26

Your question already contains the answer. As you say kinetic energy is proportional to velocity squared, so it is easier to accelerate air from 0 to 100 m/s than from 100 to 200 m/s. The same is true for the air flowing through the propeller disk. Even if we replace the propeller by a black box, or better a black disk, which simply adds a bit of pressure ...


9

The furthest glide is by definition the lowest glide angle! So if that is one of your design inputs, you should definitely go for that. But seriously, reducing weight and form drag gets you the furthest. 1. General glide distance theory With glide angle $\bar\gamma$ = -$\gamma$: $\quad C_D \cdot \frac{1}{2} \rho V^2 \cdot S = W \cdot \text{sin }\bar\gamma \...


8

Short answer: that fuel saving figure does not depend on the stator stage.[1] The aft stator function is swirl recovery, assuming its weight penalty can be offset. GE's design GE's (part of CFM) patent for that engine was filed in 2020: Unducted thrust producing system architecture US20200308979A1. From the patent, the second set of blades are optional, and ...


8

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's, 777's, and the A-380 flying on routes that have enough traffic to support them. When you have 300 passengers, it's more efficient to put them into one ...


8

The lift equation: Lift = wing area x Coefficient of Lift x air density x V$^2$ provides three variables to lift a given amount of weight: Angle of Attack, air density, and velocity. Aircraft have the least amount of drag per unit lift at a specific AoA, so best to keep it there. Speeding up a little is a very good idea but there are 2 factors with the ...


7

In a way, yes. By using smooth metal surfaces with countersunk rivets, modern aircraft use a surface with low friction already. In the past, wooden structures were varnished to give them a smoother surface. In the second World War, German crews would polish the normally matte paint of some of their airplanes to eke out the maximum in top speed. There have ...


7

You may be overthinking it. The governor will set the blade angle that provides the load on the engine that keeps it from speeding up or slowing down from the setting determined by the spring preload that resists the flyweights. You could connect the governor to a big disc brake in place of the prop and it would work the same. So it sets the blade AOA that ...


7

Well, well, well. Time to go to ... the well. "Balsa toss gliders" can be a lot of things, but they are a great place to start. If they are thrown for distance design criteria will be different from flown from a height such as from a hill or tall building. Reynolds number is a very important consideration for slow glider models. No, they are not ...


6

Your expectation is correct. A tilt-wing has a lower drag penalty in hover (but that's not the full picture). The XV-15 had a penalty of 635–680 kg, while a tilt-wing would have 23 kg, for the reason you mention. The sentence on Wikipedia unfortunately lacks the context of the reference (Flight), which is down for maintenance, but the web archive version is ...


6

Are there any designs where all horizontal surfaces support the craft in the air? Absolutely. Canards, as per the designs of Burt Rutan, for one. Not to mention the Wright brothers! Also, many "free-flight" model airplanes (which operate with no pilot guidance of any kind) have been designed with lifting tails (horizontal stabilizers), with tail ...


5

I think the main reason is that many of these planes were produced before winglets were common Look at a list of USAF planes and see what years each one were produced (I am not including every plane, but most of the common ones) C-5: 1968–1973, 1985–1989 C-17: 1991-2015 (has winglets) C-130: 1954-present E-3: 1977-1992 KC-10: 1979–1987 KC-46A: 2013-present (...


4

All the discussions of engineering difficulties and cost-effectiveness are valid arguments but based on my USAF career in program offices and in operating commands, including 4 years in TAC, it boils down to money and priorities. Once the a/c is operational the program office is concerned with sustainment. They need to provide the engineering, tools, and ...


4

The reason that efficiency is reduced during phases of flight that are flown at high airspeeds is because the angle of attack between the propeller and relative wind is reduced. If an aircraft is stationary on the ground, its propeller is taking a larger "bite" of air because there is no relative wind. When there is more air moving past the prop, ...


4

Okay guys, so I found some data from an old service publication from Lockheed. It says that the new C-130J propulsion system under standard conditions and flying 80 kts is rated "4,637 SHP, but produces 10,200 lbs". So using the equation for thrust available for a propeller aircraft I get: $T_a = \frac{\eta \cdot P_s }{V}$ with: $T_a = $Thrust ...


