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        Discussion Size at which gas becomes practical

#1 cloud_9 Feb 09, 2013 04:34 AM

Size at which gas becomes practical
 
I have flown electric, a little, and want to move to big planes, and planes that sound good (the nitro club trainer I'm training on is more fun than electrics). I plan on slow sport flying, no racing, 3D, or pattern etc.

After some reading, seems like bigger + IC = gas, but only for big planes where the extra weight is not a problem. However, I am really fuzzy on HOW big.

How big a sport plane do you need to build so that gas is a better choice than nitro? Would a 110" wingspan Cub, SIG Four Star (correction: sorry, I found out the 125 FS has 81" wingspan), or SIG Rascal, be suitable for gas? Or are they still in the "nitro is better" size?

Thanks.

#2 earlwb Feb 09, 2013 06:32 AM

The minimum size has been clouded somewhat at present. We now have working 9cc and 10cc gasoline spark ignition engines that work with the .40 to .50 glow engine sized airplanes. Before then it was 15cc and 17cc gas engines that work in .60 size glow engine powered airplanes.

But it still depends on your preferences though, glow engines are still good to use, as are gas engines and electrics too.

#3 gene6029 Feb 09, 2013 07:13 AM

I think alot depends on how much you fly. Gasoline is close to $4.00 (plus oil)a gallon around here right now & glow fuel is approx $15 a gallon. So if you fly 10 gallons a year, you may want to go the gas rout. Alot of the guys are flying that new evolution 10cc gas motor in smaller models & it has me thinking of trying one myself. They are easy starting & so far from what i've seen problem free. I like the sound also. There is a good selection today of gas motors for just about every type & size model out there. We have guys flying 50cc size airplanes on electric too at our field. The sound of a gas motor still does it for me though...Gene

#4 cloud_9 Feb 09, 2013 08:39 AM

Quote:

Originally Posted by gene6029 (Post 24080687)
I think alot depends on how much you fly. Gasoline is close to $4.00 (plus oil)a gallon around here right now & glow fuel is approx $15 a gallon. So if you fly 10 gallons a year, you may want to go the gas rout. Alot of the guys are flying that new evolution 10cc gas motor in smaller models & it has me thinking of trying one myself. They are easy starting & so far from what i've seen problem free. I like the sound also. There is a good selection today of gas motors for just about every type & size model out there. We have guys flying 50cc size airplanes on electric too at our field. The sound of a gas motor still does it for me though...Gene

Thanks guys. Gene, my thinking from the reading I've done is that you have an extra battery with gas that adds weight. Also gas has less power per displacement, or per engine weight, so you have to put in a heavier motor for the same power.

Thus, the extra weight is going to be a problem unless you are into a big plane. You examples of small gas motors makes me thing my impressions may not be right?

Jim

#5 grosbeak Feb 09, 2013 08:46 AM

Quote:

Originally Posted by cloud_9 (Post 24081171)
Thanks guys. Gene, my thinking from the reading I've done is that you have an extra battery with gas that adds weight. Also gas has less power per displacement, or per engine weight, so you have to put in a heavier motor for the same power.

Thus, the extra weight is going to be a problem unless you are into a big plane. You examples of small gas motors makes me thing my impressions may not be right?

Jim

If I understand correctly, a battery elimination circuit (BEC) will allow you to power the receiver and ignition off a single battery.

#6 Kyler1 Feb 09, 2013 09:05 AM

So to answer your question. A Sig Rascal 110 (or similar) would be fantastic with a gasser in it.

#7 gene6029 Feb 09, 2013 09:14 AM

I just looked up the total weight of my OS 55AX & its 18.52oz.( with muffler) I looked up the total weight of the Evolution 10cc gas motor & its listed as 22oz. ( muffler & ignition ) included. I guess the weight of a 2 cell battery for the ignition should be factored in. So its seems you are correct with the extra weight. On the few models i have seen flying so far, ( models in the 56"-60" ws ) it doesnt seem to have hurt them much. I build & fly Vintage models & these small gas motors look attractive to me because it allows me more flxability in being able to finish them with out haveing to fuel proof them. Most of the radio gear back then was heavier too, so the extra few ounces of weight for me is negligable since our new radio gear weighs less. I dont own one yet, but im eyeing up one of those 10cc motors for my next vintage model....Gene

#8 jetmech05 Feb 09, 2013 09:57 AM

I have been flying gas now for about 4 years...bigger aiaplanes true...but I just don't see me ever going back to glow unless it's to teach

#9 MikeCr Feb 09, 2013 10:53 AM

Quote:

Originally Posted by grosbeak (Post 24081226)
If I understand correctly, a battery elimination circuit (BEC) will allow you to power the receiver and ignition off a single battery.

