Timmer01

how long can i run a fox 46bb wide open fully leaned out turning as hard as it can? i have some castor oil in the fuel and 10% nitro. (added some castor, so i know there is more than 20%) it will be swinging a 10X6 APC. im talking, like, a hour, non stop?

Gizmo-RCU

My Feedback: (27)

I guess this might be a dumb question on my part, why would you want to distroy a good engine? The only way to tell is by doing it I guess, but it won't prove much except how that individual engine held up in your very basic test?
Let us know the out come.

Timmer01

i dont mean run till it gives up. i dont want to hurt the engine. i mean befor it does damage. if its got proper lube, not ran lean, not over speed with too small of a prop, what would it hurt? couldent wear it out, not a fox.........

on pipe

I read somewhere that when testing engines, Duke would hook them up to a 55 gallon drum of fuel, start them, and walk away for the rest of the day. If it was tuned correctly it would probably run for days, or until the fuel ran out. Usually most wear occurs on start up, and before the engine gets up to operating temperature... Ross

DarZeelon

Tim, Bruce,


Running an engine at full-bore, peaked out, is a steady-state condition.

I.e. nothing should be changing as the time accumulates... The engine's individual part temperatures should not be changing noticeably and neither should the glow-element temperature and the combustion characteristics.
Compression remains the same, as do the forces applied to the piston, the con-rod, the cylinder and the head...


Some full-size car engines do "develop" detonation over time, which means combustion characteristics do change over time in them... However, this happens over seconds of full-bore running; not over minutes, or hours. I.e. the engine initially runs normally, but begins to 'ping' after a number of seconds at this setting.

It is very different from what happens in a model glow engine.


However, even though this is also true for full size piston and turbine engines, rotor-gearboxes, Etc., their manufacturers do have time-limits imposed on being run at full take-off power (and some also for intermediate power settings).
The only 'no time limit', steady state settings they advertise are various cruise outputs.

I guess, at least for some engines, that take-off power causes a much faster metal fatigue accumulation, since both the amplitude and the CPS (cycles per second) are at their highest. The forces applied to the parts are much closer to their maximum design strength.

This, however, applies mostly to reciprocating engines, yet turbines (for which only ultimate part strength applies) also have such time limits.


However, racing .40 engines (pylon engines of all types) use the same basic parts (same sizes and materials), yet they do run full-bore at a much higher 28,000-32,000 RPM, all flight long. Despite this, they rarely blow a rod, shear the crank, crack the piston, fragment a bearing, or 'blow the jug'...

This Fox of yours will be around half the RPM, compared to a racing engine (lower CPS), making significantly less torque (a lower amplitude) and has virtually the same part strength. I guess the only way for you to know, is to use a 55 gallon drum for a fuel tank and constant pressure fuel-feed (so the engine could not go lean) and just run it until it explodes...

In the case of your Fox, I guess you may need to refill that fuel drum, after it exhausts its capacity...

EDIT: Typo.

Gizmo-RCU

My Feedback: (27)

Remember, you said fully leaned out........That means deadsticks and cooked motors? At least to me? Set it right and like Dar says it will go longer than you have fuel for.

Timmer01

yea, i didnt mean overly lean. i mean leaned to peak rpm. rich enough to not sag after it gets hot. max rpm, not max melt down.

did Duke run them WFO? (wide freaking open) or 65%?

and this would be on the ground in a test stand. not flying.

DarZeelon

Quote:

ORIGINAL: Timmer01


...Did Duke run them WFO? (wide freaking open) or 65%?

...And this would be on the ground, on a test stand; not flying.

Tim,


The Fox .35 [link=http://craftsmanshipmuseum.com/Fox.htm]Duke Fox[/link] had used is a control-line stunt engine, which does not have a throttle, so it cannot be throttled down...

However, for this test, he may have run it at a four-cycling mixture setting (where it would break into a two-cycle in maneuvers and back to four-cycle, when it returned to level flight), as one would set-up any control-line stunt engine for flight.


If he did, it would have been ~65% power... But since Duke Fox had passed on in 1991, I think there is no-one you can ask...

Lou Crane

Tim,

Another consideration is the metal make-up of the cylinder and piston...

Many/most Fox engines are cast-iron piston in steel cylinder designs. It has generally been long accepted that this combination lasts best on fuel with at least 23%-25% castor oil content - AFTER a good break-in. More castor % early-on...

Some Foxes are ABC (Aluminum piston in Chromed Brass cylinder.) These are the metals used in most recently designed engines. Too much castor is NOT desirable with ABC, AAC (chromed aluminum sleeve) or ABN (Nickel-coated brass sleeve) engines. The A** cylinders are cut with a taper that expands to the intended running fit at operating temperatures. That's why they 'pinch' when you pull them through TDC when new...

