Alright so I'm beginning building my 3rd plane (Sig Four Star 60 ARF) and after searching the forums for a couple days I have discovered a trend that I thought was supposedly a BAD idea: overpowering an aircraft. Now I'm not talking about going up an engine size if one lives at high altitudes in order to compensate for the lower pressures and decreased performance, I'm talking about strapping 1.20-sized 4 stroke into a 40-sized aircraft and running an extremely low pitch prop. Every instruction manual that I've ever read also cautions about overpowering an aircraft, claiming that the aircraft can become unstable in flight, the firewall can become weak, and if no catastrophe actually happens in flight, the warantee will at least be voided. However, in looking for an engine to pair with my Four Star 60 ARF, I've become interested in Super Tigre's line, especially the .75 2-stroke (a .75 engine in a .60-sized plane sounds pretty good, right?). According to many forums, most pilots that fly this plane recommend the Super Tigre 90 over the 75, claiming the 75 is barely enough engine (furthermore the 90 is has the exact same weight as the 75, meaning that it's performance increase over the 75 is probably pretty dramatic). How can this be, especially if Sig claims that the plane is a 60-sized plane? A 90 sounds insane!!! Do you guys have any experience with a particular engine in this plane or about the topic of overpowering in general? Let me know what you think! Thanks!!!

If I was in your position, I would put on a .91 4 stroke. But if you wanted to stick to the annoying whine of a 2 stroke (jk) then I would personally go with the 90, if the weight penalty isn't much more. I know that in the last plane I purchased, I got a .91 Magnum 4 stroke, becuase it only weighs 1 oz more than a .70, but has more power, and would suit more airplanes. So it is all up to you, and what you will fly the engine in in the future... I don't think the bigger one would overpower it too bad, if you keept he rpm's in a decent range, but still propped down. Even if you have to trim down full throttle a little, it is better than having too little power (not that the 70 would be too little though...) I hope that helps,

Scott

The FourStar 60 flies great on a .61 FX... However, a .91FX sure would rock.

I have seen the "recommended" Saito 100 in Showtimes, and they are VERY underpowered even at sea level.
A bigger engine is a more flexible option if you need to fit it to a new model. I have a Hype 3D with an OS FS90 up front. This is the minimum engine that I would put in it. Of course the throttle is always closed in down lines.

i allways use the biggest moter i can ballance on the plane without adding tail weight and also not over load the wing. wing loading is overlooked by many but a heavy plane won't fly as well as a light one. in most cases on a 60 size plane i will use a 91 2 stroke. i will also reinforce the fire wall with some tristock and pin it with some dowl rod.

randy racer

over powering a plane is based on several things. If you plan to fly it very scale like then stay within the range, on the lower end for that matter. The 3D guys need power to get themselves out of a bad problem, remember 3D flight is 50% wing flying 50% fully stalled. It may be even more like 80% fully stalled 20% flying. When fully stalled all you have it power to get you going again.

As far as the 4*60 goes. Mine started life on an OS91FS (4-stroke). After that engine finally gave up (something like 700 flights) I replaced it with a Saito 91 and it's still in there 300 plus flights later. BTW...that is not a misprint, this plane has over 1000 flights (looks like it too) on it and it only had the gear ripped out once when I decided to land and misjudged the distance to the high grass at a new field. It has trained more pilots than I care to count, given me total satisfaction and is an outright blast in the wind and should it ever plant itself, it does not owe me a thing. I'm into 33% and larger planes but I find it very relaxing to fly the 4* and it would get replaced when the time comes

For me 'overpowering' a plane is fun to 3D or just to get super nice uplines. I got a ST90 and to be frank I don't think much of it. For me a 60 2C and a 90 2C usually is using the same block and the weight is about the same. Hence, I would go for the 90 2C and not a 75 2C. I ran my WM Super Chipmunk with the ST90 and it was not very impressive. If money is not an issue then go with something like the Saito 100, light with a good punch. That would be great on something like 4* 60 ... you can fly her doing impressive big loops.

The Saito 100 is a very versatile engine, you can use that for quite a few planes from aerobatics to 3D. The ASP or TT 90 sized engines are really good stuff, less hassles and they run very well. Think about it ...

skulboep:

You cannot have too much power in an airplane. You can have too much weight if the bigger engine weighs more, particularly if you have to add tail weight to balance it. If the weight of the bigger engine is close to the same, there is no reason not to use it and lots of good reasons to go ahead. Emergency power if you get into a bad spot, larger, smoother aerobatics, and of course just a lot more FUN.

What kills airplanes is not power, it is speed. This is what the manufacturers are worried about. Every airplane, full scale or model, has a speed at which the control surfaces will flutter. When this happens, the airplane will usually self-destruct. By increasing the power you can make the airplane go faster than the manufacturers designed speed, with catastrophic results.

