Density Altitude

[Air Hog]

In this heat wave that we are experiencing at the moment and the accident yesterday at Aeroden, I don't think we always consider the density altitude when flying in this heat.
Maybe we can learn out of this. Here is yesterdays calculations for Aeroden. I am not 100% sure of Aeroden's altitude but:

Aeroden Density.JPG (54.85 KiB) Viewed 2248 times

[Tribal Croc]

Aeroden is 4100ft

[Blue Max]

Pleasde explain the above figures to us dom ouens..
During my limmited experience I have twice almost ended up in tree tops because of my aircraft stugglling to obtain hight on a hot afternoon..
Carrying a passenger or making the slightest mistake, eg taking off downwind is a sure recepie for an accident under the above conditions....
On some occasions on afternoon flights I have also experience that my aircraft functions at higher reffs than normal..
Ag sorry ek is so slim.

[Asterix]

I want to salute Airhog for starting this thread, separate from "Accidents and Incidents". We all know that this thread was posted in response to Big G's accident, and the subsequent questions that arise for us.

In starting this thread, he respects the fact that the thread on the accident is about the well-being of a fellow triker, and speculations about what happened is uncalled for. He preserves the accident thread as a place where all can enquire as to the wellbeing of our fellow triker. He makes the destinction between self interest and genuine concern.

Had this been "that other forum", we would have been into page 10, clinically speculating, blaming, preaching etc - all on the accident thread, where the hurt of the pic and family / friends were first published.

Kudo's on you Airhog, for not turning the accident thread into a technical discussion, trampling on the feelings of those involved!

[Air Hog]

All I want to say is, how many of our microlight pilots do realy know what density altitude is? As Paul has rightly asked. I am not saying this is what caused Big G's accident but I am sure it played some factor. Up draught turbulence must have been nasty in the heat that we experienced yesterday. I was at Kroon airfield at the time, installing our weather station and that is why I know what the temp was. We registered 38.5 C at 13h00 yesterday. I will not even fly a blik in that temp at this altitute. We can all speculate on what happend and Grant also gave us a rundown of what he experienced. I am just happy that he is alive and will recover from this.
I will let the boffins explain to Oom Paul all about density altitute but it boils down to you taking off from an airfield at the altitute as per the density altitute. So your performance is much less. You run much further before you take off and performace is as if you are at the much higher altitute. HOT and HIGH. Very dangerous!

[Asterix]

Oom Polla - om jou nou te antwoord in kort - MOENIE MET DAAI THUNDERBIRD PROBEER OPSTYG OP 'N DAG SOOS VANDAG NIE!! Ook nie CHG met 'n pax nie! Warm lug styg op. Al die lug is HOOOOG in die atmosfeer, en hier onder sukkel ons om asem te haal - kan jy dink hoe suffer jou Rotax? En jou vlerk het niks om aan vas te klou nie?

Moenie worry oor al die somme nie - as dit so warm soos vandag is, is dit "bier drink tyd", al waai daar geen wind nie.

[Asterix]

Air Hog - I agree fully with your post. (Also see my answer to my Fellow Vulture - Blue Max - which I love dearly.)

Again - thanks for taking the technical side of things away from the accident scene. This is what I appreciate in your original post. You proved that we are not like those "other people".

We appreciate the fact that something happened to cause a pic with 25 years in ML's to crash - we want to know what happened - in order to avoid it - but we respect the fact that the man got hurt - and we don't contaminate his accident thread with analysis.

Good thread - often overlooked aspect of flying.. Windstill but MOER warm.. DA - and small localised tornadoes (a LOT of hot air spiralling up in an intense little micro low pressure - little vacuums ..)

[KFA]

Hi guys, nice to see post about density altitude. I stand amazed as to the amount of licensed pilot's not knowing what it is. I am not pointing a finger at these pilot's but rather their instructors and the flight schools. How can you not teach your student what this is? This shows the low quality of theory being taught to our pilots. It is this lack of knowledge that kills pilot's and brings the microlight and other NTCA sections in disripute at our friends that think that everything that is not zs is from the devil. Please instructors, spend more time on the theory also, it is just as important as knowing how to handle an aircraft. Fly safe.

