There has been a great deal written about the engines we use in our large models. Some of it is good dope and some of it is someone's idea of what is correct. It's well to note that someone's idea may not necessarily bear much relationship to what is the actual fact. Everyone gets a 'wild hair' every once in a while!

Some of the best information available has been published in Model Aviation in Bob Beckman's column. If you haven't been following his reviews of the various engines, make a point of getting copies of them and keeping them on file for future reference.

Also, a couple of the magazines have published a short piece by Dario Brisighella on the small carburetors used on 99% of the engines we use. That short article should be on everyone's must read list. It's good dope and you'll understand the carb a lot better after you know how it works. It also details the type of service we can do ourselves (it is minimal) and that should be heeded by all concerned.

Basically, what Dario suggests is that as far as you should go into the carb is to clean the filter in the inlet side of the carburetor AND THAT'S IT! I f you do try to go further into it without the knowledge required, you'll mess it up and end up having to replace it altogether. Better to leave anything further than cleaning the filter to the experts at your local two cycle shop. (There is an alternative, if you really want to get into the engine, and that is to take an evening course in small engine repair such as those offered by most vocational schools and also offered as an evening course in many school systems. The fees are usually nominal and the knowledge you gain could make you the local 'expert'.)

There are several additives coming on the market to be added to the gas we use in our small engines, and I tend to go along with Dario's comment on them. He summed it up in a couple of words regarding one additive being touted as the answer to all your problems. Those two words were, "No difference!" My own attitude toward this additive is this, if you want to improve the performance of your engine, forget them. If your objective is to increase the income of the guy peddling the miracle additive, then buy it and use it. Maybe even better, buy, but DON'T use it, you'll probably accomplish your objective and do no harm to the engine!

Gas oil mixes have come in for attention as well. There have been some claims for 50:1 mixes and 100:1 mixes and almost everywhere in between. Again, my own judgment on this is to use the mix recommended by the manufacturer of the ENGINE. Quadra recommends 20:1 and I have used this since day one and won't change it. The so-called benefits of changing the mix are, I suspect, overrated and would be difficult, if not impossible to substantiate. The selection of an oil for this use is pretty wide open. I use a quality, name brand, two cycle oil and mix it as above, all the time. I buy my gas a couple of gallons at a time and mix just before putting it into my field fuel container to keep it fresh. As it happens, I use Castrol oil as it is readily available to me and is of consistent high quality. I don't necessarily recommend it to anyone, but only suggest you choose a quality oil and stick with it. One caution, oils intended for outboard use may not work as well for us. Generally speaking, an outboard engine is water cooled and will run a little cooler than an air cooled engine, particularly if that air cooled engine is tightly cowled and does run a bit hot.

Mixing oil to gas at the ratio recommended by the manufacturer of the engine is always good practice and it will both protect your warranty on a new engine and probably keep you out of trouble as well. I know of one case where a new engine (Quadra) was run on a very thin oil to gas ratio right 'out of the box'. It didn't last long as the wrist pin/conn rod connection seized up and had to be serviced. That was a sensitive area for lubrication before the bearing was changed from a bushing to a roller bearing, and this sort of thing is now much less likely with the new bearing being fitted to all new engines. Older ones which have the bushing can also be up-dated to the newer style, but this requires replacing the conn rod and piston assembly. This can be done for less than $20, so it's not all that big a deal. If you ever do have a problem with any part of this assembly, you might consider replacing with newer style. It will gain you up to a couple of hundred RPM and also give a lot less trouble with the wrist pin bearing, if you insist on running a thin oil mix.

Basically, our engines are both pretty tough and very reliable. About the only way you can get into trouble with them is to bang them into the ground, or to abuse them in some other way. Taken proper care of they'll last for many years and give good service doing so. About the only maintenance necessary is to keep the points clean and properly gapped and maintain the spacing between the flywheel magnets and the pole pieces at the correct interval for your engine. CD ignition systems require a fast crank to get them started.

