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charliemonster42 posted:Not sure how you can get it so wrong that you spin the plane while trying to maintain best glide speed, but like I said, I wasn't there. Very easy: 99% of the time pulling on the stick/yoke and raising the nose makes the airplane go up, so that response gets hard wired into our muscle memory. And when the engine quits, when you're in full panic mode, it's hard to overcome that hard-wiring and put the nose down to maintain speed when every fiber in your being is screaming "I want to go up" and your hand reacts in the normal "go up" mode.
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May 13, 2014 00:47
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According to the Wiki article on chaff, both sides invented it independently around the same time, and both sides didn't use it for about a year after inventing it for fear that the other side would copy the technology and use it against them.
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Jul 21, 2014 17:56
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Ola posted:I think this vid has been posted before, but worth repeating. The sound of the overrev and immediate self destruction is something else. I was there and saw that. There are 2 times in my life I was taken aback by how unnaturally loud something was for how far away it was. One was sailing on a sailboat and hearing a cargo ship's horn a mile or so away from us...and the other is this.
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Jul 28, 2014 01:40
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Ospreychat question: can you fly steady-state with the nacelles in any position, or are there ranges where you can only pass through but can't stay?
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Jul 31, 2014 03:45
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Um, anyone else just see that jet shooting flames out of the exhaust after the low pass? Didn't see what type it was, and if a single or twin, but I'm pretty sure it wasn't an afterburner. It flew away level with with someone else on its wing.
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Aug 1, 2014 00:21
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Nerobro posted:The physics gets a little more interesting at those speeds too. ;-) Like the air exiting the plane might be going forward in relation to the neighboring air. Correct me if I'm wrong, but this is impossible in a forward-thrust producing scenario. If the plane is imparting a forward net acceleration on the air, then the resulting thrust can only be aft. Plane pushing air forward = air pushing plane backward.
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Aug 1, 2014 01:46
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Fucknag posted:False! The engine doesn't have to push the exhaust out its tail faster than the surrounding air. The exhaust gases (which in the combustion chamber are moving fairly slowly through the engine, so just a bit slower than the plane itself. As long as the gas is accelerated backwards relative to the aircraft and engine, there will be a net forward thrust, even if the gas ends up moving the same direction as the aircraft after exiting. I still maintain true. The acceleration is the change of motion (of the air) from the old to the new one, and what the vehicle body is doing doesn't matter. Taking the vehicle as the frame of reference, a rocket accelerates material from zero relative speed to some non zero value. That's propellant acceleration aft, which gives us thrust forward. (In that case, you'd be right, and the surrounding air wouldn't matter.) An airplane takes in air at, say, 500 knots and has to expel it at greater than 500. Again, aft acceleration of propellant = forward thrust. If it expels it at 510, then from the ground, it's gonna be going backward. If it pushed the air forward 10 knots, then from the airplanes frame of reference, it's slowing it to 490 and providing negative thrust.
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Aug 1, 2014 02:34
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Fucknag posted:It really has nothing to do at all with the surrounding airstream. Think of it like throwing a softball while standing on a skateboard, so that it flies back at 90 mph; the act of throwing it pushes you forward slightly, as you're basically shoving against the ball's inertia while at the same time imparting momentum to it. Even if you're already moving 100 mph, if you throw another softball it still imparts the same force on you and accelerates you by the same amount. It has everything to do with the surrounding airstream, because you're trying to produce a force by taking that surrounding air and accelerating it. By giving it a momentum change aft, as you say, (shoving against its inertia) it does the opposite to you (forward) which we call thrust. To make your analogy applicable, you can't start with a baseball in your pocket, but rather a baseball already there in the outside environment. And even if I grant you a baseball in the pocket, what you're suggesting is that you can throw it from the skateboard and have that cause you to accelerate in the same direction. YF19pilot posted:You do realize that the XB-70 Valkyrie uses engines that can't operate at the speeds it's flying at, right? quote:The air going into and out of the engine is slower than the Mach 3+ that bird flies at. Source, please. The air going into the engine at mach 3 is mach 3. Remember we're talking about net velocity change, meaning you simply subtract what goes in from what comes out. Any speeding up and slowing down it does inside the engine (including the intake before the compressor face) are inconsequential to the overall momentum change. You can't start counting after the slowdown in the intake, because you then have unaccounted-for momentum change.
