Cold fuel= more power?

[John Carrodus]

Question - Would keeping fuel on ice in the field give increased performance? I'm running the filter and fuel line through the cramped engine compartment in my current build project. Wondering if this can be mitigated.
Flying in hot conditions brings other challenges too.

[Dan McEntee]

   You want to keep your fuel cool at the flying field, but i wouldn't put it on ice. Ice would cause condensation too form and you don't want that in your fuel. Keep it our of direct sun light and in the shade.  keeping it in an insulated box might help with keeping it at an even temperature, but don't add ice. Routing the fuel line doesn't leave a lot of options in most models. Use as large a fuel line as you can. Try to keep the fuel line from laying against anything hot, especially if you have a metal fuel filter. It will transfer hear from a muffler or crank case and boil the fuel before it gets to the needle valve. Brett Buck has posted some interesting stuff on fuel viscosity and experiments that he and David Fitzgerald have done on the subject. That stuff needs to be pinned on top some where so it's easy to find. You hear and read of hot rodders and drag racers packing their fuel lines in dry ice to condense the fuel so more will pass through the intake, but I don't think that our models have enough flow for that to be effective. In reading and thinking  about the stuff that Brett and David worked on, I think if you concentrate on getting as much fuel flowing from the tank as possible, and keep it from being heated by the engine, that's about as optimum as you can get.
   Type at you later,
    Dan McEntee

[Brett Buck]

Question - Would keeping fuel on ice in the field give increased performance? I'm running the filter and fuel line through the cramped engine compartment in my current build project. Wondering if this can be mitigated.
Flying in hot conditions brings other challenges too.

   No. In fact you want the fuel to be as "thin" as you can get it, as long as you are running suction and have to suck it through the tubing. Thin fuel means you can use a larger venturi with adequate suction. Or, the same venturi with smoother performance.

   The only real issue is the possibility that the fuel heats up over the entire flight - which would cause it to go richer and richer as the temperature goes up over the duration of the flight. This is the other reason not to pre-cool the fuel, because it will warm up slowly in the tank. I run the fuel at ambient, and it it gets heated up on the way into the engine as it flows through, that is consistent, if the tank gets too much heat from the header or muffler, it will slowly creep richer.

    I have even experimented with a fuel pre-heater built around a header. It ran *extremely smooth*, the problem with it was that it ran fairly close to the temperature at which nitromethane decomposes, which, if it happened, is liable to cause a very impressive explosion.

      Brett

[John Carrodus]

Cheers guys.
Yeah what you both say makes sense.
Many thanks for resetting my compass.
I'l now put the egg and needle away. - till my next mad scheme pops!
John

[Paul Smith]

Speed flyers used to keep their fuel in coolers, but I think it was just show biz.

I think that chilled fuel would come back up to ambient and just mess up your needle setting.  I just let everything be at ambient temperature.

[John Carrodus]

Thanks Paul.
That makes a ton of sense.
Cheers
PS That P51 what a time machine. Its hard to believe we built stuff like that way back then when you phoned somebody once a week, no TV ( basically)  antibiotics were the wonderdrug, folks dressed up to visit neighbours for a cuppa, crack was something to be repaired in the weekend and politicians represented the people- a lot has changed - but we couldn't build a better piston fighter today if we tried!

[De Hill]

Francisco, a manufacturer of racing fuels produced a Kool Kit in the early to middle '50's.

This was supposed to cool your fuel.

I never heard if it worked or not.

I have a N.I.B. Kool Kit. I'm sure it's rare, but I doubt that it is worth much.

[Carl Cisneros]

Paul
We kept fuel on ice or in a cooler for the Propalene Oxide (spelling) to
keep it from boiling. VERY LOW boiling point.
You could actually see it bubble when you set the bottle down on the hot
black top at the speed circle.
We mixed the fuel for each go right then and there. (back in the 70's.)
Carl

[Gerald Arana]

Francisco, a manufacturer of racing fuels produced a Kool Kit in the early to middle '50's.

This was supposed to cool your fuel.

I never heard if it worked or not.

I have a N.I.B. Kool Kit. I'm sure it's rare, but I doubt that it is worth much.

De,

 You might be surprised what some collector will pay for it (or not) on eBay.

Cheers, Jerry

PS: I've been both surprised and disappointed.

