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Petrol Engine for a Toot Sweet

Equivalent to a 0.35 to 0.40 glow 2 stroke

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Robin Stevens14/09/2019 11:30:51
22 forum posts
16 photos

I am currently building a Toot Sweet (Peter Miller, RCM&E September 2002) and I'm thinking of putting a Petrol engine in the nose instead of the recommended glow.


This will be my first venture into Petrol, the relative cleanness and the cost and availability of fuel is attractive but I don't know what the best option for a plane of this size would be. I will admit that my knowledge on this type of engine is low, that's why I'm posting the thread.

The plan suggests a 0.35 to 0.40 glow 2-stroke, or a 0.40 - 0.48 4-stroke. Does petrol suffer a performance penalty compared to glow or are they broadly equivalent, requiring a larger engine? Are petrol engines in this size available or should I just put a 9cc in and have almost unlimited performance?

Currently the airframe is half built and is a winter project lined up. I would like to finish it for next year to give me something aerobatic to work with and flesh out the variety in my hangar.

Peter Miller14/09/2019 11:58:53
10947 forum posts
1272 photos
10 articles

I beieve that the smallest commecial petrol engines are around .60 which is rather big for Toot Sweet,

However Just Engines can supply ingniytion systems to convert any engine to petrol. The job is not hard and might be a good option although you do have to fit about 4 ounces of extra equipment but that would apply to any ignition engine.

Robin Stevens14/09/2019 13:00:19
22 forum posts
16 photos

Ok, thanks for the tip, I wasn't aware it was possible to do an engine conversion like that. I have an SC 0.40 two-stroke that was originally intended for the toot sweet that would be useful if I can convert.

J D 814/09/2019 13:57:02
1443 forum posts
84 photos

Converting small glow to petrol is never that simple, more so if you expect it to throttle well.

Robin Stevens14/09/2019 16:09:40
22 forum posts
16 photos

I might be best to just stick with glow then, throttle response will be critical on an aerobatic model like the Toot Sweet.

I'll think about it again when I'm closer to finishing the model. I don't expect there to be any massive improvements in the small engine offerings but it could happen.

Peter Miller14/09/2019 18:37:52
10947 forum posts
1272 photos
10 articles

I would definitely go with the .40 two stroke myself.

I always work on the KISS principle and also the old saying "What isn't there can't go wrong"

Levanter14/09/2019 18:50:03
882 forum posts
437 photos

I built a Toot Sweet a couple of years ago.


Here it is with an OS 48 FS Surpass along with its little sister Yuppy Love. Fits in beautifully.


Another view.

Has not been flown yet blush


Robin Stevens14/09/2019 19:26:37
22 forum posts
16 photos

Nice colour scheme, looking good liking the eyes on the side rather than a cockpit. Looks so fish-like it could be Guppy Love

I take your point on KISS, was worth asking though just in case.

Martin Harris15/09/2019 12:54:45
9262 forum posts
245 photos

I believe the main problems with running small engines on petrol revolve around carburation and cooling.

Glow carbs are extremely simple devices which work acceptably when metering the relatively large volumes of fuel used relative to petrol. As the metering involves tapered needles, you will probably find that the adjustment minimum of one click on the knurled body is too coarse to achieve an accurate mixture setting. Walbro type carbs work well in larger sized engines but aren't really suitable for anything smaller than a .60 - and maybe .90s upwards are better suited and getting something suitable for an engine conversion may involve a large amount of luck as there is so much variety and lack of info from the makers.

Petrol engines also need more cooling as the fuel burns hotter and as the finning on a glow engine is designed to maintain the correct temperature range for methanol fuel, will be far less tolerant of any inadequacies in cooling air flow. I also have an inkling that vapour locking could contribute to problems due to the higher temperatures and higher vapour pressure of petrol vs methanol.


Edited By Martin Harris on 15/09/2019 12:55:07

Piers Bowlan15/09/2019 19:33:10
2118 forum posts
53 photos

Robin, I think if Jon (Mr Laser engines) was contributing to this thread he would advise you against trying to convert a small glow engine to petrol for all the reasons Martin outlined above, plus a few more no doubt. Probably any quality 4st engine between 40 and 60 size will be much less bother, lighter and QUIETER than a small petrol two stroke.

If it is cleanness and less cost you want why not go electric?devil

Edited By Piers Bowlan on 15/09/2019 19:34:08

Tim Flyer15/09/2019 20:45:17
1271 forum posts
234 photos

Martin explains it very well I think. Methanol is a wonderful fuel with a high latent heat of evaporation that helps draw heat from the engine. It also has a very high octane and resists pre ignition much better than petrol and allows us to use higher compression ratios and high rpm . It does require a much richer mix than petrol to burn but that is still an advantage as the fatter mixture extracts more heat . Petrol has a much higher heat or energy value than methanol ( about 10 times as much ) but it requires much more oxygen to burn so needs a far leaner mix . The difference between methanol and petrol mix, is that the petrol mixture requires around twice as much oxygen for a given amount of fuel. For smaller IC engines is very hard to beat glow for simplicity easy handing and performance.

Edited By Tim Flyer on 15/09/2019 20:59:34

Edited By Tim Flyer on 15/09/2019 21:12:19

Paul Marsh15/09/2019 21:59:26
3959 forum posts
1189 photos

There is a NGH 09 engine... Surprised no-one mentioned that.



Edited By Paul Marsh on 15/09/2019 22:00:51

Martin Harris15/09/2019 23:59:35
9262 forum posts
245 photos

I thought the OP did!

"or should I just put a 9cc in and have almost unlimited performance?"

However, the thread has moved on to discussing conversions.

Edited By Martin Harris on 16/09/2019 00:06:08

cymaz16/09/2019 06:17:14
9194 forum posts
1186 photos

I would put a glow in for that size. If you have a noise sensitive site getting a decent muffler on it would add a lot of weight.

Four stroke glow would be my choice but if you’ve got your 2 t already bolt that in.

Edited By cymaz on 16/09/2019 06:18:54

barry saint16/09/2019 09:03:00
72 forum posts
20 photos

Hi Have been flying a Toots sweet bipe for several years with a OS48 surpass,perfect combination

will do rolling circles all day long & continuous vertical rolls,great little plane,

Robin Stevens16/09/2019 21:32:23
22 forum posts
16 photos

Thanks for the recommendations I think I'm going to go with the SC 0.40 two stroke glow that I have from another aircraft that I'm retiring. Looking forward to having the toot sweet finished, everything I've heard about it makes me think it'll be a fun flyer.

My club isn't fussy about noise, we're fortunate in being in the middle of nowhere. A trusty glow 2-stroke will likely give me all the power I could need and be relatively practical.

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