# Rubber motored helicopter

1. Apr 11, 2013

### ac16690

1. The problem statement, all variables and given/known data
For a Science Olympiad project I need to make a rubber motored helicopter, and with this I need to find the best design for one. One special rule in this is that Chinook styled helicopters get 3x their original flight time, I was wondering if that would be just to encourage students to do that type of helicopter, or if they are just harder to make. Also i have been looking for formulas about the efficiency of helicopter rotors with no success. Most models I have seen were Chinook helicopters and they were made from Balsa wood. Any help with some equations to help me out with lift or drag would be helpful.

2. Relevant equations
N/A

3. The attempt at a solution
I have tried researching equations, and have also asked my teacher and she left me with more questions than answers because she wants me to figure it out. Luckily this is due May 28th so I have awhile and I was spending hours on typical helicopter designs with no avail.

Last edited by a moderator: Apr 11, 2013
2. Apr 11, 2013

### Staff: Mentor

Perhaps it's time to try some experiments, eh? It may be easier to optimize your work through experiment rather than trying to find equations for the situation.

Since balsa wood helicopter kits are common and cheap, can you think of some experiments that you can use to try to optimize a design for this assignment? And is there a way you can experiment with the dual-rotor configuration?

3. Apr 11, 2013

### Staff: Mentor

BTW, one of the optimizations used in dual rotor helicopters is synchronizing the two rotors so they can be closer together without banging into each other. How can you do that in a balsa-wood experimental model?

Last edited: Apr 11, 2013
4. Apr 12, 2013

### rcgldr

I'm wondering if the induced wash from overlapping rotors reduces efficiency. Maybe this is done to reduce size? One of the rotors could be just mounted higher than the other to prevent the rotors from colliding. The real Chinook rotors are synchornized via a shaft. The rear rotor is slightly higher than the front, but not by enough to avoid the rotors hitting each other if they weren't synchronized.

Last edited: Apr 12, 2013
5. Apr 12, 2013

### CWatters

I would be a bit concerned about stability. If one rotor produces more lift than the other it is likely to turn over.

6. Apr 12, 2013

### rcgldr

I'm wondering if tilting the axis of the rotors slightly towards each other would help. Initially an imbalance would produce an imbalancing torque, but the lower lift producing rotor would become more horizontal and the higher lit producing rotor would become less horizontal, providing forwards or backwards thrust. The forwards or backwards thrust would result in forwards or backwards movement of the helicopter, reducing the imbalance in torque.

7. Apr 12, 2013

### CWatters

Certainly worth trying. Similar to dihedral.