headhunter23

Yea u can use two drives, post pics of hull before ya do so(all angles)... selecting hull will be the worst part.

Ivan.

DRAGONFIRE81M

i thank he did pick a hull i balive its the sw26 . if he is reforing to the singel drive big22bird did . you could there easy to install and set up .but the hard part is how you would power them , brush or brushless . if you did a brush you can get away with one esc but if brushless is your way then youll be needing 2 esc .

g master

well iwas thinking about just buying a traxxas villain ex with two brushed 19t motors.Or this hull http://www.offshoreelectrics.com/pro...ero-Challenger
with same setup or two 12t motors.

DRAGONFIRE81M

well i guiss i was wrong the villain wouldmt be a good twin mini drive chose . inless you plan on cutting the transom off and redoing it . your sec chose would be like the ariganal big blue . that hull is the same size . and it will work but i wouldnt even mess with a brushled system . a brushless system from hobby city would be cheep and the way to go .

g master

but wouldnt I need two esc and motors

grael

Personally, I don't believe the back of a jetboat's riding surface needs to be flat. I think it's a matter of convenience, to match it to flat jet unit intakes. You do, however, need to soften the curve where the water has to change direction to enter the intake.

Having a flat section around the intake helps a jetboat to slide around in cornering, but if any of you have driven a conventional deep V with that modification, you probably noticed that such boats pivot TOO easily around the front section of the V.

If you are running rapids, then a flat will let you run in shallower water.

DRAGONFIRE81M

yes you well need two motors and esc . your look at around 40 -50 dollars from hobby city . youll pay $ 20 for one cheap fireball motor brushed . the one reson he need a flat serface is to mount two drives that have a sealing ring made in to the stater nozzle

DRAGONFIRE81M

http://www.youtube.com/watch?v=5UAza...e=channel_page

this is pretty much what youll get with a 31" fiberglass hull twin mini jet drives . and twin esc and twin fireball 15t on two nicad 7.2v

headhunter23

Mmmmm... dual drives, dragon is right u need regular 28-29mm jet. Dualing it is fine, I would not flatten any area. Bind the bottom of the jet to the hull. Good luck building up the back of the boat though, there is no consistent angles. Its a huge pita compared to other hulls. But it's still a great jet drive platform.

Ivan.

areseaer

Here is some good info about jet-drives in real boats
[link]http://www.ultradynamics.com/sections/educational/design.asp[/link]

I like the nacelle method for single jets in deep-V hulls. Not good for shallow water running like Grael said, but would be less likely to spin out.

DRAGONFIRE81M

yep deep v are ment for the deeper water like i run mine . it would just be to much work to try an mount two mini jet drives in the vallian hull . its more suted toa singel drive . man all this talk about dual drives is makeing me wont to do one again .

headhunter23

Hey quicksilver, final plea to give ya mini me. Goes to someone else saturday feb 28.

Ivan.

g master

so then could I just cut the jet drive intake gate to fit the v-hull or not

DRAGONFIRE81M

are you still talking about a twin drive ?

headhunter23

I'm assuming he's deciding to go with a single drive. Qmaster yes this is what I had thought about when I did mine. The only thing you need to worry about is motor with cooling still fitting as it would drop about 1/2in if your test fitting now. If it still works, do it. Lowering center of gravity is a good way to make the boat better.

g master

so what would be a good setup for a single jet drive ,I would like in the 30mph range

headhunter23

30mph range? Umm... only way you would hit that is going to the auzzies swashbucket.

http://www.swashdrive.com.au/

Which would require a zenoh motor.

Fastest I've pulled is gps 33-34km/hr in jet villain, might beable to beat that with new delta jet with villains motor slightly smaller and lighter. The only other recorded test that I've seen with the drives pulled 40km/hr but it was a dual 28mm drive. I haven't seen any other gps runs. Guys estimate their runs on here but it's extremely hard to judge unless you actually throw in gps or radar test the boat.

Ivan.

g master

well I want to use this jet drive http://www.cornwallmodelboats.co.uk/...pner_2344.html
with a brushless motor so whats the fastes i can get with this setup

grael

My boat's quite fast, might well go over 30mph:
phttp://www.youtube.com/watch?v=mF1tiDyx8bU&feature=channel

I don't think a zenoah's power to weight ratio is any better, than that of a glow plug motor when both are running tuned pipes.
They're just bigger.

Most people run nitro with methanol, so there's quite a bit more power there, also, a glow plug is less weight than an ignition system.

If you want ultimate speed, I would go for a large CMB engine (I think they mostly make marine), and a swashdrive pump.
http://www.highperformancemodels.com/CMB%20ENGINES.htm
That horse power rating is for an engine that's probably quite a bit lighter than a zenoah, and spins a lot faster too.
The Zenoah's spin close to 20k with full mods, but you would probably need a clutch to get it up to the high RPM power band.
That loses you low speed manouverability !
The CMBs have rotary valves (not sure about the Zenoahs, but most weed eater based engines don't), and porting very carefully arranged for easy breathing at any RPM.

Some of the smaller CMBs, have lots of ports, which let them run up around 40k, I think various manufacturer's car engines are set like this too.

Only problem, CMBs are expensive, they win races.
A large glow plug engine goes through a lot of expensive fuel too... petrol (gas(benzine)) is relatively cheap.

When I'm done on my CNC extruder, I'll be making some different size new pumps, I think with what I've learned so far, they'll be very competitive, but it's probably going to be at least July before I have anything good to show off.

