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#11
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Bob Kuykendall wrote:
Has anybody on this forum ever, ever looked at the OAT guage and said, hey, it's too cold here, I'd better dump water or descend? Yes. Given how effective composite sandwich construction can be as an insulator, it seems to me that what they _should_ be requiring is a ballast temperature guage... The main problem is the tail tank, which is a relatively small volume of water, isn't all that well insulated, and will freeze in a matter of a few hours if the outside temperature is low enough. In at least one case, the expansion of the ice caused the vertical fin to split open... Marc |
#12
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Then put the ballast temperature sensor in the tail tank, which should also
be insulated to help prevent heat loss. Bob "Marc Ramsey" wrote in message .. . Bob Kuykendall wrote: Has anybody on this forum ever, ever looked at the OAT guage and said, hey, it's too cold here, I'd better dump water or descend? Yes. Given how effective composite sandwich construction can be as an insulator, it seems to me that what they _should_ be requiring is a ballast temperature guage... The main problem is the tail tank, which is a relatively small volume of water, isn't all that well insulated, and will freeze in a matter of a few hours if the outside temperature is low enough. In at least one case, the expansion of the ice caused the vertical fin to split open... Marc |
#13
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"Bob Kuykendall" wrote in message ups.com... Earlier, Marc Ramsey wrote: The OAT meter is required for certification of German gliders equipped with water ballast... [slight thread hijack] Has anybody on this forum ever, ever looked at the OAT guage and said, hey, it's too cold here, I'd better dump water or descend? Given how effective composite sandwich construction can be as an insulator, it seems to me that what they _should_ be requiring is a ballast temperature guage... Bob K. http://www.hpaircraft.com I did exactly that. I contacted unexpected wave from thermal lift at the Alamogordo Soaring Fiesta last June. To climb in wave, I descended below the freezing level and allowed the skin of the glider to warm and then dumped ballast. When the water was gone, I found the wave again and made it up to 22,000 feet. I knew there would be some water left in the tanks but not enough to be a concern. Alamogordo rocks! Bill Daniels |
#14
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Warning, long post!
Freezing of the ballast tanks is not the only problem. I am "closely familiar" with three separate water ballast incidents. The first was in a 2 seat Schempp-Hirth glider with the type of tail ballast tank that has holes that one tapes over to determine the ballast quantity. Half way into a 300K out and return flight and after some straight cruising at altitudes of 16-18K feet (4500-5500 meters) it was noticed that the rudder would not move. Moderate pressure on front, back and both sets of rudder pedals would not free the rudder in either direction. It was still possible to soar the glider toward home and it was possible to thermal, though without the use of the rudder it was not pretty. On final glide at about 10K feet (3000 meters) the rudder came loose and the pilots made an uneventful landing. Inspection of the rudder area showed that the tape, which had been on the glider for some time, had pooched out and started leaking from one of the lower holes. It appeared that the water had run into the rudder counterweight slot and had frozen there. Landing without rudder could have been ugly. The second incident was on the same Schempp-Hirth 2 seat glider. The ballast drains are some distance from the wing roots and draining is visible to the front pilot while dumping the ballast. The glider was again being flown long distances at high altitudes above the freezing level. The front pilot noticed that there was a fin of ice extending below and aft of the drain opening about 2" wide, 6" high (50 X 150mm) and extending to the trailing edge of the wing. This appeared to not cause much degradation to the handling or performance of the glider, and the fin fell off upon descending through the freezing level. The valve was obviously leaking, not enough Chap Stick on the valve! The third occurrence was in a PIK-20D sailplane which had taken off with a known slow drip coming out of the wing at the back of the right side wing to fuselage tape. After a period of cruising at high altitude a thermal was entered, a pull-up was initiated followed by increasing the flaps to the thermalling setting. The stick was pushed to the right side by the flap position change and an un-commanded and brisk aileron roll was started to the opposite side from the left turn that was desired. The flaps were promptly put back in the cruise setting and the glider was able to be ruddered into the thermal from a right turn. It was determined that the flaperon on the right side was stuck in position. Some judicious wiggling of the stick was able to free the stuck flaperon and the flight continued with regular wiggles of the ailerons. Conditions were very good on the return and the speed on final glide was increased to 130 knots when BANG, BANG, BANG was heard which was followed by a gentle pull up to a slower speed. The noise soon went away and the glider was slowly speeded up again which was OK. After landing it was noticed that the tape on the bottom of the right wing was separated from the surfaces from the front of the flap forward to half chord and was stretched to 12" (30 cm) behind the wing. The problem was probably caused by a buildup of ice on the flaperon flow fence below the wing which froze the flaperon in position and then, later, on final glide, broke off and, stuck to the tape, was beating against the fuselage like a mace. Yes, the pilot involved in all these incidents knew about dumping ballast passing the freezing level but figured that it would take a long time to freeze the water in the tanks, which is true. Some guys just don't learn with experience that there might be other problems. (-; Y'all be careful out there... -Bob Korves "Bob Salvo" wrote in message ... Then put the ballast temperature sensor in the tail tank, which should also be insulated to help prevent heat loss. Bob "Marc Ramsey" wrote in message .. . Bob Kuykendall wrote: Has anybody on this forum ever, ever looked at the OAT guage and said, hey, it's too cold here, I'd better dump water or descend? Yes. Given how effective composite sandwich construction can be as an insulator, it seems to me that what they _should_ be requiring is a ballast temperature guage... The main problem is the tail tank, which is a relatively small volume of water, isn't all that well insulated, and will freeze in a matter of a few hours if the outside temperature is low enough. In at least one case, the expansion of the ice caused the vertical fin to split open... Marc |
#15
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Bob Salvo wrote:
Then put the ballast temperature sensor in the tail tank, which should also be insulated to help prevent heat loss. Even better would be to put the wing ballast in a location that doesn't require tail ballast to compensate for it. -- Change "netto" to "net" to email me directly Eric Greenwell Washington State USA |
#16
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WOW! I did not realize I needed de-icing boots on a sailplane.
Colin N12HS |
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