Does anyone here have any experience with the Cox Dragonfly .049 engine? I have one and I was thinking about putting it on a Mini Telemaster and was wondering about how long a flight time I could expect.

Also, would this engine work with a 7" prop?

Any ideas?

Thanks

Anyone???

Sorry dude, not familiar with that particular Cox engine. If it has the 8cc tank on the back it'll give you a couple-to-three minutes run time. The black cox 5x3 is always a fine choice for making good use of .049. There are those that "texaco" them. Using more head shims and lower nitro give longer run times and allow the use of larger diameter props. (at reduced power and rpms)

The Dragonfly was the .049 with the biggger plastic "clunk" tank, and the muffler/throttle
sleeve combo. Nice little motor all in all, but just a standard "product" type engine
cyl/piston wise. I always used a MA 6x3 with mine. I have several, I like em'!
Quiet, easy runners, with throttle.
The early early version had the cast crankcase, later ones were std. issue reed valve ones.
I think the early ones had a white tank, black ones later on.
Dave

Thanks for the info, guys. Yes, it has a black tank.

Any ideas about how large a prop I could swing?

Do I HAVE to use a 100% castor fuel?

Thanks.
Wren

Everyone here is gonna recommend high nitro and high castor % fuel... the only other reference I have is the white tank was the "ranger" model and the black tank is the dragonfly per the 1990-96 catologs I have , I have a 6 x 3 on mine..Dont see anything on the actual tank size for them, but it is larger than the blackwidow......Rog

[quote]WrenWright
<Any ideas about how large a prop I could swing?>

I wonder if you're really asking the question you want answered? If you treat, and tune, the Dragonfly like a Texaco engine as suggested by ptulmer then you can swing up to an 8" prop on a practical basis. But then you must fly the airplane as a Texaco time endurance competition model would be flown, i.e.: slow and gentle climb to speck-out altitude in order to maximize time aloft. If that is truly what you want to do then both engine and model should lend themselves well to the effort. A carefully tuned Texaco engine with the large tank, running a wide-blade 8" prop will easily exceed 5 minutes run time so the larger tank on the Dragonfly could concievably provide near 10 minutes of mild-mannered run. But since even the standard Texaco tank will take a model higher than it can be seen I'm afraid I see no great benefit in a longer run.
But if you are under the impression that a bigger prop will generate more power for high speed or high thrust applications then you are setting yourself up for disappointment. Ultimately no matter the size of the prop you have only so much power to turn it. Or, in old hot-rodder parlance: "There ain't no replacement for displacement".
If Texaco type performance as described is what you seek then you should be able to find reams of information about how to tune the Cox engine on this site with a bit of diligent searhing.

<Do I HAVE to use a 100% castor fuel?>

Only if you want the engine to last.

Dunno if that helps, but there it is. Tom

Tom,
Thanks for the help. Actually, the motor is going on a Mini Telemaster, so I was hoping to be able to swing a 7x3 prop; not a "Texaco" application. I wanted a little more thrust at the expense of some propspeed as this plane is a floater.
The motor does have a throttle and I don't suppose that I'll have to keep it wide open to fly it around. I was just trying to get an idea about runtimes with the thing wide open with the thought that I would throttle back to float around.
Thanks again.
Wren

Wren, you might want to pick up several of the black cox props. Maybe a 5x3,6x3, and a 7x3. Try them all. I found the 5x3 to give the best speed, so step up for lower speed and rpm and slightly higher thrust I keep saying to get the cox props because I've had very good success with them. Heck, I even use them on my Norvels! (BLASPHEMY!!!)
Fine tuning your setup takes time and is rewarding.

I'll see if the LHS has some 7x3 Cox props. If not, I'll try whatever I can find. Again, I was just hoping for a little more thrust.

Any of you guys use the Byron all castor fuel? I spied some at the LHS the other day. I have some older Byron blend fuel that was sold to me a few years ago for the Dragonfly, but I think it's a blend instead of straight castor oil. It's pink in color.