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Aug 1, 2014 05:07
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BobHoward posted:
The fuel mass is the only remotely plausible scenario, because it, like rocket propellant, starts from zero speed and any acceleration is aft. But, unlike you I don't think it's true, because the fuel mass compared to the air mass is exceedingly small. In a piston engine, it's something like 1 to 15, and in a jet engine, you're throwing heaps more air into it that you're not even combusting (but are accelerating). And that's without bypass. With bypass, add even more air yet.
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Aug 1, 2014 05:14
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Snowdens Secret posted:I'm not getting into the rest of this, but a turbojet engine can only breathe subsonic air. It doesn't matter how fast the craft is going, the air must be subsonic by the time it hits IIRC the first compressor stage, if not earlier. This is why modern-ish supersonic jets have complicated intake systems to control the mass of air entering the inlets, where expansion into the internal inlet volume reduces the velocity of the airstream. I know that, and referred to it in the very post you quoted ("the slowdown in the intake"), so I'm not sure what you're addressing here. I repeat with emphasis that thrust depends on NET momentum change, which is the momentum of the exhaust flow minus that of the intake flow before it has been affected by any interaction with the engine. (I.e., the free stream flow) e: http://www.grc.nasa.gov/WWW/k-12/airplane/thrsteq.html
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Aug 1, 2014 05:32
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BIG HEADLINE posted:Fun Fact: during one of the 'dogfight' scenes with Zeros in this film, one of the pilots nearly smacked his plane into the water after stalling too close to the ground. They left it in. And these were the days with the Pratt and Whitney engines. The Tomcat didn't come into its own until it got the F110. Is there any truth to that, though? Sounds to me like there was an effective scary movie shot, and someone got too eager to hear an exciting story about it being real and started an urban myth that way.
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Aug 8, 2014 16:06
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Another fun fact about U-2's up at operating altitude. The engine (at least some earlier versions) actually had no range to make any changes, and there was only one power setting, i.e., min and max were the same. So, to begin a descent, it would have to put out drag in the form of airbrake and landing gear. (The nose couldn't be lowered because that would of course increase the airspeed, with which they also had no range to play with.)
vessbot fucked around with this message at 21:46 on Aug 20, 2014 |
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Aug 20, 2014 21:42
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Sagebrush posted:I find this hard to believe, or maybe I'm just misunderstanding. How would you get the engine spooled up without setting it on fire? How would you ever land? Or do you just mean that the engine only had one power setting (presumably somewhere up at the top of the throttle range) that would work at high altitude? It operated normally at low altitudes, what I'm talking about is just at high altitudes unique to the U-2 (that's what I meant by "operating altitude") Jet engines have all sorts of parameters, RPM, EGT, EPR, etc. (incl. torque if it's a turboprop/shaft) Usually you manipulate one to achieve a desired power setting and monitor the rest to make sure they stay within limits. Sometimes you'll have to closely watch 2 of them, like cases in shaft engines where depending on the environmentals you might either torque out or temp out first. Well, the procedure in the U-2 was to fly at the max EGT, and at that EGT, the higher you went, the lower the EPR goes. At some altitude you reach a point where the EPR you're at is the minimum allowed. Now you can't reduce power since you're at the minimum EPR, and you can't increase since you're at the max EGT. You have one power setting.
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Aug 20, 2014 22:35
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The Ferret King posted:I can't imagine nosing it over would be an issue either. The indicated airspeed up at altitude is so incredibly low due to the lack of air density. There should be plenty of airspeed overhead for acceleration unless I'm misunderstanding something. There was no overhead for acceleration, as the airspeed window of the U-2 at high altitude was literally a few knots. A few knots slower got you to a conventional high-AOA stall, and a few knots faster got you to the mach limit of the wing. Down low this is a huge window for subsonic planes, but the higher you go, the higher the stall speed becomes (in terms of TAS) and the lower the mach limit becomes (due to temperature). The window between those speeds shrinks to almost nothing, and this is known as coffin corner. http://en.wikipedia.org/wiki/Coffin_corner_(aerodynamics) (Ignore the graph though, it's wrong.) It doesn't matter if you look at IAS (about 100 knots) or TAS (about 400), the flyable window is tiny just the same.
