Dolphin flying

Could any of you shed some light on use of flaps while dolphin flying? I.e., in my DG-400, cruising at 70 - 75 knots with -4 degrees flaps, if I fly under a cloud and want to maximize the climb without thermalling, what is the best approach in terms of shifting gears with the flaps? I assume this is dependent on many different factors, but is there a general consensus about whether or not to down-shift to 0 degrees or positive (thermalling settings) flaps when flying straight?

On Sunday, February 28, 2016 at 7:54:18 AM UTC-7, Paul Villinski wrote:
Could any of you shed some light on use of flaps while dolphin flying? I.e., in my DG-400, cruising at 70 - 75 knots with -4 degrees flaps, if I fly under a cloud and want to maximize the climb without thermalling, what is the best approach in terms of shifting gears with the flaps? I assume this is dependent on many different factors, but is there a general consensus about whether or not to down-shift to 0 degrees or positive (thermalling settings) flaps when flying straight?

My answer to this flap question will not agree with the intuition of some flyers -- here is the truth on the matter according to GW:

Flap optimization is not about airspeed; it is about angle of attack. If you are going to slow down, the time to lower the flaps is when you make that decision and start pulling the stick back increasing AOA. Conversely, when you speed up, best to raise the flaps as you begin to push.

However, there is an important caveat to this. Most gliders have a structural speed limit for positive flaps. Despite what may be performance optimal, one must never overspeed the flaps.

Should someone express a counter opinion (likely), please do not misinterpret a lack of further reply on my part.

Years ago I talked to Wil Schuemann about the system he installed in his modified ASW 12. The stick had a detent for the center position and he used it primarily for aileron control. Pitch control was almost exclusively using the flap lever except for takeoff, tow, landing, etc.

I didn't install a detent in my LS-3 but because my glider had no detents in the flap drive as it came from the factory, I started using the flaps somewhat as Wil did. As he had assured me, it was a wonderfully smooth way to fly. Pull ups were slower than I wanted in those days of dramatic zoomies so I would "help" the process along with a quick pull on the stick as I entered a thermal at cruising speed. But at the top, instead of pushing over, I'd use the flap lever to bring the nose down smoothly, than bank and snap the flaps down for thermaling. I used the stick normally to thermal because the airplane reacted faster although I wonder now if I could have benefited there, too. When I was ready to exit, I'd use the flaps to lower the nose and accelerate.

The caveat was that this worked best if the glider was set up so the stick was in the same position for slow and higher speed flight. At Wil's advice, I measured the distance between the instrument panel and the top of the stick in straight flight at min sink and again at cruising speed (defined as the lowest speed for which I would use full negative flaps) and found that with my aft CG position, it was spot on.

I'm not saying this is the best way to fly. But it might be worth experimenting with. One caution as a layman: be careful about getting too slow with the flaps in negative position. The fuselage will be rather nose high and if you were to lower the flaps quickly, the angle of attack would increase just as quickly. If you stall in that position, the wing wake could be higher than the tail, which is a nasty prescription for "deep stall." I know a pilot who apparently did just this, entered what sounded like deep stall (stable, uncontrollable, nose-high, very high rate of descent, with no ability to lower the nose) and was lucky to escape about the time he was thinking about bailing out.

Chip Bearden

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.

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).

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

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

Very interesting read, thanks for sharing and linking!