It's generally not recommended because of possible interference problems.


Mike

#10 cloud_9 Feb 09, 2013 12:48 PM

Quote:

Originally Posted by gene6029 (Post 24081386)
I just looked up the total weight of my OS 55AX & its 18.52oz.( with muffler) I looked up the total weight of the Evolution 10cc gas motor & its listed as 22oz. ( muffler & ignition ) included. I guess the weight of a 2 cell battery for the ignition should be factored in. So its seems you are correct with the extra weight. On the few models i have seen flying so far, ( models in the 56"-60" ws ) it doesnt seem to have hurt them much. I build & fly Vintage models & these small gas motors look attractive to me because it allows me more flxability in being able to finish them with out haveing to fuel proof them. Most of the radio gear back then was heavier too, so the extra few ounces of weight for me is negligable since our new radio gear weighs less. I dont own one yet, but im eyeing up one of those 10cc motors for my next vintage model....Gene

Thanks Gene. Well, my motivation is cost of fuel, but even more, flying time. Apparently the nitro motors go through a lot more fuel than the gas ones. So that is a weight factor in the other direction. I need to hear them myself but reading suggests the gas motors sound more like gas motors :)

Jim

#11 cloud_9 Feb 09, 2013 12:49 PM

Quote:

Originally Posted by jetmech05 (Post 24081703)
I have been flying gas now for about 4 years...bigger aiaplanes true...but I just don't see me ever going back to glow unless it's to teach

Why?

#12 cloud_9 Feb 09, 2013 12:49 PM

Quote:

Originally Posted by MikeCr (Post 24082122)
It's generally not recommended because of possible interference problems.


Mike

Mike, do you know how much extra weight comes with the extra battery and ignition system for the gassers? Does that include a coil?

Thanks...

#13 gene6029 Feb 09, 2013 01:41 PM

Jim, a 2 cell Li-ion pack that i use for all my ignitions on all my gassers weighs an additional 3 oz. That said, The 10cc gas motor i referred to in my post at 22oz should include the extra 3 oz for the ignition battery. Thats the motor, muffler,ignition, and battery. You should also put the ignition on its own switch so add that in. Roughly 25 oz vs 18.5 oz for the 55AX glow motor.....Gene

#14 MikeCr Feb 09, 2013 02:04 PM

Quote:

Originally Posted by cloud_9 (Post 24083113)
Why?

I don't want to answer for jet but for me it's simple. Glow sucks! Seriously though for me, glow had it's time and place and now it's done. I am now back to exclusively electric, having sold my 1/3 scale Spacewalker last fall. Liked the airplane and the gas engine on it but for right now it's just too big of an airplane to haul around and store. If I did go back to a really big airplane it would be gas. I'm building a Sig Astro Hog, it will be electric but I was seriously considering the new Evolution 60 gasser.

To answer the question of ignition battery, it doesn't have to add much weight. On my Spacewalker I was using a 4 cell NiCd 1400mAH pack for the ignition which would last all afternoon. You could get by with a smaller pack and/or different chemistry and save even more weight.

As far as fuel cost between gas and glow goes, there's more to it than the cost of the fuel. A gas engine does use much less fuel per flight than a glow engine. My Spacewalker with a 50cc gas engine would fly for half an hour on 20oz. of fuel. A glow engine of the same power would have used twice as much fuel for half the flight time.


Mike

#15 jetmech05 Feb 09, 2013 08:07 PM

Gas is cheaper, cleaner, and to me more power...when's the last time you have seen a glow stand on its tail and climb until power is pulled off.


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