I do lots of winch launching but have never even seen an auto-tow. The report says the rope length was 234 foot. Is that normal or even possible? Using a winch, at my club we get 800 to 1200 foot of launch height from 2,100 feet of winch cable - so launch height is a bit more than one third of the cable length. How on earth could you get to a safe launch height from a 234 foot rope?

Forgive me for teaching granny to suck eggs, but some readers may not have had training or experience in this. As a general comment on ground launch failures, firstly it is vital not to rotate too rapidly and not to be too steep too low. However, once in the full climb at a safe height, if a launch failure occurs, it is vital to lower the nose of the glider rapidly well below a normal glide attitude. If the nose is lowered only to a normal glide attitude after a launch failure in a steep climb, the speed may well have reduced below a safe flying speed, with the potential as here for a stall/spin. It is common to teach a rule of thumb that the nose should be lowered as far below the horizon as it was above the horizon before the launch failure.

Mark Burton, London Gliding Club, UK


On Friday, 21 June 2013 01:53:19 UTC+1, Papa3 wrote:
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.