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FAA PTS "Slips to Landing" requirement vs No-spoiler landings
bildan wrote:
On Sep 11, 12:01 am, Bruce wrote: vaughn wrote: "Mike the Strike" wrote in message ... I do know of one where the spoiler handle on a Grob 103 broke after they had been deployed and jammed full open, resulting in an off-field landing. And I know of a case where just one spoiler deployed on a glider. Causes a nasty uncommanded roll. The only solution (once you figure out what is going on) is to close the spoilers and proceed without them. Vaughn Single spoiler deployment has caused at least one fatal accident. If a linkage fails resulting in asymmetric airbrake deployment it is possible to run out of options very quickly. My thoughts are that you need to open the brakes to balance the drag and lift asymmetry. Then you can fly the aircraft through the resulting descending roll and recover. Depending on your height and speed it may be quite pressing to land, it may also be quite pressing to reduce speed... However - if this happens in a high energy state (where else?) you may already have a lot of yaw and roll inertia by the time you get the other airbrake open. Especially on a long winged open class ship there may just not be enough control authority left, and if you are very fast and/or very close to the ground the options are limited. To overcome the differential lift caused by the yaw you may need full rudder. To limit the speed and avoid terrain you may need large elevator deflection. To reverse the roll and return to level flight you almost certainly will need full aileron. You are unlikely to find such a high G, rolling pull up close to , or over Vne with airbrakes deployed in the manual. There is a reason for that "max manoeuvre speed" entry... A little math says that at 250km/h and 300m (~1000")AGL a 30 degree descent angle will give you less than 8 seconds to avoid terrain. 40 years ago I was involved in building and testing a glider with spoilers for roll control instead of ailerons. Preliminary flight tests were done on normal gliders rigged to permit one spoiler to be deployed at a time. The first thing we learned is that spoilers don't do what they are generally thought to do. The results of asymmetrical spoiler deployment vary dramatically with airspeed since drag increases with the square of airspeed but lift which is 'spoiled' pretty much remains constant with airspeed. (Any lift reduction is transient since the glider quickly re-establishes equilibrium at one G flight where lift =weight.) The bottom line was that below some airspeed like 50kts, weak roll (~10% of aileron authority) was the dominate result and above that powerful yaw was the dominate result. We found it best to regard differential spoilers as yaw control devices. Thus the concept of roll spoilers was a failure. In one iteration, spoilers were rigged to the pedals with the normal rudder fixed in neutral. With yaw spoilers, ailerons and elevator, we had a remarkably agile glider - albeit not a particularly efficient one. So, the accidental deployment of one spoiler will result in powerful yaw not roll which leads me to the subject of using one in a slip. Al relatively low speed I would expect this to be reasonably controllable. It would be interesting to test this at high speed - the yaw will be severe at full open, the secondary effect of that yaw will be a roll in the direction of the open spoiler. The uncoordinated flight is going to increase drag significantly, and the glider will start to descend. In the case of an open class/long winged glider the roll may exceed aileron authority if this happens at high speed. Even with 15m wingspan you are going to need significant control input on the ailerons. a glider one quickly finds the limit is available rudder authority. With full rudder one can use only about 15 degrees of bank while maintain a straight track. However, with one spoiler deployed, the pilot has far more 'rudder' authority in the direction of the open spoiler and a far steeper bank can be used. This results in an incredibly steep approach. This situation is 'dangerous' only to the extent the pilot doesn't understand how to control his partially disabled aircraft. Full control input on an already stressed airframe at speeds above max manoeuvring speed is not advisable - but may be the only option available. The only incident I know of the glider ended up in tiny pieces of carbon. |
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