It appears that the aerostat provides all of the lift for both parachutes. And whatever the first parachute is open or shut does not significantly change the elevation angle of the two parachutes while that of the aerostat is very high.
Under these conditions, to increase the number of parachutes or their total area as well as stability, it would be necessary to increase the dimensions of the supporting element (aerostat or kite lifter), which would become difficult from a certain threshold.
Parachute of projected area of about 5 m², with a lifter kite of 1.7 m². In spite of the high area of the lifter kite compared to that of the parachute, this one flew at a low angle of elevation (about 10 to 20 degrees) compared to that of the lifter kite (50 degrees). Moreover oscillations occurred from top to bottom. The tether of the lifter kite was attached to the periphery of the central hole.
Indeed, both Guangdong parachute device and the presented parasail device are tether-aligned AWES. They are not crosswind kites. So the power-to-area ratio is far lower than that of power kites as I mentioned. In the other hand the implementation can perhaps be easier (relatively simple control). Power to space use ratio can be comparable or higher since the whole wind area could be harnessed (while in crosswind mode some wind areas are not harnessed within the figure). And also:
And as the parasail absorbs less power per unit of area, wear could be less.
In my initial comment, I presented solutions with parachutes, showing the problems, then going to parasails as a possible solution.
The other alternative would be the implementation of power kites in Low radius loop mode. But I don’t have any ideas for yo-yo mode, other than the implementation of a control pod (close to the kite) which could be too heavy and hinder the rotations. And stacking in a train could be more difficult.
Yo Yo mode… Rotating and reeling out. Like a funnel shaped corkscrew. The shape is easy enough to understand, but to orchestrate in real life… It would actually be possible to do with a two line power kite and two people holding a reel each, I’d watch that dance.
Abstract: This report explores the feasibility of a new sea arrest system in which a UAV is arrested by a parasail attached to a ship, and aims to obtain the optimal parasail sizing for the system through aerodynamic testing in a wind tunnel. Extensive literature review was conducted to evaluate the advantages and disadvantages of current sea arrest systems such as the Skyhook used for the ScanEagle, which illustrates the relevance of having a parasail arrest system in the market. The main advantage of the parasail arrest system is that it is able to accommodate larger UAVs with higher approach speeds. In the experiments, the dimensions of the ScanEagle was used as a reference for the calculations. The rig for the wind tunnel testing was assembled manually, along with a scaled model of the parachute and parasail to be tested. Several setups were used during the wind tunnel testing to ensure the accuracy of the data obtained. The mechanism and aerodynamics of the parasail arrest system was also explained using free body diagrams. Through aerodynamic testing of the parachute and parasail, it was observed that the parasail had a significantly higher drag coefficient compared to the parachute. Based on the scaled down models, the CD value of the parasail was found to be 2.727 compared to that of the parachute which was only 0.645, giving a performance increase of more than 300%. This is beneficial to the system as a higher CD value will lead to a higher drag force experienced, assuming the planform area for the parachute/parasail is the same. The drag force will assist in decelerating the UAV, and having a larger drag force means that a smaller parasail could be used in place of the parachute. Furthermore, due to the airfoil shape of the parasail’s canopy, the parasail experienced lift which will allow it to partially carry the UAV’s weight, thus reducing the impact load during the arrest. This will prevent it from crashing into the ship, therefore ensuring a safe recovery process. As there were additional benefits of using a parasail in the arrest system such as the higher drag coefficient and lift force present, it was concluded that the parasail was a more efficient option to use in the arrest system compared to the parachute. The optimum parasail sizing was then calculated based on the ScanEagle’s dimensions.
I put in bold some interesting extracts.
If it is verified that “the CD value of the parasail was found to be 2.727” the parasail could enter High drag coefficient devices.
