Week 4: Energy as the unit of account

Specific energy, the exchange rate between height and speed, and why the aircraft charges you for every transaction

15 March 2027

The lecture that turns the rest of the course into arithmetic.

Treat altitude and airspeed as one quantity held in two denominations, and a sortie becomes a sequence of transactions in it:

• the engine credits the account
• drag debits it continuously, whether or not you are doing anything
• every manoeuvre is a transfer, and the transfer has a spread

This framing is not a teaching convenience. It came out of 1960s work comparing fighter aircraft to each other, producing diagrams that showed, for a given aircraft at a given weight, exactly what it could and could not afford. Those diagrams changed how aircraft were specified.

What it gives you here is smaller and more immediately useful: a way of answering “can I get there from this” without flying it to find out. By week 7 you fly a circuit that arrives at a chosen point with almost no energy left, deliberately — today is where that stops being alarming.

The lecture ends on the manoeuvre students most want to believe in, which is pulling up when low and slow. We will price it.

Reading#

The specific energy notes and the six worked problems. Attempt all six before the period, including the ones you expect to get wrong.