Air filter for tank backplate

Hi roddie,
I am a fan of keeping fine particles out of Cox engines.  Nice!
Here is a story,
We were 12yrs old, running BB.049s CL in school yards.
An article in a magazine suggested 'nylon stockings' as a filter.
Buddy cuts 1X2"  squares from his sister's stockings. We install them between tank/firewalls.
The effect was amazing.
Girls showed up.
And joined in the fun. Cox Cheerleaders.
They could out flip start, out fly us any day.
And they like it.
This is why I like Cox engines,
And it is the future,
Take care,
Have fun,
Dave
P.S. The nylon stocking filters worked out well !

I have a nice punch set and purchased a roll of screen material just slightly smaller than Cox screen (metric sizing -- not inch).
Anyway, I make my own replacement screens for my engines.

If you didn't see my previous posting?
Installing a screen in a Tee Dee venturi

I have also cut them slightly oversized to "dome" the screens.



I also have done this on the backplates of the old metal and plastic Bee plates.

Roddie, seems like a good idea if the motor is mounted solid enough. I have to ask what the exhaust outlet setup and wheel collar? on the needle valve is. Is that heat shrink tubing?

I also use nylon stocking filters on my Cox powered air cars to keep the sand and dirt on the road out of my engine. I also have made a nylon stocking filter that fits on my fuel tank breather as I was driving my RC homemade Cox powered air cars on a road next to the beach and I was having problems with fuel feed blockages. made the filters and the problem went away.

aspeed wrote:Roddie, seems like a good idea if the motor is mounted solid enough.  I have to ask what the exhaust outlet setup and wheel collar? on the needle valve is.  Is that heat shrink tubing?

Hi Alan, The filter media will compress flat when the engine is mounted.. except for the area (depression) on the rear of the backplate for air to enter. That entire depression becomes an air-filter when this media is used. I haven't found that it negatively affects performance.. but may require a slightly different needle-setting than you're used to.

Regarding the needle-valve; I have a short piece of med./lg. size silicone glow-fuel tubing and a steel flat-washer installed, which cures a common problem of air-leakage where the needle screws-in to the backplate. The OEM "spring" needs to be removed for this.. but if the tubing is the correct length; it will act as a spring when it's compressed. The operating-range of the needle is only a few turns.

Here's a better photo. Note that the flat-washer bears-on the shoulder just below the knob on the needle to act as a stop for the silicone tubing.



Regarding the "exhaust outlet setup"; it's a muffler that I designed some time ago.. and am still experimenting with. The outer-part of the muffler is made from two disc-shaped pieces of inner-tube rubber (butyl rubber) stapled-together.. and does look a bit like heat shrink tube in that photo, because it's wet with oil. In short; there's an inner aluminum ring (pc. of 1" tubing) with a hole drilled to accept a spent .22 ca. (long type) shell-casing which serves as a header-pipe. I recently sourced some silicone tubing that fits tightly over the header-pipe to allow for plumbing the exhaust further away from the engine. (LOOK HERE)

That silicone tubing pic. tricked my eye/brain. I guess I have seen both mods before, just can't see well enough. I was king of hoping that heat shrink would work on the exhaust to hold an exhaust stack. Just to add to the thoughts on the needle valve, I have had a motor where the needle was so loose that it pulled right out. I rubbed a bit of release agent wax over the needle threads, (oil might work too) and then put a SMALL drop of red Loctite over the needle with a toothpick, and screwed it almost in. It sealed well and now the needle is pretty stiff and holds the setting. The permanent red locktite is longer lasting than the blue. If you put too much Loctite on, it will plug the spray bar hole and the needle will be in there forever.

Hi All,
Landing/crashing vertical on a hard packed sand baseball diamond is the worst.
Cleaning Cox .049s get easier after that.
It is all relative...
Is there a scale of how much dirt/stuff can pass through a Cox.049?
I bet there are great stories here...
Thanks CEF forum,
Dave

probably slightly off of Roddie's thread topic but,
with a friend did some Cox 049 engine testing
Cox 049 surestart crankcase, grey horseshoe backplate with standard gauze filter in backplate, TD cylinder, killer bee crank, 1 head gasket, standard cox glow plug.
25 x nitro, 20 x Castor, 55 x methanol
Cox 5 x 3 safety propeller
tach with Turnigy fidget tacho
Engine held 18.7k till it emptied 1/2 ounce tank.  Peak at 19.2 K when first started and cold engine
Removed standard gauze filter from grey horseshoe backplate and ran engine again, still hot/warm from previous run
Engine held 18.7k till it emptied 1/2 ounce tank. Peak at 19K

It would seem the engine we were testing with ran just as well with the standard gauze filter as it did without it. that is not what we had expected   but we were happy with the engines output anyway.

Be interesting to see tach numbers for other cox engines with and without various filter types