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"newbie" prop question

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"newbie" prop question

Old 01-26-2009, 11:52 PM
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Sandore
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Default "newbie" prop question

Hi All,

I have a Dynaflite Piece O' Cake that had a Black Widow .049 on it that I bought & built 20+ years ago. I broke the engine in back then, possibly didn't apply proper after-run lube, but when I finally dusted that plane off to fly it recently I can't get the Cox running right. Probably has an air leak, which I will continue to work on, but after trying a few things to get it running with no success, I ordered a new .049 OK Cub engine. I broke this engine in, then cleaned it up, screwed on the 6x3 prop from the Black Widow and headed to the flying field. Started the engine, peaked it, and hand launched the piece o' cake. It was a very calm day, and I had to fight to get the plane to 20-30 feet of altitude! I tried a few more times, seeing if I could tune a few more rpm, but it wasn't until the wind picked up a little that I was able to gain altitude to fly for a few minutes.
So, I'm no expert but I think the plane is under powered. I emailed OK Engines and they confirmed that the Cub is not as powerful/high rpm of an engine as the Cox.

Now to my question: To try to correct the situation I described (where the plane will just maintain altitude with no wind), do I need more rpm with a smaller od prop and or shallower pitch, or should I try a larger od and or larger pitch prop turning at lower rpm?

Other things I am thinking of trying is the OK Cub .06 engine, which I would hope although being heavier would have more torque to swing more prop. Of course making the plane lighter would help, but the only way I can think of to do that is to go with smaller radio gear & less battery.

Any thoughts/ideas would be appreciated.
Old 01-27-2009, 12:11 AM
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Default RE: "newbie" prop question

I've never run a OK CUB, but 30% nitro fuel with castor oil could help. You might find that the CUB can put out more thrust with a different prop, like a 6x2, 5x3, 7x3, who knows except a CUB expert? There are still a few CUB runners out there.....Doug Galbreath sells specialty model supplies and he's listed under his name on the internet.
Old 01-27-2009, 12:36 AM
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Default RE: "newbie" prop question

cough up for a TD .049 they work great and are light weight.
Old 01-27-2009, 01:04 AM
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Default RE: "newbie" prop question

Hey Sandore...where do you fly? You're only a few miles from me...
Old 01-27-2009, 07:30 AM
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Default RE: "newbie" prop question


ORIGINAL: Sandore

Hi All,

I have a Dynaflite Piece O' Cake that had a Black Widow .049 on it that I bought & built 20+ years ago. I broke the engine in back then, possibly didn't apply proper after-run lube, but when I finally dusted that plane off to fly it recently I can't get the Cox running right. Probably has an air leak, which I will continue to work on, but after trying a few things to get it running with no success, I ordered a new .049 OK Cub engine.
Any thoughts/ideas would be appreciated.
Problem = lack of horsepower from anemic .049 OK Cub engine.

Myself, I'd get that BW running right before ordering anything else. Maybe Proptop has the magic pill in terms of the standard anti-leak remedies to apply to reedies.

MJD
Old 01-27-2009, 10:35 AM
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Default RE: "newbie" prop question

I was thinking the same thing...get the Black Widow running again.
Might be it just needs a new tank O ring?
Old 01-27-2009, 11:04 AM
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gabe200
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Default RE: "newbie" prop question

im using a sure start on my glider is 78 inch wing span i have no problem getting the glider to altitude the ok cub is short on power im using full size servos and a large rx pack
Old 01-27-2009, 11:35 AM
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Default RE: "newbie" prop question


ORIGINAL: gabe200

im using a sure start on my glider is 78 inch wing span i have no problem getting the glider to altitude the ok cub is short on power im using full size servos and a large rx pack
A good Cox should haul a 6 foot glider* just fine. The only time I saw one that wouldn't was at 6000' with a Queen Bee. But I did say "a good Cox".

