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In the P-38 Lightning could differential thrust be used to improve turn performance ? If so what was the procedure ?

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    $\begingroup$ I don't think this needs to be limited to the P-38, all twin engine aircraft with some distance between the wing mounted engines should exhibit the same behavior. I don't think it will though, given the dynamics of the turn force, you will be introducing significant yaw. What do you mean "turn performance"? Turn rate? or Radius? $\endgroup$
    – Ron Beyer
    May 17, 2017 at 19:46
  • $\begingroup$ Could it? According to what? $\endgroup$
    – Jan Hudec
    May 17, 2017 at 20:11
  • $\begingroup$ Ron Beyer. I meant both rate and or radius. Sorry for my imprecise language. $\endgroup$
    – Art Lee
    Jun 5, 2017 at 5:35

6 Answers 6

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According to WW2 pilots, no. Aside from the dangers in adjusting 1600hp on one side of the aircraft on the fly in the midst of a dogfight... With the P38, they didn't need to. The P38 had an inherent advantage over single engine prop fighters of its era. Its engines (and propellers) rotated in opposite directions, canceling out any torque effect. The counter rotating engines and props were considered a big secret on the P38 when it was first designed. (as if anyone couldn't look at the angle of the props on each side and tell that.)

The pronounced torque of the 1600hp-2000hp single seat fighters played a major role in aircraft handling: both in takeoff and power on maneuvers, something WW2 flight simulators never seem to reproduce. Single engine fighters would roll left far quicker than they could roll right, due to the immense torque of the engine/prop combination, aiding in the left roll but inhibiting a roll to the right. This was most evident at lower altitudes, where the air is thicker and the torque effect more pronounced.

Not so with the P38 - contra rotating engines and props canceled the torque, and the P38 could roll right far quicker than any single engine fighter. While the P38 did have several issues at high altitude, WW2/Vietnam ace Robin Olds held that nothing could beat a P38... down low. (revisit the Dogfights/Air Ambush episode for that)

So, no, they didn't use asymmetrical engine power for maneuvering with the P38 - they didn't need to. Just roll right and turn - no single engine fighter of that day could stay with you.

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  • $\begingroup$ Interesting that this answer is diametrically opposed by Spectre's new answer. Your answer was essentially "According to WWII pilots, no", while his is "According to WWII pilots, yes". I've got no clue who is right. If you have some links to back up your claim, that would give it much more weight. $\endgroup$
    – FreeMan
    Jun 25, 2019 at 11:38
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I know this question was asked years ago. But yes, differential thrust was used and was a trick up the sleeve of 38 drivers. Irv Ethel used differential thrust to escape a gaggle of 109s over Africa after his flight was jumped near Lake Bizerte in Tunisia. He taught the maneuver to other 38 pilots who then used it both offensively and defensively. The idea was to chop throttle on the side that you wanted to roll to. This could be used offensively to beat an enemy aircraft into a split-s, or could be used to rapidly reverse direction as if spinning the plane around a vertical pole. The P-38’s counter-rotating props combined with the prop’s airflow over the wings, which supplemented lift at lower speed made the Lightning capable of fantastic low airspeed and high angle-of-attack maneuvers that single-engine aircraft watched in disbelief.

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    $\begingroup$ To be slightly more precise, the end effect is a yaw moment, not exactly roll. A rolling moment will also be induced depending on the place the engines are mounted and the general design of the airplane. In the same spirit, the rate of yaw (which is what a pilot will be interested in) will depend on so many parameters that one can speak only for a particular class of airplanes. $\endgroup$
    – ares
    Jun 25, 2019 at 1:36
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    $\begingroup$ @ares "..chopt the throttle on the side that you wanted to roll to." seems pretty clear, there isn't a claim being made that differential thrust causes a roll. $\endgroup$
    – Koyovis
    Jun 25, 2019 at 2:33
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    $\begingroup$ Interesting that this answer is diametrically opposed to tj1000's answer. His answer was essentially "According to WWII pilots, no", while this one is "According to WWII pilots, yes". I've got no clue who is right. If you have some links to back up your claim, that would give it much more weight. $\endgroup$
    – FreeMan
    Jun 25, 2019 at 11:37
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    $\begingroup$ @FreeMan Here is Ethell's account of the event (originally published in Flight Journal.) It is not clear whether this became a common tactic. $\endgroup$
    – sdenham
    Nov 18, 2020 at 16:39
  • $\begingroup$ Subtle distinction: the question (and to some extent, the "no" answers) address sustained turn performance; this answer addresses roll rate. Related, but not identical. $\endgroup$
    – Ralph J
    Aug 9, 2021 at 14:49
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It depends how you want to turn I reckon. If by rudder only and if both engines are not flat out, then yeah you could up the outer engine thrust and yaw faster.

