Linked Questions

34
votes
9answers
29k views

Why do airplanes not have manual transmission?

I have limited experience with flight simulators but I have never bumped into a plane with manual transmission while, on the contrary, it's very common for other means of transportation (like cars and ...
51
votes
2answers
205k views

What is the difference between a turbofan and a turboprop engine?

I'm not an aircraft expert and I just realized that there are two different terms - turbofan and turboprop. I always had them combined in my head as a term for a large jet engine (like you would see ...
45
votes
3answers
17k views

Why is the Tu-95 so efficient despite having propellers that spin faster than the speed of sound?

I've ready many, many times that propellers are not efficient near the speed of sound because it's so hard to get a tip-speed above Mach 1. Then I came across this: It's the Tu-95 "Bear", a ...
24
votes
4answers
22k 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 ...
26
votes
2answers
24k views

What are the advantages of more than 4 propeller blades?

I have heard that propellers with more than four blades are not as efficient as 4 or less blades because of lower thrust which may result from interfering prop-streams. But I see the ATR-42/72 and ...
24
votes
1answer
9k views

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

I am designing a remote controlled airship. I will tune it so that the lift given by Archimedes' Principle will exactly balance the weight of all the structure. It will be propelled by brushless ...
8
votes
6answers
13k views

Is it possible to fly using a small engine?

I'm currently a high school student trying to build an ultralight aircraft from scratch (I'm self taught and still learning from educational videos), but I don't have much savings (about RM 2.5k, ...
6
votes
2answers
8k views

Why do turbofan engines have low pressure compressors?

In my understanding turbofan engines usually have 2 stages of compressors: one low pressure compressor followed by a high pressure compressor But it looks like the high pressure compressor ...
8
votes
2answers
5k views

What are the limitations in adoptions of GTF (Geared Turbofan) technology?

The only recent engine using GTF technology is the PW1000G, however some old designs like ALF502 or TFE731 use this technology. I understand the basic concept of the benefit obtained by the engine ...
17
votes
1answer
4k views

Why don't aeroplanes use propellers with more blades like the intake on a fanjet?

The air intake on a fanjet typically has many small angled blades. A wind pump in an American film might have many broad slatted blades. My desk fan has 3 very large scooping blades and seems quite ...
15
votes
2answers
3k views

What prevents jet engine designs with larger bypass ratios?

In commercial aviation, it seems jet engines grow and bypass ratio increase with newer engines. Here is some examples: 1963: bypass ratio: 0.96 (P&W JT8D) 1970: bypass ratio: 5.0 (P&W JT9D) ...
13
votes
1answer
5k views

What is a “high-bypass geared turbofan,” and why is it so much more efficient?

According to the article Bombardier’s CSeries Gamble Is Facing Longer Odds, this new plane from Bombardier uses a new engine technology that will improve efficiency over its rival 737 series and A320 ...
8
votes
2answers
952 views

Why do turbofan engines not have a contrarotating second fan?

Why aren't planetary gears used to have a fan in front of the fan in a turbo fan engine. Would this not lower energy consumption etc?
3
votes
1answer
918 views

Can a turbofan have a fan driven electrically so as to run at optimal speed?

I just watched this pretty dumbed-down video about the idea of putting a gearbox in a turbofan so the fan can run at its optimum slower speed while the core runs at its optimum high speed. And I ...
1
vote
2answers
534 views

What are the pros and cons of adding a gearbox to larger jet engines?

What are the merits and demerits of adding a gearbox to larger jet engines like the Trent 900. If its about torque, why not use a magnetic gearbox? What are the demerits of using magnetic gearboxes ...