I have a new OS 3500 glow engine....is it possible to convert to gas and is it worth it? Thanks WC

Some would say yes, some would say no.

Check out www.lambertsrc.com He does Super Tiger gas conversions, and I believe he's done an OS or two as well.

AV8TOR

If you want to run gas then buy a gas engine, things will be much longer lived.
UNLESS you have a special plane that only the OS will fit AND you fly it a lot. Then converting will be the way to go.

That's pretty much how I feel about it as well, though I still have an "unscratched itch" to do a Super Tiger 2300 or 3250 to gasoline...

AV8TOR

Blue,


The per flight cost difference is 90%. This means it costs 10 times as much to make one flight with 15-20% nitro fuel, than one flight with gasoline (petrol) based fuel.

There's an initial conversion cost involved, but after covering that up with the 'per flight cost difference', it definitely becomes 'worth it'.
It makes your hobby Dollar go much further and as a fringe benefit, if you installed a gas carburettor, you have a built-in pump that will make your large engine much more reliable than it was as a glow...

The real downside is that you really need to convert the rod and crank to needle bearings. If not, you will still have to run the same high oil content as on glow to allow the bushing rod to "live". I don't know if there is room in the rod for your engine to install a needle bearing. The crankpin in the crankshaft also has to be changed to go with the needle bearing in the rod. (The original is not hard enough to work with a roller bearing.)

Another potential problem is overheating. If it will be and "open air" engine on your plane, it should be alright. If it is a cowled engine, it will need to be properly baffled to assure good cooling. Gas engines run hotter than glow, and that is why they have much larger cooling fins.

AV8TOR

AV8TOR,


While it would be ideal to exchange the con-rod to one from a gas engine that has needle-bearings, if the engine is run with 5% gasoline miscible two-stroke oil, the bronze-bushed con-rod will survive (1-2% is enough for needle bearings).


As to properly baffling an engine, to provide ample cooling flow; this goes for all engines, despite glow engines having a certain advantage of being liquid-cooled by methanol's evaporation.

Several threads were opened by members, who suffered from overheated, cowled glow engines...

You can read about cooling [link=http://www.supercoolprops.com/articles/cooling_largemodelengines.php]right here[/link].

Well of course an engine's cooling system must be set up properly. I only cared to indicate that a glow engine converted to gasoline would run hotter and more attention would have to be put into it's proper cooling.

As far as the oil issue, people commonly forget that when going from alcohol to gasoline, the engine will consume around half as much fuel. Half as much fuel also means half as much oil, even if the original oil ratio is applied.

AV8TOR

AV8TOR,


It is much worse yet...

Just think of it; a gas engine consumes only 40% as much fuel as a glow engine (on low nitro), yet only has 2% oil, to glow fuel's 18%.

This means a glow engine uses ~22 times more oil per-cycle than a gas engine.
There are several reasons for this and one is that when dissolved in gasoline, the oil gets everywhere more easily than when it is suspended in methanol.

So, much more oil is needed.

The needle bearings do affect lubrication requirements, but using the same per-cycle amount (5% in gas), will give the sliding con-rod bearings enough protection, since it is better distributed by the gas.

Even our venerable castor oil, needs to be in much smaller percentage, when it is mixed in gas.


As to cooling, you are right in that a gasoline engine does not have the benefit of methanol's evaporative cooling, but even this attribute must not be abused.

A methanol engine must be cooled as if it is running on gasoline... If in doubt, make sure there is no doubt!

Say what thats to technical for me! But I run 50:1 synthetic with no problems on my glow engines. I do know an OS 160 will not convert to a needle bearing , the rod is to small in diameter to machine for it.

I "think" the BGX-1 has a weird size crank pin too.

Hi all,

my question centers on "is it worth it" on converting a glow engine to gas; Also I am interested in smaller engines/planes and want to actually reduce the power, increase the prop size compared to smaller engines, lower the idle so that the idle thrust is comparable with that of smaller engines. Now I have vintage and replica spark ignition engines and unless I got it totally wrong the spark ignition gives you better contol over the timing and hence all the above and better running, more reliable too.

Yet you say that glows idle better and the main advantage is that of fuel costs; in my case the smaller engine doesnt really use all that much fuel to make the conversion cost effective. So is it still worth it?

To explain my case;-
I have a well used Magnum 180 glow motor (I got it cheap, but it has many hours left on it, good compression anyway), its way to powerful for the smaller planes that I prefer; but not too heavy since substantual noseweight is often needed. Whilst I can throttle down, its lowest idling speed would still be too high, and uneven.
So I am interested in converting it to spark ingnition without awkward machining operations such as a conventional contact points conversion would require.
A Hall effect ignition system looks to be possible, the extra weight is not very significant as my idea is to use this on large slow models.
In fact what I want to do is to lower the revs and power of this engine (and corresponding lower idleing) so as to fit into planes normally fitted with a 90 2st (and with a lot of nose weight!) such as WW1 biplanes. It would of course be able to swing a much larger prop than the smaller engines, particularly with the controlled ignition that spark ignition allows; the revs would be much as for a chainsaw type engine I expect < 8k.

I can fit a small spark plug (a V2 or V3) into the same hole as the glow plug; or increase the hole and thread for 3/8 "V" plug if need be these being the standard vintage spark ignition sizes for 19 to 99 sized motors. Would the usual 'big gas engine' spark overwhelm this size of plug?
I can alter the HT lead, and fix the magnet and sensor without much problem I think,
the thing is would it work? and would it be practical or worth while?

As to the oil question. For spark ignition on the .29 to .60 the argument is the reverse of what I am reading here; 3:1 gasil ratio and only reduce the oil to 25% if plug fouling is a problem. The lubrication is obviously adequate, the extra oil cools the engine by carying away the heat in the exhausted oil. Btw, Colemans white gas is prefered over pump gas due to unwanted additives in pump gas

So why do the two fields of opinion differ by so much? is there an easy answer
I am not familer with engines larger than .60 2sty, so this is all new to me. My cheap 180 was a way to enter into the fun without too big a plane (if the thing could be tamed)

?

cheers

Jim

go with a gas, it is cheaper easier and you don't need a machine shop. If you want to have fun and like fooling with engines and such then convert one and play around but it will cost more.

I say "it is worth it" if the desired results end up close to waht you want. Try something new...it may be fun!!! Capt,n

Hi Ken,Capt'n an all

OK, I am probably, no definitly, going to go for it [>:], since I like messing with engines anyway and I have just had confirmation from Mike Clewes of http://www.apacheaviation.co.uk who says it can be done and what they sell is suitable for what I want doing, but recommends fitting a 10mm plug (the usual for the big gassies, and the plug is much cheaper too) .. the system IS more expensive, $75 or so, but thats reasonable its just that I am a cheapskate. (It may be cheaper by 15% or so due to tax savings)
Of course I save money in the long term... as long as I dont crash ..... too often

I will probably also reduce the carb size, and aim to get a really slow idle.
Note, with the slow running I am aiming for, the whole thing should be pretty quite even with the usual 'pitts style' muffler

fun fun fun !

cheers
Jim