There is some interesting work going on, on ignition systems using a variety of triggering methods not requiring points. I will be greatly surprised if these do not appear on the market as a retro-fit kit for many of the engines currently in use and will likely appear on some engines right from a supplier. What little I have seen in print on them looks very promising and they will undoubtedly provide great reliability when they do appear.

Starting, especially hand starting our engines can be a frustrating experience. I have received quite a bit of comment about people having difficulty starting some engines, even those without CD ignition.

If it's at all possible without totally disfiguring an engine cowl, I prefer to be able to get a finger over the carb opening in a model. I'll usually close off the opening, with the ignition switch off, and crank the engine over by hand, holding the prop in my fingers, several turns. Then turn the ignition on and start flipping. In fairly warm weather, this will usually get it going. if not, I carry a hypodermic syringe in my field box and use this to put a squirt of fuel into the throat of the carb with the throttle opened wide, move the throttle back to idle. It takes a couple of flips of the prop to get this rich mixture into the combustion chamber and while I might have to do it a couple of times, that usually gets things moving for me. The hypo needle is also a great way to get fuel into the carb if you don't want to make a hole in the cowl large enough to get your finger through. The hole required to permit the needle access to the carb is so small as to be almost invisible.

Once the engine has fired, don't try to advance the throttle until the engine has had a few minutes to warm up to operating temperature. Premature advance of the throttle is almost guaranteed to kill the engine and you'll go through the whole starting routine again!

Those engines which come equipped with a choke will not require much fiddling to get started. Simply close the choke, flip a couple of times until the engine fires, open the choke and you'll soon have it running. Some engines can be retro-fitted with chokes and it's a good idea to do so. They can be operated by hand or by a servo and some even have a two-step setting, one for full choke and one partial while the engine warms. They work very well and will take a good deal of the frustration out of engine starting.

There is one much neglected item which IMAA recommends. That's a kill switch and you shouldn't be flying without one. Avoid, if possible, running the kill switch circuit into the radio compartment. It's not all that difficult to arrange a micro-switch on the throttle linkage ahead of the firewall which will provide a kill circuit which is totally ahead of the firewall. Running the circuit back into the radio compartment can induce radio problems and there is no need to make problems for yourself. If you are still using the original carb mounting on the Quadra, you must change the direction of the throttle linkage at right angles in order to operate the throttle. This can easily be done with a bellcrank and it's not a difficult feat to add a micro switch in the right place to close on low throttle trim, killing the engine. It may well save a model for you and is a good safety feature, to back up the manual kill switch you should have in the ignition circuit anyway.

Also, if you are using a Lectra-Start system in your model, be sure to arrange a switch on the throttle set-up so that the Lectra-Start will only operate when the throttle is set to 'idle'. The way Lectra Start system is set up with a group of switches which will kill or start the engine, it's no big deal to add a switch which is closed only at low throttle settings in order to open the START circuit at all throttle settings other than 'idle'. You don't have to be an electrical genius to set all this up and the diagram should help you get it all together. (See Electric Starting System by author.)

Mounting engines has been a point of some disagreement as well. Some recommend hard mounting the engine to the firewall and some say to mount with some 'give' in the mounting. As it happens, I prefer to have a little give between the engine and the firewall. I use Lord Mounts but have mounted both ways with equal success. The advantage of the Lord mount is that vibration is shielded to a certain extent from the fuselage and therefore the radio equipment. The less vibration getting to the rest of the model, the less strain on all those carefully prepared glued joints and the less chance the radio will be interfered with by the shakes.

There is a disadvantage as well, the vibration which will now be partially restricted to the engine and mount makes a nice reliable idle a little harder to come by and this may not be acceptable. It's a case of comparing the two methods and deciding for yourself whether or not the trade off is worth it. I feel that it is and almost always provide for some dampening between engine and airframe. Quarter Headquarter's Quadra mount provides a neoprene pad between the mount and the firewall although the mount is effectively hard mounted to the firewall.

Mounting these larger engines requires a little more meat in the mounting bolts than we have been used to in conventional models. I prefer 1/4-20 bolts and blind nuts. The large blind (or Tee) nuts are not a regular item at the hobby shop but if you have access to an industrial supply house specializing in fastening devices, they will either have them in stock or will get them for you. I buy by the box in a variety of sizes and find them to be quite economical as well as very convenient. You'll probably find they can get nylon bolts for you in a wide variety of sizes as well as some things you didn't even know you needed.