Also, How many rpm's should I expect with a 6x3 prop?

14000-16000

john

14-16K sounds pretty good with a 6x3

Any ideas about a 7x3?

W/W the Dragonfly's I've owned had a relatively large venturi and didn't like big props. You won't get Texaco-like performance with one IMO. Big props/slow speeds need lower compession and small venturis to run decently.

All the ones I have run were very sensitive to needle settings and a pain unless I ran them with a small (5x3) prop....then they'd run OK. A friend tamed his down by stuffing a short piece of med. fuel tubing down the venturi opening to reduce the diameter and increase the suction/fuel draw. Amazingly, it worked pretty well and really helped smooth out the run.

Good luck!

Well, I'll just stick to the 6x3 then. This plane was originally powered with a GWS electric motor and 8x6 prop. It flew pretty well, but I have the motor and I figured that I might as well use it. It'll be fun to fly glow-powered again.

I got 10,000 rpm with a 6x4 prop. I was sort of expecting more rpm, but I'm not really sure. Perhaps a smaller prop would be better.
One thing that I thought was interesting was that the engine would run with the needle valve closed all of the way. Upon inspection, it appeared that the spring the tensions the needle valve gets smaller in diameter and wedges itself between the top of the opening and the bottom of the needle valve shoulder to maybe keep the engine from being run too lean. This one was a new one to me.


Wren

Hate to say it, but I thought that might be the case. Just like my product engines tend to like the 5x3 best also. You could easily double the rpm. You need to get the rpm up to take advantage of the hp. You could try a 6x3. That's 25% less pitch. Quite a different load. Still, I hope you picked up the 5x3 just in case.

APC makes a 6x2 you could try if you wanted to stick with the larger diameter prop.

Wrenwright,try an APC 5.7x3 prop.You will like this particular prop on the Dragon Fly.I have two of these engines and have experimented extensively over the years with different size props.This is the prop that has given me the best "all around" performance.As was mentioned earlier,the Dragon Fly engine is not a powerhouse like a Big Mig .061 a Tee Dee .049 or even a Black Widow but it does have a fairly descent throttle control(for a reed type engine) and a good "stunt" type fuel tank.Try to keep the R.P.M's up a bit with this one as it doesn't like to be bogged down with high pitch or larger diameter props.If your looking for more power out of this engine,try running a Tee Dee .049 glow plug which has a higher compression rate.Easy "screw on" performance improvement.

Wren,


Your DragonFly has some real problems if all it can muster is 10,000rpm. Even with a 6x4 it should be better than that. The muffler/throttle on those are more of a gimick than anything else. Ditch it first, you may well be suprised that the sound is not all that less with the "muffler". I don't know if the Mini Tele is a good match for a Cox reed valve. As you already know it's not the plane to use a small prop on as it needs the thrust only a larger prop can produce hence the 8 incher that you had on it before. Do you know what rpm the e-power was making?

Later,
Tim

It was getting 6000 with the 8x6 APC and electric power.
Perhaps something is wrong with my tach. I'll recheck it.
I'm using Bryron 1/2 fuel 25% nitro.

Wren,

Well the engine should love that fuel. For what it's worth I got 8,600 with a MA 8x4 on a Cox Black Widow running diesel.

Later,
Tim

Tim,
What do you think about the engine still running with the needle valve closed?
What should I be able to get the engine to idle down to?
Thanks.

Wren,

Something is wierd about that needle. Take the spring off of it and put on a piece of fuel line. When the needle is closed all the way the engine should STOP! I wonder if the tip of your needle is snapped off. This would explain two things 1) the reason the engine won't stop with the needle closed and 2) the reason that it's only reving to 10,000rpm due to you not being able to lean the engine out and it's still running rich...just a thought.

Later,
Tim

Tim,
Let me check out the needle's tip being broken. I have an old Black Widow engine from when I wa a kid. I suppose the Dragonfly's needle valve should appear as the BW's does, correct? If the needle valve is broken, where can I get a replacement?
So you recommend using a piece of fuel line in place of the spring?