# Tag Info

### How is it possible for supersonic aircraft to push air out of the way?

The idea that force can only be transferred/propagated at the speed of sound is a simplification. It's a very reasonable simplification, which works in a very wide array of cases, but it's a ...
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### Is lift in fact a kind of drag?

An 'aerodynamic force' (just one force...) appears when a body is immersed in a fluid stream. By convention, two components are chosen, one of them parallel to the stream direction, called 'drag', and ...
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### Why are heavy flaps better than just a bigger wing?

When flaps are retracted they do nothing, which is the whole point. The byproduct of lift is drag, a larger wing will create more lift, but more drag as well. More drag equals a slower cruising speed, ...
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### Could the Shuttle Carrier Aircraft do a transatlantic flight with a Space Shuttle orbiter on its back?

Short Answer A procedure had been established to return from a Transoceanic Abort Landing (TAL) site to the Kennedy Space Center (KSC) using the Shuttle Carrier Aircraft (SCA). The maximum weight that ...
• 67.7k
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### Is there any equation to bind velocity, thrust and power?

A propeller accelerates the air of density $\rho$ which is flowing through the propeller disc of diameter $d_P$. This can be idealized as a stream tube going through the propeller disc: The air speed ...
• 218k

### Why, until recently, were smooth nose sections not popular?

Because it's bloody difficult to make the curved shapes out of the materials used until recently, with the technology available at the time. The few aircraft that had it in the past generally were ...
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### Why use an airplane with non-retractable landing gear for aerobatics?

As you mentioned, drag is one of the reasons why retractable landing gears are used in the first place. But in order to use it, there are way more considerations than just drag. Scale: Size of the ...

### How is it possible for supersonic aircraft to push air out of the way?

It is only the pressure wave that can propagate at the speed of sound. This means that a molecule of "air" that is ahead of a subsonic aircraft can get pushed out of the way without hitting that ...
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### Could the Shuttle Carrier Aircraft do a transatlantic flight with a Space Shuttle orbiter on its back?

Yes, it was possible and NASA had a plan. Enterprise was taken on a European tour in 1983, visiting the UK, France, Germany and Italy. To get there, it crossed the Atlantic on the back of the Shuttle ...
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### Why are heavy flaps better than just a bigger wing?

Your concerns about heavy flaps are well founded. The designers try to get away with as few high-lift devices as they can afford to. But not fewer! If you observe the trend over the years, flaps ...
• 218k
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### Why, until recently, were smooth nose sections not popular?

First, the Commando wasn't unique in having a 'stepless' cockpit design- the Boeing 307 Stratoliner, for example had them. Other military aircraft too had them, due to a few reasons like ...
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### Is there a maximum lift to drag ratio?

With current technology the L/D might go up to 70 or 75, and going higher would require an almost impractically large wing span. Gliders need to fly in tight circles to use updrafts, and the larger ...
• 218k

### Why would maximum fly-time (endurance) not coincide with max L/D operating point?

Maximum dwell time or maximum endurance occurs when the power required is minimum. Hence, in this case, the maximum endurance speed is one where the power required is minimum, while in case of maximum ...
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### Is induced drag essentially nothing more than a specific type of form drag?

No, by definition it isn't. There is drag. Drag is caused by different physical phenomena. According to the cause, it is classified to: Induced drag Induced drag is side-effect of generating lift ...
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### Does the downwash created by induced drag increase or decrease lift?

It is not "this causes that" - all is happening together. Let me explain: For me to understand aerodynamics, it helped to disregard all that talk of vortices and induction, but focus on the pressure ...
• 218k
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### Why does NASA say $v^2$ is velocity squared rather than speed squared?

The proper technical term for the quantity is velocity, and it is a vector quantity. Speed is a colloquial name. If physicists use it, they only use it for the magnitude of velocity, but most of the ...
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### At what rpm does the tip of a 54" propeller start to incur mach losses?

A 54 inch propeller would start to incur efficiency loss at approximately 4300 rpm. At 4300 rpm a 54 inch propeller would have a tip speed of 691 mph which, relative to the 767 mph speed of sound, is ...
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### Why does adverse yaw exist?

Indeed, when an aileron moves upward, it locally generates less lift and less drag. Assume we are talking about the aileron on the right wing. The reduced lift drops that wing, rolling the aircraft ...
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### Why use an airplane with non-retractable landing gear for aerobatics?

Strictly speaking, a 'pure' aerobatic aircraft doesn't need a retractable landing gear. For such an aircraft maneuverability is much more important than speed. In fact, the aircraft can't fly too ...
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### Why are heavy flaps better than just a bigger wing?

Climb to cruise burns fuel. Adding additional drag burns fuel. Adding retractable mechanisms adds weight that burns fuel. More drag, even at higher cruise altitudes, requires larger engines for the ...
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### Why are the in-flight refueling probes of French-built fighter aircraft non-retractable?

According to Dassault, this configuration was chosen in order to reduce complexity and therefore avoid deployment/retraction problems: Failure-prone systems have been eliminated early on in the ...
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### Has there ever been a tail-dragger with retractable tail-gear?

Yes, there are. The Boeing B-17 FLying Fortress is one example of an aircraft designed with a retractable tailwheel. Source: USAAF via Wikimedia, Public Domain (USGOV-PD) Another example would be ...
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### How do Hoerner Wingtips work?

How exactly does acceleration of air occur just by having a convex underside Just like the curved forward surface of a wing does it. Imagine for a moment that the air flows along a straight path: ...
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### Why do some commercial aircraft have no landing gear cover?

Yes, it does increase drag. Anything that is not smooth, where the air flow will be disturbed, will generate drag. The 737 was originally designed only for short haul and space is at a premium. ...
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### Which books should I study to understand more about Supercritical airfoils?

Introduction to Transonic Aerodynamics Roelof Vos, Saeed Farokhi (more) Written to teach students the nature of transonic flow and its mathematical foundation, this book offers a much-...
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### Why is induced drag less on a high span wing?

You start from wrong assumptions, which explains your doubts. The line the induced drag is due to the tip vortices is as true as saying that wet streets cause rain. Also, the opinion that the ...
• 218k
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### Why does the elliptical wing have the lowest drag?

Induced drag is caused by the backward inclination of the lift vector. Lift is defined as the aerodynamic force perpendicular to the flow direction, and since lift is created by deflecting this flow ...
• 218k

### Why, until recently, were smooth nose sections not popular?

Blow-molded canopies (like the acrylic one on the P-51D) were relatively expensive in the late WWII and early post-War periods when the early-modern airliners were designed. Cost is an important ...
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Yes and in this case this is due to induced drag. This drag can be derived with the lift and drag equations of a wing : $$\textit{Lift} = \frac{1}{2} \rho C_L S V^2$$ \textit{Drag} = \frac{1}{2} \...