OS 4 stroke 20% nitro.

[Jesus Cardin]

13 hours ago, J D 8 said:

         Did you open the needle up some when on the higher nitro fuel ?

I was sure some twerking of the needles would be needed but I, simply, didn´t have time to do!

I just opened slowly the throttle with my fingers already on the high speed needle, ready to open up, but the engine quit abruptly. Then when I tried to rotate the propeller noticed an anormal friction and decided giving up trying to start the engine again till I could have a look at the workshop.

Edited December 21, 2021 by Jesus Cardin

[Jesus Cardin]

12 hours ago, Jon - Laser Engines said:

 

The OS 40 uses an ali piston, iron ring and electroless nickel plated liner if i recall correctly. For the aluminium piston skirt to pick up on the cylinder wall is, to say the least, unusual. For ali to pickup like that it must have been a lubrication issue but this would have damaged the liner as well. I saw this on a laser 240 some years back when the owner decided to mix his own fuel and i think used beef dripping or similar as an oil. Whatever he used it didnt lubricate the engine at all and the pistons were bone dry when i stripped the engine down. 

 

For the engine to have actually seized the liner must have also been damaged, and even so there is no way the fuel was to blame. 

 

Do you have any photos of the damage?

 

Sorry Jon, but not.

The problem happened 3 or four years ago and I didn´t take any photo of the piston-cylinder set. When I discovered the damage I was not very worries as I kept those parts from an early OS 40FS which suffered a worst end as it crashed against a pave stone and just broke in 2 parts, ruining the cranckase and the conrod, but without damage to the piston-cylinder set.

Having a sure backup and as I was unable of noticing any damage to the cylinder I decided trying the repair and it seems it was a success as the engine is now occasionally flown on a Spanish vintage trainer type model and it runs fine.

[Doug Moss]

[email protected]

 

Interesting that no one seems to have mentioned altitude as a factor.

Where I live and fly we are about 5500 ft amsl. Personally I use 10% nitro and 15% synthetic in two and four strokes, definitely better than 5%. We also generally have low humidity and high temperatures which must be a factor.

[Paul De Tourtoulon]

My club is 50 metres above sea level, and now and again at another club which is at 502 metres, it does change the fuel settings especially on my helicopters and of course the performance, no 3 D flying only loops and rolls to be on the safe side,,,

[Nigel R]

10 hours ago, Jon - Laser Engines said:

On the older OS engines they do recommend 20%

 

I'd imagine that would be because the US market has suffered the cult of 20% castor oil (or death to the unbeliever) since about 2000BC.

 

[Martin McIntosh]

Not really tried less oil in them except by accident and have managed to blow up two on 23%, one a broken shaft and the other a sudden bearing failure. If using Southern 20/20 I simply add more oil.

[Jon H]

Broken cranks and failed bearings sounds more like fatigue type failures to me. Lack of lubrication normally manifests itself as seizures and things like that. It just seems really odd as the engines are very well made and i cant see why they would need it. As i say perhaps its to do with their supercharging system. Makes no sense to me though ? 

 

Altitude and nitro, yea if you are in low earth orbit adding a few more % is fair enough. I have a customer up in the alps somewhere and he uses 10% in our engines and also uses a larger prop for greater blade area. Still, as you say doug adding another 5% makes the difference and there is still no need to go to 20%. I should have mentioned it before but its such a niche use case i generally take it on a case by case basis. 

Edited December 21, 2021 by Jon - Laser Engines

[Nigel R]

surely bearings are almost always rot or foreign matter? unless something is misaligned / warped / overheated... we just don't put the hours on our kit to suffer lifespan issues

 

(unless they're the cheapest of cheap from a factory still working to mid-18thC tolerances, I guess)

[Jon H]

36 minutes ago, Nigel R said:

surely bearings are almost always rot or foreign matter? unless something is misaligned / warped / overheated... we just don't put the hours on our kit to suffer lifespan issues

 

(unless they're the cheapest of cheap from a factory still working to mid-18thC tolerances, I guess)

 

yea what i meant was they are mechanical type failures rather than lubrication related. Bearing life from a wear point of view is possible even in the most well cared for engines as the loads imposed on our crankshaft are not well balanced so eventually they give up the ghost. But you are right, rust or a whack is more likely to get the ball rolling on their eventual demise. 

[Martin McIntosh]

I seem to remember that the shaft break was caused by a backfire from a weak start so I now always ensure that the tank is up to pressure and fuel flowing into the motor, detected by a slight speed up after applying the starter for a few seconds, before turning on the glow. Really only applicable to YS.

[John Stainforth]

8 hours ago, Nigel R said:

 

I'd imagine that would be because the US market has suffered the cult of 20% castor oil (or death to the unbeliever) since about 2000BC.

 

This is your imagination. The majority of model flyers in the southern US use glow fuel with 18% oil and between 5 and 20 % nitromethane, depending on the engine and personal preference. The oil is typically synthetic or a blend of 80% synthetic and 20% castor. One of the most popular fuels there is VP PowerMaster, which uses the latter blend of oil. I have no idea what the benefit of 20% castor is meant to be; all I can say is engines using that blend did not gum up after 10 years of use.

