Stingray Build

[RCnut]

OK, I read that 3 times, I think I'm with it. All sounds good. I'm a bit concerned about a shrouded prop...Isnt that what a water jet is. Ok its a bit more concentrated but i dont see where a prop inside the Ratemaster would get adaquate water from to pump out at any great speed. If its that same 36 inch stingray on you tube then I want a bit more speed. At least Rate 6.

[Subculture]

A water jet is a shrouded prop, agreed. Usually very high in pitch, and designed to pump out water into the air. They have a fancy intake swan neck to draw water up from underneath the boat and expel past the transom, you don't need any of that in a sub- takes up space, which is nearly always at a premium.

I agree the Stingray on Youtube is sluggish. Not sure what was used motor wise, I do know it used one of the Prop Shop 15 blade propulsors, the type fitted to Sheerline trafalgars which looks fancy, but they're not the best at providing thrust in model form.

A two or three blade prop is optimum, and the stingray is a pretty strealined shape so should fly along nicely with a suitable power train.

[RCnut]

As I understand it a shrouded prop has a tube type ring around it. With water being pulled thru the front. Question, where would the water be coming from to be pushed out. The ratemaster backs onto the "Transom" of Stingray and is sealed so the only way water gets to the prop is from the end of the Ratemaster. Having said that, the main hull of Stingray reduces quite a bit as it goes back to the transom so space there is not going to be used as the WTC would not fit anyway. Or have I got this wrapped around the wrong way?

[He Who Shall Not Be Named]

Think, RCnut, how you arranged your pump-jets in your magnificent SKY-DIVER model. That's what I'm advocating for your STINGRAY (though a single unit). Only difference between the standard arrangement is the inclusion of the Y-splitter, slide-valve adapter between the intake and the rotor sub-assembly. Primary suction is from the long hole in the bottom of the hull, secondary (ballast water de-watering mode) is with the slide-valve open and the PJ taking a suction on the internal water to get the model to surfaced trim.

What differentiates a proper pump-jet from a shrouded propeller (or, Kort nozzle) is that the PJ outputs a stream of water almost exclusively moving axially, with little or no radial flow; the more mass moving longitudinally, the higher the thrust.

David,

[RCnut]

Cool, Thats what I envisioned, the same PJ as used in the Skydiver, Just got a bit confused, (Sunday mode maybe) Oh the Motor is a Tornado Thumper V2 4250/06 800KV Motor, Im thinking that should give the sub enough go to go.

Mamas

[Subculture]

My thinking was to hollow out the piece I've filled out in black. Water would suck through into the ratemaster where the prop was located.

[RCnut]

Yep thats ok, I can see that working but the jets way more efficient, easy to install and allows me to get the Ratemaster to spin as well.

[RCnut]

Today I tweaked the ratemaster and did the little pod things that hang off the side fins and the periscope head unit (Not shown) Just the star bit for the back of the ratemaster and the aquasprites to do now. Then I'll be adding cabin detail, oh and I need to sort out those rear tubes.

[He Who Shall Not Be Named]

Now we're cooking, Mamas. Give me the model number and name of the pump-jet so I can get one. From that I'll work out the Y-splitter adapter. I see this also as the means of de-watering your SKY-DIVER hull.

(Tell me if I'm getting too pusher here Mamas and Andy. Sometimes I start storming around, stepping on toes, without even thinking about it).

David

[RCnut]

Graupner Jet Propuision Unit 2340, Same as in skydiver apart from I replicated the white vac forms in fibreglass for greater strength, they look messy on the outside but are perfectly smooth on the inside. And no your not being pushy, I have a limited knowlage of Sub Systems so your help and Ideas are very much appreciated, oh and I wear steel toe caps lol.

[He Who Shall Not Be Named]

Very good, you already have demonstrated that a new 'front end' (your GRP intake piece) can be made to match up with the Graupner PJ unit flange. Your picture suggest that an even simpler means of pulling the water out from within the hull, using the PJ, is possible:

Simply run a 3/8" diameter K&S brass tube down from your GRP part, situated just forward of the PJ flange, to terminate just off the bottom of the inside of your hull -- no valve. The running pump-jet always draws a suction from within the flooded boat, but with the vent valve shut, 100% of the flow will be from the normal bottom intake of the GRP part. Open the vent valve, and broach the top of the bridge, and you start moving water into the brass tube, into the PJ rotor, and out of the boat.

A variant would be the incorporation of a slide-valve to block off the face of the normal GRP part PJ intake -- that way 100% of the water flow through the PJ, with the bridge broached and the vent valve open, will be hull water. The boat will be dead in the water during the de-watering operation, but the task will take very little time at all. If you still want to be in motion as you de-water, you can 'throttle' the slide valve via a servo to achieve the head-way and de-watering rate you desire.

David

[RCnut]

Sounds bloody brilliant, I'll have to hurry up and mould the thing.

[He Who Shall Not Be Named]

I'll buy one of those PJ's and will work up a 'front end' to the PJ as described above.

David

[greenman407]

HEY Dave! Whats with the new Avatar? I was just getting used to the other one.

[He Who Shall Not Be Named]

look up, 'cube zero'

http://www.youtube.com/watch?v=3F80ZiH90mI