[peabody]

John D'Ottavio claimed that "cool was better" and sometimes used a Styrofoam box with tin foil on the outside.
Winfred did on occasion

John D also claimed that "old fuel is best"....

[Lauri Malila]

John D'Ottavio claimed that "cool was better" and sometimes used a Styrofoam box with tin foil on the outside.
Winfred did on occasion

John D also claimed that "old fuel is best"....

It's better because fuel temperature stays more stable because of styrofoam cover. I see too much fuel bottles left in sunshine, and then wondering why engine run is all over the place.
The richening towards the end of flight that Brett mentioned, you can compensate a little by tweaking the tank laterally. but it's still better to isolate the tank as well as possible and to take care that there is some cooling air not affected by engine/muffler heat for the tank. L

[Brett Buck]

It's better because fuel temperature stays more stable because of styrofoam cover. I see too much fuel bottles left in sunshine, and then wondering why engine run is all over the place.

   Heh!  What about leaving it out on the 140 degree pavement in a metal can?

     Brett

[Paul Smith]

Paul
We kept fuel on ice or in a cooler for the Propalene Oxide (spelling) to
keep it from boiling. VERY LOW boiling point.
You could actually see it bubble when you set the bottle down on the hot
black top at the speed circle.
We mixed the fuel for each go right then and there. (back in the 70's.)
Carl

Do you have any ideas for getting prop now?

I had some in the past, but it seems to have evaporated.

[Paul Smith]

   Heh!  What about leaving it out on the 140 degree pavement in a metal can?

     Brett

Leaving things in the sun on asphalt is, of course, a bad idea.  But I still think letting everything be at ambient is a better
bet than chilling the fuel and guessing about what happens when it coming up to ambient.

[Lauri Malila]

   Heh!  What about leaving it out on the 140 degree pavement in a metal can?

     Brett

Maybe better to keep some distance?

[Carl Cisneros]

Paul

You can try here:

https://www.tcichemicals.com/US/en/p/E0016?gclid=Cj0KCQiAxc6PBhCEARIsAH8Hff2sUDiezN3GmzpP7ZhvsELE5SvxxYdlQSmLMYRkqn2EZyF50wnMDEoaAphfEALw_wcB

or here on Amazon:

https://www.amazon.com/Propylene-Oxide-EM-Grade-500ml/dp/B00JKREFK0/ref=sr_1_2?crid=32IWNNXBI2FQ9&keywords=propylene%2Boxide&qid=1643392087&sprefix=propalene%2Boxide%2Caps%2C64&sr=8-2&th=1

Carl

[Lauri Malila]

Leaving things in the sun on asphalt is, of course, a bad idea.  But I still think letting everything be at ambient is a better
bet than chilling the fuel and guessing about what happens when it coming up to ambient.

The viscosity change of fuel as function of temperature is usually the biggest reason when you must adjust the needle during day. Or between flights, depending if you do several consecutive flights or let things cool between flights.
There is also a measurable difference in the measuring stability of a remote needle valve and the usual valve that's bolted to crankcase. With a classic valve engine run often starts slightly faster, and about the wingover the case temperature has raised to a stable level. but when you isolate the valve from engine heat, the flight starts slightly rich and it settles nicely just before wingover.
..and this brings to a nice off-topic -topic; The beauty of a rear intake engine, when cooling air is correctly ducted, is that it's kind of self-regulating. When the engine can freely suck the air that's been heated by it, the air density change changes the mixture ratio. Overheating; richer mix. L

[Phil Spillman]

In cool weather you don't really need as much Nitro in your fuel to improve power! Cold ait as in winter has more oxygen per measure than the hot air of summer and therefore delivers more power due to the denser air. Lately I have found that 7.5 11/11 really works quite well year round. I used this blend all summer this past season and haven't changed during fall nor winter thus far and I am having fine results!

Years ago, as in the mid '60's and 70,s when gun-ho into Goodyear and scale racing we tended to keep our fuels cool in the open car. We also mixed different fuels for each heat race and feature! Those days are gone of course since racing has been dumbed down to take the chemists out of having their fun! As sponsors of meets have gone to furnishing specific fuels for specific races.

But yes cool fuel will run much better no matter what!

Phil Spillman

[Jim Hoffman]

The viscosity change of fuel as function of temperature is usually the biggest reason when you must adjust the needle during day. Or between flights, depending if you do several consecutive flights or let things cool between flights.