* a typical 6 foot-ish gas bag glider that is - Gentle Lady, PoC, whatever.
Old 01-27-2009, 01:17 PM
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Sandore
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Default RE: "newbie" prop question

Everyone, thanks a lot for all of the various info & advice. I'm going to stay on the OK Cub path for the time being for several reasons:
1. The cub is new and it runs, as compared to my 20+ year old BW.
2. The cub uses a regular glow plug, so I can clip a regular glow plug driver onto it. I fried the original glow head on my BW, so (don't laugh) I drilled it & tapped it to accept a regular glow plug. I have no idea if the combustion chamber is now too big or too small (I machined it so the piston just doesn't hit the idle bar on the glow plug if 1 copper head gasket is installed). When I get the time to mess with the BW some more, I will try to find a replacement original type glow head for it before I experiment any more with my frankenstein head. Or maybe I'll buy a commercially available glow plug conversion head. I don't have an old style glow head clip any more.
3. The cub is made pretty close to where I live, so I get some satisfaction from lending a little support to a local business.

I was hoping that someone has some experience with various prop combos with the modern cub 049, so I will try to look up Doug Galbreath to see if he can shed any light. I suppose I should buy a tach so when I do get to experimenting I can at least measure the results.

I did try 20% (recommended by OK Engines) and 30% both with some castor added. I think I could hear a difference with the 30%, and I think I was using the 30% when the wind picked up to help me gain altitude.

A couple of guys I work with suggested the tank O ring on the BW. I tried shaving off a very thin piece of fuel tubing to replace the O ring, but that didn't work. Case gasket appears to be ok. I did find a link to some detailed instructions on how to rework a Cox engine to seal it up good, so at some point I plan to follow those instructions.

As for the lack of hp on the cub 049, do you think that the cub 06 would make up the difference and provide power of a good cox 049? Referring back to the reasons above, a call to OK Engines and $40 (plus either shipping or drive to them to get it) and I have a brand new engine with a regular glow plug on it.

Proptop, I fly at Lee Town Park and and behind the cemetery just North of there. I work out at Griffiss and a few of us at work flew there (at our Co. parking lot/yard, and also inside with small electrics) but recently were asked to stop flying at work. I have been learning with an electric foamie that I beat the heck out of, and after I got so I could fly my electric without getting into trouble I dug out that PoC that I built forever ago but didn't fly because I was afraid to bust it up. Where do you fly? I intend to round up a 4 channel trainer and join one of the local clubs to learn how to fly with ailerons. I'll probably have to unlearn some bad habits I've taught myself too...

Thanks again all.
Old 01-27-2009, 01:36 PM
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Default RE: "newbie" prop question

I'm not an expert on Cubs, but I've run my .049 Cub B (the FRV) on Sig 25% nitro, wooden 7x3, and K&B short medium/hot plug successfully on a 1/2A Brodak Cessna stunter with 40 foot dacron lines. It won't drill me into the middle of circle like one of my Bees on a 6x3.5 or 6x3 since it won't make the RPMs, but it is fun. The Cub is certainly short on power for something as large as a PoC with older equipment. I'd suggest something more like a Half-Pint or Simplex at 30" to 36" for RC. I want to do a Laumer Buttons or Twin Lizzie for mine.


ORIGINAL: combatpigg
I've never run a OK CUB, but 30% nitro fuel with castor oil could help. You might find that the CUB can put out more thrust with a different prop, like a 6x2, 5x3, 7x3, who knows except a CUB expert? There are still a few CUB runners out there.....Doug Galbreath sells specialty model supplies and he's listed under his name on the internet.
Old 01-27-2009, 03:59 PM
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Default RE: "newbie" prop question


ORIGINAL: Sandore
2. The cub uses a regular glow plug, so I can clip a regular glow plug driver onto it. I fried the original glow head on my BW, so (don't laugh) I drilled it & tapped it to accept a regular glow plug. I have no idea if the combustion chamber is now too big or too small (I machined it so the piston just doesn't hit the idle bar on the glow plug if 1 copper head gasket is installed). When I get the time to mess with the BW some more, I will try to find a replacement original type glow head for it before I experiment any more with my frankenstein head. Or maybe I'll buy a commercially available glow plug conversion head.
http://www.kittingittogether.com/

$11.00 for the head, $4.95 for the plugs. And they work really well. No point even bothering to find Cox heads. Your standard plug conversion will make it run, but I don't think you'll ever even get as far as equalling the stock plug performance. This Nelson plug head conversion is another story.

