Archive for May 2013
Porsche reveals more details on upcoming 918 Spyder hybrid
Before there was a Porsche Panamera plug-in, there was the 918 Spyder plug-in hybrid. And while the Panamera S E-Hybrid might make it to market first, the 918 is on the way, too. This week, Porsche revealed new details about the race-inspired track rocket, which serves as its most advanced, expensive sports car ever.
A lot has changed since Porsche first premiered the 918 Spyder concept carat the 2010 Geneva Motor Show. What was once an absolutely groundbreaking show-stealer is now but one of the boys. Jaguar, Ferrariand McLaren have since revealed hybrid supercars that rival the 918 in technology and performance.
In light of that ramped up competition, it's not all that surprising that the 918's output number grows yet again. When we first saw it in 2010, it had a total system output of 715 hp. At NAIAS the following year, it was upgraded to 767 hp. Rumors last summer spiked that number up over 800 hp, and as it turns out, it will land closer to 900 hp – 887 hp to be exact.
The 918 Spyder hybrid relies on three separate power units to reach that 887 hp figure. The main unit is a 608-hp 4.6-liter V8 engine fitted amidships. That engine is a derivative of the V8 used in the LMP2 RS Spyder race car and delivers engine speeds of up to 9,150 rpm. Assisting the V8 through five different drive modes are a 154-hp rear-mounted electric motor and a 127-hp front-mounted electric motor.
The rear motor is part of a hybrid module that includes a decoupler that connects it with the engine. It can power the rear axle in tandem with the engine or on its own, and the engine can also power the rear axle on its own with help from a seven-speed PDK transmission. The front motor completes an independent all-wheel-drive system and drives the front wheels with a fixed ratio. It decouples from the front axle at higher speeds. Electricity is stored in a 6.8-kWh liquid-cooled lithium-ion battery that can be charged in 25 minutes with the optional DC Speed Charging Station, 2 hours with 240-volt charging and 7 hours with 110-volt charging.
The 918 has five separate driving modes that alter the output of the three power units to give the car a multiple personality disorder that ranges from fuel-frugal electric car to fierce, track-hungry racer. The driver can select these modes from a motorsport-style "map switch" on the steering wheel.
The default mode upon start-up (assuming the battery is full) is E-Power, which uses pure electric power to send the 918 up to 18 miles (29 km). The V8 engine only kicks in when necessary. Without the V8, the 918 is working with its strong arm behind its back, but is still able to hit 62 mph (100 km/h) in seven seconds and top out at 93 mph (150 km/h).
When the battery drops below a certain level, the 918 switches automatically to Hybrid mode. This mode makes use of both electric and V8 motivation with the goal of maximizing fuel efficiency.
Sport Hybrid and Race Hybrid make use of both electric and gas motors, but they do so with the goal of performance, not efficiency. The V8 engine takes over primary propulsion responsibilities in Sport Hybrid mode, and the motors kick in to add boosting power. Race Mode seeks to optimize performance even further, with the engine operating under high load, charging the battery when the driver is not utilizing its maximum output. The increased battery charging allows for shorter, more powerful boosting from the electric motors. The final mode works in conjunction with the Race Mode – a "Hot Lap" button in the middle of the map switch directs whatever battery power is left toward motivating the fastest performance over a few laps.
The Porsche Active Aerodynamic system helps match the 918's aerodynamic characteristics to the current drive mode. When the car is in Race mode, including Hot Lap, the system angles the rear wing steeply to increase downforce at the rear axle. Two adjustable air flaps on the front of the underbody also open to create a ground effect at the front. In Sport mode, the spoiler angle decreases and the underbody flaps close, cutting drag and opening up higher top speeds. In E-Mode and Hybrid, the goal is to cut aerodynamic drag as much as possible, so the rear wing retracts, the underbody flaps close and a set of front air inlets, which are open for engine cooling in Race and Sport modes, close.
The car also uses a rear-axle steering system that moves the rear wheels up to 3 degrees to increase handling and agility. At low speeds, the rear-steering system moves the rear wheels in a direction opposite to that of the front wheels to make cornering faster and more precise, reducing the turning radius. At higher speeds, the system steers the rear wheels in the same direction as the front wheels, improving stability.
When you look at the Porsche from the back, one of the most eye-catching aspects is the big afterburner-like tailpipes jutting out from just behind the engine. These "top pipes" funnel hot exhaust gas out in as short a path as possible, promoting better heat removal and engine and battery cooling. They also give the car a hearty exhaust note.
The 918 Spyder isn't quite as advanced as the P1 or LaFerrari when it comes to weight savings, but it does employ some thoughtful measures to keep curb weight at its 3,715 pounds (1,685 kg). In addition to the carbon monocoque, its load-bearing structures and subframe are also made from CFRP. Engine components like the CFRP oil tank, titanium connecting rods and high-strength, lightweight steel crankshaft add to the weight savings. Porsche concentrates weight low and to the center wherever possible, and the 918 has a 57-43 percent front-rear axle load distribution and a low center of gravity that's right around the height of the wheel hubs.
The optional Weissach package drops just short of a hundred pounds off the 918 (curb weight: 3,616 pounds/1,640 kg) through lightweight magnesium wheels, elimination of some sound insulation and other measures. It includes a race-inspired look with visible carbon on the exterior and special Alcantara, six-point seat belts and carbon upgrades inside.
