71 votes
Accepted

Why do solar planes have many small propellers instead of fewer large ones?

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 ...
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62 votes
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What helicopter has the most rotor blades?

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. ...
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  • 9,431
62 votes
Accepted

What instructions should I give to an untrained passenger for Hand propping Cessna 172N as a pilot?

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 ...
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  • 103k
60 votes
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Why are prop blades not shaped like household fan blades?

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 ...
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  • 17.6k
59 votes

Why does flight training usually start with (unsafe?) propeller planes and not with (safer?) jets?

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 ...
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  • 2,011
52 votes

Why are push-propellers so rare, yet they are still around?

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 ...
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  • 74.2k
49 votes
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Do jet aircraft have an emergency propeller?

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 ...
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  • 98.3k
48 votes

Why does flight training usually start with (unsafe?) propeller planes and not with (safer?) jets?

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 ...
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  • 74.2k
46 votes
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What is the metal bit in the front of this propeller spinner?

It is a fitting for a Hucks Starter. Photos from Vintage Wings Canada
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  • 31.8k
44 votes

Why don't planes have a reverse propeller as air brakes?

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 ...
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43 votes

Why are push-propellers so rare, yet they are still around?

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 ...
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42 votes
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Can a plane fly backward if its propeller is in reverse?

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 ...
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  • 67.2k
41 votes

Do propeller planes give contrails like jets do?

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, ...
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41 votes

What helicopter has the most rotor blades?

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 ...
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  • 103k
40 votes
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What are the advantages of more than 4 propeller blades?

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 ...
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40 votes

Why would a propeller have blades of different lengths?

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 ...
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  • 103k
40 votes

Could propeller wash provide sufficient lift to take off - even in theory?

Yes. The wing doesn't care what is causing air to flow past it. Headwind, propwash, 747 wake, gopher sneezes. If the airplane is restrained from forward motion, and the propwash over most of the ...
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39 votes

What's the difference between a "runaway prop" and a "feathered prop"?

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 ...
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38 votes
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Would an aircraft with contra-rotating propellers longer than the plane's wingspan be able to fly?

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 ...
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38 votes
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What is this odd aircraft?

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 ...
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  • 1,675
37 votes
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Is it OK to move a light aircraft by pushing or pulling the propeller?

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, ...
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  • 29.1k
37 votes
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Why would a turboprop rev down just before going full throttle during takeoff?

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 ...
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36 votes
Accepted

Is there any equation to bind velocity, thrust and power?

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 ...
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34 votes

Were propeller airplanes significantly more "scary" to fly in compared to modern jet ones?

Old propeller airliners were much more prone to "bumpy" ride than modern jets, for one major reason: they flew lower. When I was in my early teens (almost fifty years ago), I flew several ...
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  • 14.3k
34 votes
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What do "cork screwing" and "pushing air" have to do with propellers?

All three sentences make sense to me. Firstly, the shape of the propeller is such that it cork screws through the air. The cork screw motion pulls the propeller and the plane through the air The ...
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  • 74.2k
33 votes
Accepted

Why do ground crews rotate a radial engine's propeller before a motor/cartridge start?

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 ...
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  • 67.2k
32 votes

Why would a turboprop rev down just before going full throttle during takeoff?

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 ...
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  • 103k
31 votes

Does a windmilling propeller create more drag than a stopped propeller in an engine out scenario?

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 ...
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  • 49.1k
30 votes
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Why don't helicopter blades look like other propellers?

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 ...
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30 votes

Why did WWII prop aircraft have colored prop tips?

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 ...
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