On Tower's web site there is a number of different OS 4 stroke lines - FS ultimate, FS surpass, FL... Can someone clarify on the difference between all these? Is it similar to the difference between the AX and the LA?

Also, most of the guys at my field fly Magnum 4 strokes - which OS engine is in the same category as the Magnum XL 70 RFS?

Last question is about understanding the pros and cons of using either a 55AX or a 70 four stroke in a Hangar 9 Pulse 40. From what I remember I'd get more RPM's out of the 55AX, and more low end power out of the four stroke? Anything else?

Thanks.

The Ultimate has a more sophisticated fuel system than the Surpass, hence the difference in price. If you want the best buy the Ultimate, if your budget permits you of course.

Cheers Ian

OS 4-strokes are EXCELLENT. I just got done bolting a .91 on my Skybolt. It started right up and sat in my driveway idling perfect. It runs smooth and seems to have plenty of power. That is on 10% fuel too. I know some people will say Saitos are lighter and have a little more power. That's generally true but I have experienced longer break in times on the Saitos and the need to run higher nitro (my .82 seems to like 20% for now). In my opinion, if you want a more user friendly 4-stroke, go for the OS.

The Surpass-2 line of OS 4-strokes has been out for quite a while. You'll notice that they now also have a .56 and .81 "a". These are slowly replacing the Surpasses. I can't wait to get my hands on an "a" model. The FL-70 is another story. It is an entry level engine sort of like an LA 2-stroke. I've owned a couple and they run great as long as you mount them upright or sideways. They have a carburetor that uses an air-bleed idle circuit that causes a lot of running and tuning issues when mounted inverted. Also you can't reverse the carb mounting on the FL so throttle hook up could be difficult on some planes.

For the Pulse, I'd personally run a 2-stroke. Either a .46 or .55 AX. I'm not sure why I feel that way, it just looks like a 2-stroke plane to me. A .70 or .80 range 4-stroke would definitely fly it well though, don't get me wrong.

I asked about if the OS FL-70 is great choice for a 46 UCD and they told me to install an even bigger engine, while the manual only reccomends for the 46 4-stroke engines in the range of 51-70 (something like that). That's why i chosen a 70, because is the biggest i can install. With a bigger engine, i think it will be hurt to do aerobatics. What about that?

I have a saito 100 in my pulse 60 and love it. I will prolly never have another 2 stroke glo engine agian. The os ultimate series has a built in fuel pump and is not really needed for a pulse so I would save the $100 if I were you and go with the surpas or a saito. I was gonna go with os but I liked the lighter weight and extra power of the saito. Not that it matters for the pulse but I was thinking ahead incase I wanted to use it in a 3d plane later down the road.

If there recomending a bigger engine then the os 70 a saito 82 would prolly be perfect and it weighs pretty much the same and has same mounting size. A ys63s would really be nice on it but they are a little harder to get setup properly.

The Surpass line is the mainstay of the 4 stroke OS family. The Ultimate series has the pumped fuel system, and therefore is a more expensive line of engines. The L series is a less expensive line, probably designed to make the Magnum brand (which are almost direct copies of the old Surpass design) less attractive. The Gemini and Psegaus line of multi cylinder engines are top of the line for that type of power. You won't go wrong with any of the proven line of either OS or Saito 4 strokes. I have an OS Gemini 120, and a 160 twin as well. The 160 likes 15% fuel, where the 120 twin will only tolerate 10% max. Learn what your engines like, and stick with it.

Bill, AMA 4720
WACO Brotherhood #1

What about the ratings for size - the Pulse 40 is suggested to run with a .40-.46 2 stroke, or .56-.82 4 stroke. Does this mean that one will get similar performance from a .46 2 stroke and a .82 4 stroke? What would compare to a .55 2 stroke? How do they come up with these size ranges?

Well, i appreciate your offers about Saito etc, but i really i'm stuck with OS engines here, so...[:-] I don't think that a bigger size than the 70 is needed on the UCD, what do you think?

I fly both O.S and Magnum four strokes. The 52 four stroke is equivlant in overall power to a 40 size two stroke. THe four stroke can swing a bigger prop and has better throttle response. Two things that are a pluss for a plane like the Pluse. You are not going to fly it at full throttle for more than a couple seconds at a time. What you want is quick and reilable throttle response throughtout the range and lost of low end thrust. I'm just getting my feet wet in a Phenoex Fun Star. I've got a O.S 52 in it cranking a 13x4 apc. I am flying at 1/3 throttle. In fact the meager instructions warn you not to fly at full throttle for any length as the control surfaces will start to flutter. I can't imagine a 70 on this plane, although the extra weight would be good. I had to add 6 oz of weight to the firewall and a 70 weighs just about 60z more than the 52.

I have a Magnum 70 in a Ruperts Dad, a build from plans plane that callls for a 52 four stroke. That one also needed weight up front so that is one reason I used the 70. The wingspan on it is about 8" longer thant the fun Star and the plane weights about a pound more. The seventy is a good choice for it. I crank a 14x4w APC withi it. Compairing the Fun Star to the Ruperts, the Fun Star seems to have a ton more power.

I also fly a Magnum 91 in a 4*60. Again all the power you could ask for. All three planes are not speedy, so the four strokes are great fits for them.

Don

Thanks Campgems. I agree that I'm looking for the ability to swing a larger prop, and although I didn't realize 4 strokes had quicker throttle response, it sounds highly desirable as well. I notice that on my 46AX, that before going vertical I have to hit the throttle pretty early.

However, from reading above, the 55AX sounds like it might be a better option for the Pulse. People have been suggesting the .46AX, or maybe even the 55AX. It sounds like I would need an .82 4 stroke to match the power, and that's a lot more engine than I was planning on for my second plane ($300+) The 55AX can swing a larger prop than the 46, a little more power, and won't sacrifice too much of the top end speed. What I (think) I'm going for is high speed and good aerobatic capability, not really 3-D.

There are not a lot of OS engines at my field. Other than one 46FSi on a Nexstar select, I have the 46AX in my trainer. There are lots of Magnum 4 strokes, and some Saitos. I have, by far, the easiest starting and most reliable engine at the field, and want to stick with OS. The Magnum does seem to be a performer, and the price is great for the 4 stroke, but OS has got me with this amazing new 46AX. Maybe with tax returns next year I'll get a plane set up with a nice 4 stroke O.S.

Thanks for the help.

There is a 3d flying forum of RCU where you might get a good answer.
http://www.rcuniverse.com/forum/forumid_82/tt.htm
The u-can-do, and its set up, is definitely above the level of the beginner forum.

The other thing to consider is that 2-strokes and 4-strokes deliver their power a little differently. A 2-stroke generally likes to run at high RPM while a 4-stroke has more low end grunt. As for throttle response 4-strokes are great but your .46-AX should have near instant response too along with a nice smooth idle if it is tuned and propped right. The .55-AX has a power band somewhere in between a 4-stroke and a typical 2-stroke. It has more low end and will pull bigger props than the .46 but won't quite make as many RPM's. All are great and have their place. It is also a matter of finding what you like best for the way you like to fly.

I already did it. Is just that you began the 4-stroke converstaion, so i given a shot, to see what i would fish The answers are the same as the 3D's forum, of course i had one PM here and that helps me a lot, thanks