Motoring the Firebaby

rsv1cox Fri Dec 21, 2018 11:12 am

I can't make up my mind.

I want to use a different engine like a OK Cub, or Wen Mac and I have several that are good runners, but the needle/fuel feeds are on the wrong side for me to use a remote tank. I have tried in the past to tap out the spray bar and swap ends without much success so I guess it's a Spitzy or another Babe Bee.

The diesel Ok Cub has the NVA on the correct side, but it's missing the compression piston.

I would like to use the unknown engine just in front of the Spitzy but it has such a small fuel tank, probably a free flighter that it would be impracticable and it's not been ran.

Anyone had success swapping ends on those pressed in spray bars?

Oh yes,

I want to use a remote fuel tank and a smaller engine because the other Firebaby is really nose heavy with that Babe Bee hanging out front and the tanked Spitzy would not solve the problem.

**Cribbs74** Fri Dec 21, 2018 11:19 am

Your unknown engine is a K&B infant. I am not understanding why the needle valve placement is a problem on the Cub and Wen-Mac Can you post a picture of what you are up against?

Nevermind, I see now. If you are flying level laps just route the fuel line behind and around the engine. It will probably fly fine. If you want to stunt then it will be a problem. I wonder why they decided to mount the NV that way. It doesn’t make sense.

rsv1cox Fri Dec 21, 2018 12:42 pm

Wen's, Ok's, except for diesels they are all that way.

Integral tanked engines I would think with the fuel pickup angled back for C/L flying?

Thanks for the ID on the "unknown". I have heard about it, didn't realize that I had one.

ticomareado Fri Dec 21, 2018 2:55 pm

On Wen Macs with angled one way spray bars just use enough fuel line and route it over to the other side.

ticomareado Fri Dec 21, 2018 2:59 pm

Another option with the Wen Mac is to mount it sidewinder (or partially sidewinder) with cylinder outboard and NV hanging under LG.

Oldenginerod Fri Dec 21, 2018 3:13 pm

Cribbs74 wrote:Your unknown engine is a K&B infant.

Well, sorry Ron, not actually called an infant, but I see wherer you're coming from. The .020 version was called an infant, the .035 a Torp. Jr. and the .049 as pictured was a Torpedo.

Personally, due to the weight, I'd be going for a Cub .049B. If the fuel feed turns out to be a problem then I'm pretty sure you can remove and re-install the spray bar the other way around. I think I have some already the other way.

Rod.

ticomareado Fri Dec 21, 2018 3:16 pm

Which of these engines in photo have been recently bench tested?

rsv1cox Fri Dec 21, 2018 3:26 pm

How do you do that Rod? I have used heat and brass drift and tapping hammer to no joy.

Good suggestion Victor, sidewinder. I want to use the Wen Mac in the second picture above with the angled fuel feed. It's a good runner but to do so I may have to re-do my Firebaby's front end. Which needs more trimming anyway. Sad

Bob

GallopingGhostler Fri Dec 21, 2018 4:36 pm

Cribbs74 wrote:I wonder why they decided to mount the NV that way. It doesn’t make sense.

Just a hunch, the Infant was probably targeted for free flight usage on smaller aircraft where the fuel tank wasn't subject to a lot of gyrations. 20 inch span Jetco Dragonfly comes to mind.

https://outerzone.co.uk/plan_details.asp?ID=7169

Hal DeBolt's 1953 34 inch span Livewire Kitten RC plan shows a similarly configured Atwood .049 with underside tank.
https://outerzone.co.uk/plan_details.asp?ID=275

Oldenginerod Fri Dec 21, 2018 7:38 pm

rsv1cox wrote:How do you do that Rod? I have used heat and brass drift and tapping hammer to no joy.
Bob

When I get a chance I check my collection of Cubs and see if I have recalled correctly about some being the other way. I also have some brand new spray bars so I will track down the measurements and see if they're the same diameter both ends. If so, I see no reason that they couldn't be installed the other way. I just place a 1/4" drive socket the right size over the spray bar, bearing against the side of the venturi, and squeeze it gently in the vise. I just picked up some magnetic plastic soft-jaws for my vise. When I get a chance I'll post some pictures of them. I'm hoping they'll be handy for doing miniature engine work.

ticomareado Sat Dec 22, 2018 6:34 am

RE: Cub spray bars. In fact they come pre-installed from factory in both directions and there are no separate factory part #s for LH and RH spray bars or crankcases.

rsv1cox Sat Dec 22, 2018 7:52 am

New plan. As much as I would like to use a Wen Mac or especially that little K&B I think I will opt for another Cox engine.

