Linked Questions

23
votes
6answers
6k views

In what way are the Concorde's engines considered efficient?

The Concorde is powered by a bunch of Rolls-Royce/Snecma Olympus 593 turbojet engines. Much has been said about how efficient they are at speed, and the fact that they allow long-range cruise at Mach ...
16
votes
2answers
19k views

Why do military turbofan engines use a low bypass ratio?

I know that the most civilian engines use a high bypass ratio which is good for fuel economy and noise reduction. What prevents military engines from using the same technology instead of opting for ...
14
votes
2answers
4k views

Which commercial aircraft can stay in the air the longest?

Which commercial aircraft, when fully loaded with fuel (and passengers and luggage up to its max takeoff weight), could stay in the air the longest without landing, and how long could it stay in the ...
9
votes
4answers
8k views

What determines the best glide speed?

I found the best glide speed of cessna 152 is 60 kts. My question is why it is not more or less than 60 kts? What are the factors upon which the best gliding speed is determined?
15
votes
4answers
9k views

What is the propeller efficiency, $μ_p$, of modern propellers for light sport aircraft?

Roskam's book on preliminary design gives a value of 0.7 for "homebuilt" aircraft and 0.8 for general aviation. What explains this difference in propeller efficiency? The content of Roskam's book is ...
14
votes
2answers
4k views

Why would maximum fly-time (endurance) not coincide with max L/D operating point?

This question is motivated by another SE Aviation answer where @Peter Kampf writes the following two useful bits of information: Aircraft like to fly near their optimum L/D ratio, where drag ...
6
votes
4answers
7k views

How is engine thrust measured in flight?

When aircraft engines are evaluated in a test flight, how is the thrust of the engine measured? You would need accurate thrust numbers to calculate the real-world specific fuel consumption (i.e. not ...
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?
6
votes
3answers
2k views

Can the thrust of a turbofan be increased by increasing bypass ratio?

I read that the CFM56 is based upon the F101. Id on't know how true that is, but it generated the following question: If a larger fan is fitted to a low bypass turbofan, would dry thrust be ...
4
votes
2answers
4k views

How to pick a good airfoil based on Cl and Cd

Let's assume I have 10 different airfoils graphs of Cl x Aoa, Cd x Aoa and Cl/Cd x Aoa. How do I pick the best one that will give me the most efficiency (the longest flight time)? I understand the ...
6
votes
3answers
2k views

How does turbofan engine performance depend on speed and density altutude?

I am looking at a simulation engine (jsbsim). Their turbine engine simulation requires a function, given by table, of thrust at Mach number and density altitude. Engine definitions generated by their ...
5
votes
1answer
739 views

Does the air resistance of a jet engine air intake count towards the jet's total air resistance?

Does a jet engines air intake count to the overall jets geometry dependent air resistance? Taking the Saab Tunnan as an example it's overall air resistance has to be quite low because of it's huge ...
3
votes
4answers
3k views

How can I find the optimum chord wing length for this wing?

This Aviation SE forum looks the perfect place to ask this question: people here usually make maths the root of most solutions and I think this may solve my aerodynamic optimization problem! I am ...
9
votes
1answer
1k views

How does the efficiency of a turbofan compare between take off speeds and optimal conditions?

I know turbofans are less efficient than propellers due to accelerating a smaller mass of air faster. So my question here is not comparing turbofans vs other engines, but compare how inefficient is a ...
0
votes
1answer
855 views

Which portion of combustion energy is used to spin the compressor of a pure jet engine?

In level flight at constant speed, it is correct to assume that the quantity of energy created by fuel combustion (FE) is exactly extracted by the turbine section (ME) and is used solely to spin the ...

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