Assumed temperature
 

If I enter the table with TOW and TORA I will find assumed temp is it correct?
http://s2.uploads.ru/d/rwBZh.jpg

err.........No!

It might be but that would be luck. You need to consider a couple of other things too.

Your idea is ok but you are looking at the wrong type of graph. You need a full runway analysis which includes climb and obstacles.

In the FPPM I have there are 'Takeoff climb limit' and 'Obstacle limit' graphs but they dont have any runway length entries. is it possible to determine an assumed temperature using only fppm and fcom tables?

Do you have a Training Dep’t?

Are you a flight simmer? If so, you can use your method for getting some kind of flex/assumed temperature. For real aeroplanes it is more complicated as obstacles need to be accounted for. Pilots aren't normally involved in this process, they typically have either paper charts or software in the cockpit that has been put together by performance analysis people.

You can almost do it all from information provided by the flight manual but you would need an obstacle chart for the airport so you can work out the climb gradients required.

Takeoff climb limit is independent of runway length. For any takeoff you must assure that you can meet the limitation, normally 2nd segment climb. Takeoff obstacle limits as noted above would require you to have the airport obstacle chart and then work backwards to see what weight would still allow you to miss the obstacles off a given runway.

thank you very much

one more question. what does 'environmental limit' represent and how to use it?

You can't takeoff from an airport when the actual temperature exceeds this limit, but your assumed temperature may be higher...

could you give an example? I didn't get how to proceed.

Say it's 50C. If your airfield is at 8,000ft then you aren't allowed to take off. Simply too hot for that altitude. But if your Airfield is at sea level then you are fine as the air is a bit more dense down there.

Environmental limit is based on ISA+35/39.4/40 depending on the manufacturer, so for a sea level airport the standard ISA temperature is 15C, add 35 degrees to that and you get a limit of 50C, thats the maximum OAT that you can takeoff off with. A Boeing/Airbus would give you a limit of 54C.

Assumed temperatures are a way of fooling the engine into thinking thats its hotter, therefore you will get temperatures up to 80C but the above OAT limit would still apply.

ISA temperature decreases at a rate of 2C (1.98 for the purists) per 1000 feet, so for an 8000 ft airport, ISA would be 15- (8x2)= -1. Adding +35 would give you a maximum OAT of 34 degrees for operating from that airport.

thanks gentlemen