves at much lower altitudes than when they started.

So lets assume you start with 110 gallons internal ( you got a few gallons back after take-off from vapor return, You need 12-18 gallons reserve depending on requirements. so about 95 gallons. Now can argue about the fuel used in "combat". Later in the war The USAAF figured 5 minutes at WEP and 15 minutes at military power. British figured 15 minutes at times and at other times just equivalents 5 min at combat equeled xx miles at max economy or YY miles at max lean.

You are counting on using 71 gallons an hour at "military" or full throttle at 25,000ft. Engine is starved for air so it isn't making much power. However, if you drop to 20,000ft and don't throttle back you could be burning close to 90 gallons an hour, drop any lower and the fuel consumption rises even more. The P-39s ability to "fight"at 25,000ft is suspect. You have one test with good climb figures but you have an over 7000lb airplane with about 750hp (or a bit less). While the Mustang (P51-B) isn't available for most of 1943 it has around 1250hp for an airplane a bit over 9000lbs, Early P-47 may have weighed over 12,000lbs but still had 2000hp due the turbo.
You can't escort/fight flying gentle curves and trying to maintain altitude at all costs. There is no shame in losing altitude in a fight, you just have to plan for it and plan for the power/fuel needed to climb back up. Which cuts into the distance you can fly to get home.

The combat radius of action charts used later in the war were based on.

(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 210IAS......(315 true?)
(d) Drop external tanks and/or bombs 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 IAS
(g) no account is made of decreased fuel consumption during descent.
(h) Allowance is made for 30 minutes reserve at minimum cruise power
(j) No allowance is made for formation flight or evasive action other than the 20 minutes combat.

Under these conditions (which do not include weaving or time spent with bombers)
the P-38 with 410 gallons internal was rated at 275 miles, the P-47 with 305 gallons internal was rated at 125 miles and the P-51 with 180 gallons was rated at 150 miles.
some rounding off was going on as all aircraft, with and without tanks all had radiuses that were a multiple of 25.
Now since we know that a P-39Q with 165 gallons (75 gallon drop tank) is hard pressed to match a clean P-47 with 305 gallons for range the idea that an additional 60-70 gallons is going to turn a P-39 into a long range escort doesn't look good.
BTW a P-47 with 370 gallons internal on this chart is good for 225 miles. Or it used about 30 gallons each way for the extra 100 miles. Granted it was big airplane.

Remember this is about the maximum radius. No weaving, no dog legs around known flak sites, no allowance for headwinds aside from the built in ones of not counting the climb and not counting the benefit of the descent.
And remember, beating the crap out of your engines in a "combat" climb right at the beginning of a several hour flight over enemy held territory may not be the smartest thing to do even if it does save a few gallons of fuel.

 

[Milosh]

A small point but for the few long range daylight heavy bomber missions the RAF did from May 1944, the favoured UK built escort aircraft was the Tempest. It had a decent range of 740 miles or 1,500 with drop tanks and did escort RAF bombers to the Rhur which is respectable.

Note that the 1,500 range was with two x 45 gallon drop tanks. They rarely but sometimes did use 2 x 90 gallon drop tanks on long range missions but I don't know the range,

Your call P39N or a Tempest

I have read that there was trouble with the fuel feed from the 90 gal tanks during WW2.

 

[DarrenW]

I believe I read somewhere that sometime in 1941 Bell received a special delivery of solid and liquid anti-gravitum. It is little known in todays world but features a lot in WW2 aircraft discussions.

 

[eagledad]

Gentlemen,
Thought I would add more numbers to the mix. Please find a copy of the Tactical Planning chart, which I believe would be used by USAAF planners when planning a mission. Please note that the date is June 1945. Weights include "Basic" + crew, oil, full ammunition, and fuel, Range and endurance includes
1 Allowances for warm up, taxi, run up, take off and landing (Equal to 10 minutes at max cont at SL)
2 Allowance for fuel consumed in climb. Distance and time are included in range and endurance.
3 Allowance for carrying bomb or drop tank ENTIRE flight.
Allowance for 10% net ideal range and endurance for differences in aircraft, pilot techniques etc.

Note that flying at max cruise (max continuous operating at lean mixture setting) at 25000 feet is above the ceiling of the aircraft.
It does not appear that the ranges and endurance given include any allowances for combat.

