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| 5/24 |
| 2008/8/6-10 [Transportation/Airplane] UID:50793 Activity:nil |
8/6 Q: How to defeat a B-2 Stealth Bomber?
A: Use a water spray bottle.
http://www.csua.org/u/m0x (telstarlogistics.typepad.com)
\_ Whoops!
\_ These kinds of mistakes happen more than you might think. I read
the black box account of a plane that had tape over the airspeed
intakes (to protect them while washing). The airplane was lost in
the ocean when it stalled.
\_ If an airspeed intake can crash the plane that's a faulty design.
\_ pitot (French) tube blockage (bug) is one of the most
common reasons why they crash, esp in IFR conditions.
Auto pilot depends on it too.
http://selair.selkirk.bc.ca/aerodynamics1/Basics/Page6.html
By the way I'm a private pilot, ask me any question.
\_ any good air speed measurement technologies that don't
depend on pitot tubes?
\_ Yes there are plenty, the issue is not alternative
technology but rather COST. For general aviation,
pitot tube is a proven, CHEAP, and usually reliable
instrument. As a pilot, most of your training is
failure recovery and safety. For instrumentation errors
you need to first 1) recognize instrumentation failure
and 2) how to compensate for what you think failed.
Your basic GA panel consists of the "Big 6", which
are: (top)ASI, AI, ALT, (bottom)TC, HI, VSI. Of these,
ASI, ALT, and VSI are independently working pressure
static oriented, and AI, TC, and HI are gyro operated.
It takes a lot of time to explain this but if you're
missing one instrument, you can infer its status by
reading and correctly interpreting the other 5. I'm
also missing one more instrument: Tachometer. If you
know your exact attitude (HI or visual) and the
tachometer, then you can infer AS pretty well. Keep
in mind that ASI, ALT, and VSI operate INDEPENDENTLY
regardless of battery or engine failure so you already
have lots of redundancy behind a well trained pilot.
In addition, most AI, HI, and TC, are vacuum driven
from the pump (and some even have electrical motor
backup) so as long as your engine is running it
doesn't matter if your electronics fry.
For big planes they use a combination of redundant
pitot tube+anti-defrost+(GPS+weather estimate) and
other fancy stuff. I don't know the exact details
because I don't have Type Ratings yet.
If you're curious:
http://www.flightsimbooks.com/foi/chapter1.php
http://www.aopa.org/learntofly/startfly/panel.html
http://en.wikipedia.org/wiki/Flight_instruments
\_ http://en.wikipedia.org/wiki/AeroPeru_Flight_603
http://en.wikipedia.org/wiki/Birgenair_Flight_301
second one is another blocked pitot crash. But yes, it's sort
of a design flaw and it sounds like they have better
recommendations now
\_ To be fair, the problem was the ground crews messing with the
gauges, which would have been fine otherwise.
\_ I read an article previously that claimed that this had happened
before, but the ground crew had dried out the sensors, rather
than adujsting them, so no failure.
\_ How does the B-2 fly in rain, or very humid weather where
condensation can form?
