Electric straightlines in California this weekend

[Ian Inverarity]

Anders,

I dont buy Andy Brown props, so I guess I will have to learn for myself! ;D But so far I have figured out there is a lot more to it than just trailing edge cup. I have measured more than 7.4" on props I have that dont go anywhere near 119 mph! 8)

Do any of the electric guys know if the 1945 used on the JAG boat was modified?

Ian.

 

[Kris Flynn]

if my information is correct, YEP...something like an Andy Brown one

 

[Anders_Martinelle]

Ian,you forgot to swing your prop with 27k rpm ;D ;D ;D ;D.

No your right it`s not easy but that is what you have to do.

I have not been over the 100mph mark yeat but on the other hand i have not spent any time to run "SAW trails"

But i have gone 95mph with the 1667 8).

Dan,you forget that when you run hard with your batteries and draw somthing like 100-150 amp you can only use them for 30-40 times and then it will not give you close to 100% afterwards.............

So you need to buy ALOT of batteries to be on top,to be second you will be the first looser ;D.

Anders

 

[Andrewg]

Nitro

Adelaide probably isnt on my books - but what I might do is ask Tony Jones if he will take a boat over for me

I didnt mean to sound preachy - I am interested in where this is going thats why I have stuck with it but electrics fuel packs are developing faster than I thought

Re the power last year Joerge estimated he was running 60 amps on 28 live cells (4 were dead) to run 102 mph thats 1428 watt output - this year he came back ran the same boat on 32 cells and went 111mph

Back of the evelope thats 1624w output

This year he changed motor, cells, wing profile etc

I can work out from the prop rpm what the voltage must have been (.97v or more) and it is phenomenal for a sub-c cell (from which the motor will have been trying to draw 90-100 amps.)

Using a motor calculator based on electrical characteristics of motor and cells the mtoors potential on 32 cells is in the order of 2.9 kw at 100 amps or 3.8 hp

In any event your range could reasonably be supposed to be between 3.5 and 3.8 hp.

Andy Brown the 120.579 with a 30 cc rigger using two MAC .84's which put out a claimed 5.5-6.9hp and rev to 27,000

BTW Honda had multicylcinder 2 cyl - 4 stroke 50cc in 1966 which had max ouput at 21500 rpm. Try this link you can hear a 250 6 runnign 18000 (he misses a gear going out of the pits) and the 20000 rpm 125/4 (clutch slipping par excellence!)

the one to listen for tho IMO is the 350/6 from 1967 the RC174(1967)

http://www.honda.co.jp/SoundofHonda/wgp/rc174.html

I think this is what u call crisp!

 

[Andrewg]

Nitro BTW

I am doing a 1/8th this summer in electric - Justin Antonio has the same hull and I am hoping to use it as a comparison

Andy Brown says he is pretty happy with 1/8's runnign 60 mph

In germany there is a guy running 1/8 with 1700 cell - . He has GPS'd his boat at 55mph and gets a runtime of 3.5 minutes - the video shows it running very nicely - we shall see what we can do but 1/8 looks the business for a comparison..... as the boats can be made almost exactly scale in terms of weight power etc - my feeling is 60 mph will not be a problem.

Joerg ran 3300's with much better output and runtme

If luck rains money on me - u could even see that at Adelaide!!

 

[Dan Chase]

Dan,you forget that when you run hard with your batteries and draw somthing like 100-150 amp you can only use them for 30-40 times and then it will not give you close to 100% afterwards.............

So you need to buy ALOT of batteries to be on top,to be second you will be the first looser ;D.

Anders

Anders, Joerg was only pulling the big amps for a short time during startup to get the boat on step. The SAW for electric's is only once a year, most of my racing has been oval racing and like I said, I have packs 3-4 years old. My boats are plenty competitive, it's the driver that keeps them off the podium more often then not!

From all accounts I have heard from the SAW, his cells were cool to the touch after his record breaking run.

