longer range

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You could double your present range easily by switching to a four-stroke engine. Then run only the minimum amount of nitro in the fuel.

If your plans include switching from alcohol based fuel (higher power) to petroleum based fuel for much longer run duration with the same size fuel tank, you will want to look around for an ignition system. This, with the stock carb on a four-stroke engine should double or triple your flying range again over running a two-stroke engine on glow fuel. I'm assuming that you are not worried about top speed and easy throttling.

I've been toying with a similar idea myself. My candidate four-stroke engine is an old Enya 60-4C that is built like a tank. This old engine was constructed with bushings and bearings throughout the engine, unlike some of the latest four-stroke engines. It's chances of surviving running on petroleum based fuel with regular petroleum/synthetic two-stroke utility engine oil is much better than some of the cheaper unbushed engines available today. Saito appears to be the exception to this rule because of the very highly suitable aluminum alloy from which they construct their connecting rods.

I figure Coleman Fuel with two-stroke utility engine oil mixed at 16:1, or a little fatter on the oil, should do the trick quite well. I'd load the engine down with an 11x9 APC prop, or perhaps a prop with more pitch, with a target rpm of around 5-6 k rpm. These are figures just off the top of my head. I would think that a 12 oz. tank of this witches brew would probably run for a long time. I anticipate having to shim the cylinder head in order to lower the compression, if knock is encountered.

Two-stroke engines are bad for spitting a lot of unburned fuel out of the exhaust port. It is their nature as designed since they are expected to deliver high power and not high fuel economy.

Ed Cregger

For a 3 hour flight, and likely any long duration flight, don't forget the battery life. Fuel for 60 minutes, and battery life of 45 minutes constant use would possibly result in 6 pounds of balsa scrap. Either high amp-hour batts or switching batts in flight. Wonder what that guy that crossed the Atlantic did for power????? But sounds like a fun project.

| For a 3 hour flight, and likely any long duration flight, don't forget | the battery life. Fuel for 60 minutes, and battery life of 45 minutes | constant use would possibly result in 6 pounds of balsa scrap. Either | high amp-hour batts or switching batts in flight. Wonder what that | guy that crossed the Atlantic did for power?

Maynard used something like this, if not exactly this --

Maynard stayed up for a very long time, and also had an autopilot, satellite communication gear, etc. to power!

... Though if all you need is an hour, this is serious overkill. People do 8 hour slope flights for their LSF level 5 all the time just by using LiPos, or non-rechargable Lithiums, or just solder a bunch of D cell alkalines together (in a big plane.) If you only have two or three servos that don't move much and don't bind, 4 2000 mAH NiMH cells will probably be plenty to keep your plane up for several hours.

Do note that if this plane ever flies autonomously, the FAA is likely to become interested ...

If you can get a gearbox, consider that..Optimum RPM for a prop at our sorts of speeds is around 2-3000RPM.

A smaller geared motor should easily replace a large ungeared one wit proportinate fuel savings.

Or simply go electric. an hour is like nothing for a lowish wind loading electric..

Many Thanks Ed and everyone, your advice is excellent!

The TAM5 did indeed run petrol with a electronic ignition, and to get around batteries ran an electric motor as an alternator and rectified the three phases to supply DC to the plane. Quite clever i reckon, but it is obvious that _a lot_ of tweaking of the fuel/settings would have been required to obtain the desired performance from the engine.

they spent a while perfecting the fuel, but dont give many details on the mixtures and substances they used. except they had 2kg of it.

So my best bet is to get a 4 stroke, but how can i figure out the weight of fuel i can carry? I have chosen a "Super Frontier 40" trainer, does the higher wing of the trainer type planes lend themselves to a bigger payload capacity (more fuel)?

Kind Regards, Rowan

The simplest way that I can think of is to use your target engine in the model you have specified. Set it up for glow fuel first. Why? Because I think that a three hour duration on glow fuel is very possible without going to all of the trouble of electronic ignition and petroleum based fuel.

Find the prop that flies the model most efficiently at various throttle settings on glow. Yes, this will be tedious work, but enjoyable if you are a person such as I and perhaps yourself. You will begin to get an idea of how much fuel you are going to need while performing the tests for the best props, because fuel consumption figures are how you will judge the best prop.

A couple of outboard 12 oz. tanks fed to the main fuel tank with shaker pumps (Varsane VP-20) and then regulated down at the carb with a Cline type of regulator that is driven by exhaust pressure to the main tank (put check valves in the auxilliary tank feed lines). As long as the model is flying slowly (50 mph or so), the outboard tanks, attached to the sides of the fuselage at the balance point, will not cause much of a problem aerodynamically. The VP-20 oscillating fuel pumps are used to fill the main tank individually. The Cline regulator (or the other brand) prevents the engine from being overcome by the VP-20's fuel pressure.

Again, an older Enya or OS .60 four-stroke is recommended because of their ability to run happily on 5% (or less) nitromethane in the glow fuel. Burning more nitro shortens operating time considerably.

Ed Cregger

Well in all honesty this may not be that hard. I remember an AMA Nats many years ago where Duke Fox took one of his Control Line Fox 35 engines and turned a gallon can of Fox Stunt Fuel (about 30% castor oil and 5 or 10% nitro) into a giant chicken hopper tank. There was a contest for folks to guess how long it would run. I do think that the mixture control was adjusted as the engine ran. It was run mostly in a two cycle rather than the rich setting that control line flyers often use and I am pretty sure it went more than two hours. This had to be 1965 or so. The old control line endurance record was on the order of 11 or 12 hours I think before the limited tank size (someone figured out that you could do in air refueling by pumping fuel through a tube from the middle of the circle). So the real question is how much weight in fuel can the model handle and can you control the mixture setting well enough to keep it from going either too rich or lean as it runs.

combination

Maybe diesel? Still spits fuel, but a tank is not that heavy. dunno

wws

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Actually, that might not be a bad idea for a limited three hour flight endurance. The Davis conversion head is much less expensive than a four-stroke glow engine and is a reliable piece/method of hardware.

Ed Cregger

On Sun, 16 Mar 2008 18:59:32 -0400, I said, "Pick a card, any card" and "Ed Cregger" instead replied:

Reminds me of Gilligan's Island with their three hour tour.

-- Ray

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Yep, who would have thought....?

First dibs on Mary Ann...

Ed Cregger

Haven't you heard? Mary Ann has gone to "pot"

On Tue, 18 Mar 2008 09:21:50 -0500, I said, "Pick a card, any card" and Bob Cowell instead replied:

For medicinal purposes only. She still looks like Mary Ann though. Good genes.

-- Ray