Castor oil doesn't burn at engine operating temperatures, and is good at holding heat and carrying it - physically - out the exhaust port. It is also capable of forming a layer of varnish on the piston and sleeve sliding surfaces. This works better with the iron pistons, as the varnish is mostly driven into the porous iron, and incidentally serves to maintain a nice runnng clearance over time.

Castor is NOT GOOD, for that reason, as the only oil in fuel for A** engines. Synthetic oils are generally detergent: they clean the metal as they lubricate it. That works better with the intentional taper cut into the chromed or nickeled sleeve engines; a coating of varnish can change dimensions and cooling characteristics enough that the intended hot fit may not happen.

So, if your 46BB is either iron lapped piston or iron ring type, in an unplated steel sleeve, you might do better with 15%-20% (or a bit more) of the fuel as castor, and the rest synthetic. If the 46BB is ABC (Fox doesn't do AAC or ABN, but they offer a new ceramic setup on one or two engines recently...) then a "standard" sport RC 10-10-10 fuel should work well (That's 10% each, castor, synthetic, nitro.)

Your initial post DID sound like you were trying a destruction test... As Dar detailed, your engine is sturdy and should howl at a prodigious rate for a good long time, if used as you posted a bit later - backed off a bit from melt-down-city. The oil thoughts might save a good iron engine from premature wear - the castor effects extend their useful life. If it is an ABC, too much castor in the fuel may adversely affect durability.

Happy howling! ...and if anything does wear out, Fox mfg has an excellent repair/replacement policy.

DarZeelon

Quote:

ORIGINAL: Lou Crane

Castor is NOT GOOD, for that reason, as the only oil in fuel for A** engines. Synthetic oils are generally detergent: they clean the metal as they lubricate it. That works better with the intentional taper cut into the chromed or nickeled sleeve engines; a coating of varnish can change dimensions and cooling characteristics enough that the intended hot fit may not happen.

Lou,


I cannot agree with this statement.

Some engine manufacturers have always subscribed ALL castor oil for all their ABC (and other) engines.

Such are MVVS and Sanye (Magnum, ASP, SC, SY...), for example.


I have seen no ill effect to running all degummed castor oil in any engine; both for break-in (for which even more manufacturers subscribe all castor oil) and for general running.


Before synthetic oils became widely available, all engines were run on all-castor and some were indeed ABC, since this setup was introduced in the 1968 Super Tigre G.60R engine. ABC/ABN/AAC engines have since become the norm, rather than the exception.

I don't think any problem was encountered as a result, or no manufacturer would have instructed everyone to use all castor oil lubricated fuel.

downunder

Actually it was introduced with their .15 CL FAI speed engine to overcome the heat problems with the original cast iron pistons. The ABC set up then gave a stable setting for the entire flight (short but furious ).

Castor has no bad affects on ABC/AAC/whatever engines because that's all I use in all my engines, both CL and RC, and none have shown any signs of wearing out.

As for the Duke Fox test, I don't recall any mention of how it was tuned although several years ago the story was related over in SSW by someone who worked at the Fox factory and actually witnessed the test. The test was terminated at 2000 hours because there was no evidence of any wear. The fuel of course would have been Fox's special 29% castor specifically made for the .35. Another test on the same (or similar) engine using normal RC fuel destroyed it within minutes.

DarZeelon

Quote:

ORIGINAL: downunder

Quote:

ORIGINAL: DarZeelon
Before synthetic oils became widely available, all engines were run on all-castor and some were indeed ABC, since this setup was introduced in the 1968 Super Tigre G.60R engine.

Actually it was introduced with their .15 CL FAI speed engine to overcome the heat problems with the original cast iron pistons. The ABC set up then gave a stable setting for the entire flight (short but furious ).

Brian,


I don't know everything... I admit this. So, if there is something I must find out about, I search the Internet...

You will have to take it up with Dave Gierke, as appears in [link=http://findarticles.com/p/articles/mi_qa3819/is_199912/ai_n8855982/pg_6]this MAN article[/link].


In this case, I just quoted what this person had written.

Lou Crane

Dar and Downunder, thanks for the points posted!

There are a few manufacturers who specifically state in their instructions that their engine does best on 0% castor, all-synthetic oil. (I think it was SAITO 4-cycles?, or at least some of their types?) These are not, however, high-volume production, low/moderate cost engines. On one or two USA sites, there's been discussion about these engines, and problems solved when a few users forced themselves to try all-synthetic... Exceptions prove?

