I have had a 90sp for over two years now (funny signing in here to see pepoles mufflers are still falling to bits ) and I'm getting a 120sp second hand soon. but looking at RCV's website the sizes shown for the multi blade props is identical for both engines, as is the revs range, am I missing something here, why do I need the 120 if it's going to swing the same size multi blade prop at the same revs as the 90sp. Granted the 120 shows larger 2 bladed props, but the whole point for me, and probably a lot of other customers that look at the sp engines, is the fact the sp is capable of swinging scale'ish multi blade props, surely the 120 can swing a larger multi blade prop than the 90, this info needs addressing

Walts.

I have a 120sp and I'm using a APC 4 blade 15.5x12. Runs great. I also have a Keleo exhaust. This thing is awesome.

And thats my point exactly! I flew the 90sp in a Thunderbolt, and guess what size prop I used.........Yep, an APC four blade 15.5 x12

I'm not sure but isn't a 15" 4 blade = to a 17" 2 blade prop?

Hi Everyone

My name is Keith Lawes. I'm technical director RCV

Simple answer to your question is that the 120 could swing a much larger multi blade prop but at the time we specified them there didnt seem to be anything readily availble. If there is anything available now then we would be interested to hear about it.

Also in general if you can fit a two blader it will be significantly more efficient.

You can put the same prop on both 90 and 120SP engines, but the 120 will give you more RPM for a given prop and therefore more power. The rev range figures are a little misleading as in general the 90 will be towards the lower and the 120 the upper.

Prop RPM v power is a cube law, i.e. to double your RPM needs 2x2x2 = 8x the power. So you dont need a very big increase in RPM between the two engines to give you significantly more power and performance:- If the 90SP swings a prop at 5000RPM and the 120 swings it at 5500RPM, its giving roungly 30% more power ((5500/5000) cubed!).

Hope this helps

Keith

Thats a very good and understandable answer Kieth It gives me more confidence to try and source a larger three blade prop for the 120sp, or indeed to not try and get so much out of a 15 x 13 3blade prop on the 90sp. I think that after the initial running in, I was blinkered in to trying to achieve the revs given in the manual, and this may have led to some very hot runs. My 90sp suffered a front bearing failure after a relatively short period, which you repaired under warranty. I flew it for the first time last week in a Hawker Hurricane since it came back from repair and it feels like the bearing has gone again. The engine does seem to run extremely hot, so I'll replace the bearing then treat both the 90sp and the 120sp I'm buying second hand as new engines, and go through the running in process by the book.........and some more! on the bench until I'm happy with them both before trying to fly them in a model again

Thanks,
Walts.

I have a question about the multi-blade props also. I've run a little over a gal. of fuel through my 120SP with a Master Airscrew 18x12. I followed the manual supplied with the engine and I've been able to consistently get 5500 rpm. It idles nicely at 1400-1500 rpm. It does not sag at full throttle. I then added a Zinger 18x12 3-blade thinking that I would loose maybe 500 rpm. Well, the engine only turns the Zinger at 4300 rpm! My plane is heavy for a .60 size plane (12+ lbs.) because I installed lots of goodies that added weight, plus the extra weight of that 120SP. At this point, I'm afraid the the Zinger will not fly this heavy plane at that rpm. If I switch to the recomended APC 15.75 3-blade prop, what rpm should I expect from the 120SP engine? Am I getting the proper output from this engine? If not, do I need to run it some more on the bench to increase performance? Keith, what do you suggest?

In the mean time I've contacted Biela Propellers. Check them out at www.smigla.com. They will custom-make me some 17x12 composite scale props later this year that I will test on the engine. They also will be offering 16x10 and 18x10 scale props available later this year.

Hi,

I run a Biela 18/12 (Standard blade shape) on SP120 during the last season. Prop is extremly stiff, perfectly balanced out of the package, you will be happy with the quality. The blades are broader and thicker than the APC blades. RPMs with APC are slightly higher, and I believe the top speed as well.
Have you been satisfied with the Master Airscrew? I found the blades too soft and the tracking of the blades differed about 6mm, the whole thing vibrated and did not perform well.


regards

Andi

Hey guys glad to see others are looking at the RCV engines. Joe, I guess you finally got your Corsair close to being finished. I too am close! I got the 120SP also because of the weight issue. I am trying to figure out the fuel issue. What are ya'll using and where did you get it? WHat would be a good cheap prop for break in? Joe do you have a post anywhere of you Corsair would love to see it!

Mistral,

I am using CoolPower 10% from Morgan Fuels. It contains synthetic oil only. (RCV has recently begun recommending a fuel with synthetic oil only.) I get it at my local hobby store. I works well, but I will switch to CoolPower 15% for a little more power. Josh uses it and he has much experience with these engines. Bill at BJ's Model Engines gave me a few pointers on these engines a well. Per his tests, the SPs run a little cooler on the fuels with more nitro. I used a Master Airscrew Classic 18x12 for break-in.

You can find pics of my plane in the thread "TF GE Corsair -w- 1/8 Scale Hamilton Standard Hub." Post some pics of your plane. I would love to see it.