tewitt1949

I realize this is a loaded question, but just wondering. If you had a Cox TD .049, was taken care of (not abused), with normal flying, and not run in the dirt, and had extra castor oil per gal, any idea how many 2 oz tank flights you could get out of it before it was noticable that it was getting wore out? It seems like we used to get about a season out of a motor. No idea how many flights but quite a few. Thanks Terry

digital_trucker

If you take care of the rod socket on the piston, seems like they oughta last durn near onto forever (with plenty of castor in the go-juice).

Remby

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I keep track of hours per year, and number of good flights. So far , One has over thirth hours, another very close to that number, and others with less than. Total hours on these engines are close to 90 hours total over the last five to seven years. Engines run on 25% niro, with extra castor. I do the devarnish, and after run oil, and clean them after any major crash. All Cox engines here.

The good part is, all are still going strong. The one with the most hours is one of the stronger ones, and it has not slowed down or weakened as far as I can see.

Usally use around 1oz of fuel per flight, so each plane would go around 100+ flights per season. A quart of fuel is around 2.5 hours of flight time.

This should help give you a idea, if I understood what you wanted to know.

tangerine-jack

I've been using the same TD since 1987. I never figured on or logged the flights or hours, but it has been in several airframes and must have a couple hundred flights on it. Is this normal? I don't know, never done any scientific inquiry into the topic. I would think that properly taken care of a TD should last for quite some time, at least long enough for you to feel you got your money's worth.

combatpigg

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I started flying 1/2A combat with TDs about 25 years ago. Bought a batch of 5 engines. With the help of Kustom Kraftsmanship and local gurus [including Larry D] got them all running at 23,000 or better with 5x3 props. Each engine had hundreds of flights, ran with 40% nitro only. Up until just a few years ago I still had a few working specimens of the original 5. It wasn't until I started cutting down props to try to compete with the VAs that these engines started to fail. They will run for years at 24,000 or less...but only for minutes above 25,000 with the stock weight piston. For nearly 20 years all I ran in them was 40% Powermaster topped off with Sig castor and these engines ate a lot of dirt. They also were regularly broken down and cleaned just like you would a hand gun.

tewitt1949

Well it sounds like taking care of them will make them last longer. I will admit, when ours only lasted a season, we misused them. Never cleaned them. If we got dirt in them, go fill them up with fuel, crank them over until they started and the exhaust/castor would flush them out. We knew it wasn't the right thing to do, but back then we were young and didn't care. I don't think anyone reseated the rods. Didn't know about it. Acturally a muffler might help keep dirt out of the piston area, too bad it restricts output. Thanks for your comments. Terry

Remby

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The engines are mostly stock, I use a Medallion Carb setup on mine, like them better.

I keep a log on flights, just for this purpose, to track how long I can use a engine. I even record the break down/cleanings/devarnish , everything I can think of. The flight log tells me if a plane will hold up, how durable it is over another. So far one has over 350+ flights, it just started it's fouth season of flying, well over 40 hours total on the airframe.

Using a higher nitro fuel will cause more heat, and reduce the engines lifetime. I also record the glowheads used, wanted to see what a Galabreath/Nelson would do to a engine, and so far not anything is come up, using 25% nitro.

I started the log in 2001, it's really easy once you get going with it, and it gives the data this post was requesting.

combatpigg

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In the middle of a 5 minute combat match there was never time to do a real good cleaning after a crash. The main concern was to get the engine un-flooded since the bladder continues to empty into the engine after it hits the ground. A couple of shots with a syringe full of fuel to clean off the obvious dirt hanging around and back into the air it went. In practice [sport] flying, more care was taken. The main thing to getting the TDs happy was to lap the cranks to the case for a freewheel fit. This freed up HP and let the engines run harder without run away overheating. The other thing was to get as much compression as possible without burning plugs every run. Mixing and matching pistons is the only way. Replacement P/L sets were often lousy fits.
Burning plugs every 4th or 5th run was considered normal with 40% nitro. Some engines ran best with no head shims, some needed 1, but never needed 2.
We never electric started them or ran bigger than 5x3 props on them, always kept the ball sockets tight, these are some keys to longevity that must be more important than how hard they were ran in terms of rpm. Imagine that only pulling around 6 ozs worth of C/L plane [RTF] instead of having to pull RC duty [pulling around a pound or more] kept these little guys happy too?

Remby

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combatpigg;
You raised a lot of good points. The engine life varies considerably with use. The flying I am doing is sport, just for the fun. I expect the engines will last longer with that in mind.

Have never worked a engine for top H.P. and speed, just work with stock parts mostly, keep them clean and free, always after run them now.

If you are after combat, or even scale, the demands would be higher, heat loads, weight, cooling issues from a tight cowl could lower service life, etc.

It did not matter when Cox was producing millions of engines. Now, what you have is perhaps the best you will be able to find in the future, so take care of them.

Use them, with that in mind, works for me.

combatpigg

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Remby, I get a kick out of telling the story because longevity was the least of our worries. These engines went through hell and for the most part outlasted anything else.

