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Nov 15, 2021, 09:34 PM
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Babe Bees And Tee Dees


With the highest performance (dual transfer port) cylinders and Mylar reeds, I think the reedies could perform quite well compared to the Tee Dee rotary valve .049s. In my limited experience, I'd guess the Tee Dees would have more RPM and would tend to bog less pulling into a climb. How do you compare the power bands between the Cox .049 engines?
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Nov 15, 2021, 11:19 PM
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pmackenzie's Avatar
You can see engine tests of both here:
http://sceptreflight.com/Model%20Engine%20Tests/


Black Widow has dual ports, but not quite the same as the Tee Dee ones. Also didn't have Mylar reeds.
Tee Dee peaks at 21K, the Black Widow about 16K
Tee Dee about 50% more power at peak, .145HP versus just under .08 for the reed valve motor.
Nov 16, 2021, 04:21 PM
B for Bruce
BMatthews's Avatar
I did a lot of .049 reedies back in the day. Typical was to switch to the dual port "product" or "290" cylinder. Second was to carefully select one of the bronze shim reeds that didn't make music tones when very lightly drawing air back through the reed and seat. And finally was to pick through my collection of pistons to find the one which was the loosest fit without being way too loose. Mostly that meant avoiding any that had obvious nasty scored grooves from ingesting dirt in the past. The fit that seemed to offer the best power would leak through easily when light pressure was applied to the prop and lubed with fuel or very thin 3in1 style oil. But still had a good POP when flipped smartly.

I tried a Tee Dee plug at one point but with the high nitro fuel (25%) I found that I was better off with the medium compression straight conical head... which early on came with the 290. And I believe still comes on the Cox International "product" engines.

With that combo the power was pretty good. And might have even rivaled a TeeDee that was badly fitted. But a good TeeDee would still be head and shoulders over this tuned up reed engine. Especially if the TeeDee had a drilled out venturi and was running on a pacifier or bladder pressure tank.

Bogging in a climb when running on suction is related more to finding just the right sort of needle setting. But when set just on the rich side of peak the engine will generally draw well through most maneuvers. Sometimes this means finding the rich side of peak RPM and then open up an additional 1/8 turn or so to deal with the engine unloading to a higher RPM in the air. Trial and error on that one since it's based on the speed of the model. But generally if one points the model straight up and THEN finds the rich side of the peak it's USUALLY close enough.

Oh, and one more little trick. A possible cause of needle valve issues is that air might leak past the threads. To avoid this I switch out the spring on the needles for a fitted washer and trimmed length of silicon fuel tubing. The washer being to avoid the tubing from slipping over the spring seat ridge. The tubing works in this way as both a spring and an air seal.

Mylar reeds seem to seat just right. But the thoughts above on picking the right piston to cylinder fit for reduced drag and a few more RPM is still valid. Obviously using a used piston also suggests that a rod resetting tool is a wise idea to eliminate any socket slop.

Of course all this picking through parts also requires that one has a box of spares on hand. Otherwise it's a long break in for a new piston and cylinder to "wear in" to it's optimum fit for maximum power.
Nov 16, 2021, 04:42 PM
ffkiwi
Quote:
Originally Posted by flytigres
With the highest performance (dual transfer port) cylinders and Mylar reeds, I think the reedies could perform quite well compared to the Tee Dee rotary valve .049s. In my limited experience, I'd guess the Tee Dees would have more RPM and would tend to bog less pulling into a climb. How do you compare the power bands between the Cox .049 engines?
If you want to compare power bands, then look here: http://www.mh-aerotools.de/airfoils/cox_frameset.htm then click on the 'performance' button in the left hand margin menu

Some of the developed reed units are very close to the TD-the Killer Bee (original type) being one such model.

ChrisM
'ffkiwi'
Nov 17, 2021, 02:30 PM
*******
Quote:
Originally Posted by ffkiwi
If you want to compare power bands, then look here: http://www.mh-aerotools.de/airfoils/cox_frameset.htm then click on the 'performance' button in the left hand margin menu

Some of the developed reed units are very close to the TD-the Killer Bee (original type) being one such model.

