ellysbro
Posts: 176
Joined: 10/24/2002
From: Riverside, CA
Status: offline
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I have agonized a lot over this question. There are a lot of considerations.
1. Light weight engines are good, but you need to keep the tail feathers light, else you will be adding lots of lead to the nose. My original 1/4 scale Widgeon crashed due to flap stall, and the fellow who helped me rebuild used the G&P foam tail feathers and lots of heavy fiberglass and primer. He also arranged things so that I had to put the elevator servos in the tail, hence the rebuild needed more nose ballast in the nose, and it came out six pounds heavier than my first effort, which had built-up balsa tail feathers, and pre-painted Coverite on the wing and tail.
2. I don't think you need an ST4500. The ST3250 sells for $199, and would be more than adequate power. Reliability is another story. I definitely would have on-board glow drivers for reliable idle, and, as you probably know, ST carburetors have a bad reputation, most people replacing them with OS carbs. And any inverted glow engine can suffer the glow plug going out. What you don't want is one engine failing in a twin. The Ryobi's were OK for the 44 pound first try, but the 50 pounder is a bit underpowered. They turn a 16-8 Master Airscrew prop at about 8000 RPM. Bill Price's even heavier Widgeon is underpowered with G38s. I did some bench tests recently, as follows:
JAG Ryobi 31cc, 16-8 Master Airscrew prop, 87 unleaded, 30/1 oil, 8000 rpm, Control-now in Widgeon
Super Tigre 3000, 18-8 Master Airscrew Classic, Performance Plus 15%, 9200 rpm, Perry Carb, custom muffler
OS BGX-1 3500, 18-8 Master Airscrew Classic, Performance Plus 15%, 9700 rpm, No Muffler, well-used
As you can see, even the ST 3000 has much more power than the Ryobi. The ST3250 would be even better, probably as good as the OS, although not tested here. If you can afford them, I would go with the OS BGX-1 3500, a real stump-puller, and reliable as they come.
3. I used the gas engines because they start easily, love to run inverted and are reliable as anything. Also they are very thrifty with fuel, 16 oz. tanks last almost a half hour. This saves weight, as well as cost. The Ryobi's have the carb and muffler behind the cylinder, so they fit nicely into the Widgeon cowls, without even the spark plug showing. Most gas engines have the muffler and/or the carb sticking out the sides of the cylinder. If you do go with gas, consider the new Evolution 52 from Horizon Hobby, or the Revolution 52 from Bisson. Both have less stuff sticking out the sides.
4. Another recent candidate is the new Saito 220, the largest single-cylinder 4-stroker. It should have power to spare.
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