Doom 3 BFG Edition Update 1 SKID
Latia Shiels
Finally getting a lot of my shelf of doom cleared. This one frustrated me very early on, it's a really detailed and intricate kit, but it's a bit of a nightmare to put together. Some of the parts (cab rear wall, side panels and more) attach by just lining them up by eye, no contact points, pins or nothing to hold them in place. As such its almost impossible to line everything up straight (very evident in the rear photo). Still, the end result is good, but this was a bit more of a wrestle than I was hoping for. Quite happy with my mud though
Batman v Superman: Dawn of Justice was incredibly controversial, with many seeing its poor reception and contentious nature among even hardcore DC fans as being the moment in which the "DC Extended Universe" was doomed. This reception got reflected in its box office intake, with the film experiencing a 69 percent drop in revenue in its second weekend in theaters. Quantumania has done even worse, with its 69.7 percent second-weekend drop having a much smaller intake than the DC flick. Many had debated whether the third Ant-Man film would make $100+ million domestic in its opening weekend, and while it pulled this off, it's so far been downhill from there.
And many of these films featured fan-favorite heroes who had been seen since the earliest moments of the MCU. If their and Ant-Man's adventures aren't drawing crowds anymore, it could spell doom for what Marvel Studios plans next. Guardians of the Galaxy Vol. 3 is likely a lock in terms of being a success, as those films' popularity almost transcends the MCU. Unfortunately, the deck is stacked against the recently delayed The Marvels, which notably connects to two Disney+ shows. Likewise, it remains to be seen how some of the mantle swaps will play out with the general public, as Captain America: New World Order will feature Sam Wilson as the new Cap.
The X-15 famously used a pair of steel skids as the main landing gear rather than conventional wheels, which saved weight, allowed the skids to be mounted externally (where wheels and tires would have been destroyed) so they didn't take up internal space, simplified the extension mechanism, etc.However, they were also mounted very far back compared to most conventional tricycle-gear airplanes. Rather than being just a little ways aft of the CG as usual, they were way back under the tail. This caused some unusual behavior on landing - in addition to giving the pilot almost zero pitch control as soon as the skids touched (since they were directly under the tail, the stabilizer had no lever arm to pivot around them), it did weird things to the landing loads. From NASA book SP-60, "X-15 Research Results":
The primary cause of the unconventional response is the craft'sdownward rotation onto the nose gear immediately following the maingear's touchdown. Significantly, this movement onto the nose gearcauses a subsequent rebound onto the main gear, providing a muchhigher load there than that at initial touchdown. In addition, thenose gear encounters loads that are two to three times greater than ateither of the main-gear skids. Another unique feature is that the gearloads achieve about the same maximum level whether the pilot"greases-it-on" or lands with a high rate of descent. These new gearcharacteristics have not been without problems. Much study andanalysis of the dynamic response of the airplane during landing hasled to strengthening the gear and back-up structure and modifying thenose gear so as to provide greater energy absorption.
In other words, there was actually a much higher load through the struts after the nose gear touched down when it settled back than the load from initial skid contact. NASA tech memo X-639 (19630002688 in the NTRS) even comments that if the skids were moved forward it would behave more like a regular fighter jet, but doesn't take that thought any further.
So... why did they choose to put the skids way back there rather than close behind the CG? Was it for better directional stability at touchdown with a sucks-at-low-speeds vertical stabilizer and rudder? Or was it just to provide clearance for the ventral fin stub at high landing AoA while keeping the gear short? Or, was it simply that there wasn't room left for landing gear and the required internal structure at a more conventional location? (Or as it often is, a combination of these or other factors?)
Indeed as Peter Kämpf said, the skids were only used for landing; the takeoff on X-15 was done by attaching it to the starboard wing of a modified B-52, known as the NB-52A. This was the only way it could takeoff - it couldn't takeoff on its own.
With that in mind, it makes sense to place the skids as far aft as possible, since doing so maximizes the clearance for the gigantic ventral fin. However, even that was not enough; a large part of the ventral fin had to be jettisoned (it was detachable) before landing in order to have enough clearance. The fin was deployed with a parachute, and with hope that it would land safely so that it could be reused.
