How much oil should I add to Cool Power airplane fuel to run in a helicopter? - RC Groups
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Sep 01, 2017, 01:34 PM
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How much oil should I add to Cool Power airplane fuel to run in a helicopter?


How much oil should I add to Cool Power airplane fuel to run in a helicopter?

Need some fuel and closest place does not have any heli fuel at the moment?

Thoughts? Thanks.
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Sep 01, 2017, 04:53 PM
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How much oil is in that fuel to begin with?
Add enough to have around 18~20%
Sep 02, 2017, 05:13 AM
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Quote:
Originally Posted by Brutus1967
How much oil is in that fuel to begin with?
Add enough to have around 18~20%
yeah thats all well and done but the question is how do you work out how much oil to add. i wondered this before when my local hobby stores tend to not carry it.

One thing though is the more oil you add the less nitro you will end up in your fuel. I was going to do this recently but my hobbyshop only had 12% nitro fuel.

for us not so smart math guys we need some kind of formula that with a known oil content (say 12%) and 16% nitro 5 litres how to bring the oil upto 18%
Sep 02, 2017, 03:15 PM
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Quote:
Originally Posted by bazsound
yeah thats all well and done but the question is how do you work out how much oil to add. i wondered this before when my local hobby stores tend to not carry it.

One thing though is the more oil you add the less nitro you will end up in your fuel. I was going to do this recently but my hobbyshop only had 12% nitro fuel.

for us not so smart math guys we need some kind of formula that with a known oil content (say 12%) and 16% nitro 5 litres how to bring the oil upto 18%
Using 70 ml of oil per litre of fuel (so 350 ml), would bring you close enough to 18%, and the error will neither kill your engine or your performance.

But if you want to calculate: for calculating the oil content, the Nitro % is irrelevant, you want to go to 18% oil and we'll see about the Nitro later....
1 litre fuel 12% oil, contains 88% of "something else" (AKA "the balance") which would be 880 ml.

You want to go to 18%, but that amount of balance stays the same, 880 ml... but it would now be only 82%.
Which means, 100% would be a total volume of (880/82) x 100 = 1073,2 ml

So you need 73,2 ml per litre additional oil, to end up with 18%

In a formula, it would be ((100-"original %) / (100-"desired %")-1) x (Original volume)

So if you have 5 litres 12% oil, and you want to go to 18% oil, the volume of oil to add is:

((100-12)/(100-18) - 1) x 5 L which can be written as ((88/82)-1) x 5L, Which comes down to 0,0732 x 5 L or 365,85 ml oil
Sep 12, 2017, 03:37 AM
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Quote:
Originally Posted by Brutus1967
Using 70 ml of oil per litre of fuel (so 350 ml), would bring you close enough to 18%, and the error will neither kill your engine or your performance.

But if you want to calculate: for calculating the oil content, the Nitro % is irrelevant, you want to go to 18% oil and we'll see about the Nitro later....
1 litre fuel 12% oil, contains 88% of "something else" (AKA "the balance") which would be 880 ml.

You want to go to 18%, but that amount of balance stays the same, 880 ml... but it would now be only 82%.
Which means, 100% would be a total volume of (880/82) x 100 = 1073,2 ml

So you need 73,2 ml per litre additional oil, to end up with 18%

In a formula, it would be ((100-"original %) / (100-"desired %")-1) x (Original volume)

So if you have 5 litres 12% oil, and you want to go to 18% oil, the volume of oil to add is:

((100-12)/(100-18) - 1) x 5 L which can be written as ((88/82)-1) x 5L, Which comes down to 0,0732 x 5 L or 365,85 ml oil
Thanks brutus really usefull information. Dunno whats going on with fuel recently but it actually now seems easier to just order the heli fuel. Theres not much saving in buying plane fuel and adding oil. for a 12% oil mix it would cost 1.40 in oil. seems alot of plane fuel is down at 5 and 12% and costs almost same as 12% heli fuel
Sep 12, 2017, 04:26 AM
Registered User
Just as an addition:

It gets slightly more complicated if you would want to for example change the oil content, but keep the Nitro the same. Because if you add oil, the Nitro percentage drops, but if you then add Nitro, the oil percentage drops again, which would be a never ending story.

Not many people want to do this, but actually, it is not that difficult.

Take for example your fuel 12% oil, 16% Nitro, and you want to change that to 18% oil while maintaining 16% Nitro.
You have to add both, but by how much?

For this, you have to break down the fuel in its components:

Original blend
12% oil=120 ml
16% Nitro=160 ml
72% Methanol=720 ml

Of the new blend, we know the desired percentages, and we know only one volume, but that is enough.

18% oil =??? ml
16% Nitro =???ml
66% Methanol = 720 ml.
so 1% of the new blend is 720/66= 10.91 ml
Desired amount of oil is 18 x 10.91=196.36 ml, allready present 120, to add 76.36 ml
Desired amount of Nitro is 16 x 10.91=174.55 ml, allready present is 160 ml, to add 14.55 ml

I really don't know if anybody wants to do this, but I added it just for to dot the i's when blending fuel...


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