I highly recommend this option. You will likely see a performance gain rather than a drop. And the plugs are cheaper. I bought a few a while back and they now adorn my Coxes and VAs. I've been known to give the odd Cox plug to a needy dad/son team since with the conversions available I don't care about them. Well, perhaps I better say not as much as I used to.. before I get deluged with SASE's .

MJD



Old 01-27-2009, 07:54 PM
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Default RE: "newbie" prop question

Sandore,

I like Cubs... but you need to understand their limitations, they were designed ~1950. You can also rework them for more power, but you should feel comfortable reworking engines before attempting that. Cubs are low compression sport engines. The 20%-30% nitro and 20+% lube fuel is good. You will need to try different props. I would GUESS that a 6x2 would be best.

Your Black Widow, on the other hand, is one of the most powerful reed valve engines put out by Cox.

Fix the Cox! Get the conversion head (either Galbreath or one of the turbos), clean the needle valve area, clean the reed and housing, and make sure that intake "O" ring is good. Those areas cause the most problems.

For the intake "O" ring, cut the piece of tubing with a razor blade.

I would suggest you fix the Cox for the POC and build a smaller ship for the Cub.

Just one opinion.

George
Old 01-27-2009, 09:46 PM
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Default RE: "newbie" prop question


ORIGINAL: Sandore
of guys I work with suggested the tank O ring on the BW. I tried shaving off a very thin piece of fuel tubing to replace the O ring, but that didn't work. Case gasket appears to be ok. I did find a link to some detailed instructions on how to rework a Cox engine
Does it leak fuel out of the tank when filled?

Or does it not leak, and does not draw fuel? (key symptom being that it happily runs out a prime then stops, starving for more fuel).

Or you said not running right - does it run, but something is amiss? If so, what does it do?

What fuel and prop did you use?

Those little cut o-rings can take a couple of tries to get right. Too thick and they mush so badly they are a wreck. Too thin and they don't work. Too crooked and they don't work.

That plug conversion of yours could be a major factor too. What plug is in there? Does it seal perfectly and all that? I think you already know the general sentiment about standard plug conversions of Coxes by your "don't laugh" comment.. Many have done it, but the performance always seems to suffer in some way, and at best I think some efforts run at par.

MJD


Old 01-27-2009, 10:10 PM
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Default RE: "newbie" prop question

Sandore has an interesting project on his hands, because of the challenge. He has a plane that flys about as well as the Wright Bros' did and it would be interesting to see what subtle changes could be made to put it over the top.
Weight reduction! I'm not talking about drilling a bunch of holes in balsa, but if updating the onboard equipment is doable, then he'll end up with a better flying plane. It will be interesting to hear what Doug Galbreath has to say about the Cub. He seems like a nice guy and I'll bet he wouldn't mind spending a minute to lend advice about the CUB and give his opinion about what it's limits are.

I know one thing.....before spending $40 on a .061 Cub, I'd spend the same money on a AP WASP .061 from Tower Hobbies.
Old 01-27-2009, 10:54 PM
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Sandore
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Default RE: "newbie" prop question

OK, OK, I give!

I was resistant at first, had my mind made up that I was going to try to make the cub 049 work with the PoC. I mean, it was able to pull the plane around in circles a few feet off the deck with no wind, so my thought was that if the cub had either the torque to spin more pitch or diameter, or would liven up with a few more rpm with smaller diameter or pitch, that maybe that would put it over the top to quote combatpigg. I also am not opposed to replacing the 10-12 year old full size receiver and servos with modern small stuff to lighten it up. I must have built the tail too heavy, as I had to add ballast to the firewall to get her to balance. The one flight where I did gain altitude (maybe 200'?) she seemed to float around pretty decent, I probably had a 10 minute flight which was a thrill after 3-4 of those low altitude, try not to destroy the plane flights I had just gone through.

