2012 NAMBA SAW Time-Trial - March 2-4, Legg Lake, CA

[RaceMechaniX]

An identical boat was stretched out to accomodate a gas motor. I've never run this boat, but expect it will run right around 100 with the right prop.

[RaceMechaniX]

For the T-Hydro, I thought powerful and a larger footprint would be a good start. I designed the model to take a 2280/2260 or 1527 with either a 32.200 or Hydra Ice. Everything was laid out inline, one battery between the booms, the second behind the rear boom, then the speedo and finally the motor. In order to get a decent driveline angle I had to add length to the rear. The overall length was just shy of 48" limited by the birch ply available.

Needless to say the boat was pretty heavy on 8S or 10S and drew a lot of current. I machined a 1/4 ball bearing strut and used a CMD rudder bracket with a modified kitchen knife. We ran several passes over 110, but nothing signifigant. The rigger was quite tail heavy so slow speed manuvering was difficult as the prop wanted to dictate the direction not the rudder.

Here is a video of the T-hydro running on 8S. I think a duck tripped the lights, the speed was probably closer to 110 instead of 119mph.

http://youtu.be/74iTgr7XaqE

The back-up pass had too much rudder to avoid the island

[RaceMechaniX]

After the T-Rigger I decided it would be best to stick with a lighterweight design with less motor and battery. Again the battery is placed up front between the booms, speedo right behind and the motor in the center of the tub. 3/16 cable and collet were used with a speedmaster strut and CMD rudder bracket. The hull was sized for 6s 5Ah or 4.2Ah cells and motors between 2250/2260 or 1515/1527.

The design was birch ply with carbon reinforcement again and carbon lids to cover the openings. Sponson booms were carbon tube within carbon tube. The outer tube being glued into the tub and a homogenous tube running across the entire width. Notches in the outer tubes with zip ties were used to secure the booms in place. They held most of the time, but slipped several other times. Eventually I will make some lightweight clamps to secure the tubes together. A very simple design with the right balance of components. The sponsons were also very simple wood over foam with composite ride pads. I found a local laser cutter and made several different sets of sponsons. The set I thought would work the best were about 12 mph slower than the pair that set the record.

I also made the mistake of using primer prior to shooting with Klass coat yellow. After a couple crashed and one fire the yellow paint is mostly off. The cheap Krylon blue on the sponsons is holding strong.

Video of the run: http://youtu.be/giTKdP20mI8

I am worknig on the next revision now and should have her ready for fall.

[raptor347]

Documentation at it's best. You've more pics of the brand new boat than I have of the N2 boat (RIP) after 4 years of running it.

...and the planning for October continues!!!

[lohring]

Originally Posted by RaceMechaniX

An identical boat was stretched out to accomodate a gas motor. I've never run this boat, but expect it will run right around 100 with the right prop.

You need to go over 110 with that motor, and I'm sure you can with what's been learned about props since 2004.

Good luck.

Lohring Miller

[RaceMechaniX]

Perhaps Lohring if I put the HR motor in there intead of the HT. The design is smooth as a Cadillac on the water, but it really comes down to getting off the beach with 10" of pitch or more. As you know the HR's don't have the grunt of Zenoahs down low, but I do have the RPM with a limitied amount of U2 left which I hoard just for this motor. I would hate to sink and loose this motor though. That is what really prevents me from running it in the SAW rigger. I consider it unobtanium with the fuel.

TG

[RaceMechaniX]

Originally Posted by raptor347

Documentation at it's best. You've more pics of the brand new boat than I have of the N2 boat (RIP) after 4 years of running it.

...and the planning for October continues!!!

I know better to take plenty of pictures before the boats ever hit the water as they never come back in better shape! As witnessed by the paint peeling off the Q Hydro........


I did find two pics of your P boat.......

[JfromJAGs]

Thanks for the detailed documentation. The basic running principle seams very similar to that of the JAE riggers - very opposite to what we did for the NiMH SAW riggers.

Concerning the booms you could try tape, relatively hard office tape. Some layers around the thiner tube to prevent the booms from moving sideways, use as many layers as it needs to get to the same thickness as the thicker tube. Then some more layers overlapping the just added layers and the thicker tube.

In addition I use a 1-1.2mm steel pins which go through both tubes and lock them from any movement. Thin enough to not stress the material, thick enough to hold everything in place.

Joerg

[RaceMechaniX]

Joerg,

The sponsons do resemble the block design of the JAE sponsons as they are very simple to make, however the AoA and afterplane are significantly different. I have access to a 60 Watt Epilog laser cutter for parts smaller than 24inx18in. So I made six sets of sponsons all with different AoA's and widths. I simply cut the sides, bottoms and tops from birch ply and glue onto a foam core and then add a carbon or G10 ride pad. Very simple and only costs about $25 per set of sponsons with unlimited changes to AoA, widths and shapes. They are not pretty and not as slippery as I would like, but work great for testing concepts.

