fireman7875

My Feedback: (7)

I am thinking of building a giant scale airplane. Haven't chosen a design yet but looking for a good sport flying plane that will do some basic aerobatics. Don't have to have unlimited verticle or warp speed. My question is this: what are the benefits of glow over gas and vice versa? I realize that there is an operating cost difference but there also seems to be a start up cost difference in the other direction. So why do you guys choose glow or gas for giant scale applications? Also, could you recmmend some good giant scale glow engines that I won't have to sell my truck for.

Thanks,
Brian

RaceCity

How big of an airplane are you referring to? Your glow options start to get pretty limited much above 30-40cc. ST makes an inexpensive 45cc glow engine. You could break the bank with a big displacement 4C glow engine.

Cube for Cube...glow makes more HP than Gas, but that only goes so far. You can't make a 30cc engine perform like a 60cc engine.

Sometimes there's just no replacement for displacement.

The gas engines are the king of giant scale models much for this reason. One of the most cost-effective, and time proven gas engines out there is the Zenoah line. A whole range of displacements, reasonably priced and while not the most sophisticated nor the lightest engines out there, they're proven good engines. Simple designs. Less stuff to hassle with. Maximum bang for the buck.

fireman7875

My Feedback: (7)

Probably in the 12-20 pound range. I don't want anything too big just big enough to go to the big bird flyins with. How much fuel consumption am I looking at with a large engine like a ST 2300 or a Moki 135?

Brian

loughbd

If you use a glow engine the price of fuel will hit you right in your rear pocket. Large Glow engines use a lot of expensive glow fuel. Even in an OS108, a gallon doesn't last too long. Even a 3 bucks a gallon, gasoline is still a lot cheaper.

I have a 1/4 scale L-4 with a Zenoah G-38 in it and a gallon of fuel will go bad long before it's used up. Every year I pour what's left in my can into one of my cars and refill it with fresh gasoline. I have never used a whole gallon of gasoline in a year.

I also have a Tartan twin on glow in a G-Shark. Even straight methanol and 8% oil is a lot more expensive that gasoline and that Tartan sucks fuel like there is no tomorrow.

The big problems with gas engines is size and the fact they sound like a chain saw.

There are big four cycle glow engines on the market. OS makes a 5 cylinder 3.0 cid engine and a 4 cylinder 3.2 cid engine and a 3.0 cid twin. Saito makes a 3.0 cid twin and a 4.5 cid triple. They are all excellent and sound great BUT... the price is waaaaayyy up there. They get good fuel econemy but still use a lot of fuel.

RaceCity

Even that is a pretty broad range of weights. 12-20lbs covers a lot of territory. It'll just depend on the particular airplane in question. An IMAA legal-sized "trainer" would have a radically different engine requirement than P-51. Refer to the kit mfrs engine recommendations. If a glow engine can be obtained that fits the requirement...then you have that option available.

Fuel consumption is going to be noticeably greater than your typical .46. The upside is that most large 2C glow engines use little or no nitro, and often use a blend of fuel with reduced oil content...both of which affect purchase price of the fuel.

You pay less for it, but you use more of it. Six of one...half dozen of the other.

There is just no perfect answer. If the engine requirement is much over 1.8cu in (30cc)....the vast majority of persons would choose an appropriate gas engine.

Newc

For what it's worth...I have an 80" Midwest Extra 300XS that weights 15# 4 oz. (on wheels, I also fly it on floats!). It does everyhting that I'm capable of doing and does it well enough to make me look like a pretty decent pilot

I have a Moki 2.1 on it and couldn't be happier with the engine, including the ease of starting, power, idle, sound, etc. The rule of thumb with the Moki 2.1 is that it will burn about 1 ounce of fuel per minute of flying. My experience is that this is about right if you are running full throttle all the time - which I don't since it's not needed. The only time I checked the static thrust of the engine was when it was still pretty new - only about 1 gallon of 0% nitro fuel through it - and it was running rich with an APC 20x10 prop. Thrust was 19# at only 7200 RPM.

loughbd

A minute per ounce on a 2.1 CID glow engine?? Wow, that's pretty good. The average 61 sized glow engine uses about that much. My OS108 uses at least twice that much fuel.

