Really Daft Question

Discussion in 'Aviation' started by jonwilly, Nov 10, 2009.

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  1. Anyone flown a 'Rotary' engined aircraft ?
    No didn't think so.
    I have 'Known' the following for donkeys years but never really thought about it.
    A Cab with a Rotary engine, put an input into the controls and the cab goes at 90 degrees to the input.
    ie In Yaw move control column to left and nose drops and down you go.
    Move to right and climb away.
    What my question really is ?
    Is where the controls offset to allow 'Normal' operation of the controls or did the aviators really have to learn to Push right to climb, pull to the left to dive ?
    Explains the high casualty rate in any case.
    john
     
  2. Jon, you need to define rotary. If you mean a radial rotary then your statement is true although alot of the gyroscopic precession is counteracted by the control linkages. What I do not know is how an enclosed rotary would perform as fitted to Mazda RX-8 or Norton F-1 and why it has never been taken up. There is certailnly a significant power/weight ratio saving with the latter.
    I have flown neither.
     
  3. ugly

    ugly LE Moderator

    I always thought it was winged as opposed to enginged, rotary wing ie whirly bird as opposed to fixed wing ie beaver. Fixed engine may not actually go anywhere?
     
  4. ugly

    ugly LE Moderator

    Radial rather than rotary unless we are talking wankels?
     
  5. Am I seeing a freely rotating radial engine there?
     
  6. OK, I think we need to clarify or I need educating.

    1. Radial engine. Series of cylinders, normally 5 or more that are fixed to the fuselage creating a star shape with the spark plugs on the outside of the circle, the small end fixed to an offset crankshaft and then into a gearbox. http://en.wikipedia.org/wiki/Radial_engine

    2. Radial rotary engine as above but the whole engine rotates about a fixed crankshaft and therefore the prop speed is directly related to the engine rotation speed. http://en.wikipedia.org/wiki/Rotary_engine

    3. Wankel rotary engine. Completely different design moving away from the traditional reciprocating piston concept. This is best explained as an equilateral triangle inside a circle, the void between the outside face of the triangle and the inside face of the circle create the combustion chamber. The triangle rotates and each void as it rotates becomes the intake, compression, power, exhaust phase of the four strokes. Main advantage is a standard engine produces a power stroke every two turns of the crank, a Wankel produces a power stroke every turn of the crank. http://en.wikipedia.org/wiki/Wankel_engine. I commend the wiki animation halfway down the page,

    Jon is referring to a radial rotary.
     
  7. I was deliberately vague as I was hoping only well informed folk would answer. Seems I was a tooch too reticent on info.
    I was watching one of those Made for USA TV programs and they where going on about Rotary Engines as fitted to the Stopwith Camel, i.e. Crankshaft is Bolted Solid to airframe and engine/propeller rotates.
    A good demonstration of Gyroscopic Precession, control imputes leading to A/c movement at 90 degrees to input movement and they demonstrated the 'Torque' by showing how a Tennis Ball rotated/spun above ones head could lift a 2 Kilo weight.
    However they did not make it clear, if the Pilot moved the 'Stick' to the to the right to Take off/Climb, or move stick to left to Dive/Descend.
    They also failed to explain if the controls had been 'Rigged' so that they operated in the conventional manner, Pull back for Take off/Climb.
    I am sure that once I knew the answer but time has washed away that memory.
    I find it hard to imagine that on take off you make a right control input, pull back giving a left wing down.
    I know there was a very high accident rates on a/c fitted with Rotary Engines and wondered just what the arrangement was.
    john
     
  8. Jon, I understood the question and my understanding is most of the prrecession was rigged out but there was stil an element of power up, yaw left or whatever. Without being disrespectful to the many cleverer people than me on here, this really is one for PPRuNe for hands on experience.
     
  9. Just back from my morning exercise.
    Of course most here are Heli men where the Gyroscopic precession is taken care of by the Heli designer, your forward movement of the Cyclic Stick results in a input to the Swashplate or other type of control, 90 degrees before the Blades reach the 'Front'.
    The more I think then the Less I can believe that Pilots Consciously had to think to put control movements 'IN' 90 D before and in the correct plane of rotation.
    150 HP engines where considered very powerful in those days and accidents where common and fatal.
    The Camel was a Fight winner and it's 'Instantaneous' snap to one side where engine Torque would drag would drag you round, was a life saver in a Dogfight.
    I do think we have the assembled Brain power on Arrse rather then go prrune ing.
    john
     
  10. Would there have been that much more precession than you get with just the propellor spinning round?
     
  11. MG, Yes,
    The Massive weight of the Rotating Engine, along with it's speed differential, was what was causing the problem.
    The program showed how by spinning a Tennis Ball above ones head, a rope connected to the Ball and down though 90 degrees, a 2 Kilo weight could be raised and lowered by vairing the speed of rotation of the ball.
    john
    Get a Rozzer on the job, well if they are not busy guarding the back gate !
     
  12. Back in the mists of time (around 1988) I seem to recall being shown the three effects that combine to make pedal-juggling necessary when taking off in a Chippy.

    Propwash, spiralling around the fuselage to impinge upon one side of the vertical stabiliser, causing a yaw moment.
    Torque reaction, causing the airframe to twist in the opposite direction to prop rotation, increasing the apparent weight on one wheel in comparison to the one on the other side, the drag causing another yaw moment, and
    Gyroscopic precession, when you raise the tail, as described earlier, causing another yaw moment.

    The Rotary engine of the Pup/Camel era aircraft would have a similar effect, as the Chippy isn't that far ahead, in evolutionary terms.

    ISTR reading somewhere that the main handling issues were in flight, where suddenly decreasing power (by switching off both magnetos rather than just one - no throttle control in those days) would have the cab the wrong way up in short order.

    Some other interesting background stuff.
     
  13. No references, I'm afraid, but within the last couple of years I watched a TV documentary about WW1 fighter a/c; the difficulty RFC pilots had when confronted by the gyroscopic effects of radial rotary engines was covered. Initially, the accident rate shot up until pilots were able to get their heads around the counterintuitive stick movements needed to fly such a/c. In the long run, however, the Sopwith Camel in particular became more than a match for its hun equivalents.