Fuel Consumption
 

Humbly I come before thee oh glow engine gurus.:) I wonder if there is a "rule of thumb" for fuel consumption in a given displacement. The reason for my query is that I am considering a giant scale project and am contemplating power plants for said airplane. In order to avoid straying too far from my comfort zone I am hesitant to use a gas engine and would prefer the familiarity of glow. Thus the question: is there a rule of thumb to gauge fuel consumption for any given engine displacement. I am thinking of using a ST 2300 or 3250 if that helps. Basically, am I gonna go broke flyin' the darn thing?

Brian

RE: Fuel Consumption
 

Well, any plane that can hold a 3250 probably has enough room for a 24oz tank. Mine always have or the BGX3500. I dont like to run out of fuel. With this , you could have a very comfortable 10 minute flight and not worry about running out.

RE: Fuel Consumption
 

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I think you will be amazed at how much less fuel the larger ones burn in comparison to their displacement than most of the smaller ones. There might be some scale effect at work here - just a WAG - but something is going on.

Of course, if you go Saito in the 1.80 size, you can spend a lot of bucks on fuel, but you get a lot back in return.

The state-of-tune of the engine is important, as is the fit and metallurgy - not that I'm expert. These are just some geezer observations over time.

My G2300 was good on fuel. Folks tell me that the OS 1.60FX is exceptionally good on fuel. Both use standard oil ratio two-stroke glow fuel, by the way.

The larger ST's use a reduced amount of oil in the mix, cutting expense. All of the large ST two-strokes run fine on 5% nitro or less. I know several people that guy a gallon of 10% nitro glow fuel (18% lube) and then mix it with a fresh gallon of straight methanol. They burn this in their large ST (after the G2300) with satisfactory results.

Don't be afraid of the gas engines. All you read about in the engine columns are problem engines. The vast majority have no problems, so you don't hear about them. Good luck.

RE: Fuel Consumption
 

Brian,


Any engine larger than a 1.60 (26 cc) warrants spark-ignition.

The cost of fuel per 10 minute flight, at the different consumption rates for gas and glow engine types, will be over 7 times higher for the methanol based fuel.

It becomes much worse if instead you use high nitro fuel; not the 0-5% most large glow engines will gladly run on.


You will have to invest the price difference for the spark-ignition system (~$100), but you will have much less fiddling with an external fuel-pump/regulator ($30-60), since the gas carburettor (Walbro, Tillotson) has an integral one. You will use a much smaller fuel-tank (half the glow size) so you could safely do away with C/G mounting of the tank.
And spark plugs easily outlast glow plugs in most applications.

...And you will not have to clean your model with Windex and rags/paper towels after a day's flying.

You would make up the added investment within one month of flying...


Gas Engines forum - I get your logic...

RE: Fuel Consumption
 

Yeah, it seemed like beating a dead horse but I wanted to get balanced opinions. Hey, you can't vote twice!!:D


Brian

RE: Fuel Consumption
 

This was an old rule of thumb for 2 cycle outboard motors that kind of relates and was not a perfect formula but an idea of.
10 HP wide open use 1 gallon per hour
90 HP wide open use 9 gallon per hour
Motors like 150HP did not use 15 gallon per hour There was a taper effect.
On large engines you consider special fuels cost more money like YS20/20 or Big Tigre Blend because of lower demand. Gas engines aren't for every plane because of weight. Big Tigres are cheap and will run on 0-5% nitro and byron's 16% ,Cool power 17% Or Wildcats 18% plus other brands. Factors include things like RPM a .25 running at 16,000 would in theory use the same amount of fuel of a .50 running at 8,000 RPM Just my .02

RE: Fuel Consumption
 

I have read somewhere tha a rough rule of thumb at WOT is 1 ounce per cubic inch displacement per minute for 4 strokes and 1 and a half oz for two strokes per minute.

RE: Fuel Consumption
 

Weight is a problem with gasoline engines?? Then you have never run an Ohlsson 60 with a modern ignition.

RE: Fuel Consumption
 

Don't get me wrong . Gas engines in the last few years are losing the weight. What use to be converted power plants are now designed ground up for RC use.

RE: Fuel Consumption
 

I guess using my OS240 twin, 300 twin, 240 four cylinder and OS300 five cylider is a mistake by your reasoning. I really don't think some big gasoline powered weedeater engine would look better in the front of a 1/4 Fleet than a Saito or OS 5 cylinder radial. And of course that same big gas engine would fit much better in the Cowl of a 1/3 scale Cub than say an OS320 4 cylinder engine.

Sorry, but in my opinion these airplanes don't "warrant" a big gasoline engine.

RE: Fuel Consumption
 

Bruce,


Maybe not really a mistake, but at the numbers they are sold (compared to gas engines of similar displacement), I see that no person who is serious about flying, would actually make them his engines of choice, unless they are needed for scale dramatization...

They are very high priced souvenirs.

RE: Fuel Consumption
 

No person who is serious about flying would use one???? You OBVIOUSLY have never been to an American scale contest. Contests like the Scale Masters or Hobby Shack's old Riverside four cycle contest. Or maybe the QSAA Las Vegas fly in. Or any other big scale meet. I know how many 4 and five cylinder engines we sold when I worked for H Shack and I talk to Ron Sheldon on a regular basis and know that he sells a fair number of Saito 5 cylinder 325's and the big three cylinder 450's. The 450 is quite a big seller for Horizon.

My old man has a third scale Christian Eagle with my 300 twin on Harris ignition in it. That's about $1200. The President of my club, Al Franklin has a Grumman Widgeon with TWO OS 320 four cylinder engines. I know many scale fliers who use 4 and five cylinder four cycle glow engines. I used my OS240 Gemini in a 1/3 scale Laser 200. Have you ever tried to get a Quadra 50 into a Laser's cowl?

