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Oct 20, 2021, 04:55 AM
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Monza Red's Avatar
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Brown Junior. New Aquisition. The advice of the cognoscenti is sought.


A gentleman in Mississippi, having seen my Big Guff photographed in flight, has offered me a Brown Junior Type D together with a coil, condenser and HT cable for the cost of the postage to my home. I've decided to take up his offer. The Brown Junior a 10cc side port petrol two-stroke was the first successful model aeroplane engine to be produced and was fitted to the original Good Brothers' Big Guff in 1938.

I have never owned a "sparky," so bring a wealth of inexperience to the project. The closest experience I can offer is when I competed in Pre 65 motor cycle trials on a magneto equipped BSA Bantam! Consequently I have a number of questions.

1. What sort of battery is required?

2. Where can I find a wiring diagram?

3. The original plug and points system seems to work satisfactorily but I believe that modern transistorised ignition systems are available for these old engines. Where can one buy one and what advantages do they offer?

4. I am aware that the Brown Junior is not fitted with an R/C carburetter as fitted to modern engines but that it is capable of operating at a wide speed range by adjusting the ignition timing and fuel mixture. The Big Guff is currently fitted with a Laser 62 turning a 14 x 4 propeller and straight and level flight is achieved just above tick-over. I plan to adjust the engine so that it is turning over at 3000-4000 rpm which I guess is about the same rpm as the Laser throttled down, before releasing the model. Any opinions?

4. I would like to have a remote control throttle-cut so that if the engine was not developing sufficient power to allow take off I could abort the take-off before the model careered into the long grass. Is this possible?

I am not expecting the engine for at least three weeks and doubtless will have further questions when it arrives.



Happy Landings Gentlemen.
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Oct 20, 2021, 08:58 AM
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Gary Cee's Avatar
Love that plane!

The typical coil system is similar to the "Modelectric" coil. Usually used with 3.0 volts from a pair of C or D cells in series. A single LiFe cell could work fine too. Try not leaving the power on while the engine is not running as closed points draw a lot of current and quickly overheat the coil. There are several places that offer a solid state conversion that relieve the points from switching the high current load of the coil primary.
The transistor is triggered by the points and it in turn switches the major current load.

Gap the plug around .012"


I will find you a link later for the solid state conversion, you can easily make your own as well.
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Oct 22, 2021, 06:36 AM
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earlwb's Avatar
I would add that people used to plug in an extra set of batteries in parallel to the ones in the plane. This reduced the power consumption on the on board battery pack. Sometimes the engines could be quite recalcitrant when starting. Thus if the engine was being stubborn, the starter battery pack helped to prevent the onboard pack from being discharged quickly.
Oct 22, 2021, 10:51 PM
No more wasted spark 😉
ClubFlyer's Avatar
That engine would be the icing on the cake Monza. I would adapt a modern CDi ignition system to it without ruining the original design. Make a 1/4-32 spark plug adapter. Pull the needle valve & venturi / pickup tube and adapt a glow fuel carburetor of a suitable venturi to it onto the induction tube, and run it on CDi / Glow fuel. Adapting a walbro type gas carb is going to be a project in itself. But certainly I would do the modifications in such a way that it doesn't destroy the original design of the engine.

http://sceptreflight.com/Model%20Eng...Model%20D.html
Oct 22, 2021, 11:54 PM
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Gary Cee's Avatar
Be very wary over using methanol fuels. Many of those old sparky gassers were over-stressed at the increased power levels produced by methanol.

I have quite a few of the 3/8" Champion plugs, great plugs and more robust than the 1/4-32 variety. Let me know if you need any. Looks like the factory coil, if you have that is a 6 volt unit.
In that case, a four cell alkaline is in order or a 5 cell NiCd or NiMh, perhaps a lithium equivalent.
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Oct 23, 2021, 01:20 AM
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Monza Red's Avatar
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Thanks for all of the advice gentlemen, I'm going to try it on petrol (gas) first .
Oct 23, 2021, 01:42 AM
Still gassin' it.
Quote:
Originally Posted by Monza Red
Thanks for all of the advice gentlemen, I'm going to try it on petrol (gas) first .
Just a thought: there are transistor-mods to the original ignition diagram that hook up to the original breaker points so the ignition current is not flowing through those points, eliminating interference and prolonging breaker points.
However, with a simple set of resistors (I do not know from memory how to hook them up, but it is not hard to figure out) you can hook up a modern ignition to those same breaker points and have the advantage of the auto-advance curve, as well as probably a much lower current draw and significantly reduced RF noise levels.

It's what I would do...
Oct 24, 2021, 06:19 PM
Send lawyers, guns and money
ahrma_581's Avatar
I suspect you can use an RCExl Optic kill switch for a transmitter controlled T-cut. Might mitigate the need for any throttling: timing, prop and mixture for a slow climb, then when you're ready to come down, kill it and come in dead stick.

Much more info on care and feeding of this engine in the Vintage forum, but you already know that, don'cha!
Oct 26, 2021, 11:48 AM
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Gary Cee's Avatar
Here you go, the light weight, efficient transistor trigger to use with points.
You can easily use point to point wiring and make a very compact version as well. http://www.model-engine-plans.com/pa...ransistors.htm

The site has loads of stuff for sparky running

No need to destroy the engine's built-in character
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Oct 27, 2021, 02:41 PM
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Gary Cee's Avatar
Aero-Spark Coil instructions.
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Oct 28, 2021, 08:39 AM
AMA 7224
Leadchucker's Avatar
Another source and the one I use. https://modelflight.com/product-category/engine-parts/
Larry Is a top notch old timer guy and has all you need for your Brown. His coils work great ,you are going to want the high tension lead with the 10K resistor.
I use a 1S 1000 maH lipo for powering the ignition and it will last all day unless you run the engine a whole lot plus id does away with all the booster batteries which no one sues anymore. Starting trouble back in the day were almost always from crap batteries. I did use nihms and nicads back in the 70s but lipos are lifes are the way to go now.
Marv Stern makes or made a board for old time ignition and I still have one of his setups in my Rambler with a Super Cyke. I use methanol with BeNol oil mixed 4:1 as it's legal for competition. Never use nitromethane in the older spark engines
Oct 28, 2021, 07:06 PM
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Gary Cee's Avatar
Good source, thanks.
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