Lauri, I live in a desert climate and experience big temperature swings and lean out the needle valve and/ or add nitro as the temps rise.  I have always believed the reduction in oxygen molecules per unit volume of air was the cause of this phenomenon and that is why the additional nitro helps. Why do you believe the fuel viscosity reduction is the biggest cause?

[Brett Buck]

Lauri, I live in a desert climate and experience big temperature swings and lean out the needle valve and/ or add nitro as the temps rise.  I have always believed the reduction in oxygen molecules per unit volume of air was the cause of this phenomenon and that is why the additional nitro helps. Why do you believe the fuel viscosity reduction is the biggest cause?

       I am not Lauri, but he is also running *tiny* amounts of fuel, meaning the flow rate is extremely low. Presuming he has about the same suction as everyone else, his metering/needle is much more restrictive, meaning viscosity has even more effect on how much fuel flows. Compare that to, say, David F. where he is running 8.5 ounces/flight and has gone to rather extreme measures to reduce the fuel system line drag. In that case, viscosity make relatively little difference (which is *why* we went to rather extreme measures to reduce the flow drag, to make it more like the Jett). That's also why you want low-viscosity oil (and why I experimented with a fuel pre-heater).

   The desired flow rate to maintain the mixture *does* change with air temperature, less in the afternoon. Whether that is a bigger or more pronounced issue than the fuel temperature changing and changing the viscosity might be different in different systems. Lauri is in an extreme situation, running typical power levels on 4-ish ounces of fuel, I am not at all surprised that he needs to keep the fuel at a constant temperature, or that it is a more important effect than his (relatively small) range of temperature effects on air density.

  You (and to a lesser extent, Calfornia and other west-coast people) generally have to deal with far more temperature range. Up in the desert, I presume you deal with maybe 45-105 (before you give up and go home) over a few hours. We deal with 55-105 on a regular basis, not quite as bad, and

   Overall you will Get More Power from a suction-fed engine by using thinner fuel, and running it as hot as you can safely get it, because you can handle a larger venturi. It's a similar effect to why you have to run pressure when you have very large venturi, the suction is too low to reliable pull the fuel through the lines and needle, so you have to force it. In that case, and presuming effectively unlimited pressure, you probably *do* Get More Power with colder fuel, just because it is very slightly denser (and A LOT more viscous*).

     Brett

[Jim Hoffman]

For those who care………….

Klotz makes a low viscosity version of Klotz Original Techniplate called KL-198 Lite Techniplate.  I did some very limited experimenting with it a few years back and found no performance differences I could detect in my equipment.

The Klotz spec sheet showed the two oils have essentially identical properties, including flash point, except KL-198 viscosity was much lower.  The Klotz website no longer shows the product tech sheet. I regret not downloading them when they were available.

[Steve Helmick]

Do you have any ideas for getting prop now?

I had some in the past, but it seems to have evaporated.

Propylene Oxide really evaporates quickly, so it's to be expected. A glass whiskey bottle is more suitable than a Mason jar. Small opening, very well sealed. Plastic bottles are not good enough...none of them, because it evaporates right through the pores. Refrigeration helps, of course, but not in the family fridge. With canned or bottled drinks in the garage, I'd say it's ok. Opinions may vary on that, of course. I would personally avoid it altogether. 

P.O. really lights off high % nitro well, but until you get over 60% nitro, you don't need it, because the alcohol does a decent job of that. If you wanted to run 60% nitro and 40% oil, then yeah. George Aldrich's Aeromodeller Annual article on engine rework was excellent, and he said NEVER to use propylene with alcohol in the fuel, because it caused pre-ignition. I think one or two of the Carrier events allow "good fuel", but most everything else is limited to 10% Nitro, right?
  Steve

[Brett Buck]

For those who care………….

Klotz makes a low viscosity version of Klotz Original Techniplate called KL-198 Lite Techniplate.  I did some very limited experimenting with it a few years back and found no performance differences I could detect in my equipment.

