Serious helicopter and relative speed question
Discussion
Why don't they roll over?
A helicopter hovering with rotors going round and round clockwise with a tip speed of 300mph so the rotors are doing 300mph relative to the air. So we can assume that at all points the blade produces the same amount of lift. The helicopter is facing directly north and at all points of the compass the blades are traveling at 300mph relative to the air
Now the helicopter starts to go forwards at 100 mph. Which gives you apparent wind of 100Mph from the north. So when a blade is directly north or south it will have roughly 300mph air going over the blades (yes i know it won't be due to relative vectors but we can ignore that for this question)
But when a blade is pointing west then it is traveling forwards in relation to the helicopter and apparent wind so it will have 300 + 100 so 400mph of wind speed over the blade where as the blade pointing east is traveling backwards in relation to the apparent wind so 300 - 100 so 200mph of wind speed over the blade.
Now if lift is related to windspeed then surely the blades going forwards will produce more lift then the blades going backwards.
So why don't they roll over when gong fast?
A helicopter hovering with rotors going round and round clockwise with a tip speed of 300mph so the rotors are doing 300mph relative to the air. So we can assume that at all points the blade produces the same amount of lift. The helicopter is facing directly north and at all points of the compass the blades are traveling at 300mph relative to the air
Now the helicopter starts to go forwards at 100 mph. Which gives you apparent wind of 100Mph from the north. So when a blade is directly north or south it will have roughly 300mph air going over the blades (yes i know it won't be due to relative vectors but we can ignore that for this question)
But when a blade is pointing west then it is traveling forwards in relation to the helicopter and apparent wind so it will have 300 + 100 so 400mph of wind speed over the blade where as the blade pointing east is traveling backwards in relation to the apparent wind so 300 - 100 so 200mph of wind speed over the blade.
Now if lift is related to windspeed then surely the blades going forwards will produce more lift then the blades going backwards.
So why don't they roll over when gong fast?
As has been said, the blades are jointed at the hub which allows them to change their angle of attack automatically as they are heading into the airflow and out of the airflow, thus, decreasing lift on the forward sweep and increasing lift on the backwards sweep - keeping the whole thing balanced.
The system was invented by the Spanish pioneer Juan De La Cierva who went on to build a whole range of autogyros in the 1920s and 30s. - so the system actually predates the working helicopter itself.
The system was invented by the Spanish pioneer Juan De La Cierva who went on to build a whole range of autogyros in the 1920s and 30s. - so the system actually predates the working helicopter itself.
Eric Mc said:
As has been said, the blades are jointed at the hub which allows them to change their angle of attack automatically as they are heading into the airflow and out of the airflow, thus, decreasing lift on the forward sweep and increasing lift on the backwards sweep - keeping the whole thing balanced.
The system was invented by the Spanish pioneer Juan De La Cierva who went on to build a whole range of autogyros in the 1920s and 30s. - so the system actually predates the working helicopter itself.
Okay explain in more detail how do the blades know how much to change the angle of attackThe system was invented by the Spanish pioneer Juan De La Cierva who went on to build a whole range of autogyros in the 1920s and 30s. - so the system actually predates the working helicopter itself.
Eric Mc said:
As has been said, the blades are jointed at the hub which allows them to change their angle of attack automatically as they are heading into the airflow and out of the airflow, thus, decreasing lift on the forward sweep and increasing lift on the backwards sweep - keeping the whole thing balanced.
The system was invented by the Spanish pioneer Juan De La Cierva who went on to build a whole range of autogyros in the 1920s and 30s. - so the system actually predates the working helicopter itself.
Juan de la Cierva is Spanish for John Deer, or, more gramatically correct, Deer John.The system was invented by the Spanish pioneer Juan De La Cierva who went on to build a whole range of autogyros in the 1920s and 30s. - so the system actually predates the working helicopter itself.
As you were, carry on!
thinfourth2 said:
Eric Mc said:
As has been said, the blades are jointed at the hub which allows them to change their angle of attack automatically as they are heading into the airflow and out of the airflow, thus, decreasing lift on the forward sweep and increasing lift on the backwards sweep - keeping the whole thing balanced.
The system was invented by the Spanish pioneer Juan De La Cierva who went on to build a whole range of autogyros in the 1920s and 30s. - so the system actually predates the working helicopter itself.
Okay explain in more detail how do the blades know how much to change the angle of attackThe system was invented by the Spanish pioneer Juan De La Cierva who went on to build a whole range of autogyros in the 1920s and 30s. - so the system actually predates the working helicopter itself.
Constant speed propellors on piston engines and turboporops are also able to assume the correct angle to the airflow without the need for any intervention by a controlling device or "computer" of any sort.
Bushmaster said:
Eric Mc said:
As has been said, the blades are jointed at the hub which allows them to change their angle of attack automatically as they are heading into the airflow and out of the airflow, thus, decreasing lift on the forward sweep and increasing lift on the backwards sweep - keeping the whole thing balanced.
The system was invented by the Spanish pioneer Juan De La Cierva who went on to build a whole range of autogyros in the 1920s and 30s. - so the system actually predates the working helicopter itself.
Juan de la Cierva is Spanish for John Deer, or, more gramatically correct, Deer John.The system was invented by the Spanish pioneer Juan De La Cierva who went on to build a whole range of autogyros in the 1920s and 30s. - so the system actually predates the working helicopter itself.
As you were, carry on!
