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
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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. ...
Party Ark's user avatar
  • 11k
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
  • 125k
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
  • 22.6k
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
  • 16.8k
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
  • 99.8k
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
  • 37.3k
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 ...
voretaq7's user avatar
  • 68.2k
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, ...
Stelios Adamantidis's user avatar
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
  • 125k
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 ...
Peter Kämpf'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
  • 125k
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 ...
Camille Goudeseune's user avatar
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 ...
Robert DiGiovanni's user avatar
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 ...
Peter Kämpf's user avatar
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
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 ...
Carlo Felicione's user avatar
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
  • 16.8k
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
  • 81.8k
33 votes
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What happened to the blades in this picture?

It's an artifact of how a digital camera downloads captures the image from the sensor called rolling shutter. Essentially the image is captured a single line at a time and the fast moving propeller ...
ratchet freak's user avatar
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 ...
voretaq7's user avatar
  • 68.2k
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 ...
John K's user avatar
  • 125k
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
  • 52.8k
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
  • 16.5k
29 votes
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Why does the Cessna 172S Skyhawk use only two blade fixed pitched prop?

You're not wrong, but a fixed pitch two-blade prop has a pretty big advantage: it's cheap. Cheap to buy, cheap to install, cheap to maintain, cheap to repair. 172s are predominantly trainers in FBO ...
egid's user avatar
  • 23.2k
28 votes
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Why do turbofan blade tips exceed the speed of sound while prop tips should not?

Short answer: Turbofans need supersonic speed at the fan blade tips to create their high thrust. Turbofans can tolerate supersonic speeds because the intake creates constant flow conditions ...
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
  • 61.2k
27 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
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
  • 30.4k

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