What's an easy way to get A LOT of duration out of a glow engine for a .25 - .40 size plane? I'm not looking to do exotic gas conversions, I'm not trying to cross the Atlantic or anything. I'm looking for 45 minutes to an hour of sporty performance with throttle management. I was thinking of running a .25 on 16 oz., but although I can probably figure out a way to manage the extra fuel weight, the shift in cg from full to empty might be extreme, so I'm looking at ways to accomplish this with less fuel, maybe 10-12 oz max. A .30-.40 size 4-stroke? A simple mod, like using a different carb on a certain engine? Any tips are appreciated, tell me how you would do it. Thanks!

converting to diesel will give you about twice the duration for a given amount of fuel. quite a few diesel guys in this forum that could help you with this.

if you still want the tank over the CG you could pressurize it using the crankcase and use an iron bay regulator at the carb


dave

Well, I did try a PAW .19 about a year or so ago, and it just wasn't for me. The black exhaust and smell and the extra task of adjusting the compression just wasn't my cup of tea, this is why I'm concentrating on glow. Is there a chart or a rule of thumb on average fuel use for different size 2-stroke engines? Or 4-strokes for that matter?

Maybe you could use a Perry V30 pump/ regulator so you can use as big a tank as you want w/o having the fuel mix. change on you? You can also put the tank over the C.G. and not have to worry about that problem either. You do need a 2 needle type carb. for that though.

Thanks. I checked it out at Tower, looks good. One question: It mentions tapping into the crankcase, but not where. The backplate?

There is a thread on long duration on the diesel forum which might interest you. Some stuff on there about tank design. Why do you want such a long run? Why not just land, refuel and fly some more? Just asking.

Jim

If you want to stay with glow then there's 4 ways I can think of that might help.
1. Use a 4 stroke, they're more efficient.
2. Set the max throttle opening to the minimum that gives you adequate performance.
3. Add maybe 10% gas to the fuel mix.
4. Use the least amount of nitro you're happy with.

Yeah Frank, you usually tap right in the center of the backplate, making sure the fitting is flush on the inside. Other locations can be thru the mt. lug (don't think I'd do it that way) or use a special backplate (hollow) bolt usually in the upper left bolt hole.

It's a challenge, and I like the idea of pulling up a chair and shootin touch and goes until I'm about ready to lose my mind, lol.

Just like this.

I don't believe in converting to diesel, unless you have a oversized engine for the plane you are flying. Using diesel, the trade offs is performance to flying time.

But I heard 6 oz of diesel on a OS 61 (diesel) lasts 40 minutes. Waaaaaaaaay longer than that of glow.

Just how do you convert an engine?

I guess what I am looking for is to not save money on glow fuel, or lose performance to duration like in a duration contest. I'm not looking for hours and hours on end, just 45-60 minutes of the same kind of performance you get for the usual 10 minutes on a sport ship, not wot throttle all the time, but not worrying too much about how often you use it either. So I am thinking a 24-32 oz. tank placed at the cg point with a perry pump/reg. Now for the engine. I have my eye on three of my engines, an O.S. 46fx, a Saito .72, and a Norvel .40 (just released). I'm sure the Norvel .40 would have the best duration, it's rated at almost the same power as a .46, and at 13 oz. it alone would make up for 4 oz. of fuel weight over a .46, and it is a dual needle carb, so it should work with the perry presumably. But Norvels are different and a little finicky at times, you just never know with them. Now between the OS .46FX and the Saito .72, I am taking a guess that fuel consumption would be about the same? In which case I would go with the Saito, as that would be an easier sound to listen to for such a long period, lol.

I think you'll be sadly disappointed if you expect a four stroke of equal power to improve you duration. I have a Saito 72 and it's quite thirsty. My most efficient engines are two strokes (Webra 120 and OS160).

Unless you get pretty tricky, there are only two basic ways to improve duration: 1) reduce power, 2) increase fuel capacity.

One thing you may consider is using a small carburetor and a large prop. The idea is to get the wot speed down to 7000 rpm or so. This could also improve basic efficiency depending on port timing in a two stroke or cam timing in a four stroke. I think one of the reasons the Atlantic team used old OS four strokes was because the cam timing was milder back then. They also used a tiny carb among other things

Yeah, I've discovered that Saito's are not as fuel efficient as their OS cousins. I guess that's why they are more powerful.