P-38 Dive Flaps

IMPROVING THE P-38's PERFORMANCE

Incredible as it may sound, until the installation of dive flaps the P-38's performance was limited because it flew too fast. That is, it accelerated so rapidly in a dive that a pilot might easily get into compressibility speed range in a matter of seconds.

Focke-Wulf and Messerschmitt fighter pilots recognized this limitation to advantage, and disengaged at will by merely diving steeply away from the P-38. At 30,000-ft a P-38 pilot without dive flaps desiring to get to 20,000-ft in a hurry was limited to a maximum 15-degree dive at rated power if he wanted to avoid compressibility.

Pilots were instructed to observe placarded dive speeds and angles and to watch for nose-heaviness and buffeting which were the first indications of compressibility.

But all of this changed with the introduction of the dive flaps. With the new dive flaps extended, a pilot could push over or peel off from 30,000-ft and pull out without difficult at any altitude. Whereas 15-degrees was the maximum angle for extended dives without flaps, a pilot could safely dive with power OFF at 45-degrees without fear of compressihility.

When the Lockheed test pilots talked about 45-degrees, they meant an accurately measured angle of 45-degrees. To the pilot looking over the nose, it seemed that this angle was actually closer to 80-degrees. This was the universal reaction of USAAF P-38 pilots when checking their judgment against Lockheed's dive instrumentation.

During Lockheed's first tests of dive flaps, one pilot caused quite a stir in the pilot's house (this was a Spanishstyle house near the field that Lockheed acquired for the test pilots) when he came down and stated that he had just SplitS'ed from 30,000-ft down to 6000-ft and pulled out without any difficulty. However, it wasn't long until the dive flaps were installed on production line aircraft and the pilots had a chance to learn about them.

The dive flaps were operated by individual 1.3-hp electric motors which revved up to around 15,000-rpm and actuated a screw mechanism which extended the flaps full down (to an angle of 35-degrees) in about 1.5-seconds.

Each flap was 58-inches long and extended in a V from the underside of the wing just outboard of the booms. The dive flap control switch was located on the left side of the control wheel. Pulling back extended the flaps, moving forward retracted them. It was recommended that three seconds he allowed between the extension and retraction in order to give the high-speed electric motors a chance to run down before operating in an opposite direction.

The following is an extract from a memo prepared by Lockheed test pilots regarding the use of the dive flaps:

Extend the dive flaps prior to starting the dive. We believe it is better to extend the flaps before diving because:

1) You can he sure they are operative. If you wait until you are approaching critical speed in a dive before extending them - and then they should fail - you might find yourself in a ticklish spot.

2) You will have a steadier gun platform. After all, the only reason your are flying around up there is to "make some money." Now if you want to go after a bandit 5000-ft below, you want nothing to happen that might cause you to lose him from your sights.

Say you start down and as you accelerate and start closing in, you notice your airspeed indicator winding up, and then you decided to extend dive flaps. As the flaps extend, the nose will tend to pull up and even if you put plenty of forward pressure on the control column it will be darn near impossible to keep him in your sights.

DIVE FLAPS EXTENDED AT HIGH SPEED TEND TO CHANGE YOUR LONGITUDINAL DIRECTION BY PICKING YOUR NOSE UP.

If you had put the flaps down to begin with, there would have been no tendency for directional change and you would have had a steady gun platform all the way.

Because we recommend extending dive flaps before starting the dive does not mean that there is any danger of losing them should they be extended at high speeds in a dive. We ran numerous tests here, and found that they will stand up under extreme conditions.

Whenever the flaps are extended, you will feel the nose start to pull up, and it will be necessary to apply a forward pressure on the stick to maintain direction. As speed in the dive increases you will have to increase this forward pressure - in other words, you have to hold the nose down.

We feel it is hetter not to retrim when the flaps are extended, because the resulting tail-heaviness will make it all the easier to recover from the dive.

Incidentally, you can execute a neat loop by merely extending the dive flaps and letting the nose come up and over. However, this is not recommended procedure.

DIVE WITH POWER OFF

We have found that by going into the dive with power OFF we can maintain better control - that is, we do not run into the unstable condition sometimes encountered in power ON dives, even with the flaps down. Should you start your dive with power ON in order to get initial acceleration, BE SURE TO REDUCE POWER AS SOON AS POSSIBLE, SO THAT PLA-CARDED SPEEDS WILL NOT BE EXCEEDED. THE DIVING SPEED SHOULD NOT BE ALLOWED TO EXCEED THE PLACARD BY MORE THAN 20-MPH.