4

You should avoid dated units, such as the gram-force. Now, the area under your graph is in $MLT^{-1}$ units, force x time. These correspond to the variation of momentum $∆MV$ imparted to the air by the prop. Perhaps you could use that area as a reference, when testing other props...


4

The bypass lowers the exhaust velocity of the engine. Which improves the efficiency, but limits the flight speed. In jets (both turbojets and turbofans) the exhaust velocity does not grow with the inlet velocity. That means that with increasing flight speed the delta-V decreases, which increases propulsive efficiency, but the engine obviously can't produce ...


3

I always thought of energy analysis as kind of cheating ;) I know that power input needs to balance kinetic energy increase, but it works like a black box and does not give me true understanding why it is the case. Inspired by Peter's answer I will try to analyze the situation by modelling the propeller as a disk. But not a black disk, but a moving piston ...


3

Train wins, every single time. Zero induced drag. Thanks to the magic of Timken roller bearings (in truth, plain bearings worked even better when rolling fast enough for the hydrodynamic layer to establish itself: roller bearings are only better at starting), the train's rolling resistance is effectively zero when comparing to any other mode of ...


3

Yes, there are designs using forward canards, for example the Rutan VariEze, Long-EZ and Beechcraft Starship are excellent examples. There is also the Eurofighter Typhoon. But perhaps the best example is the first powered airplane, the Wright Flyer, which used a forward canard.


2

The question does not really make sense: a helicopter is a kind of aircraft, a drone is a mode of how a vehicle is controlled. I can rip the seats and controls out of a helicopter and put some clever software, some cameras, and some transmitters inside, and boom: I have a drone that can carry exactly as much as it could before – probably even more because ...


2

Yes, it will just maintain RPM, and you have to know what RPM is appropriate for your speed and power setting—and what you want to do. Max RPM gives you most power, minimal RPM gives you least drag on idle. The maximum efficiency RPM is somewhere between, increases with power required—more power means the AoA increases and too high is not efficient—and ...


2

Based on my reading, the biggest disadvantage of hydrogen as an engine fuel is its low density. Even when stored as a cryogenic liquid, it take up more than ten times the space as the same mass of kerosene, which means the same size tanks will hold only about a third as much energy (even though hydrogen has about three times the energy content per kilogram ...


2

There are 2 major problems. First is the weight you'd incur from: Extra rotors/propellers Transmission components (the V22 already has a transmission in case of an engine failure, it's already more complex than you'd ideally want but it's necessary for safety) Structural components to support the forces from the propellers and extra transmission It's ...


2

There are savings beyond just fuel when using a electric taxi motor on a commercial aircraft. Your title seems to ask about this but the text asks only about fuel. WheelTug, a developer of an electric taxi system, answers both in a pretty thorough presentation. Direct cost savings per flight is about 210 dollars, most of which is avoidance of pushback tug ...


2

No, especially not for the conditions you stated. Even if we consider that "same exact ariplane" will not melt away at Mach 2 or 5, different phenomena start to appear at such speeds. Let's restrict speeds to below about Mach 0.5 for now. At such speeds, compressibility of air does not affect characteristics significantly, and things become easier. ...


2

Dutch Roll is a 2-dimenional dynamic stability issue in aeroplanes. A little trolley towed by a car can be used to illustrate what happens, but the small amount of roll is purely an effect of directional instability, it is a one-dimensional issue. The pic above shows a damped dutch roll. The graph shows the two coupled variables, roll rate and yaw rate, ...


2

In order to compare efficiency, you would need some way of measuring the torque exerted by the rubber band, and compare (thrust generated/torque required). You could construct a second arm&scale mechanism at 90º of the existing one that is loaded by the wound up rubber band. Momentum theory has a glossary efficiency term, the Figure of Merit. Basically, ...


2

For airplanes and cars, one approach might be to break it down to wattage per seat mile for each conveyance. Cars only need about 20-30 HP to cruise on the highway; say 22 kW. An airplane needs about 120 kW (roughly 160 HP) to have decent performance for takeoff and climb with 4 adults and a bit of luggage, and might cruise using between 50 and 75% of that. ...


1

In addition to the good answer given by @JanHudec I can add a few things. To have the same thrust with a high bypass, the engine has to be a larger diameter, which has a bunch of downsides. This tends toward more weight, longer fan-blades, more gyroscopic forces etc. It can often lead to longer landing gear except on the 737, where instead the bottom of ...


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