I recently had the opportunity to compare two radically different engine setups in back-to-back flights in good conditions. Both were in my usual airplane. On one, I had a fair bit of boost/brake by my standards, good lap speeds, etc. The second had much less boost/brake and the same lap times. Both where entirely satisfactory but the airplane flew *much* differently. The first had a tendency to be a little soft in the corners and then recover compared to the second. Most notably, the second setup had *much* more pull in the corners and *much* more feedback at the handle in the corners. It was about equivalent to adding about 3/4 ounce of noseweight, which is a pretty big difference. In the first flight with the second setup,  I ended up having some odd shapes for a while until I got used the more positive maneuver entries, and my tendency was to pull out lower since there was a combination of more control pressure and much more confidence in reaction to the slight turbulence. It was arguably less "flicky" feeling and it was not clearly better in terms of control feel with the second setup, but it was different. In fact, it felt very much like all the electrics I have flown with the very steady - perhaps too steady - run and very positive feel in all the corners no matter the position on the sphere.

   Another thing that was noticed by all was that the engine unloaded much less from launch to flight with setup number two. I ended up having to set it faster on the ground by maybe 200 rpm to get the same level flight speed.

    These two radically different setups? Well, EXACTLY THE SAME engine, airplane, tank, venturi, pipe length, prop, etc. The only difference was the fuel, and in fact the only difference was in the OIL CONTENT - the first fuel had 18% total oil and the first had 22%. The extra oil was all synthetic. The run time was just marginally shorter with the second fuel and was consistent with the loss of volatiles, so it wasn't just more nitro due to random variation. In fact, I already know that the engine does not like 22% 50/50 oil, so synthetic oil is the only way to add more.

    Fuel #1 was Powermaster 10% R/C Sport fuel and the second was Powermaster 10% RO-JETT. Both were from the VP era and both have the "true" 10% that we have been getting from VP since they took over and found that the nitro was previously down around 7.5%. Easily a match for SIG in power.

    I am not suggesting one was better than another or that you all ought to run out and add or remove oil - just that a seemingly minor change can make a massive difference in areas where you would never expect it. It's a much bigger difference in the feel than I ever got changing the compression or pipe length.

   Brett

I recently had the opportunity to compare two radically different engine setups in back-to-back flights in good conditions. Both were in my usual airplane. On one, I had a fair bit of boost/brake by my standards, good lap speeds, etc. The second had much less boost/brake and the same lap times. Both where entirely satisfactory but the airplane flew *much* differently. The first had a tendency to be a little soft in the corners and then recover compared to the second. Most notably, the second setup had *much* more pull in the corners and *much* more feedback at the handle in the corners. It was about equivalent to adding about 3/4 ounce of noseweight, which is a pretty big difference. In the first flight with the second setup,  I ended up having some odd shapes for a while until I got used the more positive maneuver entries, and my tendency was to pull out lower since there was a combination of more control pressure and much more confidence in reaction to the slight turbulence. It was arguably less "flicky" feeling and it was not clearly better in terms of control feel with the second setup, but it was different. In fact, it felt very much like all the electrics I have flown with the very steady - perhaps too steady - run and very positive feel in all the corners no matter the position on the sphere.

   Another thing that was noticed by all was that the engine unloaded much less from launch to flight with setup number two. I ended up having to set it faster on the ground by maybe 200 rpm to get the same level flight speed.

    These two radically different setups? Well, EXACTLY THE SAME engine, airplane, tank, venturi, pipe length, prop, etc. The only difference was the fuel, and in fact the only difference was in the OIL CONTENT - the first fuel had 18% total oil and the first had 22%. The extra oil was all synthetic. The run time was just marginally shorter with the second fuel and was consistent with the loss of volatiles, so it wasn't just more nitro due to random variation. In fact, I already know that the engine does not like 22% 50/50 oil, so synthetic oil is the only way to add more.

