35% Nitro Fuel

You've posted very little details which makes diagnosing a problem like yours virtually impossible. You also offered no details as to when this occurs, early in the flight, on the ground, etc. What prop are you using and what engine are you using it in? Poor needling characteristics can be associated with many different issues. The needle itself, air leaking around it, air leaking from all items associated with it's path. Have you tried to replace the plug? I mean a brand new not used plug that glows. I personally would also add another head gasket due to the fact that it will also save your plug as 35% can tear them up fairly quickly if you don't have enough head gaskets. As outside air temperature increases so does the need for slightly more nitro, cooler denser air doesn't require more nitro and more nitro can cause erratic running. To provide a better answer, you have a lot of missing information.

Hi Ken
Thanks for the reply. I wanted to get the wheels turning on the information. You have certainly started and showed how little I provided for you. Sorry about that.

The motors are in very nice condition and used hundreds of times. All .049 this time. Most running number 7 cylinders for the Venom touch sure starters. Proven motors. Pistons tight, compression good, I use the hose over the needle valve on all to avoid air leakage with a washer. I use a normal High Comp head from Cox with a single copper gasket and a 6x3 prop. I also use the 3/32 aluminum bent pickup tube with a small hose to connect to the backplate intake to ensure consistent draw on the fuel.

The "strange" occurrence is they start a easy and run fast, then about 10 seconds into the launch (my wife is the expert launcher) then they slightly fan and slow a touch. She richens the mixture a little then is acceptable for launch. The are flying but about a minute into the flight I can hear they are leaningg a touch again. So I was going to continue launching even a touch more rich. But it is overfueled at that point. So bugs me to hear it slightly gurgling early on. Bit maybe it would lean again during flight? I will of course trial and error it but with experts around thought would throw it out there.

Was running Traxxas 33% nitro car fuel with added 10% castor until I got ahold of a quart of Sig 35% that you told me since it has 10% castor and has the Klotz oil as well so didn't add any additional Castor as per your recommendation previously. The Traxxas fuel mix was running very good and consistent. All with identical parameters as described above. Maybe the SIG fuel I got is too old?

Sorry again for the fast question with few details but appreciate the kind reply.

Thanks
Iceberg

I already see some things popping into my head. First, piston tight, compression good. This means that more than likely the engine is over compressed and it by what I read needs more head gaskets. I wouldn't add one, I'd add 2 and work from there. The 6x3 prop is offering too much load. So, you could trim it down a bit and keep working from there or try a 5x3 if you have one. It sounds to me though that a 5.5 x 3 would be better than the full 6".

The 6x3 works well on a standard Babe Bee but anything with dual ports likes to turn up and a smaller prop works better in my experience in control line. More nitro equates to a bigger bang and more rpm's. Your previous fuel might not have been offering the same and the engine was just dialed in correct for it. One sign of over compression that I've witnessed is the glow head continually coming loose. Add the gaskets and check the tightness after a few flights with the additional 2.

Are you running a stunt tank with the up and down filler tubes? Typically these like to be leaned up on the ground, backed off a bit until they start to richen and then launched. Sometimes they will burble a bit for a lap or two and then lean up and jet off like a rocket. This may take a couple of tries to creep up on it. Launching too rich just won't offer the power and then it just stays rich.

Hi Ken
I'll try the extra copper gasket. Yes the head is often slightly loose and I tighten slightly on every flight to make sure. Yes I'm running stunt tanks on most. I have a several refitted Babes with the Venom cylinder and those guys are really impressive. They don't seem to be as touchy as the stunt tank? They rarely play up but I noticed they too were ever so slightly leaning too after about 18 laps they start to flutter a touch but continue around the circle for almost 29 laps before running completely out of the fuel. Those ones do not loosen the head like the stunt tank ones? Is it because heating and cooling is different with the smaller tank?

Thanks I hope to get a few dozen flights tomorrow. I will try many things including smaller prop/copper adding etc and see?

Thank you!
Ice

Your description of how your engine was running was suggestive to me that it was running over compressed. I've seen glow plugs come loose due to over compression. Most times that glow heads loosen is due to having head gaskets in which have been tightened numerous times. Essentially, they're squashed and have no rebound left in them. In a pinch, I've hung them on a x-acto over the range top in the flame and heated them to cherry red and let them air cool. The real remedy to plugs coming loose is to use only new head gaskets. Expansion and contraction generally loosens it one or two times and after that they stay put.

