just wondering which size 4 stork engine is suitable for a 60 size trainer? 80? 90?

usually a 4 ftroke is 50% larger than the recomended 2 stroke so that would put it in the 90 class

.40 size 2-stroke = .52 - .70 4-stroke
.60 size 2-stroke = .70 - 1.00 4-stroke
.90 size 2-stroke = 1.20+ 4-stroke

My preference it to use an OS 91 Surpass 4-stroke in planes calling for an OS 61 FX. Another good alternative would be the Saito 100 4-stroke. I'm currently doing a review on a World Models Super Chipmunk, 60 size. I am going to use the Saito 100 in it, but I was a bit concerned about the weight of it compared to the OS 61 FX. I was afraid I would have to add weight in the tail to compensate for the heavier engine. But after I looked at the specs for both engines I found that the Saito 100 is actually just a hair lighter than the OS 61. I haven't flown the plane yet, but it should be a nice combo.

Hope this helps

Ken

Victor - I think what is more important is you look at what you wanna do in the near future, the trainer is not going to last that long as you will out grow it. I seen trainer like the Super Frontier that I am pretty sure despite being a 60 sized plane, will even lift off on something like a Saito 82. If you are not going into 3D and serious aerobatics then engines like the ASP/Magnum/TT 90 sized 4C are good enough. If you wanna go into 3D etc then nothing will beat the Saito 100 or OS91 Surpass.

Ken - the Chippie is a super nice plane to fly. Had a ST90 on mine and it balanced out well. Later got another for EP with an AXI 4130/16 on a 6S set up. With the SA100 and a 15x6 prop it will have almost unlimited vertical.

thank you very much ! really helpful suggestions. going to buy OS FS91 surpass.

Hello; Have you considered Saito? The Saito 91 is much lighter then the OS91. The Saito 100 is lighter then the OS 91.

I would use a Saito 80 in place of a 60 two-stroke, but I'm sure the new Saito 82 would be just as good, just lighter.

A consideration is the power to weight ratio, modern Saito's weigh less then the two strokes of an equivalent output. Lighter flies better.

I have an OS91, but I have never used it, no that's not completely true; I put it in a GB Extra 300 then I put it in a GB Ultimate for a little while before I bought a Saito 91 to put in there. Good engine just heavier then it needs to be.

I built a Great Planes PT-60 about 3 years ago. I used a Thunder Tiger 61 Pro two stroke.. The four stroke GP recommends for this kit is the FS-70 Surpass. For a trainer, I think the 70 would be plenty. I do not think a 91 would be "too much" though, so I'd probably go with the 91 if my future plans were for 60 size planes.

Another thought since there's a lot of discussion about weight. My PT-60 built very tail heavy. With the TT-61 it needed about 3 ounces of added nose weight to balance.

The TT 61 is listed on Tower's site at 26.1 ounces with muffler
OS 70 Surpass, 22.1 ounces with muffler
OS 91 Surpass, 24.2 ounces with muffler
Horizon's numbers are:
Saito 82, 17.6 ounces with muffler
Saito 91, 21.0 ounces with muffler

So, in my case, a lighter engine would have just meant more lead on the nose.

I agree. in some case, light weight is not always the best choice. the model which I am about to build is a 60 trainer, do you guys think that 90 surpass with 13X6 will be fine? or I need bigger ones if yes what size thanks