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 ...
Peter Kämpf's user avatar
62 votes
Accepted

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. ...
Party Ark's user avatar
  • 12.5k
62 votes
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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 ...
John K's user avatar
  • 130k
61 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 ...
Therac's user avatar
  • 25.5k
58 votes
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How did the propellers on the B-29 stop perfectly in sync?

With the 18 cylinder radial engines in the B-29, a random shutdown would give possible propeller positions ever twenty degrees. They do not automatically stop this way. However, for staged photos ...
Zeiss Ikon's user avatar
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 ...
aeroalias's user avatar
  • 100k
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
Mike Sowsun's user avatar
  • 37.7k
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 ...
John K's user avatar
  • 130k
41 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 ...
Camille Goudeseune's user avatar
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 ...
John K's user avatar
  • 130k
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 ...
John Wiseman's user avatar
  • 1,709
38 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 ...
Robert DiGiovanni's user avatar
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 ...
Romeo_4808N's user avatar
  • 73.5k
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 ...
Zeiss Ikon's user avatar
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 ...
DeltaLima's user avatar
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33 votes
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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 ...
voretaq7's user avatar
  • 68.3k
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 ...
John K's user avatar
  • 130k
32 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 ...
GdD's user avatar
  • 53.6k
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 ...
J W's user avatar
  • 16.6k
28 votes
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How does a fan differ from a propeller?

The simple answer that covers the majority of engines is that a fan has a shroud. The possible exception are unducted fans or Open Rotor Engines, which are a hybrid between a turboprop and a fan ...
Peter Kämpf's user avatar
28 votes
Accepted

What's the use of so much torque on propellers?

Even small 1 hp electrical motors can achieve that RPM Yes, but can it sustain that RPM when something tries to stop it, that is the question. 1 hp combustion engines can get to 2700 rpm as well, but ...
Koyovis's user avatar
  • 61.6k
26 votes

Do jet aircraft have an emergency propeller?

There is a rotor, but not to provide thrust. The rotor spins in the air stream to generate electrical energy, which is used to power avionics and hydraulic pumps so that the crew can continue to ...
abelenky's user avatar
  • 30.7k
26 votes
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Why do propellors have white markings on their tips?

It is so you will see a circle when they are turning. Without contrasting bright tips turning propellers are invisible, and pose a grave risk for someone who is deaf, wearing heavy hearing protection,...
Michael Hall's user avatar
  • 25.7k
26 votes
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Variable pitch propellers: Why are they constant speed too?

How did we switch from talking about a blade's angle, to caring about its RPMs? Because of the engine. A piston engine will only run well in a narrow range of RPMs. Going too fast means lubrication ...
Peter Kämpf's user avatar
26 votes
Accepted

What is this indication on most turboprops?

This is the propeller synchronization (usually just called "prop sync") indicator, or "synchroscope." It rotates one way or the other to show the change in phase alignment of each ...
TypeIA's user avatar
  • 14.2k
24 votes
Accepted

Why are there extra restrictions on constant-speed propellers?

The engine is the same, not simpler. There is one additional level of complication to the system -- the constant speed propeller has a number of extra parts. The pilot needs to handle one more lever, ...
ghellquist's user avatar
  • 1,586
24 votes
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Why have propeller engines never been mounted on the tail in production transport aircraft?

There are two really big issues with tail mounted powerplants with propellers; weight distribution and Foreign Object Damage. Tail mounted engines move the empty C of G aft. This forces you to put ...
John K's user avatar
  • 130k
23 votes
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Why did WWII prop aircraft have colored prop tips?

That is not unique to WW2 planes, this is fairly common on most prop planes. It is to increase the visibility of a running (spinning) propeller to help people on the ground from accidentally coming in ...
Dave's user avatar
  • 101k
23 votes

Why are prop blades not shaped like household fan blades?

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 ...
Koyovis's user avatar
  • 61.6k

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