[Bugwar]

KFA I do not agree with you. All pilots have been taught to calculate density altitude but it is like looking in your mirrors every 8 seconds. You do it for the test but never again.
I remember a similar type accident involving a blik at Brakpan/Benoni airfield a while ago.

[Bundy]

A great topic, one which we do not pay enough attention too as Ultralight pilots....

DA catches out a lot of pilots especially bliks, but the effects on trikes can be disastrous too. Three factors affecting DA are Temperature, Pressure and relative humidity. Whenever there is an increase in any of these factors for a given location the DA will go up.

Longer TO rolls, poor climb performance, less engine power... these are the symptoms. It is especially a problem when taking off from short fields with obstacles to contend with. It also affects the "flare" and you need to have more bar input to maintain control on landing.

Be very careful flying on hot humid days is what I was taught. Especially when close to MAUW! To be honest, for me, conditions like that are better dealt with with an ice cold beer instead of a flip... Sometimes talking Kak in the Hanger is just as much fun as flying

Here are some classics....

http://www.youtube.com/watch?v=FD1T97UqMMU

http://www.youtube.com/watch?v=wVJJzyXQ ... 6BDCAEE8A3

Edit: In addition, the clip with the crash in it above (in which one person died...RIP) was the second accident at Cameron Park for the day! This pilot knowingly took off in bad DA with a fully loaded plane...after he was advised not to. Bad A.D.M.... and led to a non payment on the planes insurance policy... grounds of gross negligence were stated.

[Alkemac]

There is a reasonably good explanation here..

http://www.flightlearnings.com/2011/03/ ... -altitude/

More detail here..

http://www.experimentalaircraft.info/fl ... ance-3.php

[Tailspin]

I have this with me all the time.

[nicow]

You must work your density altitude out on a short runway-specially if it is a hot day.
Thanks for the info.Here is a link to a aviation calculator:
http://www.hochwarth.com/misc/AviationCalculator.html

[Chris Sibbald]

The importance of density altitude can never be over emphasised with regard to the aviator, as aircraft performance graphs are based on this. High Density Altitudes mean poor aircraft performance, which may lead to a hazardous situation if not understood fully.

Density altitude is that altitude when the pressure altitude has been compensated for TEMPERATURE. An aproximate correction of 118.8 (can round off to 120) feet may be added to the pressure altitude for every 1 degree celcius increase in temperature above the standard temperature for that altitude.

Example: Airfield Elevation 4000ft, temperature 28 degrees celcius, QNH 1030

Calculate the pressure altitude: 1030-1013 = 17 hPa x 30ft = 510ft. 4000 - 510ft = 3490ft (3500ft)

Calculate the temperaturedeviatio: 3500 x (-2) = -7 degrees celcius + 15 degrees celcius = 8 degrees. So at 3500ft the temperature according to ISA should be 8 degrees celcius. The actual temperature is 28 degrees which is 20 degrees warmer.

20 x 118.8 (120) = 2376ft + 3500ft therefore Density Altitude = 5876ft.

For each 1 degrees celcius increase above standard temperature, it can be seen that the aircraft will be operating at an altitude higher than the actual indicated altitude, which means decreased density and therefore decreased aircraft performance.

If the temp is lower than the standard temperature for that altitude, the correction must be subtracted.

Just for interest sake: ISA states that: * Temp is +15 degrees celcius
* Pressure is 1013.25 hectopascals (hPa)
*Density is 1225 gram/m3 (cubed)
* Lapse Rate is 1.98 degrees (2)/1000ft up to 36090ft and thereafter constant -56.5 degrees.
* Gravity is 9.8066 metres per second/second
* Air is dry and uniform throughout

Hope this helps

Fly Safe

[Dish]

Great first post Chris, thank you and welcome to the forum.