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

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pbehn said:
After combat, can you land and put the tank back on, to keep your combat radius? I am thinking outside of the box here.
Click to expand...

You could always link up with a KB-50 and top off to get home. I mean, if we can time-machine P-39 models, certainly we can time-machine aerial refuellers. Maybe remove the cannon in the spinner and replace it with plumbing to get the groundhog home?
 
Thumpalumpacus said:
You could always link up with a KB-50 and top off to get home. I mean, if we can time-machine P-39 models, certainly we can time-machine aerial refuellers. Maybe remove the cannon in the spinner and replace it with plumbing to get the groundhog home?
Click to expand...
Problem is, the KB-50 cruises at about 245 miles an hour.
The illustrious P-39 would have to step up their game to get in behind the tanker (while being slapped bat-sh!t silly by the wake) and make a connection.


Of course, there's obviously only one person who could pull it off and we're blessed to have him in our midst...
 
The "expert" doesn't seem to grasp that the drop tank is immaterial.
Hang a 110 gallon tank on the P-39 and you might wind up in place you can't get home from.

You are down 10-15 gallons of internal fuel after warm up, take off and climb to safe height to switch tanks.

Now what is critical is how much fuel is remaining in the the internal tanks after 15-20 minutes of combat and allowing for a 30 minute reserve.

That is the fuel available for egress from the combat area.

what was in the drop tank is smoke and mirrors.

Give him the 120 gallon fuel capacity, he is down to 105-110 when the tank (of whatever size ) is punched off. The P-39 with a tank attached is just a target for the Luftwaffe fighters.
30 minute reserve to get home is around 15 gallons. Down to 90-95 gallons.

Now the much debated combat allowance.
If the P-39s can defend the bombers by flying straight and level for 20 minutes they just might squeak out just over 30 gallons of fuel used in "combat".

If they have to do anything else, like turn, then the bets are off and the P-39s will not be able to stay at 25,000ft. The lower it goes the more fuel per minute it burns.

Unfortunately some of the P-39 charts are sheer nonsense. Both the take-off an climb charts and the range charts.

However the P-39 and other aircraft "fight operation instruction chart/s" do have a phrase/sentence that the "expert" has completely over looked.

In the box near the top that says "instructions for using chart" when you get to the notes, note "A" says...

"AVOID CONTINOUS CRUISING IN COLUMN 1 EXCEPT IN EMERGENCY"

The "expert's" entire flight plan except for landing is based around continuous cruise in Column 1 conditions.
 
Shortround6 said:
The "expert" doesn't seem to grasp that the drop tank is immaterial.
Hang a 110 gallon tank on the P-39 and you might wind up in place you can't get home from.

You are down 10-15 gallons of internal fuel after warm up, take off and climb to safe height to switch tanks.

Now what is critical is how much fuel is remaining in the the internal tanks after 15-20 minutes of combat and allowing for a 30 minute reserve.

That is the fuel available for egress from the combat area.

what was in the drop tank is smoke and mirrors.

Give him the 120 gallon fuel capacity, he is down to 105-110 when the tank (of whatever size ) is punched off. The P-39 with a tank attached is just a target for the Luftwaffe fighters.
30 minute reserve to get home is around 15 gallons. Down to 90-95 gallons.

Now the much debated combat allowance.
If the P-39s can defend the bombers by flying straight and level for 20 minutes they just might squeak out just over 30 gallons of fuel used in "combat".

If they have to do anything else, like turn, then the bets are off and the P-39s will not be able to stay at 25,000ft. The lower it goes the more fuel per minute it burns.

Unfortunately some of the P-39 charts are sheer nonsense. Both the take-off an climb charts and the range charts.

However the P-39 and other aircraft "fight operation instruction chart/s" do have a phrase/sentence that the "expert" has completely over looked.

In the box near the top that says "instructions for using chart" when you get to the notes, note "A" says...

