25 votes

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 compressor exit temperature), pressure (maximum compressor exit pressure) and stress (...
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  • 1,296
25 votes
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How does a fighter pilot calculate approach/landing speeds?

In the F-4, we had a base speed to use for each aircraft configuration, and we would add 2 knots for each 1000 pounds of fuel. If we still had any significant external stores hanging on the plane we ...
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24 votes
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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 ...
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  • 103k
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 ...
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  • 39.1k
22 votes
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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 ...
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  • 24.8k
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 ...
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  • 10.7k
16 votes

Is the takeoff power always maximum?

Is the takeoff power always maximum? No, unless it is required. Disadvantages for using full power on takeoff is higher fuel consumption, noise, and engine wear. Instead, takeoff performance is ...
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  • 120k
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 ...
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  • 25.1k
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 ...
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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, ...
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  • 241
13 votes
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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 ...
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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 ...
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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 ...
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12 votes
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Why does Vr increase with lower air density and decrease with higher air density?

Part of Part 25's definition of VR is: The speed (determined in accordance with § 25.111(c)(2)) that allows reaching V2 before reaching a height of 35 feet above the takeoff surface At lower air ...
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  • 120k
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{\...
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  • 1,406
11 votes
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What would be the ground roll and total distance to clear a 50ft obstacle given these conditions?

We round up for safety, so assume PRESS ALT=1000' and TEMP=30° Celsius, we would have a ground roll of 890' and a takeoff distance of 1645', right? Good thinking, but no. Refer to the Pilot's ...
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  • 22.2k
11 votes
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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 ...
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  • 2,953
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 ...
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9 votes
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How to calculate the Lift Coefficient for the A320?

I found a different number for $C_L$, please check your calculation: $C_L=\frac{2 m g}{\rho V^2 S}$ substitute: $ m = 50000 \textrm{ kg}\\ g = 9.81 \textrm{ m}/\textrm{s}^2\\ V = 462 \textrm{ KTAS}...
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  • 74.2k
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,...
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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 ...
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  • 5,157
9 votes
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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 ...
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  • 22.2k
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 ...
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  • 10.4k
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,...
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  • 15.6k
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? ...
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  • 16.1k
8 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}{...
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  • 6,103
8 votes

How does blade solidity ratio relate to thrust/power/torque of a propeller?

Each propeller blade is a wing in itself, and like a wing carries the weight of the plane, the propeller blade carries its fraction of the total thrust of the propeller. The more blades, the lower the ...
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8 votes

How to perform a "first principle" performance calculation?

The equations of motion are the easy part. In essence, you look at all forces affecting the aircraft (lift, thrust, drag, weight) and balance them with proper control settings (elevator, throttle) and ...
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8 votes
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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'...
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  • 41.6k
7 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) = \...
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