Model Boat Mayhem

Technical, Techniques, Hints, and Tips => Tutorials & "How Tos" ... => Topic started by: GG on November 10, 2019, 12:24:24 pm

Title: Simple RC Submarines (part 1)
Post by: GG on November 10, 2019, 12:24:24 pm
Another item that was going to form the basis of a magazine article but I'd rather it not go to waste.

Radio Controlled submarine models do represent something of a challenge to the average modeller.  It not hard to see why this is so since they do appear to be expensive, full of more complex items than the usual RC model boat.  Plus, any tiny failure or mistake that in a boat model might just leave you with the embarrassment of having to ask a fellow modeller to push you back to shore but, with a submarine model it could disappear and be lost forever......

However, there is always the 20/80 approach to this part of our hobby, that is 20% of the cost/effort which can still give you 80% of the fun.  This refers to the Dynamic Diving type of RC submarine model.  This is where the forwards motion drives the model underwater and if the motor stops, the model should resurface by itself.  These are often decried as not "true" submarines and can be tricky to keep submerged all the time.

I'll have to agree with the first point if you consider the ability to remain stationary underwater and out of everyone's sight as essential.  But, with a little cunning the latter problem of depth keeping can be overcome as a series of five such models has proven, photos of two attached.

The first thing is to realise that dynamic diving models need very little buoyancy if they are to work.  This means that they should float with their decks almost awash, Fig 1.  This may worry some but the volume of water displaced when the decks and conning towers submerge ought give you enough extra buoyancy to ensure the model will "pop back up".  Ballasting trials in the bath should give you this confidence.
Glynn Guest 
Title: Simple RC Submarines (part 2 )
Post by: GG on November 10, 2019, 12:40:18 pm
Power up the motor and the model starts to accelerate forwards.  The Rear Hydroplanes have a positive angle and the water flowing around them will create a lift force that raises the stern and in so doing, forces the model to adopt a bow downwards attitude, Fig 2.

I usually use just the rear hydroplanes on my models rather than bow hydroplanes.  Experience has taught me that they are less vulnerable to damage and it's something less to get snagged with when cruising submerged.
Glynn Guest
Title: Simple RC Submarines (part 3)
Post by: GG on November 10, 2019, 12:51:03 pm
The model should start to gently slide underwater.  If it doesn't then adjustments to the trim, get it lower in the water when stationary and/or increase the hydroplane angle. If these do not work then more thrust might be needed but not to the point where disappears from view in a second!

Now the model has two forces pushing it underwater, the vertical component of the propeller thrust and the water flowing around the angled hull, Fig 3.

Left to it's own devices in this state the model would continue to dive and leave you with the task of adjusting the hydroplane angle to make both downwards forces to perfectly match the upwards buoyancy force, not an easy job nor would it be very stable.
Glynn Guest
Title: Re: Simple RC Submarines (part 1)
Post by: GG on November 10, 2019, 01:09:33 pm
Here's the clever bit!

I used a vertical aerial wire (with 27 and 40 MHz RC gear 'cos 2.4GHz doesn't work so well in subs).  A plastic coated steel wire (as used by the plastic model fraternity) had to be used since the aerial must be insulated from the water.  This was to give me some indication of where the model was when submerged and my original plan was to fit a "drag plate" on the wire to stop it going too deep. The idea being that as the drag plate entered the water it would cause the model to change its attitude from bows down to bows up.

It was a great pleasure to discover that the drag plate wasn't needed and the resistance caused by water flowing around the aerial was enough to do this, even better, with a little trimming of the hydroplane angle this gave a stable underwater cruise.  If the model goes deeper then the aerial creates more drag and lifts the bows, should it rise too far then the aerial drag is reduced and the hydroplanes push the bows down, Fig 4.  When correctly set up you can leave the hydroplanes alone and just watch the aerial (maybe oscillating a little and slowly) as the model cruises submerged.

As I said at the start, maybe not a perfect submarine but 80% of the fun for 20% of the cost and effort..?

Glynn Guest

Title: Re: Simple RC Submarines (part 1)
Post by: TheLongBuild on November 10, 2019, 04:50:13 pm
Interesting article, glad you posted it here rather than not having printed at all.
Title: Re: Simple RC Submarines
Post by: GG on November 12, 2019, 01:49:59 pm
Thought is might be worth adding these two photos of the Nixie model.
The first shows it at rest, you really have to trim them to have the decks almost awash.  The second shows what you see when the model is properly trimmed and cruising submerged.
Glynn Guest