rajul

My Feedback: (58)

Hi all, I originally wanted to power my 4*60 with a OS61FX but I am thinking of going four stroke now. I have a bunch of questions I hope I can get some help with :

1) What is the equivalent four stroke engine to a OS61FX ? Is it the OSFS70 or OSFS91 ? Where can I get a "2-stroke to 4-stroke conversion chart" ?

2) I notice that OS offers four stroke engines with and without pump. What is the purpose and pros/cons of the pump ?

3) Can I use the same engine mounting provided in the 4*60 kit for mounting a four stroke ?

Thanks a zillion !...............

Mike99

I don't know that there is a hard and fast rule regarding conversion but I would say a sixty size plane would require at least a Saito 72. The 91 size four stroke would be a Great engine for that bird, plenty of power and allow you to get into aerobatics. Four strokes are a little more expensive, have more low end torque, but less top end speed. Mounting is different for the 91 size.

FHHuber

The 4-strokes are MUCH lighter than the 2-strokes. My .91 FS with muffler weighs less than the .61 FX without muffler.

I agree that .72 is about the correct 4-stroke equivilent to a .61 2-stroke. But... I'm going to be sticking my .91 on my 4*60 anyway.

The plans for the 4*60 show a Saito .72 as the example engine. (looks like even Sig thinks that's equal to a .61 2-stroke...)

You can use the kit's nylon engine mounts for the 4-stroke. No problem except MAYBE (haven't measured yet) the width between cheek cowls.

the pump version is for better fuel flow in some aircraft, where the tank is further from the engine. I have the non-pump version, and have had no problems with fuel flow at any attitude with the tank right behind the firewall. (similar location to what you'll get in the 4*60)

rajul

My Feedback: (58)

Hi FH, which is a better engine : OSFS70, Saito72 or YS70 considering that I am a first time user of 4C engine ? Or will I be happier if I just stick to the OS61FX and concentrate on developing flying skills rather than getting bogged down with 4C issues ? Thanks for the advice.................

FHHuber

Once you get a 4-stroke.... you won't like the 2-strokes nearly as well.


Generally...
For simplicity and reliability as a sport engine.. O.S. Thier smaller 4-strokes are meant for the sport flyer, and they'll give a lot of trouble-free service.

Saito's a bit better and YS is best for competition, such as Pattern. They tend to need more maintenance... but they give more power. (and tend to cost more...)

**********

With the modifications I'm doing to my 4*60... I'll possibly need the power of my .91. I'm thinking on the lnes of retracts, flaps and smoke. (smoke turned on can cut engine power up to 50%! Lots of backpresure.)

rajul

My Feedback: (58)

Hi FH and all, One question I have is if you compare the 4C engines from OS, Saito and YS in the 70 and 90 classes, what are the nitro content requirements and the fuel consumption like ? From some of the threads I see, it seems like Saito and YS requires higher nitro (up to 30%) and their fuel consumption is higher compared to OS. Could you kindly comment on this ? Thanks again..........

FHHuber

I can't comment much on fuel consumption of the other brands...

The O.S. .91 burns considerably less fuel per minute than a typical .61 2-stroke. I've run Powermaster 15% 4-stroke blend (16% oil), custom mix 10% nitro (10% castor, 10% synth), and Powermaster 10% sport (18% blended lube) fuels. The .91 runs MUCH better on the Powermaster 10% than on the 4-stroke blend. I ran out of my custom mixed fuel just as I finished break-in.

The trend at our field is for the YS users to use 20% nitro. And the Saito users are running 15% and 20%.

I'm looing more for long term reliability than peak power. The others running 4-strokes at our field are looking for maximum performance for Pattern competition flying.

rajul

My Feedback: (58)

Hi FH, can the OS91FS fit the provided engine mount in the 4*60 kit ? If not, which engine mount will you use ? Thanks.......

FHHuber

I haven't pulled the engine from the Fokker Dr1 yet.... but I expect no problems using the mount in the kit. The engine mount thatcame with my DRi was intended for a 2-stroke .61, and I had no problem.

the only possible problem would be if the beams are too short, as the 4-stroke has to sit further forward due to the carb being behind the case. Note that the plans show a Saito 4-stroke engine using the included mounts...

If the .91 needs a bit more clearance, I'll just cut a pair of 1/4 inch blocks to go between the nylon mount and the firewall.

rajul

My Feedback: (58)

Thanks folks! The 4*60 is a floater, and since I am not planning to add any heavy stuff, probably the .72 will be better especially at landing. The .91 will probably won't want to land even at idle. Question is whether the .72 from OS or Saito is better ? This is something I need to ponder before making a final decesion........

FHHuber

The key to landing a 4*40 is to use a long low pitch prop. I expect the same to hold true for the 4*60.

I'll be using a Zinger 14X4 on the .91. Since 4-strokes can typically idle slower than 2-strokes, I expect to be able to slow it down easilly. (and... probably have the power and torque for torque rolls. )