SHOULD the P39 have been able to handle the Zero? Was it training or performance?

[tomo pauk]

....
Germans claim only 2-4mph loss for a pair of gondolas with 20mm guns under the 109's wings.
...

Seems like the Bf 109G (early types, with cowl 2 LMGs) were loosing 8 km/h (5 mph) if MG 151/20 gondolas were installed, but, interestingly enough, just 6 km/h with mock-ups of MK 108 gondolas. However, Soviets measued up to 19 km/h difference, with vs. without gondolas.

 

[Shortround6]

The early P-47 manual is conflicted.
PRACTICE SPINS IN EXCESS OF 1/2 TURN ARE PROHIBITED.
It is in full caps in the manual, however it says that the pilot should use the recommended control settings for spin recovery for 3 full turns before trying any other combination of control settings.
Snap rolls are not recommended and should never be performed above 150mph IAS.

 

[Shortround6]

I don't know about US training but if you cant do a snap roll in training what do you do if the guy you want to shoot down does? Setting height, speed or load limits isn't the same as a prohibition.

A lot of this stuff is to keep pilots from killing themselves.
P-47 manual says it needs 1000ft to enter a spin, it needs 1000ft to recover and it loses 1000ft per turn with the flaps and landing gear up and the canopy closed. It says it loses 3000ft per turn with the landing gear down, flaps up. no mention of canopy?

Please remember that the US was losing a large number of pilots in training, many due to doing young and dumb things.
Trying to cover every possible combination of weights and loadings in a short manual was impossible. What you might be able to do with the fuel tanks near empty and with the CG at point X could well be fatal with nearly full tanks and a CG of Y.

 

[Shortround6]

The FM-2 Wildcat was not permitted to do normal spins or prolonged spins with one or more droppable fuel tanks.
Without tanks it was allowed to do all standard maneuvers.
Please note the original F4F was tested by spinning both 10 turns to the right and 10 turns to the left. Two turn inverted spins were also done to both the right and left.

 

[DarrenW]

No reduced fuel. If that P-39N had only 87 gallons then it would be only 33 gallons light x 6 pounds/gallon or 198# lighter. The N weighed 7650# loaded with 120 gallons internal, the cannon plus 2 .50 caliber machine guns and 4 .30 caliber wing guns and ammunition, and a 200# pilot with parachute. 7650# less half fuel (60 gal or 360#) resulting in an average weight for that flight of 7290# vs the listed weight of 7274#. Off by 16#. Same for the official performance tests (not different propeller tests etc) of the P-38, and P-47. Look it up.

Regarding facts, I am quoting the facts from the official government tests.

So you're still hung up on that whole "average" weight thing I see. For your opinion to hold any water the test report author couldn't have been the brightest bulb on the tree. "Gross Weight at take-off" means the total weight of aircraft at the moment the wheels left the runway, not average weight during the entire flight. Look up the definitions. I'm not making this sh--t up!!!

 

[Shortround6]

Seems like the Bf 109G (early types, with cowl 2 LMGs) were loosing 8 km/h (5 mph) if MG 151/20 gondolas were installed, but, interestingly enough, just 6 km/h with mock-ups of MK 108 gondolas. However, Soviets measued up to 19 km/h difference, with vs. without gondolas.

The thing with the P-39 is that you were yanking 2 guns out of each wing

This is a dummied up installation for a Museum on a P-39Q.
and you had two chartridge slots in the bottom of the wing.
And replacing them with the podded .50 cal.
Both the 109 and Mig 3 had nothing coming out or any holes covered over.
The under wing pods could very well have had more drag than the .30 cal installation. But we have no figures on how much drag was saved by pulling and covering the .30s and we have no real figures on a P-39Q with and without pods.

Edit, better picture.

 

[Glider]

The early P-47 manual is conflicted.
PRACTICE SPINS IN EXCESS OF 1/2 TURN ARE PROHIBITED.
It is in full caps in the manual, however it says that the pilot should use the recommended control settings for spin recovery for 3 full turns before trying any other combination of control settings.
Snap rolls are not recommended and should never be performed above 150mph IAS.

