On Monday, December 3, 2012 8:09:39 PM UTC-8, Bill D wrote:
If you are not an experienced degreed Aero Eng who has done V-N diagrams and perused the above certification requirements(I have) perhaps you should not worry about this as an issue. I am, I have, and I do worry. Look, I wish the 2-33's weren't 50 years old. I wish they were great winch gliders and would last forever but none of that is true. Winch launch puts a lot of stress on an airframe. Stress metal enough and it breaks. We seem to keep learning that the hard way. Wishful thinking doesn't help. This particular old metal glider has a number of red flags right out of the factory - unspecified weak link, dubious Vw speed and no true CG hook among them. After a half century of hard service they need to be treated with respect like the antiques they are. Do yourselves a favor. The next time you are at the airport take a hard look at your 2-33. Specifically, look on top of the right wing D-tube in the area where the strut attaches. I've seen half a dozen with patched fatigue cracks there - saw one last weekend. Yes, it was being winch launched. Why the right wing? Go sit in the front cockpit and open the spoiler half way like students are taught to land. Now try to use full left aileron like you were trying to prevent the glider from tipping over onto the right wing. If a student is going to drop a wing, likely it will be the right one because left aileron is blocked by the student's leg which is trapped by the spoiler handle. If the glider has a "CG hook" grafted onto the right side of the fuselage, get down and carefully look at it. You'll notice it hangs below the skid so it's probably been ground off. So much for Schweizer giving much thought to winch launch.

I seriously doubt from your tone that you actually know what you are talking about, as you are adding a bunch of ancedotal observations which have little to do with the original subject at hand. What is the primary difference between the BGCH and the JAR22 wrt to gust load criteria? Why are you using load factors less than 5 g's? When did I ever imply that the Schweizer line is known for good winch launch aircraft?

Nothing lasts forever, and a majority of the training fleet is antiques. With the proper weak link, or design in case of the 2-33 (Limited elevator authority, forward hook location, etc) you should not be stressing these aircraft any where near the limit load, so I don't see the design issue there. There are all kinds of design problems with the 2-33, from ergonomics to tail design, etc, but most of them are still an issue with aero tow. Having said that, there is no doubt that sooner or later, abuse and poor maintenance like you describe will cause an accident. Until that time, I won't have any qualms in ground launching a Schweizer. How many aircraft manufactures can boast only a single AD and a handfull of minor S/B's across an ENTIRE line of aircraft spanning 70 years? BTW, that AD takes care of the valid tow hook issue you mention. As you must know the AD requires a preflight inspection. Damaged parts on both "CG" and forward hooks can be very serious.. I just bought new parts for the 2 ships on my field.

Bottom line, the extreme majority of accidents in GA (98%) are not caused by primary structural failure. Almost all of those were caused by pilot error, and that is where we need to focus. So I would apply my concerns by proper maintenance (Replace bad parts, fix cracks in your LE, etc) As added protection, it should be easy to come up with a weak link that is practical, that limits wing load to something like 1.8 to 2,5g's.

Unlike the Blanik or other gliders, the 2-33 wing is not a stressed skin design, so you can do your own simple stress and fatigue analysis of the lower spar cap just outbd of the strut. I would neglect effective cap area of the skin, use a Kt of an open hole, apply the appropriate S/N cut off and assume full stress reversal. Les at K&L should have all the applicable dwgs and material callouts. It is possible he could even share with you, where the lower margins are wrt winch launching loads.

Look forward to your results...

aerodyne