Rudder placement on Hydros & riggers?

[paulwilliams]

I've run the rudder on both sides, tbh never noticed any difference. On the left, the rudder is slightly further away from the turn fin, and so has more leverage - dunno if this makes any difference...

EDIT:
Another variable is where the rudder blade is in relation to the propeller thrust cone, in other words whether when turning the rudder presents the leading or trailing edge to the water flowing off the prop. This could either magnify rudder effect, or reduce it due to running in turbulent water, or have no effect whatsoever. We need a test tank with high speed video and stroboscopic lighting. Perhaps a winter project for someone... :-)

Paul

[Fluid]

Putting the rudder far to the left - which you can do with most hydros due to their wider transoms - gives it more leverage to "load" the right sponson, helping to keep it down in the turns. But this makes the boat far more sensitive to turning left, and most hydros will respond to excessive left rudder by rolling over.

Riggers are usually lighter, wider and have lower CGs than full-bodied hydros, so loading the right sponson is far less critical - prop torque from the big wheels they spin usually does enough of that. The hooked turn fins in use today also make a big difference holding the sponson down in turns. Putting the rudder on the right works fine and reduces the usual problems with applying left rudder. Too, the rigger transom is so narrow that little is gained with a left rudder placement anyway.

I've run the rudder on the left and right of the same hydro hull and saw little if any difference. That boat had a pretty narrow transom however, and a wider transom might have seem more difference. Whatever you do, don't put the rudder right behind a surfacing prop. You'll get poor tracking, hunting and excessive drag....and too much rudder response.


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[AndyKunz]

Sport/Scale = Left, Rigger = Right.

Both kinds are hydros :)

Because it makes the internal layout easier.

And because they're generally faster that way on models, but not necessarily on full-scale (which prefers to put them on the same side as the skid fin, like a rigger).

Reynolds and Maxwell and vapor pressures and stiction and all kinds of neat things don't scale up.

Andy

PS - 50 MPH for a 1/12th scale boat is NOT a scale speed of 300 MPH because you have to use a square rule, not a linear one.

[HOTWATER]

I kind of like the fact that when the rudder is on the left, the servo pulls for right hand turns instead of pushing...

[Simon.O.]

My small rigger has it on the left
4S rigger on the right

24" shovel hydro on the left in front of the prop

All of these boats will track straight with the rudder at zero and will change direction like a pinball.

For oval hydro racing the rudders is often on the left.

[raptor347]

The best riggers I know of all run rudders on the right. The rudder is used less for ride attitude in the corners on a rigger, especially if you run rear shoes or a ride pad. Also, you can get a better turn fin placement on most riggers. The riggers I've seen with rudders on the left tend to tighten up in the turns as the right sponson get loaded, in the worst cases they spin or wind in.

The fastest sport hydros I of know run rudders on the left mostly because it loads the right sponson in the corners which aids in corner stabilty and makes up for less than optimal turn fin placement.

None of this matters if the basic boat design sucks.

[crabstick]

TBH I have always run rudder and turnfin on the right on riggers and hydros, and the boats have turned both directions well, given they dont turn left as well, but do turn, my 1/8 nitro I used to run had both on the right and would turn either direction without wanting to dig a sponson, I normally offset the driveline a little to the right also so im not sure if that counters it ?? It would also trackstraight with no rudder input. Some of the 1/8s in out club wont turn left at speed at all its over she goes if any attempt is made, which can happen avoiding dead boats in a heat race.

My Whiplash 20 for P restricted, that is in the build at the moment I am thinking I will probably go right also, as its what I have had work for me in the past.

thats my three fiddy.

[Punisher 67]

Andy

PS - 50 MPH for a 1/12th scale boat is NOT a scale speed of 300 MPH because you have to use a square rule, not a linear one.

Please no offence Darin but Andy beat me to the scale speed issue

[Darin Jordan]

Please no offence Darin but Andy beat me to the scale speed issue

No offense taken... apparently one of the mathmatical details I missed during my studies!

I still stand by the point I was making... 200mph or 300mph... directly scale up one of our models and it's not going to work very well...

[Punisher 67]

No offense taken... apparently one of the mathmatical details I missed during my studies!

I still stand by the point I was making... 200mph or 300mph... directly scale up one of our models and it's not going to work very well...

Water to models is a lot thicker material than to there full size counterparts , you can see this with anything tiny . throw it on water and it cannot break the surface tension

[Blackjack-sven]

Guess I'm the only one who put the rudder on my hydro on the right. LOL
I have only seen riggers run straight lines and therefore it would make sense that it wouldn't matter. I don't run riggers so I wouldn't know. My guess though is that if the boat only turns in one direction then the rudder should be on the inside of the turn, regardless of hull type.

[Blackjack-sven]

I still stand by the point I was making... 200mph or 300mph... directly scale up one of our models and it's not going to work very well...

To add to this. As a seasoned rc car racer, I know that scaling up an rc car would never work due to the physics involved. The A-arms on a full sized version of a buggy would just snap clean off due to weight and impact.

[Darin Jordan]

Guess I'm the only one who put the rudder on my hydro on the right. LOL

You aren't the only one... My older DH shovel that I ran in O-Sport Hydro a few years back (painted up like the '75 Oberto) originally had the rudder on the right... Worked OK... The boat was much more drivable and faster in the turns, however, when I moved it to the left... I had the boat setup so I could swap sides in about 5-minutes... so I tested it both ways... Left side won out...

[egneg]

On my Campbell classic hydro the rudder is on the right (as per instructions) and I have seen them done this way quite a bit.

[HOTWATER]

The best riggers I know of all run rudders on the right. The rudder is used less for ride attitude in the corners on a rigger, especially if you run rear shoes or a ride pad. Also, you can get a better turn fin placement on most riggers. The riggers I've seen with rudders on the left tend to tighten up in the turns as the right sponson get loaded, in the worst cases they spin or wind in.

The fastest sport hydros I of know run rudders on the left mostly because it loads the right sponson in the corners which aids in corner stabilty and makes up for less than optimal turn fin placement.

None of this matters if the basic boat design sucks.

I think that Brian has riggers down to a science! I am all ears to his advice (as far as riggers go).

Also, good feedback Darin! As Diego has mentioned...your words and theories are welcome to me as well!!

Some very good advice here guys...

-Kent