Rules of thumb

[Jase T]

Folks.

 

I am working on a desk reference document that will include (as a very small part) a list of useful rules of thumb. By this I mean ones you can actually use or may find interesting. To this end I have compiled the following list. Who has others they actually use? Please feel free to add to the list of correct the ones i have. I am only interested in ones that will be relevant to RAAus type operations so won't need to find the Null in an ADF or know the crossing distance when overhead a DME or work out angle of bank for rate one turns etc etc.... 

 

General 

·      ONUS Overshoot North Undershoot South

·      SAND Apparent turn to South when Accelerating and North when Decelerating

·      Variation East magnetic least, Variation West magnetic best

·      The air is conditionally unstable if the temperature drops more than 2° per 1,000 feet on ascent

·      If the wind differs from the runway heading by 15 degrees, the crosswind component is 25% of the wind velocity. If the difference is 30 degrees, the crosswind is half of the reported wind speed. If the difference is 45-degrees the crosswind component is 75% of the overall wind speed. If the difference is 60 degrees or more assume the crosswind is the same as the total wind.

 

Take Off Performance

 

·      A 1°C change in temperature from ISA will increase or decrease the takeoff ground roll by 10%. 

·      Takeoff distance increases by 15% for each 1000′ DA (Density Altitude) above sea level 

·      A headwind of 10% takeoff speed will reduce ground roll by 20% 

·      A 10% change in aircraft weight will result in a 20% change in takeoff distance. 

·      The maximum crosswind component is approximately equal to 0.2 x Vs1 

·      Abort the takeoff if 70% of takeoff speed is not reached within 50% of the available runway. 

·      Available engine horsepower decreases 3% for each 1000’ of altitude above sea level. 

·      Fixed Pitch, Non turbo aircraft - Climb performance decreases 8% for each 1000’ DA above sea level. 

·      TAS increase 2% for each 1000’ in a climb. 

·      Standard temperature decreases 2° for each 1000’

 

Approach & Landing 

 

·      A 10% change in airspeed will cause a 20% change in stopping distance. 

·      A narrow runway may give the appearance of being longer, a wide runway may give the appearance of being short. 

·      A slippery or wet runway may increase your landing distance by 50%. 

·      Use Vso x 1.3 (Vref) for approach speed over the threshold. 

·      Plan to touchdown in the first ⅓ of the runway or go around. 

·      For each knot of airspeed above Vref, the touchdown point will be 30m further down the runway. 

·      For each 1000’ increase in field elevation above Sea Level, stopping distance increases by 4%. 

 

Flight Manoeuvres 

·      Use ½ the bank angle for the lead roll out heading. 
i.e 30° of bank angle Start roll out 15° before desired heading. 

·      To make a 6° change in heading, use a standard rate turn then immediately level the wings. To make a 3° change in heading use ½ standard rate turn. 

·      Maneuvering speed Va = 1.7 x Vs1 

·      Va decreases 1% for each 2% reduction in weight 

·      Vy decreases ½ to 1kt for each 1000’ DA 

·      Vy Vx and Vg (best glide) decrease ½ kt for each 100lbs (45KG) under MGW 

·      Vr = 1.15 x Vs 

·      TAS = IAS (kts) + FL/2 
eg:
    FL 300, IAS = 240 
    TAS = 240 + 150 = 390 Kts 

·      Best Cruise climb speed is the difference between Vx and Vy and add this to Vy. 
Eg Vx = 65, Vy 75 
Difference is 10kts 
10kts + Vy 75 =85Kts 

 

 

Climb Planning 

·      Add 1 minute to your flight plan ETE for every 1000′ climb to cruise altitude. 
Cruise altitude = 8000′ Time to add = 8 mins to ETE 

·      To find the Rate of Climb required (ROC) multiply the % gradient by the groundspeed. 
% Gradient = 3.3% 
Groundspeed = 120 Kts 
3.3 x 120 = 400fpm 

·      To find the Feet per Minute (FPM), multiply the gradient % by 60 
3.3 % Gradient x 60 
= 200 fpm 

 

Descent Planning 

·      One degree climb or descent angle closely equals 100’/ Nm. 
 

·      To determine the NM distance to start a 3° enroute descent. 
Divide the altitude to lose ( in Flight Levels) by 3. 
e.g. 
      Altitude to lose = 6,000 (FL 60) 
      60 / 3 = 20 nm to start descent 

·      For a 3° Rate of Descent (ROD) take half your groundspeed and add a zero. 
Descent Groundspeed. 
      120 x ½ = 60 
      600 fpm ROD 

[IBob]

You may want to look at slope in runway vs landing distances, if that's relevant in your part of the world?

 

[Ryanm]

I’d be VERY careful using the rule of thumbs for performance. This will vary wildly between types.

[Yenn]

Not a rule of thumb, but worth knowing. Uphill runway you need to appear high on approach. Downhill, you need to appear low on approach.

The first couple of rules mentioned above apply only in the Southern hemisphere.

Airspeed in tens or hundreds of knots, plus 7 is angle of bank for a standard rate turn. ie 70 kts =7+7 or 14 degrees

150 kts =15+7 or 22 degrees

[Chris SS]

Height, Speed and Luck... pick any two.

 

[turboplanner]

ALWAYS be sure not to include a ROT in an equation because it will nullify the whole equation.

If that equation happens to be take off distance, you probably won't.