73
votes
Why is the Tu-95 so efficient despite having propellers that spin faster than the speed of sound?
Yes, propellers have problems at high speed, but if done right, they still have an advantage over turbofans at speeds up to Mach 0.8. Look at the inner engine gondolas of the Tu-95: They are elongated ...
- 230k
47
votes
Can these vortices be dangerous?
While @Peter Kämpf 's answer is great and sufficient to answer the question, I would like to add a clarification (which should be a posted as a comment, but is too long for this format).
In the image ...
- 71k
46
votes
Accepted
Would jet fuel for an F-16 or F-35 be producible during WW2?
Jet fuel is mostly kerosene, with some aromatic hydrocarbons mixed in for stability, temperature range and the like. You could probably run military jets on pure kerosene if they were magically ...
- 52.9k
41
votes
Accepted
How does gas turbine efficiency compare with supercharged piston engines?
The most efficient IC engines are large Diesels. At the extreme end are ship engines with better than 50% thermal efficiency resulting in a specific fuel consumption of only 0.260 lbs/hp/hour or 158 g/...
- 230k
41
votes
Is a turbocharged piston aircraft the same thing as turboprop?
They are both internal combustion engines that have a turbine in their exhaust that is used to power a compressor to pressurize the air before it is used for combustion.
In the turboprop, the turbine ...
- 793
40
votes
Accepted
Why do aircraft with turboprop engine have black painted anti-icing system?
These are rubber boot deicing systems. When ice forms on the leading edge of a wing, pressurized air is used to inflate the boot so the ice will pop off. Normally, this inflation is not permanent but ...
- 230k
37
votes
Accepted
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 ...
- 72.9k
35
votes
Accepted
Why do we refer to "power" for turboprop engines and "thrust" for turbojet/fan engines?
Ultimately what you want from all three types of engines is quantification of thrust available to push an airplane through the sky. The turbofan/jet engines are self contained and produce thrust ...
- 19k
34
votes
Why are turboprop intakes placed below the propeller?
Inertial separators are augmented by gravity when located under the engine. It is easier to discharge ingested ice and debris downward, rather than some other direction, so that is where they go if ...
- 19k
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 ...
- 126k
31
votes
Accepted
Why are propellers de-iced before the engines are started, and does ice on the fuselage affect the flight characteristics of the plane?
The props are done before starting because you need to make sure the blades and spinners are fully cleaned off while they are stationary. Otherwise, they'd vibrate like hell when starting and shed ...
- 126k
26
votes
Accepted
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,...
- 24.9k
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 ...
- 14.2k
24
votes
Why do we refer to "power" for turboprop engines and "thrust" for turbojet/fan engines?
Jet engines directly produce thrust by exhausting gas (and in a modern turbo fan also moving a lot of air around them), so fuel flow rate is directly related to the thrust that is generated.
In a ...
- 101k
24
votes
Accepted
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 ...
- 126k
24
votes
Accepted
What does the small needle + scale on this turboprop's N1 gauges indicate?
It duplicates the percent graduations in the large dial but at a finer resolution, with one percent increments. It's just to make the individual percent graduations easier to discern at a glance ...
- 126k
23
votes
Accepted
Why the lack of faster piston-powered planes?
The power requirement of an airplane grows with the cube of speed. When you fly fast with an airplane which needs to comply with a set minimum speed imposed by regulations, your drag coefficient is ...
- 230k
22
votes
Accepted
Did the XF-84H Thunderscreech really cause "900 sonic booms per minute"?
I think it is a matter of where you stand (literally).
From the front or the rear the shock waves from the propeller tips would hit your ears continuously, and the result would be constant noise.
...
- 230k
22
votes
Accepted
Is it possible to drive a prop directly from a jet engine without a gearbox?
As a side comment, there is a type of engine researched in the 80's/90's, but never marketed, where an unducted fan is driven directly by the turbine shaft without a gearbox: The propfan. It's close ...
- 71k
22
votes
Is a turbocharged piston aircraft the same thing as turboprop?
No, a turboprop is more like a jet engine with a propeller in the front instead of a fan:
Source: Wikimedia
In its simplest form a turboprop consists of an intake, compressor, combustor, turbine, ...
- 36k
22
votes
How are turboprops and other propeller planes pressurized?
Turboprops are actually turbine engines. They can produce bleed air just like turbine engines (e.g. turbofan). The bleed air can be used directly to pressurize the cabin, or it can drive another turbo ...
- 10.7k
21
votes
Accepted
Can these vortices be dangerous?
No.
The wing does a great job in straightening the propeller swirl, but adds its own vortex. Wake turbulence is dominated by the flow field around the wing.
- 230k
21
votes
Which engine is more financially economical to operate, a turboprop or gasoline engine?
Piston engines are significantly less expensive to operate, as long as the aircraft's performance and reliability requirements can be satisfied by a piston engine.
It's not just the fuel, it's the ...
19
votes
Accepted
What is this on the starboard engine of the Dash 8?
It is the engine drain mast. From the Dash 8 Series 400 airport planning document - Chapter 2, Page 40:
Dash 8 engine drain; image from Dash 8 Series 400 airport planning document
Basically, the ...
- 100k
19
votes
Accepted
How are turboprops and other propeller planes pressurized?
A turboprop plane can be pressurized in the same way a turbofan plane can: via bleed air from the compressor stage of the turbine engine. A turboprop and turbofan are not that different actually. You ...
- 54.3k
18
votes
Why do aircraft with turboprop engine have black painted anti-icing system?
They're not painted black, but a rubber (hence black) device called a de-icing boot.
Upon entering icing conditions, the system once activated will repeatedly inflate and deflate the rubber boots. ...
- 12.9k
18
votes
Accepted
What is the danger in the over-use of reverse thrust during ground operations when operating a turboprop powerplant?
One concern is Foreign Object Damage (FOD). More reverse thrust means more dirt is thrown into the air, which can then be ingested by the engine:
Damage to turboprop engines is not
as common as in ...
- 54.3k
Only top scored, non community-wiki answers of a minimum length are eligible