Lockheed P-38 Lightning - Design Study

[Ivan]

The Cowl area was modified over the last few days and along with the Exhaust Plenum and Canopy Frame pretty much concludes the planned modifications to build a P-38F.

The conversion considerably reduced the Parts count in AF99; The F model is at 1127 Parts which is almost 50 below that of the J model.
Most of the difference is in the Coolant Radiators but the Cowl area is also much lower. Both are also much lower in complexity.

One of the most difficult Parts to build was the Intake Opening for the Oil Coolers which needed a lot of adjustment to match the bottom of the Cowl.

- Ivan.

 

[aleatorylamp]

Hi Ivan,

Looks like this project is coming along very nicely indeed! Your intuitive "eyeballing" definitely looks accurate, and as always, I´m impressed by your admirably clean clean construction technique.
I´m also looking forward to the future section of your P-38 tutorial when it comes to texturing it, for more details on how to divide texture bitmaps for use on more than one part.
So far, I have had success in using only 1 texture instead of 4, for biplane wings with roundels on upper-top and lower-bottom wings only, by using convenient sections of the bitmap. I have also done this on triple fins with roundels only on the outer sides of outer fins, with only 1 texture instead of 3. However, a different matter is combining 1 texture bitmap for wheels facing sideways and 2 pilot´s heads facing in opposite directions, which I haven´t figured out yet. Anyway, further development on the Lightning will definitely be interesting!

Incidentally, re. our previous comments on twin-boom/twin-fuselage types: Maybe as the P-38 has its engines on each boom/fuselage, it would qualify as a twin-fuselage rather than a twin-boom! Thus, a twin-boom would then be one with a single engine on the central cabin-pod, which would then be called the fuselage...

At the moment I´ve resumed construction of the Curtiss-Wright AT-9 Jeep, and I was wondering if I could use your Lightning .air file to adapt it to the dimension and power specifications of the Jeep.
It was rather hotrod, and I´ll be opening a separate thread for its construction and its impressive yet unstable flight dynamics, for which I will need some assistance on your part, if you would like to participate!

Have a nice Sunday!
Cheers,
Aleatorylamp

 

[Ivan]

Hello Aleatorylamp,

Actually the texturing on the Lightning was done some time ago starting at Post #72.
That is how it changed from multi-coloured to a uniform light gray.
Even the significant mapping scales I used are shown in the posts following.
Panel Lines are just another paint job and I really hate doing those, so that may take a while.
That is also why I chose to rework the model to a P-38F instead of doing any painting.

Smilo might have wondered why I didn't use the Lightning as a texturing tutorial subject.
The simple reason is that the Lightning is a horrible subject for a texturing tutorial because it doesn't encourage or reward a consistent texturing scheme.
If you look at how many pieces of the Lightning have paint detail or panel lines that extend across multiple pieces, the answer is "almost none".
The only area I can think of that requires a matching scale is the front and rear halves of the Nacelle and that isn't even a strict requirement.
There are no patterns that go from one Boom section to another and although I textured them to a common scale, I didn't need to and it will never show.
It is just a consequence of my obsessive nature and there was no real benefit to doing it that way.

You are welcome to use the Lightning's AIR file for your purposes, but the only useful thing it will give you is the extra engine.
Even THAT won't be very useful because your AT-9 Jeep didn't have counter rotating propellers.
If you need help on the flight model, just ask.

I hope Hubbabubba will see this message because he had planned to build the WW2 Trainer Types starting with a Texan / Harvard.

The AT-9 doesn't look like a simple project, so perhaps adding in two pilots would be a bit ambitious within the limits of AF99.

I CAN warn you about one thing:
With a single engine aeroplane, the Propeller effect on the rudder is predictable.
As soon as you go from one to two engines, the effect goes away entirely!
That is why on both my B-25 Mitchell and this Lightning, the Nose Wheel is made steerable even though the real ones were not.
You would figure that with Rudders directly behind the Propeller on both machines, the slipstream effect should be pretty good, but that is not how CFS AIR files work.... <sigh>
So.... The choice was either a steerable Nose Wheel or pretty much no low speed directional control on the ground.

