lipdaddy

Thanks for all the advice. I lowered the engine to get it more aligned and converted to a flex shaft set up. I must say it's alot stronger drive then I had before.

DRAGONFIRE81M

look great man . doesnt look like you had any troble with the flex .

lipdaddy

It went together pretty easy. [sm=thumbs_up.gif] I'm hope to have the electronics in this weekend, I can't wait to get this one in the water.

grael

fuel tank just forward of engine, electronics in rear compartment with jet intake ?
Looks a lot more reliable now. Still think you are over powered though... once the engine has freed up a bit, might want to try cutting down some really big diameter props for impellors.

lipdaddy

You're spot on with the fuel tank and eletronics. I agree, it's a little over powered.....but it's what I had to work with. In time I can either change engines or cut down some props. I hope this will just run, I have no great expectations for it. I just want something to putt around with.

grael

Your boat looks good.
Myself, I'm resting on the sucess of my latest jet for a while, I'm working on building a CNC machine so I can computer CAD design my future parts... It will be a few months before I'm seeing results though, big project.

sundogz

Looks nice Lipdaddy. Now that should pump some water fer sure! I agree it's a mite overpowered, but better to err on the more side (my opinion). I'm a fan of 'too much'. If it turns out that it cavitates too much, you could easily move the transom forward, letting more of the jet drive protrude (like a stinger) thus bringing the intake back fully to the rear. I'll bet it doesn't cavitate then. And would look unique as well. Or you could just slow down a bit! (huh?) Sorry about that (?]>

If it were electric powered and suffered from vibration, I'd suggest changing from a coupler to a collet. But with that powerplant, it might be a moot point! Looking forward to it's evolution. Sundog

grael

I find other things have a big influence on cavitation.
The boat I made my GFs son, that has the water outlet under water, as it exits out the exhaust down a stainless steel tube riding at an angle, like a trim tab with holes out the bottom. Therefore, when the boat isn't planing or tilted right over in a turn, the water cooling tube isn't available to evacuate the air filling the pump cavity, especially since the outlet is also submerged at rest. The impeller is super high pitch, so until the flow volume goes up, water can just spin around the outside of the intake, with the impellor.

On my own boat, the diameter is 35mm instead of 22mm?, and the water cooling exits above water. It's also larger diameter hose, and the impellor, although still very high pitched, is not AS high pitched relative to it's diameter. Water cooling outlets from the pump that don't exit at the top also don't help. My boat only cavitates when I try to turn it too fast, and it sucks air in the intake

bayshun

I have been following the thread and wanted to put one of these jet drives into my mini rio i have been looking at a few from hobby lobby but i don't know witch one would be the right size the boat is about 12 inches long and i will be runing it with an ammo 25-32-3200 any help would be greatly apreciated

grael

You all might be interested in an experiment I did,

I damaged the drive dog end of two of my props that I cut down for impellers. Having a look around, to see what else I could use, I found an old brass stator with hub that I'd made a few years back, but never used. It has 8 short vanes, each only about 5mm front to back.

So, I cut the hub to length, machined the ends to fit, and then twisted the blades to form impeller blades instead of stator blades. The root is parallel with the direction of flow, (it should be partly twisted.)

Anyway, I tried it out, and it worked surprisingly well. It cavitates very easily, and doesn't draw water in when it's got an air lock nearly as well as a two bladed impellor, but it's got a lot of thrust, never the less.

I suspect that a well designed 3, 4, or 5 bladed impellor would work very well, given that my 8 blade "experiment" impellor works much better than I had expected.

lipdaddy

Hobby-lobby updated the website and now has some 4 blade props. Could be an option.

DRAGONFIRE81M

i have already tryed there 3 and 4 blade they have very little pitch . and would need alot of rpm to get much out of them

grael

If you can get a bigger diameter 3 bladed prop and turn it down, then you should have a higher pitch.
There are many options with metal blades, the Octura range for example. If you don't have a metal lathe, then use a jig to hold the prop with an electric drill, and fix the jig to a grinder.

Quicksilver

Yeah, metal is the way to go. As you move up in diameter and pitch, the center of the impeller will increase, but if you use metal and not carbon, the center can be much smaller.
I'd suggest anyone switching to a metal impeller to make a wear ring.Basically just a ring of thin metal, that provides a buffer between the impeller and the plastic duct of the graupner and kehrer units . This keeps the risk of a total melt down of the drive if the impeller starts rubbing against the sides of the duct.

DRAGONFIRE81M

this two props started out as 60mm and i cut them down to 29mm . they do work they both had better tack off the the 2 blade but the top end wasnt the same . also i would use a sv27 metal three blade the have alot of pitch youll just have to change your set up to 3/16 or use a coller to change the 4mm

DRAGONFIRE81M

well if some of you noticed the yellow hull and 29mm intake in the impellers pics i posted just a few days ago . the hull is a cen aqua jet gp i cut the deck off to make the mods easyer . and after makeing mods of the drive i put it together and shaved a good 1/2 -5/8 off the intake to get the right angle i was looking for . also doing the flex converson on this drive . im going to order a 36-50-2600 brushless and 100A esc from hobby city . im just waiting on my ose order for the motor mount,flex copler .

damfurst

Looks great Dragon, Can't wait to see how this one turns out.

DRAGONFIRE81M

thanks man im hopeing this one come out great im really takeing my time on this one .

Vinnystoolbox

Dragonfire sorry you're building it too quick LOL

Mine which is the same hull has been about 6 months now, just the motor to go in, which should be tomorrow i hope

DRAGONFIRE81M

yeah i still havent ordered my motor or esc . but if i had everthing i could have it done in 2-3 days . but i have been working on it for 3 weeks now

btw here is a once a prop now an impeller . it started off as a 42mm -67mm grupner prop from ose

saratogaslim

Hello All,

Very glad to have come across this thread. A lot of useful information posted. I have a request for a little advice. I am trying to decide between a swashdrive series I [link=http://www.swashdrive.com.au/Model%20Jet/Model%20Jet.htm]hydrojet[/link] and the graupner jet 5 [link=https://shop.graupner.de/webuerp/servlet/AI?ARTN=2347&SessionCheck=4711&language=en]2347[/link]. I like the fact that the swashdrive uses stainless steel for the impeller and other internal components. Does anyone have any experience with either units?

Thanks,

Slim

Vinnystoolbox

Not sure what the domed wnd on the impeller will do but should be interesting to see the results with three blades whats the difference in pitch to a standard impeller.

saratogaslim I think most people will say the swashdrive but i'm not sure if anyone has used one or not, they definitely look good, if you can afford it(price and weight) i would go for that myself.

Quicksilver

I dont have personal experience with either, however I did research a lot.....If you have the means, get the swashdrive, you cannot buy a better jet unit than that. The thing with the swashdrive over anything made by graupner or Kehrer, is the swashdrive IS a scale jet drive. It has a real impeller. It like comparing a Ferrari to a Corvette. Yeah both go fast, but the Ferrari is hand built, precision made, exclusive and has had more thought put into it than the space shuttle. This is the case with the Swashdrive, you simply cannot go wrong.

DRAGONFIRE81M

i 3rd the swashdrive. you just cant go wrong with that drive . the cone on the end will be removed to get the blades as close to the stater as possable . the pitch seems to be the same as the stock . just one more blade .

grael

What size engine ?