My 2 cents.

Eagledad

 

[Shortround6]

trying to use the criteria listed above I come up with

9 gallons for warm up and take-off but since I have no figures for the fuel used climbing at "normal power" =max continuous and since for the P-39Q there is only a 3 gallon difference between the combat climb and the ferry climb (which uses much less than normal power) I am just going to use 40 gallons for take-off and climb to 25,000ft.
on the other end 30 minutes at minimum cruise seems to be 16 gallons.
Combat is a bit tricky, at this altitude the P-39 can't even come close to making max continuous power let alone military and WEP. and since fuel consumption fluctuates with altitude (plane might burn 30% more fuel at 20,000ft than at 25,000ft) any number is a WAG. I averaged what I figured was the fuel consumption at 3000rpm (15% higher than the consumption at 2600rpm) for both 25,000ft and 20,000ft at 83 gallons an hour. 20 minutes of that is 28 gallons (rounded up)
This means that we have 40 gallons for take-off and climb, 28 gallons for combat and 16 gallons for reserve or 84 gallons that cannot be used for cruise. And a minimum 42 of that has to be out of the internal fuel could be as high as 51, depends on how much fuel is returned to main take as vapor/overflow.
Now we hit the next problem, The P-39 will NOT cruise at the desired 210 IAS with the drop tank. I have no problem with this as a "what if" in early 1943 as tactics and procedures would have been in their infancey and slightly slower plane than desired may have been used anyway.
However, if 30 gallons of the climb fuel came out of the 75 gallon drop tank ( I am not buying the 110 gallon tank in early 1943) that leaves 45 gallons left and that means roughly 45 minutes to the drop point at 275mph true (I will split the difference between the claimed penalty for the under wing pods) or 206 miles. With over 100 miles of channel to cross before you get to the Belgian/Dutch coast this doesn't look like much of an escort fighter. For getting out of Dodge, you have the 110-120 gallons minus the 42 gallons for combat and reserve. The P-39 is a lot faster without the drop tank. However larger tanks must be looked at carefully as even the 110 gallon tank could get the P-39 further into enemy territory than it could get out. Planes that ditch in the channel are lost.

However this is best case, no allowances for forming up except the no added radius for the climb ( and no, each fighter does not take-off independently and immediately set course for the rendezvous point) no allowance for having to orbit at a rendezvous point. No allowance for weaving.

 

[pbehn]

Gentlemen,
Thought I would add more numbers to the mix. Please find a copy of the Tactical Planning chart, which I believe would be used by USAAF planners when planning a mission. Please note that the date is June 1945. Weights include "Basic" + crew, oil, full ammunition, and fuel, Range and endurance includes
1 Allowances for warm up, taxi, run up, take off and landing (Equal to 10 minutes at max cont at SL)
2 Allowance for fuel consumed in climb. Distance and time are included in range and endurance.
3 Allowance for carrying bomb or drop tank ENTIRE flight.
Allowance for 10% net ideal range and endurance for differences in aircraft, pilot techniques etc.View attachment 487875

Note that flying at max cruise (max continuous operating at lean mixture setting) at 25000 feet is above the ceiling of the aircraft.
It does not appear that the ranges and endurance given include any allowances for combat.

My 2 cents.

Eagledad

All very well but that is just an historical document on the subject, we prefer made up fantasy from self appointed experts on this particular thread. I am of course joking, that is a great document, sorting out the needs of the many for planning from the needs of the individual to get home must have been a nightmare.

 

[wuzak]

Note that flying at max cruise (max continuous operating at lean mixture setting) at 25000 feet is above the ceiling of the aircraft.
It does not appear that the ranges and endurance given include any allowances for combat.

Regular escort altitude is above maximum cruise setting ceiling!

 

[wuzak]

Long range escort was a US requirement that appeared very quickly. The Spitfire could have performed a role similar to the P-47, but it was an allied joint effort.

Spitfires were used as escorts at the start of missions and for withdrawal support.

 

[Milosh]

For comparison with the chart posted earlier on the P-39.

 

[Shortround6]

So basically a P-39 with 120 gallons internal and 75 gallons external can't fly any further than a P-47 with 305 gallons internal, can't fly as fast and above 20,000ft, can't climb as well.