When you have to make up a special muffler for an installation, be sure you provide adequate circular area in the exhaust system to handle the exhaust from your engine. Many are not aware that there are limits to what our engines can do and if you choke off the exhaust system, you'll end up with an engine that can't 'breathe' properly and which will probably run a good deal hotter than necessary. If you aren't sure what is required, and can't find out, better to provide too much exit area than to provide too little.

While on the subject of engines breathing properly, DON'T change the carburetor on your engine to a larger sized carb in order to get more power. You'll probably be wasting your time and money if it isn't done with the advice of the local two cycle expert. If he says don't, take his advice and forget it.

When cowling your engine, be sure you have adequate inlet area for cooling air and be even more careful that you permit adequate exit area for the air which is designed to keep your engine running within it's temperature operating range. Getting air to the engine is important, getting it out of the cowl and away from the engine with the heat it's picked up is even more so. Exit area should exceed inlet area and, if the cowl permits, the creation of a negative pressure area at the exit will help get rid of the heat that is your engine's enemy. Good air flow is a real necessity and providing it should not be neglected.

Be aware too, that the carburetor on your engine has a vent on it which senses atmospheric pressure in order to properly meter the gasoline supply to the engine. If the cowl's internal pressure is higher than it should be, an erroneous reading will be use5 by the carb for this purpose and you may find you have an engine which is difficult to adjust properly. Naturally, this vent should not be faced directly into the prop blast for the same reason. If there is any doubt in your mind about pressure affecting the vent (it's in the center of the raised metal cover over the pump diaphragm and usually has information etched on it) provide a baffle of whatever sort is needed to protect it from direct air blast.

Carrying a spare spark plug in your field box is an excellent idea, just as you'd carry more than one prop. If you use a multi-bolt prop hub, check it from time to time, especially if you have tic'd the ground with the prop, to assure that the bolts have not partially sheered off. This usually becomes obvious if you have trouble getting the bolts to seat properly. Especially if they get tight part way into place after changing a prop. A spare set of prop bolts isn't a bad idea for your field box either.

Gasoline is much more volatile and potentially dangerous than glow fuels and should be handled with care. If you use a metal container, keep it away from any contact with batteries. DON'T carry gasoline in the passenger compartment of the vehicle if you can avoid it. Have a fire extinguisher available at the flight line and don't permit any smoking adjacent to fueling operations. Your engine may be fireproof, but you and your model are not. If possible, place the fuel tank in your model where it is separated from any electrical device which could create a spark and a nasty hazard to you and your model. Gasoline vapors are highly susceptible to explosion and it doesn't take much of a leak, coupled with a small spark to make a big bang. For that same reason, be sure the fuel system has complete integrity and cannot leak under normal circumstances. Those leaks might be terminal for both you and your model. Wherever possible, provide a positive ventilation system for your fuel tank compartment, to the outside air. One way to do this is to provide a scoop facing into the prop blast and a negative pressure outlet into the airflow, unconnected with any other part of your model. A flow of air through the tank compartment is a good way to prevent the build-up of dangerous vapor in the tank area.

Naturally, everyone knows by now that you cannot use silicon fuel tubing with gasoline. It just dissolves, swells up or falls off the connections, any one of which can prove disastrous. Neoprene tubing is the answer and it is readily available almost everywhere. The windshield washer tubing sold by auto supply houses and car dealers is quite inexpensive and readily available anywhere. There are a variety of sizes of tubing in neoprene being made and one of them will suit just about any application you have in mind.

That's not all there is to know about engines, of course, but if you know and apply what you have just read, you'll be well on your way to avoiding some of the pitfalls of using gas engines in your large birds. Some of what I have said here is opinion, but the bulk of it has been tested in my own building and flying and it has worked well for me for about as long as we have really been into BIG. I hope you got something useful out of it, and we'll do it again soon.