# A few questions about helicopters

In summary, the thrust of a helicopter rotor depends on parameters such as angular speed, blade twist, and chord length. A 2-blade rotor and a 4-blade rotor with the same chord length may not have the same thrust due to aerodynamic effects and tip vortices. In the case of a tip-jet helicopter, even with a smaller diameter, the tangential speed remains the same. For more information on helicopter flying theory, you can refer to websites such as copters.com, helicopterpage.com, and cavalrypilot.com.
Hello all, I've got a few questions about helicopter rotors.

On which parameters does the thrust of an helicopter rotor depend? If i have: a 2-blade rotor, 8 feet of diameter. A 4-blade rotor, 4 feet of diameter. Do they have the same thrust? Or the second rotor will have less thrust because of the smaller radius(and less tangential speed)?
And in the case of a tip-jet helicopter? Even reducing the diameter, the tangential speed is about the same, right?

Sorry for the stupid questions and my bad english.

I am going to assume that you are talking about lift in a hover.

Will they have the same thrust? In all likelyness no. In theory, with Ct and area constant, the thrust is going to be a function of the angular speed squared. So if the required adjustment can be made to the rotor tip speed, then in theory, you should be the same. HOWEVER, when going to 4 blades with the same chord length as the 2 blade, you will run into aerodynamic effects due to the preceeding blades in the form of tip vorticies whose strength is a function of tip speed IIRC. You would also have to look into adjusting the blade twist to attempt to keep the lift distribution along the length similar. A shorter blade will require less twist.

I guess the answer to this question really depends on how in depth you want to get.

Thanks for the answer FredGarvin, you cleared my doubts. I think i'll inform myself better on the argument. Does anyone know good links for helicopter flying theory?

Last edited by a moderator:

## 1. How do helicopters stay in the air?

Helicopters stay in the air by using the lift force created by its spinning rotor blades. The rotor blades are angled and create an upward force that counteracts the downward force of gravity, allowing the helicopter to hover or fly.

## 2. How do pilots control a helicopter?

Pilots control a helicopter using three main controls: the cyclic, collective, and pedals. The cyclic controls the direction of flight, the collective controls the amount of lift produced by the rotor blades, and the pedals control the direction of the helicopter's tail rotor which helps to counteract the torque produced by the main rotor.

## 3. What are the advantages of using a helicopter over other aircraft?

Helicopters have the ability to take off and land vertically, making them ideal for use in areas with limited space. They can also hover, making them useful for tasks such as search and rescue or aerial photography. Additionally, helicopters are able to fly at lower speeds and in more turbulent conditions compared to fixed-wing aircraft.

## 4. How do helicopters differ from airplanes?

The main difference between helicopters and airplanes is the way in which they generate lift. Airplanes use wings and engines to produce lift and move forward, while helicopters use spinning rotor blades to create lift and can also move in any direction, including vertically.

## 5. What are some common uses for helicopters?

Helicopters have a wide range of uses, including transportation, military operations, medical rescue, firefighting, and aerial surveying. They are also commonly used for tourism and as a mode of transportation for executives or VIPs.

• Other Physics Topics
Replies
36
Views
4K
• Mechanical Engineering
Replies
1
Views
1K
• Mechanical Engineering
Replies
5
Views
1K
• Other Physics Topics
Replies
4
Views
4K
• Mechanical Engineering
Replies
6
Views
814
• Mechanical Engineering
Replies
14
Views
1K
• Mechanical Engineering
Replies
19
Views
716
• Aerospace Engineering
Replies
9
Views
958
• Introductory Physics Homework Help
Replies
1
Views
1K
• Introductory Physics Homework Help
Replies
1
Views
1K