½A Texaco and the Cox Babe Bee

or

 “How frustrating can a competition class be”.

My thoughts in giving myself a fighting chance in making the 8 minute target time a real possibility.

In no particular order (as they say before announcing a winner) are the aims to be successful at this class.

  • Get as long as possible motor run from your Babe Bee consistent with adequate power to climb the model depending on the conditions
  • Choose a model that can be built down to the 8 oz per square foot wing loading in accordance with the rules
  • The model ideally should be about 16 / 17oz (though Allan Knox tells me his Skipper is 22oz!!!! in accordance with the rules) Remember that the motor is not producing the same power as it would be at 20,000rpm. Some motors may be better than others!!!!
  • The model should be as clean aerodynamically as possible Allan Knox’s “Skipper” 1948  is a good example
  • The design should have a “Clark Y” section (better for penetration / speed) though in certain conditions most sections will be OK.
  • The older the design is the better chance you have of winning (providing you max out of course)

How do you go about this task (again in no particular order) and relates to

“THE BABE BEE”

  • Use a 9 x 4.5 APC electric prop (for flywheel effect because our motor will be running at low revs)
  • Have a selection of (very clean filtered) fuel mixes available e.g. 7% nitro / 7% oil (synthetic preferred, Brian Winch recommends “Cool power” which is a castor/synthetic mix and expensive ) 10% nitro 5% oil etc (why you might ask? it is because the weather conditions make a big difference to the engine performance and you need to match the fuel to the conditions)
  • Have a rev counter available to ensure that your engine is delivering the RPM you are aiming for. (4600 – 5400rpm) depending on the fuel mix you are using the revs will be at one end of the range or the other (remember fuel consumption is governed by rpm)
  • Pick an engine that has 2 slits either side as exhaust ports
  • Get a Cox silencer
  • Remove spring starter (this can slow the revs if it keeps hitting the prop)
  • Pull the engine apart and clean thoroughly
  • Check and tighten the con rod to piston ball joint with the Cox tool for the job if slop is noted.
  • Check the reed valve for what type you have fitted and ensure that it is not damaged particularly where it seats (Mylar ones are good)
  • Replace the venturi / tank seal as this is a potential for a leak
  • Put in a fuel pickup that goes to the bottom of the tank . I use KS aluminum tube .062dia and carefully drill the back plate hole .062dia, where the original plastic hose pick up went, and fit the KS tube using Loctite to hold it in position. This is a very delicate task to ensure that it OK as there are many pitfalls E.G. swarf staying in the drilled hole, Loctite actually blocking the hole, not enough material in the back plate to take a .062dia drill without removing the pickup tit altogether (don’t ask how I know!!!) Bend the tube before actually Loctiting it in position so that it goes round the venturi to the bottom of the tank.

ASSEMBLY OF ENGINE

  • Assemble the engine ensuring that you have 3 copper shims under the glow head.
  • Make sure that when fitting the tank that the muffler is not holding the tank to crankcase joint apart (we don’t want a air leak here)
  • Make sure that the gasket between the tank to crankcase is a good one
  • Fit silicone fuel tube over the needle valve to make sure that there are a minimum of leaks

Running of engine

  • Fill tank with fuel until it overflows THEN block off the overflow and carry on filling until fuel flows out the venturi inlet, this makes sure that the needle valve passage is not blocked with castor (if that is what you decided to use) and ensures that the tank is full.
  • Close off the muffler metal slide all the way so that the exhaust only comes out the 1/8th hole. Initial starts may need a bit more opening of the slide until the motor warms up, then for economy close it right off. Priming is done with a squirt up the 1/8th hole.
  • Apply the glow plug lead and proceed to flick. The motor will feel like it doesn’t have much compression but it is enough provided the head has sealed properly.
  • Once you have the motor started and keep it running, check the RPM and depending on the fuel mix you have used it should be between 4,500 and 5,400.
  • The motor RPM will vary up and down about 3/400 RPM this is normal
  • While the motor is running slowly top up the tank until it overflows then start the stop watch and see how long it takes to run the tank dry (6 plus minutes should be the norm this depends on the fuel mix you used)
  • After it has stopped check tighten the glow head as they have a bad habit of loosening.
  • In getting ready for a competition flight make sure that that the motor has warmed up then fill the tank while the engine is running just prior to launching the model (you did remember to switch the radio on didn’t you??? as a 6 – 7minute motor run will go a long way with a properly trimmed free flight model!!!!!!!)

     Have fun chaps, don’t call me I’m at the funny farm producing another edition of Torque!!!!

          Gary Burrows.

Click HERE to download the above as a pdf document.

 

Some comments - Mark

In the photo below, engines one and three would be the ones allowable in our Vintage classes.  The tanks need to be standard as per the first one which from memory is around 5.5cc.


The second photo shows various cylinders and I have generally found that no2 cylinder gives the better duration on the allotted fuel.



Babe Bee's - love 'em or hate 'em but they certainly made an impact on the modelling scene.

Everything you ever wanted to know about them here on Wikipedia.

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