Elevator trim during Combat

Discussion in 'Flight Test Data' started by eddie_brunette, May 7, 2008.

  1. eddie_brunette

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    Did they ever use it, or was it just for level flight?
     
  2. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    You should be constantly trimming as you change airspeeds and altitude.
     
  3. KrazyKraut

    KrazyKraut Banned

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    Trim is still kind of a mystery to me :oops: I don't really know how they did/do it in real life and I don't know how I'm supposed to do it in flight sims.

    Where were/are trim controls typically located?

    In a dogfight altitude and speed change so rapidly that I would assume it'd be a hell of a lot of work to trim all the time and distract from all the other work you'd have to do.

    Do you just roughly trim based on experience (e.g. you open throttle 20 per cent -> you automatically trim "down" a bit) or do you trim once you notice your nose is pitching up or down (isn't that basically impossible in a highly dynamic fight)? How long would it take a good pilot to have his plane trimmed after a substantial change in speed and/or altitude?
     
  4. timshatz

    timshatz Active Member

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    Every time you add or take down power, the flight dynamics change and you need to change the trim to get level flight. If you're flying a regular aircraft, adding power will push the nose up, pulling back on the throttle drops the nose (although not as fast as when you add power-in most cases). Each aircraft is different, some require a lot of trimming, some very little. Usually, it depends on the horsepower and design of the bird (based on what it is made for).

    That is for standard aircraft, for the fighters of WW2, some had full sets of trim for all flight surfaces (aileron, elevator and rudder) some had only one or two. The 109 was famous for not having rudder trim (until later marks) and pilots just got used to flying with their left (I think it was left) foot on the rudder all the time to keep it straight. Whereas the P51 had a full set that were on little wheels on the underside of the throttle (my understanding of it) that you were constantly manupulating as you manuvered and changed throttle settings.

    Think of trim as a way to adjust the direction the airplane is flying without using the stick or rudder. Pitching the nose up and down or right and left by "dialing in" the direction instead of moving the stick. Easier than moving the stick as it requires no muscle power to do it and resets the "neutral" flight of the airplane (even if you have the nose pointing up, down or anywhere you want).
     
  5. drgondog

    drgondog Well-Known Member

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    The 51 had a full set of 'trim wheels' and flap control in on the control pedestal left and front of seat.

    As far as I know the first stick mounted trim tab/controls were on a P-80/T-33. I could be wrong on that but not on the Mustang trim...

    and you are absolutely right about needing to adjust trim constantly for different IAS in the 51. Many 8th AF pilots set a degree or two 'up' elevator trim while strafing to force forward pressure to stay on the target - on the theory that if they were hit or 'startled' the a/c would gently pitch up and climb out... rather than fly into ground

    I recently flew the A-10 and F-16 simulators at DM and was pleasantly suprised at how easy both are to fly, as well as how much control you do have using the trim tab buttons on the stick.. a lot more fun than cranking wheels, setting boost, mixture and prop pitch.
     
  6. model299

    model299 Member

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    Trimming during flight is indeed a function of airspeed and attitude fine control. It enables a pilot to adjust the pitch (elevator) or yaw (Rudder) or roll (ailerons) to make flight more neutral, easier and less physically demanding.

    Modern fighter pilots can control the trim with "hat" switches located on their control stick. WW2 fighters almost universally used wheels to the side of the seat. During normal "getting to the target" flying, they most certainly used trim during the flight. It simply made things less tiresome. Plus, during bombing, strafing, or long range deflection shots, I can certainly see how small trim adjustments could really help with shooting accuracy. However, I would think that during close-in aerial combat, such as having someone on your tail, a WW2 pilot simply did not have time to be fiddling with the trim wheels while performing hard and evasive combat maneuvers. It would be just another distraction. And fighter pilots don't like distractions during combat. (During combat, Robin Olds would regularly set the intercom so that the RIO could hear him, but he couldn't hear, and thus be distracted by the RIO.)

    Plus, how much trim to use can be a function of what you're doing. During their shows, flight demonstration teams usually use a lot of nose-up trim, eliminating any neutrality out of the controls. This enables them to alway exert positive control on the plane whenever they move the control column. In "the old days," before modern jets, the Blue Angles I know for sure, and probably others, used rubber bungee cords on their control sticks to achieve this effect.
     
  7. timshatz

    timshatz Active Member

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    ...and sometimes you forget how much trim you've got in like when you're setting up for final (after crusing around at 70%), pushing down on the yoke ("why is this thing so sticky?") and you let up on the forward pressure to flare and promptly pop back up ten feet or so ("Friggin' trim-hope nobody who knows what just happened saw that"- they always do).
     
