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Unfiltered Ram Air?
Greetings,
Does anyone fly with unfiltered intake air? I've owned a few experimental planes and have never considered such a thing before now. The RV-3B I purchased recently has horz FI with a selection for unfiltered RAM Air, or filtered air. I understand the idea is to open the RAM air on climb out, and then close it again on landing approach. Assuming you're not flying through visible dust clouds, just how bad is that for the engine? The whole idea rubs me the wrong way, but maybe it's not really a problem? I'd be tempted to use the filtered air all the time, but it's not really made for that. The filter is located inside the cowl where it's not cool or pressurized as much as it could be, so there's a distinct loss of power. I guess I'm trying to decide whether I should leave well enough alone, or change the system for a better, full time filtered air setup. Thanks, Rusty |
yes,
not an RV, but I currently fly a Laser 200 - no air filter. Also, ever look at the front of an Extra 300, Walter doesn't put a filter. I did put fuel injection on a 3B several years ago and the fuel servo was slightly taller than the carb pushing the air box down into the cowl. I spent alot of time finding a different ht air filter and cutting down the air box. Im not saying I dont like air filters, I do. Im just saying it does not bother me not to have one. Mutter |
This was originally the standard configuration on the RV-3 and -4.
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Thanks for the comments. This picture shows the current filter arrangement, which is certainly not ideal for full time use.
https://www.amazon.com/photos/share/...rijSjtI52clht9 I may have to fly it as the builder originally intended for now, but once I get a hangar closer to home, I'm going to probably rework this to a better full time filter configuration. Cheers, Rusty |
I have a Rod Bower RAM air mod for my RV-10
http://www.ramairforhomebuilts.com/ I typically don't open it until I get about 5,000 ft. Although, I usually don't close it on the descent. It yields about a 1" MP increase. |
My RV-3 did not have a filter. I put about 500hrs on it and it had 700 SMOH when I sold it. Although I think air filtration _on the ground_ is a very good idea, my results were excellent over a 7 year period. Compressions and oil burn were still quite good after 700 hrs on a pumped up O-320. Mine was w/o an oil filter so oil changes were every 25hrs. Maybe that helped.
Anecdotally, I once flew it wide open at sea level on a standard day and the MP gage showed almost 2" of ram air "boost". Mine had an Ellison TB on it. The plane I'm building now will be set up the same way or may have "filtered air" as an alternate source. |
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(Note: Both statements are nonsense) |
I'm currently building a -4 with horizontal induction using the Air Flow Performance Y for filtered or ram air. Its going to work but adds weight and complexity. If I could go back I would just use ram unfiltered air 24/7. I live in the AZ desert and have rebuild a handful of off road engines that have seen pounds and pounds of dirt go through them. All of them showed little problems dirt related. Our planes will see little to no dirt, I say run it the way you got it (ram air) and don't think twice about it.
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Given an IO-360 at 2700, 3" intake diameter, 1000 feet standard day, and 200 KTAS, MP rise would be about 0.9559" Hg, for a total MP of 29.812". Returning to the OP's question, there isn't any good reason to run filterless on an everyday airplane, if the system can be built with enough filter media area. By measurement, the pressure drop for my entire airbox, including filter, is 0.19" Hg, as compared to an FM-200 with a standard test bellmouth. For perspective, Rod Bower reported a bit more than that for the open butterfly in his ram air system. With no butterfly, the drop might be half as much, but not zero. We're talking about giving up filtration in return for less than 0.1" Hg, max. Doesn't make sense. Reno racers? Sure, take no prisoners. |
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