P-38 Lightning vs P-51 Mustang: Which was the Better Fighter?

If P-51Bs were in England by August 1943, why is it they were not in action until December 1943..? Makes very little sense, Mustangs napping in England while B17s and B24 getting butchered over Schweinfurt and Ploiesti..

Kurfürst said:

If P-51Bs were in England by August 1943, why is it they were not in action until December 1943..? Makes very little sense, Mustangs napping in England while B17s and B24 getting butchered over Schweinfurt and Ploiesti..

Click to expand...

During that period the aircraft were assembled, test flown, deficiencies corrected, mods completed and then eventually turned over to squadrons who began training - could this have been done quicker? Possibly. Was it prudent to work in this manner, yes - and I think the end results are evident.

Kurfurst .....

Just as the Germans had "political" problems, the USAAF also had theirs.

For them to use long range fighters in the summer of 1943, would have been an admission of the failure of the doctrine of unescorted bombing bringing about victory.

Too many generals reputations were on the line at that time.

And untill massive losses were inflicted, the doctrine wasnt going to chnage.

And IIRC P-51Bs went first to 9th (tactical) AF. After the heavy bomber losses they were, 354? FG, allowed to protect 8th AF heavy bombers and eventually switched to 8th AF which gave one of its P-47 Groups to 9th in the bargain. Or something like that.

FLYBOYJ said:

During that period the aircraft were assembled, test flown, deficiencies corrected, mods completed and then eventually turned over to squadrons who began training - could this have been done quicker? Possibly. Was it prudent to work in this manner, yes - and I think the end results are evident.

Click to expand...

Dead on. They had designated a whole new Service group and some time was spent training to assemble, put on the wings and tail, etc as well as familiarize ground crews for engine changes, etc.

..and while the first P-51B-1 left the factory for England in late August, the first batch was shipped by sea IIRC and were not assembled and ready to go until late October. The 354th FG started their familiarization with A-36's in early November and the real thing in mid November.

There were a lot of nagging issues with the radios and coolant leaks, etc which delayed full group deployment until just before theri first combat ops under Blakeslee on Dec 1, 1943

Juha said:

And IIRC P-51Bs went first to 9th (tactical) AF. After the heavy bomber losses they were, 354? FG, allowed to protect 8th AF heavy bombers and eventually switched to 8th AF which gave one of its P-47 Groups to 9th in the bargain. Or something like that.

Click to expand...

True and immediately subordinated under Kepner until May 1944, along with the 363rd FG which started ops in February, 1944.

The 8th AF 'swapped' the combat ready 358FG (P-47s) for the 357FG (great trade) to get its first Mustang Group also in February, 1944

syscom3 said:

Her dad remembers seeing a P38 in a power dive crash right off of Palos Verdes. he saw a parachute but never found out what happened to the pilot. he said the scream of that plane was a sound few people can ever forget.

Click to expand...

The first generation p-38s were prone to air compressability problems which rendered controls useless in excessive-speed dives. Air brakes were fitted to later models to correct this. This is probably the cause of the power dive crash your dad witnessed.

There is a passage in Spike Milligans war memoirs where a P-38 pilot was 'showing off' over the British soldiers in Italy during 1943 and Milligan shook his fist at it shouting "I hope you bloody well crash!" at which the Lightning dived straight into the ground.

This became known as the 'Milligan Plane Curse', but only briefly, as when he tried it again on a Bf 109 it let him down

Hi Welch,

>Which was the better fighter?

Since I have generated the data anyhow for some other threads, here is a performance comparison ...

Regards,

Henning (HoHun)

P-51 is the best fighter ever, except for the Dora.

Thanks Ho Hun for the graph. The planes seem pretty well matched.

The P-38 did have a great zoom climb.

HoHun said:

Hi Welch,

>Which was the better fighter?

Since I have generated the data anyhow for some other threads, here is a performance comparison ...

Regards,

Henning (HoHun)

Click to expand...

Which dash number J are you using? The P-38J-25 had the manuever flaps, the boosted ailerons, and the improved performance due to cooling modifications - making this the fastest, the best rolling, best turning version of all the P-38s.

Mike Williams test reports on the J's are for -1(5/43), -10(10/43), -15(7/44) and P-38L-5 (11/45). If you wish to use the top performing P-38 the P-38J-25 was a couple of hundred pounds lighter than the P-38L-5 with same engine performance, same boosted ailerons, same manuver flaps.