Babe Bee backplates generally have small venturi openings. This usually allows for easier adjustments in terms of needling but the power isn't as much when compared to a stunt tank Black Widow backplate. The larger the intake size, the needling becomes more finicky. Some backplate openings are .093" and this can do some weird things. Leaning more to .080"-.082.

The reason I asked what style tank you were using, I just wanted to know if you were launching too lean. I just wanted to know if you were leaving a little breathing room for the engine run. If launched lean, the engine will go over lean and sag.

Hey Ice! I wish I had a "pitgirl" like you do. That's a match made in heaven! If you need Cox .049 head gaskets.. "Cox International" was advertising a special on head-gaskets that had come from new Sure-Start engines that had not been run.. and had been disassembled for disposition of their separate parts. In fact; "I bought some".. to replace some of my "work-hardened" ones.

BTW.. I use only Sig "Champion" 1/2A glow-fuel in my Cox engines. I have both; Champion "25" and "35".. but the "25" is my go-to fuel. I've always stored it away from sunlight.. and tightly-capped. I like the 6" dia. props too.. but IMHO... if you're running a reed-valve engine.. you don't want to go higher than 2" pitch. The 6" X 3"/6" X 4" props are more suited to the Tee Dee (FRV/high-performance) engines. Try to find some Cox 6" X 2" L/H propellers to try on your 1/2A C/L sport airplanes. You'll need to alert your pitgirl.. so she knows to crank the engine in the opposite direction. The advantages to running a L/H prop are increased line-tension.. due to torque-rolling the model "outer-circle". The Cox PT19 "Flight Trainer" has used the 6" X 2" L/H propeller since the airplane's introduction, to help ensure successful flights.

Good to know that you're flying!

Hi Roddie
Yes my pitgirl is pretty tough to be sure. Even when rainy or below freezing still there!!

I never really have given much thought to LH props for line tension?? I have a couple LH props interested to try them.

I only have Sig 35% so will continue to troubleshoot.

I never put my teedees only once a Medallion to my CL planes although I would like to fit a tank and run 5-8 minutes. Now that would be fun!! Running at 22+ 1000 RPM!!

I'll check I think I do have some new coopers in my kit. Maybe time to change out the copper gaskets. Thanks for the tip.

Thanks bud
Ice

Ice,
See if you can buy a quart (liter?) of straight methanol at your local hardware store. You can use it to dilute that 35% nitro fuel down a bit. This will also stretch your fuel supply out a bit, yet still have the high nitro content fuel for special occasions.

I use a two fuel mix excel spreadsheet to determine how much fuel A to mix with fuel B, with a measures shot of castor oil. The component measures of the fuel does need to be known. For any commercially bought fuel without "the numbers," I assume 1:3 caster to synthetic. At worst, I wind up with a light castor oil to synth mix. I've referenced it before, and in fact, the author has shown up here once or twice before.

Thank you Andy Batts:
http://web2.murraystate.edu/andy.batts/ps/fuel.htm

Hi Jim
Thank you. Will Methyl Hydrate work? I have that now.

Thanks
Iceberg

Ice,
I'm nowhere near being a chemist.
I'm afraid I've never heard of Methyl Hydrate. A quick (and I mean two minutes) Google search leads me to believe they may indeed be one and the same.

https://forums.tdiclub.com/index.php?threads/methanol-vs-methyl-hydrate.86417/

Try it on your worst engine...5 cc of fuel to 5 cc of your stuff will yield 10 cc of 1/2-strength (nitro), and 1/2 oil mix. Add 2 cc of castor to bring the oil back up a bit. Then run a few times and check the glow plug for contaminants. If the first 10 ccs don't cause destruction/contamination, then mix a "legitimate" batch.

Substitute ccs instead of ounces in the formula. That way you are mixing smaller lots. A basic 5 cc or 10 cc syringe ought to take care of business for you. A small plastic cup will let you mix the oil into suspension by adding the fuel and methanol into the oil rather than leaving most of it behind in your measuring cup.

For the calculator, your methanol is 100% meth, 0% nitro, and 0% oil. Use your fuel blender's numbers for the "other fuel," and call the oil 50/50 castor to synth if it isn't specified on the fuel.

