Best set-up for best cornering speed

[dwilfong]

John that is exactly what the new style winglets look like fletching on a arrow.

 

[Danny King]

Not trying to put words in David's mouth, but I think that the floating transom is the fact that it has two small sponsons under the transom

that are very shallow to the strut, about 1/4" above. This is much like a 3 point, but aids in launching bigger props! Better yet maybe Andy will comment, after all it is his design!

Don

That is correct. It is more "flying" then "floating"

 

[dwilfong]

Danny you have this setup on your boat?

 

[John Finch]

I got a new gas rigger last year that Don Ferrette built for me as a one of a kind build that was too touchy for me to drive through the turns. He likes the touchy rudder while I don't, so I moved the turnfin rearward with the slotted holes that allow adjustment on the turnfin. I ended up 3/4 of an inch more rearward than original setup and the boat drove the corners the way I like to drive it. So, turnfin forward = touchy steering as the rear of the boat swings around easily. move the fin rearward = not so easy to swing the transom around. Most readers here already know that but for those that don't, this example might help, because we also need to adjust our fast turning boats to our own driving style.

David ......What is the floating rear end on Andy's new SGX? Explain.

John

Hi John,

What was the relationship to the C/G and the trailing edge of the turnfin when you got it right?

Thanks, John

John,

1 inch from the trailing edge of the Dick Tyndall turn fun at water level to the CG with full fuel tank.

 

[Danny King]

Danny you have this setup on your boat?

Yes. My older sgx 45 has it and the gas rigger has it.

 

[John Finch]

Over a decade ago, maybe 15 years ago, I had 3 SG 40 boats that I experimented with for heat racing. I changed the rear end of the boat on all three boats several times and tried the center shoe, the center and sides, just the sides, the middle shoe deeper than the outsides and then outside and center same depth etc. I keep records on all my testing and I am into book number 17 after over 30 years of testing. I love to figure out WHY on everything. That is my thing. I also changed the recurve on the bottom of two of the boats. Without going back to the book I am pretty sure the best overall setup was Andy's stock setup for heat racing. Andy and John definitely have their boats figured out. I did get just a little more speed with less recurve but when I went to only 1/8th inch recurve on the bottom, the boat would stuff every now and then. My favorite fast cornering boat is a scratch built wide body hull that looks like a sport boat. I raced it as a sport boat before adding boom tubes up front to make it a rigger class boat. It has no rear sponsons and uses only ground effects and the prop for lift. No drag back there in the turns. That boat has been completely modified at least 5 times. If fact is it a combination of three boats that I cut up and pieced back together to make what it is today. Fun Fun Fun!!!! Dick Tyndall named it scrap lumber and the name has stuck.

 

[DON MAHER]

John,

I'm in the same frame of mind! I want to know WHY, not just HOW! So your scratch built boat is a true 3 point? Does it have a recurve or is it a true flat bottom?? How wide is the bottom???

Mark Grim and I have argued for 30yrs about witch is better, a flat bottom or as I like to say, a "kick up with training wheels! LOL

Don

 

[John Finch]

Don,

It is totally flat. Best boat to drive ever! I have experimented with many of these wide body hulls. The picture of the radar gun you see on my posts is a 123 mph pass with the flat bottom hull I set the sport hydro record with at 98 mph. It was a windy day when I set the record so 98 was the best I was going to get. Also, the gas engine built by Mike Butler for that awesome pass on glass water was short lived. The piston was set at Zero head clearance and one blow off of the water took care of that engine. The secret to that speed was no boat touching the water, no turn fin, a small thin rudder and as little slippage as is possible. Hard to get as you know for two complete 330 foot back to back runs. That sport hydro is one of the three boats I passed through the band saw to make my scrap lumber heat racer. If I kept all the boats I build I would have no room in my garage or house so I experiment, cut them up, re-use the hardware and radio and start another project. One thing I learned during the SAW testing with the straight bottom is if you have as little as 10 thousandths of an inch hook at the transom (opposite of recurve) you won't launch a big prop. That is all it takes to bury the front sponsons. I will have to measure the tub when I get home.

John

Home.....9 3/8ths

 

[John Finch]

John,

Have you ever tried leaving the turn fin forward, but reducing rudder throw and increasing rudder surface area (width and/or depth)? What I have observed while at races is that the boats that seem erratic in the turns have WAY too much rudder throw.

My personal set-up is such that the wheel on my radio turned to full peg makes that perfect pin-to-pin turn. I can't see a reason to have anything more than that.

Thanks. Brad.

Titan Racing Components

BlackJack Hydros

Model Machine And Precision LLC

Brad. Yes I do that and also search for the right amount of throw to get that pin to pin turn. I agree that most of the guys we race against that have difficulty running a straight line on the course or cut people off in the turn have way too much rudder throw on their boats. They just don't understand when you talk to them about it. They are so scared they won't have enough rudder throw if they get in trouble, but it is too much throw that gets them in trouble. If I help someone on the pond who is having issues driving, the first thing I usually do is reduce rudder throw on their transmitter. I like setting the servo horn with the linkage as close to the hub as possible for more torque and less throw with the rudder linkage just the opposite for max leverage rather than dialing it into the transmitter.

Checked rudder last night......I measured my rudder throw on the wide body rigger and full right rudder on the transmitter wheel only gives 5/16 th inch of rudder deflection.