My whole idea is to cure the nose heaviness of the Cox Babe Bee rebuilt Firebaby by using a remote tank and moving the CG back. So perhaps a horseshoe mounted at 90 degrees would work or a postage stamp with a Goldberg mount. But I have contemplated using a tank mounted .020 also.

I'm pretty sure most here think the .020 is not enough engine, but this Firebaby is as light as a feather and I'm sure it would at least do circles, and probably loops.

I did receive the OK Cub diesel yesterday and it does have the compression piston unlike the other. Strange, it has the NVA on the other side supporting Victors contention. Or maybe some one swapped it. Maybe a diesel Firebaby is in the future. These are so simple and cheap (and fun) to build a whole fleet with different engines are possible. Crash one, fly another.

ticomareado Sat Dec 22, 2018 8:49 am

If you go with Wen Mac, you can experiment with far more engine configurations using the same mounting pattern, and tank. (Wen Mac and Cub .049B and D have same radial mount footprint) Plus, you're not going to shed all that much in nose-heaviness factor using a plastic back plate Cox vs. a plain Baby Bee.

rsv1cox Sat Dec 22, 2018 11:24 am

ticomareado wrote:If you go with Wen Mac, you can experiment with far more engine configurations using the same mounting pattern, and tank. (Wen Mac and Cub .049B and D have same radial mount footprint) Plus, you're not going to shed all that much in nose-heaviness factor using a plastic back plate Cox vs. a plain Baby Bee.

Thanks Victor, eventually a Wen Mac or Ok will be attached to one of these. But my motivation was to move the CG back by locating the fuel tank mid wing.

How about this?

But all that hardware isn't helping me much either.

I will position the tank under the wing and might even lose the landing gear. I can't even come close to a balanced airplane otherwise. The original model would balance well ahead of the wing if I could get there.

I'm thinking the Cox .020 would be best.

Bob

GallopingGhostler Sat Dec 22, 2018 12:39 pm

Food for thought .... Rudolph

ticomareado Sat Dec 22, 2018 3:27 pm

The weights for the Wen Macs and Testor 049s include Rotomatic starter. Stripping the starter off any of these engines will make each one as light or lighter than a Sure Start .049 and the piston/cylinder mass is much closer to firewall.

GallopingGhostler Sat Dec 22, 2018 9:19 pm

ticomareado wrote:The weights for the Wen Macs and Testor 049s include Rotomatic starter. Stripping the starter off any of these engines will make each one as light or lighter than a Sure Start .049 and the piston/cylinder mass is much closer to firewall.

What would you use for a prop thrust plate, as the front half of the Rotomatic forms this?

I know that this engine would be undesireable because of its extra weight and larger size. The A.C. Gilbert .074 and .11 Thunderheads came in both versions. I have one of the last that I bought on E-Bay from a seller who was cleaning and reassembling perhaps the last stock of them. The .074, own could dismantle their rotomatic leaving only the front housing and hub, which lightened it a little. The .11 came with both their rotomatic starter and with a narrower standard styled hub.

In a post back on Wed Jul 01, 2015 2:50 pm CEF: Questions about OK Cub .049s..., I posted the following info, may be helpful in knowing the relative power if suitable for the plane:

GallopingGhostler wrote:Summary from test reports using a 6x3 prop:

OK "A" Frog .049 OK "B" Wen-Mac Roto-matic Babe Bee McCoy Red Head Cox QZ Black Widow Testors 8000 Cox Tee Dee
BHP 0.037 0.055 0.056 0.062 0.065 0.078 0.094 0.105
BHP RPM 12,000 14,500 13,000 14,800 15,000 15,500 18,000 22,000
6x3 RPM 10,000 10,600 11,600 14,000 14,400 14,200 14,300 14,600 15,700 18,400

Overall I think these comparisons are relatively reasonable representations. Since the QZ is the start of the heritage of the Sure Start with elimination of SPI and designed by the masters Bill Atwood and Dale Kirn, it set the standard and I think that more or less this would be about where the Sure Start would fit.

Cox Pee Wee was rated by Peter Chinn in the March 1976 Aeromodeller report as having 0.035 BHP at 18,500 RPM. It turned a Tornado 5x3 prop at 10,900 RPM. Thus, the OK Cub .049's are more powerful than the Cox .020 Pee Wee, but at the lower end of the spectrum powerwise with the .049's. The OK Cubs are not bad engines, but compared with other .049's that came along later, not quite as powerful.