    Fuel #1 was Powermaster 10% R/C Sport fuel and the second was Powermaster 10% RO-JETT. Both were from the VP era and both have the "true" 10% that we have been getting from VP since they took over and found that the nitro was previously down around 7.5%. Easily a match for SIG in power.

    I am not suggesting one was better than another or that you all ought to run out and add or remove oil - just that a seemingly minor change can make a massive difference in areas where you would never expect it. It's a much bigger difference in the feel than I ever got changing the compression or pipe length.

   Brett

Good Post
I have done the same thing many many many times over the years, I did this with my 51 in the EXEL, and in the Katana, I did it with the 40 in my VECTRA, You can get both to work, however you need to not just change over for a couple of flights, but need to optimize and trim each setup for the best runs. When I used the hi power 4 setup with my Katana and the PA 51, it runs all 4 cycle everywhere, it is a little harder to set, but is perfectly doable. The 4 with 2 beeps at the top is a little easier to set with a little broader range , but I would be happy to use either at any contest, The only thing I don't care for is getting so deep into a 4 cycle that the motor does not come on at all when in the manouvers, This will hurt the line tension in the tops and in manouvers like overheads.
The 4 with 2 beeps seems to like a little more nitro than the all 4 setup. But you can control the way the motor comes on in both setups by lowering or raising the nitro content, as well as use this to adjust the run for lower/higher altitudes or hot /cooler climates

Randy

Thanks Brett, good info. 

I ordinarily run Sig Champion 10%nitro, 20% oil, half and half.  I have run a tankful of two different brand fuels, said to be the same formula.  I had to make drastic needlevalve changes, and was not pleased with the performance.  No doubt if I ran those fuels as a usual thing, I would figure out how to make them work to suit me.  So I can accept that small changes in fuel can make considerable difference in performance.

I found out that if you want CONSISTENCY and have the time and suppliers, one can't beat mixing your own. Once the ideal formula is found for the specific engine and engine run, it is always the same.

 

the only difference was in the OIL CONTENT - the first fuel had 18% total oil and the first had 22%.

There must be a typo here ?

The Powermaster RoJett blend, is it 10 nitro, 11 castor, 11 syn ?

So which of the two do you prefer ?

     By the way, there is a HUGE change in the needle position between the two fuels. Something like 3/4 turn. The overall power and run time about the same, so it must be that the viscosity is higher with the RO-Jett fuel. Maybe I should re-attach my regenerative fuel pre-heater...

   Brett

Hunh?  I think a typo here mayhaps? You go in running RoJett or any other powermaster.  I thought we all agreed the viscosity was lower with Powermaster fuels.

I don't know why, but I have really struggled with the "new" Powermaster in both my PA and DS engines.  The runs seem *much* different, even accounting for the increased nitro in the new stuff.  I wish I could get it to work, I liked 225 flights between plug changes vs 16-25 flights before the plug gets tatered on Sig fuel.  Essentially the run conditions are slightly different every flight as the plug rapidly changes due to the deposits.

Hunh?  I think a typo here mayhaps? You go in running RoJett or any other powermaster.  I thought we all agreed the viscosity was lower with Powermaster fuels.

I don't know why, but I have really struggled with the "new" Powermaster in both my PA and DS engines.  The runs seem *much* different, even accounting for the increased nitro in the new stuff.  I wish I could get it to work, I liked 225 flights between plug changes vs 16-25 flights before the plug gets tatered on Sig fuel.  Essentially the run conditions are slightly different every flight as the plug rapidly changes due to the deposits.

    Mix 5% and 10% to get the nitro back where it was.

   I had to open the needle when I switched from the "Sport" fuel to the RO-Jett fuel.

    Brett

   

I know about taters on the plug filament from the racing days.  I have never noticed a tater on a plug used in a stunt airplane. 