 

[Ian Inverarity]

Anders,

Oh yeah, I was probably only doing 22000rpm! ;D Personally I am not interested in SAW runs myself, but I like to keep an idea on the technology to see if any of it can apply to oval racing. 8)

95 is pretty good! ;D Only at 80mph so far, but prop destruction is holding me back.

Ian.

 

[Ian Inverarity]

Andrew,

Good info! ;D So the power level is a bit lower than I thought, I must admit that I used to think that for SAW setups that electric would possibly have even more power available than nitro due to only needing a short run time. I guess the next thing is how much does such a motor/controller/32 cell setup weigh? My 90 motor and pipe weighs slightly over a kilo, I am not sure what a 16oz tank of fuel weighs.

Andy's fastest time was not done with a twin, it was done with a single Mac 84. In general terms twins might even be a little slower than single engined boats, although I think Andy did get a very impressive 114mph (or something like that) out of a twin Mac 84 SG. Maybe Andy does something special to get the 27000 figure as the Mac 84's I have heard dont sound to be revving like that, but he would have the instrumentation to back that up.

Hmmm, those bikes sound sweet! 8) It seems to me from the research I have done that the ability of a two-stroke engine to rev is limited by the cylinder size, which would also have an effect in four strokes as well but it seems to me that when taken to the limit that four strokes actually rev higher.

From what I have seen here, good nitro 1/8 scales run about 90k in Australia, so if you can run in that range and for about 2.5 minutes you would be competitive with the nitro boats! 8)

But I am not a big fan of 1/8 scales, what would impress me more would be a rigger that could run with the 67 riggers at 80mph for about 2 minutes! ;D

Ian.

 

[Andrewg]

Nitro

I am **** certain the vid I saw of the run was a single .84 engined boat too

I thought the IMPBA and the AB's sites implied it was 30cc but perhaps what they show is it was set in a "30cc class"

In any event yes the power is lower

The differences are weight the torque curve in particular is radically different, electric motors tend to get more efficient as they get larger rather than less, the electrics are far more wing like and the sponson angles might make your hair curl 7-10 degrees

The 80 mph rigger is not that fanciful - I will have a talk to Dick and others and see what we can do

 

[Ian Inverarity]

Andrew,

Wow, those sponson angles are pretty high, surely the SAW boats dont run that much?

I understand that the torque curves are quite different from nitro to electric, and should make electric more tolerant of launching larger props. But a 1945 is not a large prop! I cant see why very high revs should give rise to high speeds unless that tip speed thing is a big factor. Hmmm. Still dont understand what makes them so quick... :-

Keep us posted on the 80mph heat racer... ;D

Nitrocrazed racing: Batterycrazed racing?

 

[rcrdps]

more rpms= higher water speed exiting the prop

more pitch= higher water speed exiting the prop

Since our rpms can go so high, we can use a smallish prop to occomplish the same thing. Since ya'll have lower rpms, you need to make up for it in pitch. Thus, you're back to trying to launch a high pitch prop.

Piston size has a lot to do with rpms, but stroke has a good bit to do with it too. The stroke on those high reving engines is usually quite small. American made engines tend to use a long stroke. That's why they're so torquey, but have low redlines.

Gene

 

[Andrewg]

Nitro three things seem to characteristic of saw boats

power to weight ratio

output power

thrust = the product of speed and volume thrown

the last one isnt considered to often - it seems very difficult to predict for ic motors - however for an electric motor which has very consistent electrical properties it isnt too hard to get an indicatiove or comparable figure

given the first two are taken care of then thrust with a small prop needs high rpm - say joerge had run a 24000 rpm motor the prop with twice the blade area is a 63mm dia blade

The thrust fromt his prop could have been high lets say - 19lbs or 8.5kg of thrust. About 5 times the weight of the boat

An interesting comparison calcualted the same way is that a year ago a 90 mph boat was making 3 lb of thrust for a 6 pound boat - at that stage we thought 39000 rpm was high

I think you are on the right road with tip speed. The second mechanical resistance is the diameter of the props leading edge ie sharpness. Diameter of the prop is an important factor in terms of controlling those losses.

