Electric straightlines in California this weekend

[Anders_Martinelle]

Ian, you just need to swing a Octura 2170 with 6,9" cup at 27000rpm ;D and that will give you 120mph +............

Easy ;D ;D ;D ;D ;D NO!!!!!!

Anders

 

[Ragged Edge]

When Joerg blew off he had a bad line and turned left to avoid hitting the bank. The blow off was the best choice. OUCH!!!!!!!!!

 

[rcrdps]

So it wasn't really a blow off? More of a trip? That's a good thing. That means all he has to do is rebuild it the same way and bring on the power!! His setup seems to be scalable. With most setups you have to start giving it less lift the faster you go. With his, it adjusts itself.

Anders - I wasn't trying to say it's easy..... , but judging by the videos, those that are already doing 100+ can probably get a little more with some prop tweaking. Andy Brown has already hinted that he can get more speed. Is he going to get it from the engine? Running higher nitro? From what I've read, he's already at the max for that. I haven't seen any videos where they drug for a while trying to get the prop to catch......or seemed to overrev out on the straights. They seem to have plenty of "grip" because of their diameter. That's the way the Octura props are made. They're meant mostly for oval type racing where acceleration is key. Obviously, Andy knows his props. I think that's where his gains will come from.

Gene

 

[Ragged Edge]

The boat was not badly hurt, a bit of work and it would be ready to run again. According to Arne the boat coming apart was something they had planned for and hope would happen in a crash. Much like an Indy car. A very good thing to think about at those speeds. He had a spare boat though. It happened so quick and it did not appear to have left being on step, so rather than a trip I think the left rudder caused the right sponson to lift and the rest was history. It happened to Dennis and myself as well.

 

[Ian Inverarity]

Anders,

When you say 6.9" of cup, how do you measure tht? Ie what angle is used on the pitch guage when you measure 6.9" of pitch? Because of the pitch progression of props, such a measurement is very dependant on the angle over which it is measured. ;D

I have seen 27000 rpm on the tacho with my A-90HP once...... on the starting stand!

Nitrocrazed racing: Oops, dont hold the trigger down for so long....

 

[Ian Inverarity]

Gene,

When I calculate the tip velocity I am calculating purely the tangential speed due to rotation. I suppose the vector product including forward speed might be more appropriate!

With the nitro engines there are limitations on what revs can be practically used. Flow limitations will determine a range in which the engines will tend to make best power, and I would bet that most SAW nitro setups actually rev well beyond peak power.

My point was with the rev range that nitro engines use it will be difficult to get up to the tip speed that the JAG boat used. To run well at 33000rpm I think the nitro engines would need cylinders 3.5cc in size, thus a 4 cyl motor to make 14cc! ;D

Nitrocrazed racing: Imagine the sound....

 

[Ian Inverarity]

Doug,

I think I can see why the rearward CG/ground effect tub setup would be desirable for a SAW boat. The ground effect should keep the tub very stable I would have thought. But considering oval racing boats and rough water I would guess that such a setyup would not work due to waves disrupting the ground effect.

Is this a common type of design for electric SAW boats? What about oval racing electric boats? I am wondering if the design principles would be worth looking at for oval racing. At a guess such a setup would not launch with a nitro engine due to the load on the prop.

Ian.

 

[RBidwell]

Doug you are right about the ground effects built into this hull. Arnie designed it and I am sure he would be glad to share the design parameters with you. He described the wings in the back and the shape of the tub and what effects he was designing for. I believe he hit his design dead on. I am not an engineer so did not grasp alot of what he was saying but he is willing to share with anybody.

 

[Bob Kensill]

It sounds like that in order to go fast with a nitro boat,we will have to do one of three things. One would be to get the boat up to a higher speed during launch,but before the prop hit the water. The Japanese tether boaters use a bungie launch system. Another way would be to make the prop cavitate more and then grab after the boat had built up some speed. Forcing air at the prop would help. The third way would be to have a two-speed drive system that would allow the boat to get up to speed and then "shift" to direct drive. I prefer the last choice and am working on this system.

