hello

Which one to choose, whats the best, OS is bit expensive on one side, but power and reliability wise which is better, any suggestions from OS and super tiger guys.i want to use it for aerobatics and 3D.

Highfly3D.

Eugine,


They are close in power, but from the longevity and price standpoints, the ST out-scores the OS by 4:1... At least.

The ST can be adjusted as reliably as the OS, but it will take a few more tries... The OS is easier, but the ST will slurp much cheaper fuel that the OS.

Dar,
what do you think of the fuel economy between the 2?

Dar,
I meant the fuel consumption, not the fuel economy.

Kiyoshi,


Since the OS will typically be running on higher nitro fuel and possibly have too hot a glow-plug, it will consume more fuel than the ST.

If you change the glow-plug (which might be the super-hot A3. If it is an OS #8, leave it there) in the OS to a medium heat one, like the K&B-1L, Enya #4, Novarossi C6-S, OS #8, or others and use 5% nitro fuel, like the ST will happily use all year long, both engines will, after adjustment, consume fuel in about equal amounts.

Dar,

I posted the following elsewhere in this forum. I forgot the subject but it was about ST 90 prop size and glow plug. I want to hear your opinion.

*********
I'm considering to buy a ST G-90.

I bought a GS-40 a few months ago. This is the first model airplane engine I bought since 1957. I used to fly control line. I broke it in with the ST glow plug that came with it, then after a several flights (by then i ran through one gallon of 15% nitro, Omega of Morgan fuel), I replaced it with OS A3. It seemed the power went down a little. I flew like that for another gallon in consideration of reducing deadstick possibility. Meanwhile, the engine seemed performing better each time in the last gallon.

Now i'm thinking of replacing back to ST's glow plug. I've had only one deadstick at the first flight in about 20 flights and that's because someone else (a non ST owner) adjusted the mixture. The plane landed ok but it made me paranoid about deastick.

So I compared the ST plug (tower has only one kind, so i assume ST make only one type of glow plugs) to OS A3 side by side. And I realized OS is much shorter than the ST's. Of course, that's written everywhere but I didn't pay attention, somehow). OS#8 is also medium length, shorter by about 2mm or about one twelveth of an inch, than the ST plug. Although I haven't verified but I'd imagine it would make a huge difference in the real compression, therefore the resultant power.

According to the RCU review article on GS-40 by Andrew Coholic, OS plug #8 and Tower Hobby's Tower Power Plug gave approximately 200 rpm more power than the ST's plug. And he says perhaps ST's plug is colder. I read a colder plug gives more power but idling may not be as good elsewhere. I'm going to get a tachometer sometime so I can do some comparison. Between the length of the plug and the alledged temperature, it really doesn't make sense. Also, I might change the nitro content to either 10 or 5% to see the effect.

By the way, if you want to try, you can get ST glow plug at http://www2.towerhobbies.com/cgi-bin...?&I=LXGWY5&P=7

Kiyoshi,


I have less experience with this engine.

In other threads, people are reporting a rich mid-range that cannot be adjusted out, or neutralized by lower nitro.

Read what they say.

Andrew Coholic produces conversion Diesel heads for glow engines and... furniture...
He's a real good guy.

As the [link=http://www.os-engines.co.jp/english/line_up/plug/pluindex.htm]OS Japan web site[/link] says, the A3 is good for nothing but small engines and for break-in.
This is completely in contrary to the manuals included with most OS engines.
It is a very hot plug; the hottest OS make.

It can be used in many engines, but you'd have to richen the mixture dramatically to avert detonation (what many call a 'lean-run'). This enrichment will make any engine run badly, even when not on the verge of detonation.

Using too cold a glow plug will make the engine lose RPM upon removal of the glow-driver.
This is not good either and engine have a certain glow plug heat they work best with.

Just any plug, will not do!

The Tower Power is an OS #8 clone and this OS is needlessly expensive.

A hotter than needed plug will increase your fuel consumption needlessly, as will using more nitro!
ST engines do not need, nor like, more than 5% nitro.

For the record, I've tested these two engine (OS .50 SX and ST .51) with static tach readings and flying both in identical airframes and I'm sfraid they are not close in power at all. In fact, the ST is only mid field performance-wise amongst the pack of .46s at our field. On an APC 11x6, the ST .51 did 11,800 rpm compared to an OS .50 on the same day which did high 12s on a stock exhaust or early 13s on a $15 Tower muffler that bolts right up. That's a very significant difference you will definitely notice in the air. Unlike the ST, the OS loves to rev and is just as happy on a smaller prop at 14-15k.

The OS is essentially a set and forget engine. Set the high end, set the low end for idle and transition and then fly. The .50 SX, properly set up, has exceptional throttle response. The ST, even with the requisite several hours of spray bar jiggery pokery, will never transition as cleanly or run as smoothly at part throttle as the OS.

If you run them both at full throttle, the ST will probably use less fuel, chiefly because power comes from burning fuel and the OS significantly outpowers the ST. In non full throttle usage, there is no material difference in consumption that I could notice.

In terms of reliablility, at our field, more STs have required re-ringing than have OSs - the main symptom being an inability to start by hand. Bearing reliability is more a function of user care (or lack thereof) and attendant corrosion than brand of engine. Both are pretty dependable engines when used and maintained as specified.

Both the OS and the ST are happy on lower nitro fuel.

Hmmm....Don't know how the engines are being run, but with an APC 11 x 6 propeller, we can turn a SuperTigre G-51 between 12,000 and 13,000 RPM with the stock muffler, using an O.S. #8 plug and Omega 10% nitro fuel. Any idle below 2,500 RPM or so is considered "good".