While the Porsche is on the low end of the exotic hybrid supercar output scale (the LaFerrari boasts 950 hp and the McLaren P1 903 hp), its performance is right in line with its costlier competitors. Porsche lists the car's 0-62 mph (0-100 km/h) time at 2.8 seconds, its 0-124 mph (0-200 km/h) time at 7.9 seconds and its top speed at 211 mph (340 km/h). Compare that to the LaFerrari's list of 2.9 seconds, 7 seconds, 217.5 mph (350 km/h), and the P1's list of 3 seconds, 7 seconds and 217 mph (349 km/h). It's only at its 23-second 0-186 mph (0-300 km/h) time that the 918 shows its heavier weight and lower power (LaFerrari: 15 seconds, McLaren P1: 17 seconds).
The 918 looped Nurburgring's Nordschliefe in 7 minutes 14 seconds last September - well under the 7:22 that was being discussed a few months prior. Porsche seems confident that it can push the car around the North Loop even faster, so look for that number to improve in the future.
Porsche hasn't updated the estimated fuel economy of the 918, but make no mistake: This isn't meant to be a small hybrid system increasing performance on a big, fume-spilling hypercar. Porsche says that its goal in designing the car was to combine "the dynamic performance of a racing machine with low fuel consumption." Porsche has said in the past that the 918 could return 100 kilometers on 3 liters of fuel while emitting 70 g/km of CO2. We'll have to wait for official testing to see how accurate those numbers are.
Porsche opened the order books for the US$845,000 Spyder plug-in hybrid back in 2011. The addition of the Weissach package jacks the price up to $929,000.
Source: Porsche
Thin-film solar cells could become more efficient – thanks to moths' eyes
Because moths need to use every little bit of light available in order to see in the dark, their eyes are highly non-reflective. This quality has been copied in a film that can be applied to solar cells, which helps keep sunlight from being reflecting off of them before it can be utilized. Now, a new moth eye-inspired film may further help solar cells become more efficient.
The film, developed at North Carolina State University by a team led by Dr. Chih-Hao Chang, is designed to minimize “thin-film interference” in thin film solar cells.
Thin-film interference is what causes gasoline slicks on water to take on a rainbow-colored appearance. Some sunlight is reflected off the surface of the clear gasoline, while some more penetrates its surface, but then is reflected back up through it by the surface of the underlying water. Because the two sources of reflected light have different optical qualities, they interfere with one another when combined – thus the rainbow effect.
The same sort of phenomenon can occur when any thin, transparent films are placed together. In the case of thin-film solar cells, which are made up of layered films, some of the sunlight is effectively lost at every film-to-film interface where the interference occurs.
To keep this from happening, Chang’s team created films with built-in cone-shaped nanonostructures, similar to those found on moths’ eyes. When present on the surface of one film, these structures are able to penetrate into the underside of a film laid over top of it, meshing them together almost like Lego pieces. As a result, much less in the way of thin film interference occurs between the two. This process could be repeated as several films are layered one on top of the other.
According to the scientists, the amount of light reflected by one of these nanostructured interfaces is one one-hundredth the amount reflected by a regular film-to-film interface. They now plan on using the technology in a solar device, with an eye towards commercial applications.
A paper on the research was published this week in the journalNanotechnology.
Source: North Carolina State University
NASA's OSIRIS-REx asteroid sample return mission goes to development
NASA’s first asteroid sample return mission took a step closer to reality on Wednesday, as the OSIRIS-REx project was cleared for development and testing. Scheduled to launch in 2016, the mission passed a series of detailed project assessments and now goes on to the development phase. The Origins-Spectral Interpretation Resource Identification Security REgolith Explorer (OSIRIS-REx) is intended to rendezvous with the asteroid Bennu (1999 RQ36) in 2018, carry out an extensive survey, and return a 2-ounce (60 gm) sample of its surface to Earth in 2023.
OSIRIS-REx’s mission objective is to carry out the most detailed study so far of an asteroid. In addition to returning a sample of the dust and other small particles that make up the regolith that coats Bennu, OSIRIS-REx will also study its chemistry, mineralogy and topography, compare telescope-based data with on-the-spot observations, and make a precise determination of the asteroid’s orbit.
The latter is of particular importance because NASA wants to study the Yarkovsky effect. It’s been known since 1902 that heating of an asteroid by the Sun and then re-radiating that heat affects the object’s orbit. As the asteroid turns, the face heated by the Sun turns into darkness and radiates heat. The escaping radiation produces a tiny thrust that over the course of centuries can significantly change its orbit. Considering current concerns over protecting Earth from wayward asteroids, this effect could be of great importance in assessing possible threats.
OSIRIS-REx is about 2 meters (6.6 ft) on each side and is powered by lithium-ion batteries using active solar arrays covering 8.5 square meters (91 sq ft). There are a battery of instruments for studying Bennu, but the star is the Sample Return Capsule (SRC) for bringing back samples to Earth. It’s the same as that used in the Stardust mission, that returned samples of a comet’s tail in 2006.
The samples will be collected using the Touch-And-Go Sample Acquisition Mechanism (TAGSAM). This consists of a simple sampler head attached to an articulated arm developed for the Stardust mission. During sample collection, OSIRIS-REx comes within 25 meters (82 ft) of Bennu and the arm extends. As the cylindrical head briefly touches the asteroid, nitrogen is blasted into the head for five seconds, blowing a sample into the outer wall of the cylinder for collection. If the first attempt isn’t successful, there’s enough nitrogen onboard for three tries. Once collected. the sample is visually verified, then the head is placed inside the SRC. When OSIRIS-REx next approaches Earth, the SRC is jettisoned for reentry and recovery.
The principal investigator for the mission is the University of Arizona, and the spacecraft is being built by Lockheed Martin Space Systems in Denver. The mission itself will be under the control of NASA's Goddard Space Flight Center in Greenbelt, Maryland.
The video below outlines the OSIRIS-REx mission.
Source: NASA