And we wonder why they didn't jump all over it as an escort

I would note that the engine chart for the DB605A as used in the 109 from 1942 on shows around 1100hp at about 25,000ft (7,500 meters) at 2800rpm and around 1000hp at 2600rpm, in a smaller lighter plane. It may have had more drag than the P-39. P-39s at 20-25,000ft ves 109Gs????

 

[pbehn]

The AFDU also did some comparative dog-fighting tests with the Airacobra against a Spitfire VB and a captured Messerschmitt BF 109E. The Airacobra and the Bf 109E carried out mock dog-fighting at 6000 feet and 15,000 feet. The Bf 109E had a height advantage of 1000 feet in each case. The Bf 109, using the normal German fighter tactics of diving and zooming, could usually only get in a fleeting shot. The Bf 109 could not compete with the Airacobra in a turn, and if the Bf 109 were behind the Airacobra at the start, the latter could usually shake him off and get in a burst before two complete turns were completed. If the Bf 109 were to dive on the Airacobra from above and continue the dive down to ground level after a short burst of fire, it was found that the Airacobra could follow and catch up to the Bf 109 after a dive of over 4000 feet. When fighting the Bf 109E below 20,000 feet, the Airacobra was superior on the same level and in a dive.

A similar trial was carried out against a Spitfire V. Although the Airacobra was faster than the Spitfire up to 15,000 feet, it was outclimbed and out-turned by the Spitfire. Unless it had a height advantage, the Airacobra could not compete with the Spitfire. If on the same level or below, at heights up to about 15,000 feet, the Airacobra would have to rely on its superior level and diving speeds and its ability to take negative "G" without the engine cutting out. Above 15,000 feet, the Airacobra lost its advantage in level speed.

 

[Shortround6]

My criticism of this test is that it is against the 109E, which to be fair to the British, was the only airworthy 109 they had at the time and any test was more informative than no test.
But for telling how the P-39 would have fared against the 109F let alone the G it leaves a lot to be desired.

According to William Green (correction welcome) a 109F-0 with e DB601N engine was compared to a 109E/N also with a DB601N engine.
a 360 degree turn could be made in 18 seconds compared to the 109Es 25 seconds at 3280ft. Starting at that altitude 2900ft could be gained in a "combat turn"(whatever that is) compared to only 1970ft by the "E". Initial climb rate was 3,730fpm compared to 3420fpm and 16,400ft could be reached in 5.2 minuted compared to 6.1 min.
Starting in early 1942 (?) the 109F got the DB601E engine which made 30 more PS/HP 1600ft higher than the DB601N.

 

[pbehn]

My criticism of this test is that it is against the 109E, which to be fair to the British, was the only airworthy 109 they had at the time and any test was more informative than no test.
But for telling how the P-39 would have fared against the 109F let alone the G it leaves a lot to be desired.

According to William Green (correction welcome) a 109F-0 with e DB601N engine was compared to a 109E/N also with a DB601N engine.
a 360 degree turn could be made in 18 seconds compared to the 109Es 25 seconds at 3280ft. Starting at that altitude 2900ft could be gained in a "combat turn"(whatever that is) compared to only 1970ft by the "E". Initial climb rate was 3,730fpm compared to 3420fpm and 16,400ft could be reached in 5.2 minuted compared to 6.1 min.
Starting in early 1942 (?) the 109F got the DB601E engine which made 30 more PS/HP 1600ft higher than the DB601N.

It also doesn't mention that which shouldn't be mentioned, the FW190.

 

[drgondog]

Can we agree that at least some of the Ns had 120 gals internal and carried a 110gal drop tank? This is absolutely true.

You have figured out how to figure range/endurance from the pilots manual. 120 gal + 110 gal drop = 230gal less 20 gal reserve = 210 gal divided by 62gph = 3.4 hrs less 15 min combat and 20 min reserve for landing = 2.8 hr x 230mph = 644mi divided by 2 = 322mi radius after reserves. The 230mph is the bomber speed TAS and you are weaving to stay at their speed. Drop tank of up to 175 gal was available for the P-39.

Nope. The P-39N was out of deployment when 110 gallon tanks were a.) manufactured in-theater by Brits/Aussies and b.) the P-47 had priority because they WERE used for high altitude escort.

A drop tank FERRY tank, not self sealing, May have been used to Ferry from point A to Point B but not showing up in any Flight Testing.