   I am using that to doctor my fuel to adjust the degree of break. I normally run Powermaster 10 "Air" (RC AIRcraft/sport fuel) which has 17 or 18% oil content, which we think is 5% castor and 12% some sort of thin synthetic. To reduce the "backoff" at the bottoms of maneuvers, I add up to 5% more of the Light Techniplate. The more oil, the less "backoff" there is, particularly at the bottom of the hourglass. That's what we like about the Powermaster RO-Jett fuel, which had the same thing. I can also run that with no problems. If I add any significant castor instead, I start getting the engine to "load up" on the bottom of the inside round loops. Much more "light techniplate" does not have that problem.

   Of late, I have had no need to do this because I was trying to get more "brake" in particular (after having no end of problems with the engine trying to pile-drive the airplane into the ground in any sort of wind, now corrected with other changes),  but it is a potentially useful thing to know about.

    Brett

[PaulGibeault]

Question - Would keeping fuel on ice in the field give increased performance? I'm running the filter and fuel line through the cramped engine compartment in my current build project. Wondering if this can be mitigated.
Flying in hot conditions brings other challenges too.

To answer the question: YES. For racing purposes at Muncie at 92F over the blacktop. The current AMA Open Class I record that I set in 1999 had my fuel bulb & metal fuel can kept in a ice cooler bag in the pit. I was running a very hot fuel containing 65% nitromethane and 15% propylene oxide. My Cox Venom engine ran particularly fast and stable on that day. It was the hottest outside temp I had experienced & I wanted that Prop. Oxide to stay in the mix & not gas off right away. I never let my fuel bulb touch that hot pavement. I've since flown close to that speed in better weather without having to resort to cooling the fuel. But the bottom line is I've never since gone that fast (at 92F) since.  Cooling the fuel did not hurt my performance in the least.
I don't know how it would work in any other event... Now you know.

Paul Gibeault  National Record Holder

** That's myself with Larry Renger who designed the powerful Cox Venom .049, holding the Bob Fogg version Streaker record holding model.

[Dave Hull]

Just another data point for the fuelies here:

From my testing, I found that adding a Sullivan No. 187 Double Screen filter (2-stage) slowed the flow rate by 35% in a simple gravity fed test when using 5%N--18%Klotz Original Techniplate--77%Methanol at a reference temperature of 130F.

The viscosity curve of this fuel mix is relatively flat, changing about 10% between 130F and the lowest temp that I tested, 60F.

Of course, the filter is an offset to the flow rate with constant suction/pressure at a given temperature, whereas the viscosity change affects flow thru the lines and especially thru the filter.

Dave

[John Carrodus]

Dave Hull
Thanks for that input re the MASSIVE 35% flow reduction through ( that particular ) filter.
Aw gawd- like everything in this game, I ask a question and several more mysteriously pop out of the ether- just when you think I've cracked it - Ahhh - yeah-nah, along comes another joker with a new undeniable truth that completely buggers up the theory I was proudly wrapping my head around. Oh well back to the DB!
Soooo!......New question-

 What variable, oil, nitro, air temp, ( humidity?) tank pressure, flow rate etc etc......
                ............is more important than a fuel filter restrictive factor of 35%?

Logic tells me to eliminate that 35% filter factor But still ensure clean supply to the engine.
So are brass tanks the go? Or are plastic RC type with a high flow fish tank style aerator filter clunk that can be dismantled for cleaning a much better bet? I am aware clunk tanks need special treatment and care, but might bring fewer headaches in many ways.

Somewhere in Stunthangar I read that 90% of engine run problems are fuel supply issues. It certainly seems to be a good rule of thumb.
Cheers
John

[Lauri Malila]

Just another data point for the fuelies here:

From my testing, I found that adding a Sullivan No. 187 Double Screen filter (2-stage) slowed the flow rate by 35% in a simple gravity fed test when using 5%N--18%Klotz Original Techniplate--77%Methanol at a reference temperature of 130F.

The viscosity curve of this fuel mix is relatively flat, changing about 10% between 130F and the lowest temp that I tested, 60F.

Of course, the filter is an offset to the flow rate with constant suction/pressure at a given temperature, whereas the viscosity change affects flow thru the lines and especially thru the filter.

Dave,

At what flow rate did you do your measurement? I'm looking at a fuel flow of about 0,28ml/second, and I guess Brett likes it about double of that. I can guarantee you that with my consumption, there is no difference in needle setting if I use a filter or not.
But with small consumption engines there are other reasons why the very filter you mentioned (I guess you're talking about the transparent Sullivan CrapTrap..?) should not be used. L