Nitro viz Petrol

[Andy J]

Currently have a SC 120 4 stroke in an Apache Chipmunk which needs just a shade more grunt as find I am flying on 3/4 to full throttle most of the time.

 

Am I correct in assuming I will see better performance from say a 20cc 2 stroke petrol engine or should I be considering a 150 4 stroke Nitro.  A further consideration is the desire for the engine upgrade to be fully enclosed in the cowl as currently the 120 is side mounted with the head protruding from the cowl which completely spoils the appearance of the airframe.

[Ron Gray]

The 2 stroke gasser will give you the power but the noise!!!. A 4 stroke has got to be the way forward. Having said that, what’s wrong with flying at ¾ to full throttle if, at those settings, it’s flying OK (scale)?

[john stones 1 - Moderator]

Don't think there would be much between a 20cc petrol and a 120fs personally.

[Andy J]

Find the aerobatic performance very restricted Ron and it just seems wrong to have to fly with the engine flat out just to keep it in the air.  Does fly very scale like with a nice steady and slow climb out so it does look the part if only the cylinder head did not stick out like a sore thumb.

As for noise the SC120 is far from quiet at full chat but dont know how it would compare to a 2 stroke.

[Jon H]

a dle 20 matches a laser 150 and saito 150 almost exactly on a 16x8 apc. However, the two 4 strokes have far nicer throttling and sound. 

 

One thing you might want to investigate before spending the big bucks is some new propellers. The right prop can transform the performance of a model and they are very cheap vs a new engine. Also, is the 120 giving its all? is something wrong with it?

 

So i would ask what prop you are running now in terms of size, brand, and the revs you see at full chat. Apache Chippys are 80 inch and 12-14lbs? a 120 should walk it if you are after scale type performance. 

[Martin Harris - Moderator]

It’s not just the volume of the noise but the quality of it. Especially if the 2 stroke is wearing a typical manufacturer supplied one…

 

Tinny ring ding a ding doesn’t cut it for me I’m afraid.

 

Edit: Jon beat me to it by a whisker!

Edited December 3, 2022 by Martin Harris - Moderator

[Engine Doctor]

Does your SC have good compression? If comp is low then performance will be down as well. Lots of ASP. SC and Magnum engines around with faulty heads causing low compression. Re-seating valves doesn't work as gas escapes past the bronze valve seating and cyl head. 

[Frank Skilbeck]

If you are going to change to petrol then a 26cc may be a better option, a bit more power for not much more weight or cost. As others have said noise with a petrol 2 stroke may be an issue, especially with the standard exhaust. Put a decent canister silencer on them and they sound a lot better, not as good as a four stroke, but definitely quieter and better. if you do fully enclose it then make sure you have some good airflow over the engine, the petrol engines do run hotter than the glow engines.

[David Ovenden]

I don't see why a 120FS wouldn't fly this model nicely...... if the engine is working as it should, with the right prop. My 80" Seagul chipmunk  flys great on a Saito 125 and my 85" Great Planes PT19 is a joy with its Saito 115. Neither are underpowered. I would check the timing, re set the carb, try changing the plug and experiment with other props (one change at a time to check the effects) before buying a new engine. There's a video somewhere on YouTube showing the big 85" BlackHorse chipmunk flying effortlessly on an ASP 120FS.

[Jason Channing]

Irrelevant of what some may say If you increase the Nitro , you will get more power to turn a bigger prop or more revs on the prop you have, Use a decent prop such as Falcon, Not APC and have your mixtures set correctly. The Sc will cope with 20% nitro fuel quite happily. and for info I run my lasers on low oil and low and 5% nitro .

[Jason Channing]

Should add, rather than edit, not all engines will like the extra nitro but SC will be fine.

[Jon H]

I wouldnt recommend 20% nitro. If you really need more power, get a bigger engine. The cost of 20% nitro fuel is just too high and the increase in fuel consumption will be significant. 

 

im with David on this one as the 120 should be plenty for the chippy. Could it be the curse of master airscrew causing all the problems? 

[Andy J]

2 hours ago, Jon - Laser Engines said:

I wouldnt recommend 20% nitro. If you really need more power, get a bigger engine. The cost of 20% nitro fuel is just too high and the increase in fuel consumption will be significant. 

 

im with David on this one as the 120 should be plenty for the chippy. Could it be the curse of master airscrew causing all the problems? 

Well you may have identified the problem! Looking back at my eBay purchases think the prop is a Master Aircrew K series 16x6.  Will double check when next in the workshop but can't think I would have purchased the prop for any other model.

[Andy J]

Should have also stated that currently running the engine on Prosynth 10%. Aware some are not a big fan of this brand name but I find it OK having used it for RCV's,  OS and an old Laser for the last 6 months. Service from Weston's is also second to none with delivery on the last two ocassions being within 24hrs of ordering.