Kindly point me to ANY document that states the Centerline rack Ever carried anything heavier that 500 pound bomb?

Last but not least, the P-39 Operating manual charts always express the airframe speeds in IAS - which works in your favor if the chart pointed to 230IAS at 20K - but is states Only without drop tank (75G) does recommended 2200 rpm @24"MP ----------> 200mph IAS ------> 298 TAS at 20K. The latter is a good escort speed but in both ETO, escorting 5K under the bombers is not very useful.

You don't seem to get your head around what you are reading.

Gross weigh at T.O. includes all the fuel, all the ammo, all the consumables, the fixed equipment, the pilot, the centerline rack, the guns, etc UNLESS otherwise stated in the report. The Report will further cite special preparations like taping over shell chutes, wing gun ports, the actual ammo/ballast carried if not max combat load, etc.

A well prepared Test report for speed runs and ROC tests will also state the fuel remaining at the altitudes recorded to give us techie/nerds insight to evaluate the actuals against the Analytics in Flight Performance Calcs . (BTW the P-39 nearly always fell short of Poppa Bell's engineering estimates)

America's One Hundred Thousand by Dean is very rigorous about presenting load outs for 'standard Fighter (less than full load out - but specificity in the actual load and weights) 'Overload fighter' (Full Internal Load), 'Fighter Bomber' (load out when carrying bombs or external fuel tanks').

In my own research in which I have the airframe specs from factory for Empty, Basic (w/GFE and other related weights such as residual fuel/oil remaining after mission that is not easily recoverable post flight for 'empty tanks, guns, racks') and the above mentioned load outs which are useful load items - the weights are accurately reproduced.

Weight and Drag increments are Essential reported items when Range, Climb and top speeds for given altitudes and throttle settings - and often insert Horsepower ratings per the manufacturer at those settings and altitude. A Professional report will further reduce the speed data as a function of Mach Number, Standard Temp and Pressure vs altitude.

ROC is inversely proportional to Gross Weight and proportional to the difference between Power Available less Power Required. Excess Power = Thrust x Velocity - Drag x Velocity ----------> strip weight and climb increases, add drag and climb decreases, run out of excess power and climb ceases (so to constant altitude turns.

 

[Shortround6]

Getting back to the British and why they didn't want the P-39, the first (and last) operational flight of the P-39/Aircobra I in British service was Oct 9th 1941.
The Germans had introduced the 109F back in March/April on the Channel coast and the first Fw190s were being service tested in July. The British had a pretty good Idea of how these aircraft stacked up against the Spit V and a good idea how the Spit V stacked up against the Aircobra I. They knew the Aircobra I (P-39D) wasn't going to work against either of them in the style of fighting (tactics) the British were using at the time.

 

[pbehn]

Getting back to the British and why they didn't want the P-39, the first (and last) operational flight of the P-39/Aircobra I in British service was Oct 9th 1941.
The Germans had introduced the 109F back in March/April on the Channel coast and the first Fw190s were being service tested in July. The British had a pretty good Idea of how these aircraft stacked up against the Spit V and a good idea how the Spit V stacked up against the Aircobra I. They knew the Aircobra I (P-39D) wasn't going to work against either of them in the style of fighting (tactics) the British were using at the time.

Ive just read that there were 4 "missions" two found no targets and the other shot up a trawler, the most involved were three aircraft one time. Initially at least they were taken off operations because of compass problems.
quote
By the end of September, No. 601 Squadron had received permission to take its Airacobras into action. On October 9, two Airacobras took off from RAF Manston and flew across the Channel on a "rhubarb"--a code name for a small-scale raid by fighters against targets of opportunity. On this raid, they shot up an enemy trawler near Gravelines. The next day two Airacobras visited the same area, but found no targets. On October 11, two aircraft flew to Gravelines and Calais and hit some enemy barges and then three Airacobras flew to Ostend, but no targets were found.

After these four missions, the RAF Airacobras were taken off operations because of difficulties encountered with the compass. The compass was too close to the guns in the nose, and when the guns were fired, the compass got thrown out of alignment. Deviations of anything from 7 degrees to 165 degrees were recorded. Without a reliable compass, pilots tend to get themselves lost. In December of 1941, the Airacobra was officially withdrawn from operational service with the RAF.