The complete radio control model airplane FAQ.
Should I use a gas engine, or a glow fuel engine? What are the pros and cons of them? At what size does the gas engine pay off?
This is a debate that goes on frequently, especially when you get to the 25-28% (72-82") scale aerobatic planes. It all boils down to this... I've never seen someone who has flown gas who will argue that glow is the way to go, if you can fit a gasser in reasonably. There's got to be a reason.
On this site, the application of gasoline powered flight is covered for 1.20 sized planes, floating planes, and 80+" aerobatic planes. I've even included an opinion from an owner of an 80" glow powered plane, the Midwest Extra 300s powered by a Moki 2.1.
First, here are some of the differences of each type of power:
|$2/gal. in the US
|$7-18/gal, depending on nitro content
|about 1/2 that of glow fuel
|about twice that of gasoline
|Very little fuel residue
|Usually LOTS of oil, unless great pains are taken to divert the exhaust.
|No glow plugs, NI-Starter or starter motors
|No spark plugs or ignition batteries
|Plane, Tx, gas can
|PLUS, glow driver and LOADS of paper towels
|Engine weight, RTF
|Depends on power needs and engine. Ignition systems typically weigh about 8oz as a minimum.**
I'm not going to pretend that I'm not biased. I love gas engines! I still have a few glow engines, though, and I'm about to swap one of them (a YS 1.20NC) out for a little gasser, the RCS 1.40! Ever since my first experience with a gasser, I've truly appreciated them. I realized it when I put the plane back into the car, and remembered that I had hadn't cleaned the plane--and it didn't need it! Between that, the cheap gas (usually under $2/gallon!), the lack of a glow starter or electric engine starter, I'm hooked.
The important aspect about being pleased with a gas engine is matching the engine to your application. Don't expect to be pleased with the performance of a 1/4 scale aerobatic plane if you throw a 6lb engine on the front of it! Those planes are designed to be flown with 2lb engines. If the plane is light enough, the RCS 1.40 is a great choice--you'll get a similar RTF power to weight ratio that a typical 1.20 will give you. That performance will be very satisfying if your plane is in the 9lb range, but limited to the Basic sequence if you are up near 12 lbs or more. If you are going with a heavier 1/4 scale plane, you need to go with a Saito 1.80 or a ST 2300 (for good tuning solutions, click here!)
My second gas powered plane was a Joss Stick, with wing measurements of 67" and 877sq". I put a 25cc Homey on it that I had lightened considerably, even adding a CH electronic ignition system. The dry weight of the plane was 10.6lbs, and there was plenty of power on the engine--it would actually hover it at full throttle, with the 16x6 Zinger. Unfortunately, it needs an 8 pitch prop to fly fast enough to be lively enough. In addition, the plane was just so heavy that it was sluggish, and not very fun in general. I finally ended up putting the RCS 1.4 on it, which saved the plane almost a full pound--which brought the wing loading back down to a reasonable level. The wing for this ARC was heavy to start with, so the added weight of a heavy weedwacker engine didn't help.
If you are powering a 1.20 sized floating type plane that doesn't need out-of-sight vertical, like a Fly Baby or a PT-19, or even the trainer type planes like the giant Telemaster, the RCS 1.40 is another great option for light, clean power. Just about any plane that you'd put a 1.20 on will fly well with the RCS 1.40. (Read our review of it here.)
In addition to the RCS, the light and floating planes can also be powered by a good light weedwacker conversion. (Read about them here.) The smaller 25cc range of weedies typically have weaker 1.20 performance, and usually weigh in the 3.5-5lb range, depending on the model. The 30cc engines often weigh the same, or even less than a 25--my 30cc Homey is a couple ounces lighter than my 25cc Homey. The 30's are also often considerably stronger. They can put out power that is more typical of a 1.30 - 1.40 engine. The 30's can swing a little bit larger prop, and will give you better performance. None of the small weedies, though, are really going to give you the absolute best performance in an aerobatic plane.
When you move up to the 80" aerobatic planes, the solution is simple, with only one answer: go gas! The most popular small gas engine for aerobatic planes is currently the BME 2.7 (44cc). The engine itself is lighter than a Moki 2.1, and pretty much matches the Moki for power. With the significantly reduced fuel consumption, your smaller fuel tank more than makes up for the weight of the ignition system. The ZDZ 2.4 (40cc) is reported to be slightly lighter, with the same power, but even smoother running. The Brison 2.4 is a good engine that's a little smoother than the BME, but it weighs about 1/4lb more, and you have to go down in prop size by a full inch to get the same RPM. I sure noticed the difference when I upgraded my MW Extra from the 2.4 to the 2.7.
In conclusion, gassers are great, clean power plants. They make your plane more enjoyable if you match the engine well. Once you fly with gas, you won't want to go back. rcfaq
Here's what Todd had to say recently on the IMAC mailing list:
Another little gas engine vs big glow engine debate...
Having been both routes I can safely say that they both will fly that airplane. As with most things in life, there are pros and cons to both. You will definitely pay more in the long run for glow fuel if you fly a lot. My Midwest Extra 300XS/Moki 2.1 combo burns a little over 2 oz/min at close to full throttle. I use the recommended 24 oz tank and can easily fly over 15 minutes at normal throttle settings. The take-off weight is only a little higher but the engine/ muffler/ mount is a little lighter than the BME/ muffler/ mount/ ignition/ battery. Also, soon into the flight the weight becomes a non-issue, only at takeoff and its really not much more. I had to add a Cline fuel pump which is a little bit of a hassle and you wont have to do that with the BME. The rpm's on a 20 x 10 Menz standard are the same. The BME's I have seen certainly shake a little more than the Moki if vibration would be a consideration. There is no more hassle to running the Moki once its broke in than running a gas engine...Prime it, glow clip on, flip spinner backwards and stand back. To say that gas engines don't have hassles just isn't true...just read this list for a while (e.g. ignition, reeds, etc. etc.). [note: the BME 2.7 doesn't have reeds.] The Moki will leave a big, gooey mess which the BME wont (I am getting tired of that :-) ). When all was said and done I saved a little over $150 by going the Moki route but I have already spent that on fuel (Sig FAI at $10/gallon). IF I did it over I think I would consider a little gas engine (BME 44 or ZDZ 40) because I fly a lot and it will save you $$ in the long run. This size plane is the break point on gas v glow, any bigger and gas wins hands down IMHO. Oh well, enough rambling! Todd
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Revised: April 18, 2006 .