John

 

[John Beardslee]

I got a new gas rigger last year that Don Ferrette built for me as a one of a kind build that was too touchy for me to drive through the turns. He likes the touchy rudder while I don't, so I moved the turnfin rearward with the slotted holes that allow adjustment on the turnfin. I ended up 3/4 of an inch more rearward than original setup and the boat drove the corners the way I like to drive it. So, turnfin forward = touchy steering as the rear of the boat swings around easily. move the fin rearward = not so easy to swing the transom around. Most readers here already know that but for those that don't, this example might help, because we also need to adjust our fast turning boats to our own driving style.

David ......What is the floating rear end on Andy's new SGX? Explain.

John

Hi John,

What was the relationship to the C/G and the trailing edge of the turnfin when you got it right?

Thanks, John

John,

1 inch from the trailing edge of the Dick Tyndall turn fun at water level to the CG with full fuel tank.

Thanks John, I'll bet your log also says you checked the C/G dry so you could see the variable as the tank empties right?

John

 

[stan simpson iv]

If you want to go fast thru the turn's,have low lap time's and you have been paying attention to oval records being set. The simple answer is build a JAE...

 

[Brad Christy]

John,

With a 1" wide rudder blade, that's over 17 degrees of rudder movement. I'm considerably under 7 and turning on a dime.

I'm going to say that, at the rear-most point of the rudder on my Crapshooter45, I've got less than an 1/8" of movement with the transmitter wheel at full right. I actually drill a new hole in the control horn on the servo so I can attach the clevis closer to the servo shaft, which allows for slower articulation of the rudder.

I'd bet that if you were to slide your turn fin forward and reduce your rudder throw, you'd get through the turns much faster. The erratic behavior your seeing is due to your exaggerated rudder throw, not the position of your turn fin.

Thanks. Brad.

Titan Racing Components

BlackJack Hydros

Model Machine And Precision LLC

 

[John Finch]

John B.

Yes John I have the dry number too on all my boats but that depends on how much fuel I use and how much I want to have extra for emergencies like jumping the start or running around a bunch of dead boats in rough water at slower speeds. My best setup is the widebody rigger because the tanks are saddled to the sides of the 5 inch rails right at the cg so the CG never changes full or empty.

Brad,

Wow, that is record trial type setting on your boat. That has got to be an awesome fast turning boat!

John

 

[Brad Christy]

John,

That/s not a record trials set-up. That's our heat racing set-up.

This thread was started to discuss set-ups for getting around turns the fastest. This is how we are making that happen. Adequately sized turn fin and rudder, width AND depth, and pushing the turn fin forward, with the CG slightly behind the CL of the turn fin.

Thanks. Brad.

Titan Racing Components

BlackJack Hydros

Model Machine And Precision LLC

 

[Terry Keeley]

Why do you think the JAE's turn as hard as they do? Look at where the turn fin is in relation to the CG...

 

[JRXHydros]

Why do you think the JAE's turn as hard as they do?

Ride, ride my see-saw,

Take this place

On this trip

Just for me.

Ride, take a free ride,

Take my place

Have my seat

It's for free.

 

[Christian Lucas]

Hi,

the reason that the JSEs turn good are that the sponson has no slip edge outside and the sponsonboom are so wide that the rigger can not easy roll outside . 1983 i build my saw electric rigger with similar wide and only straight cut sponson . at less speed it turn very good without turnfin . And with lower 2-4 degree angle of attace of the sponson it turn better and with high angle 5-7 degree it will stay hard on the watersurface getting no side grip.

But Brad Christy has the best. Place the turnfin forward of c.g. and you need only a smaler turnfin and a smaler ruder . You have to level it out that all the force are not to strong

 

[John Finch]

Brad,

I am running gas engines and the problem is my cg is now at one inch behind the trailing edge of the turnfin so moving the fin forward puts the turnfin further forward from the CG. That screws up the dynamics. I am thinking the gas boats I run put more weight behind the boom tubes than a nitro boat, so getting those dynamics correct on a gas boat would mean somehow getting the engine more forward in the boat. This is where the sport boat has an advantage over the rigger in that the engine can be moved more forward because there is no rear boom tube. That is the primary reason My fastest cornering boat is a wide body sport boat converted to a rigger with only a forward boom tube. I suppose I could move the front sponsons rearward to get the proper dynamics. I believe the crapshooter has already done that for your setup and with a lighter nitro engine you can be spot on.

John

 

[John Beardslee]

Brad,

I am running gas engines and the problem is my cg is now at one inch behind the trailing edge of the turnfin so moving the fin forward puts the turnfin further forward from the CG. That screws up the dynamics. I am thinking the gas boats I run put more weight behind the boom tubes than a nitro boat, so getting those dynamics correct on a gas boat would mean somehow getting the engine more forward in the boat. This is where the sport boat has an advantage over the rigger in that the engine can be moved more forward because there is no rear boom tube. That is the primary reason My fastest cornering boat is a wide body sport boat converted to a rigger with only a forward boom tube. I suppose I could extend the front sponsons more rearward to get the proper dynamics. I believe the crapshooter has already done that for your setup and with a lighter nitro engine you can be spot on.

John

Hi John,

Sounds like just a sponson design issue or turn fin mount issue to leave the rear boom in its place and get the c/g fin relationship where you like.

Thanks, John

 

[Grimracer]

Hi,

the reason that the JSEs turn good are that the sponson has no slip edge outside and the sponsonboom are so wide that the rigger can not easy roll outside . 1983 i build my saw electric rigger with similar wide and only straight cut sponson . at less speed it turn very good without turnfin . And with lower 2-4 degree angle of attace of the sponson it turn better and with high angle 5-7 degree it will stay hard on the watersurface getting no side grip.

But Brad Christy has the best. Place the turnfin forward of c.g. and you need only a smaler turnfin and a smaler ruder . You have to level it out that all the force are not to strong

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