drac1

My Feedback: (4)

If the volume to weight conversion is accurate, wouldn't the oil and Nitro percentages be the same?

1QwkSport2.5r

No. 20% by weight is not the same as 20% by volume. The conversion from weight to volume or vice versa is accurate, but the equation isnt that cut-and-dry. The conversion that needs to take place is not a simple volume measurement to a weight measurement. Its a weight per volume measurement; I use grams per milliliter. 29.5735mL = 1 fluid ounce. This simply says for every XX volume, it weighs YY.

I'm not going to beat this horse anymore. The guys that disagree with my method - so be it. I'm not trying to force you to do what I do. I do what I do because it makes more sense. Why burn more nitro than necessary? That stuff is expensive. My engines run superbly on my fuel, have more than adequate lubrication, and always tune like a dream.

Have a fantastic Sunday folks..

drac1

My Feedback: (4)

As engine manufacturers use volume for their recommendations, mixing by volume is the accurate way to mix. If you mix by weight, you end up with percentages different to the manufacturers recommendations.

If some use weight because it saves them money in nitro, then it would be just as simple to reduce the volume from eg. 20% to 18%.

To end up with a manufacturers recommended mix by using weight, it would still have to be the same as if using volume.

1QwkSport2.5r

Well, when I burn up all 10 of my engines from not using the fuel the manufacturer recommends, I'll let you know. Hint: it's gonna be a LONG time. Better hold your breath and call the glow fuel police, I'm breaking the manufacturers rules.

Better tell me how bad I am for not following the manufacturer's recommendations on break-in too. Well, except for my Jett. I heeded Dub's advice on that one. [&:]

I'll let the other forum experts interject here and take over giving advice, suggestions, and anecdotes as I don't feel I'm qualified to do this stuff.... Sheesh..[:@][:'(]

wheelan

this is one time when metric wins, get yourself a 1 litre metric measure, very simple, 1000 mills =1 litre so 15% oil is 150 mill and 850 methanol =1000,, 20% oil is 200 mill and 800 methanol and so on, i personally dont use any nitro and less oil 12.5% in 4 strokes and 15% in 2 strokes and engines run and idle fine its the high oil content that effects the glow, i add a bit of castor to my klotz 200 and have no issues with bearings or rust, i dont run the fuel out or use afterrun oil, been running this for years, its the KISS formula...

drac1

My Feedback: (4)

You are getting a bit carried away. The topic is about the accuracy of volume verses weight mixing. I never mentioned anything about engine failure due to the fuel mix you use. If you choose to use a different mix that's up to you.
Just don't try to say mixing by weight is more accurate, when in reality all you are doing is changing the mix ratio which can be accomplished easier by using volume.
Sheeesh.

1QwkSport2.5r

Put jug on scale, add desired amount of methanol, nitro, and oil. Shake, go fly. Volume is that much easier? Hmm okay.

I'll stick to my plan, you stick to yours. End of story.

drac1

My Feedback: (4)

Put jug on bench, add methanol to appropriate mark, add nitro to appropriate mark and add oil to appropriate mark. Doesn't get much easier than that.

To obtain a specified mix from a manufacturer, volume is the easiest as that's what they do. Otherwise whatever works for each person.

As bjr said, there's more than one way to skin a cat.

Sounds like you are concerned about how your fuel mix will affect your engines as you brought it up voluntarily. Hmm.

wahoo

My Feedback: (59)

DINGDING DING DING...We have a winner !!!

bjr_93tz

Maybe I haven't been clear. ALL my fuels are mixed to obtain final percentages expressed as VOLUME as this is what I believe the vast majority of engine manufactures mean when they provide such percentages in their manuals. If a particular premix company mixes ther fuel to the percentages but uses weight instead, they should state that clearly on the label as it shouldn't be the norm.

I choose to use scales to mix my fuel rather than a graduated beaker or some other bottle with lines on it because it's EASIER and less messy for me. In order to use scales I use the density of each chemical I add to the brew, so I can add the right weight of chemical to achieve the correct volumetric ratio.

Maybe I'm stingy, but it allows me to turn the fraction of a gallon left in my fuel jug back into a whole gallon (or some other quantity) of the same stuff, or some other quantity of a different set of ratios. Waste not want not? I try not to leave fuel lying around for more than 4 weeks if I can use it in something else.

Back in the day, I used to mix my fuel a litre at a time in a bottle and pour them into my larger fuel tin for the day and my engines required minor re-tuning with each different batch. Using scales I don't notice this as much.

