# Tag Info

## Hot answers tagged performance-calculation

### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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 ...

### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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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) = \...