Author Topic: Questions about Cox tank backs (Read 3210 times)

ken cook · « **on:** April 29, 2007, 06:24:10 AM »

Recently, I had about 4 or more of my tank backs for my black widows crack. Larry feel free to chime in here. I recently purchased 4 tank backs and 1 conversion 8cc kit. And you think gas is expensive. My older tank backs have no filler vent pipes, the new ones have one and a small vent hole. The 8cc tank has no stunt pipes, my old ones do. This tells me that there might be consequences with long time inverted flying with no stunt tank. Is this the correct assumption? Prior to purchasing the newer tank backs, I pulled some older die cast baby bee tank backs out of storage. I installed these on the black widows and plugged the two filler pipes on the tank back. The engines ran but not quite the same. I found during starting the cylinder was spitting fuel out all over as if it was too rich. My theory is that the baby bee tank back has too small of a intake hole. I haven't taken the engine off to check it yet. I then installed the new tank backs on the older black widows. I now have the old stunt tank with the new tank back. What is going to happen with this set up? Is fuel going to pour out if I go inverted? Its a bit difficult to cap the new arrangement on the new tank back unless you epoxy the holes closed. I really don't want to do this with these newly purchased jewels. Do you think it would be wise to just change the tanks to the newer style ? I have some real good runners here and just seeing them in a box is a real heartbreaker. Thanks, Ken Cook

George · « **Reply #1 on:** April 29, 2007, 08:17:58 AM »

Toward the last, Cox used the Texaco setup with the fill and vent on the backplate and the tank unvented. They also switched from an aluminum tank to a plastic one, I believe. At one time I could not tell the difference (online site add pictures) between the Babe Bee, the Black Widow, and the Texaco. All appeared to use the unvented tank setup and the Sure Start front end.

Again, this was from looking on the Cox site...perhaps the pictures were not correct.

George

Paul Smith · « **Reply #2 on:** April 29, 2007, 08:32:28 AM »

I'd say, just epoxy shut the holes in the Babe Bee backplate.

These engines are really picky-picky about tiny leaks, better safe than sorry.

You can just drill 'em out if you want to change back.

ps:
Not all venturis are created equal. Mike or gauge the air intake to get what you need. You can't always get what you want.

Larry Renger · « **Reply #3 on:** April 29, 2007, 09:18:01 AM »

I agree about epoxying up the holes. Those backs are Nylon, and the epoxy will be easy to remove if you ever need to.

Also, beware, some C*x engines made in the late '80s (before I went back and fixed the problem!) had larger openings in the backplate than the venturi. Bad, bad news for good fuel draw. The venturi should be the same size or larger than the hole in the backplate.

Also on old backplates, check the screen, if it still has one. They can be really blocked up with old, congealed castor oil. I just remove the screen and smooth the inlet to remove the screen retention ridge.

Clancy Arnold · « **Reply #4 on:** April 29, 2007, 01:30:01 PM »

Larry
You are a man after my own heart! I have been removing the screen and trimming the venturi end off of the plastic "U" backs for 2 years. It gives more space between the firewall and the venturi allowing better air feed. I trim the plastic back to the ledge that the screen was against. Have never had a problem since. Now I will start doing the same to my metal tank backs also.

Do you know of a source of plastic backplate/motor mounts for Cox 020 Pee Wee's?
I hate the idea of drilling a hole in the side of the metal tank to run a separate fuel tank.

Clancy

minnesotamodeler · « **Reply #5 on:** April 29, 2007, 04:14:59 PM »

Go ahead, Clancy, the tanks are too small anyway...thinking about it, I realized these little engines were originally designed for free flight, never needed more than a 30-sec. engine run, why add weight using a bigger tank? Too bad for us.

--Ray

Robert McHam · « **Reply #6 on:** April 29, 2007, 04:33:27 PM »

Ray, what you said about FF just reminded me of an article (with pictures) of how to reduce the run time in that big ol' Pee Wee .020 tank! I remember reading that article and I almost was brought to tears laughing!
It involved cutting pieces of wood, about 1/4"X3/16" and placing short lengths, four or five pieces inside the tank to reduce the space inside! I can't remember the model for which the article was written...I need to dig that thing up and re-read!

Robert

Larry Renger · « **Reply #7 on:** April 29, 2007, 09:16:09 PM »

I think I saw that someone skeletonized a Babe Bee (NOT Baby Bee) or Pee Wee tank, and the back with a Dremel tool to make a very lightweight mount similar to the support designed for the Thermal Hopper. Then he used an external tank. In addition, there was a firewall/reed & venturi unit made for some RTF (PT-22?) by Cox . Or just pick up a Tee Dee .020 and have GOBS of power.

minnesotamodeler · « **Reply #8 on:** April 30, 2007, 02:12:27 AM »

It happens I have a TeeDee .020, have only run it on a test stand but I can attest to the GOBS of power, all right! Being a front rotary intake, it won't run backwards, my major irritant with reed engines in general; and of course you can put any size tank on it you want. I imagine it would fly most any 1/2A plane designed for the milder .049s. It is a definite no-no on my 15' lines...don't know what I'm gonna do with it--1/4A combat, anyone? Or, what would you call it, Cockroach Race?

--Ray

Ralph Wenzel (d) · « **Reply #9 on:** April 30, 2007, 09:56:49 AM »

Put it on a Snapper, Ray . . .

minnesotamodeler · « **Reply #10 on:** April 30, 2007, 12:52:00 PM »

Actually, Ralph, I've thought about that, and I think it would fly it fine, maybe on the old 1/2A standard 27' lines...I'd have to put a full ounce, or more, of lead in the nose to balance it, though. An extended-nose Snapper? It would work. You may see it yet.