Dar, I agree that some castor is no threat to recently developed mass-produced engines in most usage conditions, so long as there is ample synthetic to prevent possible varnishing complications.

As to the introduction of synthetic oils to the general (USA) market, I think K&B's 100, 500 and possibly 1000 were offered in the 1975-77 time frame either with castor or with "X2C" - a clear synthetic lube of some kind - as either all or a major part of the oil fraction. Many nicely varnished iron in steel engines run on X2C fuels lost that coating, and there was much discussion of the fuel ruining many engines. Racers, of course, had been using UCON (the staining blue stuff) for a few years by then, with varying results. Where the very first application of tapered-sleeve, aluminum piston engines was done? - I'll rely on those who know the facts. BTW, do the mfrs still cut the pistons non-round to work with the uneven cooling from port exposure (bypasses: cold, exhaust:hot) and from different cooling metal mass as in the piston pin supports?)

Later, I'd read of CL racing and combat fliers having problems with dependable needle setting for a full flight with all-synthetic oil. Frequently offered solution was to be sure there was 3%-5% castor. Later, there was a scare about the quality of castor oil. I think that's been discussed thoroughly in this site...

Going back to Dave Gierke's series on model engine testing (Flying Models magazine, 1970's) for a moment. Sure, that's 30+ years ago, and some synthetic oils have vastly improved over time. When Dave G tested the available oils for burning temperature and ash production, he found that castor does, indeed, remain "usefully intact" at the highest operating head temperatures, thus does carry heat out the exhaust on the heated droplets. Synthetics can burn away at such temperatures - or could then - ADDING to engine heat, and NOT contributing to cooling.

Also note, for most A** engines nowadays, that I've handled anyway, IF the mfr provides a decent operator manual (not always the case), it is either explicitly spelled out, or can be found in the "break-in" notes if you look sharply: Do not try to break these engines in by slow, rich running. Most Op Manuals I've looked at suggest several brief runs in moderate 2-cycle so the engine reaches intended temperatures. With a good cool-down between runs (occasionally mentioned as for heat-cycling to relieve machining stresses - which some in here point out isn't fully applicable for brass and high silicon aluminum...). There are usually also warnings NOT to force the engines through the TDC 'squeak' unnecesarily, as that can cause damage to the intended fit at operating temperatures.

Slow, rich, cool running has worked well for ferrous metal engines for a long time, as the metals expand less on heating, and for certain steels, machining stresses do need to be relieved. ST G21 series CL engines are good examples. Magazine columnists, here in USA, discussed 'baking' the sleeve and piston (separated, of course) for a certain time and temperature to "grow back" to unstressed dimensions, then hand lapping to fit BEFORE running the engines. The alternative break-in was described as requiring considerable time before the engine was ready for CL combat or racing, and as being a considerable load on the connecting rod...

Anyway, I always value your contributions to this and other engine related forums (fora? - no that's a brand name.) I'll agree to differ, occasionally, when I think I should, and hope you will continue doing the same. I've learned a lot I could never find elsewhere!

DarZeelon

Lou,


Thank you for elaborating on this issue.

As to Saito and four-stroke engines in general, their very high exhaust gas temperature (compared to two-stroke engines), creates a deposit that badly cakes and fouls the valves.

YS engines also have the fuel system components and diaphragms that are susceptible to sticking, if castor oil is left to dry on them.

These are the reasons some of the manufacturers advocate the use of all-synth fuels only...
...And then there are Sanye (ASP, Magnum, SC,SY) four-strokes, for which all-castor is the subscribed fuel...

As far as engine protection is concerned; a synthetic lubricant that can protect an engine better at high temperature, has yet to be invented.


As to the plural form of 'forum'; I believe 'fora' is acceptable, as is 'forums'... I prefer the former, as does Dave Hobbs...
...And English isn't even supposed to be my mother tongue - Hebrew is...

There are other words...You will not hear the word 'viri', even though it is the correct Latin plural form of 'virus'... People use 'viruses' instead... You can read about this [link=http://web.utk.edu/~hirst/460/nouns.html]right here[/link].

jessiej

Sad to say Dar, these fora provide plenty of evidence that many who have English as their mother tongue know little of it.

jess

downunder

Let me go a little further on the subject of running an engine hard. The car guys seem to have never ending problems with broken or worn out rods and bearings. Most appear to be happy if they get 10 hours of running before buying a new engine. So my son decides to get into cars and asks me what fuel to use so I say let's use our normal plane fuel, true FAI or 80/20 all castor. OK, so we run it in my way (4 stroking at full throttle doing huge figure 8's then slowly leaning it out for about 40 minutes) then he goes racing. With much raised compression it goes as hard as the others using 25% nitro and peak revs were a little over 36,000 on a short straight.

