Hi members!
Here is my question:
Should i buy a 4str. or a 2str.engine so as to install it in my all new Hangar 9 F4U-Corsair?
When i say 2str. i am between OS 61FX and OS 91FX{maybe the second}
and for 4str. either the YS 110FZ or OS 91FS or OS 120 FS Surpass.
What do you think?

It's up to your personal preference. You saw videos showing how my flew with the YS 110FZ in the nose. A four stroke would sound "more" like a radial engine anyway. OS 91FS would also work just fine. OS 120FS is way too heavy for this plane.

I ask only because 4str. are not so reliable as 2str.
2str.may not have the torque of a 4str. but it is much more easy to run and maintain!

I only use 4 strokes, and they are more reliable than 2 strokes and easier to tune. Engine reliability also depends on the engine operator. If you don't have the ear and skill to tune an engine, then of course it won't be reliable.

yes.
Ok.
I have a YS 53 FZ and i had posted a topic regarding the problem at high rpm!!![8D]
A 2str. like the OS 91FX won't have any similar problem!
Also what do you think,
is the OS 91FX o.k. for my Corsair?
Your's with the YS is absolutely perfect,but i don't have the money to buy!!![]

OS 91FX will work just fine in the Hangar 9 Corsair.

I would have to think twice before buying the OS .91FX. While I haven't ran the engine myself, I don't recall hearing anyone say that they were glad that they bought one. If someone is glad that they bought this engine, please jump in and add your two cents. I would like my faith in OS two-strokes restored.

Comments have ranged from not worth the money, to not powerful enough for the size/money, etc. I normally try not to comment on engines that I have not tried myself, but I woud do a bit more research before plunking down the money for that engine. When faced with the same decision, I bought a Chinese ST G90. No, it's not the most powerful .90 available, but it doesn't cost $200 either. I have owned and operated ST G90s before without a problem. At least it is more powerful than the Webra .91, which is another good engine to consider.

Not long ago, I bought the SK .80 from Kangke. Since then, they have introduced a .90. I Wish I had waited.

If you can afford an OS FS-91 Surpass, you are getting close to the price of a Saito 1.00 four-stroke. I do not know where you live or how the prices for Saito engines are there, but it is something to consider if you live in the USA. It is a much more powerful and lighter engine than the long of tooth OS FS-91.

By the way, four-strokes tolerate varying prop loads a bit better than most two-strokes, but when they are the same displacement, the peak torque produced by a two-stroke is usually greater than a four-stroke. YS engines can sometimes be excluded - but not all of the time.

Four-stroke engines will generally lug a larger prop for a given displacement because they are not as sensitive to the woes of preignition, as two-strokes often are. However, adding a head shim under the head of a two-stroke will retard the timing enough to swing larger props than the same engine in a stock configuration. Shims are cheap. Additionally, most two-strokes get along fine on 5% nitro fuel. In many instances, four-strokes lose some of their power generating and tractability luster when running fuel with only 5% nitro in the fuel. I mention this because you seem concerned with economy.

As you can see, there are many things to consider. Fortunately, most of the things to consider have been discussed at great length on RCU and other resources. Good luck making the best decision for you and your needs.

Hi.
Yeah,maybe your Chinese engine works well,but...
I don't know if i will ever trust an engine like your's or gms etc.
That's because i never saw one of them running and also i think that quality is expensive!!!
Also these manufacturers don't have the machining and maintenance as other OLD companies like OS!
But anyway the problem is the engine decision!I don't have right now the money to go with a 4str.like YS 110 FZ,but if i had them i would!The most important think that i am thinking is reliability and quality.That's y i am thinking the OS 91 FX.Because you know that this engine really works!

Good luck with the OS 91FX.

You will be pleasantly surprised how easy to operate and maintain are the 4-strokes nowadays. So I can assure you that won't be your worry.



If you haven't thought of the new OS 120 AX 2-stroke, it will completely fit in the Corsair cowl, as it is dimensionally almost as small as a 61 FX, and about the same weight too, within a few oz. This 2-stroke is tuned for low RPM (8500 ~ 9000) so you can swing a good prop like 16x8. It will look nice. In fact, it is the only engine that will adequate fly that plane while still fitting into the cowl with the furnished muffler, except for RCV SP or Jett 105~120 BSE.