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Aug 20, 2014 22:41
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Nerobro posted:
 And I'm sure the thrust was a lot less than 60% of that at sea level max. Off the cuff I'd throw out 20% if not less. vessbot fucked around with this message at 00:23 on Aug 21, 2014 |
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Aug 20, 2014 23:32
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Aeronautical hilarity: https://www.youtube.com/watch?v=4AubU5FeUIs A-4 formation barrel roll where one guy is buddy tanked to the one in front
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Sep 4, 2014 05:42
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Yeah, it's oil and not grease. It's easy to morph one to the other in storytelling if you're not too familiar with the subject matter. But there are antique engines flying around (I've got some time behind 2 of them) with greased valve rocker bearings. You go around the engine with a grease gun on all the zerk fittings every flight, and every couple of flights you take the rocker covers off and hand-pack the entire rocker box.
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Sep 9, 2014 23:03
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Phanatic posted:Wait, what? You're right that they'd have more asymmetry of lift, but what he meant they'd "fix" was the result of that asymmetry, the disks tilting opposite directions. The fix for the asymmetry itself is the rotors going opposite directions and cancelling out each other's asymmetries.
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Oct 9, 2014 20:09
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Tremblay posted:For reference we pay warbird operators to drop us out of their bomb bays. Due to insurance issues I think there is only one that this is still possible with. My old boss told me he did this with his T-6 until someone smashed his face on the horizontal.
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Oct 13, 2014 22:17
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Scratch Monkey posted:https://www.youtube.com/watch?v=q48Swb2ATww At the 6 minute mark and onward, we see a bunch of footage of the left wing with the aileron clearly up, but the plane is not banking. Can anyone guess/know what gives? I'll post the answer tonight.
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Oct 16, 2014 15:16
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EightBit posted:Going to guess that the aileron on the right wing is also up, acting as spoilers to control the airspeed. High altitude operation makes for strange requirements on turbine engines, probably can't throttle down any further but was going too fast. This one's the closest so far, but still a ways to go. They had other, more conventional ways to make drag.
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Oct 16, 2014 16:18
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http://allthingsaero.com/military-aviation/aircraft/gallery-world-s-fastest-formation?page=1 Just saw this pop up on another forum (Anyone else here on PPW?) They weren't allowed to set up a flight to easily take this photo, so the story involves a complicated plan involving good old moxie and derring-do, a wrung-out race Merlin struggling to keep up with a SR-71 on a standard mission climb profile, multiple NORDO formation changes, terrain-masking approach into military airspace to avoid radar, and relying on the closeness of the formation to blend with other aircraft once on radar.
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Oct 16, 2014 16:28
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slidebite posted:How dare you doubt this wasn't posted here before! Mea culpa! I missed it before.
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Oct 16, 2014 17:48
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Linedance posted:none of this makes a lick of sense unless the author was suffering from dementia or something. Bugsmashers get taken across oceans with specially installed ferry tanks regularly.
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Oct 16, 2014 21:29
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CommieGIR posted:Its neighbor over there looks quite sexy. Hinds are many awesome things, sexy is not one is them...
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Oct 16, 2014 22:44
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azflyboy posted:I'm pretty sure it's the gust control, which deflects both ailerons upwards to reduce the structural loads on the wings and tail for flight in turbulent air or higher speed flight in smooth air. And you are right! The ailerons and flaps are all deflected up (i.e., the flaps are at a negative setting) which decreases the camber of the wing and lowers the CLmax. That means that if it flies through an upgust that takes it to the critical AOA, it will make less lift than it would otherwise and therefor make less stress. In addition to that, the ailerons go up more than the flaps, which moves more of the lift inboard and thereby reduces the wing bending moment for the same total lift condition. I thought this was the cleverest thing when I first read about it. Now I can't find the Youtube video where I saw this, but the 787 has something similar that automatically kicks in above some certain G.