Equally the P-51B (either -5 with 1650-3 Merlin for high altitude optimization or 51B-10/15 with 1650-7 Merlin for low to medium high altitude optimization would be a better choice against the P-38J-25 (or P-38L) based on period introduced into combat

How did you perform your turn performance calculations when you need to account for a.) NACA 23016 airfoils (inboard) with an 8 degree fowler flap in manuever, b.) a NACA 4412 airfoil outboard of the nacelles, and c.) improved roll due to boosted flaps.

If you did not account for these factors, your results for turn performance are very questionable. Ditto climb and top speed for 'best versus best' of combat Mustangs and Lightnings.

drgondog said:

How did you perform your turn performance calculations when you need to account for a.) NACA 23016 airfoils (inboard) with an 8 degree fowler flap in manuever, b.) a NACA 4412 airfoil outboard of the nacelles, and c.) improved roll due to boosted flaps.

Click to expand...

a) You don't have to care about airfoils. All you need to know is power on stall speed at known weight and altitude, flaps up or down. The P-51 had combat flap setting also.

b) see a)

c) Calculation is for sustained turn rates. Banking into turn (where roll rate and inertia comes into play) is a different matter altogether.

Incorrect. Basing turn performance on stalling speed is very misleading. If we were to do so then the Bf-110 B-17 were excellent turn-fighters, both having a stalling speed below that of many fighters. So do you believe they were great turn fighters ?

Timppa said:

a) You don't have to care about airfoils. All you need to know is power on stall speed at known weight and altitude, flaps up or down. The P-51 had combat flap setting also.

Timppa - not true in this case for the reasons I stated. In the case of the P-38J-25 for example, you not only have two airfoils to look up for Clmax but also note that the Clmax for the 23016 with 8 degrees of manuevering flap deployed is CONSIDERABLY more than for the NACA 4412. Sooooooo - how do you calculate and plug 'CL' for the Entire wing into your induced drag calcs?

c) Calculation is for sustained turn rates. Banking into turn (where roll rate and inertia comes into play) is a different matter altogether.

Click to expand...

Correct and irrelevant to my questions - the improved roll rate was only my way of illustrating that the P-38J-25 and beyond not only had good sustained turn rates but could, in reality, play in the horizontal for real - insted of a flight test entering into a turn in one direction and staying there.

drgondog said:

Timppa - not true in this case for the reasons I stated. In the case of the P-38J-25 for example, you not only have two airfoils to look up for Clmax but also note that the Clmax for the 23016 with 8 degrees of manuevering flap deployed is CONSIDERABLY more than for the NACA 4412. Sooooooo - how do you calculate and plug 'CL' for the Entire wing into your induced drag calcs?

Click to expand...

Cl = L / (A * .5 * r * V^2)
Clmax = L / (A * .5 * r * Vstall^2)

L=W at stall speed
It is actually hard me to believe that you don't know this already. You really dont need to know the airfoils when you know the stall speeds.

Timppa said:

Cl = L / (A * .5 * r * V^2)
Clmax = L / (A * .5 * r * Vstall^2)

L=W at stall speed
It is actually hard me to believe that you don't know this already. You really dont need to know the airfoils when you know the stall speeds.

Click to expand...

I do know this.

L=W at all speeds to maintain the same altitude. For turning flight it is the lift vector in the opposite direction from the gravitational weight vector - and hence a function of the bank angle.

I have a problem with your simplistic approach to CLmax when discussing this P-38 with manuevering flap model - unless you KNOW what Clmax is for the P-38 with manuevering flaps deployed. I have not found these values for the P-38 with just manuevering flaps deployed in either power on or power off level flight. All I have seen are stall values in Level flight for a.. ) clean, and b.) full flap deployment conditions.

If you have it (Vstall with manuevering flap (only) deployed) then your approach is a very good place to start but you also need the drag contribution for the free body force model.

If you don't, then here are some issues.

Namely 1.) where can you find CLmax values for the NACA 23016 airfoil with fowler flap at 8 degrees deflection (my copy of Theory of Wing Sections - Abbot and Doenhoff, didn't have it), and 2.) how are you going to factor in all additional parasite/trim drag for a high turn manuever (different for level approach landing) including the significant addition of drag due to the deployed flap?


Absent the data there is an approach but I am not sure how elegant it would be
For the calculated analytical pre-design approach having only airfoil section/flap data (no wind tunnel or flight test data) you have to look at the NACA 23016 airfoil, the NACA 23016 w/fowler flap, and the NACA 4412 data and ask a couple of questions.

First questions - Are they both going to stall at the same time in a turn? Independent of which stalls first (hopefully inboard), will the actual stall break point be the same for high G turning flight as it proved in level flight? The two engine/two wing section model is more difficult to analyze.

