RCV 120sp investigation

[J D 8]

  RCV engines today make engines for UAV's although they are no longer rotating cylinder, more like the Webra / HP engines with an overhead rotating valve.

[Nick Cripps]

12 hours ago, Jon - Laser Engines said:

Is buying models an addiction? if so i think i need one of those support groups to help me. 

This forum is the support group, Jon!

 

I always felt that the RCV design was a solution looking for a problem...

[Jon H]

In some respects i agree Nick but the general concept is fair enough. The use of large props at low rpm is good for noise in the air, the slimline nature is good for warbirds and a clean cowl. 

 

Unfortunately these good points are countered by the bad. Gear noise is a big problem, the clean cowl idea is thwarted by the fact that the engine is still air cooled so cooling holes need to be cut and the engine is very critical on its manufacturing tolerances meaning its expensive to produce. The volumetric efficiency and anti knock advantages of sleeve valves on full size engines are also not recognised on engines as small as ours. 

 

Add to that some curious design choices internally it does become a bit of an oddball. 

 

Still, i am enjoying playing with it even if it shaken my test bench apart and pours a continual stream of hot oil from the breather all over my hand while running. 

 

[Jon H]

Its been a while....

 

I have continued to fiddle with the RCV but have not really made much headway. I always thought that compression with the dodgy ring was part of the problem so i decided that i would use my new lathe to make one. 

 

Getting carried away i made 4..

 

 

One was fitted and compression was much improved before i even ran it. I got the engine fired up and it seemed to run quite well but was very difficult to tune. 

 

When the engine was at idle i noted the carb barrel was moving about and there was significant end float in the barrel. I whipped off the carb and after some drama (see my lathe thread for details) i knocked up a new barrel screw. 

 

I tried to run it again but it wouldnt start due to lean slow run mix. Clearly the tighter fitting barrel screw changed the mixture, which was a good sign. 

Once i got it going the engine was so much nicer to use. I gained 300rpm top end revs due to better tuning stability and halved the idle rpm. Transition was better, the engine ran quite smoothly, cleanly, was quite frugal and no longer shows any signs of overheating as well as holding its tune. 

 

I now see 4400rpm peak and 4300 continuous on the 20x16 apc. According to the manual the engine should idle at 2000rpm prop but that is 4000rpm on the engine. A 4000rpm idle? i dont think so. Following the updates i can now idle in the 1000-1200rpm range and this is much more where i think it should be. This is on 5% nitro 15% oil fuel as before. 

 

For the first time the engine has run well enough for me to really consider it a viable powerplant for a model long term rather than just for playing and testing. I am also quite convinced now that the recommended props are too small as the engine performs very well on this bigger prop. 

 

I was considering an escale seafire as a good test bench for it but they are crazy money at the moment. I will have to find a cheaper test mule before i commit the big bucks. 

[Paul De Tourtoulon]

You mean the 1.6m  Seagull Seafire ?.

[Jon H]

3 hours ago, Paul De Tourtoulon said:

You mean the 1.6m  Seagull Seafire ?.

 

yea. they were called escale for ages and i know them as such

[Paul De Tourtoulon]

I don't know how long your RCV is but the prop driver to 'false' fire wall is 12.5cm , you can cut the 'box' false firewall off which will give you an extra 48mm

[J D 8]

I still operate a 60sp in my Seagull SNJ and it would drive a larger prop no problem, did operate for a while with a 3 blade job but went to a two blade for the look [ full size only had a two blade] With the 15inch prop I have only an inch ish clearance when running level on a take off run.

   One thing with these engines is you do need to have a strong stiff firewall/bulkhead mount. The fore and aft movement of the piston results in some different stresses.  I do like the noise, much like a full size radial on a low fly past.

[Jon H]

At idle rpm the fore/aft motion is very apparent on the bench. My bench is falling apart though and i have to be a bit careful to prevent the engine flying off over the fence. Building a new bench is on the list of things to do over winter.