Loops and Eights (2 of 2)
Loops are among the simplest shapes in aerobatics, but unless you have an easy-to-apply method they can be quite difficult to judge and consequently decide on the correct downgrades to apply.
Look at the Basic Loop diagram on the left. Note that:
- The exit point is at the same level as the entry point.
- The four quadrant radii and centre points are all the same.
- The centre-top point is exactly above the start point.
Wherever you see these 3 'truths' you can be sure that the loop is genuinely round.
So: For every loop, in your mind break the shape into the four 90° quadrants for easier comparison.
Put a pencil or pen up against the start point, and use this point and the 1st quarter loop as your reference. Now you can describe the remaining quarters, particularly their radii and end points, by comparing them with the first quadrant and the location of the original start point. Note also the angle that each quadrant describes about the centre of the first arc - this should always be 90°. If it's well flown and the shape really looks like the one above, then it's probably worth a ten.
Here are some classic errors in the sketches on the right:
- The 1st half is fine, then the radius gets smaller at the top. The 2nd half is tighter, and the exit significantly higher than the entry.
- The 1st half again is fine but the top is flattened with increased radius. The 2nd half is larger than the first, and the exit is significantly lower than the entry.
- This one has a definite "Lazy Sunday afternoon" style - possibly with the same stick position until the end.... then a big pull. The 1st half radius tightens towards the top as the aeroplane floats at below stall speed inverted, then in the 2nd half it falls freely until increasing airspeed gives the elevator some bite and 'down-rush' anxiety tightens the radius again to a low exit. Not good!
- In this half-loop the 2nd quadrant radius is tighter than the 1st, leading to a smaller 2nd half and early exit not over the entry point.
- Here is the opposite fault, where the 2nd quadrant has been forced to a larger radius to 'float' the top and avoid (4) - making the exit too high and once again not above the entry point.
- In eights it is also necessary to judge the relative size of both the looping elements. Use the pencil to 'fix' the start as usual, then with a finger or by reference to some local cloud feature make a judgement about the size of the 2nd loop and the exit trajectory.
As you watch the figure, for every radius variation, missed angle point, entry and exit height mis-match you see, simply accumulate the penalties below and subtract them from 10 to reach the final figure score:
- Arc radii A small but noticeable variation: -1 point
- A more significant but not serious variation: -2 points
- A large variation significantly changing the figure shape: -3 to -4 points
- Missed angle Where the 'top point' is < or > 180° from the bottom point: -1 point per 5°
- Height mis-match A small but noticeable error: -1 point
- A more significant but not major error: -2 points
- A large error that significantly changes the figure shape: -3 to -4 points