✈️ Exclusive Benefits for Readers
Verified codes to save on your next trip.
Today we will talk about the Mach speed and its indicator located inside the cockpit in all types of aircraft.
Some time ago I had the audacity to answer a question about the importance today of the MACH number indication.. Obviously the comments were immediate from many young commander pilots who said that I had no idea what I was saying.; which doesn't surprise me; what if it surprised me, and a lot, was that other veteran pilots, They also thought the same and did not understand what I wanted to say.
Post written by: William Casalins
Aeronautic engineer
FIA Foundation
The answer was: "Currently it's useless, that served more than anything to navigate" and the aeronautical community fell on me (including fighter pilots), except for one other pilot who knew exactly what he was talking about let's see if I'm wrong.
The speed of sound and the shock wave
The Mach number is the ratio of the true speed to the local speed of sound.. This is a dimensionless expression of velocity, so at a speed of Mach 1.0 goes to the local speed of sound. The speed of sound at sea level is equal to 662 knots (in the air). Mach 0.8 at sea level corresponds to a true speed of 528 kntos (o Mach 0.8 equal to 528 torn between 662 knots). The speed of sound in air decreases with altitude due to a decrease in temperature..
Even though the plane flies at subsonic speeds, in some portions of this (especially of the wing) may be traveling at supersonic speeds (as shown in the figure 2) it is there where the famous shock wave that destroys part of the lift is produced, creates great aerodynamic resistance and also stability problems. It is from there that the swept wing is born, which is really used to make the "cheat of the century" to the relative wind at high speeds.
All of this is of great value to the designers and builders of the aircraft.. For the pilot it is an additional knowledge of the machine and its performance. What could be its additional utility? In future chapters we could talk more about this (in the language that any Airplane Hobbyist could understand)
mach indicator
Engineers scrambled to make innovations so the pilot would have less work to do, They put an autopilot on it and it did almost nothing, So the airline owners told the plane makers: "hey, give them the job of navigators since these manes(the pilots) They don't do anything anymore" (they had already given them part of the work that the radios did- operators, making radio equipment easier to use; and if, the radio-aids gave the final blow to the navigators. Now with the G.P.S. and satellite navigation, who knows who's next. We already know that the position of the flight engineer (with so much automation) died. The owners of the companies believe that their employee is not doing enough and every time the engineers make a breakthrough and remove a crew member, they jump for happiness (one less union to deal with) and a salary less to pay. Soon we will see passenger planes with only one pilot.
The mach indicator that related true speed to the local speed of sound and told the pilot the ground speed (G.S.) no need for a calculator (if the wind was calm). A remarkable advance for the time.
Actually the Mach indicator in subsonic flights indicated a percentage of the speed of sound at that height. For instance, if the indicator shows .80 that means you go to 80% of the speed of sound at that height, but what is that speed of sound?
I mean, what is it for you? Because if it is so that you do not pass at dangerous speeds (that they are) They put an indicator on the instrument (barber pole, that changes with the factors that affect it) so that you do not reach it and do not exceed it, plus certain alarms that sound when critical speeds are exceeded.
indicated speed
It is the speed of the plane with respect to the air that surrounds it and it is obtained by a team that consists of some dynamic shots , static and an instrument that shows them to you in a measure that you can interpret Knots, Km/h. etc. .on those are based the performance of the airplane and the limitations, We already know that air behaves under certain circumstances like an incomprehensible fluid., However, as speeds and operating heights increase, it begins to behave differently and the performance and behavior of the aircraft change. ,obviously the equipment that works with that ambient air also. At low flight levels, the speeds shown by the instrument and the real ones with respect to the ground were very similar, as you got higher and faster those speeds tended to be very different and it ceased to be a benchmark for navigation.
true speed
We already said that the indicated airspeed and the true airspeed are very similar at low levels of flight., in the formula, we can notice that as ALT gets smaller or equals to 0(at the sea level) the I.A.S. They are very similar or the same as the T.A.S. then it becomes a good measure to know how fast I am moving on the earth and predict how long it will take me to reach my destination, we must remember that the fuel that keeps us in the air is not eternal, and thus make a calculation of how far I am going to travel before running out of empty tanks or that night catches us in a visual flight.
TAS = IAS + (0.02IASxALT/1000)
It is very desirable to know at all times the true speed that gives us the main data to calculate our estimates..
Ground speed
We must remember that air speed and ground speed are not always the same., in fact, hardly ever, but at low altitudes and with calm wind those speeds are quite similar. The plane does not care about the speed over the ground, he only cares about the speed with which the air passes through his wings and the control surfaces and other parts. But the pilot yes and the ground controller too (especially before there were no such sophisticated radars) to make their estimates and the other to make their air traffic ordering.
Examples
As a picture is worth a thousand words, an example is worth more than 100 explanations.
Let's suppose that we are flying to 32000 feet tall level 330, the speedometer tells me 291Knots, I want to know how long it will take me to go 80 nautical miles that shows us the D.M.E of a station.
We take out our calculator or our flight computer and it gives us.
- T.A.S. = IAS+(0.02 IASxALT/1000)
- T.A.S.= 291+(0.02(291) x3200071000) = 291+186=477 miles/hour
- 477/60=7.95 miles per minute.
- TIME =DISTANCE/SPEED
What would happen if: we look at our MACH indicator that marks us 0.8, we move a point, and we divide it to what the D.M.E.?
- TIME =80Miles/7.95 (miles/minute) = 10.06 minutes.
GPS.FMS
Countless navigation systems have been invented each time better than the previous one, now you can navigate by satellite and with an error of a few meters, all the information you need and (the one that doesn't) you can also get it in real time, on your own smartphone and on the plane, the manuals, the systems, checklists etc.. you can't get lost anymore, the company that owns the plane keeps track of you, you can send the technical problems of the plane long before landing and everything that we never imagined a few decades ago. you get on the plane, manages from the fly, you relax and look at the landscape.
Conclusions
At the beginning we only flew with the indicated speed and from there all the limitations were taken, at low altitudes, this was very close to reality and as all the flights were visual, there was no problem. Later it began to fly higher and faster, the speeds no longer matched and "complicated" calculations had to be made to approximate instrument flights (for long flights, navigators were needed) so the engineers (who never sleep) they invented an instrument that gave you the true velocity on the instrument, you only needed a DME distance and a watch to make your estimates. Even so, it was too much work, and then those "infamous" engineers improved the equipment and invented the GPS that gave you the speed and the real position, the wind component and the estimate just by looking for a desired point. But even so they did not settle and then they put everything on a big screen, even the plane was drawn on a map in real time on a trajectory to follow, taking all this into account, Can you tell me what your MACH indicator is used for today?, knowing that you also have an IAS indicator, which is equivalent (for performance and flight limitations) and that you already have all the flight data on navigation resolved on a map on a screen?
In this picture, among many other things, the T.A.S tells you. (479) and the G.S.. (482) which means you have a tailwind component of 3 Knots
postscript
I am not a pilot, I am a flight engineer, and flying CARAVELLE, a free throw, an instructor captain, Major JAIRO GARCIA taught me all this that I am telling you now, the co-pilots and some commanders (in times when there was no G.P.S.) they were surprised how he gave them the times for the descent and the exact fuel data. In fact, I'm not belittling the mach indicator, on the contrary, I am stating that at one time it was underutilized by some aviators who did not fully understand it. If any pilot has something to add, welcome the contribution.
I want to thank the collaboration of Yerson Leonardo Angarita
All drawings and photos were obtained from Boeing
✈️ Exclusive Benefits for Readers
Search here for hotels ALL over the world at the best price.
