14 votes
Accepted

Why don't piston engines feather on shut down?

Hydraulically operated propellers feather the same way on both recip and turboprop airplanes, by dumping the oil supply that drives the blades in the fine pitch direction to the sump so that coarse ...
  • 114k
7 votes

Does an orbital trajectory reduce my required lift for high mach numbers?

We can calculate this by comparing the centrifugal force to the force of gravity: $$ F_\text{centrifugal} = m \omega^2 r $$ $$ F_\text{gravity} = G \frac{m M}{r^2} $$ The ratio is then given by $$ \...
  • 50.3k
5 votes
Accepted

Computing an Energy-Maneuverability (E-M) Diagram for an Aircraft

I call those diagrams turn rate diagrams, because that is plotted over airspeed. Never mind. Am doing this right? I think so, your result looks fine. Now let's start with the explanation how to ...
4 votes

Does parasitic drag increase exponentially with velocity?

You've messed up your units. $\rho$ has units of $\rm kg/m^3$, area has units of $\rm m^2$, and velocity has units of $\rm m/s$. Putting this all together: $$ \left[\rm Drag\right] = \rm\frac{kg}{m^3}\...
  • 375
3 votes

A review of $\eta$ efficiency factor for propellers

Efficiency ($η$) Cannot Exceed 1 Law of conservation of energy prohibits that. A glider routinely creates 20x lift force than its propulsive force: the vertical component of gravity, which is sine ...
3 votes

Is $\eta \frac{P}{V} $ using aircraft speed valid for thrust calculations?

The drag of the prop is consuming the engine power, not the planes forward speed! Power output of the engine seems to get confused with the kinetic energy state of the moving aircraft F×V or mV2/s. ...
  • 4,773
3 votes

Computing an Energy-Maneuverability (E-M) Diagram for an Aircraft

Generally, these diagrams are produced from extensive flight test and data collection. You cannot get sufficient accuracy from the simplified equations you are using. Computational Fluid Dynamics ...
2 votes

Computing an Energy-Maneuverability (E-M) Diagram for an Aircraft

I wrote a simple turn code in Matlab. Here is the EM / Doghouse plot at sea level. It looks like it agrees with your chart. The reason we don't see the Ps curves 'close' inside the CLmax line is ...
2 votes

Computing an Energy-Maneuverability (E-M) Diagram for an Aircraft

Here is a sample EM diagram for an F-16. Note that we do not expect all of the Ps lines to intersect the CLmax limit. It looks to me like you may have a problem with your induced drag term not being ...
2 votes

Is $\eta \frac{P}{V} $ using aircraft speed valid for thrust calculations?

By including the efficiency factor $\eta$, the author gave the expression $T=\eta\cdot\frac{P}{v}$ the needed flexibility to be correct for a propeller and piston engine driven airplane. Efficiency is ...
2 votes

Does a lift to drag ratio of 100 imply an unattainable performance ratio of 1?

Lift to Drag, (L/D), is just a ratio, so it is perfectly possible to be greater than 1.
2 votes
Accepted

Why are V speeds the last to be uploaded into a FMC?

Because the V speeds are critical to the takeoff performance for the configuration you are departing in, and the FMS won't let you enter them until all the other data is in place, like fuel weights, ...
  • 114k
2 votes

A review of $\eta$ efficiency factor for propellers

This question, which is remarkable, appears to largely relate to a misunderstanding of general theory. Consequently, we are caught on the horns of a dilemma: To what extent are we, as responsible ...
2 votes

Does a lift to drag ratio of 100 imply an unattainable performance ratio of 1?

When people say that $L/D$ is a measure of aerodynamic efficiency -- they are using the word efficiency very loosely. They are simply using it as a generic term for 'figure of merit'. When people say ...
2 votes

Does a lift to drag ratio of 100 imply an unattainable performance ratio of 1?

There's a bit of confusion here between a generic ratio and the ratio defining efficiency (or performance or figure of merit or whatever you want to the name it). The ratio between two quantities is.....
  • 4,773
1 vote

Does parasitic drag increase exponentially with velocity?

Aerodynamic forces can be expressed in dynamic pressure $q$ and a reference area of the aeroplane (usually the wing area $S$). In order to account for the shape of the plane, dimensionless ...
  • 60.5k
1 vote

Does parasitic drag increase exponentially with velocity?

Seeing as how both lift and drag vary as the square of the airspeed, it would surprise me enormously if parasitic drag, (except for small edge case effects), was any different. An exponential ...
1 vote

Does a lift to drag ratio of 100 imply an unattainable performance ratio of 1?

But of course! Perhaps my view of this issue regards coming to terms with understanding the propeller thrust issue, and its relationship to the lift to drag ratio. Somebody asked 'what is performance ...
1 vote

Does a lift to drag ratio of 100 imply an unattainable performance ratio of 1?

L/D is a ratio of forces, so it can be greater than 1. A reduction gear also produces more output force (torque) than input torque. It does so by trading rotation speed for torque. That's precisely ...
1 vote
Accepted

Does a lift to drag ratio of 100 imply an unattainable performance ratio of 1?

Terms can get kind of sloppy here. If you are truly talking about the ratio of Lift to Drag, it would be best expressed as a ratio of one number to another. If someone talks about a Lift to Drag ratio ...
  • 19.4k
1 vote

A review of $\eta$ efficiency factor for propellers

The power consumed by drag in a gliding aircraft is simply its weight times its best rate of descent in feet per second. So a well-designed glider glides on less than 20 horsepower. This means to turn ...
1 vote

Computing an Energy-Maneuverability (E-M) Diagram for an Aircraft

Here is a simple contour plot example done in Excel... It is a form of a 3D surface plot -- where your viewpoint is from directly above. The red column ends up being the X-data. The blue row ends up ...

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