There are many examples of Pilots notes being on the cautious side. On three occasions I have spun a Hunter T8 where the pilots notes state that intentional spinning is forbidden, the notes also tell you what to do in a spin and she behaved perfectly.

 

[Graeme]

Any sales agent worth his salary/commission should have been able to at least estimate any performance penalties from extra equipment and have written in suitable adjustments to the performance penalty/cancellations sections of the contract.

Does the original RAF/Bell contract (worth 9 US million?) still exist somewhere? Love to read it.

 

[DarrenW]

It would seem that snap rolls weren't considered too dangerous to perform in the F6F, as their is no mention of them in the maneuver restriction section of the pilot handbook that I have:

 

[pbehn]

Spitfire instructions are sections 12 and 13 in this pdf.

 

[wuzak]

The P-39N pilots manual is not online, or at least I can't find it. I can find manuals for the K/L and the Q.

This chart is from the P-39K which was equipped the same. Empty weight 5658# including radios, oxygen equipment and fluids. The third column shows normal gross of 7648# including 120 gallons of fuel, oil, guns, ammo, armor plate and glass, and a 200# pilot with chute. First column is with a 75 gal drop tank, second column is with a bomb. Most all P-39s weight chart looked like this.

Interestingly, that chart shows the 120USG internal fuel is divided into 104USG normal and 16USG overload.

 

[DarrenW]

Climb with tank is not shown on P-39N test, so I don't know for sure.

The graph below is for the P-39K and is representative of the earlier P-39s (D,F,K and L) with the 8.8 supercharger gears and weighing approximately 7650#. As you can see, the dotted line is with belly tank, the solid line is without. This indicates a 300-350fpm lower climb rate with the tank.

Also please notice the curved line between 12500' and 15000'. That represents the point at which the pilot decreased rpm from 3000 (max) to 2600 (max continuous or max cruise) after the 5 minute mark complying with the time limit for those earlier engines. This reflects a substantial decrease in climb rate due to the lower HP for 2600rpm. The heavy dashed line at each 5000' interval is my estimate of climb after the five minute limit was increased to 15 minutes in mid '42. Just for fun.

Also notice the "SECRET" stamped in the upper right corner. View attachment 487690

Hey wait a minute, the chicken scratch on that graph looks eerily familiar..... lol!

 

[Elmas]

Seems like the Bf 109G (early types, with cowl 2 LMGs) were loosing 8 km/h (5 mph) if MG 151/20 gondolas were installed, but, interestingly enough, just 6 km/h with mock-ups of MK 108 gondolas. However, Soviets measued up to 19 km/h difference, with vs. without gondolas.

The problem was not (only) the drag and loss of speed. The problem was that these two weights very far from the CoG augmented substantially the Momentum of Inertia, damaging quite a bit manoeuvers around longitudinal axis.

 

[Shortround6]

The problem was not (only) the drag and loss of speed. The problem was that these two weights very far from the CoG augmented substantially the Momentum of Inertia, damaging quite a bit manoeuvers around longitudinal axis.

There were a number performance problems with the under wing gondola on the Bf 109. Loss of climb being one of them in addition to the loss of roll rate (or loss of roll acceleration/how fast a roll could be started), both being more important than the loss of speed.
In the case of the P-39 however they were yanking out 50lbs worth of .30 cal guns and 36lbs worth of ammo and replacing it with a 75lb gun and 90lbs worth of ammo. about and 80lb increase (not including weight of the pod) on each side. The Germans were adding about 150lbs not including the pod to each side. P-39 already had some weight in the wings (fuel tanks ) so the percentage change is not as great. Likewise on a percentage basis, the P-39 was a lot heavier than a 109, the weight of the .50s on the P-39 should not affect climb to the extent the under wing pods did to the 109.

 

[drgondog]

Would this indicate no pressurization of the drop tank?

Milosh, IMO - yes. That said, a field mod to tap from instrument vacuum system was common - in mid to late 1943. That said, by that time there was not a high altitude requirement for the P-39 and the first Field mods were by Cass Hough in VIII AF ATS for the P-47C/D, then P-51B-1 for external combat tanks.

