I got few PM's asking for more info on a particular plane-vivat powered by a sm30 gas. I couldn't answer those questions myself, so I have sent a mail to the owner of this model- Piotr Urbanski. This is what he has written to me:

"Basic reason for being interested in gas for a pattern plane is of course the cost. Because my son is also involved in the hobby, we spend a lot of money on fuel, we have used about 250l (about 55 galons) of fuel (with 25% nitro) last year.
For the money we have spent on fuel, we could buy few gas engines. I also wanted to popularise the hobby.

It was very easy for me to get a gas pattern plane under 5kg. After weighing the powerplant (motor+exhaust+prop+motor mount+ignition) I realised that sm30 30 is just 400g(14 oz.) heavier than YS 1.40. The weight is so smalll beacuse, I have used my own, very light motor mount, pipes made by Stefan Gaudynski (100g-3,6oz for YS and 130g-4,6oz for sm30) and prop-wooden or carbon(about 70g-2,5oz lighter than APC).

My VIVAT with YS 1,40 (2003) weighs 4350g (9lbs 10 oz), so I knew that with gas it will be under 4800g (10lbs 10oz). Now I know that for converting pattern planes I have to choose models that weigh with YS 1.4 under 4400g (9lbs 12 oz), is quite wide at the cowl part (beacuse of 3 motor mounts used) and that have wings mounted using a pipe (carbon), because you have to move the wings forward in order to get the proper CG. Vivat is OK for this reasons, I only had to modify the front of the fuselage.
Here are my thoughts about flying:
Very powerful powerplant-it goes straightly up on 1/3 of the throttle!!!
Model is much faster than when using a Yamada, so I changed the prop from 17x12 to 18x10, and I also plan some changes to the motor, which maybe will decrease this huge amount of power, but will help in throttle managment -especially at low and medium RPM's.
Right know it is good to fly in the box with 150-170m (about 500 feet) on both sides) flying really big loops etc.

What is really great about gas is the incredible consumption of fuel- 0,35l (13 ounces) fuel tank gives me about 20 minutes of program flying!
After problems with tuning the engine, it starts by hand ( I haven't taken off the cowl for 30 flights.

If anyone is interested in buying a Vivat-which is really great for converting to gas look at www.modelairpol.com "

So that's it for now- if anyone is interested in any details just feel free to ask - I will try to answer them.