# Tag Info

### Is my airspeed calculation code correct?

If you apply the law of cosines to the triangle formed by the vectors $\vec{A}$ (Airspeed), $\vec{W}$ (Wind) and $\vec{G_S}$ (Ground speed), where $\vec{G_S}=\vec{A}+\vec{W}$, you get: |\vec{A}|=\...
• 531
Accepted

### How to determine the maximum forward airspeed of a plane in an unaccelerated flight?

EDIT: I added a calculation at the end of the answer Thrust $T$ produced by a propeller is: $T=\eta \frac{P}{V}$ where $\eta$ is the propeller's efficiency, $P$ the power supplied to the propeller ...
• 4,299

### Does optimum IAS for climb vary with altitude?

Your equations aren't quite right. For example, you use IAS where CAS is intended. And drag power is V D, not V D / W. (Energy is force times distance and power is force times velocity.) Additionally, ...
• 31
Accepted

### Why does true airspeed decrease with altitude?

The power that can be produced by a normally aspirated piston engine reduces with altitude -- as you note, the air gets thinner. This is typically modeled as: $\frac{HP}{HP_0}=1.132 \sigma - 0.132$ ...
• 555
1 vote

### Speed change in IFR flight in class C or D airspace

Yes, as long as ATC did not assign you any speed restrictions and so long as you comply with any applicable chart-listed speed restrictions and with things like 14 CFR Section 91.117, obviously. See ...
• 11
1 vote

### How to determine the maximum forward airspeed of a plane in an unaccelerated flight?

Your "givens" include a table of Cl/Cd versus airspeed. Therefore it is simple to prepare a graph of Cd/Cl versus airspeed. From this, you can prepare a graph of (Weight * (Cd/Cl)) versus ...
• 19.3k

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