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Oct 16, 2014 23:39
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Aerial refueling ain't got nothin' on that
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Oct 17, 2014 16:21
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CommieGIR posted:Don't forget your 10 knot difference between its never exceed speed and its stall speed. By the way, I put that picture up there to replace the previous one which was complete nonsense 
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Oct 18, 2014 04:25
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BIG HEADLINE posted:Yeah, you're right. Still, the only F-35 with an internal gun is the CTOL variant for the Air Force. Yup, especially considering a few years ago there were two in civilian hands, so I'm sure they didn't beat the military to the punch. There's also at least 2 flying Mig-29s.
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Oct 18, 2014 04:39
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BobHoward posted:I dunno if I'd call that "seriously proposed". It's just the pretentious wanking of a self-promoting "designer", not anything anybody capable of real aeronautical engineering ever took even slightly seriously. It's a taildragger  e: at least he took yaw stability under more serious consideration. (Or, far likelier, coincidence) vessbot fucked around with this message at 21:43 on Oct 18, 2014 |
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Oct 18, 2014 21:39
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Fucknag posted:I was thinking mechanical failure more so than low fuel. If your tanks are dry, you're pretty much bailing anyway, and something like a capacitor could probably store enough energy to keep the plane level for long enough to eject safely. It's more than having enough time to eject, it's to power the computers and flight controls long enough to actually land somewhere if there's an airport within gliding distance. https://www.youtube.com/watch?v=Puia_yQxir8 vessbot fucked around with this message at 04:19 on Oct 19, 2014 |
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Oct 19, 2014 04:13
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Psion posted:
That, as far as I'm aware, would go to the Goodyear FG-2 Super Corsair powered by the 4360. I can't find which dash number of the engine, but most of them are 3000+ horsepower. (I know the Goodyear corsair is stretching the definition of "production," but there you have it.)
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Oct 22, 2014 01:52
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Sam Hall posted:I really like the Siemens-Schuckert fighters; they dealt with the rotary engine torque problem by having the prop and engine counterrotate. 160hp rotary engine spinning 1800 rpm clockwise, driving a HUGE prop 900 rpm counter-clockwise through a gearbox. How the gently caress is this less complicated than just turning the drat thing around and bolting the case to the front of the plane  MrYenko posted:The Martin AM-1 Mauler used the Wasp Major as well, and was probably more "production" than the F2G, or any of the other late-war prototypes. Good call. MrYenko posted:The vertical stabilizer of a single engine propeller-driven aircraft general isn't generally installed parallel to the centerline, either. It's generally at a slight angle, which is to provide roughly the correct counter to the p-factor of the propeller at cruise speed and cruise power. ... which means that at higher speed and lower power, now this offset corrects for an effect that isn't there anymore (or, at least, is reduced) so the airplane will try to yaw right, requiring left rudder. This is more pronounced on some planes than others, but the Citabria/Decathlon one is a biggie as far as bugsmashers. Almost every student will head back to the airport at the end of their first acro lesson and try to correct for this yaw problem with aileron, putting us into a nice forward slip with about 5-10 degrees of left bank. They put a rudder on there for a reason!
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Oct 22, 2014 05:13
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Fucknag posted:A lot of them just had various flavors of starter motor, but a good few had inertia starers. Spin up a big flywheel, either by hand or (later) an electric motor, then engage a clutch to transfer the flywheel's energy to the engine to get it turned over. It let them use a much smaller (lighter!) motor and battery, which is pretty important on aircraft, especially early ones. https://www.youtube.com/watch?v=Ecosb5mSDwo Don't forget rope wrapped around the spinner pulled by truck. e: pulled by  https://www.youtube.com/watch?v=RbmUBGGCZhc ... or windmill start of rear engine from prop blast of front engine (the front engine itself is started with compressed nitrogen, an adaptation of the Coffman-type starter to make it easier on the engine by the elimination of shock) ... or, pneumatic starter that dumps compressed air right into the cylinders. This is how Russian M-14 engines (such as on the Yak 52) are started. ... or... this! https://www.youtube.com/watch?v=t9xS4tFhrTw vessbot fucked around with this message at 05:33 on Oct 22, 2014 |
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Oct 22, 2014 05:17
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Eej posted:Man reading up on WWI planes makes me realize how utterly insane pilots were back then. Flying around in a wood and canvas contraption powered by a spinning engine with less horsepower than a modern day midrange sportbike, vulnerable to basically any firearm on the battlefield, hoping your dumb engine doesn't just spray all its oil into your face and your synchronization gear actually works and you don't shoot off your own propeller. Synchronization gear... only after it was invented! Before that, it was metal deflector plates on the back of the prop.
