Damnathius

I've read in several threads on this forum that we should not use props with less than a 10" pitch on the SP series engines.

Why not? It seems to me that the important thing is that we do not over rev these engines, and perhaps this is why the steep pitch recommendation. However, when we increase the diameter of the prop, we can also decrease the pitch to maintain a reasonable RPM range. I run a 24x8 prop on my 120 SP, and it tachs out at 4400 RPM sitting still on the ground.

What am I missing here?

Thanks,

Dave

RCV Engines

Hi Dave

It is not a dumb question at all.

Your 24 x 8 prop should be fine on the 120SP. We generally do not recommend any pitch under 10, however this is solely because most modellers do not run such large propellers. As with all engines the important element is how you load the engine and by using a 24 dia prop with an 8 pitch, the load should certainly be fine for the 120SP.

I hope this helps
Regards
Laurenne

Damnathius

Thanks Laurenne,

I kind of figured that the important aspect of running these engines was to maintain a "range" of operation within RCV's specs, avoiding over-revving AND overloading with a given prop size.

WarpdSpazm

If I can add in on this thread.
What would be the "ideal" max rpm ranges for the 90 and the 120? I'm still not sure as to which I will purchase yet.

It may sound crazy, but I am calculating to swing a large 4 bladed prop, hence the looking into the 120.

Using the standard math from Zinger's website, a 20-12 (an RCV rec. size) on 2 blade I come out with an 18-10 4 blade (as a starting size of course) This is pretty close to the perfect scale diameter of 19.5" Though with the above theory of changine pitch to keep the RPM range, I could again mathematically work out a 20-8 (and round the tips down to 19.5") now taking the vain assumption for converstations sake, that any of these (18-10, 20-8, or any size in between) would fit in the rec. RPM range, would that make it a usable prop (with the dislaimer that it won't ruin the engine - flying the A/C is a whole 'nother story I assume).

Hope I didnt' confuse you too much.

thanks

~Ray

RCV Engines

Hi Ray

In answer to the max rpm ranges - the ideal is between 1,400 at idle to 5,500 at max. This is the same for all of our SP series engines.

In regard to your calculation, I am unsure how the Zingers' website calculates their maths.
We understand that the general rule for 2-blade to 3-blade is decrease the diameter by 1" and increase the pitch by 1". It is also our understanding that a similar rule applies for a 3-blade to a 4-blade. Based on this we would recommend an 16x14, or 18x14 or similar.
Saying this however, we have also tried an APC 15.5x12 4-bladed prop with the 120SP and this performs well........rules are there to be broken ;o)

The best bet is really to try a couple of different propellers yourself and see how they perform with your engine/plane combination.

I hope this helps, but if you have any more queries, we will be very pleased to (try and) help.

Best regards
Laurenne

WarpdSpazm

Just FYI, They have a 2 -> 3 or drop 2" in diameter. from 2 -> 4 2" in both....

http://www.zingerpropeller.com/_2_blade_.htm

It does seem contrary to your method which I have also heard. The only way I'll know for sure is to buy about 10 varying props and test them all on the exact same engine. Maybe not when I see 16+ inch 4B's running $60 a pop.

And, as I forgot to actually ask last post... The major benefit of the 120 over the 90 would be to swing a larger prop at the same RPMs (be it 2B,3B or 4B), correct?

Thanks again, and I promise to give you some returns on all the work I've made you do

~Rm

RCV Engines

Hi Ray

I see. Perhaps wooden propellers have different requirements??

Also I agree with you on the testing - it could become very expensive if you purchased lots of propellers. I would recommend running an APC15.5x12 4B first, as this has been proven to be okay. I would also recommend you keep the pitch up slightly, with a 2-blade, do not go lower than a 12 or 10, and with a 4-blade, do not go lower than a 10 or 12.

With regard to the 90SP and 120SP. The major advantage/difference is that the 120SP is a more powerful engine (in exactly the same way as the OS120 is more powerful than the OS90, although the difference in power between the RCV 90 and 120 is slightly less.
Anyway, the 120SP will certainly pull larger propellers at the same RPM.

We are always happy to help, so please don't hesitate to ask if you have any more questions

Regards
Laurenne