Posted Saturday, April 18, 2020 @ 06:06 AM
Hiya Fellow Fournicators,
While staying indoors for fear of catching this virus, I’ve been keeping my mind occupied with aviation by reviewing video footage of my last display practice.
For no apparent reason, the final avalanche in my sequence went more crisply than I think any avalanche has before, although I cannot see any reason for that on either the cockpit-cam or fin-cam footage. It also seems very nearly symmetrically aligned with the top of its loop, which is normally difficult to achieve given the 65-knot maximum allowable speed for kicking the rudder.
As a reminder, an avalanche is a loop with a flick (snap) roll at its apex.
This is it: https://youtu.be/sthVckgm4v8
As I say in the notes, It appears elongated horizontally because I had to play the clip on a wide screen TV and then record it with my iPhone because I cannot currently find a way of directly downloading the footage from the old Sony camcorder I was given (without instructions) by my late mate Alan Washington.
Anyhow, feeling that this was the best avalanche I’ve flown, and given that I still have a few tufts left on my wings, I thought I would investigate the fin-cam footage for clues.
Nine stills follow from that footage.
In this first one the aeroplane has already rotated nearly eighty degrees from initiation of the flick roll. All the earlier frames were just too dark for me to make out what was happening with the tufts, but here it is quite clear and the right wingtip’s smoke makes it even more clear. The right wing is completely stalled, with an angle of attack at the rear of the smoke pod of about 45 degrees, while at the front of my wingtip sight it is nearer 75 degrees.
Ignore the 45-degree line just ahead of my smoke pod. That is my 45-degree wing-tip sight for establishing 45-degree up- and down-lines when I fly open-canopy.
What I find particularly interesting is that, judging by the directions of its trailing-edge tufts, the left wing also seems to be completely stalled out as far as the inboard end of the aileron, although the airflow seems to be at around sixty degrees to the span, and almost pointing along my sunburst stripes, suggesting a lot of slip (or is it skid?) is taking place .
In the second picture the right wing’s AoA is even higher: about 85 degrees at the front of the sight although perhaps a little less at the smoke outlet. The left trailing-edge tufts are now streaming forwards more, but still at about 45 degrees to the trailing edge.
Looking at the third picture, the right wing-tip is now clearly travelling downwards through the air.
But looks at what’s happening over on the left wing (which should theoretically still be flying). Every single one of the tufts is streaming forwards in one way or another, although the flow is still generally towards the root inboard.
The fourth picture shows me virtually upright, and therefore a few degrees past half-way through the flick-roll.
The right wing is still completely stalled, as you would expect, with approximately a ninety-degree AoA, but now the airflow immediately aft of the left outer aileron is flying nicely – but only the outer half of it. The airflow behind the inner half of the left aileron is still chaotic, and along most of the inner left wing it is clearly flowing forwards.
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