screamin' Babe Bee

Nice but it was surging a bit , notice at the end the was KIM's Mud Dabber with the two space hoppers on it lol . I have gotten 21.200 from a reedie but I quit horsing with it after the 1st. reed speed . I don't think I have ever seen one throw the rod out the case has anyone ? Thanks Roddie Eric

It sure screams but it's no wonder, as there is practically no load. A flywheel is a load only when accelerating, unlike a propeller that requires more power as the rpms increase. But it does also show that a reed valve is not the limiting factor when top rpm's are sought.

pkrankow wrote:1 2 3 4 5

this post can be deleted please.

Could not agree more....I hate seeing COX engines being intentionally killed..

balogh wrote:

pkrankow wrote:1 2 3 4 5

this post can be deleted please.

Could not agree more....I hate seeing COX engines being intentionally killed..

I'm sorry. Didn't mean to cause a stir. I see something like this as educational rather than destructive. This particular engine appears to be a stock Babe Bee.. and I have designs on running a throttled-one in my homemade rigger. Being throttled.. I hope to have success using a lightweight flywheel (as compared to the common Dumas and Sterling ones for 1/2A) and not have to worry about engine "run-away" before launching.. or if the boat flips over.

No offense, Roddie...we all learn from posts like these....I just simply regret the lil sucker running with no heat sink

roddie wrote:

balogh wrote:

pkrankow wrote:1 2 3 4 5

this post can be deleted please.

Could not agree more....I hate seeing COX engines being intentionally killed..

I'm sorry. Didn't mean to cause a stir. I see something like this as educational rather than destructive.

I agree on the educational point of view. This time a Babe Bee might be "sacrified to science" as test engineers (I used to be one) say... But it shows that a reed valve doesn't start to float until at quite high rpms. Or at last that is what I think is the limiting factor in this case.

Now, the next thing to solve is how to make the engine run 30k with a load

Thanks Andrus and Kari. The Cox .049 reedy is "my engine of choice".. when it comes to my own personal experience. It's frequently over-shadowed by it's rotary-valve counterparts; of which I have only recently acquired two..  and have not run them yet. (Tee Dee .049 and .051)

Aero-engines seem to have a whole different set of dynamics happening than a surface-model has. The load on the crankshaft must differ quite a bit between swinging an aero-prop vs. running the engine in a car or boat. Then there's the effective-cooling. How much will the engine need in it's operating environment? A clamp-on heat-sink seems to be first order when running enclosed in a car.. and a water-jacket in a boat having a drive-shaft/water-prop. High-nitro fuels are said to run cooler.

The stock Babe Bee is obviously capable of very high rpm's. I believe that aero-props come nowhere near the engines potential for maximum performance. They're quite adequate for their purpose but.. if the engine is capable of 25k+ rpm's... loading it with an aero-prop that gives you an avg. 17.5K is only utilizing 2/3 of the available power. The balancing of the little aero-prop is probably more critical than an engine of larger displacement.. with more rotational mass. (Roddie psycho-babble) I'm looking to tap 20k+ from a stock reedy (Babe Bee w/Ace venturi throttle) for my out-rigger hydro. Available props were an issue. Dumas had been the only supplier of water-props specifically sized for Cox engines. Their .049 prop has a 1" dia. but is a hydro-dynamically inefficient prop. by today's standards. I have found some 1" surface-drive props that I want to try. I think that will get me in the ballpark.



I designed a PVC flywheel to fit back over Cox's cam-style starter-spring. I can add rotational-weight it if needed.




Hoping this will allow winding-back with thumb/finger for starting.

I also made smaller flywheels for friction-wheel starting.



All these need testing.

1/2A Nut wrote:Most peaks hit 29k+ some hit 30k+ best read 30,540 rpm / would be easy if he would
keep it running at peak longer reads may have been even higher with some needle
tweaking. But without cooling its better he did short runs. Note this debunks all claims
that a reed engine cant function past 25k.

I have this engine reduced in weight for speed application.
The idea is to swap out a TD .020 at 29g with minimal
weight gain. Carbon 3.8 x 2.8 prop on 35% nitro should hit 31k

It can't for very long. I've replace enough damaged piston/cylinders from ball joint separation to know, they might run at really high RPM, but not for long, ask any mouse racer.

Mark Boesen wrote:
It can't for very long. I've replace enough damaged piston/cylinders from ball joint separation to know, they might run at really high RPM, but not for long, ask any mouse racer.

Or NMMTPA member for that matter. I got a box of carnage with that NMMTPA lot I bought on eBay. Holes in crankcases, con rods seperated from the pistons, broken con rods, tops of pistons cracked, and broken cranks.

roddie wrote:........ I believe that aero-props come nowhere near the engines potential for maximum performance. They're quite adequate for their purpose but.. if the engine is capable of 25k+ rpm's... loading it with an aero-prop that gives you an avg. 17.5K is only utilizing 2/3 of the available power. ...........

Roddie

while the shaft load curve of a propeller is steadily rising with the 3rd power of the rpm, the engine output power curve is kind of parabolic, first rising, then reaching its peak, after which power will  decline with further rpm rise .  It means the engine will not  produce more power at higher rpm than in its peak power point, which is at lower rpm than the unloaded max rpm.. This is no different with boat and car applications where the load on the engine is proportional with the rpm, but the power produced by the engine is parabolic.

With the good mating of load and engine power characteristics you can achieve that the load curve of the aero- or boat propeller, or the drive system of a car will intersect the engine power curve at its peak, which is not necessarily at the peak rpm of the engine. (The load and power curves intersecting each other in a coordinate system means that the prop requires the same amount of power to be swinged at a given rpm, as the power the engine produces at the same rpm, and this will be the point of equilibrium i.e. the duty point in their cooperation) Power is the product  of torque and rpm, and torque typically declines with the rpm increasing.

I used this graph before to analyse why in colder weather the same 010 engine swings the same propeller slower than in warm weather notwithstanding the increased air/fuel charge amount in cold weather, but it may help here to understand the prop-engine collaboration in general. The parabolic power output curves of COX engines are courtesy Martin Hepperle, the rising load curves are my estimates only for demonstrational purpose.

(Sorry if my above bookish essay is a no-brainer because you were already  familiar with the issue. )

KariFS wrote:

roddie wrote:

balogh wrote:

pkrankow wrote:1 2 3 4 5

this post can be deleted please.

Could not agree more....I hate seeing COX engines being intentionally killed..

I'm sorry. Didn't mean to cause a stir. I see something like this as educational rather than destructive.

I agree on the educational point of view. This time a Babe Bee might be "sacrified to science" as test engineers (I used to be one) say... But it shows that a reed valve doesn't start to float until at quite high rpms. Or at last that is what I think is the limiting factor in this case.

Now, the next thing to solve is how to make the engine run 30k with a load

I misread the OP and thought he had lightened the .049 below the weight of a .020. This would be a serious, ridiculous even, amount of metal removal. I then tried to edit the post after re-reading the OP when something happened and the computer(s) refused to cooperate so I put some numbers in. After that took I asked my post to be removed, which it was but after it became an item via reply.

yes, it is really cool to push an engine to the practical limit however the ball joint is not a good construction to these ends. Pushing an engine to the mechanical limits always causes self destruction of the engine whether it is NASCAR, drag racing, or model speed.

I would like to see this engine preform for what it was built for.

Phil