as promised, here we go with another “How to” article.
These articles are intended to help Beginners to make IF a better experience for them and to give other SIM pilots a nice atmosphere and realistic traffic while being in LIVE mode.
In real, this is quite complex stuff! – Not everything will be explained in full detail or to the level of the real world complexity.
I just want to give you an “idea” and help you to be able to fly in IF and let it look real.
This time I would like to discuss “reduced thrust take off’s”, so the heavy ones really look heavy;-))
So, …for all the true Professionals in this forum, …you do not need to continue reading and please forgive me for simplifying the whole story very very much;-)
To begin with:
Every evening, when I sit in my office at the airport, around 6 PM and in case of westerly winds, I do see a Boeing 777-200F by FedEx taking off from runway 26R. This flight is a daily scheduled short ferry (empty) flight to a EDDF, just 45 minutes away.
It is unbelievable, the 777 climbs like a rocket, very silent though, around twenty degrees nose up with a climb performance of over 4.000ft/min (acc. flightradar). The plane starts to level off even before the runway threshold, just not to burst the assigned initial altitude.
Important to notice: the pilots are taking off with, what is called “reduced” or “flex” thrust. They do not use the full potential of their huge engines and still have this enormous performance. They also use the regular flap setting for take off (Flaps 5 on a -200 in most cases).
So, why do I tell you this?
In IF I see a lot of guys taking off and climb even more steep and a lot faster than the empty FedEx 777 I observed.
Well, …unless these planes are also completely empty (no passengers, no cargo) and also have almost no fuel on board, or have a headwind component of 20+ knots, or use Flaps 20, …I have to assume the pilot just push the throttle to the upper end of the range. Folks, …this is highly unrealistic!
Why do you take off with reduced thrust?
In the real world, there are a lot of reasons, why aircraft take off with reduced thrust:
- reduce the stress on the engines and thus extend their life time
- noise reduction
- fuel consumption
- passenger comfort
- efficient use of the runway (see explanation below)
So, short and simple, you just apply as much thrust as neccessary to get the aircraft up in the air under the given rules, regulations and performance data.
How do you calculate the right amount of thrust for Take Off?
Well, first of all, in IF we cannot do it like the real pilots, because we do not have all the data nor the performance charts.
In general, the calculation is a combination of taking into account environmental factors (e.g. weather), aircraft related factors (e.g. weight) and the runway (length, condition). Just to give you an idea what I am talking about. in the real world you need parameters like:
- Runway length, or more precise -but not a bit complete-:
- Take Off Run Available (TORA) length of the runway available for the take off run (without a clearway)
+Take Off Distance Required (TODR) length of the runway you need to take off under given parameters
- Acceleration Stop Distance Available (ASDA)
- Acceleration Stop Distance Required (ASDR) Neccessary remaining runway to stop an aircraft from V1, eg. because of an engine failure)
Runway altitude (air becomes thinner the higher you are;-)
- Temperature (also influences the thrust potential of an engine)
- Barometric Pressure
- Take off weight (the heavier, the more thrust and runway is needed)
- Wind & Direction (40kts on the nose?-great, 25 kts from the side?-bad)
- Runway condition (brake coefficient), Dry, Damp, Wet, Contaminated influences V1 also
- 35ft above ground clearance over the threshold and V2
All these parameters will be used to determine the Take off speeds (V1, VR, V2) and the subsequent thrust you have to use (see image below).
V1 is computed with, lets say 145kts.
On a 2,5km runway you need to make this speed gate much faster in order to have sufficient ASDR (length required to stop the aircraft from V1) than on a 4,5km runway. Thus, you would have to apply more thrust. If some parameters limit you too much (which happens), e.g. a rwy is not very long and you are to heavy for the given conditions, the aircraft may become weight restricted for a take off (less passengers and cargo).
Now it also becomes clear, why it does not make any sense, to take off on a long runway with full thrust: You have all the negative impacts and you gain nothing.
How do you measure Thrust?
Below you see an image of a modern jet engine.
The first fan stage is called N1 and most engines indicate the amount of thrust as a percentage of N1, e.g. 89%.
Some engines however, use EPR, the engine pressure ratio. E.g., the IAE V2500 engine on some A321 uses EPR as the parameter to indicate the amount of thrust applied.
In IF it looks like this:
Please notice the small green N1 indication on the left side above the thrust lever. In my opinion, that is the right thrust indication, showing 90%, while the thrust lever is at 70%! - I always use the N1 indication.
By the way, in the real world, a pilot reduces the thrust by pretending the FMS, that it is very hot (max 65 degrees C). The computer will subsequently reduce thrust to the maximum possible under these conditions.
So?-How do I pretend in IF, I take off with reduced thrust?
Well, first of all, as we do not have a FMS in IF, we have to reduce thrust manually.
Different aircraft have different characteristics, also in IF.
So, if I try out a new aircraft, I set myself on rwy 12 in KOAK and figure it out by pure testing. These are the conditions and ranges I use
- No wind
- Flaps (5 or 10)
- Trim 10 (light) – 15(heavy) degrees up
- Try to be airborne after two third of the rwy
- VR between 14xkts (light) and 16xkts (heavy)
- After the rotation, try to maintain a pitch of about 14 degrees and observe the speed: it should not continue to rise (if it does, you applied to much thrust)
And then I set the weight in the menu in three different situations: light, normal, heavy and take off several times. Thats the way of figuring out the VR speeds for different weight situations. By the way, as we do not have engine failures yet, V1 is of no immediate importance.
The N1 thrust setting ranges bewteen 80% (light) and 94% (heavy).
Try yourself, you will soon figure out what Thrust/Speed/Flaps/Trim/Weight setting gives you the result, that lets a heavy bird look heavy:
- You lift off no earlier than after 2/3 of the runway
- Your initial climb speed stays around the 16x-17xkts until you reach acceleration altitude (e.g. 1500ft AGL) in order to speed up (drop the nose then)
- You cannot raise the nose over the range of 10-20 degrees without rapidly loosing speed
Thank you very much for following me this far;-)
Finally I have another picture, that I took today. A heavy A340-600 on a 12h flight lifting off. As you can see, it s not climbing steep.
I appreciate any comments or suggestions
If you are searching information regarding strobe lights, descent calculation, or about the correct attitude for landing, you maybe find something useful in my other posts