Performance and Limitations

For aircraft with a gross weight of more than 4,000 lb, the normal-category limit load factor is reduced. A safety factor of 50 percent is added to the limit loads given above — that is the ultimate load, where structural failure is expected, not merely damage (PHAK ch. 5).

This matters commercially because the ACS performance maneuvers — chandelles, lazy eights, steep spirals, eights on pylons — are often flown in the utility category, and utility category typically means a reduced weight and a restricted CG range. Check which category your loading actually puts you in.

In a coordinated level turn (PHAK ch. 5):

Stall speed rises with the square root of the load factor. An airplane that stalls at 45 kt unaccelerated must be kept above roughly 64 kt in a 60° bank (45 × √2.0) to avoid stalling. Load factor increases at a terrific rate after a bank reaches 45° to 50°, and at slightly more than 80° it exceeds even the acrobatic 6 G limit. A 90° banked constant-altitude turn is not mathematically possible. For the average general aviation airplane, the practical maximum for a coordinated constant-altitude turn is about 60° — going from there to 70° adds roughly 1 G, bringing it close to the yield point. Past 70° the rate steepens sharply, which is the whole point of the curve.

V_A is the speed below which you can move a single flight control, one time, to its full deflection, for one axis of rotation only (pitch, roll, or yaw), in smooth air, without risk of damage (PHAK ch. 5, ch 8).

What it does not cover — say this explicitly, because it is the trap:

• Multiple full control inputs in one axis (the rudder reversal case)
• Full control inputs in more than one axis at the same time
• Turbulence beyond "smooth air"

V_A must be published in the AFM/POH of recently designed airplanes. For older GA airplanes it approximates 1.7 times the normal stalling speed — a 60 kt stall gives about 102 kt, and stalling there imposes a load factor of the square of the speed increase, 2.89 G.

Because the wing has to generate the limit load factor, and at a lighter weight it reaches that load at a lower airspeed. Lighter airplane, lower V_A.

Put another way: the wing stalls (and thereby relieves the load) at a lower speed when the airplane is light, so the speed at which the stall relieves the gust load before the structure is overstressed comes down with it. Always use V_A for today's actual weight, not the placarded gross-weight number.

1. Start with the current empty weight and empty-weight CG from the airplane's actual W&B record — the latest amended sheet in the AFM, not a POH sample.
2. List every load item with its weight and its arm: front seats, rear seats, baggage areas (each with its own limit), and fuel at 6 lb/gal for avgas.
3. Multiply weight by arm for each item to get moment.
4. Total weights and total moments, then CG equals total moment divided by total weight.
5. Plot on the envelope — check both the weight limit and the CG range, and note whether the plot falls in the normal or utility envelope.
6. Repeat for landing weight with fuel burned off, because the CG moves as fuel goes — in many airplanes it moves aft.
7. Check every phase, which is exactly what S1 requires: takeoff, cruise, and landing all inside limits.

You do not fly it. The fixes, in order of preference:

• Move load forward — shift baggage from the aft compartment to the forward one (within each compartment's own weight limit), or move a passenger from the rear seat to the front.
• Add ballast forward, secured, if the AFM permits it and you compute the required amount rather than guessing.
• Reduce aft load — leave bags behind.
• Change the fuel load, but only after checking which way fuel moves the CG in this airplane.

Then recompute and re-plot. And check the landing CG too: an aft-CG problem often gets worse as fuel burns.

• Reduced longitudinal stability — the airplane is less inclined to return to trimmed pitch, and control forces get light and imprecise
• Higher stall risk because the tail-down force needed is smaller, but recovery from a stall or spin becomes more difficult or impossible
• Higher cruise speed for the same power, which is why it feels good until it doesn't

A forward CG costs you performance instead:

• Higher stall speed
• Higher required tail-down force
• Higher effective wing loading and heavier control forces
• Limited elevator authority in the flare — shows up as a nose-first arrival on a short-field landing

Forward CG degrades performance; aft CG degrades controllability, and that is why the aft limit is the one that kills.

