2 vs. 3 blade

[awfireman]

Hello everyone,

I have a question....what are the benefits of 2 vs. 3 blade props and vice-versa? I just purchased a Kyosho Jetstream 888 ve. Its a very fast boat out of the box and runs super-smooth with no porpoising or chine-walk. Im pretty impressed. And its self-righting which is a added bonus. The stock prop is a 1.6p 40mm 3 blade plastic and want to experiment with a two blade CNC but want to know the benefits (or draw-backs). Will I gain speed with a 2 blade? I just ordered a couple graupner 2 blades from OSE...1.6p in 40mm & 42mm. Should I try a CNC 3 blade in 40mm & 42mm? Will a CNC prop be an upgrade over a plastic prop? Sorry for so many questions...I dont know much about props but want to learn.

TIA

-Fireman

[dmitry100]

supposedly the 3 blades handle better on the water and generate more torque

and the 2 blades are a bit more efficient

[fweasel]

3 blades will dig better out of the hole because of the additional surface area and can offer better acceleration. 2 blades will have less load at higher RPM and are typically faster and more efficient.

The 640/2 prop you ordered will most probably be slower than the stock prop. The 642/2 would be the better choice of the two options.

The bigger change here is going from a plastic to a metal prop. Plastic props will flex under load, which decreases their pitch and thrust. A metal prop of the same size will have thinner blades that are more efficient and will hold their shape. Metal (stainless, brass, copper beryllium) props are typically purchased "raw" and need to be sharpened and balanced first. CNC aluminum props come sharpened from from the machine, and need little to no prep work. They are also fragile and can be damaged easier than the other metal types. They're inexpensive and good for experimenting with setups until you find the right prop.

[NativePaul]

I would argue that Graupner carbon props are the best props available IF you have a clean lake and aren't pushing huge power though them, if you have lots of floating crap on the surface or are putting more than about 1kw through them they won't last long though. The K series 1.4 pitch are better than the S series 1.6 pitch versions.

Strangely the very thing fweasel doesnt like about them (the flex) is what makes them so efficient, the highest load on the prop is under acceleration and the Graupners flex a little and reduce their pitch ruducing current and cavitation resulting in a boat that accelerates better but gets better runtimes, they are so good a friend of mine made some moulds of the 2318.36 he was using in his Mono1 and had some cast in alloy, his alloy props looked and measured exactly the same, but he couldnt get runtime and he lost speed. Likewise one of the TP CNC ranges is a rip off of the graupner K series, and is amoungst the better of the aluminium alloy CNC props but again they dont quite stack up to a real Graupner 1.4 carbon.

[fweasel]

NaivePaul, when I said plastic, I was referring to the cheap injection molded style props. You're right, the Graupner carbon props are nice, and super sharp right from the bag. Your description of the variable pitch reminds of of turbos with variable vane compressors, best of both worlds.

[ray schrauwen]

Doesn't someone make a CNC prop with very similar or same design?
I wish there was a SS or Berillium version...

I would argue that Graupner carbon props are the best props available IF you have a clean lake and aren't pushing huge power though them, if you have lots of floating crap on the surface or are putting more than about 1kw through them they won't last long though. The K series 1.4 pitch are better than the S series 1.6 pitch versions.

Strangely the very thing fweasel doesnt like about them (the flex) is what makes them so efficient, the highest load on the prop is under acceleration and the Graupners flex a little and reduce their pitch ruducing current and cavitation resulting in a boat that accelerates better but gets better runtimes, they are so good a friend of mine made some moulds of the 2318.36 he was using in his Mono1 and had some cast in alloy, his alloy props looked and measured exactly the same, but he couldnt get runtime and he lost speed. Likewise one of the TP CNC ranges is a rip off of the graupner K series, and is amoungst the better of the aluminium alloy CNC props but again they dont quite stack up to a real Graupner 1.4 carbon.