That is why a bigger engine is usually combined with a lower pitch prop. The lower pitch keeps the speed down and turns the higher power into more THRUST, for better acceleration, better vertical performance and more constant speed through maneuvers.

A 61 two-stroke with an 11x7 prop will fly your 4* as fast as it wants to go, but you will not have much vertical or extra power for emergencies. Using a 91 two-stroke with a 14x6 will give you about the same speed but your up-lines will be MUCH better and you can fly around at reduced throttle, which uses less fuel, makes less noise and less vibration, and the engine will last forever.

Bottom line; use the biggest engine you can without adding tail weight to balance, reduce the prop pitch to keep the top speed within the range of the recommended engines and learn throttle control to keep from over-speeding on your down-lines. Your airplane will perform much better overall and will last forever (or until you crash it )

Jim

And to add one more point to what Jim just said. A very lightly built airplane can be shaken apart by a big single engine glow/gas plane even after balancing the prop/spinner. The nature of a single just causes vibrations.

If you overpower then throttle management is a must

I love the hot rodder's adage "There's no replacement for cubic displacement", but it just seems a waste of money, if nothing else, to put a huge engine on a small plane. I like scale flying (meaning anything the full scale version is capable of) so I don't get too radical, but I will usually put an engine in that is capable of comfortably turning a scale diameter prop. That usually gives a more than adequate reserve of power, but allows you to stay in the lower end of the power band for "normal" flying.

Their are 5 or 6 of these at our field and all but one are OS FX91 and a vary nice running 75 tower.........mine had the FX91 and I flew it for 5 years before selling it. Look at the engine weights not the cc size. The 91 is a great combo for the 4*60, and that size engine has a lot more plane choices later down the road.

I had (sold it) a 4*60 with an OS fs91. was perfect combination. There is no such thing as too much power. If you can balance the bird, and have prop clearance, then go for it. power helps, if you get in a tight spot. Use the throttle to control the engine. Main thing with big engine on small plane is use throttle and go to low pitch prop.

If it calls for a 60, then a 75 will do real good, and a saito 100 will be just right!

Bruce

Hey everybody,

Yeah, I know that a 4-stroke would be awesome on this plane, but funds are an issue so I was thinking 2-stroke. This was another reason why I wanted to stray away from the O.S. FX line of engines (61 and 90), as they are EXPENSIVE. In fact, this will be a new experience for me as every engine that I've ever owned has been an OS or a Saito. I had heard some great things about Super Tigre and hence was interested in the 75 and 90, and they are also in my price range!

tIANc, you mentioned that you had some problems with Super Tigre engines and recommended a 90 2C? What kind of engine is this and where can I purchase/find more information on it (I am guessing that 2C is an abbreviation for something)? Any details on your problems with the Super Tigre? Does anyone else know anything about this matter? Thanks!

Erik

Bury this deep within the "for what it's worth" pile and remember, you didn't pay anything for it.

I think it all depends on how you fly. If you have no throttle control and treat the speed stick like it's an on/off switch, then get the smallest engine you can and wind that little bugger out until the cows come home. If on the other hand (no pun intended), you have the cpacity to hear the engine in the air and the mental awareness of how to decrease the scream, then get a larger engine and fly with a larger prop, spinning slower. I think (again, FWIW) a larger engine, spinning slower IS much more scale than a tiny engine screaming for all it's worth to get the plane off the ground. It'll last longer too! There are some guys at our field that I wouldn't WANT to have something big enough to do damage, but, then there are others that have grossly over-powered planes that fly very scale like and smooth.

A larger engine that wieghs the same as a small one can work just as well, in any situation as the tiny one and can go beyond what that little engine could ever imagine. Like one guy said here, shop wieght, not size. Plus, it just might teach you something new to do with your left thumb. [sm=thumbup.gif]

skulboep, 90 2C is just another way of writing 90 two cycle.

skulboep: Some people like Super Tigers, but most of us don't. My personal experience includes two ST90s and both of them were terrible engines. They could not be made to run clean in the mid-range (even by the Super Tiger experts) and they vibrated so badly that one of them shook all 12 of the fuselage servo mounting screws loose in two flights. (Yes, the plane was a total loss.)

On the other hand, the OS 91FX is not one of OS's best. I'd suggest that you take a look at the Thunder Tiger Pro 91. Cheaper than the OS and gets good reports from it's owners. Stay away from the Magnum 91XLS. It is an exact copy of the OS and has the same problems. (Imagine that!)

Jim

I would stay with the OS line and forget the SuperTiger stuff. I've tried 3 different ones and all had issues with keeping tuned. They would run great for a flight or two then need retuned again.

Saito and OS engines are basically tune and forget with the occansional high speed retune for temp changes

Remember, you get what you pay for

See above, I've had OS engines run several hundred flights without so much as a hickup. My Saito 91 is the exact same way. I know of several OS46AX's and OS50's with several hundred flight on them and still making tons of power

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These are, indeed, confusing times.

