4 Stoke Recommendations

I had my first experience with a 4 Stoke engine the other day. Other than weight, what are the downsides. I saw a Saito 53 turning a 14x5 prop that seemed to run very smoothly and consistently.

Any thoughts about using 4 stokes? In the plane I saw, the nose had been shortened quite a bit to accomodate the heavier engine. How is this going to effect aerodynamics?

All thoughts welcome.

Well, Randy, I will jump in since no one else seems to be starting this one. Maybe once I reply there will be others who can add their observations on this subject.

4-strokes are becoming one of those "issues" at the moment, since there is some usage of 4-strokes in world class competition--most notably in Europe and Asia. I think one of the reasons is the lack of available and cheap (make that "inexpensive") nitro in some of these regions. Also, FAI competition limits engine size to .61 in a 2-stroke, but a 4-stroke can be up to something like double that. (Now we are starting to think BIG!) Four strokes have found their way into RC competition for the same reason. Couple this with the fact that modern 4-strokes are getting more powerful than their older brothers, and there are a few examples that are, also, getting lighter. ("More powerful", "lighter", good code words for a CL stunter.) A 4-stroke, by its very nature, will generally produce more torque and be able to turn a larger prop at slower speeds, much to our liking. However, they can't do a 4-2-4 very well. (Joke---since they are a 4-cycle they can't 2-cycle at all. And they don't 8-4-8, either.) What they do, and do well, is run at a pretty much constant rpm throughout the pattern.

So, the advantages, as I see them, are the opportunity to use a larger engine and the ability to turn a larger prop. And their power is very consistent and very controled. The greatest disadvantage is weight, and the fact that you won't see them producing much, if any, additional power up on top (which is the very place that you need it the most).

And when you consider the weight question, consider this: You spoke of a 4-stroke turning a 14 x 5 prop. My Magnum 53XLA 2-stroke conversion, a ball bearing engine weighing 10.7 ounces (but, unfortunately, now discontinued by the manufacturer), will turn a 14 x 5 prop with a nice, dull roar authority, (we regularly use a 13 x 5.5 three blade). But the 2-stroke does give that extra boost on top that is lacking with most, if not all, 4-strokes.

There are some people trying them right now. Windy Urtnowski is presently working on a 4-stroke development program. Some engines that have been tried seem to work reasonably well, and others (as in some 2-strokes) have failed miserably.

They don't have to run so rich, so they do use less fuel for their size. But they are still heavy. "Weight!" Say that out loud and it might be good advice to most people unless you are one who wants to be the first on the block to be doing something different.

I don't know. The first time someone wins the Nationals with one, everybody will abandon their pipes and switch to 4-cycles. That's the way the pattern has been since the beginning of time. Of course, if somebody were to win with a fan jet, we would see everybody converting to them, too. We all want to think that whoever won had the advantage because of his equipment.

I'm not really looking to use one. I was just impressed with the consistent run and the seeming ease of use. Weight is an issue, but not one that can't be overcome in other ways.

Randy, at the last Skyraider's meeting, Mr.B17 brought along his Saito .56 (they don't make a .53). What I recall from various questions and answers was that while the engine weight was a bit more than a ST .60, the fuel weight was a little less, tank ditto
for a near match. He said the Saito was lightest in the size range (and most costly), and the WORST in fuel economy, by far.
Other points, you have to avoid high rpm; float the valves, break the engine. And yet you still have to adjust the speed of the model. It would seem that you would have to set the speed more with prop pitch and restrain the rpm with prop blade area and diameter than ever before. Is there good power available? Paul said his Saito would pull a "Bad News" at 4 second laps, which no ST .60 he ever had would do. Restricting the venturi bore is a part of the equation, but richening the needle valve does nothing. I have some drawings and the original throttle from Paul to make a "fixed throat carby" for it, but I'm not sure when I will get to it, or exactly how I will do it. Perhaps eliminating some potential for vacuum leaks will even things out more. I think he had some strange speed variations. And not real quiet, either. I'm not too keen on the complexity of the critters. Lots of little bits that will need adjustments and stuff. It seems that it would be smart to buy a quality unit, and I'm not sure just how many brands there are available, but the Saito, OS and YS seem to be top drawer. Enya is barely a player in this country, which may be sad but true. Magnum and Thunder Tiger make good glow engines, but not much is known yet about their 4 strokes. There are other 4 stroke model engines. Webra has a .90, there is/was an English brand, and the HP .21 and .49 now made by RJL. Nils has a Magnum 4C, but I dunno if he's run it yet. The real test is going to be how well the cam, valve guides and seats work after 500 or 1,000 practise flights. Crash damage is also likely to be severe/fatal. How about a PAW .40 diesel? Mine is scheduled for a Bucaneer 746, and I expect it to be a great combo. Steve

Steve,

Your right, it was a .56. shows what happens when you type without looking. Is RJL making HP?

All the things you point out are a concern, particularly the complexity issue. I'm not even sure I want to stick with pipes due to the dinking around needed. I'd just like to fly. I flew Pat Johnston's Epiphany with a Neumann reworked Magnum 53 (probably where I got the "53") not too long ago, and the plane is a killer. Goes where you point it, stays where you put it and seemed to handle pretty strong wind and 4000 foot altitude great. Just flip and go.

There's something to be said for that.