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Small PAW advice

How do the current PAW 80s perform.

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Peter Miller27/03/2017 11:16:59
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A friend in Australia has asked me for some advice.on using a PAW 80 for some low key flying. He is considering either an MP jet or a PAW 80.

As it is some 25 years since I used a PAW 80 I tought I would pick the brains of those with more current experience

Jon - Laser Engines27/03/2017 11:27:15
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I have a PAW 149 which is a great little engine. Alas its been laid up for some years (almost 15) without a home but i get it out periodically and give it a run to prevent the castor setting solid. It always fires up with ease and i cant really fault it. I do run it on less oil than recommended (20% castor) and its been fine on this diet its entire life. It wasnt deliberate, as a youth i asked for some diesel fuel and was given a bottle with 20% castor not the recommended 30% and didnt notice until years later after the engine had consumed several litres. But it has always run well on it and on the one occasion i did strip it to remove some gummed castor i couldnt see any wear on anything and there was still plenty of goop in the crankcase so i have stuck with it and cant really see it as an issue.

I am looking for an airframe for the engine as im eager to get it in the air again.

Peter Christy27/03/2017 11:44:04
1552 forum posts

I've got a PAW 80! Great little engine, but quite fuel sensitive, and those little 6x4 props have *really* sharp edges - even when sanded!

Mine is in a half-size Super 60 (30" span). There's some video of it in action at the PANDAs event last year, about 1'30" in:

Mine has a muffler fitted, and it flatly refuses to start on D-1000 (the "easy-start" diesel fuel!), but goes like a dingbat on D-3000 (the contest stuff!)! However, the general advice is that D-3000 doesn't have enough oil for plain bearing engines, so I've compromised on D-2000.
Its quite sensitive on the needle (as you'll see from the video) but once sorted, it pulls really well. I started off with it on a 7x4, which made it easier to start, but it pulls better on a 6x4.
I think they've re-named it to PAW .049 these days. What other changes have been made, I don't know.
Enjoy!
--
Pete
J D 827/03/2017 12:22:12
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I also have an 80,not in an aircraft at the moment but gets put on the test stand now and then just because.

Goes well on a 7x4 and D1000 but is open exhaust.

Peter Miller27/03/2017 12:23:28
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Is it really essentila to use castor oil. I don't remember that from my youth. (in the days when you walked into the chemist witha bottle ans asked for half a pint of ether) Try that today and see what happens!!!

GONZO27/03/2017 12:43:49
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AFAIK all commercially available model diesel fuel uses castor oil. The only cases that I can think of where normal mineral oil has been used is with the v/small special diesels and then it was SAE 40/50 motor oil. Don't know for sure but I would think that using synthetic(that's if it will mix with paraffin and ether) would be a short fast road to a replacement engine. A point you are probably aware of, the smaller the engine the lower the fuel usage. Therefore the lower the amount of oil going through the engine. But the wearing surfaces do not go down in proportion to the reduced displacement. It is therefor necessary to up the % of oil in the mix to ensure adequate lubrication in small displacement engines.

Jon - Laser Engines27/03/2017 13:32:04
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Posted by Peter Christy on 27/03/2017 11:44:04:

Mine has a muffler fitted, and it flatly refuses to start on D-1000 (the "easy-start" diesel fuel!), but goes like a dingbat on D-3000 (the contest stuff!)! However, the general advice is that D-3000 doesn't have enough oil for plain bearing engines, so I've compromised on D-2000.

D3000 is the same 20% castor content as my southern modelcraft fuel. If im honest i think the 30% castor argument is out of date as my Laser 4 stroke diesels run on 15% synthetic without any trouble. That said my PAW 60 (10cc) didnt seem impressed by that fuel, although in all fairness i didnt spend much time trying to sort it out and i didnt have the best prop either so i need to run it again and check it out.

Gonzo is quite right about commercial fuels containing only castor, but if you ask nicely im sure someone will mix you something else. Just dont tell the diehard diesel boys or you will likely be chastised and placed atop your burning model

Peter Miller27/03/2017 14:12:23
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I have just been having a talk to my engine guru Tom Crompton.

