Interesting video about gyroscopic force

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muffled500hp
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Interesting video about gyroscopic force

Post by muffled500hp » Sun May 19, 2013 7:43 pm

https://www.youtube.com/watch?v=ty9QSiVC2g0

Add in the thrust force of a propeller and imagine how much of a beating our power train is getting on our boats.
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PeaRiverOpossum
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Re: Interesting video about gyroscopic force

Post by PeaRiverOpossum » Mon May 20, 2013 8:32 am

Cool :salute: Applies in more ways than most realize I bet...I think about this every time I see someone doing 360s with the hammer down.

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plumcrazy
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Re: Interesting video about gyroscopic force

Post by plumcrazy » Mon May 20, 2013 9:26 am

the forces are tremendous and them dd cady guys all ways blame the prop when a crank gives way ....
all i can say is check your riggin faseners and mounts on your boat every time you saddle up....

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Re: Interesting video about gyroscopic force

Post by gobblerD » Mon May 20, 2013 9:30 am

Now I know why I tend to ride in a circle the faster I cruse on my unicycle. :shock:

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Re: Interesting video about gyroscopic force

Post by sseater » Mon May 20, 2013 10:01 am

thats why i dont do 360's with my boat and hold the gas down like some people. imagine the force its putting on your crank...
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Re: Interesting video about gyroscopic force

Post by BluByU2 » Mon May 20, 2013 12:14 pm

That was a good visual explanation, and is one of the reasons I don't do 360's or rapid, radical movements unless I have to get out of a bind. Smooth, and steady is the name of the game for this old fart.

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Re: Interesting video about gyroscopic force

Post by WaterWalker » Mon May 20, 2013 3:59 pm

Keith: interesting post & comments:

The following is a worst case scenario of gyroscopic + torque roll forces in an airboat maneuver that is very likely to sink you:

Take a;

Right hand rotation large wide say four blade propeller on a,

Gearbox installation that mounts the engine higher than a belt drive for a higher CG.

Use a low ratio reduction unit of say 2.68/1 that multiplies the engine torque onto the propeller.

Have a large horsepower engine of say 600 HP & 600 lbs. Ft. engine torque at about 5200 engine RPM.

This torque is multiplied by the ratio at 2.68 times then to equal about 1600 lbs. ft. torque at the prop center of rotation.

On an 8 ft. wide boat at the rear gunnels and say 7 ft. wide at the bottom turning chines your maximum flotation bouncy then has a 3.5 ft. arm from the boat center line to the left or right.

The torque arm to the left and right rearward gunnels (at 8 ft. wide) then is 4 feet each way. So 1600 lbs. ft. max power prop torque divided by 4 feet is 400 pounds of torque roll at the rear gunnels. On a right hand rotation propeller the torque roll is downward at port (left side) and upwards at starboard (right side). Picture two full size men (two hundred pounds each) standing on your port rear gunnel holding on to the outside of the cage.

Now lets place the mature (say 200 lb.) driver in the port and rearward operator position that adds more weight to the left downward typical torque roll forces.

Now lets start to max accelerate from an idle position in deep water while instigating a hard left turn with this boat. As the prop spins up to top RPM, gyroscopic forces set in as a result of the left turning rate. (Weight of prop X RPM X rate of turn in degrees per minute). These forces are at 90 degrees to the direction of turn of the airboat.

It turns out that with a right hand rotation prop (as seen from the rear of the boat) the gyroscopic forces of a left hand turn push downward on the transom and lift the bow up about the boat CG.

So now we have;

A heavy driver in a left rear operator seat in the boat already giving a small left & rearward list of the boat.
Then we have the torque roll equal to two heavy guys hanging off of the left rear gunnel of your boat.
Then we add the considerable downward gyroscopic forces of the spinning propeller pushing down on the entire transom and raising the bow while in a hard left turn.
As the boat moves forward in the turn it begins to ride up onto the water on its starboard side like a water skier trying to "get up" raising the starboard side while the rearward port side (with those two heavy guys hanging on) is falling into the receding waters being pushed down by the starboard side in passing.

When the boat then lists to port beyond a stable point the high center of gravity of the engine goes over center and the boat rolls on over to the port side and sinks!

Few air boaters will stay on the rudders and throttle while this is all happening but some have. They got wet.

When could this happen to you?

say you have been drifting at idle and the wind has moved your bow away from the direction you want to go. A quick turn to the left is be shortest direction to point your boat where you want to go and you begin all this in a hurry before your friend in the other boat gets away from you.

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Re: Interesting video about gyroscopic force

Post by DuckBoat » Mon May 20, 2013 6:55 pm

David (WaterWalker)

Thanks a ton for the great post. For those like me that do better with pictures, I put two below, can you confirm that I got it correct?

So all things being equal, since I have a Left hand propeller, I should stay away from a hard start turning right or slow right hand turns? Also, any advise on a 180 stop.

Left hand propeller rotates counter clockwise
Image

Right hand propeller rotates clockwise
Image

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Re: Interesting video about gyroscopic force

Post by HAMMERHEAD » Mon May 20, 2013 7:00 pm

IVE OFTEN WONDERED HOW ENGINE ANGLE UP OR DOWN EFFECTS TORQUE ROLL. ANY THOUGHTS?

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Re: Interesting video about gyroscopic force

Post by MonsterMudfish » Mon May 20, 2013 9:05 pm

:scratch: :scratch: :dontknow: :dontknow: :scratch: :scratch:
KCCO

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Re: Interesting video about gyroscopic force

Post by glades cat » Tue May 21, 2013 9:16 am

Here's another good video on Gyro Effect on Aircraft Dynamics. It shows the forces acting as a wheel/propellor changes direction.
Vertical forces act on the craft as a boat turns left or right.
Correct me if I'm wrong, but it seems as if a left turn on a left-hand rotation propellor would tend to raise the stern and lower the bow and is proportional to the rate of change.
As an aircraft guy, I have to convert all this stuff to left-hand rotation.
No wonder our boats perform evasive maneuvers better in one direction than the other.