 

One thing to watch out for on both sides of the pond is lousy fuel that does not contain what is says on the label. This may have contributed to the idea that nitro make no difference to power. I routinely check the fuel I buy by weighing it and doing a simple mass balance of methanol, nitromethane and oil, given the densities of these three ingredients. The first thing to check is the volume of fuel you've been sold, and the easiest way to do that is to weigh an identical container filled to the same level with water and subtract the weight of the dry empty container. The last batch of Optifuel I bought here in the UK (12% nitro, 18% nitromethane) passed this test with flying colours. Not only did the mass balance suggest the fuel contained exactly the proportions stated on the label, but the volume of fuel was very generous!

 

My own findings (in the US) re fuel consumption with different nitro percentages are at odds with some of the views that have been expressed on this site. I realise that the climatic conditions there, and the low altitude, and the fact that we took the baffles out of silencers to give the engines more power, were different to typical conditions in the UK. (I am very surprised by how much difference even modest differences in altitude make, but those can be largely compensated for by using propellors with different pitch or diameter.) I highly respect the views of Jon on this site - and follow all his advice wrt Lasers - so I intend to do some new tests myself in the UK in the coming year with different blends of fuel, particularly regarding fuel consumption.

[Don Fry]

Now John, I’m well oiled by, (beloved’s Birthday, champagne and rose hip syrup, red wine, nice dinner). I must state you may have hit the Bourbon early. That lot makes no sense whatsoever, even given my inebriated state.

[John Stainforth]

3 hours ago, Don Fry said:

Now John, I’m well oiled by, (beloved’s Birthday, champagne and rose hip syrup, red wine, nice dinner). I must state you may have hit the Bourbon early. That lot makes no sense whatsoever, even given my inebriated state.

Please elaborate on what does not make sense to you. I may have expressed myself badly.

(I am living an alcohol-free existence!)

[Don Fry]

Not too impressed by paragraph one, but let that pass.

Paragraph two. Can you explain the physics behind the assertions on how by weighing you get proportions of a mix of three components.
Paragraph three, observation, if I fly my big hack, fitted pitot tube giving speed through air, in vertical flight, until it is going out of site, that’s the thick end of a thousand meters, apx 3500 feet on your side of the Atlantic, it does not slow down in the flight, it just trundles up at the speed the throttle set at the start gives it. It won’t go for ever, the fuel air mix, is changing, but it’s not that fussy.

Well done, no alcohol. Not for me though.

Edited December 22, 2021 by Don Fry
Last sentence added

[Jon H]

fuel weighing can be a very accurate way of measuring as weight is not impacted by temperature were as volume is. This is why full size aircraft weigh the fuel aboard as its more accurate when you are talking about many tons of fuel. A small change in temperature makes that lot expand/contract a fair amount and you might end up short fuelled on a hot day. Its also handy from a weight/balance point of view. 

 

The issue with doing it with glow fuel is you need to make assumptions. of your 5L of fuel, with whatever proportion of oil and nitro you can quickly work out how many ml of each you should have. You can then use their densities to work out what they all should weigh, add it up, weigh the bottle (presumably an empty bottle from the last batch) and subtract that to see how close you get. The problem is, you could easily get the weight you expect but the ingredients might not be in proportion as you are assuming they are exactly in the proportions they should be and are assuming a spot on accurate 5L to begin with. Unless you measure the contents of the bottle to the last ml it will never be that accurate, although it might reveal glaring errors. If you buy your fuel from a reputable brand, it certainly will not be worth the fuss. 

 

Fuel consumption with high nitro can be significantly higher especially if the engine is not tuned for peak performance. As we know nitro has oxygen in it which is released when burning. To prevent the mixture going lean you need to open the needle and let in more fuel, so overall fuel consumption is higher. High nitro fuel also makes engines less peaky on the needle so finding optimum mixture is not very easy as there is no defined peak. This leads to very rich running which chews up fuel. A friend had a saito 150 in a P47 and wanted me to test fly it. On 15% nitro and 16oz tank it ran for 3 minutes...3!! I suggested we lean it off and got half a turn out of it. This then upped out flight time to 4 minutes ? While i have never tried it with a saito 150, i know a laser 150 using 5% nitro would fly for at least 15 minutes on that much fuel, and probably as long as half an hour depending on the throttle use. My Enya 155 4 stroke runs for ages on a 12oz as well. 

 

I know they are different engines with different efficiencies, but still. 4 minutes? I work on the basis that anything less than 7 is not worth leaving the ground for. 

