Which Engine?

I am nearing the end of building a 60" wingspan Yakovlev Yak-52 model aircraft for my son to add to his flying collection, but cant make my mind up whether to use a .46 two stroke engine, or a .70 four stroke engine, I have both engines to hand so cost is not an issue, but until I decide, the build is at a halt, because the positioning of servos, and the route of the throttle pushrod past the fuel tank, and other considerations are affected by the engine choice.
What would you do, two of four stroke?

Re: Which Engine?

I'm so far out of date, I didn't even know you could get 2 stroke and 4 stroke model airplane engines. The last time I had one was over 50 years ago when the only model airplane engines available were either Diesel or elastic bands.

Re: Which Engine?

It's quite High Tech nowadays Mick, a .46 2 stroke is about 7.5cc, and a .70 4 stroke about 11cc, just like full size vehicles the 2 stroke is very revy and delivers power high up the rev range, the 4 stroke has more torque at lower revs, but both have similar bhp. Normally 4 strokes are mounted upside down, in this case, it will probably be the .46 as the character of the plane is best suited to it.

Re: Which Engine?

I think the biggest diesel engines back then were only about 1cc, and they had just introduced glow plug engines. The newer engines must be a lot more powerful - mind you, for a 60" wingspan, it would need to be. My biggest plane was only about 24".

Re: Which Engine?

The sons largest model at the moment, is a 100" span aerobatic CAP 232, you are limited by all up weight at most flying clubs, anything to heavy needs a CAA exemption certificate.

Re: Which Engine?

It's a while since I made any model aircraft, but for larger motors I think I'd tend towards a 4 stroke.
(I have a vintage 6.3 cc single cylinder, spark ignition 'Mechanair' 2 stroke motor in a box here.)

Re: Which Engine?

Don't know a lot about vintage motors, apart from the fact that they seem to be worth a few bob to devotees, modern variants can be unpredictable, so I can only guess that early versions could be tricky.