Graham.

headhunter23

grael your the one guy i keep hoping sticks a gps in his boat!

g master

those engines look great thing is I cant have nitro where I drive my boat so thats why I was thinking brushless

smokesboards

as far as speed is concerned I always used to over guestimate, especially when talking about RC cars etc, and the reality is that (most times) it aint going as fast as you think.

So far I have set targets for my knockoff jetsprint at 20mph (32kph) and after I modded the boat fully (3s lipo, 28mm BL3150kv, bearing mod etc...) i still only acheived around 14-15mph (22-24kph).

Since re-modding the graupner jet with 2 impellers inline (like the hamiltons), and extended the internals I have managed to get a constant 19.6mph(31.5kph), with peak speeds of 22mph(35kph) (I guess this peak speed is when the boat "jumps" out of a high speed turn.)

PS. has anyone managed to get the knockoff jet to leave the water (jump) without a ramp?
I will try to film my next run, but have managed to drive downstream flat out (river running at 4mph ish), then throw the boat into a hard turn, which sends the boat spinning between 360-540deg rotation, and the best bit is the boat actually leaves the water completely by about 2 1/2 inches for approx 270deg of the turn! I couldnt beleive it when I did it by accident the first time but I managed to do this at least 5 times before the batts died. (I had allready been running for a while before this happened)

PPS. What is the highest speed recorded for a Knockoff?

PPPS. Im using a Garmin Foretrex 201 which weighs 2.75 oz (78 g).

headhunter23

smokes... unfortunately we had to run the jet villain along side the knock off as my gps was too heavy. We pulled 22-23km on ... geez i think it was the red motor... so 3200rpm/kv 25amps max 7.4v... haven't done my buddies and his cousins 3900kv 40amper yet. Perhaps this spring. Would like to see your boat run gainst deltajet... should be very close at those speeds.

Ivan.

grael

No GPS !
I look now and then, but haven't seen any small GPSs in the shops to do the trick.
My ASP carburettor is really really unreliable, I've rebuilt it a few times already, trying to get idle and idle jet, main jet to stay set, second to last run, the whole carburettor came loose, (I'm very careful not to overtighten, because it can crack the lower wall of the carb)
Last run, I put a big ding in my rebuilt front, because the battery lead broke off from my soldered joint to the power switch... (lack of maintainence on servo box[:-]

I was up in Palmerston North (New Zealand) today, and managed to check out an RC shop, GALTECH, huge planes, great variety of RC stuff. First I've had a good look at brushless motors, mostly outrunners for air cooling though. very few can handle more than 500 watts. It's a lot of power, but an ASP 40 like I have (glow engine) is supposed to put out over a KW:
Displacement: 6.46cc
RPM range: 2,000-20,000(r.p.m)
Output: 1.05/17,000(kw/r.p.m)
Weight: 540g
And I have a tuned pipe on mine, so it's probably running to 25,000 or more, and with higher torque, so I'm guessing it's closer to 1.6KW output...

So, for those of you wanting really high speed on brushless, here's what I think you need to do:

Get a longer, skinnier hull.
Go for an aerated stepped hull, the cross section has lower air drag, but without the aeration of the undersurface, it would have higher water drag.
Don't worry about the intake loosing suction, the stepped sections allow the important riding surfaces of the hull to maintain more controlled immersion anyway.
Use a high torque impellor, if necessary, going to a lower KV motor. Spinning a low pitch impellor faster can generate a theoretically equal speed to a high pitch slow impellor, only if you don't consider the effects of drag:

An impellor that spins 180 degrees to move water back one diameter moves slower through the water than one that spins 360 degrees to movement the water one diameter back. The extra turns of a low pitch impeller gives more "grip", but the stator allows a much higher effective pitch than on a normal un-enclosed propeller. Higher pitch reduces impeller "drag", which has a square of the velocity relationship, i.e., double the speed, quadruple the drag.

On the same theme, you have a trade off between entrapped weight of the water in the jet pump, and drag of the pump walls.
In a bigger pump, to get the same thrust, you don't need as much water speed in the pump, it's litres per second that relate to kg thrust, so at any given rate, a lower speed in the pump will give less drag on the pump walls. Really excessively big though, and the thrust will drop off, as the boat speed increases. Most jet pumps don't come even close to this though.

The river running speed boat often use multiple stages, I think the way this works, is that the outlet speed is really high, so that as the boat speed increases, it still has a much higher exit speed for the jet in reverse... imagine if your jet speed out the back was 20km/hr for example, if the boat was going 20km/hr, then there would be nothing to make the boat go faster.

Graham

grael

I think I get maximum speed when I'm running in rough water, and the boat get some air in the intake after launchin itself off a wave, the air doesn't slow it down much, but when the stern hits the water again, the engine is probable up from around 25k rpm to 30k rpm +, and the impeller grabs the fresh water, the flywheel releases the stored rpm increase, ant the boat's off, launched over another wave.

This is a movie of my boat when I had the .25 engine in it, smaller engine, less speed, but on choppy water, it gets enough air that the pipe can work, and it goes a lot faster. I'd also taken it to a couple of local beaches, that would have been amazing video to see, I was in raptures seeing how it handled on the bigger waves, but at the moment, it's got too much speed to do that, unless I excercise considerable personal restraint on the throttle
http://www.rcuvideos.com/video/start...oppy-water-avi