Bob

 

[rcrdps]

Ian,... yeah, I understand the hp curve. Just didn't seem to me that they had much problem at the low end for SAWs. That's the best thing about electrics..... we have all the low end, so we can pull as big a prop as we dare, and won't have a problem getting it on plane. But for the high end, we want the same thing as ya'll. Least diameter we can plane with, so that we can use that power for more pitch.

We don't use Joerg's design for ovals or SAWS.........."yet". That why he has the record. ;D Seems to me that with wider sponson mounts, it would work for oval too. To me, that's the design we've all been looking for. We run riggers because they don't blow over as easy....... but that's kinda a problem. That means they use almost all hydraulic lift. We all know water is more drag than air. Regular hydros seek to overcome this, but in doing so are more unstable. The better you run it, the more likely you'll blow off. Run a little faster and you will. With his design, you get the air lift and it adjusts to your speed. I think we will start seeing this more often. I would think to overcome the "taildragger" with nitro, you could just stick those little sponsons back there like you do anyways. Once up to speed, it lifts off of them. As far as ground effect and waves go, I don't think it would be any different than a conventional hydro. They ride in ground effect too.

Gene

 

[Ian Inverarity]

Bob (krpnova)

I thought of using a 2 speed type gear transmission from a 1/8 scale car with a 21 motor. I didn't really look into it that much, but from what I could see the ratio would be too low, ie the prop too slow with the standard ratios available.

Another possiblity to allow the launch of larger props and possibly higher speeds would be to use systems to control the power band of the motor better, ie using a system to change the tuned pipelength, back-pressure and mixture dependant on revs and speed. But these systems would also add weight, which is a problem for SAW boats! :-

I have had thoughts about the bungee system before too! A little tricky, but could work enabling the launching of props with higher leading edge pitch. But such a system could be a little scary if it goes wrong..... And hooking up a running boat to a primed big rubber band is not something I would like to be doing.... ;D

Ian.

 

[Ian Inverarity]

Gene,

The SAW nitro boats have little problem launching because the hulls are designed to enable them to do this, are made very light, and because of the engine setup. I am reasonably certain that most nitro setups rev way past peak power because if they were setup so max power occured at the revs for top speed then the power curve would dictate that the boat would not be able to get there! :-

While there probably is some ground effect involved with conventional tub designs, the modern trend in nitro riggers is towards very narrow tubs, so I would say the the ground effect would not be as significant as it is on the JAG boat.

At lower speeds conventional riggers do get most of their lift from hydrodynamics, which is good in a way because relying on aerodynamic lift makes the boats sensitive to pitch and wind conditions, so not using aero lift means these things can become less of a factor. But at the very high speeds the aerodynamic lift becomes significant again. Air has to flow out from under the sponsons, and I am sure that sponson and hull design could get significant benefits from some moving ground plane wind tunnel testing investigating this flow and modifications that could be done to improve stability.

I am guessing the primary aim of the JAG design in relation to its CG and ground effects would be stability at high speed. But for oval racing boats, I would guess that waves coming through would destroy this ground effect and the back of the boat would drag in the water.

I guess the only way to really find out is try to make such a boat into a oval racer! ;D

Ian.

 

[TimD]

Ian + Bob K,

What about using a clutch - possibly in conjunction with a 2 speed. This will allow the engine 2 pull sufficient rpm before the prop was engaged and get over the low speed launch problem.

I doubt a centrifugal clutch would be up to the task - perhaps a mechanical "dog clutch" or similar ???

Tim.

 

[Andrewg]

Nitro crazed

the amps were no where near 150. Dicks reference to the controllers relates more to an electric motor drawing most amps at 0 rpm - so for a .2 seconds or so the motor could be ripping maybe 150-190 amps if the cells will supply them - this can heat the controllers sufficiently so that under acceleration they just cant stay cool and pop their lot or burn.

BTW electric brushless have been run at over 100,000 rpm... the electric plane racers regularly run theirs up in the mid 50,000- 60,000 rpm

An interesting comparison in a 12 cell mono and a 3.5 mono - very close for a hacker powered 26" Maus and Seaducer 3.5 CMB - but electric runtime is not there .... yet, maybe by the end of summer

Electric stuff is just at the beginning. The motors like nitro are not going to leap up in efficiency but the cells will.

