Linked Questions

24
votes
4answers
21k views

Why do turbofan blade tips exceed the speed of sound while prop tips should not?

It seems that the tips of the fan of a turbofan engine can and do break the sound barrier: The GE-90 has a fan diameter of 3124 mm and a rotational speed of 3475 RPM. Their circumferential velocity ...
24
votes
7answers
7k views

Given the same engine, why install a gearbox on a turboprop but not on a turbofan?

I am reading the book Mechanics and Thermodynamics of Propulsion, by Hill and Peterson. I found out this image while reading the chapter 5, "Thermodynamics of Aircraft Engines": Why would there be a ...
12
votes
6answers
5k views

For an electric airplane are propellers the only option for propulsion?

This is for an electric airplane (so no fuels for combustion): Are propellers the only option? Is there a turbine-jet possible with only air intake, electrically compress, and a turbine and nozzle ...
11
votes
4answers
4k views

How is the D8 Double Bubble aircraft by NASA so efficient?

How does the 'double bubble' fuselage cross-section of the "Double Bubble D8" aircraft (developed by MIT for NASA) help improve overall efficiency by around 70%? Image credit: NASA/MIT/Aurora Flight ...
17
votes
2answers
16k views

Do helicopter rotor tips regularly go supersonic?

In my question about helicopter noise, I made the assumption that one reason they are so darn noisy is that the main rotor tips go faster than the speed of sound. @FreeMan questioned whether that was ...
14
votes
2answers
9k views

What is the “area rule”?

The "area rule" states that the supersonic drag on an aircraft is related to the total area on part of the aircraft. What is the exact definition of the rule? Why does this happen?
4
votes
3answers
3k views

Why are the top speeds for jet engines higher than for propellers?

I realize turbines are more efficient than piston engines, but if that were true, then why don't turbo-props reach jet speeds?
7
votes
2answers
3k views

How does blade solidity ratio relate to thrust/power/torque of a propeller?

for quite some time I was using ABBOTT formula for static thrust estimation on a two-bladed propellers: $$ T=6.8\times10^{-5}\times D^{3}\times p\times RPM^{2} $$ $T$ is Static Thrust (N); $D$ is ...
5
votes
2answers
1k views

Is 1 propeller always more efficient than 2?

Based on other answers I've read here (1) (2) (3), a single large blade propeller is the most efficient type of thrust you can get. There are 2 reasons for this (as I understand it). Firstly, ...
2
votes
3answers
583 views

Is the purpose of variable pitch propellers to maintain an optimal angle of attack?

I recently had a discussion with an aviation expert, who works as a Flight Instructor, about constant speed propellers - variable pitch propellers - on light piston aircraft. I have always known that ...
3
votes
3answers
572 views

What is compressibility drag?

I don't mean wave drag here. What is compressibility drag, which is understood to be a form of miscellaneous drag?
3
votes
2answers
160 views

What are the relative efficiencies of the various stages of a counter rotating propeller?

After going through the CFD results of a drone project I am involved in, I noticed that the data shows significantly increased (+10%) thrust generation at the second stage of a counter-rotating, 2-...
6
votes
1answer
412 views

How are the Tupolev Tu-95's blades shaped?

The Tupolev Tu-95 "Bear" seems like an awfully cool piece of innovation with its unusual contra-rotating supersonic-tipped props. From what I've been reading it sounds like it's been the only mass ...