But that is an uncomfortable and slow way and generally not how it is done, usually pilots bank the aircraft, tilting the lift vector. That is a big vector and can provide much more centripetal force than the yaw scenario: the wings provide lift, and increasing the AoA a bit creates much more force.

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The vertical tail is dimensioned to fly with one engine out, the wing is dimensioned to support the weight of the aircraft. Difference between engine thrust and weight is easily a factor 5, often more.

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Obviously, I am no stranger to grave digging.)

I noticed that for this question there is not a single reference in any of the existing answers and the top two directly contradict each other. While it is impossible to prove a negative (that no one ever used differential thrust in a P38 to improve handling) it is possible to look at how the aircraft was supposed to be used.

A 1943 P38 training video (essentially one long blur with narration) makes no mention of such a procedure. It does describe a means to increase maneuverability by using partial deployment of flaps as well as a mechanical stop for the flap control expressly designed for that purpose.

An exhaustively referenced P38 site describes the outward down rotation of the props as causing difficulty beyond that of a normal twin engine aircraft when a single engine takeoff occurs, as this exacerbates the effect of P factor. Combat pilots may make use of extreme characteristics to gain advantage, though this violent effect is not described anywhere on the site as being used in that way.

Losing one of two engines in any twin-engine non-centerline thrust aircraft on takeoff creates sudden drag, yawing the nose toward the dead engine and rolling the wingtip down on the side of the dead engine. Normal training in flying twin-engine aircraft when losing an engine on takeoff would be to push the remaining engine to full throttle to maintain airspeed; if a pilot did that in the P-38, regardless of which engine had failed, the resulting engine torque and p-factor force produced a sudden uncontrollable yawing roll and the aircraft would flip over and hit the ground.

This was a deliberate design decision and a change from early model's inward down as it increased the aircraft's stability as a gunnery platform.

The YPs were substantially redesigned and differed greatly in detail from the hand-built XP-38. They were lighter and included changes in engine fit, and the propeller rotation was reversed, with the blades spinning outward (away) from the cockpit at the top of their arc rather than inward as before. This improved the aircraft's stability as a gunnery platform.

Based on a different recommended means to improve maneuverability and the design choice of stability over single engine controllability, the use of differential thrust was not commonly used in flying the P38.

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  • $\begingroup$ Is it safe to assume that the 2 quotes come from the linked site? $\endgroup$
    – FreeMan
    yesterday
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    $\begingroup$ @FreeMan Yes. The page is huge so the quotes can be used to find the relevant section. $\endgroup$
    – Pilothead
    yesterday
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In flight, differential thrust has only adverse affect. The only benefit of asymmetrical thrust would be to facilitate yaw in stalled condition or during taxi.

A stalled example of using asymmetrical thrust would be facilitating a hammerhead maneuver.

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Reading all this information on the question “ did pilots use differential trust during combat “

The answer is “ most likely not” Although the p38 is one of the best fighter with two engines it will fly well on one and it could defend it self.

During combat you don’t like to lose speed. Only if that energy is retained. Alt over energy.

Going slow the propeller factors (P factors ) Is tremendous. Going slow and pulling one engine will render your plane uncontrollable for a brief moment. Loss of control is no good in battle .

Gong fast the yaw moment can be created bij rudders too. So why pulling that engine. With rudders there is no adverse yaw. Just controlled yaw.

Going high and pull a engine is very unwise. The plane fly true thin air, speed limits are totally different. It can stall easily and or go transonic very quickly. Meaning..there no place to go to un controlled flight. At high altitude you keep the speed up to the best corner speed.

But maybe below 15000 ft pilots have used it. low the air is thick and with some practice it could flip the plane like a snap roll or hammerhead. But please check that manual as airframe limitations are probably telling you not to.

Realise such an event is a wilde ride ..

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