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Rules Of Thumb

Gulfstream G450 Performance

Where do these rules of thumb come from? Mostly here: Rules of Thumb.


 

Aim versus Touchdown Points

Rule of Thumb:

The main gear will touchdown behind the pilot’s aim point a distance seven times the distance between the pilot and the main gear (plus flare distance) when the airplane is flown on a 3 degree glide path.

Source: Deck Angle.

Angle of Attack

Rule of Thumb:

Commit the Angle of Attack for L/DMAX (usually 0.3) to memory, it is your best glide and endurance speed and can save your life.

Source: Angle of Attack.

Approach VVI

Rule of Thumb:

A 3 degree glide path descent rate in feet/minute is equal to one-half the ground speed in nm/hour times ten.

Source: Approach VVI.

Circling Approach Offset

Rule of Thumb:

To provide circling offset when approaching a runway at 90°, overfly the runway and time for 15 seconds (Category D) / 20 seconds (Category C) before turning downwind. To provide offset when approaching from the opposite runway, turn 30° away from heading, time for 60 seconds (Category D) / 70 seconds (Category C), and then turn downwind.

Source: Circling Approach.

Course Intercepts

Rule of Thumb:

To intercept a course inbound: Charlie Brown plus 30, the head always falls.

Rule of Thumb:

To intercept a course outbound: Tom Collins plus 45, the tail always rises.

Source: Course Intercepts.

Crosswinds

Rule of Thumb:

A thirty degree crosswind is equal to one-half the full wind factor.

A forty-five degree crosswind is equal to three-fourths the full wind factor.

A sixty degree crosswind is equal to ninety percent of the full wind factor.

Source: Crosswinds.

Descent Gradient

Flight levels divided by nautical miles equals gradient.

Nautical miles per minute times descent angle times 100 gives vertical velocity in feet per minute.

Source: 60 to 1.

ETE Adjustments for Block Times

Rule of Thumb:

Timing ETE Adjustment for TAS decay with descent:

  • add 6 minutes when 70 nautical miles out
  • add 5 minutes when 60 nautical miles out
  • add 4 minutes when 50 nautical miles out
  • add 3 minutes when 40 nautical miles out
  • add 2 minutes when 30 nautical miles out
  • add 1 minute when 20 nautical miles out.

Timing: It takes 20 seconds to taxi 1/10 of a nautical mile at 18 knots.

Timing: A standard rate 360 degree turn loses 2 minutes, a half-standard rate 360 degree turn loses 4 minutes.

Timing: A 60 degree turn off course for time X followed by a 60 degree turn back to course for time X and a 60 degree turn back on course will add time X to the en route ETE.

Source: Block Times.

Fix-to-Fix

Rule of Thumb:

To fly a fix-to-fix: You are the tail, target is the radial, higher DME is the edge of the card, lower DME is inside; draw a line, transpose the line.

Source: Fix-to-Fix.

Fuel Burn

Rule of Thumb:

Cruise fuel flows in the G450 are generally 4,500 / 4,000 / 3,500 PPH during hours one, two, and three. From that point on you can budget 3,000 PPH.

Source: G450 Performance-En Route.

Glide Path

Rule of Thumb:

Nautical miles per hour times ten divided by two gives a good three degree glide path VVI.

Source: 60 to 1.

ISA

Rule of Thumb:

Standard Temperature is 15°C minus 2°C per thousand feet above sea level, until 36,000’ after which it becomes constant at -56°C.

Source: Properties of the Atmosphere.

Maneuvering Speed

Rule of Thumb:

When recovering from an unusual attitude, wind shear, or anytime maximum maneuverability is needed, the closer the airplane is to VA maneuvering speed, the better.

Source: Maneuvering Speed.

Radar

Rule of Thumb:


At 40,000', setting 0° tilt on a 24-inch radar grazes the ground at 200 nm.

At 30,000', setting 0° tilt on a 24-inch radar grazes the ground at 150 nm.

Source: Radar Tilt.

Range

Rule of Thumb:

While the angle of attack at which L/DMAX occurs remains constant with weight, the airspeed at which this occurs decreases as the aircraft becomes lighter.

The aircraft’s maximum range will occur at an airspeed higher than at which L/DMAX occurs.

To obtain maximum range, the thrust of the aircraft must be reduced as the airspeed for maximum range decreases with decreasing aircraft weight.

Maximum range Mach does not change for conditions of headwinds or tailwinds on most turbofan aircraft.

Source: Maximum Range.

Smoothness

Rule of Thumb:

Apply small pressures to the nose wheel tiller to avoid taxi jerkiness: apply a small pressure and wait to see the response before adjusting pressure.

High deck angles are permissible on takeoff and initial climb out, so long as all negative G forces are avoided when reducing pitch.

On landing apply wheel brakes with an initial pressure and wait for a reaction; cold-soaked brakes rapidly increase effectiveness as temperature rises during initial application.

Source: Smoothness.

Stick Shaker (High Altitude) Speed

Rule of Thumb:

During a maximum weight climb to altitude you will get the stick shaker at a Mach twenty higher than your altitude in thousands. At 20,000 feet it occurs at Mach .40, at 30,000 feet at Mach 0.50, and at 40,000 feet at Mach 0.60.

Source: G450 Flight Envelope.

Teardrop Angle

Rule of Thumb:

A holding pattern teardrop angle of 120 times the turn radius divided by leg length will provide an on course roll out, no wind.

Source: Holding Pattern Teardrop Angle.

Top of Descent

Rule of Thumb:

Start descent at three times your altitude to lose in thousands of feet to achieve a three degree gradient.

Start descent at four times your altitude to lose in thousands of feet to achieve a 2.5 degree gradient.

Source: Top of Descent.

Rule of Thumb:

When descending from above 35,000', start down at four times your altitude to lose and select a 2.5° flight path angle on the guidance panel. You can steepen the angle to 3.0° once below 35,000'. When descending from below 35,000', start down at three times your altitude to lose and select a 3.0° flight path angle.

Source: G450 Performance-Descent.

Turn Radius

Rule of Thumb:

Rule — At 25 degrees of bank, turn radius is equal to nautical miles per minute squared, divided by ten.

Source: Turn Radius.

Rule of Thumb:

A standard rate turn radius is equal to nm/min divided by 3.

Source: Turn Performance.

Visual Descent Point

Rule of Thumb:

A Visual Descent Point is found by subtracting the touchdown zone from the Minimum Descent Altitude and dividing the result by 300.

Source: VDP.

Visual Pattern Geometry

Rule of Thumb:

Visual pattern: fly a downwind displaced by 2 nm, turn base at 45°, descend 900 fpm, roll out at 600’, 2 nm from touchdown zone.

Source: Final Turn.

Revision: 20120424
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