Cyclic Hardover

My Feedback: (3)

I have the 2300 and I do not consider that a large engine. Now my BGX 3500 will keep up if not surpass many 50cc gassers. Nothing against a gasser but thats the way it is

NM2K

My Feedback: (14)

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That is a beautiful Extra, especially sitting on floats.

Speaking to the OP:

One of the things that I have noticed is that the larger glow engines do not seem to burn as much glow fuel in proportion to their size. There may be exceptions, like Bruce's Tartan, but the OS 1.60FX and the Super Tigre G2300 are similar in fuel consumption when compared to the piped .60 size engines that I used to power my pattern ships with in the late Seventies, early Eighties. They too consumed about 1 oz. per minute of precious glow fuel.

I really like the new lightweight SPE engines that are out now. I have a 26cc engine from BCMAE and a 40cc engine on the way from Brillelli. These are new generation light weight powerplants that will fit easily into most ARF models that are made for 1.20 to 1.40 size glow engines. They provide plenty of power for aerobatics and the price of the engines is comparable to glow engines of similar displacement. The SPE engines by these companies burn a mix of gasoline and oil and are fired via a spark plug.

DarZeelon

Brian,


For the reasons mentioned by others here, I would say the 'break even' point is around 20 cc, or 1.20 cid.

It is true that glow engines cost less, due to the ignition system that they don't have and also make somewhat more power.

Glow engines run at an ideal power stoichiometric ratio of about 5.5:1 and gas engines run at about 13:1.
So glow engines use 2.364 times more fuel.
Methanol makes less BTUs per weight unit; 9,970 vs. 19,000, so gas is 1.906 times more energetic.

Dividing the amounts and the ratios will eventually show the glow engine makes 24% more horsepower than the gas engine, at the same RPM. If the same prop is used, the glow engine will spin it about 7.4% faster than the gas version.

But, for the same flight duration, a gas engine would need only 42% of the fuel that a glow engine would use. That is less weight to take-off with, partly countered by the weight of the ignition.

Cost is the main issue, with glow fuel (low nitro) costing 3 times as much and being used at 2.364 larger amount, so payment for fuel is 7 times greater for glow engines, over gas engines. This is partially counteracted by the $100 cost difference between the engines. It will take a small fraction of the engine's life to cover this difference.

Gas engines last nearly for ever, even with 2-3% oil... Can't say this about glow engines. Another advantage for the gas.

I put the break-point at 20 cc...

DarZeelon

...And gas engines have their own fuel pump, less hassle to get the engine set up for flight, compare to that Perry/Iron Bay/Cline that you have to install on nearly all large (15 cc and up) glow engines.

This further reduces the magnitude of the cost difference and gas engines have better reliability too.

rajul

My Feedback: (58)

Good points Dar!

DarZeelon

Thank you, Mike.

I try to do this.

Flyer95

My Feedback: (1)

IMO there is only one advantage in using a small 25-35cc gasoline engine and that is the operating costs.
If you practise many hours each time you go out then gas becomes cheaper quickly. For a weekend flyer the economical benefits are very small. But there are more things to consider than just fuel costs. A large high quality glow engine is as simple "read easier" to operate as a 40-sized glow.
With a gas engine you must make sure to put the batteries in the right places to avoid RF interference and you must have kill switches...... They smell bad and the niose is not as pleasant unless you put a cannister muffler on them. Gasoline engine takes more preparation and gas fuel is not as safe as glow when you fly it or even when you crash it somewhere it can start a fire.


Dar,
Are you saying a castor oil burning large glow engine would wear out or be unreliable? Which engine are you refering to? I happen to fly big glow engines for many years and can assure they will not wear out or deadstick.
I have seen and read about many modern and nearly new gas engines where overheated and trashed or the crankcase was broken and destroyed during the operation for some reasons?

