Flex temperature.

 

Flex temperature is always set up by the pilot to calculate take off performance, in many jet powered Aircrafts but except Boeing, they called it as a assumed or de-rated Temp.

Many passenger assume that pilots apply full power or thrust at the time of take off but it's actually not,

If you have observed that, after take off engine sounds decreases litter bit, in case of Airbus.

Well, this is because of the flex temperature, and the climb power settings.

prior to every take off pilots has to perform take off calculations, taking manufacturer into account,

Starting with Aircrafts Take off weight, then local ATIS information analysis.

Now take a one example-

Now , as you can see here it is briefing about take off speeds V1, Vr, V2 of Airbus a320 and also given the flex temperature of 58 at the time of take off, so we have to select flex temperature of 58, on to the performance page-

Now the FADEC( FULL AUTHORITY DIGITAL ENGINE CONTROL UNIT) assumes that outside air temp is +58 degrees, and therefore FADEC reduces the power purposely to reduce the engine wear in such a expected high temp.

And then, when applying the thrust levers to the "d10th" position or you can see at highest position. The FADEC will give your 85 percent of take off performance-

Results of using highest Flex temperature-

The results of using high flex temp is that speed is higher for lift off the plane, because plane can not accelerate as quickly as possible, and therefore using of more Runway could results into shorter stop distance in case of rejected take off.

So the conclusion is that lower the flex temp, maximum the power required to the engines for take off. 

And the higher the flex temp less the power required, and less the wear and tear of engines.

Now, how can the passenger get to know which flex temperature is chosen after take off?

You can feel this difference in a noise, at the shorter Runways airport, because of the shorter distance of the Runway the pilot sets the flex temperature highest on take off roll, and this can leads to the high power to the engines and Aircraft take off shortly by using less Runway length. due to this high power settings to the engines are literally roar and become so noisy at the time of rotation speed and suddenly after take off while reaching to the thrust reduction altitudes, pilots set the take off thrust to the climb thrust like below-

And you then fell a power change and reduction in Engine noise,

Now in the sum of, you would say flex temperature is the speed balance between the stop margins avialable on the runway

And the longer engines life and lower the fuel burn.

But in case of Boeing Aircrafts it is totally different,

Now, maybe if you are sitting in the Boeing and you gently lift off into the air and once you reaching to the thrust reduction altitudes and Suddenly more power is applied.

Some take off on the Boeing, thrust for the take off are reduced even below the climb thrust.

Now let's say de-rated power is-

T/O= 75%

And climb power is at

Climb power= 85%

You can feel the increases in 10% of power at the time of thrust reduction altitude. This is the reason for Boeing Aircrafts becomes more noisy after take off.

How does a stealth technology works?

The B-2 spirit stealth bomber is one of the most iconic plane that ever been built it's stick fine wing design makes its impossible to visible in any kind of radar, and it is incredibly fuel efficient.

The rise of stealth Aircrafts are back track to world war-1 when the German attempted to use transparent canvases to make the plane difficult to spot, but that plan was failed because of using transparent canvases, make the plane more visible-

As we know radar works by sending the short pulses of electromagnetic energy in the form of radio waves.

Radar cross-section- A measure of targets ability to reflect radar signal in the direction of radar receiver. 

The B-2 has a 52m of wing span, it has been  reported  to have the same radar cross section as like of large Birds on the radar screen.

The core concept behind the B-2 design is the reflection, it was designed to reflect the radio waves-

Away from the source so that they never get a chance to be detected by any kind of radar, the aircraft is designed with complexities of modules and with super computers,  additionally the B-2 has it's fine wing design and it's engines are embedded within the aircraft that's why it is impossible to detect.

Beyonds it's shape the B-2 is designed with advanced composite materials which are capable of absorbing and dissipating the incoming radio waves, 

The skin of the aircraft is made from advanced carbon fiber  reinforced plastic,  while leading edge of the aircraft are made from or painted from small particles of iron and which absorbs the electromagnetic energy and convert it into a heat-

As per now the B-2 spirit bomber has  the first efficient Aircrafts in terms of stealth technology before the made of F-22 raptors, and F-35 lighting II, combat fighter jets.

But,  the stealth technology Aircrafts from Russia is the su-57, it has some problem with the engine due to this it can not be a proper stealth Aircraft. 

And as per defense experts  J-20 is the copy of USA F-35 lighting II, is not a proper stealth Aircraft, because J-20 is detected by the Indian su-30 MKI,on may 25th 2018 as per Indian air Force. That's why USA is always dominanting the sky as compared with other countries.