 

[Shortround6]

When trying to figure out the weights of some of the test aircraft we have to be careful of some of the minor and not so minor changes between some versions that sometimes are not important enough to make short lists.
A change in the Aircobras was the propeller shuffle. We have a handle on the difference between the Aero Products prop and the Curtiss prop used on the K and L (and earlier aircraft) finding weights for the later propellers is harder, I don't have any but an 11'7 prop is not going to weigh the same as a 10'3" prop. a minor detail is that at some point they changed nose wheels.

P-39K (?) it is what the caption says with balloon Front tire and small wheel.

P-39N with a low profile tire and bigger wheel.
Maybe they weighed the same and maybe they didn't?
I would work back from the "Q" when figuring weights for the N rather than working forward from the K & L.

 

[pbehn]

A lot of this stuff is to keep pilots from killing themselves.
P-47 manual says it needs 1000ft to enter a spin, it needs 1000ft to recover and it loses 1000ft per turn with the flaps and landing gear up and the canopy closed. It says it loses 3000ft per turn with the landing gear down, flaps up. no mention of canopy?

Please remember that the US was losing a large number of pilots in training, many due to doing young and dumb things.
Trying to cover every possible combination of weights and loadings in a short manual was impossible. What you might be able to do with the fuel tanks near empty and with the CG at point X could well be fatal with nearly full tanks and a CG of Y.

Perhaps this is just a question of progression in training. Almost every activity requires people to learn the basics before going on to more advanced "stuff".
From the attached US pilots spent ten weeks each on basic, advanced, advanced single engine, fighter transition and finally operational training and fighter transition this was changed during the war but I presume there was some time when pilots were told to stop "flying by the book" and learn how/when the rules could be broken.

https://www.quora.com/How-many-hour...required-of-Allied-pilots-during-World-War-II

In the RAF pilots flying a Spitfire needed the permission of their C/O before performing spins regardless of whether they had their "wings" or not, which is similar in principle to the above.

 

[P-39 Expert]

So you're still hung up on that whole "average" weight thing I see. For your opinion to hold any water the test report author couldn't have been the brightest bulb on the tree. "Gross Weight at take-off" means the total weight of aircraft at the moment the wheels left the runway, not average weight during the entire flight. Look up the definitions. I'm not making this sh--t up!!!

No, you are not making this up. See the post you replied to. If as you say this P-39 had only 87 gallons, then the weight would be reduced by only 198# (33x6).

 

[P-39 Expert]

When trying to figure out the weights of some of the test aircraft we have to be careful of some of the minor and not so minor changes between some versions that sometimes are not important enough to make short lists.
A change in the Aircobras was the propeller shuffle. We have a handle on the difference between the Aero Products prop and the Curtiss prop used on the K and L (and earlier aircraft) finding weights for the later propellers is harder, I don't have any but an 11'7 prop is not going to weigh the same as a 10'3" prop. a minor detail is that at some point they changed nose wheels.
View attachment 487800
P-39K (?) it is what the caption says with balloon Front tire and small wheel.
View attachment 487801
P-39N with a low profile tire and bigger wheel.
Maybe they weighed the same and maybe they didn't?
I would work back from the "Q" when figuring weights for the N rather than working forward from the K & L.

The "Weight and Balance Chart" for the P-39K that I posted earlier was one page before the chart for the P-39L, shows a difference of 50# from the K so I would guess that was the difference in the two props. The only real differences in any of the P-39 models were propellers, (different versions of the same) engines (incl. reduction gears), radios and wing guns.

The front "balloon tire" was on all the P-39s (D,F and K) until the L (and M,N and Q) switched to the slimmer tire.

 

[DarrenW]

Yes, but we never determined what the "official" normal loaded weight of a P-39N-1 truly was. And besides this, how would any of us here really know for sure what equipment was removed or added for that particular flight on 17 October 1942? All we have to go by is what is stated in the report. Gross take-off weight means just that - the weight of the machine at take-off. That's not the same as average weight, which is calculated after the flight is finished.