He tells me that synthetic is fine for small engines and as he builds really tiny diesels I guess that has b=to be OK.

Peter Christy27/03/2017 18:00:56
1552 forum posts

Jon: That's interesting that D-3000 is 20% castor. I was under the impression that it was less than that, but I've just looked at the MT website and you are quite right! (They didn't used to publish the formula "back in the day"!)

I would have thought 20% would be more than enough for any engine, but I'm not a real engine expert! I know how to set them up and maintain them, but the finer points of fuel formulation are outside my area of expertise!

I know my PAW 1.49s loved D-3000, and throttles superbly on it. Maybe I ought to switch the 80 to it after all! It certainly starts more easily and is less critical on the needle valve on it.....

--

Pete

Jon - Laser Engines27/03/2017 18:57:16
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I don't want to pull this too far off the OP but oil in fuel is something we at laser are looking into carefully. as many will already know we recommend 15% as a maximum with 10 being far better. I have been running on 5% oil on some of my engines for over a year now with no issues at all and my nitro car engine also runs on only 10% oil.

We believe that when glow engines first came about 20% castor oil was a safe bet for a number of reasons. Things like machining tolerance, material quality, and oil quality all play a part. over the years most of those things have improved such that they are no longer an issue and synthetic oil now outperforms castor in many respects. So we are looking at reducing our oil content as much as we can but this means a great deal of testing and we do need some margin of safety in case some bright spark tries mixing his own fuel and either gets his maths wrong, or uses very poor quality materials.

Model diesel engines go back even further than glow and in the early days the castor oil was all they had and the 30% quantity was in there in part to fill the gaps and make the thing seal up and run. Again quality improved but diesel development was more or less killed off by glow and its rare to find any 'modern' ABC style model diesels with I think the Irvine 20 being the only example. I'm sure someone will correct me if I'm wrong.

Our laser 4 stroke diesels just did not work on 20% oil as they just choked on it and dropping to 15% synth helped massively. My PAW 149 and 60 run brilliantly on the 20% SMC mix and I have also run my old DC, AM, and an old Frog on this fuel without issue.

In any case, as with many things in modelling oil ratios in fuel are one thing that is in the 'but we have done it this way for XXX years, why change it?' category and to be honest I think the reason we are where we are is simply because no one has gone back and checked out if we really need this much goo in out fuel. Petrol engines don't, and while the petrol has some lubrication properties in a two stroke it has none in a 4 stroke and certainly the difference does not explain why a glow engine 'needs' 20% oil and a petrol engine 2%.

Another misconception is that less oil means more wear and more oil means less that is not strictly true. If you have enough oil for satisfactory lubrication, and then you add more, you don't get more lubrication and less wear as lubrication was already just fine. But if you take away oil and have insufficient oil for lubrication it will seize solid in a matter of moments. All this nonsense about more oil protecting you if the engine overheats or is run lean is also wishful thinking.

In any case I will keep using 30% ether, 2% ipn (or 2EHN) and 20% castor in my 'classic' diesels as they run well on it and its easy to get. My Laser diesels will use the same mix but with 15% synth oil instead as MT mix it for me. I am sure I could run the classics on the synth fuel as well but the castor is part of the nostalgia I guess! On glow I will be moving more of my engines over to 5% oil as its really clean and lovely and I need to do more testing.

 

 

Edited By Jon Harper - Laser Engines on 27/03/2017 19:00:07

Peter Miller27/03/2017 19:33:33
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Actually Irvine did a .40 diesel too. I had both for reviewing in my Engine Bay days.

I remember lending the .40 to a friend. His throttle came adrift at abouthalf throttle early in tye flight one evening.

He nearly had to land in the darklaugh

Peter Christy27/03/2017 19:56:31
1552 forum posts

That's a very interesting post, Jon. For glow engines, I switched over to fully synthetic years ago, and have never had any issues. I've used Bekra heli fuel in all my engines (heli or not!) for many years without any issues. Ben Godfrey (who formulated it) was an old friend of mine, and had come up via racing motor bikes. There wasn't much he didn't know about two-strokes!