If not, where this AoA occurs to cause one or the other part of the wing to stall is a major 'point' of interest.

Second question - given the assymetrical forces on the P-38 in a turn versus the same wing/flap config in a level flight condition, how much parasite drag is added to that particular summation of level flight CDinduced and CDparasite force balance to result in an increase in stall speed - and how many less degrees AoA will that be? The known factors to increase the parasite drag over level flight are the rudder trim drag, the elevator trim drag, the aileron trim drag.

The wild card is change of spanwise and chordwise velocity vector changes - particularly around wing/boom area - which affect Lift/Drag how in comparison to say a 109?

CLmax as a function of AoA for a specific airfoil may be found in the sectional plots, then extrapolated from 2 D to 3 D by taking into effect AR and form factor or it may be obtained in flight tests under controlled conditions - but published CLMax for your example under those conditions are usually obtained for a.) LANDING conditions, or b.) level flight clean stall - power on and off.

Now that we have that behind us - lets go back to manuevering flight with the P-38J-25/L with Manuevering flaps deployed?

1. So, what is Vstall in level flight for the P-38 with maneuvering flaps deployed (only-not in landing configuration with full flaps) and how do you know this? I have not been able to find a source on this and that is why I asked the question. If it isn't available from a reliable source it has to be calculated.

2. What is the induced drag and parasite drag increase in value at say 250kts (or 300 or 220) when the manuevering flap is deployed in a minimum radius and/or max turn rate turn? Assume power required does not fall below power available for the model.

3. What is the total drag of the P-38 at each step in the velocity profile as either the bank angle changes or speed changes as the 38 bleeds energy and trim drag increases with rudder and elevator deflections?

Granted, this discussion does not need to be as complicated when the P-38 is clean as reasonable extrapolations are obtainable by published flaps up/flaps down data for stall speeds for a particular weight and power on/power off condition.

To repeat - I have not been able to find the P-38 wind tunnel or flight test data to get just the level flight Clmax for deployed manuevering flaps. If that were available then your second equation would be a good place to start to figure out where in the turn the P-38 could turn no tighter/faster.

Do you have these handy? If you do, then you have what you need to do this model.

There is a lot of good detail here but the real question is how does Henning do his calculations. He is the one who is quick to produce the charts for this and other threads and must do some calculations to arrive at those charts but no one knows how he does them.

Glider said:

There is a lot of good detail here but the real question is how does Henning do his calculations. He is the one who is quick to produce the charts for this and other threads and must do some calculations to arrive at those charts but no one knows how he does them.

Click to expand...

There is that.

One has to start with Thrust = Drag to maintain equilibrium for a stated condition. For level flight L= Weight.

Looking to various flight test docs, published data sheets etc will get you conflicting info but if you have the following:

Velocity at a specific Hp/Boost condition then you can obtain Thrust.

CDo (Parasite drag for level flight), then you can combine with Thrust and Lift to arrive at Total Drag (Induced and Parasite)

When you have that you can start with Power available versus Power required to test whether Thrust available is adequate to maintain equilibrium in the model.

The tricky parts are that a.) you must have the available HP at the altitude you are modelling for (not a constant) and Hp is density/altitude related, b.) the Cl max will be tested at low airspeds/high AoA as the bank angle increases and the Lift must be adequate to offset the weight (always vertical), c.) the change to drag components (induced drag increases in contrast to parasite drag at lower speeds, opposite in higher speeds) and as elevator and rudders deflect in a high G turn, their individual drag components change from level flight conditions.

Soren and I used to go round and round on the importance of each factor but he understands they are present.

So, as you have noted in your usual razor sharp questions - where is the HoHun's math?

Gene Davidson (Crummp) definitely knew what he was talking about. I quit screwing around because too many factors like reliable HP to altitude and Boost charts aren't 100% available for all the ships that everyone wants to compare, nor is Cd0 and now in the question of the P-38J-25/P-38 L, is the actual ClMax for the wing/manuevering flap data available. Trim drag is another tricky factor - and a potentially major one for high g/large deflection turns.

As usual Glider, you put your finger on the sore spot.

drgondog said:

I have a problem with your simplistic approach to CLmax when discussing this P-38 with manuevering flap model - unless you KNOW what Clmax is for the P-38 with manuevering flaps deployed. I have not found these values for the P-38 with just manuevering flaps deployed in either power on or power off level flight. All I have seen are stall values in Level flight for a.. ) clean, and b.) full flap deployment conditions.

Click to expand...

Check this link

The Math Behind Turning