I have one OS 91 and several Magnum 91 four strokes they all turn a 14x6 APC @ 10k sustained, this engine turns a 14x6 APC @ 8950.
That is a huge difference in power. I think it is very misleading to state
"Comparing it to the other normally aspirated .91 four strokes I've flown, the RCV .91s power is right up there: ..."
That is just my opinion.

Thanks for the great post and look into the compact RCV engines. I have been keeping my eye on these engines for quite some time now and will probably end up purchasing one. The engine appeared to run flawlessly on the test stand and I have no doubt that RPMs will continue to increase as the engine breaks in. Although the rotating sleeve design may produce more parasitic internal drag than some engines, this engine will have less airborne drag due to its more compact profile. I like it!

I had flown the same plane with the OS 91 and noticed no difference in performance between it and the RCV. I'm sure with a bit more time on the RCV, its top RPM will increase. I've found peak RPM is not always the true indicator of an engines power and performance.

"I've found peak RPM is not always the true indicator of an engines power and performance."
hmmmm...
Well Rich...
What do you find is an indicator of engine power and performance then?
...Just trying to learn...
NYCRC

All of this conjecture may very well be explained by differing performance in the air. Don't forget before we start slamming people that engines behave differently in the air than they do on the ground. Peak RPM on the ground does not totally indicate what an egine will do when it "unloads" in the air. As different as this engine is it may "unload" more in the air than other brands which would explain the author seeing very little difference. If you need anymore proof ask yourself why we set our engines rich on the ground.

BTW nice review I have often wondered about these engines thanks for going through the trouble to write up your experiences.

Originally Posted by nycrc

"I've found peak RPM is not always the true indicator of an engines power and performance."
hmmmm...
Well Rich...
What do you find is an indicator of engine power and performance then?
...Just trying to learn...
NYCRC

I agree with Rich. For my SK engines,Kangke Tech department advised that
the engine should be kept on 11000-11500 RPM s max on ground to obtain best result due to port timing,so propeller should be chosen accordingly.The torque is the first factor here because of the port timing issue.If you overrevv then overheat problems occur.
If you want more info pls. take a look at the threead:
http://www.rcuniverse.com/forum/m_45..._1/key_/tm.htm
Especially Post #:49,106,113

Lightning,
I wasn't "slamming" anyone so please don't turn the blow torch my way.
My question is if you are seeing 1,000+ rpm difference on the ground, all things being equal such as fuel, prop, weather, etc., isn't that a big difference?
As far as unloading in the air, unless somehow mechanically limited such as valve float, etc. wouldn't the two engines still show a significant difference in flight performance?
As far as "torque" and "horsepower", when grounding running the engine with flying prop isn't that a "loaded" condition and the engine characteristics in flight, except for extreme orientations, such prop hanging, etc. be pretty much the same?
I read the linked thread. Interesting about the tappered bore not being able to tolerate too rich running and needing heat to expand. I wonder if the engine would be safe to run in cold climates like here in the northeast in winter?
Like I said...
Just trying to learn.

I just had to try one of these designs so picked up the .58 RCV about a year ago. At first I was dissappointed with the high idle speed necessary to keep it running. However, now, after a gallon of fuel, it is outstanding in performance, low idle, low fuel consumption, lots of power, instantainious throttle respons, great fuel draw etc. It is now my favorite 4 stroke and will run well over 12 minutes on an 8 oz. tank at full throttle. I actually have it mounted with the throttle assembly at least an inch above the top of the fuel tank with no fuel draw problems and no problems with inverted flight with the throttle assembly now an inch below the tank, no change in RPM or power nor idle--fantastic.

Hello NYCRC,

I see you just joined, so first of all let me welcome you to RCGroups! There are a lot of great people here that are always more than happy to help anyway they can.

The RCV I tested is a ringed engine. And a little different sort of ringed engine to boot. At the time of the RPM readings it was approximately half way through the recommended break-in. I'm sure RPM will increase as it continues to break-in. As I flew the plane the engine did seem to be getting stronger with each flight. I’ve had some engines take close to over two gallons of fuel before they were performing at their peak. I’m sure it will attain the mystery RPM difference as it finishes breaking in..

