Dolphin flying

On Tuesday, March 1, 2016 at 5:50:58 PM UTC-5, wrote:
On Tuesday, March 1, 2016 at 3:07:03 PM UTC-5, wrote:
Can anyone point me towards literature on this subject?
I wonder if anyone has done simulations, calculating the cost of those 6.5G pulls for example.

Wil Schuemann wrote an article for Soaring Symposium back in the late 60s called "The Price You Pay for Flying McCready Speeds". He did a monumental amount of calculations comparing dophin technique pulling and pushing to match the STF according to McCready vs flying simply at two selected airspeeds. Over a cross country flight, choosing to fly at the two selected speeds equated to a much better flight in terms of speed achieved. I once had a discussion with a world class pilot who stated that the drag incurred by pulling and pushing the stick is much greater than most people appreciate. Read the literature in the Soaring Symposium on Competitive Flying authored by Wil Schuemann. Indirectly, that may also validate the use of flaps as being more efficient than using the stick (elevator).

The Price You Pay for McCready Speeds: http://www.betsybyars.com/guy/soarin...a/72price.html

Very interesting read, thanks for sharing and linking!

The Schuemann article is very interesting, indeed -- thanks for posting it!

On Tuesday, March 1, 2016 at 3:04:06 PM UTC-8, wrote:

The Price You Pay for McCready Speeds: http://www.betsybyars.com/guy/soarin...a/72price.html

Oldie but goodie. Speeds tend to be a bit higher now with modern gliders having a knee in the polar that is at a bit higher speed, plus more water capacity.

There's nothing wrong with McCready theory - in theory. The considerations beyond McCready for pilots are, first, as Wil pointed out, the achieved cross-country speed penalty for cruising a bit off McCready optimal STF is not that great and options open up when you fly a bit slower in terms of search radius, ability to sense lift, less G-induced losses in getting slowed down within the diameter the thermals you encounter so you don't miss good lift, etc. There's zero benefit to flying faster than McCready so the bias ought to be slower on average to open up that option value.

Second, McCready applies in a theoretical world of consistency and certainty in terms of lift ahead versus lift behind you as well as search altitude versus inter-thermal distance, lift strength distribution, wind speed and direction versus task leg orientation (which themselves can vary with AATs). Soaring weather is stochastic and the expected probabilities ought to affect how we fly - especially as circumstances like altitude, time of day, the look of conditions ahead all affect that probability distribution.

The fundamental tradeoff in flying fast is the probability of getting stuck or landing out versus the probability of finding a good (or better) thermal ahead before that happens. Again, read the Cochrane article on flying faster that nicely covers many of these topics. There is also the issue of searching for lift (or more importantly the best lift) in areas where you have indications that there ought to be a good thermal, and how much altitude there is to gain if you strike gold with a boomer. No point in searching around close to cloudbase.

Based on the above, there a places and times when I'll S-turn (or even fly a clover-leaf) to find the good lift I expect might be there somewhere, particularly in cases where there's a marker like a cloud, a terrain feature or when I'm coming to the end of a street where prospects ahead are less certain. If lift is widely distributed and variable I more frequently attempt to expand the area searched under a cloud to see what's available. On occasions where I'm flying with another glider I typically find I pay a fraction of a mile for the option to search in an S-turn versus steam ahead - that's when it doesn't pay off. When it does pay off I'll often find that I arrive at the next thermal later but hundreds to more than a thousand feet above the pilot I'm flying with (depending on what he finds up ahead).

That's the great thing about soaring - it pays to think - most of the time.

9B

On Friday, March 11, 2016 at 11:13:56 AM UTC-5, Andy Blackburn wrote:
Based on the above, there a places and times when I'll S-turn (or even fly a clover-leaf) to find the good lift I expect might be there somewhere, particularly in cases where there's a marker like a cloud, a terrain feature or when I'm coming to the end of a street where prospects ahead are less certain.

I agree, 9B. I recall a day back in the 70s (the 1970s, just in case there's any question from the younger crowd) down at the old Cordele regionals in August. Yes, it was hot, humid, gnat infested, and plagued with T-storms almost every day. But we flew almost every day.

I'd lost time starting early until, like clockwork, the day broke open and I finished in mid afternoon not long after it really got good. I managed to launch again, then had trouble working up for a start. The clouds still looked good but the day had clearly peaked and the better thermals were harder to find. Rather than plunging ahead, rejecting every soft thermal under a promising cloud and running for the next established cloud a bit farther out than before, I slowed up as I came under the cloud and did S turns and search patterns until I found the [inevitable] strong core. It seemed like a more cautious, possibly even slower way to fly than the exuberant way I'd come home an hour earlier. But I felt like I couldn't afford to drive low late in the day waiting for the good thermal. On the final leg, I was a lot more patient waiting for the "get home" thermal I needed and cruised in to find I had won the day with, IIRC, a 10-15 mph faster speed than my first trip. Hmmmm.

I've never forgotten that lesson. True, it's not always applicable. Often I slow too soon or do a little search and fall behind another pilot who is more resolute on driving straight ahead. But when it's uncertain, it can really pay off to exercise a degree of caution. It costs a lot less time to search a bit for a good thermal near the bottom of my desired working band than it costs searching for and thrash around in a survival thermal down low.

Chip Bearden

Chip its interesting that as a lowely 1-26 driver, I have found that the Go-a-little-slower, S turn to find the better lift, and stay in the better part of the thermal band, has become standard operating procedure for me in trying the stretch out some longer and actualy faster xc flights. The schuman principle appears to apply even to the lower performance end of the spectrum.
Dan 1-26 #225