Hi Jim
You say not a chemist however sounded pretty awesome too me. Yes I think too that this Methyl Hydrate is Methanol.

I've done a 10% mix for some test runs. That is added 10% Methenol to my 35% nitro fuel. Might add a dash of castor too.

Let's see.

Thanks
Ice

Ihave already done tests with methil hidrate, a kind of antifreeze for diesel trucks I believe I already used it with a mixture of diesel fuel with nitro also wit gasoline that works I have not noted any damage to the engine to make sure I use a max oil Not the best stuff for performance engines it work u can save $$ using this i have Find 4L in canadien tire store cost is low I think I will have to do more testing wit gaz in cars application To se if posible option for cars that run in a lower rpm range

Gentlemen,

I don't fly for points or standings, so mixing fuel is about getting my engines to run well, consistently over the long haul rather than peaked-out for power.
OK, with that disclaimer out of the way...

According to Sig, their 35% is already 20% oil (50/50):
35% Nitromethane
20% Lubricating Oils
(1/2 Castor, 1/2 Klotz)

Iceman, mix your methanol 4 parts to one part castor oil. Then you oils will stay the same across both fuels...no need to doctor the oil.
If you then mix 2 parts Sig to 1 part meth/oil, you will wind up with 1/3rd less nitro for the batch...about 23%.
1 to 1 cuts the nitro in half.

You should be able to do this in such a small scale that you should be able to tweak your fuel in order to minimize engine reconfigurations while maintaining the good performance you seek. Then keep up with your "custom" blend.

Thanks Jim

That is very helpful. I didn't get my dozen flights today only about 4. Wind was above 40mph so called off after fourth flight as don't like it when planes is bobbing around like a cork.

I'm like you Jim. Want best performance day in day out.

Reality appreciate the comments. Will look at and follow.

Thank you!
Ice

So whats the nitro percentage on this stuff? Dosn't say on the can anywhere! KI

If I remember that mix was 20%. I bought those about 45 years ago. But 20% rings a bell. They had higher performance that was 25% I think??
Ice

I have a blue can also...as I recall the orange and white can was higher test than the blue can. I really don't remember...its been awhile!  All my old cans are full ! I opened the blue one last year to fire up some long dormant BabeBees. Fuel is still good after decades of storage!

About 11 years ago got a real nice stunt plane deal from eBay. The pink/ purple plane. Sorry forget name right now. I'm the deal was a tool kit and a can of the orange Cox fuel. Fuel was 30 plus years old and ran first class still!!
Maybe they used lead back then??
Ice

OhBee,
Look left and just under latest topics. Find the INFO section. All of the Cox original blends are posted for your reading pleasure! Look under Cox Related Other Documents for "Glow fuel," "Flight Power fuel," and "Race Power fuel."

Iceberg wrote:About 11 years ago got a real nice stunt plane deal from eBay. The pink/ purple plane. Sorry forget name right now.

The Hyper Viper maybe?

Or maybe the Super Sport Trainer #32...

Hi Balogh
You're right that one Super Sport Trainer #32. You sent me the manual for it last year. Sorry I had just forgot the name.

It flew pretty good. But the balsa stunt planes fly like 10 times better than the rtf plastics.  The plastics are too heavy. But when we were 10 years old the rtf plastic was great because store to flying was like an hour.

Actually my PT-19 I have now is pretty light and flies 7out of 10 for speed and response. Because it is very light even though made out of plastic. I did find though that rubber bands MUST be changed every day never leave for a few days as a couple times wing band broke then motor band broke. Fortunately soft landing and no damage but ALWAYS change rubber bands daily.

Thanks Andras my friend. Hope you can get some flights in with current issues in Hungary!!!

Iceberg

I will say that while reading through the posts many things here I disagree with. Of course these are my beliefs and I can only offer my experiences ans suggestions so take them as you may. Old fuel is good for one thing, running old engines and doing so on a test stand. Don't go out to fly with 20-30 yr old fuel and expect your day to be stellar because it won't be. I've seen this time and time again and just because it makes the engine run, doesn't mean it's perfectly good. This is the same for glow plugs, just because it glows, it's not always good. Put a new one in and reap the benefit. Unfortunately, they're becoming increasingly expensive and now's the time to switch to turbo or Nelson plug adapters and stock up. The initial impact of cost will quickly pay for itself as the current supply of Cox glowheads diminish and costs rise.