"AVOID CONTINOUS CRUISING IN COLUMN 1 EXCEPT IN EMERGENCY"

The "expert's" entire flight plan except for landing is based around continuous cruise in Column 1 conditions.
Click to expand...

On the other hand, the Groundhog can tunnel home and bombers be damned.
 
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P-39 Expert said:
You went to a whole lot of trouble to quote combat radius on 87gal internal and a 75gal drop tank. All P-39s would hold 120gal internal and carry a 110gal drop tank, same as what was at the fighter bases in east England.

And don't climb to 25000' at combat setting (careful, Flyboy doesn't know what that means, he can't find it quoted anywhere), use the ferry setting so that it takes you 31min and you don't burn up your engine. And you will have traveled 110mi (170IAS average = 220mphTAS). But don't figure that into your range because you may not be heading to your target.

Learn how to use the Flight Operation Instruction Chart (range chart). It doesn't include any figures from the Takeoff, Climb and Landing chart. Total fuel 230gal, less takeoff and climb reserve 20gal, 20min combat at 25000' 25gal, and 20min landing reserve 10gal leaving 175gal. Divide that by 62GPH = 2.8hrs flying time x 267mphTAS = 748mi. Divide by 2 for radius 374mi. Warmup and takeoff on internal, switch to drop tank as soon as gear/flaps are up and climb speed is reached. Simple form up as lead pair take a wide turn to target vector and the 7 following pairs make progressively narrower turns to form up the 16 plane squadron and vector to target. Cruise starts even before the 20gal T/O/Climb allowance has gotten you to 5000' as your climb to 25000' is on target heading. Drop tank fuel 90gal (110gal less 20gal T/O reserve) gets 387mi (90 divided by 62gph = 1.45hrs x 267mph). When the drop tank runs dry switch to internal and start home. If combat occurs and the drop tank is dropped before it is empty then combat radius will be shorter, just like any fighter carrying a drop tank. If combat occurs just as the drop tank runs dry then deduct combat allowance 25gal and landing reserve 10gal from the 120gal internal fuel (85gal left) and come home at 330TAS (85 divided by 62GPH = 1.4HR x 330mphTAS = 452mi).

Learn how to use the correct chart, it's much easier to use and more accurate.
Click to expand...

I think it is best for you to show your workings graphically.

That is, post pictures of the chart your using and highlight the sections where you source your numbers.

PS you assume that the P-39 has 120 USG of internal fuel, when most of later models had only 87 from the factory. There were kits to bring them back up to 120 USG, but how many were made and installed. But how did that effect weight and performance?

Sure, if they were going to be used for escort they would likely get the extra tankage.

I think there was on squadron sent to Britain as part of the 8th FC, but they quickly swapped them for Spitfire Vs. What were they thinking?
 
FLYBOYJ said:
And in most cases not flying over 5000'
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I think he very much plans to fly at 25,000ft, he just doesn't explain how his planes get there :evil4:

His whole premise seems to be built around the speed in the chart the P-39 (without drop tank) can fly while the engine gasps for air at 25,000ft.
If he drops to 20,000ft the plane is slower and burns more fuel per hour and at 15,000ft the plane is slower yet while burning 66% more fuel per hour than 25,000ft.
 
Shortround6 said:
I think he very much plans to fly at 25,000ft, he just doesn't explain how his planes get there :evil4:
Click to expand...
Exactly! :evil4:](*,)
Shortround6 said:
His whole premise seems to be built around the speed in the chart the P-39 (without drop tank) can fly while the engine gasps for air at 25,000ft.
If he drops to 20,000ft the plane is slower and burns more fuel per hour and at 15,000ft the plane is slower yet while burning 66% more fuel per hour than 25,000ft.
Click to expand...
I think we both know by now that there are errors in those charts, this was mentioned several times during this ordeal but there is some data that is somewhat useable. What is interesting to compare some of the chart information against the performance tests at P-39 Performance Tests, but I think you have mentioned this pages ago.

But I think our friend will only bring that up if it enforces his arguments!
 
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