 

[rcrdps]

Just a couple more thoughts.......

Someone either here or another forum mentioned that some speed records are set with stock engines. Also, I remember when I had a 3.5cc outboard, that the stock class had an oval record over 50mph(I think).

So what's the difference between a stock engine and a highly modified one? The stocker probably has more backpressure and is tuned for lower rpms. It's theoretical peak hp might be lower, but the hp band is probably a lot flatter. That allows them to launch a better prop. As we've seen from the electric numbers, it can be done with lower hp. How much lower is the question.......

How well does an exhaust throttle work? Seems that one could be used to give better low end. Maybe only hit half throttle till the engine spools up?

Just a few ideas.

Gene

 

[Spraguepsycho1]

has anybody ever tried a variable belt drive (snowmobile cvt type) transmission on a nitro boat? I think having the rpm's at peak hp along with the constantly changing ratio could work quite well, not to mention the ability to set it up to shift to overdrive. starting with 1 inch pullies on both sides of the belt could give you 2:1 off the launch, all the way to 1:2 at top speed if you had the power to pull it, and max hp the entire way instead of having to wait for the engine to build rpm's. Another benifit would be the ability to idle while standing still, since the drive clutch wouldn't begin to partially engage until you hit the throttle. Just a thought from a newbie, I've been racking my brain over this prop speed thing since the night the record was set, and I watched the video. lol Oh also wondering if this might help fight cavitatation since the prop might increase speed more gradually.

 

[Bob Kensill]

The "Snowmobile Torque Converter" is the most inefficient drive system there is. The drive system that I am working on is a hydraulic clutch. It will slip a "predetermined amount" to allow the engine to rev without all the drag from the prop. The clutch will lock up after the engine reaches high enough rpm to pull the prop. Right now the unit is the same diameter as the stock flywheel and only about 1/2' longer.

Bob

 

[Spraguepsycho1]

sounds like it should work good for the launch, but won't that still limit shaft speed to whatever rpm's the engine can turn? I was just looking at the overdrive possibility.

 

[Mike Nowicki]

If you build a boat that is designed just for SAW you can launch a prop that is to big for your HP . I think overdrive is the way to go.

Mike

 

[Bob Kensill]

I have a boat that is just for SAW and sometimes it is almost impossible to get it up on the pipe. I run a 40 Eagle SG with a strong "Bluehead" Mac 67 on 65% nitro with some other goodies in the fuel. I am running an Andy Brown Octura 2170 SAW prop. Top speed to date has only been 92mph,but I'm looking for 100mph.

Bob

 

[Andrewg]

Re my earlier psot on the power of Joergs boat

This is still ok

"I can work out from the prop rpm what the voltage must have been (.97v or more) and it is phenomenal for a sub-c cell (from which the motor will have been trying to draw 90-100 amps.)

Steve Hill has just published some data on the discharge profile of 3300's which as he notes suggests Joerges cells were probably puting out 60- 70 amps so the motor output was likely 1680-1960 watts or 2.2 to 2.6hp

 

[Ian Inverarity]

Andrew,

Is that all? ??? Wow! Makes the speeds even more amazing! Possibly strong 21 engines put out a similar power, and my mod 90's might put out up to 3 times as much!

Given that higher tip speeds can probably produce more useful thrust, there has to be more to this very high speed, otherwise people would simply run step-up gearboxes on their nitro motors, when in fact reduction boxes are quite common on 21's and 45's in europe and more people are trying them for oval racing.

I am still interested in what the weight of something like the JAG boat powertrain would be to get an idea of the power to weight ratio. For example my 90 boat probabaly has in the region of 6hp and weighs about 4.8kg ready to go, a bit more with fuel.

Ian.