Predator size saw rigger

[Simon.O.]

O.k most of you know my smaller rigger that is about the same size as a predator.
I have previously run it on 3 cells to the 8S (4400kv) motor. With the 432 it ran over 90kmh and was fine until it hit something and then cartwheeled down the pond to become a kitset. I got it all back and all is good.

Now I run it on 2 cells to the 7S that Ben kindly sent me.
I am keen to poke the 7S into the Canard and run the rigger, now strengthened, on 3 cells with the 8S motor but this time use a 430 prop.
It gives me a estimated 40k + rpm at the prop loaded. I know this is well up in saw teritory but is it really out of line ?

The 432 was a bit of a handfull and I will use a 430 on another hull anyway.

Worth a try ??

[andym]

It's always worth a try Simon, what were the temps like with the 432?

[Ub Hauled]

Simon, I ran my Blizzard (+- 24") in a SAW event on 2s, I hit 71mph (114km/h) on chop. It handled great for the type of water I was running, had I glass water, who knows...
I have to say that it was nerve wrecking specially knowing that my hull was made out of wood and w/o any type of reinforcement...

[Simon.O.]

Andy It was hard to get temps on that 3S run with the 432 because it was at least 5 minutes before it got back in on the end of a tow line with a fair amount of water inside. All the electrics survived.

Jan I do remember that you had run a wooden hull this size and am glad to know that I am not the only one nuts enough to try.

I compiled a lot of my findings on paper last night and came to the conclusion that regarding Amps and heat (watts) I will be fine, the expected speed at about 50mph is on the edge but doable.
My big concern and the reason for this post was spinning a prop at over 40 grand.

I'll wait now for a glass smooth morning and give it a whirl. Until then I'll keep the 7S in there and run it with a 632.

I'll let you all know when this happens.

[Ub Hauled]

Simon, how long do you wanna run each time you go out? Is it a couple of passes and then come in to chk speeds, temps, etc or do you wanna stay out a bit longer? When I went my speed i had a V935 prop, stock other then s/b. 2 passes and maybe a third one would be possible, with my setup, I had a NEU 1509/1D inside.

[Simon.O.]

I am happy to do 2 passes and bring it in for health checks.
When I last ran 3S on a 8S can I did 5 passes of a 70m stretch before it all went bad.
I am easy with the usual workings of testing insane SAW setups.

I can assume thus far that spinning a prop at over 40krpm is not really a bad thing.
Just a nuts saw thing.

[NativePaul]

Over here most 5 minute Hydro oval setups both 2s and 4s are close to 40k, I have an oval setup in a mini cat that spins about 50k and while I'm struggling for runtime it does make an immense sport setup and I'm sure I'll get the right amount of cut on a x427 and get the run time at some point, as I see it the only problem with high RPMs is they are much more sensitive to the props you have to use, too small and all you get is cavitation but you have to increase the load very slowly as it only takes a tiny change in prop size, cut or pitch to make a huge difference in the amp draw.

[Ub Hauled]

Paul, is that at the prop or nominal RPM?

[Simon.O.]

Slight change in plan here.
The 3S pack that was going to go in here is now back in the small Cat on the 12S motor with the 637 prop as per Jesses recomendation. That is a wicked setup.

I am now back to a good 5000mAh 2S pack and the 7S motor (5070kv)
I really like the X632 on this rigger with this motor, however I no longer have the 632 as gravity+H2O beat it.

I need a new prop and can easily grab another 632 but am interested in other options. Amps is not a big issue here, I need high rpm so therefore lower diameter props are the go.

I can do x632 or a Y534 for the same calculated figures, I do not know which will be faster on the day.

Any suggestions as to a wicked prop for this setup. 1732 cut down to 30mm ?? Stock 632 ??

As a point of reference, this rigger screams well on a 432.

[NativePaul]

Nominal based on 4800kv and 3.5v/cell with 3 cells, I made my mini cat just big enough for all the gear without thinking of the eagletree so unless I grow the kahunas for a run with the hatch off and the datalogger hanging out I'll never know 100% what's going on inside.

I would guess that the X632 would rev a little higher and be a little faster than the Y534 but a cut 732 may be faster still, I love X6 props just wish they were available in more sizes.

[Simon.O.]

I did it.
3 cell to the 7S to a 432 prop.
The numbers stack up to 46krpm and mid 60's for speed.
I had a kind officer radar it for me on the second pass and got 101kmh or 63mph.
I'll not be doing that again because if something goes wrong at that pace I'll lose the boat for sure. 92kmh nearly destroyed it once.
I'll keep in on 2 cells for now and replace the 632 or get a 1732.