After 40 hours of running (and one plug change) he asked me to check it out. The bearings were as new, the rod had .001" ovality at the big end and no detectable play at all at the rod/piston fit. The piston/liner fit wasn't great so that needs to be changed. I guess the moral to the story is that you can run an engine hard for quite a long time so long as you use a decent oil and enough of it.

PS (and here's the edit )
Fora (capital F) are an extremely good high performance engine so I suppose fora (small s) is ok as a plural .

rainedave

My Feedback: (1)

So, what's the plural of Kaos? In Greek, nouns ending in "os" are typically made plural by changing the "s" to an "i" so that would mean Kaoi can refer to two or more Kaos models.

David

XJet

Indeed an interesting discussion...

I think that if he'd conducted those tests today with more modern synthetics he might have been in for a surprise.

My own testing clearly shows that some synthetics appear to have a *greater* cooling effect than castor.

How can the do this?

Well while castor is busy breaking down into a sticky mess or being expelled from the engine as a droplet, *advanced* modern synthetics absorb an incredible amount of that heat through the latent heat of vaporization.

A drop of castor carries far less heat energy with it than a drop of advanced synthetic does as it undergoes phase change from liquid to gas.

I've performed and documented some *very* interesting tests by heating small carefully measured quantities of castor, Morgans and Klotz (PAG-based) and Coopers (Ester-based) oils to very high temperatures.

Now if they simply flashed away in the blink of an eye and left the metal surfaces unprotected there'd be a problem however, it appears that when I heat 5ml of castor and 5ml of advanced synthetic to precisely the same temperatures, the more *advanced* synth takes far longer to boil away than you'd think. Indeed, the castor congeals into a nasty tar-like substance long before even *half* the volume of the synth has boiled off.

Why is that?

Because as the synth is undergoing a phase-change, it is absorbing a huge amount of the heat. No such heat-absorption occurs with the castor so it gets hotter quicker and polymerizes into tar while the synth is still there providing liquid lubrication.

As soon as I get the time I'll publish the results, but suffice to say that some (but not all) modern synths are *much* better than the old ones and that there's more to high-temperature engine protection than just the boiling/flash-point of the oil being used.

And to put this to a real-world test, I took a modern .52-sized ABC 2-stroke engine, mixed up some fuel with 5% nitro and 12% advanced synth (no castor) then tuned the engine so lean that it was sagging badly when the nose of the model was held vertical.

I flew several long, hard full-throttle flights with that model (using over a liter of fuel) in an exercise designed to see how much damage would be caused by overheating and resultant failure of the oil film.

On inspection there was *no* piston scuffing, no measurable ovalling or wear on the big-end and the tach showed there was no loss of performance. I was very impressed.

So it would appear that we must treat some of this older research with a little caution some 30+ years down the track and realize that in some (but not all) cases, synthetic model oils are vastly superior to what we used to have and that while Castor is an absolutely amazing natural product (which I use a small percentage of in all my fuels), synth doesn't necessarily mean inferior.

The reason I use a little castor is primarily for corrosion protection and because I believe that the ultimate film-strength of castor is higher than even the best synthetics although that's something I'm about to test shortly.

Timmer01

so you think it will run for a short time before it starts to hurt ites self.

DarZeelon

Quote:

Original: downunder

...I say let's use our normal plane fuel, true FAI or 80/20 all castor. OK, so we run it in my way (4 stroking at full throttle doing huge figure 8's then slowly leaning it out for about 40 minutes) ...



Fora (capital F) are an extremely good high performance engine so I suppose fora (small s) is OK as a plural .

What's with you, Brian?

Are you again not bothering to follow my procedure [>:]? Why don't you get a hold of yourself?


Compared to the 3-4 gallon P+L life, some users are getting with a very rich break-in on low-oil, higher nitro fuel, I must say the 40 hours you observed is quite reasonable...

However, I believe this term could have been significantly longer, had you done the break-in at a somewhat leaner mixture setting (i.e. at a rich two-cycle setting), using a 25/75 castor/methanol fuel mix (or maybe even 29% castor oil, like the Fox .35 fuel).

The increased oil content would have successfully protected the con-rod bushings, at least to the same degree as the richer running procedure you followed.

AND

...the P+L would have been running at optimum temperature, for a more perfect mating.


As to the English issue... I don't think 'sora' (that is what you implied, before re-editing...) is quite the correct plural form of 'forum'... Gotcha!

XJet

I don't think I understand what you're asking.

XJet

I agree Dar.. it looks as if all that cold running has severely reduced the P/L life compared to what it could have been.