Are you after unlimited vertical without a stall (still visible, of course)? Then you will need more than a typical .61 sized two-stroke up front. No, the .75 or .90 probably won't provide unlimited vertical either, in their stock form.

Today's .75 and .90/.91 engines are made from smaller crankcases that are often shared with their baseline .61 engine (but big for a .61). As a result, the new .90's do not offer the staggering amount of power that such a displacement would provide had the engine been designed as a .90 to begin with. Why? Because there is not enough material in the block after boring it for the larger piston/liner to provide the necessarily larger port ducts to feed such a displacement at its highest capability for producing the most power. Yeah, kind of a rip-off. You (the manufacturer) call it a .90/.91, but it doesn't produce the power of a dedicated .90/.91. To add insult to injury, the .61 variant is so large and heavy that it too turns out to be best used as a paperweight.

Were I forcing myself to buy the Super Tigre engine for this model, I would go with the .90 too. If you are going to carry the weight, you might as well have what little extra power the .90 produces over the .61 or .75.

If you just want to fly it like a normal sport model with no 3D or infinite vertical in mind, any .61 to .90 will do the job.

The model was designed in a time when the term .60 meant something different than it does today. The 4*Series were designed for serving as a gentle low wing model for the student pilot that had just graduated from a Senior Kadet or Seniorita. They were designed to be low wing floaters that flew slow and stable in order to help the newbie get the hang of flying a low wing model. They were not structurally suited for overpowered (eggcrate wing design) and quite often they would have their wingtips get into oscillation when flown very fast. Some even experienced wing failures due to overpowering (kit versions).

This model shines best when flown at moderate speeds with an engine intended to power it in such a manner. If you want to go fast and hotrod, buy something else.

The only four-strokes that I would mount on such an ARF are the very light weight and small, relative to other four-strokes, Saito .80 thru .91. It would probably fly well on a .72, but I haven't tried it as yet. The .80 to .91 four-strokes will provide about the same power as the originally intended .61 two-strokes, maybe a tad less, but will not burden the model with the extra nose weight of say an OS.91 or Magnum .91. Not that the latter two engines do not do a good job of powering the model. Their extra weight can be problematic in some instances. Still, a stick-on lead weight near the tail post of the model can often compensate adequately for the heavier .91 sized engines.


Ed Cregger

skull - what Jim said about the ST90 is VERY real ... it shook rattled and rolled my Super Chipmunk. When I ran is side by side with my TT61, it had a bit more power only. I was talking about the ASP 91 ... they are really cheap but they do run well. It runs happily on 5% nitro. Not sure who sells them in the US. In Malaysia the OS46AX is USD120, a TT46 about USD90 but the ASP52 is only USD75!

Here is the UK distributor's website and the reviews are pretty accurate as far as I know. http://www.justengines.unseen.org/ASP91sr.htm

If I had the 4* 60 I would go with a nice Saito 100 ... that engine is so lovely.

save up your $$ and stay with a OS or thunder tiger pro. both are very good. super tiger not so good.

randy racer

I've got an old 4 star 60 that I use to test stuff on, and buddy box people with, it generally flies with a Magnum 61 2c, and flies very well. It doesn't go vertical, but it has more than enough for anything that you'd do with a 4* 60. it'll do all the basica aerobatics, and has more than enough power to get you into and out of trouble. I flew it a few months ago witha Supertigre 90 that I wanted to test prior to putting it into something I care about, and it obviously had more power, but there wasn't much point to it, it was still a 4*. Meaning, it wasn't going to do 3d stuff, it just had more power to climb. Flying it took more throttle control, but end result was that instead of flying around at half throttle, I flew around at a little under half. Basically, with a 4*, put whatever you have on it, it'll fly fine.

On Supertigres, like some posts above have said, some hate them, some love them. I wouldn't say I love them, but I think they are great engines. I've had a bunch of them in from 40 size up to 90 size, and all ran very well, would idle forever, and didn't need to be messed around with constantly. The 90s have a more finicky idle needle that if not adjusted properly will make the midrange rich and effect transitions, but even with them set wrong, they still run great, and put out a lot of power. I've got one now on the front of an OMP Katana 70V2 profile, and it's a great engine. Hovers around half stick, and rockets out, transitions well, and I can count on it to stay running when it's pulled back to idle.

I have seen a H9 60 sized mustang with a YS 1.10. That might be pushing it a little. He was a good piliot but wide open the hole time.

Hi Guys ........... Ed nailed it perfectly. His comments are eggzakly on course!


Bruce

Ed: I also agree with most of what you said, but I do need to correct you on the above statement.

The OS 61 2-stroke weighs 23.4oz with muffler. The OS 91 4-stroke weighs 24.2oz with muffler and the Magnum 91 4-stroke is about the same. I doubt that 8/10 of an ounce is going to be problematic in a 7-8 pound airplane.

Jim