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Re: Interesting video about gyroscopic force

Post by WaterWalker » Tue May 21, 2013 1:47 pm

DuckBoat:

Your rotations are correct. Your pictures however show girlie looking props with good curves and tiny tips. Personally I have always liked larger tips. Curves are always good.

The following explanations apply mostly to slower speeds in displacement conditions. When going fast and in a solid planing condition, these forces have a much reduced effect.

With a Left Hand rotation (counter clockwise as viewed from the rear of the boat) propeller (generally a belt drive and/or an aircraft style) the operator is most likely centered or on the left side of the boat (Port side). Operator on the left works to offset the resulting right side down propeller torque roll. Turns to the left, against torque roll then are more stable and especially so in deep water turns at slow speeds.

With Right Hand rotation props (Most often gear boxes on automotive engines), the downward direction of the torque roll is on the left side of the boat and having an operator position on the left (Port side) adds to torque roll. Accelerating turns to the right in deep water are more stable.

In 180 degree emergency turns, I would take the direction that would likely miss the obstacle as first consideration. Otherwise I would turn in the direction generally most stable for my boat as explained above.

GladesCat:

A good video on gyroscopic forces.

I know you are correct that gyroscopic forces on a LH rotation prop (as viewed from the rear) raises the transom in a left turn and lowers it on a right turn. With my dyslexia, I had checked it in real time with my hand spun toy gyroscope the other day as I made the earlier post.

Summed up, the discussion above would seem to defy logic. It states that to turn away from the heavier side of the boat is most stable and one wound think the boat should heel over to the outside heavier side in such a turn. In reality though this is not the reaction that happens. The reason why the boat does not heel over can also be explained.

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Re: Interesting video about gyroscopic force

Post by CarMotorBarge » Tue May 21, 2013 10:31 pm

WaterWalker wrote:DuckBoat:

Your rotations are correct. Your pictures however show girlie looking props with good curves and tiny tips. Personally I have always liked larger tips. Curves are always good.

The following explanations apply mostly to slower speeds in displacement conditions. When going fast and in a solid planing condition, these forces have a much reduced effect.

With a Left Hand rotation (counter clockwise as viewed from the rear of the boat) propeller (generally a belt drive and/or an aircraft style) the operator is most likely centered or on the left side of the boat (Port side). Operator on the left works to offset the resulting right side down propeller torque roll. Turns to the left, against torque roll then are more stable and especially so in deep water turns at slow speeds.

With Right Hand rotation props (Most often gear boxes on automotive engines), the downward direction of the torque roll is on the left side of the boat and having an operator position on the left (Port side) adds to torque roll. Accelerating turns to the right in deep water are more stable.

In 180 degree emergency turns, I would take the direction that would likely miss the obstacle as first consideration. Otherwise I would turn in the direction generally most stable for my boat as explained above.

GladesCat:

A good video on gyroscopic forces.

I know you are correct that gyroscopic forces on a LH rotation prop (as viewed from the rear) raises the transom in a left turn and lowers it on a right turn. With my dyslexia, I had checked it in real time with my hand spun toy gyroscope the other day as I made the earlier post.

Summed up, the discussion above would seem to defy logic. It states that to turn away from the heavier side of the boat is most stable and one wound think the boat should heel over to the outside heavier side in such a turn. In reality though this is not the reaction that happens. The reason why the boat does not heel over can also be explained.

David Wine
I disagree with the idea that turning against the torque roll is more stable. With everything else being equal, it is safer to turn into the torque roll under heavy acceleration because you are less likely to roll the boat. Take my deckover for example. It has a gearbox. When I turn hard left under heavy acceleration, the torque roll is pushing to the port side of the boat while the inertia of the boat is pushing to the starboard side (outside edge of the left turn). These 2 forces partially cancel each other and lower the chances of rolling the boat.

When I turn to the right under heavy acceleration, the torque roll is still pushing to the port side of the boat and the inertia of the boat is also pushing to the port side of the boat. These 2 forces don't cancel each other and you increase the chances of rolling the boat because of the higher force to the outside edge of the right turn.

This same logic is also why it is easier for a gearbox boat to turn left than right. It is easier to get the boat to tilt to the left (port side) for a left turn and more difficult to get the boat to tilt to the right (starboard side) for a right turn.
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Re: Interesting video about gyroscopic force

Post by Wild Bill » Tue May 21, 2013 11:07 pm

CarMotorBarge wrote:DuckBoat:


I disagree with the idea that turning against the torque roll is more stable. With everything else being equal, it is safer to turn into the torque roll under heavy acceleration because you are less likely to roll the boat. Take my deckover for example. It has a gearbox. When I turn hard left under heavy acceleration, the torque roll is pushing to the port side of the boat while the inertia of the boat is pushing to the starboard side (outside edge of the left turn). These 2 forces partially cancel each other and lower the chances of rolling the boat.

When I turn to the right under heavy acceleration, the torque roll is still pushing to the port side of the boat and the inertia of the boat is also pushing to the port side of the boat. These 2 forces don't cancel each other and you increase the chances of rolling the boat because of the higher force to the outside edge of the right turn.

This same logic is also why it is easier for a gearbox boat to turn left than right. It is easier to get the boat to tilt to the left (port side) for a left turn and more difficult to get the boat to tilt to the right (starboard side) for a right turn.
[/quote]

Yeah I preferred spinning my gearbox boat to the left as well :D

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