Remember that the P/L interface actually doesn't need or benefit from a lot of oil we have 2-stroke engines that will run happily on 100:1 fuel/oil ratios so even 10:1 is *plenty* for the piston/liner in a model-sized 2-stroke. It's been traditional to run more because we have bushed conrods and not roller-bearings.

Running an ABC engine cold does nothing but wear the piston down prematurely and place excessive stress on the crankpin and conrod (for so long as the pinch remains which might not be long if run cold for too long).

Dar's guidelines for the breakin of an ABC are right on the money and although I know Brian has run tapered-bore engines at a rich 4-stroke without producing any damage, it's clear that this is *not* a desirable practice and just because damage didn't occur in his tests doesn't mean it won't occur on other occasions.

downunder

Then I guess I'm safe in saying that just because damage didn't occur in your oil tests this doesn't mean it won't occur on other occasions .

Lou Crane

XJet,

Thanks for your report on the latent heat of vaporization comparisons! Fascinating! None of the following is intended as an attack on your revelations, but as an honest quest for further understanding of complex happenings in such brief times...

An off-the-wall question: How did the temperature you used compare to the 450°F-510°F range Dave Gierke found at the head fins of his test engine, an ST (?G21/?) 40? BTW, he took his readings when the engine was running well-peaked and steady - they were not flash readings, as I recall.

Did your tests consider the extremely brief duration of oil's exposure to the max temperature indirectly read outside the chamber, i.e., at the head fins?

Example: At 15,000 RPM, we have 250 revs/second, or 0.004 sec/rev. The power stroke takes a bit over 90° shaft rotation prior to exhaust port opening.That would be 0.001 sec duration. Not all of the combustion stroke is at optimum-burn conditions as piston motion increases the volume and reduces the imposed compression. I wonder how well the burn expansion maintains compression for efficient burn. Personal opinion - based on charring trace in a 'small-bubble squish band head' engine - is that the optimum conditions do not last very much of the entire stroke. That engine charred only inside the bubble; the (flat) squish land took NO coloration. That's an extreme example, but if the optimum burn conditions endure for 10° shaft rotation, the time available is only 0.00011... seconds, in our hypothetical 15K example. And, with the increasing volume above the descending piston being no longer optimal, the temperature may well fall rapidly below the momentary peak, even if still high enough for productive power output...

Or is that relevant? We can pass our fingers through the hottest point of a candle flame without injury for several reasons, if we do not delay the motion. (Skin moisture, delay in nerves sensing heat, time rate of heat rise on the skin surface, etc.) Is there such an influence on converting the oils in the manners you describe?

I hadn't considered the heat absorption needed to vaporize synthetics, thanks for that! Do they then burn, or pass through the exhaust as vapor? Or is there a way to determine that? IF they do burn, is there a way to compare the resulting combustion heat contribution and the phase-change heat loss? I suspect that they do burn, as very little exhaust oil coats models, run with mostly-synthetic RC general use fuels, used in typical fashion.

I am not concerned about lubrication if they do burn, on the down-stroke. Then, burning is exposed to the piston head, cylinder head and newly uncovered cylinder walls as the piston descends. The moving contact surfaces - piston skirt and still-covered sleeve walls - should still have an oil film between them. The upper cylinder is then freshly re-lubricated by the incoming charge to be compressed for the next combustion, thus the up-stroke will be pretty provided.

Sorry to have tossed in that forum/fora comment: It was intended to be a joke...

XJet

We're all learning and I welcome input, challenge, comment of all kinds it's the best way to learn ;-)

I performed the test at a range of temperatures from 150 deg C through to (from memory) 300 deg C

No, my test was basically to see how the oils stood up under extreme temperature. The commonly touted belief is that synthetics burn or boil away leaving an engine unprotected while castor remains or polymerizes to provide greater protection.

Given the quite significant time taken for the higher-quality synths to actually vaporize, I believe that loss of protection due to this flashing of oil to vapor is not the issue some might believe. Even if the piston/liner has reached such extreme temps, the constant replenishing of the oil-supply with each stroke would seem to be adequate to provide protection.

I have more testing to do on that. I do know that no matter *how* lean I ran the engine I used in torture testing the best synth I tried, there was always *oil* residue in the exhaust, even with the oil volume at 12%. So while there's almost certainly some vaporization, there's obviously still a good deal of oil passing through in liquid form.

I didn't test to see at what temperature the oil might ignite (there was no ignition of any of the oils in my test but there was also no exposure to a naked flame). I'll see if I can get the vapor to ignite next time I run the tests.

Hey, nobody said we had to be serious all the time did they? :-)