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Gas or Glow...Does Size Matter?

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Richard. W.12/02/2019 15:46:25
71 forum posts

Checking out various engines on the web, I notice the size of gas/petrol engines getting smaller.

I like the idea of gas for their prop swinging ability, economy of fuel and because they're less fussy of tank position but I can't help thinking that with something like a 10cc gas engine, once you factor in the extra weight for the battery pack, ignition and kill switch, the choice of airframe (scale subjects) would be limited.

Surely for engines of this size which aren't heavy drinkers, a decent 4 stroke would be more viable?..... I can certainly see the benefit from 20cc and up but below that size I'm unsure.

Several members at my club run gas motors but all are around the 35 to 50cc mark. Only one of them is a scale fan like myself and he's never thought about the smaller engines.

Perhaps in something vintage, like "Black Magic" or similar, they'd look the part and do the job for some relaxed summer flying?

Any thoughts? Experience?......I might risk a punt on the RCGF 10 and have a good look through my plans.

Bob Cotsford12/02/2019 16:05:54
8583 forum posts
477 photos

I ran an Evolution 10cc petrol motor for a few years. Power wise, it's the equivalent of a good 46 two stroke or 61 four stroke able to turn up to 13" props, just as well as they are pigs to silence effectively. As you point out you also have the bulk and weight of the ignition battery to carry. You also have an extra fuel container to lug around as they can't be run on the same fuel as larger petrols.

I didn't buy a second one, but I did buy 52 two strokes and 61 four strokes. I think that says it all for me!

ps - it would be massive overkill for a Black Magic which only needs a 30 size glow motor, I flew an 84" Eros vintage model on a 48 four stroke and that spent most of it's time on less than half throttle.

Edited By Bob Cotsford on 12/02/2019 16:09:21

Richard. W.12/02/2019 16:16:05
71 forum posts

Thanks for your input, Bob. thumbs up

The fuel mix was another point and I'm glad you reminded me.

Brian Dorricott 112/02/2019 16:29:33
102 forum posts
2 photos

Richard. A. Try the OS G5 plug and dispense with the battery/ ign pack and spark plug. Got one on my NGH 9cc runs well on the ground but not maidened yet . Replace spark plug with OS petrol G5 glow and start like a like glow and I didn't even have to tune the needles ! Its basically what OS have done for their 10cc petrol 2 stroke can't remember model number !

Brian Dorricott 112/02/2019 16:37:09
102 forum posts
2 photos

Where did that A come from ? Richard looked it up OS GGT10 uses the G5 glow plug , good enough for OS good enough for me .

Bruce Collinson12/02/2019 21:01:58
537 forum posts

Noisy. Observation suggests to me that in the larger sized petrol 2 strokes, there’s a huge after market in silencers and their typical airframes will accommodate a wide range of silencers. Some of them are effective. A smaller frame, especially scale, may be harder to configure with an effective silencer.

There’s a peculiar bark at an annoying, long range frequency with many/most petrol engines so it’s a potential problem depending on your site rules. I gave up with a DLE 20 which was pretty well ideal in every other respect and chopped it in for a Saito.

On the weight point, the Toni Clarke Zenoah setup runs on a 1s LiPo which weighs very little. I’ve no idea about your target weights but I doubt whether the ignition system would be a weight determinant, especially when offset against the much smaller tank you can use. As for an extra 5 L fuel can, I found it the least of the issues in flying glow, leccy and petrol on the same day. Oh yes, there’s the smell too unless you shell out for Aspen.

Hope this helps. Keep us posted.


Richard. W.12/02/2019 23:46:58
71 forum posts

Some great feedback coming in, guys. Thank you all. smile

I'm lucky in that my club patch is fairly isolated and doesn't have as many restrictions as some. Obviously safety regulations are enforced and you couldn't run an unsilenced motor but we don't have to actually measure noise levels... That said, I have been told about the DLE 20 being loud. The suggested fix is to plug one of the outlets and restrict the other. Yes, there's a drop in power but for my flying needs and subjects, that wouldn't be an issue.

Good point about offsetting the battery weight with a smaller tank, Bruce. Another thing to consider. face 22 ......The weight issue was just something I thought about for the smallest petrol motors. For 20cc and above, I wouldn't be concerned and especially with some of the really short nosed, biplane types the added weight up front is a bonus.

Bob Cotsford13/02/2019 09:27:43
8583 forum posts
477 photos

RE the ignition unit weight, I had my Evolution in a Frog Mustfire and for that model the ignition just meant that I didn't need lead in the nose to balance the model.

Tim Flyer13/02/2019 11:52:54
1290 forum posts
236 photos

Stock DLE 20s sound awful. 4stroke motors are so much better noise wise . I hate flying with some pilots who use poorly silenced 2s petrol. It’s very hard to hear my own plane. So many are just like airborne chainsaws. Other than cheapness I can’t se any real advantage in small 2s petrol .

Nigel R13/02/2019 13:19:55
3916 forum posts
678 photos

They don't seem to be so very cheap by the time a decent silencer is costed up...

I'm not parting with my 60 sized glows just yet. They are well developed engines, have decent silencers, and if tank position is a problem several of them are pumped. The 4 strokes stay, too!

I hear there are some competitively priced and UK made 4 strokes kicking around these days...

Bruce Collinson13/02/2019 13:28:49
537 forum posts

seems to be a consensus emerging. Richard W, what you allude to, bung/constrict the stock exhaust outlets, got the DLE 20 below 82dB but only by a whisker, cost 900 rpm and was unacceptable. Bit like battery-only cars, far too heavily compromised to be practical, yet.


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