     It's actually a pretty significant problem. We never had a big problem until we got to the PA61, but at one point we were getting something like 30-35 flights on a plug using straight SIG. The power drop is pretty severe. With the Powermaster, I have never gotten any significant deposits on the element and I change plugs about once a year, right before the NATs, out of habit.

    Brett

I noticed the problem when I ran the OPS 40 and  VF 46. and the PA 40, It really had nothing to do with the PA 61. Your right about the power drop, but even worse is the bad run inside vs outsides and having to screw the needle in to keep the RPMs up, not to mention that sometimes the engine will shut off in some maneuvers when the taters are present.

   We only started having issues when we got to the 61. We occasionally had a slight "frosting", but never a big round blob.  Same with heat issues, I never fragged a pipe on a 40VF or PA40, and no problem with the PA61 here. First run at Muncie, that familiar carbonizing epoxy smell. It's a matter of much more power being generated in a slightly bigger space.   For "Equal Time", same thing seemed to be happening with the RO-Jett 61 for the brief time I experimented with it. Ran well otherwise.

   First run after a plug switch, you feel like a hero!

    Brett

   We only started having issues when we got to the 61. We occasionally had a slight "frosting", but never a big round blob.  Same with heat issues, I never fragged a pipe on a 40VF or PA40, and no problem with the PA61 here. First run at Muncie, that familiar carbonizing epoxy smell. It's a matter of much more power being generated in a slightly bigger space.   For "Equal Time", same thing seemed to be happening with the RO-Jett 61 for the brief time I experimented with it. Ran well otherwise.

   First run after a plug switch, you feel like a hero!

    Brett

I am convinced it is coming from the chemical that they use tin castor to extract the juice...  It was about that same time when it all went bad.  and fuel with the least castor seems to make the less  taters.....   hmmmm  I need to get to work on Aero-1 Tater remover......

Randy

I am convinced it is coming from the chemical that they use tin castor to extract the juice...  It was about that same time when it all went bad.  and fuel with the least castor seems to make the less  taters.....   hmmmm  I need to get to work on Aero-1 Tater remover......

  Yeah!  Hydroflouric acid! Use it once and you can guarantee you won't be worried about taters any more.

    I think that it is more likely some sort of polymer from the anti-foam ingredient. Scrape off the carbon and they look like tan plastic. You get more taters if you put armor-all in the fuel.

     Brett

A long time ago I use to filter all my fuel through a coffee strainer before I used it. I wonder if that would help???

Derek

Well I mixed fuel with only pure methanol , nitro, and the Bakers castor Sig uses, plus 1/2 Klotz oil, no anti foam  no armor all ,  got taters very quick so  doesn;t seem to me to be that , leave out the castor and taters go away

  Maybe something, but not likely the solvent used to extract the oil from the bean. With the "bad castor", it forms a precipitate that is related to xylene, which is what they wash the beans with to get the last bit of oil. They then heat the oil to drive off the xylene. I tested some of the "bad castor" from the only known source, Red Max, and the gas chromatograph showed xylene (and not much else in the way of volatile contaminants, the next biggest volatile was water). Baker's AA packaged by SIG and the stuff I got from Powermaster showed *no* xylene or anything else aside from a very small amount of water. And didn't form any precipitates.

   The SIG disaster fuel from the 95 NATs had something that was clear and gelatinous floating around in it, but I never tested it and it wasn't know to be a tater producer. Subsequently, I have found nothing untoward floating around in SIG fuel and it ran fine aside from taters. By that time I didn't care and gave the bad 1995  fuel to some RC guys, and it didn't work worth a damn for them, either!  The blamed it on "too much oil".

    Brett

    

Another funny thing with newer castor is that it now forms dark sedimate at the bottom of a gallon where it did not in the past, this is a gallon of Baker's. Other brands of castor oil I have bought do this even worse.
Looks like something is settling out of the castor or at least heavier and going to the bottom, the bottom layer is still castor oil, but stained dark brown, or oxidized brown.