Eric Mc said:
thinfourth2 said:
Eric Mc said:
As has been said, the blades are jointed at the hub which allows them to change their angle of attack automatically as they are heading into the airflow and out of the airflow, thus, decreasing lift on the forward sweep and increasing lift on the backwards sweep - keeping the whole thing balanced.
The system was invented by the Spanish pioneer Juan De La Cierva who went on to build a whole range of autogyros in the 1920s and 30s. - so the system actually predates the working helicopter itself.
Okay explain in more detail how do the blades know how much to change the angle of attackThe system was invented by the Spanish pioneer Juan De La Cierva who went on to build a whole range of autogyros in the 1920s and 30s. - so the system actually predates the working helicopter itself.
Constant speed propellors on piston engines and turboporops are also able to assume the correct angle to the airflow without the need for any intervention by a controlling device or "computer" of any sort.
As i thought the collective and cyclic effect blade pitch to allow control or are they seperate systems.
Also when i said "know" i didn't mean a computer as steam engines "knew" what speed they where rotating at via the governor weights which lead to the expression "balls out"
My understanding was that the blades flap up or down depending on whether they're going into the air or away from it. The movement of centre of gravity is accounted for by allowing the blades to lag (hinge backward and forward).
I was under the impression that the angle change was to control the disc after the 'flap'. The flaps and the reaction time would mean that the entire disc would be pitched up unless changing the blade pitch was used to bring the disc level again. I might have garbled this - it's been at least two years since I did powered lift.
You could also read Foundations of Helicopter Flight by S J Newman.
I don't wish to patronise, but have you considered the effects of the different relative air speeds of the blades on the helicopter's top speed? It's called the speed trap and was pushed to the limit by the Westland Lynx in the 80's. It still holds the helicopter speed record of 249 mph.
I was under the impression that the angle change was to control the disc after the 'flap'. The flaps and the reaction time would mean that the entire disc would be pitched up unless changing the blade pitch was used to bring the disc level again. I might have garbled this - it's been at least two years since I did powered lift.
You could also read Foundations of Helicopter Flight by S J Newman.
I don't wish to patronise, but have you considered the effects of the different relative air speeds of the blades on the helicopter's top speed? It's called the speed trap and was pushed to the limit by the Westland Lynx in the 80's. It still holds the helicopter speed record of 249 mph.
Edited by RDE on Saturday 31st January 12:24
RDE said:
I don't wish to patronise, but have you considered the effects of the different relative air speeds of the blades on the helicopter's top speed? It's called the speed trap and was pushed to the limit by the Westland Lynx in the 80's. It still holds the helicopter speed record of 249 mph.
Correct. The limitation is posed by the fact that to fly much faster, the tip of the forward moving rotor would need to travel at the speed of sound, so unless you can crack the supersonic rotor blade problem the helicopter cannot travel faster than one third the speed of sound.Edited by RDE on Saturday 31st January 12:24
Helicopters can't fly, they are so ugly the Ground repels them!!
As you know, there is a bolt in the rotor assembly that is quite critical. It holds the rotor onto the shaft. In a fit of wisdom, it was termed the "Jesus bolt."
The apparent reasoning was that only the good grace of the Savior kept it from failing. Failure of the Jesus bolt quickly gives a helicopter the same aerodynamic properties enjoyed by the common household brick.
As you know, there is a bolt in the rotor assembly that is quite critical. It holds the rotor onto the shaft. In a fit of wisdom, it was termed the "Jesus bolt."
The apparent reasoning was that only the good grace of the Savior kept it from failing. Failure of the Jesus bolt quickly gives a helicopter the same aerodynamic properties enjoyed by the common household brick.
The blades dont magically decide if they are flying into or out of the wind!
What the OP is talking about is dysymmetry of lift. The side of the disc approaching the wind has more lift than the side retreating from the wind..... Eventually the effect gets so bad the aircraft rolls to one side and pitches up... this is the maximum speed that aircraft is capable of....
To compensate for this the blades are allowed to flap up and down..
The blade flaps up on the advancing side and down on the retreating side... this helps to solve the problem, but interestingly introduces another... the rotor disk will "blow back" and is more likely to come into contact with the tail boom.... this blown back disk is also less aerodynamic....thus reducing efficiency at speeds near maximum
If you really want to have your mind melted by stupidly logical but complicated helicooptery stuff... get a copy of "principles of helicopter flight by W.J. Wagtendonk"
Makes you think really...
What the OP is talking about is dysymmetry of lift. The side of the disc approaching the wind has more lift than the side retreating from the wind..... Eventually the effect gets so bad the aircraft rolls to one side and pitches up... this is the maximum speed that aircraft is capable of....
To compensate for this the blades are allowed to flap up and down..
The blade flaps up on the advancing side and down on the retreating side... this helps to solve the problem, but interestingly introduces another... the rotor disk will "blow back" and is more likely to come into contact with the tail boom.... this blown back disk is also less aerodynamic....thus reducing efficiency at speeds near maximum
If you really want to have your mind melted by stupidly logical but complicated helicooptery stuff... get a copy of "principles of helicopter flight by W.J. Wagtendonk"
Makes you think really...
thinfourth2 said:
So the hinge does this allow the blade to rotate around the central axis of the blade to change its pitch or is it an actual hinge that allows the blade to flap up and down
As i thought the collective and cyclic effect blade pitch to allow control or are they seperate systems.
Obviously you've heard of cyclic pitch control, but perhaps you haven't twigged that this is the mechanism that solves your problem.As i thought the collective and cyclic effect blade pitch to allow control or are they seperate systems.
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