There are already lithium technolgies giving much 2.5 times the duration and weighing about 1/2 as much as current NiMH technology but they are expensive and illegal for racing

The good news is the real costs of the Lithiums are declining rapidly.

Ultimately it seems at the moment we will see a convergence - fuel cells running electric motors. Think about a IC fuel tank feeding an motor with more than twice the energy conversion rate.

I have already seen a minature fuel cell making an 80 watt output - that was a couple of years ago. If these come on line we are going to see some stuff which will blow us all away.

 

[Ian Inverarity]

Tim,

Well, as far as I know a centrifugal clutch will slip and burn out of it is wet or oily, so that would be a problem. And a 'dog' clutch, by definition has no slip, which means the engine would free-rev up to the engagement and suddenly engage at 15000rpm or whatever! Not going to work....

Some sort of mechanical plate clutch or maybe a sealed version of the centrifugal clutch might work. Or maybe a torque converter! ;D

Nitrocrazed racing: Anyone got a hi-stall for a 90?

 

[Ian Inverarity]

Andrew,

I dont doubt the potential at all! ;D You are preaching to the converted! (well sort of, I am not about to go electric yet)

I am trying to get a handle on the amount of power that the JAG boat or similar would have to try to understand why it is so fast. Power is not the only factor in SAW speed at all, the two fastest nitro records in Australia were set with near stock or stock motors. But from my calculations the power that the JAG boat would have would be around the same or less than a good 90, albeit in a totally different rev range.

I agree that in their current form the nitro motors are not going to leap up in efficiency, but with development significant gains could be made. Just look at F1 car engine technology, the 3.5 litre V10 etc of '89 vintage revved to around 14000 rpm and made about 600hp, now the 3 litre V10's rev to 19000rpm and make close to 900hp!

Without the cubic dollars that are spent in F1, even a 50% increase in power like F1 would be hard to imagine from the nitro motors in their current form, altho if someone was willing to sacrifice the engines and money, I do think some super light, very short lived SAW nitro motors could make a lot more power. Our engine rules are not at all restrictive tho, so that if people were willing to put in the time and effort, things like turbochargers etc might be able to improve the power out of sight! Like the 1200hp 1.5litre F1 engines of the mid 80's....

Cant see it happening tho! What might be more useful is some multi-cylinder engines to increase the revs available. These would be heavier and more expensive tho.

Maybe some of you electric guys should come over to the nats in Adelaide and put on a demo for the nitro guys! ;D

Ian.

 

[Anders_Martinelle]

Ian, i buy my props from Andy and i think the put the cup on the last 25% of the blade.

It`s always easier to buy them done then to sitt there and not have a clue.

Even so that`s not the right way to learn how to get the speed in a prop.

I think Andy used 7,4" cup when he ran 119,8mph...

What he uses today you can only guess but it`s close to that...

Anders

 

[dale]

WELL heres my two cents, 115 mph thats cool but what dose he get two passes then the batteries go flat ??? charge all day for that plus the cost of a good motor,speed control,batteries thats got to hert the wallet, but i would not mind seeing the big speeds nitro smells better than burning electronics.

 

[Dan Chase]

WELL heres my two cents, 115 mph thats cool but what dose he get two passes then the batteries go flat ??? charge all day for that plus the cost of a good motor,speed control,batteries thats got to hert the wallet, but i would not mind seeing the big speeds nitro smells better than burning electronics.

Dale, actually he did 122mph pass and the average of the 2 passes was 120.7mph, the fastest pass was his second. The initial outlay of cash is higher for fast eclectics, but we don't have to keep buying fuel all year, I have batteries that are 3 & 4 years old I'm still using. It takes on average 30-45 minutes to charge a pack.

I can't argue that nitro smells a LOT better then burnt electronics!

 

[Roy Munoz]

I got to see the vido of this record run last night and all I can say is W O W They were back to back runs...