- Ivan.

 

[Ivan]

Lockheed P-38F - Details

Details for the P-38F-1-LO from the Pilot's Flight Operating Instructions Manual (T.O. No. 01-75F-1) re as follows:

Tactical Empty Weight: 13,300 pounds (as compared to 14,400 pounds for the P-38J)
This weight specification includes
12,150 pounds - Aircraft Empty Weight
292 pounds - 4 x .50 Cal Machine Guns
206 pounds - 1 x 20 mm Cannon
2.0 pounds - Gunsight
5 pounds - Photographic Equipment
32.0 pounds - Oxygen
234.72 pounds - Armour Glass and Armour Plate
200 pounds - Pilot
128 pounds - Engine Oil

Disposable Loads
720 pounds - Forward Fuel Tanks - 120 Gallons
1080 pounds - Aft Fuel Tanks - 180 Gallons
600 pounds - .50 Cal Ammunition - 2000 Rounds
90 pounds - 20 mm Ammunition - 150 Rounds

70 pounds - Additional Engine Oil - 9 Gallons

Gross Weight
15,900 pounds

Although no bombs are listed, the weight of Drop Tanks may bring the Gross Weight up to 19,800 pounds.
Since we cannot carry drop tanks, we will substitute bombs for the extra disposable weight.

Apparently the early F models were all pretty close to 13,300 pounds.
The P-38F had a Tactical Empty Weight of 13,200 pounds
The P-38F-5-LO had a Tactical Empty Weight of 13,400 pounds
The P-38F-13-LO, P-38F-15-LO and P-38G-15-LO were all back down to 13,300 pounds.
The other G models were back down to 13,200 pounds.

The differences appear to be Armament and Armour weights.

.....

 

[Ivan]

P-38F Engines

The P-38F used Allison V-1710-49 and V-1710-53 (F-5 series) engines.
(The Right Hand and Left Hand Rotation engines were different model numbers)
There was no provision for War Emergency Power.

Maximum (Military) Power was 1325 HP @ 15,000 feet using 47 inches Hg.
This Manifold Pressure could be maintained up to 30,000 feet.

This power output is a bit below that for the J model which had a Military Rating of 1425 HP and a War Emergency Rating of 1600 HP.

The early model Lightnings had less maximum speed but cruised a bit faster because apparently the new Radiators and Intercoolers added quite a lot of Drag.

- Ivan.

 

[Ivan]

P-38F Flight Model

Engine Tuning turned out to be fairly simple.
After adjusting the maximum Manifold Pressure down to 47 inches Hg, Friction and Supercharger settings were also lowered a bit and the results are close enough to satisfy me.

Engine Tuning Method is described in this Tutorial:
http://www.sim-outhouse.com/sohforums/showthread.php?77148-Engine-Performance-Tuning-Tutorial

Sea Level Speed is now 335 MPH with 1260 HP. (Take Off Power should be 1240 but with only 44 inches Manifold Pressure)
Maximum Speed is now 414 MPH with 1316 HP at 25,000 feet

Maximum Speed is also 414 MPH with 1484 HP at 17,400 feet. This is way too high but is a consequence of how CFS handles superchargers.

Service Ceiling is just a touch over 40,500 feet with 50% fuel which is about where I wanted it.

Maximum speed is 5-10 MPH above were I wanted it, but is in the right range according to various sources.
Coefficient of Drag is unchanged from the J Lightning, but cruising speed at the same throttle setting should still be higher because the engine output will be a bit higher with the same Manifold Pressure due to the slightly reduced Friction values.

Screenshots show a bit more of the new Cowl from below.

- Ivan.

 

[aleatorylamp]

Hi Ivan,
Sorry, with all the to-and-fro on other things I forgot I hadn´t answered your post below on this thread.
It will definitely be very interesting to see the differences in performance of the P38F in the .air file. I´m looking forward to that.
At the end I followed your suggestion on the .air file not really being useful for the AT-9 other than for its being a twin-engined machine. The two pilots within the AT-9 do make the cabin interior difficult with only AF99 as well, but we are dealing with that.
Cheers,
Aleatorylamp