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Oblique flying

Discussion in 'General Discussion' started by Alex Baxter, Jul 22, 2016.

  1. Alex Baxter

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    I was just wondering the best way to get the most economical flying, in terms of battery usage.
    I would guess fairly high speed at a steady altitude, high speed would use the same amount of battery as hovering, I would guess, as it's simply easing the load on the front two motors and increasing it on the rear two motors. (I reckon, but stand to be corrected)
    Now the tricky question. Is it more economical to fly 'square on' ie with the axis of the aircraft in line with the line of flight, or rotating the aircraft 45 degrees so it has a 'leading' arm. I've not tried it, and I guess it would be fairly hard to prove either way in ambient conditions. It's just an idle thought, I'm happy with flight times, range etc with my P3....
     
  2. BigAl07

    BigAl07 Moderator
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    High speed does not use the same amount of energy as hovering. Hovering (in calm windless conditions) doesn't use a lot of energy because you're just developing enough lift to equal the effect of gravity.

    To move forward you have to ALSO create that much lift and more because to move forward the aircraft tilts toward the direction of flight causing you to lose some of your lift that was counteracting gravity. Since we don't have wings or any lift generating surfaces we have to create all of our lift from the props which are powered. The more lift we create the more energy we use.

    The most efficient flight would be hovering if pure flight time is the goal. Any time you initiate a climb you use more power and at the same time you save some when you descend but it's not proportional. A 100% climb rate is much greater demand on the power system than a 100% descent is a relief on the power system. It does not descend (intentionally so) at the same rate as it ascends.
     
  3. Alex Baxter

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    Hi Big Al, I hear what you're saying, but...
    Moving in any direction is cutting power to one or two motors and increasing it to one or two others, I don't see how it'll take more energy unless you're gaining elevation, you're simply still overcoming gravity, not creating more lift. I've never tried this theory in practice, but I wonder if flight times hovering or moving are wildly different, I doubt it. I guess that say dropping 10% on RPM on two motors and increasing RPM by 10% on the other two to achieve the tilt required for forward flight may take more power but I'm sure it's not much. I guess the theory could be proved by hovering on a calm day using GPS against hovering on a windy day and comparing flight times, keeping above ground effect height. Any ideas on the oblique flying, my main interest?
     
  4. Alex Baxter

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    BTW BigAl, I'm a big Al too, being 6'3"....
     
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  5. BigAl07

    BigAl07 Moderator
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    When the aircraft tilts (in order to create movement) a portion of the lift is no longer in line with the pull of gravity so you have to either create more lift (more RPM) or you lose altitude. So even if you dropped 10% on the front and allocated that same 10% to the rear motors you still have to increase motor RPM (and battery draw) to maintain the same level. It takes more to move forward than to hover even if all other factors are the same.

    The above principle is why when flying a "conventional" aircraft when we make a turn the wings are no longer creating lift in direct opposition of gravity so we introduce an amount of Up elevator which creates more lift to maintain a constant altitude.

    I'm sure if there was a way to measure it you might see a micro-fraction benefit from it but these aircraft are so "dirty" and create so much drag I don't think you'd benefit from it other than capturing some good fly-by video. Between the amount of turbulence from the props, lack of sleekness in the air-frame, the crap dangling below the aircraft you have a LOT of drag and nasty air all of which make it hard to "clean things up" without physically changing the aircraft design/layout.

    LOL I hear ya. 6'4" and let's just say I've never been called "petite" .
     
  6. Alex Baxter

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    Ah yes, of course, the propellers will be thrusting at an angle, so you'll lose a few percent of thrust that way, so need a bit more RPM, good call. On the oblique flying bit, it's just an idea that interests me, more than likely never to be proved either way. Thanks for your input, even bigger Al....
     
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