            Do with it as you may, there's no need to alter your Sig 35% fuel. It has a proven track record from all levels of flying that places it above and beyond others. It works out of the bottle as intended. You can't offer a 1/2A engine a hot enough fuel and as it stands, 35% nitro is a standard for most that have been in the hobby.

              Keep in mind as the temps increase, so does your need for more nitro. You make more power in the cold and props are more effective in the cold vs the other way around. You can still use the higher nitro but reduce the compression by adding another head gasket if the engine offers signs of being over compressed. The crackle of exhaust note changes as the nitro increases. Lend your ear to the engine and listen for this as you can use it as a tool to define what is actually happening. Not all head gaskets are the same thickness. Know what you have. You may need double the amount because I have head gaskets here that are only .002" thick and some are as thick as .008". Some engines are more critical than others but finding that happy medium can generally be found within a few minutes of testing. Be aware though that higher nitro is also harder on plugs if your deck height is too shallow.


           I also read the regards to the 6x2 prop. I personally dislike that prop as I find it to do nothing but beat air. That's what it was designed to do. It's a beginner prop for a new learner designed to not offer speed so one can get the hang of flying the model at extremely and barely stable speeds. So if this is your style of flying, I would say by all means use it. If you use the 6x2 prop and you use 35% nitro it will send the rpm's way above the engines torque curve it was designed to run in. The prop could easily increase the rpm's 500-700 and the additional nitro could possibly add that much as well. While it's been stated it adds line tension, I will quickly dispute that as well.

           Line tension issues that are low are generally a result of the plane not built correctly. This can be several issues one mainly being a warp in the wing that most never even see. This is easily built into a wing especially a open framed wing and it can happen to a sheet wing. The next problem is rudder offset. I say this time and time again and I still see many offering advice to put it in. One, you don't need a rudder. This is a piece of wood on a 1/2A that's decoration, when you offset it to the side it doesn't make the plane fly better. It makes it worse however, not only do I see it still being used, the myth that it provides line tension is just that. It detracts line tension yet it still is used.

              Speed is what offers line tension, you need to get the plane to speed as quickly as possible and maintain that speed. Rudder offset provides drag, drag reduces speed. Rudder offset makes the plane fly yawed to the circle, yawing the plane exposes the inboard side of the fuse to the airstream creating further drag. You want the plane to fly tangent to the circle. What many don't realize is that this also impacts where the fuel is inside the tank, therefore the fuel isn't always where it's supposed to be nearing the end of the run and the engine begins to suffer fuel starvation. The end result is your not using all of your fuel up and your not getting a good engine run. So what was deemed to be used as a tool for generating line tension ends up crippling performance.

            Next is engine offset, totally not needed and it can also offer similar problems as I mentioned above. However, canting the engine two -3 degrees to the side on a beam mounted engine can also be used as a way to assist fuel draw as it tends to help line up the spraybar centerline with the pickup of the tank. It may not entirely place the centerline inline but anything one can do to get the pickup centerline as close to the spraybar inlet or centerline is always helpful. This is what makes full bodied planes work better than profiles. The tank is directly behind the engine therefore unlike a profile which essentially has to overcome centrifugal force and make the fuel travel further, it runs better.

            Line rake is the next adjustment that is always questioned. While it's been said to hang it by the leadouts and insure that the nose is pointed downwards, that's not always true. You need to fly the plane. While sweeping the leadouts back offers more line tension, it only does that in level flight. As soon as you pull the plane into a wingover, you now lose line tension because you strangled the plane due to yawing it out too much. Once again, speed creates line tension. You don't maintain the speed, you lose line tension. This is why you don't want to use a high pitch prop in control line. It goes like stink in level flight offering lots of tension but when you pull it into a manuever it loads the engine too much killing off speed. The engine can't go uphill in 4th gear, it needs to be downshifted into 2nd.

       Some might read this and say what is all this mumbo jumbo but actually some of the runs that I read about can be diagnosed as a result of what I've typed on here. Again, these are my experiences with control line. I have done much experimenting over the years but as it was said to me early on, watch the guy with the good engine runs. What does he use for props? What fuel does he use? Why does his plane fly better than the rest?