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#16
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Double Release Failure
On Sep 10, 8:27*am, Frank Whiteley wrote:
On Sep 10, 2:37*am, (Alan) wrote: In article Jim Beckman writes: At 14:13 08 September 2009, FBCompton wrote: Important Timing Aspect: *The glider (in low tow) must not touch down much before the towplane -- this can be a hazardous aspect -- touching down well before the towplane and stalling it. *The glider wings are still carrying the weight of the glider while it is flying. *Once the glider touches the wings stop lifting and the glider creates more weight drag on the towplane, which if still well above the runway will be slowed and may stall. * This seems counterintuitive to me. *When the wings stop lifting, the induced drag goes away, so the drag on the towplane should decrease. *The only added drag is friction in the glider's main gear. *What am I missing here? Jim Beckman * It seems backwards to me, too, but I have asked tow pilots about this, and I was told that they feel the drag decrease when the glider comes off the ground on the takeoff roll. * I guess those wheels have a lot of drag. * * * * Alan Behind less powerful tow planes, I generally note a 3-5 knot jump in airspeed immediately following glider lift off. Frank Whiteley Brake pucks and shoes are always in light contact with the disks or drums to eliminate 'lost motion' so as to provide immediate braking action. Although small, this friction is not negligible. Aircraft tires are made from natural rubber which has very good wet and dry traction but also has higher rolling resistance than synthetic rubber. A single glider tire is also loaded heavily - sometimes beyond the load rating limit which increases rolling resistance still further. It's reasonable to expect these taken together would result in noticeable rolling resistance. On a slightly different tack, I've had badly worn drum brakes lock up on touchdown all on their own without input from me. Normally, this is not a problem and serves as a reminder to service the brakes. If the brake locked and/or a tire blew while landing on tow, the results might be 'interesting'. |
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