condensation can form? -- OP |
| 5/24 |
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| www.csua.org/u/m0x -> telstarlogistics.typepad.com/telstarlogistics/2008/08/photos-and-vide.html what went wrong: Small errors, it now turns out, caused a large accident. A B-2 has four computers, called the flight control system (FCS), that translate the pilot's cockpit inputs into movement of the plane's control surfaces. The moisture distorted the plane's air-pressure readings and confused the FCS badly enough to cause the crash, the first one of the B-2's career. February's crash was caused by maintenance crews trying to do the right thing: They saw the wrong data and recalibrated the sensors. However, once the moisture evaporated, the sensors "fixed" by the crew were actually set incorrectly and were feeding the flight computer false data on airspeed and air pressure, which is used to measure altitude. "The pressure differences were miniscule, but they were enough to confuse the FCS, " Maj Gen. Floyd Carpenter, who headed the Air Force's investigation, tells PM. triggering a premature takeoff, automatically driving the airplane into a 30-degree, nose-up pitch and overruling the pilot's efforts to regain control. |
| selair.selkirk.bc.ca/aerodynamics1/Basics/Page6.html Airspeed Errors due to blockages Airspeed errors can occur if either the Pitot tube or the Static vent become blocked. It is not uncommon for the Pitot tube to become blocked on the ground, either by bugs, or ice. The airspeed will not increase as it should during the takeoff. The pilot should reject the takeoff and have the problem repaired. But, what if the Pitot is blocked in flight, or the Static vent becomes blocked. Blocked Pitot in Flight In the diagram to the right the Pitot tube has become blocked in flight, by ice. When this first happens, if the aircraft is in steady flight the pilot will not realize there is a problem because the ice simply seals the pressure inside the Expandable Capsule When the aircraft descends for landing however the pressure inside the capsule will remain constant, whether the aircraft accelerates, or decelerates. As the aircraft descends the static pressure will increase. Thus, the indicated airspeed will decrease as the aircraft descends regardless of the actual airspeed. Blocked pitot tube There have been some infamous accidents caused by this situation. One involved the crew of a Boeing 727 who saw their airspeed increasing as they climbed. Even though the attitude of the aircraft was much more nose up than it should have been they were convinced that the airspeed was becoming too high. Eventually they pitched the nose up so high, in their efforts to slow the aircraft down that they entered a spin. Blocked Static Vent in Flight In the diagram to the right the Static vent has become blocked in flight. As long as the aircraft remains at the same altitude the Airspeed indicator work normally since the correct static pressure is sealed in the case. When the aircraft descends the static pressure in the case will be lower than it should be. Thus, the airspeed will begin to read progressively higher as the aircraft descends. If the aircraft climbs the airspeed will begin to read progressively lower. |
| www.flightsimbooks.com/foi/chapter1.php Flying on Instruments with Flight Simulator by Jonathan M Stern Chapter 1 Flight Instruments Six flight instruments form the basis of flying on instruments. Other than the need to know where you are, why do you need instruments in the airplane? Believe it or not, the human ability to sense which way is up is easily deceived in an aircraft. Balance control, other than through visual cues, comes from your inner ears. When you fly in clouds or in areas of restricted visibility, you depend on your inner ears to tell you which way is up. Six flight instruments are found in almost every instrument-equipped aircraft (Figure 1-1). Flight Instruments (figure) Airspeed Indicator The airspeed indicator shows the indicated airspeed of the air-plane in nautical miles per hour, commonly called knots. The airspeed indicator, vertical-speed indicator, and altimeter are components of the Pitot-static system (Figure 1-2). Pitot-Static System (figure) Three instruments--from left to right, the vertical-speed indicator, altimeter, and airspeed indicator--operate from the Pitot-static system. The Pitot tube and static vent are mounted outside the airplane. The Pitot tube is positioned so that its front faces into the stream of air--the air rams into the opening. The static vent is usually flush-mounted on the side of the airplane so that there's no impact air measurement--in other words, the air doesn't rush into the vent. The airspeed indicator works by measuring the difference between the ram air pressure in the Pitot tube and the static air pressure in the vent. To fully understand how these instruments operate, you have to understand some characteristics of air in the earth's atmosphere. Because air has weight, as you ascend from sea level, there is less air above you and, therefore, less weight on you. The rate at which the weight of the atmosphere changes isn't constant, but at the altitudes at which most single-engine airplanes fly, each 1000-foot increase in altitude results in a pressure decrease of approximately one inch of mercury. Airspeed Indicator (figure) When the airplane is parked on the ground, the Pitot tube senses the ambient air pressure (assuming no wind). Since