On Thursday, June 20, 2013 8:07:12 PM UTC-4, Bill D wrote:
There are a bunch of troubling things in this report. I have a lot of ground launch (auto tow) time, but it's a bit dated, so maybe I've forgotten. IIRC, our target speeds were on the order of 50MPH or 55MPH in zero wind, not 70. This was with a Grob and 2-33, but I can't imagine that 70 is right.



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From the DG1000 flight manual:

"Recommended winch launch airspeed 110-130 km/h (60-70 kts.)."



Theoretically, the best airspeed for winch launch is that which give the angle of attack for best L/D. With the extra wing loading due to the rope pull, it would certainly be in the 60 - 70 knot range.

Right... but IIRC, the vehicle speed is less (significantly?) than the airpseed when the glider is in the aggressive climb portion of the flight profile. If I read the report correctly, it suggests the tow vehicle was briefed for 70. I have to go dig up the diagram, but the airspeed is the additive of some climb vector involving the secant or arc-tangent or some other function on my old Ti-35 that I no longer remember how to use, no? Like I said, it's been 25 years since I was doing 3-5 ground launches per day, so I could easily be off base.

With the increased interest in ground launch, I do think it's useful to revisit some of the old rules of thumb that used to be well known. Sure, we need the SOP and manuals (which are still out there), but it seems to me that it's good to review the underlying physics every now and then.