Hello,
I'm trying to decide on an engine and have a few basic questions.

There is a .45 abc with 1.5hp at 16000rmp, 16000rpm max, and a .51 ringed with 1.5hp at 15,500rpm, 15,500 rpm max. What is the advantage of the larger engine here?

Are there any disadvantages to a remote mounted needle valve?

All the engines I'm looking at range from 1.5hp to 1.8hp(Tower's Brand?)...Is this enough of a difference to be considering?

I currently am flying a trainer but want an engine that will hold it's own in club dog fights, hopefully towing around Hangar 9 Sundowner 50 ARF, Phoenix Giles 202 46, or something similar (low wing sport, 5-7lbs). Thanks.

First of all, the HP rating is pretty much a fable. This is a projected horse power rating based on the ability to even reach that RPM. Unfortunately, with most of these engines, to efficiently run, the prop necessary is usually larger than ones that would even allow attainment of 16K rpm. The actual RPM range is about in the mid 12's for 40 - 46 engines and goes down from there.

And at that RPM range, the prop noise would be just about unbearable.. and the engine would probably not last very long.

Now some will, some are designed for that RPM range, but not the general collection of sport engines produced by Super Tigre, OS, Evolution, and others.

The advantage of the larger engine is usually in the power or torque that it generates. The larger mass of a larger prop will usually result in more torque, usually more horse power. As you cans see, HP ratings are subjective. Larger engines will generally produce more power.. in the form of torque and will turn larger props much easier.

The OS AX series has a needle valve that is located at the carb but is rotated so that it points rearward giving access to it much easier than when they are perpendicular to the prop shaft and carb. Fingers don't get abused when they are angled back like that.

With rear mounted needle valves, the obvious advantage is that they get your fingers away from the prop. The bad part is that they are usually made of plastic and can break easily. Another disadvantage is that they take up space behind the engine which, in some models, may not be at a premium.

CGr.

Hi there!

Manufacturer's horsepower ratings are as good as meaningless to you. Ignore them. Choose your engine based on the engine's size class, cost, weight and the manufacturer's reputation for reliability and service.

You're looking at large 40 class engines. Many manufacturers will design a basic .40 size engine, and then offer basically bored out versions at .45 and .51 or even up to .55. They're all based on the same case, and often the same crank, so the larger displacement engines will often be both lighter and more powerful. Judge the engine's power by looking at the props that people swing with them. A .40 will typically use a 10x6 prop, while a .45 will use an 11x6 prop and achieve similar RPM's.

Look at the rated RPM's where they give the hp numbers. Over 15K rpms! When we choose a prop for a sport engine (anything non-competition, generally), we choose one that will put the engine in the 10K-13K rpm range for good life and good power. That horsepower rating is similar to if Honda were to rate your civic's engine at 300hp at 10Krpm. Great, but who's gonna turn it that fast, and how long would it last? No-one. Not long.

If you're looking at specific engines, ask about the specific engines. Problem there is, it's often a "ford/chevy" debate. Most of the well known engine manufacturers (OS, Saito, Tower, GMS, Supertigre, Thundertiger, Magnum etc, etc) make good engines. Some have particular quirks, and people here know them to have them. They'll let you know, and suggest options if you've chosen one they wouldnt' recommend.

Also it would be helpful to know what plane you want this on NOW! There are lots of great 40 size sport planes you can move to later, but match the engine to the plane you HAVE.

For what it's worth, I've played recently with the OS46AX, the Supertiger G45 and the Evo trainer engine. The OS was easiest to tune and break in, the Supertiger was harder to break in, and slightly harder to tune, the evo was a breeze to break in but finnicky to tune. The Supertiger and the OS put up nearly identical RPM's on the 11x6 (about 13,100-13,300), and the evo was behind a bit (about 12500). The OS has been most reliable in teh air, but all have been pretty damned good!

J

I have the impression that you are fairly new to flying. As CGRetired said, the hp is a fable. In my opinion, you should be looking for a reliable, easy to operate, relatively trouble free engine.

Some of the most "User Friendly" engines I have encountered have been (in no particular order): OS 46 FX/AX, Thunder Tiger Pro 46 and Evolution 46NT. 99% of these engines will run reasonably well right out of the box, require little (or no) breakin and are fairly easy to fine tune.

While ringed engines will last longer than an ABC/ABN engine, they require a substantially longer breakin period and in many cases are not only heavier, but will not achieve the same rpms as an ABC/ABN engine.

The big advantage to a remote needle valve is that it keeps your fingers away from the prop. The big disadvantage is that many of them are made as part of the backplate of the engine. In the event of a crash that may damage the needle valve, the backplate needs to be replaced.

As for the Tower (made by GMS) engines, while they are a little more powerful than other makes (due to the muffler ), they tend to be plagued with air leaks and poor transition problems. If you get a good one it is fantastic, if not, you will be pulling your hair out trying to correct the problems. I have had 3 Tower 46 engines and every one was a dud. I spent more time TRYING to find all the air leaks than I did flying.

Hope this is of some help.

I agree 100% with what CGRetired said.
A better question would be what specific engine would be recommended based on brand, model and size.
Horsepower rating are often not quoted accurately so the best advice is from people that actually have flown various engines and have first hand knowledge on performance and reliability.
Right now, my choice for an engine based on your criteria would have to be the OS 55AX.
That said I have not flown every engine in that size, I have only flown the OS 55AX, OS 46AX, ThunderTiger Pro46 along with Magnum 52 4 stroke and OS 70 4 stroke (and a range of 40 size engines) I have heard good things about the Tower Hobbies .75 but I don't know if that carries over to their other sizes.
PS: I also agree with the other posters, I was still typing while they were posting

I'm pretty much between the Magnum XLS-46, SuperTigre GS-45, and SuperTigre G51. On RCU's reviews page, the SuperTigre wins out, mostly to leaky carb on the Magnum. However, the Magnum is in stock now, and has the rear needle adjustment (which sounded good at first). SuperTigre's appear to be on the heavy side, so the G51 is appealing in that sense.

