Gas turbine engine with transmission

A gas turbine engine comprising:

• a core engine having a rotatable high pressure spool;
• a low pressure spool rotatable independently of the high pressure spool;
• a low pressure compressor rotor located upstream of the core engine;
• and
• a transmission having a variable transmission ratio and including:
• a control gear rotationally supported on a rotatable control ring, with rotational axes of the control gear and of the control ring being perpendicular to one another,
• a first rotatable ring gear meshed with the control gear and in driving engagement with the low pressure spool,
• a second rotatable ring gear meshed with the control gear and in driving engagement with the high pressure spool, and
• a gear train having an input gear in driving engagement with the low pressure spool and an output gear in driving engagement with the low pressure compressor rotor, the control ring being in driving engagement with at least one gear of the gear train.

A method of adjusting a speed of a low pressure compressor rotor of a gas turbine engine having low and high pressure spools free to rotate independently from one another, the method comprising:

• rotating the low pressure spool at a first rotational speed;
• driving a rotation of the low pressure compressor rotor with the low pressure spool through a first portion of a transmission such that the low pressure compressor rotor rotates at a second rotational speed, the first portion defining a variable ratio between the first and second rotational speeds;
• rotating the high pressure spool at a third rotational speed;
• and
• adjusting the variable ratio through a driving engagement of a second portion of the transmission with the first portion, the second portion being drivingly engaged with the low and high pressure spools such that the variable ratio is adjusted based on a difference between the first and third rotational speeds.