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Removable, low-friction air-screen for Killer Bee backplate

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Removable, low-friction air-screen for Killer Bee backplate

Post  balogh on Fri Feb 26, 2016 2:36 pm

Until today I have used  Babe Bee backplate screens sold by Bernie as make-shift air filters tucked into the venturi of Killer Bee backplates. I know a screen may be found counter-productive on a Killer Bee plate that has an increased venturi diameter for better airflow, but the field I fly my planes always poses the danger of the engine sucking in flower seeds and dust.

I did not see too much choking effect with a screen in Killer Bee backplates i.e. the engine runs fine with it, but I decided to make it even less of a choke by using a patch cut from a tea filter bag. This is a plastic filter, finely woven, and resists nitro fuel. Because it does not occupy the venturi cross section inside like the steel screen I used before, I expect even lower choking effect than with the steel screen.

I cut 2 holes on the patch one on top one on the bottom and pulled them over the spraybar fuel nipple and threaded ends so as to secure it, and a small rubber ring is also added to press the filter on the venturi body for better sealing against unfiltered air.

Disregard the quality of my first tailoring attempt. For comparison of the mesh size, a genuine screen is also shown here.

I will tach it tomorrow.

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Re: Removable, low-friction air-screen for Killer Bee backplate

Post  roddie on Fri Feb 26, 2016 5:28 pm

Another filtering media you can try is polyurethane. Room/window air-conditioners use it on the intake-side. It's inexpensive.. and a package would last a lifetime.

I've used it for fuel-tank cushioning too. It's only 6.35mm (1/4") thick. A 19mm square piece could be tucked between the backplate and firewall. I can definitely understand your concerns about the open air-intake. A fouled reed really puts a damper on the fun. With my suggestion, you may need a horseshoe-shaped spacer-plate or stand-offs. The media will compress otherwise; probably decreasing the air-flow. Either way.. there isn't much space between the throat and the firewall as it is. I have this back-plate too.. and I think I'll try an experimental firewall that has some channeling for more air. Maybe just one slot to act as a high-rise manifold does on a hot-rod engine.

Here's a pic of the filter-media.




It helps isolate vibration when running a hard-tank on little profile C/L models.


I like the tea-bag filter. I've never seen the plastic type. I should check at work. The company is Ireland-based.. and there's various boxes of Irish teas in the pantry. It seems tedious; your method of attachment.. but I don't see any other way to secure it.

Edit..

Here's some pics of a piece I just cut. It's hard to tell how much the media compresses, affecting cross-flow. A center slot-channel in the firewall would provide expansion-space for the media.. assuring good air-flow.



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Re: Removable, low-friction air-screen for Killer Bee backplate

Post  balogh on Sat Feb 27, 2016 1:18 am

Thanks Roddie

Your solution also makes sense and is worth a try for unobstructed air flow. It mounts obviously easier than mine that occupies less room though and also allows Bernie's throttle application.

The teabag I used is from a Messmer tea box I met in the restaurant of a hotel I was put up this week in Germany. Not all the filter teas come with plastic bag, most have paper tissue bags. This one has plastic that stood my quick nitro test.
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Re: Removable, low-friction air-screen for Killer Bee backplate

Post  roddie on Sat Feb 27, 2016 8:23 am

balogh wrote:Thanks Roddie

Your solution also makes sense and is worth a try for unobstructed air flow. It mounts obviously easier than mine that occupies less room though and also allows Bernie's  throttle application.

The teabag I used is from a Messmer tea box I met in the restaurant of a hotel I was put up this week in Germany. Not all the filter teas come with plastic bag, most have paper tissue bags. This one has plastic that stood my quick nitro test.

I'm sorry Andras, I forgot all about the snorkel-throttle that you're using. Embarassed Do you suppose that the snorkel might hold the tea-bag mesh in-place on it's own.. without the rubber-band? I'm thinking it may also seat/seal better when you press the two together?

Being my crazy self.. I started thinking this morning about more options for air-filtering. I don't know if these would stay in place or not.. but they're easy to make.



It would depend on the choke-tube's inner diameter. These inserts I made are 6.35mm (standard paper hole-punch size) and might be a good fit. You could install one down through the open throttle-barrel using a small dowel or something similar?



If it worked.. it would be serviceable by making a tiny music-wire "pick" to hook the filter and pull it out. No need to remove the engine. It places the filter further away from fuel too.. although I've found the filter-media to be fuel-proof. Polyurethane generally is, to a large extent.
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