What is scale dramatization? We aren't dramatizing anything. We make scale model airplanes reproducing models of real airplanes and use big 4 cycle engines in them. They fit better and don't sound like a flying chain saw.

Souvenirs??? A souvenir is a coffee cup you buy at Niagra falls or a stuffed bear from Yosemite, or a plate from Seattle, or a little brass copy of the Eiffel Tower. Have you ever seen the Jet rally here in the States?? Guess what they use. Gas Turbines and they cost a bit more than a big 4 cycle engine. The lastest offering is a turboprop engine. Guess what that sells for. Guys will buy it and they will use them in scale model airplanes just like they buy and use the OS 240 4 cylinder, the OS320 four cylinder, the OS Sirius 5 cylinder, the Saito 325 five cylinder and the Saito 450 three cylinder four cyle engines.

I own several multi cylinder four cycle engines and they sure as heck aren't souvenirs. I can just see me bringing home a new OS inline four cylinder with a little card on it that says, "a little reminder of your stay in Tokyo, Japan" and saying "honest Honey it's just a little souvenir from my vist to Japan." Of course she will come back from Thailand with a little 5 carat Blue Saphire as a souvenir.

RE: Fuel Consumption
 

Bruce,


Seriously, take a group of average R/C hobbyists and see how many of them are flying a giant scale aircraft (that needs a 1.60 engine, or larger). You would see it is now 25-30% of them.

And of those, how many are using a glow engine. I guess it will be about 1 in every 5 of those.

And of those big glow engines, how many have multi-cylinders? About 1%...


So, one modeler in every ~2,000 uses a large, multi-cylinder glow engines. And that is in the rich USA.

These people might really stand out in a group, flying very special planes that make the most exquisite sounds...
But this is hardly a force to reckon with.

...And it is very far fetched from making the use of large glow engines economically justifiable.

RE: Fuel Consumption
 

I would love to get myself a big "4-stroke" multi cylinder glow engine one day. For me the engine sound is a big part of flying rc planes. It is an added dimension to rc planes. Ofcourse these engines are very expensive but so is everything that is top of the line. Just look at turbine engines. How many are actually using these and how many others are just dreaming about one day actually have one...

RE: Fuel Consumption
 

I have a ST 2300 and I am surprised at the fuel consumption rate. It only uses slightly more that my 46 size engies. I fly with a 17oz tank and can easily fly for 14 minutes more if you reduce the throttle.

RE: Fuel Consumption
 

I have heard of two. One ounce per cubic inch, and one ounce for a .91 sized engine, but I wonder if the former is a rounded version of the latter?

RE: Fuel Consumption
 

Dar,

Just love your "numbers". Just exactly where did you get them?? When was the last time you flew in the US? Pulling statistics out of the air just doesn't make it. I must assume you never flew the scale contest circuit like I did. That's where you see the big multi cylinder four cycles and in this country scale is a big deal.

RE: Fuel Consumption
 

Just curious.... How much does a gallon of 30% nitro run in Israel?

RE: Fuel Consumption
 

James,


Nitro costs about $70 a gallon here...

5% nitro glow fuel is on average 75 NIS, which is about $17.50 a gallon.
I have not seen 30% nitro fuel here on sale, but the heli guys use it.

I guess it would cost about $40 a gallon.

RE: Fuel Consumption
 

Brian,

Gas is WAY easier to use than glow. The engine uses much less fuel, is more reliable, lasts longer, and does not make a oil mess all over your plane. I set the needles on my gas Zenoah ONCE and never have to touch them again, no matter what the weather, etc. etc. Where is the downside to this ????

So what you are saying is that you want to stick with all the hassle and drawback of glow, because you dont want to make a change for the better... You ever used a weed whacker, or lawnmower ? You start them, they run great every time, and you and forget it. Thats gas :D Chances are, you are already familiar with gas, you just dont realize it.

JettPilot

RE: Fuel Consumption
 

I have been to 11 flyins this summer, and I have seen everything from DA 50's to DA 150's land dead stick. And My Tower .75 has never ever landed dead stick in the 10 gallons I ran through it so far, all this summer. I don't think you can say they are more reliable, I have seen my share of electronic ignition engines with problems. I have seen ZDZ's, 3W's and many other makes of engines have alot more problems than I have ever experienced with glow.:D

RE: Fuel Consumption
 

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This is what I noticed with my G2300. I was surprised at the modest fuel consumption and very pleased with the gentle handling characteristics of the engine.

My ASP 1.08 of a decade ago or longer was similarly mannered.

I suspect that since folks do not usually expect a large engine to swing its props at over 13k rpm, the milder timing/porting is paying off in economy.

RE: Fuel Consumption
 

Well I guess I consider glow relatively hassle free because, honestly, I just don't have any trouble with ANY of my engines. I understand what you're saying though about the mess and all that. It would be nice not to have to wipe my plane down all the time. I have run many weedeaters, chainsaws, lawnmowers, etc so I am familiar with the engines. I am getting a gas engine now though. So I will be building a giant scale project soon![8D] Thanks for the advice.

Brian

RE: Fuel Consumption
 

Thats really not that much more than in the US, about $50 here.

RE: Fuel Consumption
 

That is why I suggested ZENOAH gas engines. They have a magneto ignition system that is on the engine, no batteries, no electronics, just start it like your weedwhacker or your lawn mower and they will run all day. Some of the more exoctic engines that you mention do have thier problems, I would not run them either.

JettPilot