• Atmospheric conditions — pressure altitude, temperature, and humidity, combining as density altitude. High, hot, and humid means less thrust, less lift, and longer distances.
• Airplane configuration — flap setting, weight, and whether gear and cowl flaps are where the chart assumed.
• Airport environment — field elevation, runway slope, surface (dry grass and soft surfaces add substantial ground roll), obstacles in the departure path, and wind, including the tailwind component that penalizes a landing far more than a headwind helps.
• Pilot technique — rotation speed, whether the airplane was accelerated to the chart's exact liftoff speed, drift control, and how promptly the airplane was cleaned up.
• Loading and weight and balance — heavier means longer roll, shallower climb, higher stall and approach speeds, and a lower ceiling.

Because the chart describes a new airplane, flown by a test pilot, on a dry level paved runway, at exactly the charted speeds. Yours is not that airplane.

Named gaps to state:

• Engine no longer producing rated power; propeller no longer at nominal efficiency
• Airframe with antennas, dents, dirt, and paint the test article did not have
• Technique that is a knot or two off the chart's speeds — a small error, compounded across the whole ground roll
• Runway that is not dry, not level, or not clean
• Wind that is gusty and momentary rather than the steady component the chart assumed

The mitigation is a stated margin, not optimism: add a fixed percentage to computed takeoff and landing distances and treat the result as the requirement. Say the number you use and why.

• Reading the wrong chart — short field versus normal, or the wrong flap configuration
• Failing to interpolate, or interpolating between the wrong pairs of lines
• Wrong pressure altitude — using field elevation instead of setting 29.92 and reading, or forgetting the correction
• Ignoring the chart's conditions and notes — the fine print carries the runway surface, the wind assumptions, and the leaning procedure
• Using gross-weight numbers for a lighter airplane, or the reverse
• Distance to a 50 ft obstacle versus ground roll — reading the wrong column is how a "sufficient" runway becomes a trees problem

Airspeeds:

• Indicated — what the ASI reads
• Calibrated — indicated corrected for installation and position error
• Equivalent — calibrated corrected for compressibility
• True — calibrated corrected for density
• Ground speed — true corrected for wind

Altitudes:

• Indicated
• Pressure — indicated with 29.92 set
• Density — pressure corrected for nonstandard temperature
• True — actual height above MSL
• Absolute — height AGL

Performance charts almost always want pressure altitude and outside air temperature as inputs, and they hand back distances and rates that assume the airplane is flown at the charted indicated speeds. Density altitude is the concept that explains the result; pressure altitude and temperature are what you enter.

On the back side of the power curve, more power is required to fly slower, because induced drag rises as speed decays. Below the minimum-drag speed, a speed reduction increases total drag, so holding altitude at a lower speed takes more power, not less — and the airplane is speed-unstable: left alone, a speed loss compounds.

Where you meet it commercially:

• Short-field approach behind the power curve
• Go-around from a deep-flap steep approach
• Slow-flight portion of a power-off 180

AFH notes that flap extension beyond about 30° produces significant drag, and the sink rate it creates has to be controlled with power — reduce power too early and you arrive hard, too late and you float (AFH ch. 12).

The recovery from the region of reversed command is always the same: lower the nose and add power, in that order of urgency, and accept the altitude loss.

The glide ratio does not change with weight — the airplane's lift-to-drag ratio is a function of angle of attack, and the best-glide AOA is the same at any weight.

What changes is the speed at which that AOA occurs: a heavier airplane must fly faster to hold the best L/D angle of attack, and it descends faster while covering the same ground distance. So a light airplane glides the same distance but at a slower speed and a lower rate of descent — more time aloft over the same footprint.

Practical consequence: the POH best-glide speed is usually published at gross weight. Flying it light means gliding slightly fast, giving up a little of the distance you actually have. This is exactly the calculation behind altitude selection for glide distance in Task I.D.

Within roughly one wingspan of the surface, the ground interferes with the wingtip vortices and the downwash behind the wing. Induced drag drops sharply, so at a given angle of attack the airplane needs less thrust to fly.

On takeoff this is a trap: the airplane will lift off and accelerate in ground effect at a speed at which it cannot climb out of ground effect. Forcing it off early leads to settling back onto the runway or mushing into the obstacle. Fly the chart's liftoff speed.

On landing it is the float: the same drag reduction means the airplane wants to keep flying at a speed that would otherwise be descending. The fix is speed control on final, not technique in the flare — every excess knot is float, and float is runway you planned to use for stopping.