The placement of the skids did have an effect of increasing the nosewheel load, resulting in a "see-saw" type of loading back onto the rear skids, but the engineers who marveled at this may have underestimated the contributing loss of wing lift (from lowering of AoA) to the "secondary load peak".
Moving the skids closer to the CG would follow conventional wisdom of "taking it on the mains" but would increase the chance of an uncontrollable nose pitch up if the nose wheel hit first, which would have resulted in a heavy tail strike. Touching down on the rear skids first would help lower AoA and reduce airspeed before the plane fully touched down$^1$.
Due to complexity, weight, and precious space occupied inside the fuselage, wheeled landing gears were not an option on such an experimental airplane. Tires' heating would have been an insurmountable problem, too: on the SR-71 for example, the tires of the main landing gear "contained aluminum and were filled with nitrogen. They cost $2,300 and would generally require replacing within 20 missions"; plus the "air-conditioning system was also used to keep the front (nose) landing gear bay cool" (source: Wikipedia). The skin-friction heating increases more or less with the square of the Mach number and since the X-15 was flying at twice the Mach number of the SR-71 it meant a far higher airframe temperature. Main landing gear in the form of simple skids were therefore the only viable solution.
Putting the landing gear just behind the CG like in most conventional design was also not doable: to avoid tailstrike at the high angle of attack of the approaching phase, their struts should have been very long, heavy and bulky (think about the Concorde). So the skids had to be located far back on the fuselage.
But there was also another important aspect to drive the placement of the skids. During approach, in order to compensate for the high AoA and high sink rate, the horizontal stabiliser had to be set at a quite negative deflection to trim the aircraft. Upon touchdown, both the AoA and the sink rate went immediately to zero and the horizontal stabiliser suddenly found itself generating a huge download. Now, if the main landing gear were located just behind the CG like in a conventional design, this huge download on the horizontal tail would have made the aircraft pivot around the main landing gear and sink the tail into the ground. The skids had therefore to be placed well behind the CG to avoid this effect. Theoretically there was an optimal distance behind the CG, somewhere halfway between tail and CG, but it would have been not enough to avoid tailstrike and the skid were finally placed at the far end of the fuselage. This gave the X-15 a quite peculiar landing: upon touchdown with the skids the nose was forced down quite abruptly; then nose suspension got compressed and then extended back pushing the nose up; this up-nose movement downloaded on the skids suspension which then got compressed and extended back as well. After a couple of back and forth jumpings, the X-15 came to slide on the lakebed. This video from Wikipedia shows this behaviour quite well.
New regulations that went into effect on December 15 purport to help restaurants prepare for winter road conditions that could jeopardize customers' safety if cars skid into dining areas, which are often set up in blocked-off parking spots and on sidewalks. Restaurants now must fill their roadway barriers with sand or soil. For many, this rule requires adding interior walls and bottoms to the structures, or ripping out the plants that restaurateurs added earlier in the year. Most restaurants also will be forced to add "a plastic water-filled barrier in front of the roadway barrier facing oncoming traffic," per the DOT, which says a street's crash rates and traffic volumes will determine which restaurants are exempt. Reflective tape must be added too. The tape and plastic barriers will be provided by the city.
The Jets (5-3), who snapped a 12-game skid against AFC East opponents by beating Miami three weeks ago, couldn't change their fortunes against the Patriots - even while debuting their stealth black alternate helmets.
When the asteroid hit, it punched a hole in the Earth. Most of the rock in the area was vaporized, but some of the remaining rock in the crater's center surged back up, creating a plateau. Had the asteroid hit straight on, that plateau would have been even (picture a rock dropped into mud from above), but instead, it has a 60-degree slope (picture a skid mark from a rock thrown sideways into mud).
The researchers also found that the angles of the rocks at the center of the plateau and at part of the outer rim of the crater aligned, which indicated the direction the asteroid moved as it created the giant skid mark.
Within a minute of the impact, the asteroid had bored a hole nearly 100 miles wide into the seafloor, vaporizing sulfur-rich rocks as it skidded deeper into the Earth. That created a bubbling pit of molten rock and super-hot gas. The contents of that fiery cauldron skyrocketed, creating a mountain-high plume of gaseous sulfur and Co2 that blotted out the sun for decades afterwards.
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