737-700 horizontal stabalizer question
 

Last week while on a SWA flight from KHOU to KLAS, I had a window seat a few rows behind the wing. This was an early morning flight, flying more or less from east to west. The sun evidently was at such an angle, that it cast a shadow on the wing from the horizontal stablator. Had to be the horizontal, as the length of it was proportianal to the actual size. Now here's my question: We encountered "rapid intermittent chop". During this event, I noticed that the shadow would move forward and backward upon the wing, quite rapidly. What was happening back there on the tail? Was the stablator actually 'flexing' during the 'chop', or could it have been 'stablizer trim' moving the stablator rapidly?---- thanks ahead

Stabiliser trim is so slow it's almost imperceptible, and only operates in short duration 'blips'. There would be a bit of tail shake. It wouldn't be elevator movement- they barely move even in quite heavy turbulence, so even though the sun was shining almost horizontal, it wouldn't have shown. It's tailplane shake.

In tubulence the whole aircraft is moving slightly relative to its flightpath - in yaw, pitch and roll - that's why you can feel it. It is therefore constantly changing the position of its parts relative to the sun, which is fixed. Therefore the shadow of any part will be moving slightly in resonance with the turbulence effect. This is what you were seeing IMHO, not any movement of the stabiliser relative to the rest of the airframe!

was gonna say that the turbulence would've moved the aircraft relative to sun thus changing it's shadow...

The main wing is far more flexible than the stabiliser. Maybe the moving shadow effect was the wing itself flexing up and down.

I seem to recall sitting at the back of a 757-200, in an aisle seat during a fairly choppy approach, and was interested to see how much the fuselage flexed.

Maybe this was a factor on the 737-700, as some of these stretched versions can't be that much shorter than the 757-200.

r

Thanks all. My computer was down for a couple days, and unable to reply. I guess it was 'tailshake' as 'not-so fantastic' states. Do not think it was the main wing flexing, because the shadow was definitly moving forward and backward. Am thankful that the shadow did not 'suddenly disappear'while staring at it!!!!. Thanks all