The reason the Pratt’s take so long to startup all depends on if it’s been sitting overnight or just flown in and the engines are still hot. If it’s been sitting overnight and the engines are cold, the engines should startup within 1 minute. If the plane is turning around and the engines are still quite warm, the crew must turn on a mode in the cockpit called dual cooling. This means the N2 fans spin up to 10-15% for between 1 - 5 mins depending on the temperature outside and EGT temp (all controlled by FADEC). The N2 spinning in dual cooling allows the EGT and engines to cool down quicker to prevent any damage from occurring compared to starting up when warm and having damage to the crank and possible bending. After the time elapses, the engine the crew have decided to start first will then begin a 1 minute dry turning stage before then introducing fuel and start, hence the longer startup time. The second engine on the other hand will stop spinning N2 to reduce elec power. Once the first engine has started and the start switch is selected in run on the second engine to start, the second engine follow the same procedure of dry turning for 1 min.
The problem is that all the heat rises to the top of the shafts/fans/etc. while sitting stopped, causing them to bow slightly due to uneven thermal expansion. Spinning them at low speed for a short time allows the temperature to even out so everything is straight.
@@FlightAce100 The LEAP needs it for warm starts as well, but doesn’t have dual cooling so they need cooled separately, and doesn’t have a timer on the ECAM, only a cooling indication.
![SCENIC Emirates Airbus A380-800 Approach and Landing into Sydney [1080p60]](/img/n.gif)
The reason the Pratt’s take so long to startup all depends on if it’s been sitting overnight or just flown in and the engines are still hot. If it’s been sitting overnight and the engines are cold, the engines should startup within 1 minute. If the plane is turning around and the engines are still quite warm, the crew must turn on a mode in the cockpit called dual cooling. This means the N2 fans spin up to 10-15% for between 1 - 5 mins depending on the temperature outside and EGT temp (all controlled by FADEC). The N2 spinning in dual cooling allows the EGT and engines to cool down quicker to prevent any damage from occurring compared to starting up when warm and having damage to the crank and possible bending. After the time elapses, the engine the crew have decided to start first will then begin a 1 minute dry turning stage before then introducing fuel and start, hence the longer startup time. The second engine on the other hand will stop spinning N2 to reduce elec power. Once the first engine has started and the start switch is selected in run on the second engine to start, the second engine follow the same procedure of dry turning for 1 min.
The problem is that all the heat rises to the top of the shafts/fans/etc. while sitting stopped, causing them to bow slightly due to uneven thermal expansion. Spinning them at low speed for a short time allows the temperature to even out so everything is straight.
@@michaelcorcoran7444 Why is this only necessary for the PW engines and not the CFM LEAP?
@@FlightAce100 The LEAP needs it for warm starts as well, but doesn’t have dual cooling so they need cooled separately, and doesn’t have a timer on the ECAM, only a cooling indication.
Typical Wellington weather to welcome you
Nice video
Thanks!
the 744😢😢😢😢
Nice PTU
Nice video! Two months before Covid started to ruin things🤣
Flown NHA as NZ573 AKl to chc
Hope you found a flight to Wellington from Auckland
czcams.com/video/jKluPjJppn4/video.html