53
votes
Accepted
Do the Mt. Everest rescue helicopters have modified engines to operate at high altitudes?
No, the helicopters are standard production versions. The Eurocopter AS350 is a common model used for these operations.
In 2005, Didier Delsalle landed a Eurocopter AS350 B3 on the summit of Mt. ...
- 73.8k
26
votes
Why does a turbine helicopter need to spin a tail rotor?
Well, that’s complex. Where should I begin?
The main job of the tail rotor is to use its long lever arm and directed force/thrust (horizontal lift) to counteract the torque of the spinning main rotor....
- 16.6k
16
votes
Accepted
How exactly is the free shaft part of a gas turbines controlled?
The free turbine is literally just a windmill that generates torque when the wind blows on it. You could actually just stick it outside the engine itself behind the tailpipe and it would do the job, ...
- 136k
15
votes
Are there helicopters with vertically mounted turbines?
No a turboshaft cannot directly drive the rotor without a reduction gear, the rotor torque is too high for the ungeared turbine torque. The rotor blades are much longer than those of a prop or fan (...
- 62.9k
10
votes
Accepted
Why does it take so much fuel to start a jet engine?
The first figure, 1 litre per mile, is very wrong. The second, 39 to start, is most probably the fuel required for a warm up from a cold start. The Abrams tank weighs 62 tonnes, so you won't get 1 ...
- 4,533
10
votes
Accepted
Does a turboshaft's exhaust provide any thrust?
Yes, the exhaust of any engine does provide some thrust (very little for piston engines).
The amount of jet thrust for turboprops is in the range of 4%-15% of propeller-produced thrust. For a ...
- 30.1k
8
votes
How exactly is the free shaft part of a gas turbines controlled?
To answer the questions:
“How can it exactly spin freely from the main turbine?”
The free shaft i.e. the power turbine is not connected mechanically to the gas generator spool and can turn at ...
- 75k
8
votes
Why does a turbine helicopter need to spin a tail rotor?
The turbine output is very hot and therefore needs to be shielded in some way if it is to be routed through any part of the helicopter. This shielding adds cost and weight, so it's generally avoided. ...
- 81
7
votes
Accepted
What is the purpose of variable stator vanes in the power turbine part of a free shaft gas turbine?
When you take a turboshaft engine and subject it to large and sudden load changes, that it doesn't have to cope with in an aircraft, like during gear ratio changes in a tank, you get very sudden ...
- 136k
6
votes
Why does a turbine helicopter need to spin a tail rotor?
The turbine engine of a helicopter has very little exhaust thrust. They are turboshafts, designed to extract every bit of useful energy for driving the main rotor shaft. From Wikipedia:
A ...
- 62.9k
6
votes
Turbofan ‐ turboprop/shaft hybrid?
Cutting some corners to keep this simple but:
Turbofans make more thrust than turbojets, because they employ a large fan driven by a jet engine. This way it can accelerate a large amount of air, and ...
- 30.5k
5
votes
Can a gas turbine be able to switch from torque to thrust?
The main way to convert a gas turbine to provide thrust rather than shaft horsepower is to attach a large fan or propeller in place of the previous load. For example, the GE CF6, which powers aircraft ...
- 73.8k
4
votes
How are compressor disks connected to the shaft?
Your question:
Here is a section view of a sample and I indicated the connection
area.
What type of connection elements are used there? Anything
related will be helpful.
From the title of your ...
- 80.9k
4
votes
why are turboprop/turboshaft engines rated only in horsepower and never in ft-lbs of torque like diesel engines or electric motors?
The reason a Diesel engine has a torque figure and a horsepower power figure is because max torque and max horsepower occur at different engine RPMs. Have a look at any performance curves of a piston ...
- 4,533
3
votes
Benefit of a deswirl vane for a turboshaft helicopter engine
This is a very good question. However, there is a slight error in your question, which is causing the confusion.
