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Lancair 320 ram air?
Few weeks ago, 2 Lancair 320/360s stopped at my airport. I went over to get a
better look and found their engine air intake does not have any air filter. Are they designed this way? Would bugs be a problem? Does it shorten the TBO? |
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On Wed, 24 Dec 2003 23:56:38 -0600, RR Urban wrote:
I can't address what Lancair is doing, but.... my early RV-3 has UNFILTERED RAM AIR. However, when carb heat is applied.... the alternate air path is through a filter setup under the cowl. All is still going well after 700+ hours. Oil consumption is a quart in 15-20 hours. To date, bugs have not been a problem. There is an inlet screen and I'd guess the occasional small bug just gets sliced, diced and digested uneventfully. A swarm of locusts could be a different story. g The only thing I have discovered so far is that the ram air path, as originally implemented, affected fuel distribution to the cylinders somewhat negatively. The cure is vane(s) properly positioned in the air path or just use Van's later style intake air setup. [I have a MM-1 buddy with a similar ram air setup with the same damn fuel distribution issue.] Barnyard BOb -- over 50 years of successful flight that is most curious bob. my aircraft has a brackett foam airfilter (replaced annually) on the air inlet and none on the carby heat. the reasoning is that carby heat is only applied when well off the ground and the risk of contamination is small. the problem is not bugs imho the problem is grains of sand. you sure the builder didnt rig it up backwards? Stealth Pilot |
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that is most curious bob. my aircraft has a brackett foam airfilter (replaced annually) on the air inlet and none on the carby heat. the reasoning is that carby heat is only applied when well off the ground and the risk of contamination is small. the problem is not bugs imho the problem is grains of sand. you sure the builder didnt rig it up backwards? Stealth Pilot +++++++++++++++++++++++ It is neither curious nor backwards. The few RAM AIR designs I have encountered, ALL do WITHOUT the filter for max ram effect - even the certified Mooney. However, Mooney does have a mode that employs a filter when RAM AIR MODE is not desired. In effect, I do the equivalent with carb heat mode. FWIW.... Loss through the filter appears to be unacceptable to those engineers that care to max performance with RAM AIR designs. Perhaps those more knowledgeable will add their 2 cents??? P.S. The RAM AIR topic has been addressed here in the past. I'm surprised you are not somewhat familiar with the topic. Barnyard BOb -- |
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On Thu, 25 Dec 2003 12:15:46 -0600, RR Urban wrote:
that is most curious bob. my aircraft has a brackett foam airfilter (replaced annually) on the air inlet and none on the carby heat. the reasoning is that carby heat is only applied when well off the ground and the risk of contamination is small. the problem is not bugs imho the problem is grains of sand. you sure the builder didnt rig it up backwards? Stealth Pilot +++++++++++++++++++++++ It is neither curious nor backwards. The few RAM AIR designs I have encountered, ALL do WITHOUT the filter for max ram effect - even the certified Mooney. However, Mooney does have a mode that employs a filter when RAM AIR MODE is not desired. In effect, I do the equivalent with carb heat mode. FWIW.... Loss through the filter appears to be unacceptable to those engineers that care to max performance with RAM AIR designs. Perhaps those more knowledgeable will add their 2 cents??? P.S. The RAM AIR topic has been addressed here in the past. I'm surprised you are not somewhat familiar with the topic. Barnyard BOb -- I'm not sure how much manifold pressure is lost going through a well designed filter. But, for the sake of argument, if we assume a loss of 0.5" HG manifold pressure, my O-360 power spreadsheet tells me that would be about a 4 hp loss at a 75% cruise condition at 7500 ft, or about 3% of the power. A 3% power loss would give about a 1% speed loss. If you want to compensate for the loss in power by increasing the rpm, you need about a 150 rpm increase to get the same power you would have had with no air filter losses. These numbers are specific to the Lycoming O-360A series engines, but I would expect similar percent power losses for the same MP loss for any normally aspirated engine. The power loss would be roughly linear to the amount of MP loss. -- Kevin Horton RV-8 (finishing kit) Ottawa, Canada http://go.phpwebhosting.com/~khorton/rv8/ e-mail: khorton02(_at_)rogers(_dot_)com |
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The Mooney I flew would gain 1" using the ram air feature. I don't
know if that is standard or how accurate the gauges are but that is what we always showed. Jerry Kevin Horton wrote: On Thu, 25 Dec 2003 12:15:46 -0600, RR Urban wrote: that is most curious bob. my aircraft has a brackett foam airfilter (replaced annually) on the air inlet and none on the carby heat. the reasoning is that carby heat is only applied when well off the ground and the risk of contamination is small. the problem is not bugs imho the problem is grains of sand. you sure the builder didnt rig it up backwards? Stealth Pilot +++++++++++++++++++++++ It is neither curious nor backwards. The few RAM AIR designs I have encountered, ALL do WITHOUT the filter for max ram effect - even the certified Mooney. However, Mooney does have a mode that employs a filter when RAM AIR MODE is not desired. In effect, I do the equivalent with carb heat mode. FWIW.... Loss through the filter appears to be unacceptable to those engineers that care to max performance with RAM AIR designs. Perhaps those more knowledgeable will add their 2 cents??? P.S. The RAM AIR topic has been addressed here in the past. I'm surprised you are not somewhat familiar with the topic. Barnyard BOb -- I'm not sure how much manifold pressure is lost going through a well designed filter. But, for the sake of argument, if we assume a loss of 0.5" HG manifold pressure, my O-360 power spreadsheet tells me that would be about a 4 hp loss at a 75% cruise condition at 7500 ft, or about 3% of the power. A 3% power loss would give about a 1% speed loss. If you want to compensate for the loss in power by increasing the rpm, you need about a 150 rpm increase to get the same power you would have had with no air filter losses. These numbers are specific to the Lycoming O-360A series engines, but I would expect similar percent power losses for the same MP loss for any normally aspirated engine. The power loss would be roughly linear to the amount of MP loss. |
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Kevin Hortonwrote: I'm not sure how much manifold pressure is lost going through a well designed filter. But, for the sake of argument, if we assume a loss of 0.5" HG manifold pressure, my O-360 power spreadsheet tells me that would be about a 4 hp loss at a 75% cruise condition at 7500 ft, or about 3% of the power. A 3% power loss would give about a 1% speed loss. If you want to compensate for the loss in power by increasing the rpm, you need about a 150 rpm increase to get the same power you would have had with no air filter losses. ++++++++++++++++++++++++++++++++++++++++ For the sake of argument, if we assume... My *RAM AIR* only yields 0.75" HG with NO filter... it's not difficult to understand why a filter is anathema to the designed RAM AIR system. Barnyard BOb -- |
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