Data processing: measuring – calibrating – or testing – Calibration or correction system – Pressure
Reexamination Certificate
1999-04-09
2002-09-10
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Calibration or correction system
Pressure
C702S033000, C702S099000, C702S130000, C702S183000
Reexamination Certificate
active
06449573
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to apparatus for use in an aircraft, and is particularly adapted for and intended to be used in small aircraft. The purpose of the apparatus of the present invention is to provide a device which will, at any instant in time, determine the ambient temperature and barometric pressure of the air where the aircraft is presently located, whether it is flying or on the ground, and to provide a readout of pressure density—otherwise also known as density altitude. The present invention may also provide further displays for specific aircraft performance characteristics, at any instant in time.
BACKGROUND OF THE INVENTION
Any aircraft pilot has, of course, great concern about the performance of the aircraft that he/she is flying. Accordingly, the pilot relies on a great variety of instruments which are mounted in the cockpit of the aircraft within his/her field of view. Of course, in larger multi-engine aircraft, and especially commercial aircraft, as well as in high performance aircraft such as military aircraft, there may be very extensive instrumentation. On the other hand, in small single, two-seater or four-seater, single-engine aircraft of the sort used by recreational flyers, bush pilots, and the like, there may be a paucity of instrumentation—the aircraft being provided with sufficient instrumentation to permit it to be safely flown, as determined by the manufacturer of the aircraft.
However, no aircraft is provided with an instrument which will give a dynamic reading of pressure density, which is sometimes referred to as density altitude. Knowledge of the pressure density at any instant in time is required to determine requirements or flying characteristics such as ground roll necessary for safe takeoff of the aircraft, or for a determination of true air speed over ground. Other performance characteristics are more particularly described and discussed hereafter. However, it must be understood that it is the importance of density altitude, and the manner in which it affects other readings, which is primarily being dealt with.
Of course, it is well understood that the higher the altitude—generally, altitude is determined as being the altitude above sea level—the less dense the air. Likewise, the warmer the air becomes, the less dense it will become. It must also be understood that what is called an altimeter in an aircraft, especially a small aircraft, is not in fact an instrument which measures precise altitude above sea level. In fact, the altimeter is actually an aneroid barometer which measures atmospheric pressure. There is, therefore, an indicated altitude, but that indicated altitude must be corrected for local conditions—a process which is well known to aircraft pilots, particularly as they are preparing for takeoff. Especially, the flight altimeter settings for the aircraft must be adjusted by the pilot to the airport elevation and station pressure, with the current ambient temperature having to be taken into account when the pilot is calculating the length of the ground roll which is required for takeoff.
Moreover, as will be discussed in greater detail hereafter, atmospheric pressure and temperature conditions are dynamic, and are constantly changing. It is well known that atmospheric pressure and temperature will affect flight performance of the aircraft, as well as its takeoff and landing conditions. Thus, the need for dynamic and real time knowledge of the pressure density becomes understood.
There are a number of different readings or indicators of altitude which may be referred to or required to be known at any instant in time by the pilot of an aircraft. Again, it must be understood that an altimeter in an aircraft is calibrated to show height above sea level under standard atmospheric conditions. Standard atmospheric conditions are 29.92 inches of mercury and 59° F. However, local conditions of temperature and pressure will most likely not match the standard conditions.
Indicated altitude is the altitude which is shown on the altimeter of the aircraft. If the altimeter is set to the current atmospheric pressure, corrected to sea level, the indicated altitude will be approximately equal to the height of the aircraft above sea level.
Pressure altitude is the altitude which is shown on the altimeter when the pressure is set to 29.92 inches of mercury.
Density altitude—or pressure density, as it referred to herein—is the pressure altitude which is corrected for deviations from standard temperature. It is important for the pilot to know the pressure density or density altitude in order for him/her to calculate the required runway for ground roll in order to takeoff, and to determine the rate of climb of the aircraft once it has taken off. Particular embodiments of the present invention will provide those data automatically to the pilot, upon an appropriate query and input of necessary parameter data to the apparatus of the present invention.
It will be understood that takeoff on a hot day from an airport with an elevation well above sea level will require much greater ground roll than a takeoff from an airport at sea level on a cold day.
True altitude is the actual height of the aircraft above sea level. If the altimeter in a small aircraft has been set to local pressure, corrected to sea level, than the indicated altitude is approximately the true altitude of the aircraft above sea level.
The other two types of altitude, absolute altitude and radio or radar altitude, require that the aircraft be equipped with a radio or radar altimeter, and are beyond the scope of the present discussion.
The effect of normal pressure variations on true altitude may be quite profound. Pilots are warned to always recall that pressure variations will change from time to time, as they fly across country, as the day warms up or cools down, or as a weather front may be moving into the region where the aircraft is operating. If a pilot is flying the aircraft having a constant indicated altitude, the aircraft is, in fact, being flown in a constant barometric pressure—the aircraft is following an isobaric profile. Thus, if the aircraft is flown at a constant indicated altitude into an area of lower barometric pressure, it is flown “downhill” into a pressure valley; and, if the aircraft is flown into an area of higher of barometric pressure, it climbs a pressure hill.
Pilots of small aircraft that fly into an area of low pressure may notice a pressure drop of as much as 0.5 inches of mercury over a distance of as little as 200 miles in a severe weather front. Since atmospheric pressure above a given land point will decrease by about 0.1 inch of mercury per 100 feet of altitude, the pressure effect can be quite profound—in the example given above, as much as 500 feet. Moreover, as the temperature changes, the density of the air will also change; therefore, flying into a low pressure area on a warm day, with the temperature rising, may indeed have profound affects on the flying characteristics of the aircraft and particularly on a determination of where the aircraft is actually located in altitude.
Examples of the manner in which temperature will affect pressure density or density altitude are now given. As stated, the international standard for zero feel of pressure density or density altitude is 59° F. at sea level and 29.92 inches of mercury. However, at sea level and 29.92 inches of mercury, if the temperature rises to 80° F., the pressure density will rise to 1,200 feet. In other words, the same air density will occur at sea level and 29.92 inches of mercury at 80° F. as will occur had the aircraft taken off from sea level at 59° F. and 29.92 inches of mercury and climbed to 1,200 feet. Likewise, as temperature goes down, pressure density will go down. For example, if the temperature is 52° F. and the barometric pressure is 29.92 inches of mercury at 2,000 feet, the pressure density will also be zero feet—that is, the same conditions prevail as they did at sea level and 59° F. and 29.92 inches of mercury.
Another example is that, at 8,000 feet
(Marks & Clerk)
Hoff Marc S.
Tsai Carol S
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