# Estimates

## Estimate standard rate turn bank angle

divide the true airspeed by 10 and add 7. e.g.

100 knts=> 15.38 => 100/10+7 = 17

300 knts => 39.5 => 300/10+7=37

## Estimate Pressure Altitude

Determine pressure altitude by using this formula: (standard pressure minus your current pressure setting) times 1,000 plus field elevation equals pressure altitude.

e.g. field elevation is 5,000 feet, (29.92 – 29.45) x 1,000 + 5,000 = 5,470 feet.

## How to calculate temperature?

ISA at sea level: 15° C

Temperature lapse rate 2 C or 3.5 F per 1000 feet.

Given FL270; 27 x -2 = -54° C. -54° C +15° C= -39° C

## How to calculate the approximate base of the cumulus clouds?

What is the approximate base of the cumulus clouds if the surface air temperature at 1,000 feet MSL is 70 °F and the dewpoint is 48 °F?

As a rule of thumb, divide the difference between the temperature and dew point by 4.4 to determine the height of the cloud base. 70° F - 48° F = 22. 22 / 4.4 = 5 (in thousands of feet). Add the field elevation of 1,000' to the 5,000' to find 6,000'.

## How to calculate TAS?

Add 2 percent to the CAS for each 1,000 feet of altitude. At 10,000 feet, you are flying approximately 20% faster than your indicated airspeed.

```
TAS = altitude / 1000 * 2% * CAS
```

## How to calculate Density Altitude

Density Altitude = Pressure Altitude + [120 * (Outside Air Temperature – Standard Temperature)]

15°C at sea level, decreasing by about 2°C per 1000 feet of altitude

```
8000 ft => 15-2*8=-1
```

## weight of fuel

100LL ~6 lb per gallon

## How to estimate fuel burn?

lb per hour = power / 20;

e.g.

- Citabria 118 HP / 20 => ~6 ga / hour
- C172 180 HP / 20 => ~9 ga / hour.