27
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Why does the takeoff N1 limit start to decrease below 30°C OAT?
There are basically 3 limits that the engine faces, temperature (maximum turbine entry temperature or maximum combustor exit temperature or sometimes maximum first stage HPT stator exit temperature), ...
- 1,564
27
votes
Accepted
How does a fighter pilot calculate approach/landing speeds?
In the F-4, we had a base speed to use for each aircraft landing configuration, to which we would add 2 knots for each 1000 pounds of fuel. If we still had any significant external stores hanging on ...
- 5,546
24
votes
Accepted
Why do we still interpolate in performance tables?
I was in the technical publishing business (flight and maintenance manuals) in another life. Tables are used as an alternative to graphical plot presentations in flight manuals, and make it a little ...
- 125k
22
votes
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Is the takeoff power always maximum?
Takeoff power is almost never maximum engine power.
Maximum power affects engine life as it brings significant wear to the engine. IIRC, if max power is used on takeoff, the crew must log an entry in ...
- 39.6k
22
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Why does V1 increase with headwind and decrease with tailwind?
V1 is the maximum airspeed you can accelerate to and then stop again without running out of runway. For the sake of simplicity, let’s assume that happens at the midpoint of the runway.
If there is a ...
- 27.6k
18
votes
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Why is "clearway minus stopway" used in V1 adjustments?
What is the difference between clearway and stopway?
The definitions linked in the question for a clearway and stopway are fairly adequate.
AC 150/5300-13A Airport Design
Clearway - is an area ...
- 12.2k
16
votes
Why do helicopter performance charts for hover out of ground effect (HOGE) have a "knee"?
The knee is a result of having the engine "flat rated", that is rated to a power limit that is below its potential wide open throttle horsepower at sea level, a very common practice with ...
- 125k
15
votes
Why do we calculate 25% more of TODR?
This is called a "safety factor", and I was actually taught to use 1.33!
When you look at the POH or AFM the numbers and charts they present for performance figures were invariably ...
- 31.1k
14
votes
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Why aren't large, low-speed propellers widely used?
You are not wrong, it is more efficient to accelerate a large mass by a little than a small mass by a lot.
This is due to momentum being linear with speed and mass, while energy is linear with mass ...
- 8,531
14
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Why does the takeoff N1 limit start to decrease below 30°C OAT?
What you see is called a flat rated engine. It means the maximum thrust from the engine is constant below the flat rated temperature (usually 30°C). Above that temperature, thrust will decrease due to ...
- 53.6k
14
votes
Why does V1 increase with headwind and decrease with tailwind?
Some additions to StephenS answer, here is a more detailed picture:
VR is the speed at which you should take off your aircraft, as defined by the aircraft weight, ...
- 241
13
votes
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How is Fuel needed to be consumed calculated when MTOM and Actual Mass is known
Your thinking is correct, the fuel needed to be consumed is indeed the actual ramp mass - MTOM. That results in 3 kg of fuel.
What you forgot is to convert the weight into a volume (note that the ...
- 53.6k
12
votes
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How to calculate the DC-4 landing distance with this graph?
Follow the arrows in the graph.
You start with the gross weight on the right X-axis and move straight upward until you intersect the correct field elevation. In the graph the line starts at 58,000 ...
- 228k
12
votes
Why do we still interpolate in performance tables?
For most of the information in those charts there is not a single formula which would cover all aspects. The graphical way is the simplest and has other advantages, too:
With a formula it is easy to ...
- 228k
11
votes
How do you convert true airspeed to indicated airspeed?
Short Answer
Getting to grips with Aircraft Performance and Calibrated Airspeed are two good places to start!
The short answer:
From TAS to IAS $IAS=f(TAS)$:
$$IAS = a_0 \sqrt{5\left[\left(\frac{\...
- 1,406
11
votes
Accepted
Can the energy dissipated in a power-off descent be calculated and expressed in horsepower?
Horsepower = weight(lbs) * sink_rate(fpm)/(550*60)
It really is that simple.
Background
At a constant airspeed glide, kinetic energy isn't changing, only potential energy. So we know that all the ...
- 4,722
10
votes
Accepted
Why is my calculated seat-miles per gallon of small aircraft higher than of big aircraft?
All else being equal, your intuition is correct that a larger aircraft will be more efficient (in a gallons per seat-mile measure) than a smaller aircraft. That's why there are big aircraft like 747'...
- 48.5k
10
votes
Why do we still interpolate in performance tables?
The equations, if they exist, are often rather non-linear and not enjoyable to calculate on the fly.
I do not have an equation for the RPM at a given pressure altitude for a Cessna 162, but if I may ...
- 951
9
votes
What are the takeoff and landing speeds of a Learjet 45?
The takeoff and landing speeds of aircraft can usually be found in the performance section of the aircraft light manual. They are not fixed and vary over a wide range depending on various factors like,...
- 99.9k
9
votes
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What is the maths behind the descent rate calculation?
From Gypaets' answer
$$DescentRate = 0.0524 \cdot GroundSpeed$$
But the Ground speed is in nautical miles per hour [NM/h], and the descent rate is in ft/min.
So we have
$$DescentRate \left[\frac{ft}{...
- 6,567
9
votes
What is the maths behind the descent rate calculation?
Just take a look at the geometry, the ground speed and descent rate vectors are perpendicular to each other.
If $\gamma$ is the descent angle, the formula you are interested in is:
$$tan(\gamma) = \...
- 4,282
9
votes
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Calculating Ground Speed - E6B vs Pythagorean Theorem
Course and heading are not the same. Course is the direction of your path over the ground. Heading is the direction you are pointed (and the direction you would travel through a still airmass).
In ...
- 5,551
9
votes
Accepted
Should a runway overrun be expected if takeoff is begun with one-engine-out?
You will not achieve book performance if you don't fly with book configuration.
See the portion of DeltaLima's answer here, including emphasis added by me:
[Takeoff Distance Required] has the ...
- 23k
9
votes
Can the energy dissipated in a power-off descent be calculated and expressed in horsepower?
That power is sink rate x glider weight. If you use m/s for sink rate and newton for weight, you'll get the power in watt. Advantages of SI...
It's easy to understand why it is so. Within a uniform ...
- 10.8k
9
votes
Do pilots of piston/prop aircraft have discretion to determine how much runway is required for an intersection departure?
For the first part of your question, yes. It is always the pilot's discretion to either request, or to refuse/accept an intersection departure if offered by the tower.
To the second part, yes as well,...
- 24.1k
9
votes
Accepted
Help me understand the A220-100 takeoff chart
I believe that you are correctly reading the chart, however, I think you are reading the wrong chart. The chart in your question appears to be the chart for ISA +15C and for the lower performing ...
- 32.4k
8
votes
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Is trigonometry used by commercial pilots?
Note that this answer was given to the original question, Do pilots need to use trigonometry as part of their routine job? If so, when is it most used and for what? ...
- 16.5k
8
votes
Accepted
How can the wind speed and direction be calculated from on-board measurements?
With the set of parameters available to you, you cannot do this.
If you have the actual track instead of the desired track, you will be able to calculate the wind.
The simplest way to do this is ...
- 81.9k
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