As for the booms, we did end up using radio box tape as a butt joint to keep the booms from slipping. In fact in worked quite well in a few crashes allowing to the booms to slide with the sponsons absorbing some of the energy. And although the booms are very easy to replace if broken, it's much easier to cut the tape off and slide the booms back over and reapply the tape. There are threaded inserts in each of the boom ends with screws and fender washers to keep the sponsons from sliding off completely. Some kevlar string is epoxied to the inserts running inside the booms from side to side to hopefully prevent both booms from breaking and loosing connection for floatation.

IMO what sets the two design apart is the tub aero characteristics. I believe your tub along with Chris Harris', Mike Bontoft’s & Gerardo Brandao's all add lift through the tubs shape in addition to the sponsons/ride pads and prop. Mine along with the teammates (Mark, Chris, Brian, Don, etc) all have neutral tubs that control lift with the sponsons/ride pads and prop.

Tyler

[JfromJAGs]

I can only speak for us, but for our boats you are right. With the heavy NiMHs we wanted to have lift from the tub - but also aerodynamic stability. We tried to "fly" the boats - which only works in a small window of speed for a given design and weight. So a pure LiPo boat would look a bit different compared to the older boats - but we would probably stick to the same principles.

Joerg

[Darin Jordan]

Originally Posted by JfromJAGs

I can only speak for us, but for our boats you are right. With the heavy NiMHs we wanted to have lift from the tub - but also aerodynamic stability. We tried to "fly" the boats - which only works in a small window of speed for a given design and weight. So a pure LiPo boat would look a bit different compared to the older boats - but we would probably stick to the same principles.

Joerg

I need to use YOUR principles to make my next M2 (1-cell, any motor), and N1 (2-cell, 17.5T ROAR STOCK) Hydros... Both could benefit from some additional lift...

[RaceMechaniX]

I agree and from my experience once I found a good AoA and ride pad width the speed window was pretty large, i.e. no bad habits were found going faster. Now the challenge is to reduce the load on the prop and increase efficiency to reach higher speeds.

Tyler

[lohring]

We worked a lot with ground effect lift enhanced with air traps. The advantage is that ground effect lift is a very sensitive function of height. The disadvantage is that the center of lift moves forward rapidly as height increases. That gives the classic hydro blow over. Where that movement doesn't matter it can be very effective.

Another of my favorite concepts is using air rudders rather than a water rudder for directional stability. They need to have a lot of area, so two rudders look better than one. The boat can be designed to partially lift it out at speed, but still use the water rudder for slow speed steering. Since air is 800 times less dense than water, air rudders designed for the higher speeds should have significantly lower drag. I've won bets on the negligible effect of streamlining the parts of the boat in the air. It's whats in the water that is critical. We increased boat speed more with water rudder changes than any other change.

Lohring Miller

[RaceMechaniX]

Lohring I would agree with your assessment, but in the same argument a wetted rudder is 800 times more effective at countering propwalk than an air rudder. Have you and Mike every tried running that gas rigger with a real short rudder and air rudders?

TG

[lohring]

No, but I think Joerg has. That's where I got the idea. Actually, the drag would be the same on an air rudder with 800 times the area of the water rudder, so my thought is you use the water rudder at low speed where you need steering and the fixed air rudders to hold the boat straight at speed. We always tried to get our boats to run straight by angling the strut. You can also offset the shaft. I'm not sure what is the best solution, but it's easy to adjust the strut angle.

Lohring Miller

[JfromJAGs]

Yes, we always used static air fins to stabilize the boats at high speeds, but we still needed a rudder to counter react the prop walk on startup and acceleration and to maneuver the boat at slow speed. Any rudder, air or water, will not work at high speed as long as there is no pivot point up front. We try to avoid such pivot points - like a turn fin or only a single sponson in the water - so from a certain speed on, the boat will (and shall) only go straight.

The biggest difference between 2004 (boat ran in a slight arc and hit the bank) and 2006 (boat ran dead straight) was the amount of strut offset. In 2004 the motor torque pushed the right sponson into the water, while the left one was flying. This made the boat turn to the right into the bank.

Joerg

[Christian LRK]

Wy Not thinking about counter running propellers at this powerlevel and speed like dragboats .As there are limited high pitched propellers on the market wy not turning x440 left and right hand at say 100000 rpm.Tip speed is ok and a motors are also to get .Possible also to use a lower speed outrunner with a 1:5 planatary gear from modelairplane but using it to rev up .At high speed you will also need no rudder in the water.I have testet also a torque counter propeller form modelhelicopter integrated in a airrudder ,so you can activ force the back of the boat against propwalk .i used a small one from align 250 heli with a little slowflyer motor to drive it.The propeller turn a constant speed and the servo controll the pitch ,left or rght ,so you can steer in all directions and can turn the boat resting in the water to do the back straight.No need of power from the main drive .