the difference between the pressure in the Pitot tube and the pressure in the static vent is 0, the airspeed indicator indicates an airspeed of 0 When the airplane is in flight, the pressure in the Pitot tube is greater than the ambient pressure measured by the static vent. This pressure difference is indicated as airspeed on the airspeed indicator. When the airplane is operated at other altitudes or in nonstandard atmospheric conditions, the indicated airspeed doesn't accurately reflect the true airspeed. But true airspeed can always be calculated if temperature, pressure, and indicated airspeed are known. Measure True Airspeed For Flight Simulator purposes, your true airspeed can be estimated by multiplying your indicated airspeed by 1 plus 15 percent for each 1000 feet above sea level that you're flying. True airspeed is not the speed at which the airplane moves over the ground. To compute groundspeed, any headwind must be subtracted from, or any tailwind must be added to, the true airspeed. Altimeter The altimeter is the only instrument which shows how high the airplane is above some level. The altimeter has two hands like those of a clock and a small indicator that appears near the numbers on the outer ring of the gauge. The small indicator indicates tens of thousands of feet. The altimeter in Figure 1-2 shows an altitude of 4720 feet. The altimeter is an aneroid barometer that displays pressure in feet above sea level (mean sea level), not above ground level. The altimeter cannot work accurately unless the pilot sets it to the current altimeter setting, which is the pressure at sea level under existing atmospheric conditions. The Federal Aviation Regulations require pilots of radio-equipped airplanes to keep the altimeter set to the "current reported altimeter setting of a station along the route and within 100 nautical miles of the aircraft." The altimeter measures the barometric pressure in the static vent. Altimeter (figure) Vertical Speed Indicator The vertical speed indicator, like the altimeter, is connected only to the static vent. The vertical speed indicator shows whether the airplane is flying at a constant altitude, climbing, or descending, and if climbing or descending, at what rate. The face of the instrument is graduated in hundreds of feet per minute, with the top half showing climbs, and the bottom half, descents. Vertical Speed Indicator (figure) Attitude Indicator The next three instruments--the attitude indicator, turn coordinator, and heading indicator--are gyroscopic instruments. Each instrument uses a gyroscope to maintain its orientation relative to one or more of the axes of the airplane. The attitude indicator, as its name implies, indicates the attitude of the airplane relative to the earth's surface. The instrument displays airplane pitch (whether its nose is up or down) and airplane bank (the angle the wing forms with the horizon). Marks around the top half of the instrument on some versions of Flight Simulator indicate angles of bank of 10, 20, 30, 60, and 90. Attitude Indicator (figure) Turn Coordinator The turn coordinator is actually two instruments in one. The airplane replica in the middle of the instrument rolls proportionally to the roll rate of the airplane. When the bank angle is maintained, the replica indicates the rate of turn. When the right or left wing of the replica is aligned with the lower mark, the airplane is turning at a rate of 3 per second (so a full 360 turn takes two minutes). The other instrument in the turn coordinator is called an inclinometer. The inclinometer shows whether or not use of rudder and aileron is coordinated. If the ball in the liquid-filled glass tube moves outside of the center of the tube, the rudder and ailerons are not coordinated. If the ball moves to the outside of the turn, the airplane is skidding. If the ball moves to the inside of the turn, the airplane is slipping. Uncoordinated flight can always be corrected by applying sufficient rudder pressure on the same side as the ball so that it returns to the center of the tube. This is known to student pilots as "stepping on the ball," because the rudder is controlled by pedals; pressure on the left pedal coordinates the turn if the ball is to the left of center, and pressure on the right pedal coordinates the turn if the ball is right of center. Flight Simulator gives you the option of flying with auto-coordination. This lets you control the ailerons and have the proper amount of rudder automatically applied. I recommend that you use auto-coordination for learning to fly on instruments. Later, if you want, you can try what you've learned without auto-coordination. Turn Coordinator (figure) From left to right, these three turn coordinators show left standard rate turn slipping, coordinated, and skidding. Heading Indicator The third gyroscopic instrument is the heading indicator. The heading indicator is used because a magnetic compass only works accurately when the airplane is flying straight and level in unaccelerated flight. Any time the airplane is banked, pitched, accelerated, or decelerated, the magnetic compass gives a wrong reading. The heading indicator solves this problem by using a gyroscope instead of a magnet. Bearing friction causes the heading indicator to creep from the heading to which it has been set. Therefore, the heading indicator should be reset to the magnetic compass every 10 or 15 minutes, but only when the airplane is straight and level in unaccelerated flight. |