[Don Fry]

Yes Jon, I weigh stuff for the reasons you say, but John Stainforth is claiming he has a method of working out, by weight, the proportion of oil, nitromethane, and methanol in fuel. 
All the information I can see coming, is if you take the fuel to standard temperature, 4°C. Take a known volume, and weigh the known volume, you get the relative density of the mixture. To get any accuracy, as you say, needs laboratory grade equipment.
That relative density result still does not give any information as to the relative proportion of the three components. A bit light handed with the oil, fuel is heavier, a bit heavy handed with the nitromethane, fuel is heavier. Same result, two different errors.

I assume the oil is one oil, not say a mix of synthetic and castor. If it is a mixture, read 4 components. 

[John Stainforth]

Don, I think you should tell me what does not impress you about my first paragraph, in which I have stated the facts as accurately as I am able to.

 

One has to assume that the stated proportion of oil is correct. In the case of the Optifuel I mentioned, the content of both the oil and the nitromethane have to be right up to the full amounts stated by the supplier in order to explain the weight of the fuel. The nitromethane content would only be seriously in error if the suppliers had inadvertently added a lot more oil than stated, which is unlikely. The weights are easily measured on digital scales that are accurate to fractions of a percent. The estimate of the volume of water (via weight and density of water) is accurate to within a few cc's in 5 litres, i.e., parts per thousand. The densities at standard temperature and pressure are obtained off the internet. The whole measurement procedure only takes a few minutes. With the assumptions above, only three measurements are necessary: the weight of the fuel+container, the empty weight of an identical container and the weight of the latter filled to the same level (as the fuel) with water.

 

 

Edited December 22, 2021 by John Stainforth

[John Stainforth]

I meant "normal" temperature and pressure (i.e., 20 C), not "standard".

[Don Fry]

Paragragh 1, you have a view. I disagree. Each to their own.

 

I’m not arguing. You don’t trust the mixers of the fuel, but assume you can trust their oil mixing, both proportions of caster to synthetic, which have different relative densities , and quantity, added. And you don’t mention inaccurate methanol addition, after all it's relative density is in the same ballpark. And if they get that wrong, why shouldn’t they get the nitromethane wrong as well. BTW, wet fuel is also heavy. As I was taught, to AssUMe, is to make an ass of you and me. My experience of mixers is they get it right, the motor tells me that, and that is a lot of fuel.

 

[aidan mcatamney]

I use Optifuel 12 in all my two and fourstroke engines and they run great.    Merry Christmas to all.  

Edited December 22, 2021 by aidan mcatamney

[Maurice Dyer]

Two topics I love to read on here; batteries (how to/what's the best). And nitro motors ( how much/which oil)

 

Navel gazing and good entertainment.

[Paul De Tourtoulon]

8 hours ago, Maurice Dyer said:

Two topics I love to read on here; batteries (how to/what's the best). And nitro motors ( how much/which oil)

 

Navel gazing and good entertainment.

Yes, it's like listening to a political debate,,,,,?

[Frank Skilbeck]

Oh er, I regularly make up 5% Nitro by mixing 10% and straight on a that looks about 50/50 basis, and low oil content for my Laser 150 by mixing 10% with straight methanol on the same basis. My engines always seem to run alright, but I did have to change the bearings on my early 80s Laser 61 a couple of years ago.

 

Getting back on topic, I have acquired a NIB Saito 40a, my first Saito, just fitting it in a model and note the instructions state commercially available fuel with 10-20% nitromethane and synthetic oil, so I would think an OS 40 on 20% would be fine. 

[aidan mcatamney]

43 minutes ago, Frank Skilbeck said:

Oh er, I regularly make up 5% Nitro by mixing 10% and straight on a that looks about 50/50 basis, and low oil content for my Laser 150 by mixing 10% with straight methanol on the same basis. My engines always seem to run alright, but I did have to change the bearings on my early 80s Laser 61 a couple of years ago.

 

Getting back on topic, I have acquired a NIB Saito 40a, my first Saito, just fitting it in a model and note the instructions state commercially available fuel with 10-20% nitromethane and synthetic oil, so I would think an OS 40 on 20% would be fine. 

You will love your Saito 40.  I have one in a small trainer 25 and it never misses a beat.  So so reliable just like my other Saito engines.  I run it on Optifuel 12, the perfect combination.  Enjoy your Saito and great sound too.  

[Jon H]

1 hour ago, Frank Skilbeck said:

 

 

Getting back on topic, I have acquired a NIB Saito 40a, my first Saito, just fitting it in a model and note the instructions state commercially available fuel with 10-20% nitromethane and synthetic oil, so I would think an OS 40 on 20% would be fine. 

 

Saito do have a much higher nitro tolerance than OS. Their combustion chamber design, compression ratio etc are different to the OS so i would recommend against direct comparisons of this nature. The OS 40fs can be a little vicious with a desire to throw props if you upset it. As mentioned before, Enya engines did the same and they provided a head shim for use with high nitro to prevent props making a bid for freedom. 

 

This is another reason i always just recommend 5% None of this faff or worry about things falling over. 

 

My Saito 45 and 45 specials run fine on 5/15 nitro/oil despite the instructions telling me i must not use full synthetic fuel and up to 30% nitro.