DarZeelon

Amir,


What I am saying is that gas engines last seemingly forever.

This is even though they have a very small percentage of oil in their fuel.

The lubricity of a petroleum based fuel, in which any type of oil is dissolved at very small percentages, is better than methanol based fuel, even with 20-22% castor oil (even better than synthetic oils).

Any engine will be destroyed if run consistently over-heated.
Any con-rod bearing can become seized, whether a needle bearing in a gas engine, that had one of the needles break, or a bronze bushed glow engine bearing. This would cause a catastrophic failure.

Wear is lower in gas engines, but failure can happen in both.

Even large glow engines eventually wear out.

When the cost of the fuel that you use is just 14%, you can take a chance that a catastrophic failure would happen and in a big glow engine, it can also happen.

But there are so few large glow engines, that you may never hear about such a failure.

Newc

Thanks, Artisan. It does draw a crowd when it's flown on the floats. Not necessarily a good thing when the crowd consists of jetskis and pontoon boats that seem to always stop to watch right in the landing area!

I've never needed a pump of any kind and never had a fuel draw problem, so don't agree that this is an issue.

As to the comments from a number of folks about the difference in operating costs due to the price of the fuel...I'm not one of the guys practicing for Top Gun, Scale Masters or even IMAC - just a weekend flyer. Therefore, the cost difference isn't an issue. In fact, I buy my fuel at Toledo and the price last year was (as I recall) $10/gallon for 0% Nitro and $11/gallon for 10%. I actually run 10% in my Moki primarily for convenience (use same fuel for all planes except my YS), but have also noticed - haven't done back-to-back comparisons - that the 10% allows low idle speeds and very easy starting even in cold weather.

DarZeelon

Jim,


You answered your own question...
Most people using large engines use them in planes that are not merely 'Sunday fliers', but models that must operate properly at all attitudes.

With a large glow engine and a large fuel tank, if you adjust the engine to run well at part throttle, in nose-up hovering attitude, when you put the nose down to level flight attitude, at the same part throttle setting, the engine would be running so rich, it will not respond well to the throttle and would even detonate and backfire, possible throwing the prop, due to the sheer mass of fuel accumulated in the crankcase, that shoots up into the combustion chamber, as the throttle is advanced.

Don't believe this, ask those that use Mokis and OS1.60 engines in 3D planes.

They all need and have pumps for that purpose.

With 10% nitro, gas costs just 13% of the glow fuel that you need...

fireman7875

My Feedback: (7)

Wow, what a wealth of information. I appreciate all the responses that you all have offered. I like the idea of using gas because of the operating cost difference. I am pretty much a weekend flyer but I can imagine that using a gallon of glow fuel every time I go to the field would get pretty annoying. On the other hand, I am a little fearful of the learning curve of operating a gas engine. I have some experience with them in weedeaters, chainsaws, blowers, etc, but not planes. I know that if my glow engines break down I can take them apart and rebuild them. I don't know how confident I am about that with gas. Thanks for all the help. I may have more questions later!

Brian

Flyer95

My Feedback: (1)

Dar,
3% petroleum based fuel can not be better than 20% castor oil based fuel. If that was true then the gasoline engine manufacturer would never put a needle bearing on the connecting rod for gasoline operation.
We can take an example like the good old Super tiger S3000K for which 10% castor oil and methanol was the recommended fuel and the engine would last many many years on that fuel. When converting to gasoline with the CH ignition system it is still recommended that a twostoke fuel with 10% towstroke oil is to be used to protect the connecting rod. In other words the petroleum based fuels are not any better than the castor oil based fuels.
Another good example is the OPS engines with needle bearings for which only 5% castor oil and the methanol for the balance was the recommended fuel. They could turn huge props on that fuel and would last forever.

Newc

Didn't ask a question, gave some input. And as for your assumptions about my flying, you couldn't be much more wrong. When I say
all it is saying is that I'm not spending the amount of time in practice as are they. Didn't suggest that I don't do 3D or any other kind of flying that requires massive and immediate attitude changes without any transition problems.

