Sunday, June 17, 2012

Summer heat

                          However, we need to remember that high temperatures can have serious effects on our performance. Cockpits can reach temperatures well above ambient, especially if they include large areas of perspex, and pilots could experience dehydration unless they drink sufficient water. Sunburn, apart from its own effects, can be associated with dehydration. Take water, cover your head and exposed areas of skin when you are in the cockpit or out and about on the airfield, and remember that you may remain relatively dehydrated because of alcohol long after its initial effects have worn off.
                           Of course, it is not only the pilot which may experience reduced performance. High air temperatures reduce air density and consequently reduce both engine power and the lift force available from the wing. Take-off distances can increase dramatically, so make sure you carry out performance calculations carefully.
                            It may also be worth considering the effects of temperature on your fuel. Fuel contents are normally indicated and checked by volume, but produce power by mass. A tank full of warm fuel will not contain as much calorific value as one containing cold fuel, and expansion in increasing heat may cause fuel to flow out of the vents. Hot fuel is more likely to vaporise in the fuel lines, producing gas bubbles which may not be cleared through pumps (vapour lock). Avgas should have no serious vaporisation problems, but the danger of vapour lock is the reason why the use of MOGAS is not permitted above temperatures of 20 degrees C. If our tanks contain MOGAS we need to either keep the fuel cool, or stop flying!

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