1. Junior Member
Join Date
Jul 2012
Posts
1

## Gyroscopic Precession

Hey Flight Simmers!

It has been a long, long time since I took high school level Physics. I am currently studying for a pilot's license and really want to make sure that I understand how gyroscopic instruments work.

Here is a picture of a gyroscope as shown in the flight training book, "From the Ground Up".

Gyroscopic Inertia is described as, "The tendency of any rotating body, if undisturbed to maintain its plane of rotation. When the rotor in Fig. 54 is spinning abouts its axis A-B, the direction of this axis will remain fixed in its space, regardless of how the base of the gyroscope is moved around it."

My understanding:

If the rotor is spinning as its current position clockwise along A-B, and I pick up the entire gyroscope and flip axis F 180 degrees, then the rotor will still move as it is along axis C-D?
Likewise, if I turn F 360 degrees, then the rotor will continue to spin along its axis in the same direction.

Correct/Incorrect?

Precession is described as "the tendency of a rotating object, when a force is applied perpendicular to its plane of rotation, to turn in the direction of its rotation 90 degrees to its axis and take up a new plane of rotation parallel to the applied force...A push applied in the direction of the arrow G would cause the rotor in its supporting ring to tend to rotate around the axis C-D."

My understanding:

If I apply a force (G) to turn the instrumental 90 degrees to the left along pivot point F, based on the laws of precession, the rotor will also turn 90 degrees along C-D to the left. So now the rotor will be parallel to the applied force and spinning "flat faced".

Correct/Incorrect?

Thanks!

2. The easiest and least confusing way to understand a gyroscope is to go to a toy store, buy one, and play around with it.
It is much easier to understand when you can actually see what happens.

3. Originally Posted by rockinrobin
The easiest and least confusing way to understand a gyroscope is to go to a toy store, buy one, and play around with it.
It is much easier to understand when you can actually see what happens.
True

4. The same can be done on a bike. When a bike is in motion its wheels become like gyros.When you desire to turn on a bike you just lean into the direction you desire to go and the wheel and bike will turn in that direction.

5. Senior Member
Join Date
Mar 2005
Location
Hawaii - PHHI
Posts
1,665
Discussing bicycle dynamics will probably cause as many arguments as discussing lift.

scott s.
.

6. Getting your own gyro and playing with it would be the best bet. When I was in my avionic training in the USAF the instructor had some Gyros in the class that he spun up, so that he could show us how they work and stuff. It was very helpful

7. Member
Join Date
Apr 2010
Posts
202
Picture rolling a tire down the street with your right hand. To make the tire turn right, you would have to apply a force away from you at the top of the tire. That would make the front of the tire turn right. That's because the force acts 90 degrees ahead of, and in the direction of, the applied force.

I hope I remembered that right.

Art

8. Junior Member
Join Date
Apr 2010
Posts
2
Your second statement " If I apply a force (G) to turn the instrumental 90 degrees to the left along pivot point F, based on the laws of precession, the rotor will also turn 90 degrees along C-D to the left. So now the rotor will be parallel to the applied force and spinning "flat faced"." is incomplete. If a force is applied to a rotating gyroscope (or rotor system in my case) the force will manifest itself at a point 90 degrees later in the direction of rotation. If you want a helicopter (US counterclockwise rotating system) to bank left the force is applied at the 12 o'clock resulting in blade movement at the 9 o'clock helodriver

9. This is also why there is a built in 90 degree displacement in helicopter flight control system. Moving Cyclic fore and aft causes the swash plate to rock side to side.

10. Junior Member
Join Date
Mar 2012
Posts
25
Originally Posted by InsyleM
This is also why there is a built in 90 degree displacement in helicopter flight control system. Moving Cyclic fore and aft causes the swash plate to rock side to side.
Discovering this phenomenon (known as "control phasing") was one of the reasons helicopters took so long to develop. If you think learning to fly a helicopter is difficult, try it where the controls are rigged intuitively -- that is, where applying left cyclic tilts the swashplate left, giving maximum rotor blade pitch on the right side of the rotor disc. On a helicopter with counterclockwise rotation, this will result in the aircraft pitching up!

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•