However as I have been reading all of these responses the recurring theme is obvious, and I have decided that I need to let the dead horse RIP and focus on the BW again for the PoC, and as a few of you have suggested, find a smaller plane project to use the cub with. I am in the mood for another kit project anyway.

As for the BW, it's been about a year since I last messed with it, but it did not leak from the tank. It would run through the prime and quit most of the time, like it was starving for fuel. I got it so it would run with the needle valve almost fully open, maybe only engaged about 1/2 of a thread. If I remember right it would run like that, sloppy rich, for a whole tank full, but if I tried to close the needle a 1/4 turn at a time it would sometimes lean out a little but it would usually die, and it wouldn't restart at the same needle setting where it died. It was fresh O'Donnell (?) 30% fuel with some castor added, and a 6x3 prop. About my "don't laugh" comment regarding my homemade glow plug head, I don't know about the general sentiment, but I can imagine that as a non-engine expert, and a non-machinist, my attempt is not likely to work all that well. I had fun making it though, and if it ever runs with my head I will be tickled. I think one of those Galbreath heads may be in my future. I've done the fuel tubing slices thing, but I will keep trying.

Old 01-27-2009, 11:53 PM
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Default RE: "newbie" prop question

or if you dont want to spend a lot of money you can buy cox glow heads from mecoa the turbo plugs are nice or Galbreath heads
Old 01-27-2009, 11:55 PM
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Default RE: "newbie" prop question

Sandore, I've never messed around with the fuel tubing slices, I just give up and buy some Sullivan brand small tubing and route a line out the side of the Cox tank to a remote tank. I like the Hayes brand fuel tanks, they are simple to set up, fairly light and a 1 or 2 oz tank will give you a nice long run.
Old 01-28-2009, 12:05 AM
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Default RE: "newbie" prop question

heres a sure start with a turbo plug runs nice
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Old 01-28-2009, 12:10 AM
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Default RE: "newbie" prop question

Gotcha - the general sentiment about standard plug tapped Cox heads is that they are certainly a way to get the engine running again and with respectable results, but they usually result in something like a 1000-1500 rpm loss, although I don't know if that is a safe blanket statement or not. And with the ready availability of the Nelson conversion head, which uses much more reasonably priced plugs that work great, and costs little more than a new Cox head will fetch - these days it should almost be a standard. Plus the more we use them the more likely they are to remain available for a long time too.. this is worth thinking about, 1/2A fans. You know how manufacturers can come and go, much as we hate to see that ever happen. Even manufacturers with such amazing histories as Cox.

I think you have one of two problems:

1. Crud in the fuel system. I'd say the less you have disassembled the motor, the less the chance that you have/had a leak at that o-ring, and the more likely you have crud in the fuel system somewhere or another similar fuel impediment:

- make sure the fuel pickup tube is attached, in good shape (it's likely stiff as a board but if it is sound then you can live with it) and oriented to the bottom of the tank.
- the nipple to which the fuel pickup attaches is a classic hiding spot for a wad of gunk. As a matter of fact, this very afternoon I cleaned up an old but little used Golden Bee for a buddy (I do NOT want to give it back). I thought I had cleaned and checked everything, but lo and behold it would not draw fuel, first hardly at all and then none. So I stripped it again, and that's where I found the reclusive booger. I blew it out with contact cleaner and the engine started and ran on the second flip with the needle out 3-1/2 turns.
- this has nothing to do with current problems, but does that fuel now have at least 20% total oil? 22-23 maybe..?

2. But yeah, you could really have a leak there if you are having problems making the seal work.

3. Beyond those, maybe check over the reed valve - is it there, does it seat and pass the suck-blow (gently) test, acting as a one-way valve?