| www.aopa.org/learntofly/startfly/panel.html Medical Certification Learn to Fly A Panel Discussion What are those gauges and needles telling us? BY PETER A BEDELL At first sight, the instrument panel of even the smallest airplane can be an overwhelming sight. An array of gauges, dials, knobs, and digital displays can make newcomers wince at what faces them. It's comforting to note, though, that most of the instruments found in training aircraft are surprisingly simple and user-friendly. The most important instrument in the initial training phase is the big transparent one over the glareshield, or dashboard if you will. The windshield is the primary flight instrument for visual flight rules (VFR) flight. In VFR conditions, the airplane's instruments are used as references rather than a reliance in maintaining proper flight attitude. Although it's tempting to stare at all those little needles and gauges winding away as the airplane climbs and turns, the windshield, with its built-in horizon, provides the best reference to the airplane's attitude. When the weather gets bad and the windshield becomes opaque with clouds, we rely solely on the information that the instruments provide in order to maintain the proper flight attitude and desired course to get us to our destination. Let's take a look at the cockpit layout of a typical trainer. The center column in a Cessna 172, for example, has the fuel selector valve at the bottom just above the floor, the elevator trim wheel halfway up, and the power controls (throttle and mixture) at the top of the center column near the pilot's right knee. Unlike the car, the throttle is operated with your hand, and ground steering is performed by your feet. Taxiing an airplane is a little awkward at first but comes easily with time. Above the power controls, in the center of the panel, is the radio stack. In basic trainers, there is generally a communications (com) radio and a navigation (nav) radio. In aircraft equipped for IFR (instrument flight rules, which means able to fly in the clouds we just mentioned) flight, there are generally two com and two nav radios as well as a host of other navigational equipment. Directly in front of the pilot are the flight instruments. There are six principal instruments: the altimeter, directional gyro or heading indicator, attitude indicator, vertical speed indicator, turn coordinator, and airspeed indicator. These instruments ensure that the airplane is at the desired pitch and bank whether it be a descending, left turn or just straight-and-level flight. These instruments are so important that they are found in virtually every powered aircraft, from the smallest trainer to the space shuttle. The attitude indicator, or artificial horizon, displays your flight attitude, or what you should see out the windshield if the weather were to allow it. It has blue shading on the top, depicting an artificial sky, and a black or brown bottom, representing the ground. A fixed miniature airplane lies in the middle of the instrument, giving the pilot a tail view of what the airplane's attitude is. Markings along the rim of the instrument depict degrees of bank. If the miniature airplane's wing is in line with the third mark, the airplane is in a 30-degree left or right bank. This instrument runs on gyroscopic, vacuum, or electric power, and in the most sophisticated aircraft, the pilot may be looking at the depiction on a TV-style, miniature cathode-ray tube. In most airplanes, the altimeter lies to the right of the attitude indicator. the big hand marks hundreds of feet, and the little hand marks thousands of feet, just like minutes and hours on a clock. For those training in the Rockies, or those who happen to get some stick time in a high-flying airplane, there is a thin marker needle that depicts altitude in tens of thousands of feet. Some altimeters have a combination digital and analog display, but most altimeters in training aircraft will be strictly analog. Underneath the altimeter is the vertical speed indicator (VSI). It tells the pilot what rate the airplane is climbing or descending in feet per minute (fpm). Although the VSI in our general aviation trainers reads up to 2,000 fpm, we'll be lucky to see the needle sweep past 1,000 fpm in a climb. To the left of the VSI, and under the attitude indicator, lies the directional gyro (DG), often called the heading indicator. Because the magnetic compass, another very important primary flight instrument (usually attached to the glareshield or windshield), floats in fluid and sloshes around during turbulence and maneuvering and naturally lags or leads turns, depending on direction of the turn, it's hard to get an idea of what your heading really is. Not only is it easier to look at, it doesn't lead, lag, or slosh around like the compass. It does not have a north-seeking magnet and therefore must be set to match the compass heading before takeoff. When on the end of the runway, for example, if you are lined up with the centerline, the runway numbers should approximately match your heading, so set the DG to the runway numbers before starting your takeoff run. The DG is subject to precession, which causes it to wander over a period of time. About every 15 minutes, if the airplane is straight and level, check and reset the DG to the compass heading. In a turn, the miniature airplane banks in the direction the real airplane is turning. You may ask, "Why have an instrument