YS users have enough to deal with without the fuel changing a bit

As long as the final amounts are within a percent or two by volume of what the manufacturer recoomends (no matter what method you chose to acheive it) then your engine's in with a fighting chance.

EDIT: Hey that's almost my calculator!! Mine's the 9850G It's a bit clunky but I like it and it's good for finding the roots of an equation when I'm too lazy to work it out properly.

drac1

My Feedback: (4)

That's exactly how i thought it should work if measuring by weight. The end result would be the same as if using volume. If you measure by weight alone then the volume percentages will be inacurate.
I don't waste a drop of fuel either. I catch the overflow and put back into the bottle as well.
I mix a coolpower bottle at a time (3.8 litres) and always use the whole bottle before using the new bottle. I very rarely mix fuels if it can be avoided.
I don't worry about storing fuel for extended periods, it can sit for months and never had any issues with tuning my YS's. The same goes for different fuel batches. If i have to touch the needle, it usually indicates something is wrong.

bjr_93tz

Yep, I mix up the YS fuel in my coolpower bottle as well 3.7L at a time when it's serious practice time. I try to avoid mixing fuel in humid weather as well. Gee if these guys think mixing fuel is can be made over-complicated, they should see the trouble we go to to fly a straight line

1QwkSport2.5r

I go at this to measure by weight specifically, not by the volumetric equivalent. For some reason, this seems to be the more accurate method. But as was said, indeed there is more than one way to skin a cat. I have mine, you have yours. Both work and the engines run. That's all that matters, right?

Sport_Pilot

How can mixing by weight be more accurate when all of the componets have different densities? And different types of oil? 20% castor would be a diferent amount than 20% synthetic!

As far as accuracy, you can be just as accurate with volume as weight. If a beaker is not accurate enough for you, then use a burete.

IMO its not necessary to be very accurate. You won't notice the diff in 19% oil or 21% oil, or even the same difference with nitro. and you would have to be pretty sloppy to be 1% off as that is 1.28ounces.

rgburrill

Wow.  I just buy 15% CoolPower and let them figure it out.

bjr_93tz

I really hate writing this but please read the earlier posts as it has been covered. Those that use weight know the densities and apply it for it.

IF my scales are reasonably accurate then I'm good for ~+_1 gram per quantity, for my 500cc graduated cylinder (~ 1 foot high) I'm good for about +_ 5 grams. Not a huge difference but if I'm mixing 1 litre for my DZ170 I'd need 98g to get my 10% oil content. 5 grams would put that oil content between 9.5% and 10.5%.

I tend to agree with this, it's not about accuracy, it's more about precision so you get the same mix each time especially if you're mixing smaller quantities.

I'll be the first to admit that it's an unnessary level of attention to detail to go into for the vast majority of aeromodellers, but mixing using a set of scales for the quantites I use means one less container to clean out before and after the process and it affords greater flexibility, until the scales auto shutdown while pouring [:@] That gives the 'ol grey matter a workout....

Sport_Pilot

If youdon't mindpaying over double the price that works fine.

Sport_Pilot

The point is that this doesn't gain you anything and just opens you up to error. If you are correcting for densities, then you are just using volumn percentages in an over complex manner.

Using a beaker or measuring cup doesn't have any errors from a scale, the only factor is heat expansion of the beaker or measuring cup, and since room temp is close to the temp used for such standards this would be the most accurate way of measuring.

It is unnessary for anyone, including serious racers. If more accuracy is required then use a burete, not a scale. You won't find nitro drag racers weighing their fuel, except during setup to verify the weight of a full tank of fuel.

Correction to the above, the nitro drag racers do mix by volume but they verify with a hydometer. This won't work for us because of using threeingrediants instead of two.

combatpigg

My Feedback: (3)

A reply to this thread in general...but nobody specifically.
Never before has so much been said about so little.
..except I guess I'll add my 2 cents.
Instead of buying a metric measuring cup I just ask my calculator this, "21% of 128 ozs is how much"..?
Then the question is re-written into "math talk".
the word "of" is always changed to "times" [x]
xx% is written in decimal form... [.xx]
the word "is" or "equals" is converted to [=]

.21 x 128 = 26.88 oz

Of course you can always mix in 100 oz quantities [doing the calcs in your head] and continue to rebel from the metric system that got rammed down our throats.
The conversion to metric cost [hurt] the average American, but helped the rest of the metrically based World.

bjr_93tz

I agree it doesn't gain me anything but you haven't understood the earlier posts if you felt the need to make the comment you did. And it's not overly complex because it's required if you CHOOSE to use a set of scales to mix your fuel instead of a measuring container. BOTH methods have advantages and disavantages and I understand them and choose to use the method that offers me the most advantages.