[NativePaul]

Yes, the TP power type M CNC alloy props are VERY similar to Graupner's carbon K range. Made from 7075t6 they are a good bit stronger, but not quite as efficient as the CRP originals.

Maybe try a Dr Prop CNC stainless prop, I dont know if the Naviga shape are probably only good for Pltd for you guys as they are so thin, but they are an efficient shape and are way thinner and sharper than I can get away with on a BeCu prop, even my experiments that folded were much thicker, they are top notch if you can afford them. I wish I had a dozen of them rather than the box of Octuras and ABCs that I have. He also does a shape VERY similar to an Octura that may be better for your heavier boats with more power, but I havent seen one in the flesh, so dont know if he makes them thick enough to handle the huge power you have available in the full on classes.

[awfireman]

I would argue that Graupner carbon props are the best props available IF you have a clean lake and aren't pushing huge power though them, if you have lots of floating crap on the surface or are putting more than about 1kw through them they won't last long though. The K series 1.4 pitch are better than the S series 1.6 pitch versions.

Strangely the very thing fweasel doesnt like about them (the flex) is what makes them so efficient, the highest load on the prop is under acceleration and the Graupners flex a little and reduce their pitch ruducing current and cavitation resulting in a boat that accelerates better but gets better runtimes, they are so good a friend of mine made some moulds of the 2318.36 he was using in his Mono1 and had some cast in alloy, his alloy props looked and measured exactly the same, but he couldnt get runtime and he lost speed. Likewise one of the TP CNC ranges is a rip off of the graupner K series, and is amoungst the better of the aluminium alloy CNC props but again they dont quite stack up to a real Graupner 1.4 carbon.

I put the Graupner K series 42mm on my Jetstream in it has to be 10mph faster than the stock prop. Thing is fast. I do have a question....the stock drive dog doesn't fit exactly (smaller) as the groove on the Graupner is larger than y drive dog. My flex shaft is 4mm....do you know where I can get another 4mm drive dog to fit the graupner prop. While it used the stock for testing ( heat,etc) I dont want to run it like this for too long. Also, although it was a bit windy today, the boat seemed to flip much easier...do you think I need to add weight toward the front of the boat? I set the strut/stinger to 1 (it was at zero) and did nothing to the trim tabs. Any help would be much appreciated!

-Fireman

[Speed3]

Interesting. In my experience the graupner will give a big increase in runtime.

But the octura 442 and 642 give me much better acceleration and a few mph faster than the graupner k42.

2 blade vs 3 blade in my experience a 3 blade was slightly faster than the 2 blade. But the 2 blade draw a little less amps. Diameter to diameter.

[Tbauer]

I had similar results, that being the 3 blades were a bit faster

[NativePaul]

Yes that is right speed3, the Graupner carbons are so efficient that an Octura of the same size is not comparable, if you find the right prop size using Graupners and want to move on to the much sturdier Octuras, you will have to go one size down to with the same pitch to maintain similar amp draws.

In your K42 example the closest Octura props would be an M440 and an x637, both of which would suffer in acceleration in comparison, though if your coarse is big enough, and the boat is light enough on its feet, you may get a higher top speed from the X637.

[Speed3]

Yea I would say a 637 probably would give similar amp draw.

And the graupner k42 like would win that race. Better acceleration and a think it would give a bit more top speed.

But octura x442 vs graupner k42 about 59 mm total pitch. If you doing a short sprint race the octura will win. In my experience.

[NativePaul]

Yes but it is not a fair race as the Octura would be pulling more amps and making more power. As I said Octura M440 is similar load to Graupner K42. A Graupner K45 is a bit more load than an X442, but is much closer to it than a K42.

[dasboata]

my general rule is 2 blades for cats and 3 blades for mono

[rol243]

my general rule is 2 blades for cats and 3 blades for mono

Chris, what is the prefered prop for sport hydros in oval race trim ? 2 or 3 ?