  8. kool kitty89

    kool kitty89 Well-Known Member

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    One thing to note also is that, while most WWII fighters used tabs to trim some had variable incidence tailplanes, the Bf 109 for example. (as well and th Me 262, operated by an electric motor, which would allow some control in recovering from critical mach)


    Also (though not elevator related) the changing power settings on a prop driven a/c will change torque and require rudder trim changes.
     
  9. buzzard

    buzzard Member

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    EB,

    From what I've read, a lot of fighter pilots (esp early model P-38 drivers) saved their butts with the elevator trim when encountering compressibility-induced nose-tuck during hi-speed dives in combat. It allowed them to pull out in the thicker air at low altitudes without incurring catastrophic structural failure.

    I think that qualifies as the use of trim in combat.

    JL
     
  10. kool kitty89

    kool kitty89 Well-Known Member

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    The P-38 used a simple tab right? (a trimmable tailplane would have helped a lot)

    Lockheed also tried a full-span elevator servo tab to aid recovery, it seemed to work, but as shown in testing this made it easy to overstress the tail at high speeds with catastrophic results.
     
  11. eddie_brunette

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    I've also read that they have done that with the '38. The only other quote i've read of is Mr Bud Anderson using his little trim wheel, but during actual dogfighting - none


    "There were three little palm-sized wheels you had to keep fiddling with. They trimmed you up for hands-off level flight. One was for the little trim tab on the tail's rudder, the vertical slab which moves the plane left or right. Another adjusted the tab on the tail's horizontal elevators that raise or lower the nose and help reduce the force you had to apply for hard turning. The third was for aileron trim, to keep your wings level, although you didn't have to fuss much with that one. Your left hand was down there a lot if you were changing speeds, as in combat . . . while at the same time you were making minor adjustments with your feet on the rudder pedals and your hand on the stick. At first it was awkward. But, with experience, it was something you did without thinking, like driving a car and twirling the radio dial." Col Anderson
     
  12. eddie_brunette

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    in turning fights?
     
  13. seesul

    seesul Active Member

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    ...maybe stupid question, but during the dog fight there´s no time and sense to change it, right? Sorry, I´m not a pilot...
     
  14. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    Never a stupid question....

    I've flown simulated combat in jets and some recips and your're right, there isn't time to trim but most of the encounters I were in only lasted a few seconds at a time before we 'knocked it off." It was usually before and right after I've found myself trimming.
     
  15. seesul

    seesul Active Member

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    O.K. Thanks!
    In modern aircrafts, isn´t there an automatic self-trimming system?
     
  16. Kurfürst

    Kurfürst Banned

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    A few notes:

    1, Full set of trim wasn`t quite a standard, for example the Spit (presumably other RAF s-e fighters as well) didn`t have aileron trim. It depended on the design practice of the country of origin, and the operational role of the aircraft (long or short ranged interceptor). Full set of trim was largely useful for long transition flights.

    2, Somewhat related to the above, it wasn`t only the 109 that didn`t have rudder trim - the 190 did not have one either, nor did they have aileron trim. The reason for this was the desing practice in Germany - planes under 5 tons TO weight were not required to have rudder trim.

    3, Neither the 109 or 190 had received rudder trim (late 109s had Flettner tabs on the rudder to decrease control forces), though some bad-wheater fighters had PKS autopilot fitted which controlled the rudder angle. Both had variable incidence tail units, where the whole tailplane moved, rather than just trim tabs on the control surfaces. On the 109 it was operated by a double handwheel - one controlling the Flosse or variable incidence tail unit, and the other wheel operating the flaps, the idea being you could lower the flaps AND compensate for it with trim at the same time. The 190 had electric flaps and similiar tail unit.

    4, OTOH, both the 109 and 190 had FIXED trim tabs on the ailerons and rudder, which could be set on the ground to give neutral trim for specific flight regimes, ie. could be set to be neutral during typical cruise speeds. The 109 (perhaps the 190, too?) also had a profiled vertical tailplane (like a wing), which helped to counteract torque forces.
     
  17. drgondog

    drgondog Well-Known Member

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    In a P-51 the left hand would more likely stay on the throttle than trim wheels but you might trim it after running full throttle in a chase..
     
  18. Soren

    Soren Banned

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    The variable incidence horizontal stabilizer of the Bf-109 is also the reason behind Bf-109's ability to pull out of high speed dives sooner than P-51's P-47's.
     
  19. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    Yes
     
  20. drgondog

    drgondog Well-Known Member

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    Just finished reading through Nowarra's book and didn't see reference to variable incidence horizontal stabilizer and all the close ups of the K tails I saw had a sheet metal fairing at the horizontal/vertical stabilizer junction.

    All have movable elevators which would make them mighty big trim tabs.

    So, which versions had a 'slab tail'?

    And what data would suggest 'sooner' pull outs?
     
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