Linked Questions
22 questions linked to/from Why is max endurance different for jet and props?
24
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6
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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 ...
20
votes
2
answers
26k
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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 ...
17
votes
2
answers
10k
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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 ...
15
votes
4
answers
15k
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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
2
answers
5k
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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 ...
10
votes
5
answers
14k
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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?
9
votes
1
answer
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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 ...
6
votes
4
answers
10k
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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 ...
6
votes
3
answers
3k
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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 ...
6
votes
2
answers
11k
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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
1
answer
1k
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 ...
6
votes
3
answers
4k
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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 ...
6
votes
1
answer
851
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Does one-engine cruise consume less fuel than two-engine cruise?
Scenario 1. A two-engine airliner experiences rapid depressurization and makes an emergency descent to 10,000 ft, and diverts to the nearest airport.
Scenario 2. The same two-engine airliner ...
5
votes
3
answers
5k
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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?
5
votes
3
answers
4k
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How come a turboprop can't reach speeds as high as a turbofan?
I understand that turbofan powered aircraft can reach much faster speeds than turboprops like the C130 Hercules, and I can't imagine a turbofan turboprop powered 737 would be of any use really, but as ...
5
votes
1
answer
837
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How do I obtain the max endurance altitude?
There are excellent explanations of the physics that determine maximum endurance speed here, here, and here.
I was thinking of aircraft that have to be "on station" without an indicated altitude and ...
4
votes
3
answers
579
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Why does Vx have a relationship with thrust but Vy has a relationship with power?
https://www.boldmethod.com/learn-to-fly/performance/vx-vy-altitude-and-where-they-meet/
After I watch this article, now I understand the relationship between altitude and the rate of climbs.
But I ...
3
votes
1
answer
558
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What is the most simple plane lift equation that gives realistic solutions?
I need the most simple lift equation that once solved with Mathcad gives a realistic vertical speed of a plane and implicitly the altitude h(t).
Also the drag eq. (1) leads to a good solution, a Vh(t)...
3
votes
4
answers
6k
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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 ...
2
votes
1
answer
212
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Solutions to improve the aerodynamic behavior of a UAV
So I'm working at a project of a UAV with the follow characteristics:
Rectangular planform
Conventional tail
The fuselage is just a metal/aluminum rod
So we need to improve its aerodynamic behavior/...
0
votes
1
answer
1k
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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 ...
0
votes
1
answer
647
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Is it possible to create a direct supersonic airflow to a turbofan's afterburner in order to enhance the performance or reduce the fuel consumption?
so I found out that SR-71 Blackbird is using what's called "turboramjet" and I find the idea a bit appealing since they say with such engine, the Blackbird is more fuel efficient at it's top speed. I ...