Your comments about the attitude of the plane are so completely wrong as to be laughable, as is your comment
We use Moki engines - without any pumps - for 3D (I assume that's what you meant) all the time.

Some gasoline engines are good engines and I never was saying that they weren't. I was simply trying to respond to the original poster's request for input. I gave data-based information regarding the use of a Moki, not antecdotal and incorrect information.

DarZeelon

Amir,


MVVS used to have the needle bearing con-rod in the glow versions of their 26 and 35 cc engines.
They no longer do.
These big glow engines now have bronze bushed con-rods, with the needle bearing item reserved only for the gas versions.

The oil needs specified by MVVS for the glow version is 10% pure castor oil. Synthetics are disallowed specifically.
This was the same when the needle bearing con-rod was in the glow versions!

The gas versions required 3 1/3% lubricant for the first gallon and 2 1/2% from then on.

What CH Ignitions are doing is to cover their *****es, by telling you to needlessly use too much oil... You should know that.
They want no one to be able to blame them for any wear that occurs.

Jim,


It is my experience and that of others, including a thread I participated in recently.

A large fuel tank makes it a problem to adjust for all attitudes; exactly as I wrote in my previous post:

This is hardly a laughing matter.

I am talking about very experienced modelers, who are having mixture setting problems with big glow engines; not novices that are making every error possible and then some...

Flyer95

My Feedback: (1)

Dar,
If 10% oil is too much for the gas converted ST 3000 with bronze bushed conrod then why on earth would people put conrods with needle bearings in them? Yes because it was needed if they wished to use 3% oil instead of 10%. There is a conrod kit with needle bearing available for this engine. Another example is a big gasoline engine manufacturer who also had problems with the "needle bearings" on conrods on the early 50cc gasoline engines and these conrods didnt last very long. They changed the materials and the design I think and the problems where solved. So one can not only blame the type of lubrication.

Newc

I can't be blamed for your "very experienced modelers...having mixture setting problems with big glow engines". As many people know, experience doesn't always translate directly into expertise.

I know - based on actual experience and not taking somebody else's word for it - that a 2.10 Moki without a pump and with a 24 ounce tank (plenty 'large' for the engine) - is not at all difficult to tune for all attitudes, including the one that you seem to think is especially difficult. Perhaps your "experienced modelers" don't correctly install the fuel system, and therefore shouldn't blame the engine.

This is my last post in reply to anything that Dar says since he doesn't seem to me to be responding based on any of his experiences, or actual knowledge, but is basing his comments on those of others.

DarZeelon

Jim,


There is absolutely no need for you to respond.

All,


Besides the experience of others, I have an H9 Ultra Stick Lite, with an MVVS 1.60 in the nose and the stock, 22 oz. tank that came with this ARF. I was using exhaust pressure assistance to pressurize the tank.

The size of the engine and fuel tank causes a 'head' difference of about 7", between tank full, in level flight attitude and tank full, in nose-up, hovering attitude.
This fuel level difference rose to 12" with the tank nearly empty.

Any claim Jim can make will not change the fact that fuel draw is much harder for the engine, in the nose up attitude, than it is in level flight. This draws significantly less fuel at nose-up attitude, compared to level flight attitude.

I encountered exactly the situations described in my previous posts, since I adjusted the low-end for hovering.

This caused the engine to cut-out in prolonged part throttle level flight, as the throttle was advanced, often by back-fire...


Anyone running an engine with such a great fuel level differential, will encounter a similar problem, unless a pump/regulator is used to equalize the fuel pressure (or if very high nitro fuel is used - a wide stoichiometric ratio range - this will make the problem a bit less acute).


If Jim doesn't think this fuel level difference has any affect, he and his buddies probably fly their large glow models inside NASA's 'Vomit Comet', with no gravity...

ir

Actually, it occurs on smaller engines as well. My experience was with my .30 size heli, even with a header tank; it leans out even on 1/4 main tank. Its always a compromise. Can imagine a bigger tank when its being emptied it will more pronounced.