Turbine power, is determined by the ratio of total pressure across the turbine (and ...
- 4,533
3
votes
Do Military Turboshaft engines have a distinctly different sound from Civilian ones?
I think your friend is playing a joke on you. I have worked with helicopters since the late 1970's and there is no way to distinguish military from civilian simply by engine noise. You may be able to ...
- 13.2k
3
votes
Turbofan ‐ turboprop/shaft hybrid?
Turboshaft produces torque, not trust. It is a turbine with a power shaft or an accessory drive. It uses the torque to produce thrust, but there is a variety of power consumers, for example, a ...
- 191
3
votes
Can coaxial rotors be mounted on a piston engine like the Lycoming O-320?
Stan Hiller's earliest helo designs were coaxial and used relatively small 4-cylinder aircraft engines to drive the coax transmission, so it is indeed possible to power a small coaxial helicopter with ...
- 22.2k
3
votes
Accepted
Why is the turbine that drives the compressor is placed before the free turbine in a gas turbine engine?
The compressor-turbine spool, the "gas generator" in turboprop/turboshaft lingo, or "core engine", in a turbofan, has to come ahead of the power turbine because the turbine has to ...
- 136k
3
votes
Accepted
Why does the gas turbine recuperator hugely increase efficiency but slightly decrease the peak power?
I understand that the heated intake air will burn more efficiently with the fuel and that's why recuperators increase efficiency.
Actually that is not the reason.
When applying a recuperator to a ...
- 1,817
2
votes
Accepted
How can an N1 speed change and an N2 remain the same?
Most rotorcraft use a fixed rotor speed (note that slowing the rotor speed could bring benefits in some flight situations, but that is not applicable here) flying different operating/flight conditions....
- 1,817
2
votes
Accepted
Why does the torque curve of free shaft gas turbines keep gradually dropping as RPMs increase?
Let's start with this example:
Start up the turbine with no load connected to the shaft, then advance the fuel flow rate to the maximum allowable value. The output shaft will achieve some (very high) ...
- 22.2k
2
votes
How are compressor disks connected to the shaft?
In effect, this question is related to In a turbofan what holds the spinning axis?. This question has an excellent answer that closely relates to this question (but isn't a duplicate). The following ...
- 1,817
2
votes
Why is the first turbine in a turboprop (or turboshaft) connected to the compressor?
You can only use for shaft horse power what is available after the energy to drive the compressor is subtracted. This subtraction is done by the high pressure turbine. Any energy left in the exit flow ...
- 237k
2
votes
Accepted
Can a gas turbine be able to switch from torque to thrust?
I suppose the F135-PW-400 powerplant on the F-35B does just that.
A turbine engine is used to create high enthalpy gas which can either pass through a turbine to produce mechanical work or pass ...
- 75k
2
votes
Can a gas turbine be able to switch from torque to thrust?
Most turbine engines designed to drive some sort of mechanical system such as a hydraulic pump and electrical generators are not designed to provide thrust because their fuel controller can only run ...
- 13.2k
1
vote
why are turboprop/turboshaft engines rated only in horsepower and never in ft-lbs of torque like diesel engines or electric motors?
Because it's less useful for aviation application.
For diesel and electric, or ground vehicle and industrial motors in general, lack of peak torque is a problem (engine/motor stall), but for ...
- 3,078
1
vote
Benefit of a deswirl vane for a turboshaft helicopter engine
Thanks for the discussion - Penguin. However, for reasons below, I am not convinced of your explanation.
The formula for turbine power you quote is for a turbofan engine. For a turboshaft engine, ...
- 11
1
vote
Where should I find a Pratt & Whitney Canada PT6 operator's manual?
Found it here
https://www.manualslib.com/manual/812510/Pratt-And-Whitney-Canada-Pt6a-Turboprop.html?page=1
First hit on google for "Pratt & Whitney Canada PT6 operator's manual"
- 8,795
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