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70

Because they are very lightweight and fragile. Therefore, thrust and propulsion mass must be distributed over span - a single, large propeller and motor would put too much force into the structure locally. Also, it would require a higher landing gear to give the larger propeller the required clearance. You are right about the higher losses. However, these ...


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 ...


57

Light Propeller Aircraft, if flown within their design limits, are just as safe as jets. If you do a proper and thorough daily inspection, you are far less likely to suffer any form of mechanical failure in the air. In saying this, the majority of all crashes, be it in a Jet Powered Airliner or a Propeller Driven Light Aircraft are caused due to pilot error. ...


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 ...


47

There are many disadvantages, they seem to outweigh the advantages. Here are two: A pusher prop is working in a disturbed airflow, causing increased vibration and noise If the propeller is fitted behind a wing, each propeller blade is passing through the separated boundary flow twice each rotation. These cycles create additional noise and lower the ...


45

In the hands of an inexperienced pilot, a jet is definitely the unsafer choice. Due to the general higher speeds, there is less time to recover from errors and they require more anticipation to be ahead of the game. Small errors will grow into large errors in relatively short time. In slower aircraft there is more time to correct. In addition, jet and ...


44

Planes with a variable pitch propeller can have a pitch range which twists the blades such that they provide reverse thrust. This started to become a common feature on high-performance airplanes in the 1930s. Not all variable-pitch propellers can produce reverse thrust, however. The constant speed props on small propeller aircraft usually don't, because the ...


44

I think you might have heard about the Ram Air Turbine, which is deployed in case of some aircraft in case of loss of main electrical power supply. From A320 Systems briefing: In case of total loss of all main generators, the RAT is automatically extended and drives the emergency generator via a hydraulic motor. The location of the ram air turbine ...


43

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


41

Fly? No. Wings generally only produce enough lift to keep an aircraft aloft when air is flowing over them in their intended direction. If you reverse the airflow over the wing (by moving backwards in the air, for example) the wing would no longer be producing the necessary lift, and the aircraft would "descend at an extremely rapid rate" until a normal ...


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

Jet engines are only efficient at high altitudes and high speed (25,000+ feet or so and 300+ knots or so true airspeed). The cost of making and operating an airplane capable of flying there is very high, and most general aviation flights have no need of such performance (or expense) hence, propeller airplanes. Reciprocating engine propeller airplanes are ...


40

Yes they can. That image from wikipedia showing B-17s is more descriptive Contrails originate from condensation of vapor coming from internal combustion engines, regardless of being turboprop, turbojet/turbofan or cylinder engine. Vapor is a byproduct of the hydrocarbon (fuel) being combusted with the atmospheric oxygen.


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, ...


39

It didn't arise ONLY during takeoff, but it is most noticeable then for several reasons The engines are at maximum power, therefore producing maximum torque You've got a very good reason to need to be travelling in an exactly straight line (the runway) You're travelling at fairly slow speed, so your vertical stabilizer is less effective - at higher speeds, ...


38

Short answer: This design will probably work, but it will not be very efficient. It can be tweaked into flying, but when you start tweaking, you would continue such that the outcome would look differently. Now let's look at your questions one by one: How feasible is it to use a propellor larger than the wingspan? Is there any law of physics that ...


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 ...


37

A couple of my CFIs have asked me to help them park the airplane (in absence of a tow bar) when I was pushing the airplane by putting one hand on the hub and the other on the propeller near the hub, and them (the CFIs) pushing the tail down and nose wheel elevated. But according to AOPA, it is not a good thing: ... never push or pull on the prop blades. ...


36

Because the pilot is taxiing the airplane with the props in the beta range (turboprops turn into landsharks if you don’t do this and you end up really riding the brakes to keep the speed down), then on takeoff, the propellers move into a maximum power setting, the engine snarls and slows a bit under the increased workload.


34

You are right, more blades are bad for efficiency (follow the link for the definition). Ideally, a propeller should have only one blade. Every additional blade will cause disturbances which interfere with the flow on the other blades. When engine power increases, the propeller disc area should also grow, but this growth is limited by the resulting speed of ...


33

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 ahead is $v_0 = v_{\infty}$ and the air speed aft of the propeller is $v_1 = v_0 + \Delta v$. The propeller effects a pressure change which sucks in the air ...


33

Radial engines - especially older large-bore designs like you find in WWII era warbirds - can suffer from a phenomenon known as hydraulic lock. Basically while the engine is off and cooling some oil from the crankcase seeps past the piston rings in the lower cylinders, and collects there. When you try to turn the engine over with this oil in the cylinder ...


32

It's because he was taxiing in DISC (discing, or flat pitch making the prop like a big disc), which is in the ground beta range, then coming out of it. Beta range is a mode where propeller blade angle is directly controlled by the power levers, and the propeller RPM is controlled by an Np governor in the fuel controller modifying gas generator (the engine ...


31

The pusher design is more efficient, because the suction forward of the prop reduces flow separation, and the accelerated flow behind it is not streaming around the fuselage (or wing), where it would create additional friction drag. In case of the Do-335 (see picture below), the single-engine top speed was 30 km/h higher with the rear engine running than ...


30

The prop tips are painted for visibility, to show that the prop is turning. This is especially important when the aircraft engine will be running in close proximity to people on the ground, but is also helpful in alerting the crew of other aircraft that the engine is running, and the aircraft might be moving soon. For visibility, the tip color should be in ...


30

It appears to be a Celera 500L, owned by Otto Aviation Group. This article has more information: "Unmasking The Bullet-Shaped Mystery Aircraft After It Reemerges At Victorville" The registration also provides us with a designation for this mystery plane—the Celera 500L. It is the only aircraft registered by the company with the FAA. The War Zone ...


29

A South Vietnamese Air Force Cessna O-1 landed on the USS Midway at the end of the Vietnam War. Fixed-wing VNAF aircraft usually flew to Thailand, and the naval evacuation was carried out by helicopter (with crews sometimes ditching in the water after the flight decks ran out of room), but this O-1 pilot wound up making his first carrier landing, with his ...


29

Peter Kämpf's answer covers the systems that prop planes actually use for reverse thrust. The alternative presented in the question is a total non-starter for several reasons. It's a complex and very heavy system. Unless there was somewhere on the centreline you could mount this engine and prop, you'd need not just one of these things but two, for ...


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 ...


27

Helicopter blades need to be long and thin. The diameter of the rotor disc determines the efficiency of the rotor at low speeds and can be compared to the wing span in fixed-wing airplanes. The rotation creates strong centrifugal loads at the blade roots which grow with the square of the tip radius at a given rotation speed, so they cannot be tapered much. ...


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