We can notice the similarity between the shape of the parasail and that of many parachutes with a high drag coefficient on the following point:
On other points the following site offers interesting information:
The fabric of our parasails is crafted from 6.6 ripstop nylon yarns, silicon-coated on both sides to prevent air penetration. This silicon coating also protects the parasail fabric from corrosive chemical reactions that can occur when in contact with salty sea water. To ensure longevity and vibrancy, our fabrics are stained with UV doped pigment to resist fading under the sun.
We offer two different fabric qualities to cater to different budgets. Our standard series fabric has a thickness of 1.6 oz and boasts an average service life of 2500 flights or more. For those seeking a lighter option, our professional series fabric weighs in at 1.3 oz and can endure approximately 5000 flights or more, depending on usage.
This seems to lead to a longer lifespan than what we are used to seeing on other soft wings.
Conversely, a parasail contains many separate pieces of fabric. This is why I am tempted to qualify it as a network kite (unlike the parachute or the parafoil), even though the said elements form the whole shape.
If one of the scaling possibilities is linked to the existence of separate elements, even if they are not identical kites flying together, we could reconsider the different forms of kite networks.
On the photo of a parasail below, we see the elements that are separated by vents and vent slits:
For example, imagine that for a multitude of Daisy, you use a sort of giant parasail connecting them all and forming the kite network…
Thus we assume that a kite network can scale far more than a unit which composes it, in the classic conception of a kite network made of identical and autonomous units. For what? Perhaps thanks to the air spaces between the units, and not exceeding the limits of the fabric according to the bridle per piece.
But in this case the air spaces between the not necessarily identical and non-autonomous elements of a whole forming a single kite could have the same utility. And here we have the parasail, which is indeed an existing example of a starting kite network, and which could be reworked for an AWES yo-yo, or as a more easily achievable (?) giant lifter kite.
Sure a parasail has been proven to work as a kite.
Who doesn’t love an Air-Bear
Air bear isn’t as heavy as a full sized bear
In towed mode behind a boat the average minimum take off speed for a parasail with passenger is ~6.5m/s
Surely we can find panel configurations with higher lift performance (maybe less stable) than that
For a yo-yo use, I am interested in the indications below if they are true:
For tethered-aligned AWES a huge drag coefficient leads to a higher thrust. If the Guangdong AWES (video) was equipped with parasails instead of umbrellas (parachutes) the thrust and the power would be higher, and each unity would have autonomous lift.
And it seems that parasails fly at an angle of elevation of about 25-35 degrees when we look the photos. So this confirms that the lift coefficient (Cl) is likely high. That said parasails can be made in several versions. For a lifter kite, 35 degrees is not enough. But for power generation, this is a value we found for other AWES (yo-yo, flygen, rotary) in (quasi) crosswind flight. Power generation induces a strong horizontal component.
In fact, the parasails are already prepared for the marine environment. That said, I would have liked to have other recent indications of lift and drag coefficients (Cd and Cl) than in the abstract (a huge Cd of 2.727 that I mentioned leading to a thrust coefficient above 3), as well as examples of elevation angles for which I did not find than hypothetical values, such like 36 degrees, from exercises:
If 30 or 35 degrees is a typical value, parasail elevation angle could be compared to average (the central point of the flight figure) elevation angle of crosswind yo-yo (SkySails) or flygen (Makani).
Onshore, perhaps higher elevation angles and lower efficiency could be achieved in order to harness higher winds, and also to use less space.
An old document provides some information about parasails from page 107:
Effective Drag Coefficient Averages of the effective drag coefficient for each drop are presented in table 111-V. These values were based upon the nominal area of the canopy. The averages for all drops with nominal rigging were calculated to be CDeff = 1.43.* […] *Lift and Drag Coefficients Average values of the nominal lift and drag coefficients for each drop are presented in table m-V. These values were based upon the nominal area of the canopy. Averaging these values for those drop tests with normal rigging enables the determination of representative coefficients for lift and drag. These averaged values are CLo = 0.51 and CDo = 0.49.
I think the large difference between the two values of coefficients corresponds to that of a parachute at the start of opening then a fully open parachute.
For those drops without rigging modifications, the average L/D was approximately 1.04