Sensing airspeed in an aircraft A passenger aircraft uses tw

Sensing airspeed in an aircraft. A passenger aircraft. uses two Piton tubes for speed sensing. One tube is aligned parallel to the airplane and the other is perpendicular to it. each equipped with a pressure sensor. For an aircraft. flying at 11,000 m, calculate the readings of the pressure sensors in each of the tubes and the differential pressure if the airplane flies at 850 km/h. The temperature at that elevation is -40degree Neglect any effect the speed may have on air density inside the tub Suppose that the lateral tube becomes blocked with ice at 11,000 m and now the aircraft. climbs to 12,000 m What is the error in the speed reading, assuming the airplane has not changed speed and the temperature remains the same as at 11,000 m?

Solution

Ans: here iam explaining about sensing airspeed in an aircraft:

The pitot pressure is a measure of ram air pressure. which, under ideal conditions, is equal to stagnation pressure, also called total pressure.

The pitot tube is most often located on the wing or front section of an aircraft, facing forward, where its opening is exposed to the relative wind.

a)

As is also the case for sound waves, the Doppler effect is not noticeable if the speed of the source is very small compared to the speed of the waves. Someone walking toward you and talking does not sound like Mickey Mouse; the receiver here is your ear and it is not sensitive enough to detect the shift. The expression for the shifted frequency f of electromagnetic waves relative to the source frequency f₀ is given by f=f₀[(1+)/(1-)] where =v/c and v is the speed of the source

and c=3x10⁸ m/s is the speed of light; >0 is when velocity is toward you. If is much smaller than 1, it may be shown that the fractional change in frequency is |f-f₀|/f₀. For example

suppose the source is an airplane with speed 300 m/s (about 700 mph) and the frequency is 90 MHz. Then |f-f₀|/f₀10^-6 or the Doppler shift is |f-f₀|90 Hz. A tuner does not have nearly the sensitivity to detect a 10^-4% change in frequency.

b) speed of sound:

Speed of sound does not remain constant.

Since the local speed of sound is dependent only on temperature, it varies with temperature (decreases with decreasing temperature).

Local Speed of Sound = 38.94 x Square root of Temperature

Temperature is in Kelvins (K) or Absolute (A). Kelvin = °C + 273

Mach Number is the raio of TAS to Local Speed of Sound.

MN = TAS/LSS

Converting TAS to Mach:

Machmeter :

It can be proven mathematically that the Mach number is a function of the dynamic pressure divided by the static pressure.

The instrument therefore contains the elements to find:

1) Dynamic pressure (an airspeed indicator i.e a capsule fed with pitot pressure inside a case fed with static).

2) Static pressure (an altitude capsule.

Therefore a machmeter is basically an airpseed indicator and an altimeter interacting in the same case.

he airspeed capsule acts through a system of linkages to move a ratio arm.

The altitude capsule moves the ratio arm in another direction.

The effect this has on the ranging arm depends on how the altitude capsule moves the ratio arm.

The ratio arm ultimately moves the pointer that indicates Mach number.

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