I am new- in the process of building my first plane: Hobbico Nexstar, which requires a .46-.50 size engine, so that's my first need. The RTF version comes with an OS .46 FXi, with a rear mounted needle valve; the reviews say a Magnum is a good substitute here.

The reviews are slightly higher for the SuperTigre .45, and even higher for the G51, which is lighter, but like Campy said, the RPM's are rated at 500rpm slower than the .45.

If you hadn't noticed, I'm buying from Tower because of deals they have and some credit I have left over.

Thanks.

The OS 46 FXi is a great engine. I had the Nexstar Select and few the heck out of it. That was several years ago and that plane is still out there training people, and the engine still runs strong. OS's are very reliable and in my opinion, are worth the consideration and teh extra few bucks you may pay for them.

CGr.

The rpm's Campy was talking about (re: ringed engines acheiving less than ABC types) isn't the rated maximum RPM's, but what that engine will achieve with the same fuel and prop as another.

You might have a ringed 40 and a non ringed 40, both by the same mfr (for arguement's sake). You might feed both Omega 15% and have 'em spin a 10x6. The ringed engine might manage 12,000 rpm once it's broken in, while the ABC might be doing 12800 with the same stuff.

The stated maximum rpm's are given as a guideline. You can expect that the engine will not come appart immediately up to that speed. Much like the redline on your car, you don't aim to achieve it (often).

J

Pretty much all of these size two strokes will have no problems running up around 15K, it is actually easier on the engine than lugging it down at 10K. You cannot compare to a car engine they are not designed to run full throttle all the time like a aircraft engine.
The supertigres are good engines and will last a long time.

I'd argue that the SuperTigre is far more "leaky" than the Magnum, and I'd demonstate this on my ST .61's and .75 which will run even after I've plugged the intake hole with my finger! ( and yes the ring seal is in there, this is not the point of the leak... ).

The OS are a breeze to tune and set up, but also don't overlook the Tower engines too. They are a great deal for the money, but require a bit more break-in and TLC. ( you are advised NOT to touch the needles as they come, until you've run at least a tank or two through them. ).

So with the SuperTigre .45abc and the .51 ringed: They both utilize the same prop size range for operation, although the 51 can use up to an 11" prop for break in. The .51 is almost 1/2oz lighter, but the .45 should spin at a higher rpm. I'm still having a tough time understanding which one would be better.

Also, the "Ford/Chevy debate" is now a Super Tigre/Magnum debate; all thoughts are welcome and encouraged! =)

Typically ( with exceptions ) if you are comparing engine sizes from the same manufacturer, as you are, then the engine with the higher displacement will be more powerful.

1/2oz does not make a lot of difference on a plane this size...

However USUALLY a .51 engine tends to be more powerful....

BUT, ABC cylinders often have tighter fit ( more compression ) so they may produce more power than a slightly larger engine...

That is why the given H.P. ratings are so similiar on the two engines.


And round and round it goes!


The difference in RPM's will hardly be noticible.
The difference between the two in power may not be noticible.

The question is which one will last longer.

Some ABC's fare much better than ringed engines... but the reverse can also be true based upon the ABC liner materials.

For me "there be dragons here", so someone more familiar with the metalurgy involved in ST engines may want to chime in.


But my ST .75's do leak like sieves... I'm not happy about this.

The engines run great. But I've gone as far as putting in completely new carbs to eliminate the leak.

I suspect that the carb is leaking along the rubber covered low needle valve area.

Everyone has a good laugh when I land my ST equipped planes and even though I have the carb fully closed AND I cover the intake with my thumb, the engine keeps running and running until I pinch off the fuel line completely... even then it takes a few seconds to turn off.

All else being equal there's no difference in HP between a ringed and ABC engine. The apparent difference in compression is only when you turn them over slowly (as when starting) where's there's a bit of time for some pressure to leak past the ring gap. Once they're running there's no time to leak. AFAIK only OS offer a choice of ringed or ABn but even with their engines the ringed is reserved for their helicopter engines which actually operate normally at higher revs than used in planes (rings are more forgiving of dirt ingestion). Ringed engines though are limited to around the 20,000 area where the ring can start to flutter, or vibrate, in the ring groove.

HP figures are just for advertising to make you think brand A is better than brand B. Jett are more honest about it and simply say that if you use x% nitro and size/brand prop then you'll get 17,500 revs or whatever.

In my book, the ST G51 is a very good engine but it's ringed so takes some time to run in completely. If it ever wears out after your kids have grown up then you just buy a $10 ring and wait until the grandkids have grown up .

Ah!

Thanks for clarifying that.

I know there were many complaints about the deterioration of the original O.S. AB liners, but I believe that has been cured with the more current engines.

So which to choose if all else is equal and you will not be approaching RPM limits?

Most people never wear out an engine, but do damage by running lean, in dirt, or crash. Cheap fuel and lean runs get most.

If your interests are in boring holes in the sky at high speed, go with the ABC technology. If you are flying along at low power settings, a ring engine works better.

Nothing on this size engine is going to blow up at the peak power rating rpms. But you have to match the prop to the airframe.