CDScaleDesigns Sopwith Pup

[Manish Chandrayan]

Hello Martin, yes that is based on my personal experience. I had bought one from Weston UK long back (think 2008/9 maybe) bench ran it then and was horrified to note the hot case while running it on the bench (my standard check being able to momentarily put my finger on bottom of the case while the engine was running). That led me put the engine away . During the lockdown bored took the engine apart and was able to service the engine and run it again. Was informed by Weston that the hotter running is normal. Flew the engine on my Goldberg Chipmunk where it was sufficiently exposed in side mount configuration and it performed satisfactorily.

Best was the quizzical looks from others at the filed who wanted to know what kind of two stroke was it and were told it wasn't one 😃       

Here is a short video of the engine being test run post the lockdown rebuild, I may have used the original muffler elsewhere and hence used one from OS 95 that was hand

 

Edited April 17 by Manish Chandrayan

[Paul De Tourtoulon]

I have had 2 of the RCV .58's, both ran hot, both less powerful than an OS.48fs, high idle and doesn't like Castor oil,

the best running I got out of it was with 10% nitro and 12% synthetic oil, os F plug and I did make a finned head from an Irvine .53 to cool it down better, and also put another rubbish carburettor on it which gave me a better idle, "however", it never packed up in the air on me.

[Martin Harris - Moderator]

How strange for Paul - using a fuel with no castor!

 

I can't say that I've noticed any sign of overheating but my version (91) sits in the front of a very vintage (re-engined several times) circa 1982 Stearman, nicely exposed to the breeze between the dummy cylinders.  I hesitate to say this but I promised the old boy who "gave" me (I managed to persuade him to take some money) the model when he was downsizing, that I would use the several gallons of Duraglo 10% (6% castor/9% synthetic) that came with it which was "the one and only" fuel recommended by the distributor before Westons (oddly, one that they distributed) and have largely honoured the pledge.  The old boy used to bore (and often exasperate) club members by constantly harping on about this recommendation.  Strangely, once Westons took over the engines, their fuel became the only suitable one!

 

Could he have had a point?

 

The idle seems quite normal and I don't recall 58s having problems - perhaps they redesigned the carburettors at some time? 

 

There shouldn't be too much problem arranging good cooling in the Pup, Lindsay, as long as you don't fall into the trap of thinking the wide open spaces of a rotary's cowl will provide it.  Rather counterintuitively, what actually happens is that hot air pools in the cowling around the engine and any airflow takes an easier route. A dummy engine or suitable blanking plate to encourage air to flow over the cylinder and head, coupled with a suitable exit should do the job.  It looks like BEB was mounting it inverted so a good exit should be easy to arrange.

 

 

[Paul De Tourtoulon]

11 hours ago, Martin Harris - Moderator said:

How strange for Paul - using a fuel with no castor!

Yes on plane engines, but some of the 2.1/2.5 and 3.5cc car engines would not run properly and especially the racing 2.1cc Rossi car engine would not run with  castor in them but would run happily on 15% nitro and 10% synthetic oil all day.

 

 I did have my own model shop for 20 years and mixed and sold ( very successfully ) my own make of fuel, all different,

 Car, plane and Helicopter.

[Manish Chandrayan]

Martin, when I said the RCV ran hotter, I did not intend to say it was overheating. It was more like, that's the nature of the beast!. Especially when I first ran the engine I was rather surprised. But then the engine never failed me in flight. I mostly mix my own fuel and have to rely on what's available in terms of synthetic lubricant so sometimes it would be 100% synthetic Klotz techniplate or the 20% castor mixed Klotz super techniplate. I think I ran the engine on both and did not face any issues.

On a different note I do have a NiB 91 CD that is saved for a suitable project someday. And for the sheer experience of it I am trying to acquire one of the SP's    

 

I too would suggest that Lindsay run the RCV on the model, that is what the original builder intended to use.  I am sure he will face o issues once correct baffling is in place. 

 

     

[Lindsay Todd]

Thanks for the insight guys as I said not to familiar with RCV so always good to get direct feedback. I will bench run before I use on the model anyway just to check set up etc but sounds like all should be ok. Its not exactly my first model of this type so very familiar with radial cowls and cooling issues etc. Hopefully we'll get a dummy engine in place to assist and possibly help with balance as obviously most of the radio and electrics are all shoved up the front end, bit of a squeeze at this scale, so much easier on a 1/4 or 1/3rd scale job! I do intend to complete as BEB intended, a good friend, colleague and much missed.

Linds