P38 Performance

[Baloo]

Can we get the 38 to go a bit faster?? 

[LCADolby]

That doesn't even stat which P38 variant 

[Baloo]

Sorry lol, but it's the P-38L-5/10-LO - albeit the J too was faster than it's German counterparts, especially after they came out with the modification kits for the dive flaps and hydraulics and what not.

[GScholz]

First you need to understand what you have posted. That chart shows the max dive speed before entering compressibility. It does not show P-38's max level speed. These are the "do not exceed" speeds when diving. All the dive flaps do is keep the speed under this "red line".

[Drano]

All the dive flaps do is keep the speed under this "red line".

Is there ever gonna be a point in time when people understand that the dive recovery flap on the later 38s is not a "dive flap" as most people would percieve a dive flap to be? It doesn't slow you down one bit. Not a bit! That idea is a myth repeated by folks that didn't educate themselves about it. What it does do is change the airflow around the tail structure so that the pilot has some measure of control at these higher speeds where there was basically none in models prior. It attempts to pitch the nose up so you don't bore a hole in the earth--which had been a problem. That's all it does. There is no alternative use.

[Banshee7]

Is there ever gonna be a point in time when people understand that the dive recovery flap on the later 38s is not a "dive flap" as most people would percieve a dive flap to be? It doesn't slow you down one bit. Not a bit! That idea is a myth repeated by folks that didn't educate themselves about it. What it does do is change the airflow around the tail structure so that the pilot has some measure of control at these higher speeds where there was basically none in models prior. It attempts to pitch the nose up so you don't bore a hole in the earth--which had been a problem. That's all it does. There is no alternative use.

And it is explained very well in Warren Bodie's book!

[colmbo]

What it does do is change the airflow around the tail structure

I think what the flap actually does is change the center of pressure of the wing, not change airflow around the tail.

[Baloo]

My bad homes, here is more info  

Flight Tests on the Lockheed
P-38J Airplane, AAF NO. 43-28392

 In level flight at 19800 ft., the critical altitude for 70" hg. manifold pressure, 3000 RPM, and 26,300 limiting turbo RPM, a maximum speed of 419 MPH was attained. At this altitude a high speed of 402.5 MPH was attained at 60" Hg. manifold pressure. At 24000 ft., the critical altitude for 60" Hg. manifold pressure, 3000 RPM, and 26,300 limiting turbo RPM, a high speed of 413 MPH was attained.

       At sea level a maximum rate of climb of 4040 ft/min was attained at 70" Hg. manifold pressure and a rate of climb of 3570 ft/min at 60" Hg. manifold pressure and 3000 RPM. The service ceiling of the airplane was 39,000 ft., and the absolute ceiling was 39,700 ft.
    

====================================================

Flight tests were conducted on the P-38L airplane, AAF No. 44-25092, at Wright Field, Dayton Ohio and Miami Depot, Miami, Florida in order to obtain a performance and range check of the data given as tentative figures in Pilot's Flight Operating Instructions, AN 01-75-1.
       Level Flight Performance

       The following speed data was obtained with the airplane in the clean configuration. Data is corrected to weight at altitude as given in Figure 4, Appendix A and NACA standard day conditions.

       a.    True speed at sea level at war emergency power, 1530 BHP and 3000 RPM, was 342 MPH.

       b.    True speed at critical altitude, 26,000 feet, at war emergency power, 1495 BHP and 3000 RPM, was 416 MPH.

       c.    True speed at sea level at military power, 1395 BHP and 3000 RPM, was 331 MPH.

       d.    True speed at critical altitude, 26,200 feet, at military power, 1385 BHP and 3000 RPM, was 408 MPH.

       e.    True speed at sea level at normal rated power, 1110 BHP and 2600 RPM, was 302 MPH.

       f.    True speed at critical altitude, 32,200 feet, at normal rated power, 1138 BHP, was 400 MPH.

[Baloo]

And to placate the whole dive flap business, here is an excerpt from the manual itself:

DIVE RECOVERY FLAPS.—P-38L and Later P38J
airplanes are provided with dive recovery flaps to improve
the dive recovery characteristics of the airplane.
As described above, the airplane without these flaps becomes
very nose heavy and starts to buffet above placard
dive speeds. This condition is caused by a high speed
stall and a consequent decrease in lift in the wing producing
the nose heavy condition. The dive recovery flaps
which are installed under the wings between the booms
and the ailerons, restore the lift to this portion of the
wing and thus cause the uncontrollable nose heaviness
to occur at a higher speed. The flaps also add some drag
to the airplane, which in conjunction with the higher
allowable dive speed, permits safe dives at a much steeper
diving angle. The dive recovery flaps should be extended
before starting the dive or immediately after the dive
has started before a buffeting speed has been reached. If
the airplane is buffeting before the dive recovery flaps
are extended, the buffeting will momentarily increase
and then diminish. With these flaps extended, the nose
heaviness is definitely reduced but the diving speed
should never be allowed to exceed the placard by more
than 15 or 20 mph. With the dive recovery flaps extended
before entering the dive, angles of dive up to 45° may
be safely accomplished. Without dive recovery flaps extended,
the maximum angle for extended dives is 15°.
Diving characteristics are better with power off than
with power on.

