We fly off rough fields in my country. This year the monsoon finished late (usually it finishes in Sept-Oct but this time it was raining in Nov). On the field we are using, they have just burnt some dry grass and are cutting the green grass. Its a polo field and the season for that has also just started. Since the field was unprepared, till last week I was flying my cheap hack: Phoenix Tiger40 with an engine with scuffed piston. Now in the coming week I want to fly one of my prized airplanes mainly because the Tiger's engine doesnt seem to have much life left. But last week we had burnt grass, grass shavings and tiny bugs (running away from the fired grass) all over the airplane.

Now, I have 2 airplanes: GP Reactor 46 with the 55AX at 8-o-clock and Topstar (Flip3D) with a FS91SII inverted.

With the Reactor, the carb is infront of the engine so there is more likelyhood of dirt, shavings etc entering the carb. But then again there is only prop infront of the carb so less stuff will be raised

With the Topstar, the carb is further back inside the cowl behind the cylinder block and between the cylinder and firewall and facing right way up (because the engine is inverted) so more shielded. But since its further back, the likelyhood of the material being raised by prop and landing gear going into engine is more.

So my question is which one should I put together? Also, what effect will the shavings, dirt etc have on either of the two engines? I dont want to use filters as the power output will drop

Ameyam

Dirt in the engine is never a good thing but I honestly dont see the harm in the grass, unless it found a way to clog fuel delivery. The grass is soft and the internals moving oughta chew that stuff up and never know it was there.. dirt, not so much.

May be it will help if I post pictures of the two set-ups

Ameyam

Maybe you should try an air filter?

There are commercially available units, like Bru-Line, or you can just put a small piece of womans stocking (like a piece of panty hose, etc. ) across the carb intake...hold it in place with an O-ring stretched around the carb stack.

Just a bit here: can I use some old cotton socks? I would cutoff the required amount of material and hold in place with wire tie. Then will it hold in place?

Ameyam

I would not recommend cotton sock's material; as stated above, nylon sock or panty hose are a better option.

Whatever the filter material is, it gets soaked in oil and fuel, which increases the filtering effect but also the resistance to the intake.

The idea is to use as much surface of filter as possible and rather coarse material.

I use Bru-Line filters in my engines and I heve not noticed any drop in power.

For the same reasons that you explain, RC cars and truck use filters all the time.

Here you can find some ideas of materials and shapes:

http://www3.towerhobbies.com/cgi-bin...=RF&search3=Go

OK, pictures are attached. This is the Topstar with the FS91SII. Its similar to the UCD 60 or flip 3D. It a veteran airplane. You can see the carb inlet behind the cylinder block. I have included a picture with the cowl fitted

The last one is from a couple of years ago

Ameyam

Using a piece of ladies' stocking is standard here in the US for dusty fields. It doesn't affect power output at all and it will keep debris out of your engine.

Grass is, in fact, very abrasive. Animals which eat grass have high crowned teeth which wear down over their life.

While I dont disagree with that, I do think that if a small glow engine ingested the amount of grass that a herbivore consumes in even an hour's time, I would say that there are bigger fish to fry.. besides that, steel and chrome are harder than the enamel on a tooth isnt it?? not sure about the aluminum but I wouldnt think that a few blades of grass would hurt anything, perhaps someone has experience that can tell me this is possible?????

Ok, we are drifting. I was informed that the field is better today. Couldnt go myself coz I had a small operation yesterday. So I put together the airplane the best I could. Its a ageing warhorse as you can see and I am going to need an "airworthiness" certificate from my mentor. It is much better flier than the Reactor (read as much slower) and easier on the nerves when in 3D

Ameyam

OK I'm telling you "different"...

I had a blade of grass sucked into the intake which caused a dead stick as it wrapped around the "cat eye" needle exhaust.

Another time one made it into the cylinder and was not expelled.
Instead it stuck to the head walls, carbonized and lead to a ruined piston ring in very short order.

Grass does not belong in your engine.

Ya didnt have to make sound like I was being a D***.

I stand corrected, grass CANin fact harm internals.

Not intended as an insult... I guess I missed adding the smileyface to convey a joking response. Sorry.

Cool man, no foul.. Ihonestly didnt think grass was as evil as it is.. love these forums, learn new stuff all the time!

Any 0.46 two stroke engine at 10,000 rpm sucks from the surroundings as much as 75 cubic inch of air each second.

That is the air contained in a cube with width's sides of 4.2 inches each second.

Dust, little stones, green or dry grass, metal, charcoal and carbon particles (which are very hard) can be ingested by the engine during take-off.

Actually, cellulose has a crystaline structure that can be abrasive on metals, just like paper towels are.

good point, the air can have some pretty nasty nasties in it that we also are exposed to, the small IC engines are no different.. they see the same things our lungs do just at dramatically higher speeds

I've had engines last a very long time that have sucked some grass into them.
While I don't abuse my engines, I don't pamper then either...or run aircleaners on them unless they're in a car. Grass and dirt are part of our flying fields...they're not going anywhere anytime soon. And on take off and landings in fresh cut grass chances are you're going to suck a little in.

I would be more concerned with lean runs and rust prevention...two things far more detrimental than a little grass