Which is more versatile? I'll be sticking with 40 size planes for awhile, and this engine will start in a high wing semi-scale plane, hopefully Sig Rascal 40.

Future planes will include sport/pattern and bipe.

Also, can either/both of these run on the same 10% fuel that's in my 46AX?

Thanks.

For those size engines and the size planes they may be goin in Id get the 55AX. Its not a super revver but is strong. Look in the GP revolver thread in the arf section. I believe theyre gettin em over 100mph with the ax. Now for bigger planes I would lean towards the 4 strokes.

The .55-AX will be more versatile. It will work in anything from 40 size trainers to 40 size high performance aircraft. The .56 4-stroke looks to be an excellent engine too. It will be great for most 40 size trainers and mild aerobatic aircraft (Rascal included). When it comes time for 40 size planes with higher performance though, a .70 4-stroke would be a better candidate than the .56 in my opinion.

I'd love to get my hands on one of these new alpha series 4-strokes and see what they are like.

Both engines should run perfect on 10%. My .55-AX does just fine on it as does my .91 4-stroke. )15% may be better for the 4-stroke but 10% definitely works)

The Rascal has a very small engine compartment and installation is tight. That really limits the size and type of engine you can squeeze in there.

The problem with the OS 4-strokes is price. If money is not a concern I am sure they run great but I do prefer Saito if going that route. I think either engine choice would be fine, but of late I have been partial to 4-strokes.

The only 70 size OS four stroke Tower has is the 70 FL series, and it's not even in stock. Also the planes mentioned above I think are all up to a 5x size four stroke. I would get the 91 if I wasn't limited to size (I drive a Civic[&o])

One other thing about the .55-AX... every time I fire it up I get a smile on my face. It starts so easy every time and runs so well that it is almost hard to believe.

Same goes for my .75-Ax.

Of course my .91 4-stroke runs wonderfully too.

I'm exactly the same way with my 46AX, it's amazingly easy and forgiving, which is why this poll is limited to OS (and also Tower's affiliation with OS/Hobbico which allows them to have the easy pay option). I love that thing so much!

55ax alot more powerfull thatn a 56 4 stroke. very user friendly and a nice engine ....

See below. My 'signagture' pretty much says it all for me.

So youv never tried a 4 stroke..?

I always pick the airframe first and then match with the powerplant.

Your putting up two engines that are not even compareable. The .55AX will outperform that .56 FS any day. If you had asked about a Saito .82 FS then it would have been a different story.

I've got the 46AX that's not quite tweaked for reliable runs but it will be soon (still kind of new). One of our more senior members has the 55AX on a Kadet Senior and I flew it last week. A superb engine! The low end on it was perfect and even the high end, which we didn't use much on the Kadet, has such a low note with the new muffler design that it wasn't much louder than a similar sized four stroke.

Well that's why I asked about it here I wasn't really sure how they would compare. They are the biggest engines of each class that I can get and that I could squeeze in a couple of different air frames I'm considering.

From what I've read, the rule of thumb for comparing four stroke with two stroke is taking the plane's suggested engine size, for example .40 two stroke and multiplying it by 1.7. Of course this is a very rough estimate and you'd be better off by looking at which props they will swing at how much RPMs. Note that with a four stroke you'll gain response from the engine but will sacrifice a little of top speed. Not to mention the fuel efficiency of four strokes, their real-like sound and their price $$$

The weakest engine you're considering will pull a Rascal 40 ARF, a Venus 40 ARF, or an Ultimate Biplane .40 around with plenty of authority.

I flew my most recent Phoenix SeaBee ARF with a Magnum XL .52 RFS, which is considered the weakest of the .52 to .54 four strokes. With a Fox Miracle Plug and 10% Wildcat fuel, it was turning a Master Airscrew 12x6 at 10,000 rpms and the plane performed wonderfully. I enjoyed terrific vertical thrust, knife edge flight across the horizon, and snap rolls so fast they were a little scary!

Any ball-bearing .46 2-stroke would be plenty of engine for the three airframe categories you're considering. Any .52 4-stroke would be plenty of engine as well. Proper tuning and propeller selection go a long way toward maximizing your engine's performance.

The .56a 4-stroke from O.S. would be a significant investment up front, but that would literally be an engine you could be flying a decade or more from now. I think the .55 AX would be a great engine on any of the airframes you're considering, but I don't think it would be an easy engine to hide under the cowl of a Rascal .40 ARF.

If you love O.S. Max engines, I don't want to try to talk you out of them. I just can't help but think that the Saito .62A or Thunder Tiger F-75s four strokes might be smarter buys for the money. The Saito .62A is readily available at $209.99, which is about what the O.S. Max .56a 4-stroke sells for after discounts. At $169.99, the TT F-75s is barely more expensive than the O.S. .55 AX 2-stroke.

At the end of the day, either one of the engines in you poll would work great, as would the O.S. FL-70 4-stroke. Good luck and good shopping!

Thanks. Didn't realize the 55AX would be that tight in the Rascal. I think that's the plane I want, though I could always put my 46AX in the rascal and fly the Dolphin with the 55AX? Then I could throw a nice big prop on that plane, too, which could be nice.

Tower has a deal for OS engines where you can pay in 3 monthly payments, so while the cost of OS is a little higher, they are actually easier to pay for ($40 to $70/mo versus $200+ up front).

I would love a four stroke in the rascal, but it seems like the four stroke is a lot more money and a lot less versatile. Also the four stroke I mentioned is larger than the recommended size for the Rascal, so would it be a tight fit as well?


Ken, do you remember how things fit in the Rascal when you did your review? Do you think there's room for either of these?

Thanks.

Here is a pretty good review of the four stroke, 10% and 15% fuel and lots of prop sizes http://www.flyrc.com/articles/osfs81_engine.shtml

The 46AX and 55AX are close to the same size on the outside. From the online manuals.

Thanks. Looks like the biggest and most important difference is 5mm in height from mounting lugs to top of engine.

The poll was unanimous up to the first 14 votes, and is now close to 3:1 in favor of 55AX.

I'm strongly considering the 55AX - I looked at the manuals for the two engines and the same size prop is recommended for each, and as much as I want the sound of a four stroke, I can't justify spending the extra $100; that $$$ could go toward a plane or new receiver or something. Also, while the 56 four stroke is large for some of the above air frames, it is in the lower range of planes I might be considering in the future, while the 55AX will be plenty of power for most any 40 size plane.

thanks guys.