An article of J.J. Sinclair, published in the Newsletter of the Cape Gliding Club, Worcester SA
About the author:
JJ Sinclair retired from the Air Force in 1974 after 22 years of service. He flew as crew member on:
B-29 (left gunner)
KC-97 (boom operator)
B-52 (navigator & radar navigator)
After retiring, JJ established an FAA Certified Glider Repair Station in Placerville, California, and operated that facility for over 20 years. He has flown 1000K zig-zag in his LS-7 as well a 1000K triangle in his Nimbus-3, but takes more pride in having flown Silver, Gold and Diamond Badge Flights in the wooden Duster that he constructed in 1973.
Good morning, class. Today we will be discussing an alarming statistic. In the past 30 years our soaring area has witnessed five fatal accidents in the mountains and three of these accidents have occurred within the last five years! Would one of you work up a trend analysis on those statistics?
Thank you Mr. Kelly.
All these accidents involved experienced pilots flying modern sailplanes and most of them impacted with high energy, indicating a stall situation. Why would an experienced aviator inadvertently stall his aircraft, especially near the rocks? Everybody now look at the graphic, the top sailplane represents us flying into the page as we approach a mountain on our initial pass. We stay 300 feet away from the rocks and keep our speed up (minimum 120kph).
Is that safe enough?
Lets just suppose theres trouble lurking out there in the form of a gigantic gust, a really strong thermal, a violent wind shear. For the purposes of our discussion well just call it a “zephyr” and its going to apply a differential rolling moment to our theoretical sailplane.
Whats a differential rolling moment?
Good question, Mr. Green, it happens when our right wing flies into lift that is much stronger than what our left wing is experiencing. We are constantly looking for this, arent we? We call it light wing and turn into the wing thats coming up as soon as possible, because theres probably a thermal on the light wing side. Ever try to turn into the light wing and have the machine refuse to turn?
Sure, happens all the time and we say something like, “Turn, you big beast, turn!” Whats happening? Why wont the ship turn into the rising wing? Because, the thermal is stronger than the authority available in our ailerons. Another way to state this is; The thermal is trying to roll us left and we are trying to make the ship roll right. The result is a Mexican stand off and we fly straight with full right stick and rudder applied.
Now class, look at the second sailplane in the graphic. Thats us, still flying into the page, but the zephyrs got us and its rolling us left into the mountain. We have applied full right stick and rudder, but the zephyrs stronger than the controls and were still rolling left and theres rocks over there! Why is this happening? It is estimated that our ailerons can only counteract a differential moment of 2,5 m/s. Let’s say there’s 6m/s under our right wing and only 1,5 m/s under our left wing. Reasonable figures? Sure, we see 6m/s all the time on the Whites and in the Sierras, only near this damned mountain its mostly under our right wing!
Now, look at the third ship. Were in real trouble, arent we? There are rocks and trees up there on our canopy where the sky is supposed to be! Were experienced aviators and we dont panic, we continue to hold full right stick and rudder and apply forward stick to make the rocks stay away from our canopy.
STOP ACTION. Class, remember what we learned in before? We can stall a ship in any attitude and at almost any airspeed, cant we? I believe it was in chapter 6 that we learned how to do a snap roll. All you had to do was slam in full rudder and full back stick and the airplane would do a snap roll in the direction of applied rudder. Can we stall a ship while inverted?
Yes we can! OK, resume action.
Were flying 120kph, holding full right rudder and the stick is now in the right forward corner. Whats the ship likely to do? It might try to snap roll to the right, but the zephyr probably wont allow that, so Im betting it will just stall and fail and we have another mysterious high energy impact on the side of a mountain, dont we?
Does it have to be this way? Are those of us who choose to fly close to the mountains, destined to become a high-energy impact, some day? NO!
I see Mr. Seamons has his hand up. OK, Sir whats our question? How do we prevent smacking the mountain? Good question, I was just getting to that. First of all, there are days where I wont get within 1.000 feet of the rocks. If Im approaching a mountain and the turbulence is so bad that things are flying around the cockpit. I dont get within 1.000 feet of the rocks.
Let say Im approaching the Whites, Im holding 65 knots and things seem fairly smooth. My computer tells me the westerly wind should make the canyon up ahead, work. But, what if theres a zephyr in the canyon? What if it tries to roll me into the mountain? As I get within 300 feet of the rocks, I roll the ship into a 30 degree right bank and hold it there with a bit of top rudder. Why? Because, I ‘m already banked away from the mountain, so if a zephyr tries to get me, Im ready apply all three control inputs to fight it with right stick, right rudder and back stick to make it turn away from the rocks.
I also follow all the normal rules about never turn directly into the mountain, always S-turn an area for a beat or two before attempting to circle. If I fly by an area that shows 1,5m/s lift for 20 seconds, I turn away from the mountain and come back through the lift area to verify it really is workable lift. If it is, I turn 90 degrees away from the rocks, roll wings level for a count of 3 (you know 1000-one, 1000-two, 1000-three) then I turn back into the mountain. My 3-second burst flying away from the rocks gives me plenty of room to finish a turn into the mountain, but Im still not committed. As I face the rocks again, I ask myself; am I 100% sure I can finish this turn? Only if the answer is an unequivocal YES, do I continue. If Im not completely sure, I roll the other way and continue S-turning the area. If I do continue the turn, I may shallow out the turn as I come parallel to the rocks and let the ship drift in close, if that’s where the best lift is. I do this while holding a 30 degree bank angle AWAY from the rocks.
OK, thats enough for today, class dismissed!
Oh, one more thing, always keep an escape route open! You may see some of this material on the quarterly exam. Mr. Kelly, you may give your accident trend analysis, first thing Monday morning, please hold it down to two minutes maximum.