I wouldn't touch the 91 FX w/ a 10' pole, unless you so feel adventurous. Get the Magnum 91 2-stroke for all the power, half the cost and none of the trouble.

Thunder Tiger 91 2-stroke hopefully has the performance of a 91 FX without all the maintence phenomena. But the jury is still out on that. It doesn't come with a muffler, not that it will mean anything for a Corsair.

If you don't care about enclosing the engine inside the cowl, then OS 91 Surpass will pull it around. It is a stupid engine, by that I mean I have not seen anybody who cannot successfully tune that engine. But if you want to do some low pass speed contests with your friends… get the YS 110. OS 120 Surpass 4-stroke will stick out too much, and make it way nose heavy. Saito 100 may be too light which will require some lead weight. Thunder Tiger 91 4-stroke is a good choice too.

Sorry if I didn't narrow down your choices.

Oops, I just saw this post, and if you have a 91 FX that works, all the power to you. I personally have seen a club friend whose 91 FX has inconsistent behavior, despite his full devotion into tuning. There are probably some tricks into getting that engine to run right, but I don't know them.

I, however, have owned the Magnum/ASP 91 2-stroke, and I can tell you that it is worth much more than it costs. It is much more consistent and reliable than my friend's OS 91 FX, and it pulls even a little more rpm than his on the same prop, possibly due to muffler difference. I will let you know that I got mine from Bonpar on the other auction site for just over $100. Maybe OS has ironed out all the issues of 91 FX by now. I am not about to do a $200 experiment though, when Magnum is around. Yes, OS' external finish looks nicer, but it's cowled anyway, isn't it? Magnum 91 XLS is ABC, and OS 91 FX is ABN. You be the judge which will last longer.

So you prefer a 4str. like YS 110FZ for speed.
Yes but i think that the OS 91FX has more power than the YS 110FZ,isn't it?
Also YS engines are very very expensive:
OS 91FX-->210$ [from Centralhobbies]
YS 110FZ-->324$[-//-]
Also nitro for YS engines is expensive too...{20/20 lower percentages}
But also i want to ask sth else.
When the OS 91FX unloads,won't my Corsair be a speedy?I think that it will be a quick scale warbird!
{Hangar 9 suggests 60-75 2str.}

I don't understand all the fear and loathing of the FX .91. All half dozen or so at our field run impeccably. The two I've helped set up have broken in and run exactly as you'd expect an OS engine to run. I don't doubt that the documented issues existed but I guess I'm surprised the problems weren't sorted under warranty.

The YS 1.10 is definitely more powerful than a stock piped FX .91 but the FX .91 is more powerful than all naturally aspirated four-strokes up to 1.20. See the following tests all run on the same day (four-strokes on 20/20 and the FX on 15/18 fuel):

APC 14x8 -
OS FX .91 - 9700 rpm
OS Surpass2 .91 - 8900 rpm
Saito 100 - 9200 rpm
YS 1.10 - 10,300 rpm

APC 13x10 -
OS FX .91 - 10,000 rpm
OS Surpass2 .91 - 9700 rpm
Saito 100 - 9550 rpm
YS 1.10 - 10,700 rpm

If you put a tuned full length pipe on the FX .91, it may approach or exceed the performance of the YS 1.10.

Although expensive, the YS 1.10 is a real work of art. Its power per dollar ratio is actually very good in comparison to other four-strokes.

Heck...put whatever motor suits your fancy (and your wallet) in the H9 Corsair. The .91FX isn't a bad choice either. I have to chuckle at the tales of woe and misery regarding that motor. Perhaps they sent all the good ones to NC, but I've yet to see one that didn't run exceptionally well in our club (and there's a good many of them here with which to form a reasonably informed opinion).

No tweaking required. Most of the guys run a tank of Cruel Power through them for "break in" and then off into the wild blue yonder.

I can't recall ever seeing one act up. Interesting isn't it? Sometimes actual field results run contrary to online heresay.

That's y i say that the 91FX is a very good choice.You pay 209.99$ at Tower and you buy an engine that you know it will work in any condition!