--Ray

Mike Spiess · « **Reply #11 on:** April 30, 2007, 02:55:01 PM »

Hey Ray I also have a .020 TD I'll send a picture of both the .020 and the .010

minnesotamodeler · « **Reply #12 on:** April 30, 2007, 04:52:25 PM »

At least that way we'll have proof positive it's really an .

Larry Renger · « **Reply #13 on:** April 30, 2007, 07:31:51 PM »

My last Snapper was built REALLY LIGHT, coming in at 4 ounces. Using a floppy balloon tank and a Holland Wasp engine, it weighed 4 ounces. Clear Hobbypoxy on the wood, Litespan (now Koverlite) on the wings. I still needed to lengthen the nose 1/2 inch to balance for ideal performance. It flew a competitive pattern in the near 400s, which was good for me at the time.

A Tee Dee .020 would have been plenty of power, and in fact was the first engine I had on the plane. Never could get it to run consistently. I think a bladder tank is required for that setup. With the stock firewall position and the Tee Dee .020 the plane was unflyable (even by Bob Whitely!!!)

minnesotamodeler · « **Reply #14 on:** May 01, 2007, 07:57:56 AM »

Quote from: minnesotamodeler on April 30, 2007, 04:52:25 PM

At least that way we'll have proof positive it's really an .

Well it happened again...trying to say "oh-ten" with an exclamation point and get a silly happyface instead. I repeat: I don't use those things (don't mind if you do, I just don't) so whenever you see one in a msg of mine, know it is inadvertent. A little irritating, actually, to not be able to say what you want to say the way you want to say it...
the wonders of modern technology.

--Ray

minnesotamodeler · « **Reply #15 on:** May 01, 2007, 08:09:34 AM »

Quote from: Larry Renger on April 30, 2007, 07:31:51 PM

My last Snapper was built REALLY LIGHT, coming in at 4 ounces. Using a floppy balloon tank and a Holland Wasp engine, it weighed 4 ounces. Clear Hobbypoxy on the wood, Litespan (now Koverlite) on the wings. I still needed to lengthen the nose 1/2 inch to balance for ideal performance. It flew a competitive pattern in the near 400s, which was good for me at the time.

A Tee Dee .020 would have been plenty of power, and in fact was the first engine I had on the plane. Never could get it to run consistently. I think a bladder tank is required for that setup. With the stock firewall position and the Tee Dee .020 the plane was unflyable (even by Bob Whitely!!!)

I'm not surprised at all, it must have been majorly tailheavy...could easily hang an .020 another inch out, maybe further, to get the CG where it belongs. I AM surprised, however, at the notion of a 4-ounce Snapper with an .049 up front still being tailheavy...mine weighs around 5.5 and balances about right. You must have achieved most of the weight reduction in the front, or else that Holland Wasp is lighter than most .049s. All that I have weigh around the 2 oz. mark (Coxes, Norvels, VAs, Brodak) while the .020s are around 1 ounce.

Off topic, I finished my ShedDoor for the PeeWee .020--18" span, weighs 3 oz. ready to fly including exterior tank. Flight report imminent.

--Ray

--Ray

Larry Renger · « **Reply #16 on:** May 01, 2007, 10:47:27 AM »

The Wasp IS incredibly light, 1.3 ouces with mounting bolts and Aluminum bullet spinner. Balloon tanks don't weigh much of anything either.

minnesotamodeler · « **Reply #17 on:** May 01, 2007, 02:23:11 PM »

1.3 oz....that's it. Just a little heavier than those .020s! Any plane you build with the Wasp in mind better have an extended nose, huh? Good to know, especially if I acquire a Wasp myself.

Interesting. How did they achieve the weight loss (.75 oz. or more!) in a Norvel clone? Have they shaved parts so thin as to be fragile? Could you lay the parts side-by-side with a Norvel .061 and see what gives? (Lotta questions)

--Ray

Larry Renger · « **Reply #18 on:** May 01, 2007, 04:49:40 PM »

What we have heah, is a failuah to communicate. My fault, I forget that the "Wasp" name has been used more than once. Probably more than twice, even. I was talking about the Holland Wasp weighing 1.3 ounces, and that was what I used on my Snapper. The AP Wasp .061 wieghs nearly 2 ounces and would tear the wings off a Snapper unless you added carbon fiber! I flew mine just once with an Atwood Shriek, and it was a blur. The (old) Wasp went right back on!

minnesotamodeler · « **Reply #19 on:** May 02, 2007, 07:43:06 AM »

Ah, OK, Holland Wasp from yore...I had one once, in the 50s? Is it that old? Recall it being a very good-looking engine, fat crankshaft housing, very graceful design in an era of awkward-looking 1/2A engines. Not that great a runner, though. Is my memory accurate?

--Ray

Larry Renger · « **Reply #20 on:** May 02, 2007, 10:25:11 AM »

Nope, you are thinking of the Holland Hornet, a much later and more powerful engine. The best ones were comparable to a Tee Dee, but much more variable in whether you got a "runner" or not. They are extremely popular ($$$) with the nostalgia FF bunch.

minnesotamodeler · « **Reply #21 on:** May 02, 2007, 10:34:35 AM »

Correct you are; Holland Hornet. Mine wasn't that good. I have no idea whatever happened to it.

Marvin Denny · « **Reply #22 on:** May 04, 2007, 09:12:54 PM »

I have several old Atwood Wasps and a couple of Atwood shreiks. They were very good runners with a 5 1/2 X 4 Kavan prop and 15 % nitro. I don't remember any of them that didn't run quote well.
I have been thinking about building a Stunter for one of them of the design I flew in 1950 and 51 of my own design. I still have the templates for the parts, but no plans. Hope I can remember all the things I did to them.

Bigiron