60

Special mention for Raúl Pateras Pescara de Castelluccio (good article) who was fond of lots and lots of rotor blades, settling on sixteen for most of his designs, although his Model 3 had twenty. Pescara's helicopters may look a little comical (and dangerous!) but they are an important part of early helicopter evolution, pioneers in the first fully ...


58

That is crazy. DON'T just rely on an person who's new to airplanes and only training is 5 minutes of showing them what to do, who may or may not react correctly when it springs to life, as the only thing preventing the plane from heading off somewhere while you try to dive clear. Don't. Do. It. Tie the tail. To something. Anything. Use the passenger and ...


54

1) Airspeed, 2) Forward motion, 3) Size constraints. Just to begin with. Household fan blades are extremely slow, so they need more chord to push a meaningful amount of air. Aircraft propellers approach the speed of sound at their tips, and low drag is critical. All things equal, more span and less chord is more efficient. Reducing the airspeed for props ...


43

It is a fitting for a Hucks Starter. Photos from Vintage Wings Canada


41

The most blades I've seen are 8 on the Mi-26. Source But the highest theoretical lifting efficiency is achieved with the fewest blades and experiments have been done with single blade rotors (with a counterweight - there were vibration problems that couldn't be resolved). So in practical terms, the most lift for the least power is achieved with a 2 blade ...


40

You are right. They are unequal length blades. Schempp refers to the propeller as being "noise optimized" and you can see that the blades are free to flap (forward) like helicopter blades (which flap up) so that the asymmetric thrust axis from having the propeller disc offset from the rotational axis doesn't place bending loads on the hub. And obviously, ...


38

A "run away prop" is caused by a failure of the pitch control mechanism of a constant speed propeller. Feathering turns the prop blade as close to 90 degrees to the wind as possible, minimizing the effects of the airstream. This obviously reduces drag and is used when an engine is shut down. A run away condition is created when the propeller malfunction ...


28

I would not follow the advice in the forum. While the reasoning that a windmilling prop does create more drag is sound, I have seen no empirical evidence that says how much it actually translates to in Feet Per Minute. The only studies I have seen have been inconclusive on the subject, and say there's a number of factors that you can't really control in that ...


22

Some household fans are shaped like airplane propellers, the ones that need to move a lot of air at the highest speed. For a given motor, they have the highest efficiency, but the tip effect makes them noisy. They are best suited for industrial applications. For inside the family home there are other considerations: Silence. Best if we don’t hear the fan ...


22

I’ll second John K’s answer. Do not attempt to hand prop an airplane without receiving professional instruction on how to do it safely. It is a real easy way to get seriously injured or killed, as this idiot almost found out. It should also involve two competently trained people, one to do the hand propping, and the ...


16

The answer: it depends. Generally, a stopped propeller will be stalled, and so creating little drag. A windmilling propeller, conversely, usually will not be stalled, will be extracting energy from the airstream, and using that to turn the engine (which typically takes a moderate amount of energy), which will increase sink rate. However, should you stop the ...


16

The driving variable here is airspeed, not pitch attitude per se. Your airplane naturally goes faster when you put the stick forward and decrease the wing's angle-of-attack, and this changes the prop rpm. Your pitch input is changing the wing's angle-of-attack which leads to an airspeed change. Even with the engine switched off, the aircraft would fly (...


15

Feathering isn't really an issue, if you can feather a prop on an engine further inboard you can do it on the tip too. There are 3 major drawbacks that come to mind: The wing structure has to be stronger: engines are heavy, the further out they are the beefier the structure has to be to hold them. Stronger wings mean more weight and possibly a thicker cross ...


13

The prop regulates engine rpm using a flyweight governor (functionally similar to the ones on steam engines) which drive propeller pitch coarse or fine as required to keep rpm constant, regardless of throttle setting. The governor either controls an electric signal (curtiss electric) or engine oil pressure (hydramatic propellers) to provide the driving force ...


12

That is the Douglas DC-6 / C-118/R6D Liftmaster. This specific plane was built in June 1947 with modifications for presidential use. It is well known for flying US President Truman. It was the first presidential aircraft that received a distinctive exterior. It actively served USAF until 1965 when it was transfered to an USAF museum. It is now on display ...