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Oct 22, 2014 21:37
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Platystemon posted:There’s also an argument to be made that the rocketry program had a terrible cost/benefit ratio and helped the Allies by siphoning German resources from conventional armaments. That wasn’t Von Braun’s motive, of course, but in hindsight perhaps it was for the best that he continued his work. "… those of us who were seriously engaged in the war were very grateful to Wernher von Braun. We knew that each V-2 cost as much to produce as a high-performance fighter airplane. We knew that German forces on the fighting fronts were in desperate need of airplanes, and that the V-2 rockets were doing us no military damage. From our point of view, the V-2 program was almost as good as if Hitler had adopted a policy of unilateral disarmament." (Freeman Dyson)[45]
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Oct 31, 2014 16:53
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Mach number has no direct relationship to the air load on the vehicle. The higher you go and the thinner the air gets, the dynamic pressure (what equivalent airspeed* is bases on) decreases for any particular Mach number. For example, at the U-2 operational altitude, its true airspeed was around 400 knots and .67 Mach, while it's equivalent airspeed was around a quarter of that, 100 knots... or the same as everyone's first solo cross countrty in a 152. A more extreme example is the space shuttle at the beginning of reentry. Mach 25 but an EAS of a few knots. So what matters here is not just that it opened at a high Mach number, but a high Mach number at a low altitude. And setting speeds and altitudes aside, even more important is that it opened at a totally wrong phase of flight. It's for drag and stabilization on reentry, so opening at the beginning of powered flight means something going terribly wrong. * roughly meaning indicated airspeed vessbot fucked around with this message at 16:04 on Nov 3, 2014 |
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Nov 3, 2014 16:02
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Tsuru posted:Besides the massive difference in dynamic pressure, M1 in terms of TAS is also much slower at +50000ft than below 10000ft due to the temperature difference. Very true, I just wanted to leave it at one variable. But this makes the effect of EAS reduction for a given Mach with rising altitude even stronger, yes. edit: Actually, wait. It's the opposite. If we ignore the EAS change due to density, and look at only TAS, then airspeeds for a given Mach go up with altitude. So the temp difference tends to make EAS rise at a given Mach number with altitude, but this is outweighed by the stronger effect of density reduction. second edit: No, I (and you) was right the first time. I got mixed up with what factor I was holding constant. With rising altitude (really, cooling temperature): A constant TAS yields a higher Mach number. A constant Mach number yields a lower TAS And with rising altitude: A constant TAS yields a lower EAS A constant EAS yields a higher EAS So EAS takes a double hit, first from the Mach to TAS, and then from TAS to EAS. vessbot fucked around with this message at 04:25 on Nov 5, 2014 |
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Nov 5, 2014 03:07
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The Locator posted:Automot... err.. Aeronau... err.. Aeromotive Insanity? How about a tractor with a 3350? https://www.youtube.com/watch?v=xaqjv0HbxyE
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Nov 7, 2014 02:44
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iyaayas01 posted:This is one of my favorite little details about the Pred/Reaper. Neat! (But why does it have to be horse hair and not any other type of string that's not subject to this type of problem?) This got me thinking about other low-tech solutions to problems, and I thought of the standby compass on the MD-80. By the time its place was to be designated on the instrument panel, there was no more room. So what did they do? Put it on the back wall of the cockpit, and put a mirror on the panel to look at it through!
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Nov 11, 2014 07:16
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