OK so you can hit exactly the same part of the line every time. When I use my graduated beaker I'm usually plus or minus 5g in 500cc which depending on the fluid is about 1% error at best. Using a gallon coolpower bottle that 1% goes right out the window.

I never weighed the fuel I used to mix for my GP road racing bikes either as plus minus 20cc in 20 litres of fuel was less important than other parts of the bike setup.

I'd like to think the OP can take away from this is that the key is to mix the proportions by volume and that there are two valid ways to obtain those volumes.

Perhaps we can continue this burete fetish you have over in LTUP .....

1QwkSport2.5r

I think people intentionally look for crap to argue about. I find myself getting defensive because some guys here are so bent about one way being the only way that my way has no creedance. Just because everyone else does it one way doesn't necessarily make it "right".

I've learned a lot from this and made a few notes. Thank you.

On a side tangent - what synthetic oil do you guys that mix your own prefer to use? I haven't found too many synthetics that mix with methanol that are cheaper than $70 a gallon. Klotz is $40 a gallon through SIG but I'd like to use something better than Klotz.

JPMacG

My Feedback: (2)

The by-weight versus by-volume discussion has been rehashed many times, particularly in th fuels forum. Many times I have heard that mixing by weight is more accurate, and this has been stated by some who seemingly are very knowledgible.

I'm not talking about the specific gravity thing - I know that if you are mixing by weight and your recipe calls for volumes you need to adjust the weights according to the specific gravities of the components.

I am very confused about why some knowledgible people say that mixing by weight it is more accurate. I know that the different ingrediants in glow fuel have differing coefficients of expansion. So if you mix by volume your mixture is slightly temperature dependent. You won't get exactly the same mixture if you mix at 90 degrees F as you would if you mix at 40 degrees F. But that error is so small it isn't worth worrying about.

Is there something else going on here that I don't understand? Any chemists on board?

Sport_Pilot

Probably because the viscous oil clings to the measuring cup, so you have to rinse this off or compensate to be as accurate, providingthe scale is accurate. But otherwise one is not more accurate than the other. But with weight you are no better than the scale. Volume will not have that factor thrown in.

1QwkSport2.5r

The oil clinging to the container doesn't affect me because I put my fuel jug on the scale and add to it, no need to use a separate container. But hey... I'm doing it the hard way. What do I know.

bjr_93tz

Back in my chemistry days it was all about balacing equations and a thing called stoichometry where in a simplified world 2 hydrogen atoms plus one oxygen atom would yield one water molecule. The mass of each atom is known and (apart from slight variances) is fairly well fixed so if you combined X mass of Hydrogen atoms with Y mass of Oxygen atoms they'ed (under the right circumstances) all combine to give Z mass of Water molecules with nothing left over. The volumes that these atoms and resultant molecules occupy is highly variable.

From this it's safe to conclude that every time I add the same mass of uncontaminated fuel component to the mix I am adding the same number of molecules (give or take one or two ) so the ratio of molecules tends to remain similiar. Small changes in a component's density due to temperature will alter the number of molecules per unit of volume so changing the molecular ratio but maintaining the volumetric ratio. This is a hair that's too fine for me to split and doesn't factor into my decision to use scales but is a valid point of debate between chemists. As a side note, apparantly Aerogel came about because two chemists challenged each other to remove the water from a jar of Jam (Jelly in the US I think?) without the shrinking the contents.

Even if I then went on to mix my fuel for a whole day, I'd be really surprised if each charge of fuel entering the cylinder was the same, as there's oil floating around different parts of the engine that gets picked up in different orientations and who knows what being blown back past the piston into the crankcase ready to go around again. One of my road going two-strokes with oil injection only puts in a dribble of oil every couple of hundred revolutions and relies on the fuel ar from the carb to "wash" it into the engine so that's hardly a stable arrangement but it works well enough for it's designed purpose.

With model engines the fuel mixes we use have been arrived at pretty much by trial and error ie, running too lean? make the fuel jet hole bigger, Engine seizing up? add more oil until those magic 4:1 and 3:1 by volume mixes became rule of thumb. I doubt there was any real chemistry involved at the time or a need by the end user today but it is of interest...