It seems that for whatever reason we have a lot of newbee's to gas engines on Flying Giants these days. Personally I see that as a very good thing and I'm sure all the guys in gas feel the same. In order to better facilitate your conversion over to gas I thought I would create a thread telling you the basic differences in gas vs glo so you can find most of the answers to the many questions you have in one place. I'm sure there are those of you out there that will have other questions not covered here but, hopefully, this will answer most of your basic questions and at least put you into a position to start your build and conversion into the wonderful world of large scale gassers! Here goes!!

There are a few things different about gas engines as opposed to glow. First off is you'll need a gas stopper for your fuel tank as the ones that come with them will disintegrate in gas. You'll also want a remote switch for your ignition. 42% make a very nice opti-kill switch. I use RCats RC-100 solid state switches but the 42% is just as good and you won't need to solder anything. The switch should be between the Electronic Ignition Module (EI) and the manual switch for the EI. It plugs into your Rx and allows you to shut your engine down instantly from your Tx. VERY important for safety. For the engine side of the house you'll want to run a 4.8 volt pack unless you're using regulators. ANYTHING above 6.0 volts will destroy your EI. That means a 6.0 volt battery pack as they charge above 6.0. I run a 4.8 NiMH pack (1200-2700 MaH) for my EI with a standard manual switch and a 6.0 NiMH pack for my Rx and servos. Use a heavy duty manual switch for your Rx as a regular switch will not allow enough current flow for the servos in a large plane. I use the MPI switches with the charge jack and LEDs but there are many out there.
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The engine is normally mounted using aluminum stand-offs. Simply line it up on your firewall, cylinder pointed down, and drill the four holes for the bolts to come through the back side of the firewall into the stand-offs. You'll want the stand-offs to be long enough to get your proper distance at the cowl opening. If this puts your carb within 1" of the firewall you will have to cut a 1" hole in the firewall to make sure you have an un-obstructed air flow to the carb. Use large washers under the four bolts as that will keep them from compressing the wood over time. You can mount the EI on the side of the engine box if there is room under the cowl. The important thing is to keep it away from the Rx. I usually mount the EI on one side of the engine box and the EI battery on the other side. The servo for the throttle can be mounted in the fuse but make sure you use plastic ends on the linkage. You cannot have any metal to metal contact between the engine and the throttle or choke servos.
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You should also "pin" your firewall as these engines pull very hard and can pull it out. To do this simply drill a line of 1/8" holes through the sides, bottom, and top (if it has one) of the engine box into the edge of the firewall. Then insert short lengths of 1/8" hardwood dowel painted with epoxy and let harden. You can also use this opportunity to fuel proof your engine box by painting it with thinned epoxy (use alcohol to thin it) or clear polyurethane varnish.

The fuel system is also set up different on a gasser. You will have a fuel dot to fuel through, lots of places sell them, and a two line setup. The pickup line coming from the tank will have to have a tee in it. The tee line will go to the fuel dot. The straight line to the carb. On the vent side of the tank, the other line, you will need to run it on top of the tank, or at least above the tank, and put a loop or two in it and then run it out the bottom of the fuse. This will keep it from siphoning. Also notice that this is NOT silicone tubing. You will need to get Tygon tubing or another "gas proof" fuel tubing. 1/8" tubing is fine for a 50cc engine.
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The choke can be run off of a servo or set up manually. I have run both. My DL has a manual setup I made using the little composite arm that comes with the DL, a 2-56 swivel end and an old 2-56 threaded control rod. I did the same with my XYZ 50 HP but ran the rod out through the side of the cowl. Works fine. I do have to reach just inside of the cowl to engage the one on the DL so if you do this make sure you switch your EI off at the Tx before reaching past the prop. Always remember, glow props hurt but gas props remove body parts.
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The last thing you may encounter with a gas engine is a problem with the metering valve caused by swirling air inside of the cowl. This can cause the engine to die because the metering valve isn't reading the correct atmospheric pressure. Here's how I make sure that doesn't happen. I remove the plate over the metering valve, it's the plate on the side of the carb with the little hole in it, and drill and tap that little hole out to accept an 8-32 pressure nipple from an old glow muffler. I then thread that into the plate and carefully grind off the excess on the back side of the plate so it can't damage the diaphragm. Once the plate is back in place you can run a piece of fuel line from the nipple to inside of the fuse where the air is still. I run mine into an old pill bottle or film container. If you do that make sure the container is not air tight.
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As you are running a 50cc gasser you will need to get the proper prop. I run a Vess 22A or 23A on mine and it's fantastic. Just be sure and use a drill guide to drill the prop and drill it from the back side. I always align mine so the prop is at the 1-2 o'clock position when looking at the engine from the front with the engine on the compression stroke. It makes it a bit safer to start as your hand goes directly away from the prop when you spin it. Also make sure that you open the front of your cowl up to get good air flow over the cylinder of the engine. Gas engines run much hotter then glo and really need a lot of cooling.
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Then there is tuning your engine. First you will need some 87 octane gasoline mixed at the recommended rate with whatever break-in oil your engine manufacturer states. Here's a simple and fool proof method for adjusting the engine after that. Your Walbro carb has two needle valves. Adjust the high end, marked with an "H" until you get maximum rpm. Then back it off counter-clockwise, rich side, 1/8 of a turn, or about the width of the slot in the needle. Then adjust your low end to get a good transition without hesitation. This will make your engine a little rich for break in and give you great performance. More in-depth information on tuning can be found here. https://www.flyinggiants.com/forums/....html#post3925

http://www.youtube.com/watch?v=6bOYEZZkDhk


Should you ever have to reset your timing here's a good video on that.

TDC and ignition 2 (6 min 36 sec)

Of course you will need to convert over to high torque metal gear servos for the larger planes but you should be able to get the information on those from the manufacturer of your plane. Just keep in mind that you'll need powerful servos for a 30% plane with strong rods and swivel ball ends. Below is a picture of the ones I make up using 4-40 all-thread and CF tubing. The metal servo arms are also highly recommended as the plastic ones tend to strip out the spline.

If there's anything I left out or any questions you have feel free to post them, PM me, or ask any of the members on Flying Giants. There are a great bunch of people here and all willing to help out a newcomer to the world of giant scale gas.

Al

What about cooling baffles for a twin?

There are as many ways to do baffles for twins as there are planes as much of it depends upon the cowl design. I would suggest you find someone on FG that has your plane and engine and ask them what they did.

Great thread AL!

I made this thread a stickie!
nice work.

Thanks Sleepy!! I hope it helps some of our newbees!!

Al....no top on the engine box?

I didn't use one on this plane but did re-enforce the firewall with heavier gauge aluminum angle to make up for it.

I did see the aluminum angle....just thought a top would add to torsional stresses releif from the motor revs. Of course it would be something else to remove to access equipment.