Question about VP fuel

[Dave_Trible]

For many moons we have used Byron's fuel and was very happy with it-actually still using the last few gallons I could find.  They aren't making model fuels any more.  We bought 10-12 gallons of VP fuel from somebody, several different mixes.  Some is GMA 10% and 5%, 20% oil.  This fuel is NOT red.  The VP website doesn't say-is this all castor or does it have a clear Synthetic oil in it?  Somebody in the know please spill the beans......

Dave

When this is used up we will be mixing our own but need to know what we are using with this PowerMaster.

[Dan Berry]

GMA label is 22% oil - 50/50 castor/ synthetic.

[Brett Buck]

For many moons we have used Byron's fuel and was very happy with it-actually still using the last few gallons I could find.  They aren't making model fuels any more.  We bought 10-12 gallons of VP fuel from somebody, several different mixes.  Some is GMA 10% and 5%, 20% oil.  This fuel is NOT red.  The VP website doesn't say-is this all castor or does it have a clear Synthetic oil in it?  Somebody in the know please spill the beans......

Dave

When this is used up we will be mixing our own but need to know what we are using with this PowerMaster.

      As noted above. I would also add that the synthetic oil they are using is not red to begin with, as far as I know it is clear/amber. They add the dye - the purple dye fiasco being one example. I got a couple of cases of 10% RO-Jett that was completely colorless after I special-ordered it, not wanting to stain my airplane.

     I am not sure what the "20% oil" refers to, the baseline GMA is 22% 50/50 as noted above and the RC "Air" (by which they mean "aircraft") has 18% 5/13. RO-Jett was 22% (5% castor and 17% low-viscosity synthetic).

   My engine will not work on GMA, it loads up on inside corners.

     Brett

[Dave_Trible]

Thank you guys.  Kevin (son in law) had texted me asking, and I may have gotten him wrong about the 20-22%.  At the moment he is trying it in a Veco .61.  The can has no detail about the oil on it.  I just told him to add oil in combination as we normally do and see what happens.  It's been a while since I looked at what we bought but some of it was "AIR" which my be more to our liking for piped engines.  Maybe the older cross scavenged engines we use on profiles and such will work OK with the GMA.  Their website says the "AIR" is 80% Synthetic and 20% castor.  My RO Jett .76's don't seem to run as smooth on that much synthetic as a rule.  I usually run about 24% oil on them (50/50) so I will add just castor to that and see.

Dave

[Dave_Trible]

Kevin found the answer posted on some website-it's 50/50.

Dave

[Brett Buck]

Sounds like an oil viscosity issue, Brett. Can you have full synthetic fuel from the same supplier, with same synthetic oil (probably Heli fuel)? Then you could dilute down the castor % to the level that causes no more issues.
I've found that even going from 5% castor to 2,5% makes a big difference.
Just a thought.

Lauri

    In this case, I am going from 5% castor to 11% castor, that is enough to screw it up. 22% total oil (5%/17%) works fine. So it's the castor for some reason - I doubt that it is simply the viscosity in this case, just because we have taken some measures to make sure it is much less draggy than normal, and it didn't change with the regenerative fuel heater (which ultimately proved unnecessary with the 61, and ran dangerously close to the range that causes nitro to decompose).

     Brett

[frank williams]

A couple of verses from my standard songbook.

The problem is almost always the ratty /loading up on inside maneuvers.  Oil breaking free from the crankcase due to sudden g load changes should affect both inside and outside.  But its always the pesky insides.  Lauri doesn’t know what we’re talking about because he doesn’t run with the cylinder facing down.  The modelers across the pond figured this out long ago, but us yanks keep building planes with the cylinder in line with the inside maneuver g loads.  It makes a difference to try to keep the ignition (plug) free from junk.

Castor content makes a difference, but mainly I think due to the increased viscosity.  Yes it varnishes, but it is useful in lubrication and heat management.
 
Lauri’s use of a rear intake motor is excellent.  We go to extremes to reduce the drag of the fuel in the line from tank to venturi.  We use extra large fuel lines to reduce the head loss and large filters.  The advantage of the rear intake motor is that there is about 3 inches less fuel line in the system.  This is about a 40 percent reduction in the total head loss due to fuel flowing in the lines.  The result, better draw.

Another advantage of the rear intake motor is that it is the ultimate crankcase stuffer.  The volume of the hole, the length of the crankshaft is a bunch.  The rear intake motor draws better due to this volume reduction as well as the pressure to push the gas into the cylinder is higher.

The thread was about VP fuel.  The heli was mentioned.  It is definitely a lower viscosity overall fuel, not a bad choice for out piped motors.

[frank williams]

You do bring up something that I hadn’t thought about before, the direction of crank rotation.   I always envisioned a rear exhaust motor as being perfectly symmetrical if in the horizontal orientation.  The ports and internal case shape are mirror images of each other when mounted horizontal.  But, indeed the spinning crank is influencing the “goings on” in the case and probably does cause a bias toward inside or outside maneuvers depending on the rotation direction.  So maybe that accounts for your 40 degree preference.

[frank williams]

One more song from my repertoire …..

Noting that you have six ports (I assume intake ports) and a couple of exhaust ports, you might be disposed to port leaking, depending on the fit of sleeve to case.

The ST60 (especially ones with perry ports) will not fly stunt when the interference fit of sleeve to case is removed.  The perry ports reduce the distance between intake ports and the exhaust port holes in the sleeve.  Without the tight fit of sleeve to case there is leakage between the intake and exhaust around the outside of the sleeve between case and sleeve.  Draw is reduced and pumping is reduced.  In the case of the ST60 with a “honed case”, it runs ok till it warms up a little and the case expands and the leaking begins, then it won’t hold a four cycle.

[Dave_Trible]

I haven't had too much trouble with loading up save for one of my .76s.  I think that is about how I run them-very low RPM with a higher pitch prop and very long pipe.  They are in a four stroke with only an occasional bleep into a two.  About the same with the .61s, which will run well either way-fast or slower.  The .76 just doesn't.  It seems only in it's element in the slower mode (me too).  The one exception about the inside stumble is the one I have with the natural/silver head.  This was the early version and I think it was timed little different (same with my .61s).  They will produce a very tiny bit more power and consume slightly more fuel but have slightly different characteristics.  I usually throw in a new plug and it's OK for a while.  I will try a different fuel mix on that one, something I hadn't considered.

Dave

[Brett Buck]

I haven't had too much trouble with loading up save for one of my .76s.  I think that is about how I run them-very low RPM with a higher pitch prop and very long pipe.  They are in a four stroke with only an occasional bleep into a two.

  I would guess because the 76 runs much hotter, just by virtue of being bigger. Low revs and near a 2-stroke mean *lots* of load, light fuel consumption (for an engine of that size) also means higher temps.

    An additional interesting feature- the "regular" 136 degree exhaust timing version of the 61 seems to run OK with GMA, although I don;t care for the way it runs overall. I run the 144 degree version in a constant 4-stroke at about 10100 ground revs with a 3.75" prop, it never hits a 2 until it's out of gas. The 140 degree version runs about like you describe your 76, although I run that at around 9600 with 4.1" of pitch (which I am working to reduce for performance reasons). Neither the 144 nor the 140 likes GMA, and it really likes the high synthetic content fuels, including straight 18% synthetic.  With 4.1" of pitch it has *far too much* tendency to break into a 2 under load, as you would expect.

     I adjust the run in terms of boost/break with oil content - the more oil, the less break.

     I think this is another "internal ballistics" issue as before, this time Lauri's  "plug shield" probably would make a difference.

   Brett