ChrisM
'ffkiwi'
The difference between reedy and TD .049 is noticeable!
Nov 17, 2021, 02:47 PM
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I'd guess a plastic backed "killer bee" type with a Mylar reed would compare well. Does that "290" cylinder fit all Cox crankcases? And how about removing the screen from the intake of that plastic back?
Nov 17, 2021, 06:37 PM
ffkiwi
Quote:
Originally Posted by coriolan
The difference between reedy and TD .049 is noticeable!
I'm not aware of any published full engine tests on the Killer Bee 049 or 051....but the rpm figures on a Cox 5x3 indicate a performance similar to the TD....this of course is the original Killer Bee with the lightened piston, tapered cylinder, TD style ported cylinder, better balanced crankshaft and mylar reed...plus the 1702 head....so all the stops scrwed out in terms of what you could realistically get out of a reed valve 049. As I understand it-they were a little bit fragile-especially in the piston department, and the later ones-call them Killer Bee-II, were not as high specc'ed

ChrisM
'ffkiwi'
Nov 21, 2021, 02:26 PM
B for Bruce
BMatthews's Avatar
Quote:
Originally Posted by flytigres
I'd guess a plastic backed "killer bee" type with a Mylar reed would compare well. Does that "290" cylinder fit all Cox crankcases? And how about removing the screen from the intake of that plastic back?
All the .049 and .051 cylinders and cases use the same thread size. Same with glow plug thread size. Cox is pretty much the Lego of the small engine world

In fact this fact was used in an April 1 article in a magazine about a "zero displacement engine". Pictures of a Cox .049 with a glow plug screwed into a crankcase were included. The premise was based on the RPM to displacement between .049's, .020's and .010's. Plotting those points on a graph showed an odd line that implied that as the displacement got to zero that one could expect about 50K RPM... Just don't ask about torque though...

Removing the screen might give a slight RPM increase. But at the possible cost of some fuel draw.

In a fit of trying to get my reedies to be all that they could be I even grafted a TeeDee venturi and needle onto a product engine backplate. The tach did say it was something like 500'ish RPM better. But the runs were a week or so apart. So conditions of the day could account for that sort of difference. It was so slight a difference and increased the mounting difficulties so much that I didn't go any further.
Nov 21, 2021, 02:45 PM
*******
Quote:
Originally Posted by flytigres
I'd guess a plastic backed "killer bee" type with a Mylar reed would compare well. Does that "290" cylinder fit all Cox crankcases? And how about removing the screen from the intake of that plastic back?
https://www.adriansmodelaeroengines....php?cat_id=108
Nov 22, 2021, 11:57 AM
Registered User
On the Cox Engine Forum we had a little contest and the reedies top speed was 63 mph and the best TD speed was 72 mph. These were not speed planes but average to better than average examples. I even used the same plane but had longer lines for the TD. I find the reedies can run well but it seems that air leaks from the tank setup, front bearing and the reed flutter at higher revs. slows them down. I held the Canadian record for a time at 82 mph with a TD. 100 mph or so was about the best that some of the more serious guys could get.
Nov 22, 2021, 08:32 PM
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Thread OP
How were these .049s configured? Modified intakes, port timing, glow heads, plastic backs, propellers, nitro?
Nov 23, 2021, 01:42 PM
Registered User
On the CEF, you could do what you wanted, but mine was a stock TD and the reedy was a TD cylinder both with 10% nitro. I used the Nelson Plug head mostly because I don't have many TD heads any more. I really don't fly the reedies or even Cox stuff any more because our rc field needs a muffler and a way of stopping the motor. I ran the Conquest a bit lately. You could use what you wanted for nitro though. For AMA rules 10% fuel for all speed events, which is a good thing IMHO. Hopefully it is ok to post this. https://www.coxengineforum.com/t1230...hlight=contest
Nov 30, 2021, 05:53 PM
Registered User

Back in the early 70s, .....


I ran some hot plastic backed .049s with Tee Dee .051 piton, cyl.& TD Cyl. heads, & with a slight reaming of the venturi they just screamed! I also dig a Baby Bee the same way with good results, & also a Golden Bee. Its true that the best results are had with a lot of spares to pick & match. I didnt have that many or I could have done better. Laramie. (old hot rodder)


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