bogateer

Regarding the circa 1996 high performance versions of the .049 and .051 Killer Bees. Is there any way to properly identify (and potentially subsequently obtain) the proper cyclinder and piston combination for these engines? The only writeup I could find said they used "sub-induction" (which I have hear of, read, about, might be able to explain superficially, but would be hard pressed to identify one). Something in the vague recesses of my memory suggests these particular models may have had tapered cylinders and pistons as well but I could easily be getting this confused with another engine. Is there any way to identfy these parts? I know some Cox cylinders are marked and others have enough identifying features to make this possible. Is that the case here?

Thanks,

Rob...who is now only beginning to discover the plethora of nuances amongst the Cox herd.

PS When I was a kid all I had was a Golden Bee and a Baby Ringmaster...that's all there was. I flew it and flew it and broke it and fixed it and flew it and flew it some more. At what point did all this become so complicated?

combatpigg

My Feedback: (3)

You can make your own high revving pistons from any Cox stock. Dickeybird did a thread a few years ago about how to lay a drill motor over on its' side and use it like a lathe. I think he called the thread "poor mans' lathe".
The piston material is soft and all you need is a Xacto blade to shave the skirt. Before you thin the walls, you want to raise the skirt to obtain about .008" SPI. Shave the skirt till it's paper thin. You will see a significant rpm increase if the intake is opened up as far as the casting allows and if the crank journal is relieved like a stock KB is done. Any reed in good shape will get the job done, I've seen the Surestart reeds support close to 30,000 rpm.

cyclops2

What are the steps to .008" SPI ?

combatpigg

My Feedback: (3)

Bring the piston to TDC then scratch a mark in the skirt at the bottom of the exhaust port. Remove the piston and shorten the skirt .008-.010" above the scribed line. Take note of the factory finish of the piston skirt edge, so you don't get tempted to over chamfer or radius the edge too much after machining. You want a nice clean opening and closing event, but you don't want too much oil scraping either. A lot of the benefit of doing this is simply making the piston lighter. 400-500 revs per second is what they run at with a racing prop.

ProBroJoe

CP... I've read about this Magical Killer Bee that you and PT toyed with for a while. I find it hard to believe that any Cox .049/051 (reed or crank induction) will turn 25-30K... I would love to see one in action. I have a few TD's here and even on 30% they don't turn much more than 19-20 K on a 5 x 3 - the Norvels on the other hand consistantly turn in the 22,500 range with ease....

Now, I'm not calling anyone a liar here... I've just never seen it - somebody PLEASE prove me wrong! [)]

combatpigg

My Feedback: (3)

PBJ, the most I ever had a stock TD turn a 5x3 was 25,000 0n 40%. This was years before I learned about the piston and crank tricks. Way back when, C/L combat flyers wouldn't be able to compete with a TD doing much less than 22,500...might as well stay home. When the AMEs and VAs came out, the die hard TD users began cutting the 5x3s down and that kept them in the game, but the ball sockets crumbled at 26,000+. The planes performed very well with the small diameter props, but not easy to hand start an engine with just a nub for a prop blade. Once the Cyclons came out, TD combat became a seperate nostalgia event.
Years later I learn about the engine tricks here at RCU and get a Surestart up to 24,000 with a 4.2x4 APC. Then Patrick sends me a KB to look at and possibly hop up, but there wasn't anything to do because it was already turning a 4.2x4 about 28,500 on 45% [and just a check of the parts fits]. The key to longevity at the much higher rpm has to be the KBs lighter piston.
In the video of the Blink, you can hear it running and unloading.
If you still had access to bins full of pistons and hot liners to work with for custom fit sets, this level of performance wouldn't be so hard to match. The limiting factor with all reedies except the KBs is being able to open the air intake plenum to allow the high rpm. I think the short shaft of the KB has less drag than the TDs, so all else being equal the KB has more power potential than the TD. I have seen for myself that the reed is not a limiting factor. There is no doubt that the rpm numbers I got were real, you could just put the tach away and listen to the difference.

Larry Driskill

Joe,
When I was running TeeDees in the 70s and 80s I usually had several engines and tried to keep three running well. My engines were usually competitive.

I found some old notes from CL 1/2A Combat.

In Las Cruces, NM on 7 Aug '88 a KK TeeDee .049 was turning a Cox black 5X3 23,000 on 40% fuel with a TeeDee plug and 85 degree temp.

In Virginia on 21 April, 1983 on TeeDee was turning a Top Flight 5&1/4X3 22,000 and another was turning 22,300. But, on 16 Feb '83 a new, stock TeeDee had only turned the 5&1/4X3 18,000.

When I de-pitched or shortened a prop to turn over 24,000 I broke Cox parts.

TeeDees with the cylinder timing set, a GloBee or TeeDee plug, a properly fitted shaft, and a good piston and sleeve would nearly always turn a Black Cox Rubber Ducky over 20,000 (when mounted on a rigid motor mount). A really nice engine would turn another few thousand and during that behavior it would sometimes break . . . .

In the 90's I turned my Norvels and VAs in the upper 20s and a good engine would turn the little glass props over 30,000. They would also, sometimes, find a way to break and rod or a shaft.

ProBroJoe

Larry, CP, thanks for the clarification - I guess I haven't fiddled with mixin' and matchin' and tunin' enough to get them to wind up! The best I've ever been able to do with a Sure Start was a bout 18,500 on a 5x3 rubber ducky... and that was the one that unloaded to 20-something in the air and snapped the crankpin off.

Sounds like I shouldn't give on 'em just yet!

-Joe

combatpigg

My Feedback: (3)

PBJ, if you ever get a good P/L specimen, try to build a super KillerBee or TD with the lightened piston. Also....take some volume out of the Galbreath or TD heads, raise the liner a little and run enough nitro to blow a plug every 3rd or 4th run with a 4.2x4 or 5x3 APC. If you see slight pitting on top of the piston, you have it just right [)]. My hardest runners had either 1 or no head shims.
BTW, I've broken TD crankcases, but never a crank.......until I tried diesel.

ptulmer

My Feedback: (5)

PBJ, wanna fly the new Blink w/ that particular engine? On 35% it winds up pretty good, so you won't need to put out any cash except return postage for the engine.

ProBroJoe

Well PT, if that's all the more you care about your airframe, then sure, send it my way - I'll be happy to reduce it to a pile of toothpicks for ya!