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Heeling

R/C Submarine modelers

Heeling

Postby modelnut » Sat Oct 18, 2008 5:17 pm

Hello!

I have just seen a video of a dynamic diver that inspired me even more to try building an R/C sub. But in the video the boat heels noticeable away from the vertical when turning --- it rolls in the direction off the turn. A friend says that this is due to control surfaces that are too small (i.e. diving planes.)

Is this true?

With the cost of scratchbuilding an R/C sub being what it is I would want my first to have as few avoidable flaws as possible.

What can be done to keep the sub stable in a turn?

-Leelan
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Postby JWLaRue » Sat Oct 18, 2008 7:05 pm

Leelan,

My experience is that a roll in a turn is due to either the torque from a prop running at high speed and/or not enough weight down in the keel.

Dynamic divers do need to run faster in order to maintain any kind of submerged depth, so getting one to not roll in a turn is going to be a trade-off. You could consider trimming the boat such that its surface trim is closer to the water, meaning that less speed is needed to drive the boat down. Placing that weight down in the keel would also be a plus.

-Jeff
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Postby Sub culture » Sun Oct 19, 2008 5:54 am

Leaning in to a turn is caused by the conning tower/sail. As the rudder yaws the stern of the boat, the sail/tower- which is in effect a fixed control surface- increases it's angle of attack resulting in an increase in pressure on one side- this will tip the boat over to one side.

Some boats, like the Skipjack class are particularly prone to sail induced roll.

In a lot of cases the roll is desirable, as it enables the stern planes to help bring the boat around in a tighter arc.

You can counter it by increasing the stability of the boat, by adding weight in the bottom, like Jeff says, or you can reduce the sail area or add a counter sail underneath the craft.
'Why are you staring at an empty pond?'

Want to dive your boat in crystal clear water? Then you had better Dive-in- http://www.diveintomodelsubmarines.co.uk
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Postby modelnut » Sun Oct 19, 2008 10:50 am

Thank you!

That's what I thought. More ballast or more keel, nothing like a sailboat's keel of course, just something to keep the boat centered.

-Leelan
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Postby JWLaRue » Sun Oct 19, 2008 1:25 pm

Sub culture wrote:Leaning in to a turn is caused by the conning tower/sail. As the rudder yaws the stern of the boat, the sail/tower- which is in effect a fixed control surface- increases it's angle of attack resulting in an increase in pressure on one side- this will tip the boat over to one side.


Ahhh...but I have (also) experienced the rolling effect even with subs running on the surface......

-Jeff
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Postby Sub culture » Sun Oct 19, 2008 1:44 pm

JWLaRue wrote:
Ahhh...but I have (also) experienced the rolling effect even with subs running on the surface......

-Jeff


Single screw boat with a very low metacentric height?

Torque roll caused by the prop. You can offset that by increasing the metacentric height, or by shifting weight to one side to counter the torque.

Sail induced roll can be much more significant however.

Andy
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Want to dive your boat in crystal clear water? Then you had better Dive-in- http://www.diveintomodelsubmarines.co.uk
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Postby JWLaRue » Sun Oct 19, 2008 2:02 pm

Exactly.
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Postby modelnut » Sun Oct 19, 2008 6:34 pm

From Mike Crisafuli's site:
Leelan Lampkins is in the process of refining his Nautilus. The obvious difference is the redesigned tail. Noting that Aronnax thought the monster might be a giant narwhale, Leelan was looking for a surface profile more like a whale than a shark. The new tail fin is normally below the waterline and in any case not obvious even when rolling seas expose the propeller.


Here is the design I am aiming for:
Image

Of course, I have a lot left to learn before my boat gets wet if she ever does . . .

-Leelan
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Postby Sub culture » Mon Oct 20, 2008 1:37 pm

You shouldn't get any problems with sail induced roll with that boat.

Rudders look a little on the small size, I'd increase the area by about 30%

Andy
'Why are you staring at an empty pond?'

Want to dive your boat in crystal clear water? Then you had better Dive-in- http://www.diveintomodelsubmarines.co.uk
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Postby modelnut » Mon Oct 20, 2008 2:39 pm

Increase size, check!

Can't expand along the vertical axis. Would drag on the ice or break the surface. Would expanding along the horizonatal axis work?

According to the plan. As they are now, the lower rudder is roughly 3 x 2.5 inches and the upper rudder is mostly there for a propeller guard.

The sub's main hull will be 38.25 inches long with a diameter of 4.5 inches. She will be 72nd scale.

May finally put the rudder aft of the propeller. Haven't made up my mind yet.

What would you suggest? And what dimensions for the rudder?

-Leelan
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Postby Sub culture » Mon Oct 20, 2008 3:04 pm

I'd at least make the existing rudders fully flying i.e. no fixed forward part as shown on the drawing.

Andy
'Why are you staring at an empty pond?'

Want to dive your boat in crystal clear water? Then you had better Dive-in- http://www.diveintomodelsubmarines.co.uk
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Postby modelnut » Mon Oct 20, 2008 3:31 pm

Cool. I have a SKIPJACK hull that is serving as the model for my build. (It is in the same scale so there is less fudging.) The SJ has fully flying rudders etc.

Sanding the main hull now. 8)

-Leelan
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