All engines are designed to have a torque curve. This can be altered by port\valve timing, carburetion, exhaust back pressure, air intake, etc. Actually manufacturers could probably provide much more rpm than the engine produces, but at a sacrifice to the “usable” power band of the engine. (i.e. low end verses midrange, verses top end, etc.)

There have been many threads and entire books written on engine performance. And all of them by people a lot sharper than me on the physics and statistics.

Unless you have an onboard data recorder, it would be impossible to determine what is actually happening RPM wise in flight compared to on the ground. I’ve had a good strong wind come up and change an engine a few hundred RPM on the test stand. It would be interesting to see what actually does happen to a glow engine comparing flying upwind to downwind.

Ø What do you find is an indicator of engine power and performance then?

I had flown this plane with around five or six different engines, both four stroke and two stroke. So had a good indicator of how the plane performed with each engine. I‘ve had engines that turned a third more rpm than the other on the same prop, that didn’t fly the plane as well as the slower engine. All related to the torque curve and type of flying being done.

Putting the physics issues aside, and maybe I’m old fashioned. But to me how the engine actually flys the airframe I install it in, is the biggest indicator. Not very scientific, but it has always worked for me.

Once again welcome to RCGroups!
Rich

I looks like a similar design to the HP VT.21 and VT.49 four strokes. The Hp had just the combustion chamber that rotated, the glow plug and exhaust are on opposite sides of the engine, and also gains better performance after about 2 hrs of breakin time. The only problem The HP four strokes had was their power to weight ratio. They were heavy engines. I hope the RCV's overcame that problem.

Originally Posted by chashint

I have one OS 91 and several Magnum 91 four strokes they all turn a 14x6 APC @ 10k sustained, this engine turns a 14x6 APC @ 8950.
That is a huge difference in power. I think it is very misleading to state
"Comparing it to the other normally aspirated .91 four strokes I've flown, the RCV .91s power is right up there: ..."
That is just my opinion.

Sorry if my first post was read as a flame.
It was not intended to be.
The review of the engine is excellent, well written, and with some real RPM numbers included on several props, a lot of work went into it and this is very much appreciated.
The RPM numbers I posted for the OS and Magnum 91 four strokes are not peak numbers, the engines fly at these RPMs.
Since the fuel I use and the fuel used in the review is both 15% nitro and the prop is APC 14x6 the setups are roughly the same, I am near Dallas, TX so altitude is not helping me.
I think the RCV is a really neat engine and if it fits in a cowl where you would have to cut a hole to make a different 91 fit and the RCV has enough oomph to get the job done then it could be a very good choice.
After the engine gets a couple of gallons of fuel through it I would like to know if the high end improves.
Until then I still think 8950 compared to 10k+ is a lot of difference.

One little sort of "warning" for anyone buying an RCV .91CD...

Be sure and remove the little vinyl cover over the crankcase vent before you run it!

I could NOT get my new .91CD to run properly on the break-in stand. After a lot of frustration, buyer's regret, etc., I noticed I had not removed the vent cover (and I think it IS mentioned in the manual).

Once I removed it, everything was fine.

I haven't mounted the engine in a model yet, but I'm hoping to find a home for it over the winter and put it to use next season.

Good flying,
desmobob

In the RCV engine thread over in RCU the representatives from RCV state to expect 9,000-9,200 (minimum) with the 14x6 on it. The engines are run, tached out, and are shipped if the engine meets the minimum RPM of 9,000. Unlike at least one reader in here, I understand the value of torque and how well torque will fly an airplane and how that airplane will respond to an engine with good torque. The engine appears to have instantaneous throttle response and comes up extremely quick to max RPM. This feature will really make a plane respond quickly to the pilot's input and should put a pretty good smile on his or her face!

Hi guys

I thought I would put my twopence worth in here, even though late.
The RCV design means that power keeps increasing with use unlike conventional engines.
The other thing that is highlighted, which is correct is that RCV produce very torquey engines, this is just as important as rpm in how a plane performs.
We get loads of feedback on our engines from existing customers, and truthfully, I have never heard anyone disappointed with the power in comparison to conventional 4-strokes in the same size, even when the engine is hardly run.

Best regards
Laurenne
RCV