Honda Civic Forums banner

1 - 8 of 8 Posts

·
Registered
Joined
·
5,006 Posts
Davyw22 said:
ok explanision the air is thinner on a hot day therfore its harderd for it to take off so a bit of cold air would help to create lift on the wings i lve my r/c planes bossanova ftw
The figures published in the Flight Manual for the performance capabilities of a certain model of aeroplane are always related to standard atmosphere (29.92 inches of mercury at 15° C at sea level). However, only rarely will the aeroplane actually operate under conditions that approximate standard atmosphere. Any increase in temperature or altitude means a decrease in the aircraft's optimum performance.

Air density decreases with altitude. At high elevation airports, an aeroplane requires more runway to take off. Its rate of climb will be less, its approach will be faster, because the true air speed [TAS] will be faster than the indicated air speed [IAS] and the landing roll will be longer.

Air density also decreases with temperature. Warm air is less dense than cold air because there are fewer air molecules in a given volume of warm air than in the same volume of cooler air. As a result, on a hot day, an aeroplane will require more runway to take off, will have a poor rate of climb and a faster approach and will experience a longer landing roll.

In combination, high and hot, a situation exists that can well be disastrous for an unsuspecting, or more accurately, an uninformed pilot. The combination of high temperature and high elevation produces a situation that aerodynamically reduces drastically the performance of the aeroplane. The horsepower out-put of the engines decrease because its fuel-air mixture is reduced. The propeller develops less thrust because the blades, as air foils, are less efficient in the thin air. The wings develop less lift because the thin air exerts less force on the air foils. As a result, the take-off distance is substantially increased, climb performance is substantially reduced and may, in extreme situations, be non-existent.

Humidity also plays a part in this scenario. Although it is not a major factor in computing density altitude, high humidity has an effect on engine power. The high level of water vapor in the air reduces the amount of air available for combustion and results in an enriched mixture and reduced power

Mountain airports are particularly treacherous when temperatures are high, especially for a low performance aeroplane. The actual elevation of the airport may be near the operational ceiling of the airplane without the disadvantage of density altitude. Under some conditions, the aeroplane may not be able to lift out of ground effect or to maintain a rate of climb necessary to clear obstacles or surrounding terrain.

Density altitude is pressure altitude corrected for temperature. It is, in layman terms, the altitude at which the aeroplane thinks it is flying based on the density of the surrounding air mass.

Too often, pilots associate density altitude only with high elevation airports. Certainly, the effects of density altitude on aeroplane performance are increasingly dramatic in operations from such airports, especially when the temperature is also hot. But it is important to remember that density altitude also has a negative effect on performance at low elevation airports when the temperature goes above the standard air value of 15° C at sea level. Remember also that the standard air temperature value decreases with altitude.

In order to compute the density altitude at a particular location, it is necessary to know the pressure altitude. To determine the latter, set the barometric scale of the altimeter to 29.92" Hg and read the altitude.

Density altitude can be calculated for any given combination of pressure altitude and temperature, by using the circular slide rule portion of a flight computer.

That's my explanation ;)
 

·
Premium Member
Joined
·
1,030 Posts
Considering it took him 2 minutes to type it, I'd guess it was actually Wiki that knows it's stuff :D
 

·
Registered
Joined
·
5,006 Posts
Although if you think about it, I could have been typing it in the reply box since the topic started at 23:01. That leaves me exactly 30 minutes since the topic started :)

But yeah, I didn't write that. Was just interested in what Davy said so went looking.
 

·
Premium Member
Joined
·
1,030 Posts
Haha, aye, I had considered that, but considering Davy's post was quoted (granted that could have been added later) I figured Wiki would have been involved as you seem to like that site :D
 
1 - 8 of 8 Posts
Top