WARNING
Although the dive recovery flaps greatly improve
the diving characteristics of the. airplane,
dangerous buffeting and nose heaviness will
still be encountered at diving angles above 45°
if the diving speed is allowed to exceed the
placard limits by more than 15 to 20 mph.

[Karnak]

Is there ever gonna be a point in time when people understand that the dive recovery flap on the later 38s is not a "dive flap" as most people would percieve a dive flap to be?

I long ago got it even though I don't fly 38s much.

Make sure to always call it a dive recovery flap.  Never call it a dive flap or dive brake.

[Baloo]

Make sure to always call it a dive recovery flap.  Never call it a dive flap or dive brake.

^ That. To appease our fastidious friends. 

[GScholz]

So lowering the "dive recovery flaps" into the airflow does not increase drag significantly?

My bad homes, here is more info  

Flight Tests on the Lockheed
P-38J Airplane, AAF NO. 43-28392

 In level flight at 19800 ft., the critical altitude for 70" hg. manifold pressure, 3000 RPM, and 26,300 limiting turbo RPM, a maximum speed of 419 MPH was attained. At this altitude a high speed of 402.5 MPH was attained at 60" Hg. manifold pressure. At 24000 ft., the critical altitude for 60" Hg. manifold pressure, 3000 RPM, and 26,300 limiting turbo RPM, a high speed of 413 MPH was attained.

       At sea level a maximum rate of climb of 4040 ft/min was attained at 70" Hg. manifold pressure and a rate of climb of 3570 ft/min at 60" Hg. manifold pressure and 3000 RPM. The service ceiling of the airplane was 39,000 ft., and the absolute ceiling was 39,700 ft.
    

====================================================

Flight tests were conducted on the P-38L airplane, AAF No. 44-25092, at Wright Field, Dayton Ohio and Miami Depot, Miami, Florida in order to obtain a performance and range check of the data given as tentative figures in Pilot's Flight Operating Instructions, AN 01-75-1.
       Level Flight Performance

       The following speed data was obtained with the airplane in the clean configuration. Data is corrected to weight at altitude as given in Figure 4, Appendix A and NACA standard day conditions.

       a.    True speed at sea level at war emergency power, 1530 BHP and 3000 RPM, was 342 MPH.

       b.    True speed at critical altitude, 26,000 feet, at war emergency power, 1495 BHP and 3000 RPM, was 416 MPH.

       c.    True speed at sea level at military power, 1395 BHP and 3000 RPM, was 331 MPH.

       d.    True speed at critical altitude, 26,200 feet, at military power, 1385 BHP and 3000 RPM, was 408 MPH.

       e.    True speed at sea level at normal rated power, 1110 BHP and 2600 RPM, was 302 MPH.

       f.    True speed at critical altitude, 32,200 feet, at normal rated power, 1138 BHP, was 400 MPH.

So 416-419 mph at 26k... and 342 mph at SL...

Seems OK to me?

[Drano]

So lowering the "dive recovery flaps" into the airflow does not increase drag significantly

That's not really the idea so no. Whatever drag they might add is of a secondary nature. Besides, compared to other "dive flaps" do they look "significant" to you? Think Stuka, Val, SBD, hell even a Ju88! They all have what would be considered dive flaps. They ARE specifically designed to slow you down in a dive. They are large, sit almost perpendicular to the airflow and because of this, when deployed, they produce loads of drag.

To be clear they are not, repeat, not, designed to slow you down. They're designed to help you control the airplane by rerouting the airflow in the vicinity of the tailplane at high speed so you don't auger. That's why they pop out just a bit and at a shallow angle to the windstream. Just enough to do that job.

[GScholz]

From what Baloo posted above:


"DIVE RECOVERY FLAPS.—P-38L and Later P38J
airplanes are provided with dive recovery flaps to improve
the dive recovery characteristics of the airplane.
As described above, the airplane without these flaps becomes
very nose heavy and starts to buffet above placard
dive speeds. This condition is caused by a high speed
stall and a consequent decrease in lift in the wing producing
the nose heavy condition. The dive recovery flaps
which are installed under the wings between the booms
and the ailerons, restore the lift to this portion of the
wing and thus cause the uncontrollable nose heaviness
to occur at a higher speed. The flaps also add some drag
to the airplane, which in conjunction with the higher
allowable dive speed, permits safe dives at a much steeper
diving angle. The dive recovery flaps should be extended
before starting the dive or immediately after the dive
has started before a buffeting speed has been reached. If
the airplane is buffeting before the dive recovery flaps
are extended, the buffeting will momentarily increase
and then diminish. With these flaps extended, the nose
heaviness is definitely reduced but the diving speed
should never be allowed to exceed the placard by more
than 15 or 20 mph. With the dive recovery flaps extended
before entering the dive, angles of dive up to 45° may
be safely accomplished. Without dive recovery flaps extended,
the maximum angle for extended dives is 15°.
Diving characteristics are better with power off than
with power on."

[Baloo]

No, not significantly, some is synonymous with little...where as significantly is synonymous with big