Dynamic Soaring Blows My Mind

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Marc Zeitlin

Exalted Grand Poobah
Joined
Dec 11, 2015
Messages
868
Location
Tehachapi, CA
This is a combination of ridge lift and dynamic lift. How much is ridge and how much is dynamic soaring?
0.01% and 99.9%, respectively (insert hand waving here).

Should dynamic soaring flights be made over level ground if they are a demonstration of the capabilities of dynamic soaring?
Dynamic soaring involves extracting energy out of the difference in airspeed through a shear layer - there's no requirement that the shear layer be level/horizontal. Ridge lift is merely a vertical component of the airspeed due to deflection by the ridge of the wind blowing over it - no shear layer is required. Airplanes running a ridge extract SOME energy from the rising air, but only enough to maintain altitude and airspeed - they do not accelerate to 10X their normal cruising airspeed (which, given the cubed ratio of power to velocity, implies using 1000X as much power to do so, give or take). So while a tiny bit of the energy used in these demonstrations comes from the vertical component of the airflow, almost all of it is coming from the dynamic soaring aspect.

To clarify, a level surface with some surface roughness as in the open ocean where nature demonstrates dynamic soaring.
While that's certainly where albatrosses (and maybe other sea birds) demonstrate it, it's hardly the only location where dynamic soaring can occur - anywhere there's a decent shear layer could be used, and in these RC cases, it's on the side of a hill, because that's where the shear is the strongest so the most amount of energy can be extracted.

Still - Very interesting!
That's for dang sure.
 

Bille Floyd

Well-Known Member
Joined
Sep 26, 2019
Messages
434
... It is mentioned in Helmut Reichmanns book about cross-country soaring. ...
Read that book, and I use his theories , for finding the best lift, inside a
thermal, (basically never do the same 360, in the same place as the last one) ; is
Sad, how he died ! :(

Anyone know , what the speed record is , for full scale manned gliders ?

Bille
 

Laromin

Member
Joined
Mar 16, 2015
Messages
6
Location
California
The ground speed is taken with the glider going downwind. But still impressive.
No, upwind for sure,at least relative to the prevailing wind. The wind speed underneath the shear layer tends to be modest,and depending on conditions is mostl opposite to the prevailing wind close to the ground.
 

Bille Floyd

Well-Known Member
Joined
Sep 26, 2019
Messages
434
Carbon Windex had a 300 kt Vne.
Seriously , "Impressive" numbers !!
That was a Sad ending ; how they went out of business, with
the factory and all the molds burning down. :(

This devise would have made a Great, E-powered airplane !

Specifications (1200C)[edit]
Data from Sailplane Directory and company website,[1][9] Jane's All the World's Aircraft 1988-89[8]

General characteristics

  • Crew: one
  • Length: 4.92 m (16 ft 2 in)
  • Wingspan: 12.1 m (39 ft 8 in)
  • Wing area: 7.41 m2 (79.8 sq ft)
  • Aspect ratio: 19.75:1
  • Airfoil: Radab KTH-FFA 17%
  • Empty weight: 175 kg (386 lb)
  • Gross weight: 310 kg (683 lb)
  • Fuel capacity: 20 l (5.3 US gal; 4.4 imp gal)
  • Powerplant: 1 × König SC-430 3-cyl. air-cooled two-stroke piston engine, 15 kW (20 hp)
  • Propellers: 2-bladed Radab variable-pitch feathering Epoxy/Kevlar propeller, 1.05 m (3 ft 5 in) diameter
Performance

  • Maximum speed: 270 km/h (170 mph, 150 kn) level flight
  • Cruise speed: 210 km/h (130 mph, 110 kn) 50% power
  • Stall speed: 70 km/h (43 mph, 38 kn) powered
  • Never exceed speed: 350 km/h (220 mph, 190 kn) in smooth air
  • Max rough air speed: 252 km/h (136 kn; 157 mph)max fuel no reserves
  • g limits: +9 -6
  • Maximum glide ratio: 36:1
  • Best glide speed: 100 km/h (54 kn; 62 mph)
  • Rate of climb: 2.5 m/s (490 ft/min)
  • Rate of sink: 0.61 m/s (120 ft/min)
  • Minimum sink speed: 80 km/h (43 kn; 50 mph)
  • Wing loading: 41.83 kg/m2 (8.57 lb/sq ft)
  • Power/mass: 16.1 kg/kW (26.45 lb/hp)
 

malte

Well-Known Member
Joined
Feb 5, 2011
Messages
136
Location
Flensburg / Germany
A note on the history of dynamic soaring: I stumbled across an old booklet "Handbuch für dne Jungsegelflieger" (Manual for the young glider pilot) by Stamer and Lippisch, printed 1930. In the glossary "Alphabetisches Verzeichnis besonders in Gleit- und Segelflug häufig vorkommender Fachausdrücke mit kurzer Erläuterung", dynamic soaring is mentioned:

1614764279619.png

Dynamic soaring: In contrast to the usual kind of soaring in updraft a - for the time being only theoretically existing - kind of soaring through utilisation of variations in speed and direction of horizontal winds is called dynamic soaring.


So the smart minds in soaring have figured out the possibilities quite early in history, even if technical means in aircraft construction did not enable them to utilise it. Since this is a more popular booklet for young glider pilots, I reckon there will be some scientific articles published on the topic way before 1930. (I don't have the time to trace it back though).
 

aivian

Member
Joined
Apr 9, 2019
Messages
6
So the smart minds in soaring have figured out the possibilities quite early in history, even if technical means in aircraft construction did not enable them to utilise it. Since this is a more popular booklet for young glider pilots, I reckon there will be some scientific articles published on the topic way before 1930. (I don't have the time to trace it back though).
Lord Rayleigh's observations of albatrosses "The Soaring of Birds" from 1883 is generally thought to be the earliest study of dynamic soaring. His analysis was largely qualitative but clearly lays out the basic ideas of dynamic soaring. As you show, the early literature of soaring is mostly in German. A lot of it is also not captured in a way that is easily searchable, but the basic theory was certainly worked out analytically by the late 1920s. Barnaby has a pretty good analysis of optimizing crossing a ridge line which includes dynamic soaring effects in his 1930 "Gliders and Gliding."

For all of the impressive analysis, the performance of early gliders was such that dynamic soaring (and to a large extent even speed variations in conventional soaring) was effectively irrelevant, but it is impressive how comprehensively soaring theory was worked out ahead of design and construction technology to fully take advantage.
 
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