Luna_Rendezvous

I think the key point here is "IF" there looked after/cleaned regularly then yes they will last a long time. Steel wool that cylinder and get that yellowy brown stuff off it is important!

vertical grimmace

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Combatpig is right about the rpm as well. I found that anytime they went over 24,000 they died very soon. I flew combat with mine as well, and found that getting any more rpm than that killed them.
Funny story, I was flying a combat plane one day and the wind came up super strong. Over 30mph I would guess. All I could do was fly a figure eight down wind and ride it out. Well I could hear my engine unloading and revving faster and faster as the engine was doing no work as the speed of the airplane increased. It was going so fast you would have thought a Nelson was on the front of that little 1/2 A. Then all of a sudden it stoppped and off went the prop! A sure sign something broke in the engine. Sure enough the rod broke. That engine sounded as if it had gone over 30,000.

Remby

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I cut the props down to 5.5x3, and run 25% nitro. Thats about it, I am guessing the RPM seldom gets over 22,000, but how would one know when it is in flight?

Hae never broke any engine part from over REVs,but that will most likely change now.

combatpigg

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Well the 24,000 mark is taken on the ground.......figure a little combat plane allows 10% unloading. The actual inflight red line would be that much higher, closer to 27,000 then.

MJD

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If you fly a constant distance from yourself as in a large circle to minimize/eliminate Doppler effect and can identify the pitch of the engine via some tuning aid - a penny whistle, a harmonica, or something of that nature (I am being serious here.. really!) - it is easy to calculate the rpm. Moonlighting as a musician helps [8D]. Get a buddy to film it (for the audio) and figure it out after the flight. You can get pretty darn close.

MJD

flyinrog

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I know I saw this somewhere, didnt they(Cox) hook up a cox .049 engine to a 55 gallon drum and it ran for like 32 days straight?...something like that?...Rog

Mr Cox

I've heard (no pun intended) that audio can be used but there's one thing I don't understand, an engine running at e.g. 20,000 rpm would then do 333 turns per second (i.e. 333 Hz) and this would be a rather low base tone, clearly this is not the case....!?

MJD

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It is, but the sound spectrum from the engine is complex. If two sounds are happening at the same frequency but out of step, you will hear all kinds of higher overtones.

The sound from an engine is composed of many elements - induction noise from the carb which is out of step with the exhaust, prop noise, vibration, the exhaust itself etc. The induction noises etc. that fit between exhaust pulses would result in a strong second harmonic (one octave up) and more that would result in a variety of audible tones above the fundamental related to the rpm.

When you listen to the tone of a piano it has a far cleaner and perhaps less pronounced overtone spectrum than the cacaphony coming from an engine exhaust, and the fundamental is very clear and up front. With a running engine you'll hear a lot of the first and perhaps second harmonics and higher due to induction noises occuring between exhaust pulses, and prop noise - two tips versus one passing the same spot in the air results in a pitch one octave above the fundamental for example - and whatever else.

I just made a spreadsheet with RPM versus frequency and pasted the output here. Note that A 440 is the A above middle C. For those that don't know this, doubling the frequency of any tone results in a tone sounding one octave above, or halving it in a note one octave below. Each note in a chromatic scale varies from the note adjacent to it by 2^(1/12), or about 1.0546. The formula here in the frequency column uses the first A 220 (A 440 being a standard tuning note) and each cell below it is 2^(1/12) x the cell above it.

Pitch Frequency RPM
A 220 13200
Bb 233 13985
B 247 14816
C 262 15698
Db 277 16631
D 294 17620
Eb 311 18668
E 330 19778
F 349 20954
Gb 370 22200
G 392 23520
Ab 415 24918
A 440 26400
Bb 466 27970
B 494 29633
C 523 31395
Db 554 33262
D 587 35240
Eb 622 37335
E 659 39555
F 698 41907
Gb 740 44399
G 784 47039
Ab 831 49837
A 880 52800

If you identify the pitch but the octave is deceiving due to all the noise, reason should prevail. After all you will know whether the rpm is half or twice what it ought to be according to this. IOW if you figure out it is about an F#/Gb, and you have a 5.5-3 on a 1/2A that seems to be running right, you'll know it is 22,200 versus 11,100 or 44,400. Unless you hang out on the extreme speed forum, in which case it will definitely be at least 44,400..

Of course this also explains the octave drop in pitch when you richen up a 2-cycle eninge so that it is 4-cycling, with the dominant exhaust pulses occuring half as often.

MJD

Remby

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I think the engine is always running sharp, never flat.

MJD

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Especially with APC props.

vertical grimmace

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Mine always ran E#. Or is it F flat? Somewhere around there!

MJD

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It's all funny, but it does work if you have no other way to get a check on in flight rpm.

MJD

vertical grimmace

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SO I could check my RPM with my guitar tuner? A = 440 typical tuning on my 6 string and my engine will be turning 26,400 RPM? Wow, now I can consolidate my 2 favorite things: Music and Model airplanes!

MJD

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Mine too. But I'm a trumpet player..

Well, if you can get your engine to play an A above middle C then you get bragging rights on 26K for sure! Me, I'd use a tach. Actually, that's a good idea, I might snag a tuner next time I'm running an engine and see if it locks on.

MJD

Remby

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I have a number of flights on DVD, recorded from a few models. So, if I do take the guitar tuner, and have it listen to the DVD, I can, using the data above, find the in flight RPM?

If so, that is very cool!

And everything I would need is handy.