[Jason Channing]

In reality the increase in fuel consumption is not that noticeable to the point of being insignificant, if I increase from 20 to 30% the difference in power is very noticeable, but again the fuel consumption is not dramatic, 

[Paul De Tourtoulon]

Master airscrew props are pretty rubbish, a good APC and your Prosynth  10% are perfect.

[Frank Skilbeck]

Looking on the internet a 15 x 8 prop seems to be a favourite for an ASP/SC120 and it should turn it at around 9,500rpm, according to a prop thrust calculator this should be just over 7kg static thrust, so as others have said maybe a change of prop is all that is required.

 

I remember on my mates 1/4 scale Pup on an OS120FS he changed the prop to one that look scale, it went from flying well to being barely able to get off the ground.

Edited December 4, 2022 by Frank Skilbeck

[Jon H]

50 minutes ago, Jason Channing said:

In reality the increase in fuel consumption is not that noticeable to the point of being insignificant, if I increase from 20 to 30% the difference in power is very noticeable, but again the fuel consumption is not dramatic, 

 

The difference in fuel consumption between 5% and 20% is massive though. You can be looking at upto 50% greater consumption for nowhere near 50% more power. you could run a bigger engine on 5% and use less fuel than the smaller one on 20%, all while getting more power. 

 

6 hours ago, Andy Joyce said:

Should have also stated that currently running the engine on Prosynth 10%. Aware some are not a big fan of this brand name but I find it OK having used it for RCV's,  OS and an old Laser for the last 6 months. Service from Weston's is also second to none with delivery on the last two ocassions being within 24hrs of ordering.

Master props are a bit naff and i would swap it for something else. Try 15x8 and 16x6 but from another brand. I would also recommend trying some other fuel as i tested some prosynth in an ASP and it didnt give its all running far better on other fuels. I dont just hate on prosynth for no reason. I deal with countless broken engines and its always the same fuel. I have also tested it on a variety of engines and found that many, mostly 4 stroke, simply dont run well on it. So my issue is with the quality and performance of the fuel. The quality of the service is not really that important if the product is no good.  

[Jason Channing]

Sorry but the fuel consumption increase is no where near 50%,(why not call it 80% and people will believe you) marginally higher yes but nothing significant , Based on practical experience on a vast array of models on a daily basis. The reality is not quite what you describe. The fuel is more expensive but that is life and suits me fine.

 

 

 

 

Edited December 4, 2022 by Jason Channing
added data regarding fuel

[Jon H]

1 hour ago, Jason Channing said:

Sorry but the fuel consumption increase is no where near 50%

 

 

 

 

 

It was when i tested it. 

 

[Martin McIntosh]

For my 2P`s worth, I scaled up my Chippy to 1:5 (81"), it has a YS 110 on an APC 16x8 and goes like the clappers but the 20% nitro, besides being expensive, plays havoc with the paint. Got hold of a really good OS 120 fs at a show but unfortunately it is much longer than the YS so cannot be retro fitted. Swapped the YS 110 in my 2m Dalotel for this and the performance is the same on the same prop.

Your problem is undoubtedly the lousy, noisy MA `prop`. Petrol would just give you a lot of extra noise plus weight and complexity for no increase in power.

[Paul De Tourtoulon]

3 hours ago, Jon - Laser Engines said:

I dont just hate on prosynth for no reason. I deal with countless broken engines and its always the same fuel. I have also tested it on a variety of engines and found that many, mostly 4 stroke, simply dont run well on it. So my issue is with the quality and performance of the fuel.

That's because you don't put 1% or 2% of castor in it,,,🤣

 

 

Sorry back to the table to finish off my Scallop Madras curry,,,,

[Jon H]

2 hours ago, Paul De Tourtoulon said:

That's because you don't put 1% or 2% of castor in it,,,🤣

 

 

Sorry back to the table to finish off my Scallop Madras curry,,,,

 

You might as well pour treacle in the fuel for all the good castor does 

[Paul De Tourtoulon]

😆

2 minutes ago, Jon - Laser Engines said:

 

You might as well pour treacle in the fuel for all the good castor does 

Send me some and honest I will try it,,,

Edited December 4, 2022 by Paul De Tourtoulon
i knew that you couldn't resiste jon,,,

[Andy J]

Thanks all. Had not heard before that MA are far from the best so an APC 16x6 is now on order. Have a wooden 17 x 6 so will give that a go next time we get a sunny day here in Bedfordshire but its too darn damp and cold for me at the moment. May have an odd 15 inch prop which I think may have originally came with the airframe when purchased some years back.