The slugs, or flecks in the bad fuel from the 90s may have come from them adding Lubricin N-1 , as it will fleck castor very badly, and makes the fuel almost unusable. I run all of my fuel thru 3 built in filters when pumping into the plane, so that seems to help a lot.
It would be very helpful if we knew for sure, exactly what was causing the problem with the fuel vs glow plug

Randy

I'm thinking some sort of defoamer or *whatever* might be involved in the manufacture of the oil(s), so its in there already in trace amounts when you buy the oil. You didn't add it, it was already there...

If all the castor oil suppliers are now using xylene to finish the extraction and then heating the xylene extract to distill out the xylene that is the source of the problems.  Castor oil has a highly reactive chemical structure.  Heating it during distillation would cause it to polymerize rapidly.  Regular vegetable oils, like soy, canola, linseed oils are polyunsaturated and will polymerize from oxygen in the air(useful in paints and varnish) but don't do it in a model engine to the degree castor oil does.

Castor oil tends to wet metals and doesn't burn from heat.  It just starts forming more and more varnish.  True ABC motors with ball bearings really don't need castor oil for lubrication, maybe just a few percent in case the motor gets a lean run.  Cleaning the piston is cheaper than replacing it.

Another reason to minimize castor is that it has a lot more impurities in it than synthetic that can literally take a year to really dissolve in the alcohol.  Some of the synthetic oils have a similar problem.

....Castrol M, blokes here in Oz have been using this stuff for years with no issues.

I've used Castrol M for over 50 years with no problems whatsoever, apart from some carbon, although right now I'm experimenting with a little synthetic added to see how well it keeps the carbon deposits away.

Castor beans are first dried out then run through a press to squeeze most of the oil out. The remnants are then recycled back through the press to extract a little more oil. That's called second pressing and applies to all pressed castor. What's left over after the second pressing is called "cake" and still has a small amount of oil which further pressing can't extract. The pressed oil is filtered and then goes into settling tanks where it's degummed. This is the preferred oil for our engines as used by Castrol and Bakers, usually called AA.

Back to the "cake". From memory it still has about 5-10% of the oil still in it and that can only be extracted chemically. This can be mixed with pressed oil but is no longer an AA grade because of some chemical remnants like the xylene Brett mentioned. I seem to recall Brett mentioning (long ago) that the xylene could be the cause of white flakes appearing in cold weather. This absolutely doesn't happen with Castrol M because I've had occasion to put fuel in my fridge freezer when checking for water.

Hi Chris

The castor I use is AA  castor only?  so It still is a mystery as to exactly what is going on

Randy

Hey Randy, what can I say bar the fact that Castrol M works regardless of its (or others) rating.

Can you get some M and try it out perhaps?

  Didn't have to be cold weather. I put some Red Max castor oil in regular fuel, and it precipitated out in a few days. Tried the same with other brands and it didn't happen.

    Brett

Yep.. that was the worst of all the fuel/ castor problems, many people have never went back to their fuels yet.

Randy

Yep.. that was the worst of all the fuel/ castor problems, many people have never went back to their fuels yet.

   Even if they fixed it, I am not sending one cent to those guys. I was a big user of Red Max fuel for a while, then when I called to order they basically wouldn't sell me what I asked for, and told me that they knew I didn't need it. That wasn't helpful, then I started tracking down this business with the precipitate, and that's when the REAL BS started. I ended up talking to two different people and they started lecturing me on what I really needed, which they knew because they talked with a Top Expert on stunt engines - and let's just say was not too impressed with their choice. Then they made demonstrably false statements. The BS stayed on their website for years, maybe it's still there. They did backtrack on the "good castor isn't available" but even when they did that they claimed that they had never suggested otherwise.

  I won't do business with them anymore.

  Actually both David and I have had very good response from the VPS people that now run Powermaster and they have been quite helpful. So even a relatively HUGE firm like VPS can listen to people and respond usefully

    Brett