Interestingly, when Bekra came out at first, I believe it was only 15% oil. It certainly ran very cleanly, compared to what we had been using! IIRC, it only got upped to 18% because OS were threatening not to honour warranties on engines run on less than 18% oil!

As a matter of interest, what synthetic are you using in your diesel fuel? I ask, because I know that not all oils dissolve equally well in all fuels! Castrol used to do two different castor oils - one for petrol and one for methanol, and heaven help you if you picked the wrong one!

One of the worst things about diesels is the horrible oily residue left by the exhaust. It seems to get into everything, and the smell lingers for ever! Anything that is easier to clean off has got to be an improvement....!

As an aside, I recall many years ago, Mick Wilshere of Super-Tigre fame had a friend who worked for Shell. This "friend" recommended some new synthetic oil they were working on, which he reckoned would be ideal for model engines. It was! Mick mixed a few gallons of the stuff, and handed it out for people to try. No engine problems whatsoever, but the STENCH was unbelievable!

Even transporting a tightly sealed bottle of it in the car left a stink that lingered for weeks! And when it was spread through the atmosphere by a screaming two-stroke......

Well, I leave you to imagine why it never caught on.....!

disgust

--

Pete

J D 827/03/2017 20:58:24
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Was that cod liver oil then ?wink

Jon - Laser Engines27/03/2017 23:21:47
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Hi Pete

Bekra is good stuff but we have had issues with rusting when customers use bekra 16. That said its hard to blame the fuel entirely as there are many factors that can make it worse.

All of my engines are running on ML70 oil and this is working well. The diesels too run on this but the ether and paraffin still make a right old stink....its lovely! In any case, my understanding is that while some oils are soluble in either petrol or methanol, ether gobbles up almost everything so in model diesel fuel its not so hard to get oils to mix nicely.

Peter Christy28/03/2017 09:04:44
1552 forum posts

Cheers, Jon! Yes, fresh diesel smells wonderful! Its the exhaust residue - usually a black oily goo - which isn't so good!

I agree that high nitro fuels do tend to promote rust, and I'm always careful to run my engines on 16% bone dry at the end of a session. Its less of a problem if the engine is in regular use.

As another aside, I managed to persuade MT to make some Bekra straight - no nitro! They don't advertise it, but its perfect for Super-Tigres, and other engines that don't like nitro!

--

Pete

Doug Campbell28/03/2017 09:25:12
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Back to the original post your friend would be more than happy with a modern PAW 049. They are more powerful than the original 80 but handle just as easily. There is also the Redfin 0.5 to consider. The Tbr versions are cracking engines, modern technology in a vintage looking case.

To avoid gummed up engines the current trend is to run a tankful of "afterflight" fuel through the engine at the end of the day. This is a mineral oil based fuel, I use castrol GP 50. This flushes the castor out and keeps the engines nice and free for ages. I think it is really beneficial in the smaller engines that can become quite choked internally with castor residue. I used castrol gtx/duckhams multigrade for years in diesel fuel with no ill effect so it wont harm the engine.

Paul Blakeborough28/03/2017 11:48:47
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Nobody has said much about the MP Jet (Classic) ... I presume the Classic is the one Peter mentions in the initial post ?... however, I've used 4 of them now and can't really fault them... they run a treat (Tried various fuels) ... a vintage feel.. if I could muster a complaint, I'd like the crankshaft/prop thread a little bigger, but except that they're a great engine. I have to say some other types are a little more annoying and can be a "pig" to start and run faultlessly.

Jon - Laser Engines28/03/2017 12:56:29
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Are they still available? i cant seem to find them on their website.

I know that MVVS used to do diesels as well, i always wanted one but could not afford it at the time

Peter Miller28/03/2017 13:51:02
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I am told that they are available from someone in Canada Not sure about here

Paul Blakeborough28/03/2017 14:11:16
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There's one on ebay... just noted... try Flitehook ?

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