**Cribbs74** Sat Dec 22, 2018 10:36 pm

I am really quite surprised about the Testors 8000. So much so I had to look for myself. Sure enough, it’s spins a 6x3 faster than a Cox Black Widow.

The outward design is awful though. Very clunky and not easily adapted to much. They engineered a strong running engine though. It really hurts to say that... Doh!

ticomareado Sat Dec 22, 2018 10:47 pm

Two options for thrust plate on Wen Macs stripped of Rotomatic starter:

1- Grind down steel starter clutch plate mounted on improvised mandrel on drill press with a file. Yhe guts fall out of the shell first and then keep grinding remainder of shell to 7/16" or so diameter. This is the slow way. Can be done in a flash on a lathe.

2- Easy simple way is drill out an aluminum or brass Bee thrust plate and squeeze her on with the prop.

GallopingGhostler Sat Dec 22, 2018 11:15 pm

ticomareado wrote:Two options for thrust plate on Wen Macs stripped of Rotomatic starter:
1- Grind down steel starter clutch plate mounted on improvised mandrel on drill press with a file. Yhe guts fall out of the shell first and then keep grinding remainder of shell to 7/16" or so diameter. This is the slow way. Can be done in a flash on a lathe.
2- Easy simple way is drill out an aluminum or brass Bee thrust plate and squeeze her on with the prop.

Thanks for the inputs. Sounds a little involved. Without a lathe or milling machine, I don't know if I would want to generate my own prop thrust plate. Personally, I like the Rotomatic starter for its ease of engagement, was always impressed how it worked. I'd just use it where weight wasn't a problem.

Cribbs74 wrote:I am really quite surprised about the Testors 8000. So much so I had to look for myself. Sure enough, it’s spins a 6x3 faster than a Cox Black Widow. The outward design is awful though. Very clunky and not easily adapted to much. They engineered a strong running engine though. It really hurts to say that...

The product donor engines affectionately known as the "Pipe Bomb Engine" rely on the RTF special mounting system. This one is a challenge to reuse on other aircraft.

The non-product engine version with tank was easy to mount, fits the Cox .049 tank back bolt pattern. It mounts as a sidewinder for CL use.

Sceptre Flight Model Engine Tests, Testors 8000

This is what the engine looks like on my Goldberg Swordsman 18:

**Cribbs74** Sun Dec 23, 2018 12:10 am

Yes, that’s the one I was referring to. It’s big and clunky. Not streamlined at all. Also quite long now that I see it in use. Not knocking the the performance whatsoever, just thinking they could have made a more astheticly pleasing engine. I know the difference between that and a pipe bomb.

Better take that sticker off the rudder... Devil

I wouldn’t want anyone to mistake that for a Cox engine lol!

Edit: Before anyone gets upset I am just playing around. Merry Christmas Lighting The Tree

GallopingGhostler Sun Dec 23, 2018 12:19 am

Cribbs74 wrote:Yes, that’s the one I was referring to. It’s big and clunky. Not streamlined at all. Also quite long now that I see it in use. Not knocking the the performance whatsoever, just thinking they could have made a more aesthetically pleasing engine.

Emphasis was on production costs, obviously. It's cute in its own ugly way. Wink

Better take that sticker off the rudder...
I wouldn’t want anyone to mistake that for a Cox engine

Well, we could .... Huh...

But seriously, originally it had a Cox Babe Bee engined mounted. lol!

The Testors 8000, OK Cub "A" and Cox tank engines all share the same bolt mounting pattern. Popcorn

**Cribbs74** Sun Dec 23, 2018 12:22 am

That Cub is a much nicer fit.

ticomareado Sun Dec 23, 2018 7:28 am

Yes, the Cub looks much better and the 8000 is enough power to make the Swordsman a proto racer trainer

GWILLIEFOX Sun Dec 23, 2018 8:56 am

FOX 049 and 07 also use the same radial patttern

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	OK "A"	Frog .049	OK "B"	Wen-Mac Roto-matic	Babe Bee	McCoy Red Head	Cox QZ	Black Widow	Testors 8000	Cox Tee Dee
BHP		0.037		0.055	0.056	0.062	0.065	0.078	0.094	0.105
BHP RPM		12,000		14,500	13,000	14,800	15,000	15,500	18,000	22,000
6x3 RPM	10,000	10,600	11,600	14,000	14,400	14,200	14,300	14,600	15,700	18,400