Hope there is something there helpful to you. That's what I'd be fooling with anyways.

Always remember: Clean Cox are happy Cox! [X(]

MJD
Old 01-28-2009, 12:17 AM
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Default RE: "newbie" prop question

I almost forgot: the other reason to get the Black Widow running is that simply they are dm fine little engines and deserve to be running at about 18 grand or better on a nice sunny day with a grinning pilot standing somewhere below.

The Cubs were OK in their day but not in the same league. Good fun if you lighten the wagon a bit and give them a fighting chance. 36"-44" old-time FF designs and that sort of thing are a nice match. How coincidental, those are the wingspans of the two Tomboy versions. Lots of nice choices out there. I might also suggest if you plan to order a SOYY kit you do it earlier than later.

MJD
Old 01-28-2009, 12:51 AM
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Default RE: "newbie" prop question


[quote]ORIGINAL: Sandore

I have no idea if the combustion chamber is now too big or too small (I machined it so the piston just doesn't hit the idle bar on the glow plug if 1 copper head gasket is installed).
(quote)

I bet the idle bar plug is a big part of the problem. I think a head with a regular short plug that just clears the piston would work better, (smaller combustion chamber).
Al
Old 01-28-2009, 01:08 AM
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Default RE: "newbie" prop question

Quote by CP:
"Sandore has an interesting project on his hands, because of the challenge. He has a plane that flys about as well as the Wright Bros' did and it would be interesting to see what subtle changes could be made to put it over the top.
Weight reduction! I'm not talking about drilling a bunch of holes in balsa, but if updating the onboard equipment is doable, then he'll end up with a better flying plane."

All true. And this may sound like a reach but if the covering is Monokote then it too can be stripped and a lighter substitute put in its place. This alone could make a huge difference on this planes flyability.
The radio gear though would be my top priority, then covering replacement. Both of which will require some effort.

Robert
Old 01-28-2009, 03:25 AM
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Default RE: "newbie" prop question

ORIGINAL: Sandore
... About my "don't laugh" comment regarding my homemade glow plug head, I don't know about the general sentiment, but I can imagine that as a non-engine expert, and a non-machinist, my attempt is not likely to work all that well. I had fun making it though, and if it ever runs with my head I will be tickled. I think one of those Galbreath heads may be in my future. I've done the fuel tubing slices thing, but I will keep trying.
The big difference between the standard plug and the Galbreath/Nelson or the Turbo is that the standard plug seals at the top of the threads and has a larger plug cavity (where the coil is) whereas the Nelsons and turbos seal at the bottom and have smaller cavaties. The results is that the standard plug increases combustion chamber size which, in turn, decreases power.

If you have room in your head to fit an idle bar, it is probably sitting too high. If you want to try your head (after the engine is running) have it fit so the bottom of the standard short plug is level with the combustion chamber...neither recessed nor sticking out.

George
Old 01-28-2009, 10:09 AM
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Default RE: "newbie" prop question

I also forgot to mention there is nothing to laugh at regarding your head conversion, many have tried this in frustration over the situation over plugs. There is no reason yours will not work, but as mentioned by gcb set it up to give it a fighting chance. But it is worth noting that the commercial conversion head works better in general and ends up costing less in the long run, and very little more to start.

MJD
Old 01-28-2009, 10:09 PM
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Default RE: "newbie" prop question

Were you using the O'Donnel r2r 30% sport fuel for cars? The car/heli centered place I buy some things from sells that and racing fuels. The have shown me their list and they have airplane fuels for sale, too. But none with the nitro % I want for 1/2A. If the 30% r2r works well for you I might want to buy from them next season.

I bought turbo plugs there made by O'Donnel to use with the Valentine turbo plug head I have. The hot plug for small car engines seems to work well with 25% Sig with some extra castor oil. They are also about $4 less than Rossi or OS turbo plugs.

ORIGINAL: Sandore

OK, OK, I give!

It was fresh O'Donnell (?) 30% fuel with some castor added, and a 6x3 prop.

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