Skip to main content
56 votes

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 ...
xxavier's user avatar
  • 11.1k
55 votes

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 ...
Cort Ammon's user avatar
43 votes

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, ...
GdD's user avatar
  • 54k
34 votes

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 ...
jwenting's user avatar
  • 16.1k
33 votes

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 ...
tegginamaniss's user avatar
33 votes

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 ...
Pilothead's user avatar
  • 20.2k
27 votes
Accepted

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 ...
Peter Kämpf's user avatar
25 votes
Accepted

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 ...
aeroalias's user avatar
  • 100k
20 votes
Accepted

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 ...
Jan Hudec's user avatar
  • 56.3k
20 votes
Accepted

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 ...
Jan Hudec's user avatar
  • 56.3k
17 votes

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 ...
DeltaLima's user avatar
  • 83.5k
16 votes

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 ...
aeroalias's user avatar
  • 100k
16 votes

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 ...
aeroalias's user avatar
  • 100k
16 votes

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 ...
Mike Sowsun's user avatar
  • 37.8k
15 votes
Accepted

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: ...
Peter Kämpf's user avatar
14 votes
Accepted

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 ...
Peter Kämpf's user avatar
14 votes
Accepted

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 ...
J W's user avatar
  • 16.6k
14 votes

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 ...
Zeiss Ikon's user avatar
  • 17.1k
13 votes
Accepted

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-...
mins's user avatar
  • 74.3k
13 votes
Accepted

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 ...
Peter Kämpf's user avatar
13 votes
Accepted

What is profile drag?

The composition of total Drag as it is shown below: Thanks to DRAGBUSTERS... This document can solve this question, and analyses the drag in detail. Profile Drag Definition: Profile Drag is the ...
Lidakis Manolis's user avatar
13 votes
Accepted

What is compressibility drag?

Let's do a Gedankenexperiment: Think of air streaming around a body as flowing inside a stack of flexible tubes. The walls of the tubes are impenetrable, infinitesimally thin and follow the local ...
Peter Kämpf's user avatar
13 votes

Why don't smaller powered airplanes have better lift-to-drag ratios?

There are plenty of smaller power planes that achieve those numbers; motorgliders. And motorgliders with L/Ds in the high teens and low 20s are pretty efficient cruisers. So the real question is; ...
John K's user avatar
  • 132k
13 votes

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 ...
FreeMan's user avatar
  • 16.3k
13 votes

Is it possible for a plane to accelerate easily from 30 to 45 mph in flight while it struggles to reach 30 mph (the engine runs at constant power)?

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} \...
MaximEck's user avatar
  • 1,867
13 votes

Can induced drag be negative?

Can induced drag be negative? Not for the full configuration, but for parts of it. Induced drag is part of the reaction force when a stream of air is deflected. This reaction force is split into one ...
Peter Kämpf's user avatar
13 votes

Do symmetrical airfoils generate induced drag?

If an airfoil is producing lift, then it will be producing induced drag. Both cambered and symmetrical airfoils have an angle of attack at which they produce no lift, no induced drag, and no pressure ...
Neil_UK's user avatar
  • 435
12 votes

Why use an airplane with non-retractable landing gear for aerobatics?

In the case of the Red Bull Air Race, the engine and propeller are specified by the race officials, and must remain unmodified, so the airframes are designed to get the most out of that combination. ...
tj1000's user avatar
  • 8,787
12 votes
Accepted

How is drag created from wingtip vortices?

Wingtip vortices don't create drag, just as wet streets don't cause rain. Lift creation and viscosity create drag. Drag is composed of pressure drag and viscous drag, and induced drag is one part of ...
Peter Kämpf's user avatar
12 votes
Accepted

Is aspect ratio efficiency related to the momentum added to the air?

You're almost there. The difference lies in the kinetic energy required to move a certain mass of air, not in the air's viscosity. Copying freely from one of my earlier answers: The force to keep ...
Sanchises's user avatar
  • 13.4k

Only top scored, non community-wiki answers of a minimum length are eligible