that shows the airplane's bank when the attitude indicator already does the job?" The answer is that by banking the real airplane so that the miniature airplane's wings are lined up with the turn coordinator's lower reference marks, you can use the instrument -- along with a stopwatch -- to make timed turns. Line the little airplane up with the marks, and you'll turn at 3 degrees per second. Hold that bank, and in 15 seconds, your heading will change by 45 degrees; In case the heading indicator and/or attitude indicator fails. With the turn coordinator, a stopwatch, and the trusty old magnetic compass, you can turn to specific headings with a fair degree of accuracy. So the turn coordinator -- which is electrically powered -- is a backup in case the vacuum-driven attitude and heading indicators give up the ghost. The other component of the turn coordinator is the inclinometer, better known as the rudder ball. This is a black ball in a liquid-filled, curved and sealed tube. That is, to prevent the airplane's tail from skidding to the outside of a turn or slipping to the inside. In a skid, the ball will roll opposite to the direction of the turn; To prevent slips or skids, pilots are told to "step on the ball," meaning apply pressure to the rudder corresponding to the ball's location. Our final important flight instrument, the airspeed indicator, is easy to relate to. Much like your car's speedometer, it tells you how fast you are going in either miles per hour or knots. If knots confuse you, just remember that for every 100 knots, add 15 to get your speed in miles per hour. The average Cessna cruises around 100 knots, or 115 mph. Unlike cars, an airplane's groundspeed is affected by winds, and our actual speed over the ground will vary, depending on the winds aloft. Airspeed indicators are color coded for quick recognition. The yellow arc is a danger zone and can be penetrated only in smooth air. A red line depicts the "never-exceed speed," the speed at which structural failure may occur. Lastly, the white arc depicts the safe speed zone for deployment of flaps. Finally, there are engine instruments, and once again, like your car, they are designed for a quick scan to make sure the needles are in the green. Most general aviation trainers have an analog tachometer mounted near the primary instruments as well as an amperage meter, fuel gauges, and oil pressure and oil temperature gauges. Although a guided tour of a particular airplane by a certified flight instructor is the best way to become accustomed to the instrument panel, this quick and dirty description will undoubtedly help decipher some of the initial shock of seeing all those gauges for the first time. |
| en.wikipedia.org/wiki/Flight_instruments vertical speed indicator Most aircraft are equipped with a standard set of flight instruments which give the pilot information about the aircraft's attitude, airspeed, and altitude. Altimeter Gives the aircraft's height (usually in feet or meters) above some reference level (usually sea-level) by measuring the local air pressure. It is adjustable for local barometric pressure (referenced to sea level) which must be set correctly to obtain accurate altitude readings. Attitude indicator (also known as an artificial horizon) Shows the aircraft's attitude relative to the horizon. From this the pilot can tell whether the wings are level and if the aircraft nose is pointing above or below the horizon. This is a primary instrument for instrument flight and is also useful in conditions of poor visibility. Pilots are trained to use other instruments in combination should this instrument or its power fail. The indicated airspeed must be corrected for air density (which varies with altitude, temperature and humidity) in order to obtain the true airspeed, and for wind conditions in order to obtain the speed over the ground. Magnetic compass Shows the aircraft's heading relative to magnetic north. While reliable in steady level flight it can give confusing indications when turning, climbing, descending, or accelerating due to the inclination of the earth's magnetic field. For purposes of navigation it may be necessary to correct the direction indicated (which points to a magnetic pole) in order to obtain direction of true north or south (which points to the earth's axis of rotation). Schempp-Hirth Janus-C glider Instrument panel equipped for "cloud flying". The heading indicator is replaced by a GPS-driven computer with wind and glide data, driving two electronic variometer displays to the right. Heading indicator Also known as the directional gyro, or DG. Sometimes also called the gyrocompass, though usually not in aviation applications. Displays the aircraft's heading with respect to magnetic north. Principle of operation is a spinning gyroscope, and is therefore subject to drift errors (called precession) which must be periodically corrected by calibrating the instrument to the magnetic compass. A turn coordinator displays rate and direction of roll while the aircraft is rolling; displays rate and direction of turn while the aircraft is not rolling. Internally mounted inclinometer also displays quality of turn. edit Arrangement in instrument panel Most aircraft built since about 1953 have four of the flight instruments located in a standardized pattern called the T arrangement. The attitude indicator is in the top center, airspeed to the left, altitude to the right and heading indicator under the attitude indicator. The other two, turn-coordinator and vertical-speed, are usually found under the airspeed and altitude, but are given more latitude in placement. |