10

No. The RC model there is using counter-rotating rotors because the upper rotor with the stabilizer bar has a specific function that makes the model controllable in the first place. The Chinook already benefits from built-in anti-torque control so that would be a waste of time and oodles of money on the real one. Fun fact about the Chinook: it can climb ...


9

A windmilling propeller creates much more drag, by an order of magnitude at least. The obvious example is an autogyro or helicopter in autorotation, which drops like a stone if the rotor stopped. Drag is a function of blade area for a stopped rotor and a function of disc area for a windmilling one. The difference is most pronounced for large rotors with few ...


9

You are not wrong, it is more efficient to accelerate a large mass by a little than a small mass by a lot. This is due to momentum being linear with speed and mass, while energy is linear with mass but quadratic with speed, so the same momentum can be obtained more efficiently by slowly pushing a large amount of air, e.g. with a large propeller. The ...


8

The Chinook DOES have contra-rotating rotors, in a sense. The front and back rotors turn in opposite directions. (Actually, the correct term for this is "counter-rotating".) Read more on this elementary physics page about torques and angular momentum-- https://learn.parallax.com/tutorials/robot/elev-8/understanding-physics-multirotor-flight/rotation-...


8

I think it should be obvious that a fan blade is basically a wing travelling in a circle. So the question is what makes a wing a good wing? In theory and in practice (wind tunnel measurements or fuel consumption measurements of real planes) a long skinny wing is significantly more efficient than a short wide wing. The most efficient wing for a given airfoil ...


7

Because lift propellors need to provide static pressure to inflate the airbag and hover. This means more fan blades to stop backflow. The thrust propellors need to provide force which is a combination of static pressure and airflow but relies mostly on airflow. This means less fan blades to facilitate large airflow.


7

They are more like an aerobatic airplane that's flying upside down. The wing of the propeller blade keeps moving in the same direction but it just rotates so it operates at a negative angle of attack to make lift in the opposite direction from normal. The blade is in a socket in the hub that allows the blade to rotate on its long axis. The blade root has ...


6

It's because the critical case that autofeather caters to is engine failure right after V1, on takeoff, where the normal identify/feather drill uses up precious time. An engine failure on a missed approach or go-around starts well above the low energy state of an engine failure after V1 and there is much more time and energy margin to do the normal ...


6

the further apart the engines are, the worse becomes the yaw in an engine-out situation. but spacing them (and their fuel tanks) further apart along the span of a wing allows more even distribution of load stresses.


5

The difference between a ducted propeller and a turbofan is mainly determined by the difference between a propeller and a fan. A propeller has relatively few blades, which are relatively long and slender. A fan has many blades, with a relatively large chord. Like a household fan. A parameter to catch blade count and chord relative to blade length, is the ...


5

I believe it's an Ilyushin Il-18. Pic from here:


5

The drag is significantly more for a windmilling propeller. Both aerodynamic drag and energy lost in the engine contribute. I estimate you will sink at least 200 FPM faster if you let the prop windmill. For aerodynamic drag, it's impossible to convert this into a feet per minute estimate because it varies so much with the design of the propeller and the ...


5

A propeller has an optimum AoA, where the thrust/drag ratio is highest. A variable prop can maintain this optimum AoA at a wide range of speeds, thereby reducing fuel consumption. That's all it does. Fixed wing propellers have a dilemma that at take-off they require maximum thrust, and in high-speed flight the engine will need to be throttled back to ...


5

The key thing to think about is that the first stage doesn't just accelerate air downwards, it also causes it to rotate ("swirl") in the same direction as the first stage propeller. This happens because the first stage propeller, being an airfoil, generates both lift and drag. The lift corresponds to air being accelerated down the axis of the duct; the drag ...


5

Beta props are pretty rare on anything smaller than Twin Otter or King Air or Porter or Turbo Beaver. Can't speak for MT's system, but most beta mode systems use mechanisms to switch control of propeller blade angle from the propeller rpm governor to the throttle. Beta mode is the mode of throttle or power lever control of blade angle, with engine torque ...


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