Flight Envelope
The V-g diagram and glide polar for your aeroplane, at your weight. Manoeuvring speed drops as you get lighter — most pilots guess that the other way round.
Gross is 2,550 lb. At 2,550 lb the stall is 53.0 KCAS and Va is 103.
Read these off your own aeroplane — the arcs on the airspeed indicator and the placard. The defaults are a starting point, not your aircraft.
Vs1 × √3.8 = 103.3 kt, against a placarded Va of 105. That is position error and placard rounding.
Below Va (103 kt) the wing stalls before the structure breaks, which is why full control deflection is survivable there and not above it. The corner walks left as the aeroplane gets lighter — at 2,040 lb it would be 92 kt.
Best glide and minimum sink are different speeds. Best glide is the furthest — it is the shallowest ANGLE. Minimum sink is about 52 kt, roughly three quarters of best glide, and buys the most TIME rather than the most distance. Slow down for a hold, speed up for a field.
What a V-g diagram is actually telling you
It is the set of speeds and load factors the aeroplane can survive. The curved left edge is the stall — lift goes with the square of speed, so pulling n times the weight needs √n times the speed. The flat top and bottom are the structure: 3.8 g up and 1.52 g down for a normal-category aeroplane, and the airframe is not certified past them.
Everything outside the shape is either a stall or a bend. There is no third option, and the two boundaries meet at exactly one point.
The corner is manoeuvring speed, and it is the whole chart
Where the stall curve meets the structural limit, the aeroplane stalls and reaches its limit load at the same instant. That is Va. Below it, a sharp pull stalls the wing before it breaks anything — the wing lets go first, and letting go is survivable. Above it, the structure gives first.
It is derived, not looked up: Va is the stall speed times the square root of the limit load factor. For a normal-category aeroplane that is √3.8, about 1.95 — so Va is very nearly twice the stall speed, on every aeroplane in the category.
Lighter means a LOWER manoeuvring speed
This is the part most pilots have backwards, and it is why the weight slider is the first control on the page rather than a footnote.
A lighter aeroplane needs less lift to fly, so it stalls slower — and since Va rides on the stall speed, Va comes down with it. Burn off fuel and your turbulence penetration speed drops. Flying yesterday's Va at today's weight means flying above the corner, on the side where the structure gives first.
Enter the CALIBRATED stall speed, not what the tape reads
The Va relation closes in calibrated airspeed. Position error near the stall is several knots on a light single and it does not cancel: use a 172's indicated 48 and you derive a manoeuvring speed of 94, against a placarded 105. Eleven knots low, on the one speed you would pull to in turbulence.
So the page checks itself. It derives Va from what you typed and compares it against the placard you also typed — if they disagree by more than a few knots, something is on the wrong scale, and it says so instead of drawing a confident wrong chart.
Best glide and minimum sink are not the same speed
The glide polar shows both, and the gap between them surprises people. Best glide is the shallowest angle — it takes you furthest, and it is the number to fly toward a field. Minimum sink is slower, about three quarters of best glide, and buys the most time in the air.
Sink rate is speed multiplied by the drag-to-lift ratio, so slowing down can win even where the glide ratio is slightly worse. If you are gliding toward somewhere, fly best glide. If you are waiting — for a restart, for help, for a decision — fly slower.
What this does not do
It draws the certificated envelope, not a gust envelope, and it says nothing about how close to the edges anything should be flown. It also cannot know your aeroplane: the defaults are a starting point for the type, and the numbers that matter are the ones on your own airspeed indicator and placards. Type those in. Where a figure has no authoritative public source we have said so rather than implied one.