| en.wikipedia.org/wiki/AeroPeru_Flight_603 The crew declared an emergency and requested an immediate return to the airport. Faced with the lack of reliable basic flight instruments, constantly receiving contradictory warnings from the aircraft's flight computer (some of which were valid and some of which were not), and continuously believing that they were at a safe altitude, pilot Eric Schreiber and copilot David Fernndez decided to cautiously begin the descent for the approach to the airport. Since the flight was at night over water, no visual references could be made to convey to the pilots their true altitude or aid the pilots in the descent. Also, as a consequence of the pilot's inability to precisely monitor the aircraft's airspeed or vertical speed they experienced multiple stalls resulting in rapid loss of altitude with no corresponding change on the altimeter. While the altimeter indicated an altitude of approximately 9,700 feet, the aircraft's true altitude was in fact much lower. It struck the water approximately twenty-five minutes after emergency declaration, making the pilots realize the true altitude of the airliner; for twenty seconds the pilots tried to make the airliner climb. The static ports are critical to the operation of virtually all of those flight instruments that provide basic aerodynamic data such as airspeed, altitude and vertical speed, not only to the pilots but also to the aircraft's computers, which provide additional functions such as warnings when flight characteristics approach dangerous levels. The blockage of all of the static ports is one of the few common-failure modes resulting in total failure of multiple basic flight instruments and as such is regarded as one of the most serious faults that can occur within the avionics systems. The design of the aircraft did not incorporate a system of maintenance covers for the static ports. Such covers are commonly employed in aviation for blocking access to critical components when the aircraft is not in operation and are generally a bright color and carry flags (which may have "remove before flight" markings). Instead, the design of the aircraft and the relevant maintenance procedure called for the use of adhesive tape to cover the ports. As a result of the blocked static ports the basic flight instruments relayed false airspeed, altitude and vertical speed data. Because the failure was not in any of the instruments but rather in a common supporting system, thereby defeating redundancy, the altimeter also relayed the false altitude information to the Air Traffic Controller, who was attempting to provide the pilots with basic flight data. This led to extreme confusion in the cockpit as the pilots were provided with some data (altitude) which seemed to correlate correctly with instrument data (altimeter) while the other data provided by ATC (approximate airspeed) did not agree. Although the pilots were quite cognizant of the possibility that all of the flight instruments were providing inaccurate data, the correlation between the altitude data given by ATC and that on the altimeter likely further compounded the confusion. Also contributing to their difficulty were the numerous cockpit alarms that the computer system generated, which conflicted both with each other and with the instruments. This lack of situational awareness can be seen in the CVR transcript. The fact that the flight took place at night and over water thus not giving the pilots any visual references was also a major factor. At first, the investigation put the responsibility for the accident on the flight deck crew. edit Legal Settlement In November 1996, Mike Eidson, a Miami lawyer from Colson Hicks Eidson, said in an interview that many of the passengers survived the initial impact and drowned afterwards. Mayday (Air Crash Investigation, Air Emergency) stated that the manner of the crash resulting in the drowning was responsible for the large settlements given to families of the victims. blame was not apportioned to supervisors for poor procedures or the flight crew for inadequate pre-flight checks. The Flight 603 incident contributed to the demise of Aeroper, which was already plagued with financial and management difficulties. The suit was filed against Boeing in federal court in Miami in May, 1997. After extensive litigation the parties agreed to transfer the case against Boeing and Aeroper to an international arbitration in Santiago, Chile, for a determination of the damages. |
| en.wikipedia.org/wiki/Birgenair_Flight_301 autopilot reaction, increasing the pitch-up attitude and reducing power to lower the plane's airspeed. Investigations showed that the plane was actually travelling at 220 knots. edit Investigation and final report The Dominican Republic government's Direccin General de Aeronutica Civil (DGAC) investigated the accident and determined the following probable cause for the accident: "The crew's failure to recognize the activation of the stick shaker as a warning of imminent entrance to the stall, and the failure of the crew to execute the procedures for recovery from the onset of loss of control." pitot tube was blocked, but were unable to determine what was blocking it. However, investigators suspected that some kind of insect could have created a nest inside the pitot tube. |