I've been into rc cars/monster trucks for about 4 years and am just getting into flying. Everyone in the car/monster truck world know that it's a complete no no to run the engine for any amount of time without the air filter attached because of small dust particles that can/will damage the engine when introduced into the carb. Why is it that rc plane engines don't need them? Surely there are tiny dust particles at the flying field (when taxiing, taking off and landing).

It might be a good idea to use a filter if there is a lot of dust around on a grass airstrip, but, generally speaking there is nowhere near as much dust in the air as there is experienced by a car.

-David C.

It is usually needed in windy conditions when there is a high chance of airborn contamination. Most aeromodelers don't worry about that.

Mainly it's because the EPA doesn't know we DON'T use them

You used to be able to get a filter for airplane engines. Fourmost used to market them I believe. But they came loose when fuel soaked the rubber and they were a bit power restrictive (clogged easily). Glow aircraft engines where never designed with filters in mind, think of the extra room that they would need in the front of your aircraft. Yuck !!! [&:]

BRU-Line makes an excellent air filter that stays on the carb with a small wire-tie. I use them as additional insurance and piece of mind. I fly off of a grass runway and have not noticed any decrease in engine performance by using the filters. If this type of set-up won't fit, an air filter can be made by cutting a small patch of nylon stockings and securing it over the carb.

A small scrap of panty hose material stretched over the intake works, tie it off with string and CA glue.

I use Brulline carb air filters on all my engines not because I fly off a dirt strip but because I occasionally stick the engine in the dirt during crashes. There are plenty of other places for dirt to get in so I stop the easiest and most sensitive one.

they dont need em on planes cuz they generaly are on the ground kicking up dust for a shorter period of time.

I think air filters are as important as fuel filters - especially here in sandy Florida. I like the Bru-Line filter but it does extend into the prop on some engines. In that case, stockings are a fair substitution.

Dirt in you engine will sand down the insides quickly which is why I also don't think you should taxi any more than necessary and break-in you engine on a stand that is a few feet off the ground.

From looking at torn down used engines, we need 'em but don't bother with 'em

keep in mind, for the MOST PART any truly destructive particle is going to be heavier than air, thus it won't be found hanging around the sky much. you landlovers have it hard that way

If you are flying a model with an inverted engine from a grass or dirt/sand field, an air filter is a good idea. Ground-running churns up a bunch of small stuff! Bruline filters seem to work fine as far as I can tell. I even use them on upright engines, but maybe I'm overly cautious. Cheap insurance, and they do simplify cleanup after an in-the-dirt crash. Dzl

Well there is more "dirt" on the ground than in the air.

They have them. I use them on some engines... You just need to weigh the effect of adding an additional failure point to the lower level of dirt typical in air. Actually, mostly what I've seen is flying insects that get sucked in and cause flame outs. I think that is probably more an issue than any dirt on a flying vehicle. I use to fly on farm land and the number of insects eating up all of the agriculture was enormous....

Think about the size of even the tiniest particles floating around even in the air compared to the clearances used in our engines. Bruline filters are cheap and even if they only halve the amount of stuff getting drawn in they have to be worth it. Use the fine element and not the coarse one though. Another benefit is they trap any fuel that might get sprayed back out the carb so your engine stays cleaner on the outside as well.

If you have bug problems, get a heli, put sugar on it, and hover above the crops. Bugs are generally considered soft debris, and are really no match for the hard components of engines. i have seen them put small engines out of business and i have seen engines vaccum up the unsespecting dopes and throw them out again without any problems at all

One reason we tend not to use them as much in airplanes as cars/trucks (that applies more to beginners, but to all of us) is that, well, umm, my engines usually die for reasons other than excessive wear. Usually has to do with excessive deceleration...

Droopy

My Norvel has a bug screen over the carb, first time I'd seen that on an aircraft engine....

lol...I'm talking grasshoppers... They don't hurt the engine...they just don't burn very well compared to the methanol....flame them out and you end up with an unplanned emergency landing. Where I fly now though I don't have much of an issue....even the dirt/dust is pretty minimal.

I kind you have to weigh where you fly.

i didn't know that an engine would eat a grasshopper and not even have to be flushed out.

Hi guys,

First reply here. Thank you for having me in this forum.
Actually, this air filter question brought me here and I would like to try to understand a little bit further the proper function and the physics behind air filters.

Although I know the main role of air filters is to block any particles to enter the carburetor, I do have the concern of the amount of air that enters the engine, which can lead to a rich mixtures (and some cases, specific cone designs can lead to poor mixtures).

My question is: manufacturers like Desert Aircraft and others, don't provide any information regarding the proper air filter to install (they dont even suggest the customer to install it). So, how do you choose the filter mesh? Is it just a matter of testing several solutions? Or is there any other way around like flow simulation, etc?

Thank you very much for your time here guys.

It has been said that you don't need an air filter on a boat that never comes to shore, and a plane that never lands. As long as the surface area is large enough and the mesh is large enough to be unrestricted, it should be fine. That would be less restricted than the carb by a large margin to allow for dirt clogging it. Nylons are probably OK, but over maybe at least a square inch. Not just the 3/8" or so that is commonly on an average motor. For myself, I am more concerned about clean fuel than the air. Cars are right in the dust and dirt though. Some guys that smash planes a lot like in combat place a piece of rubber tubing over the intake, so when it crashes, it seals it off. It still gets dirt in the bearings though. For flow simulation, you can blow through the carb hole, and then the filter and compare the restriction. If you want to spend time making a flow meter, and like that sort of thing, that is ok, but you can tell that way. As for funnel shapes, I doubt that makes any difference on 2 strokes. Maybe a 4 stroke with a high pressure blower of whatever sort. Welcome to the forum.

My local hobby shop no longer carries the Bruline air filters and I couldn't find them at Tower Hobbies. Are they still made, and if they are, who carries them?

Bruline filters I believe have been gone for many years now and its understandable, there was just no market. I have not seen anyone using anykind of air cleaner now for perhaps eighteen years or so. There of course was the old trick of cutting a disc of your wifes silk
stockings and rubber banding it over the venture I suppose, heck do they still make silk stockings?

One trouble with the Brulines is when the fellows had a crash and the subsequent engine dirt bath the filters where the first thing to peel off doing no good at all.

Don.t know, for me any of that was just never worth the effort one way or the other. Perhaps another issue is many I believe simply move on so fast to bigger or so called better engines that most engines seldom see enough use for any kind of micron protection to make any kind of difference.

John

Thanks John, Because I fly almost entirely off grass or dirt I used to use those air filters on anything with an open (non cowled) engine bay. As pointed out, they didn't fit in most cowls so it was trainers and non scale sport planes that had the air filters. I still have several planes in the hanger with the filters on and two unused new filters still in the package. Not much need for them these days as I am using much larger engines and planes with cowls now. Thought maybe my LHS dropped them cause they now sell only electric planes! Yes, no glow or gas powered planes just electric, mostly RTF foamies. Time marches on but I don't, I still fly glow power and even build a kit or two now and then.