RCU Forums - View Single Post - In-Line Twin projects
View Single Post
Old 10-05-2014, 06:09 AM
  #205  
Jeremy_H
Senior Member
 
Jeremy_H's Avatar
 
Join Date: Aug 2013
Posts: 444
Likes: 0
Received 0 Likes on 0 Posts
Default

The 32 is the front engine, it's the one that is in effect a normal installation, and not impacted by the second engine.

However, it's academic now as I sussed it.

After I posted here last night a dug around a bit deeper on the net regarding the bypass system. What I hadn't come across before was the position the T off should be in, and the missing element proved to be that. It seems the best place to leak off the surplus pressure is as close to the needle valve as possible, with the very best position being on the carb itself. Buried in Perry's site a little was a note on bypass systems, and there it's reported as needing to be 1" from the NV. On these engines I went for rear mounted NV's for safety, but that's left me with a handicap in the length of tubing between the needle and the carb which moves a Tee off position over two inches from the carb. Add the length of tubing I had and it was way off the mark. Reading around this need for the bypass to be close seems universal, so whilst the 40 seems quite happy like it is as soon as I moved the tee off to immediately before the NV on the errant 32 and re-ran the setup procedure it all came good. I changed the 40 to this close T arrangement too but it didn't seem to make any difference to the engine that was working already .

I now have what I need, and with the tests carried out with tanks at deck level I can revert back to the original design of cockpit without any silly pseudo air intakes. It just all got a lot simpler.

By the time I'd finished today I had engines behaving as if they were in a regular installation. The only remaining issue on the 32 is the thing that pretty much all RC engines do, over cool if on idle for a long time, needing to be coaxed back into throttling out. The rear 40 doesn't do this, it keeps heat in the head much better being reversed I guess, but this is a minor problem which can be cured with on board glow power. I've been looking at an auto system which rolls off according to RPM and I might go that way for the hell of it, but it's costly so I may just have a couple of micro servos on switches in the radio box 'Y'd into the throttle servos, to give an on/off for low revs for little cost. It would be nice to be able to launch without running a high idle when carrying this thing to the lakeside .

https://www.youtube.com/watch?v=4a-mfEhPY3k&feature=youtu.be And now a complete diversion, for an Airboat to come. I've always wanted a Four Stroke Nitro motor, but the cost has put me off, so having such success with the budget SC motors I have now ('Super Crap' as they are called) I've bought their version of a 91. I've no idea what I'm going to put it in

Attached Thumbnails Click image for larger version

Name:	IMAG0489.jpg
Views:	55
Size:	2.27 MB
ID:	2037370