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John Tee20/09/2020 19:19:04
901 forum posts
73 photos

Just wondering. As I haven't spent too much on modelling this year, I have been looking at some bigger models. Am I right in saying ( think I read somewhere) that petrol engines are lower powered than our usual two strokes. I have several 20 and 25 cc Super Tigre 2 strokes and don't really want to spend out on a petrol engine and the accessories if I can help it. It may never come to pass but I like the thought of a bigger model.

John

Martin Harris20/09/2020 19:26:14
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9552 forum posts
258 photos

I'd agree with that. As a rule of thumb, I'd say that a 2 stroke petrol is roughly the equivalent of a 4 stroke glow.

John Tee20/09/2020 20:48:26
901 forum posts
73 photos

Thank you Martin. So if a 30 cc petrol is required I could use my Super Tigre 2000.

john

Jesus Cardin20/09/2020 21:02:36
102 forum posts
22 photos

It is most like Martin says, but petrol engines have evolved in recent times -as well as glow four stroke ones!- and if a gas 30cc is requird for the model, I should rather go with your Super Tigre 25cc.

John Tee20/09/2020 21:18:55
901 forum posts
73 photos

Thanks Jesus

John

Frank Skilbeck20/09/2020 22:04:10
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4845 forum posts
107 photos

You could check online rpm reports for the different engines and then decide, e.g. a search using a DLE 30 suggests 7200 to 7300 rpm on a 19 x 8 prop, around 2.7 HP, a ST2000 gives around 9,400 rpm on a 16 x 8, around 2.9 HP.

Friend had a Supetigre 25cc in a Wilga designed around a 30cc petrol, don't think we ever used full throttle, was off the ground on 60% throttle or so.

John Tee20/09/2020 23:22:26
901 forum posts
73 photos

Thanks for your input Frank

John

Robin Colbourne20/09/2020 23:35:22
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697 forum posts
17 photos

Many of the early generation petrol engines were derived from strimmer engines, so they were side port induction which limited power output. Others used chainsaw parts, e.g. Quadra, which were still sideport induction but often had reed valves to speed up port opening and closing.

Modern two stroke petrol engines, purpose-made for model aircraft, use shaft or rear drum/disc induction which offer opportunities for greater control of induction timing.

Methanol gives off less power than petrol by weight, but an engine can burn more of it, its higher octane rating allows higher compression ratios and it runs cooler, hence its popularity in some forms of motorsport. Why race car drivers love methanol

Edited By Robin Colbourne on 20/09/2020 23:35:45

John Tee21/09/2020 16:01:30
901 forum posts
73 photos

Thanks everyone, given me some things to think about. I have collected the Super Tigres over the years and never fired them up all used motors

John

Edited By John Tee on 21/09/2020 16:03:22

mal brewer21/09/2020 18:19:45
334 forum posts
1 photos

Hi John, don't know if you have been informed, those big Supre Tigers don't require nitro in the fuel, and only 10% oil. I always used to buy 20% oil straight fuel, and dilute it with an equal quantity of neat methanol. Nowadays, of course, you can buy 10% oil fuel.............Mal

Frank Skilbeck21/09/2020 18:42:50
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4845 forum posts
107 photos
Posted by Robin Colbourne on 20/09/2020 23:35:22:

Modern two stroke petrol engines, purpose-made for model aircraft, use shaft or rear drum/disc induction which offer opportunities for greater control of induction timing.

Edited By Robin Colbourne on 20/09/2020 23:35:45

Most of the rear carb models from the likes of DLE etc use reed valves, it's only the engines with a front carb that use shaft induction. The additional power mainly comes from them being tuned for model aircraft use (that and not worrying about noisewink)

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