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#51
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Ram air
On Jun 3, 7:54 am, wrote:
On Jun 2, 9:45 pm, Billy Crabs wrote: let me try to explain myself better, the amount of air that is drawn into an engine is in direct coralation to cylinder volume and the cam shafts "lift and duration" A valve can only stay open as long as the cam lobe holds the lifter up, therefore only allowing as much air/fuel as was scientificly formulated for the cylinder. for instance, lets say you have two guys who are going to breath in deep, now even if you are blowing an air hose in their faces, they are only going to be able to inhale as much as there lungs will hold. Now lets say they are inhaling pot and when they blow out its put into a "turbo", the turbine spins and sends the unused pot back to their lungs, but it's still only as much as they hold in their lungs(cylinder volume) Air density in the cylinder is governed by its pressure and temperature. MUCH more air can be forced into the cylinder if the manifold pressure is boosted; this is the principle behind getting more power out of a given number of cubic inches. You need to do some studying on the matter. I have, and I teach this stuff in college. Dan I wonder if ram scoops were ever installed near the prop tips. Probably too expensive for GA, but a WW2 A/C with tips spinning at what(?) 500-600 mph would give a nice pressure boost. I've read dual phase superchargers were used in recon A/C to get the speed and altitude. Ken |
#52
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Ram air
Ken S. Tucker wrote:
I wonder if ram scoops were ever installed near the prop tips. Probably too expensive for GA, but a WW2 A/C with tips spinning at what(?) 500-600 mph would give a nice pressure boost. I've read dual phase superchargers were used in recon A/C to get the speed and altitude. Ken First off I doubt it overcome the drag it would create. Second, what do you think the tip speed is on an average GA plane is? Follow this link and learn a thing or two. http://www.pponk.com/HTML%20PAGES/propcalc.html |
#53
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Ram air
Stealth Pilot wrote:
On Mon, 02 Jun 2008 19:51:47 -0400, dave hillstrom wrote: On Mon, 2 Jun 2008 14:12:26 -0700 (PDT), Tony wrote: Ram air is only as useful the allowing air to get to your carburater faster but is not necessarily used. When your piston is on its intake stroke(vaccum) your combustion chamber can only draw in enough air that is in conjuction to the chambers volume and all other air that is present after the compression stroke is exported to engines smog devices and is recirculated only AFTER being filtered. All engines come off the assembly lines, be it an airplane motor or a vehicle motor, to draw the amount of air that it needs to run at opptimum performance. Ram Air is a myth and don't try to throw "turbo" into the conversation because turbo is recircualted exhaust and still has unburnt fuel in the fumes. I think you are quite wrong. Ram air in fact gives us a half inch or so more manifold pressure, and that increases the total weight of the air-fuel mixture in the cylinder. Reduce your 'it doesn't matter argument to an extreme to see how it fails. As for turbos, the turbine is powered by the exhaust gasses coming from the engine, the exhaust gas itself is not reintroduced into the cylinders. The turbine itself could be powered by an electric motor, for that matter. That was the model for my tongue in cheek comment about using a shop vac to increase manifold pressure. will you marry me? dave the term is not foo and bar. foo *is* a term from another war and another airforce but the term you've so successfully stuffed up is fubar fubar is a vietnam era acronym of F***ed up beyond all recognition. your sig line is a snafu (situation normal all F***ed up) Yore 'rong. foo and bar are metasyntactic variables. They aren't acronyms (they're metasyntactic variables). Like being the John and Jane Doe of computer engineering - placeholders. Fubar predates WWII. -- nuts |
#54
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Ram air
On Jun 3, 10:18 am, "Ken S. Tucker" wrote:
I wonder if ram scoops were ever installed near the prop tips. Probably too expensive for GA, but a WW2 A/C with tips spinning at what(?) 500-600 mph would give a nice pressure boost. I've read dual phase superchargers were used in recon A/C to get the speed and altitude. Airspeed off the tips is the same as the speed off the inner blade areas, due to the pitch washout across the blade span, so there'd be no advantage to having scoops behind the tips. The propeller's blades are flying at an AOA of between 2 and 4 degrees in cruise flight, anywhere between the tips and hub, because of that pitch variation. See Figure 6-4 of this page: http://www.allstar.fiu.edu/aero/flight63.htm Dan |
#55
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Ram air
On Jun 3, 11:18 am, wrote:
On Jun 3, 10:18 am, "Ken S. Tucker" wrote: I wonder if ram scoops were ever installed near the prop tips. Probably too expensive for GA, but a WW2 A/C with tips spinning at what(?) 500-600 mph would give a nice pressure boost. I've read dual phase superchargers were used in recon A/C to get the speed and altitude. Airspeed off the tips is the same as the speed off the inner blade areas, due to the pitch washout across the blade span, so there'd be no advantage to having scoops behind the tips. The propeller's blades are flying at an AOA of between 2 and 4 degrees in cruise flight, anywhere between the tips and hub, because of that pitch variation. See Figure 6-4 of this page:http://www.allstar.fiu.edu/aero/flight63.htm Dan Dan it was a trick question I asked you. It's the basic aerodynamic physics of the standard centifugal supercharger compressor operating principle. I tossed you a zinger, cuz you claimed to be a teacher in a college and I couldn't resist :-), don't worry about it, hardly anyone get's that one correct, and I hope you get a ha-ha-ah from it. I mentioned, "dual phase superchargers" as a hint. Here's the answer: the ram-air pressure acquired at the prop tips is equal to the loss of pressure against the centrifugal force pushing air - via ducting - into the prop center that one obtains at the prop tips. Now you know the rest of the story. Regards Ken |
#56
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Ram air
On Jun 3, 1:45*pm, Billy Crabs wrote:
On Jun 2, 11:33*pm, Billy Crabs wrote: On Jun 2, 11:08*pm, wrote: On Jun 2, 8:00 pm, Billy Crabs wrote: On Jun 2, 5:12 pm, Tony wrote: Ram air is only as useful the allowing air to get to your carburater faster but is not necessarily used. When your piston is on its intake stroke(vaccum) your combustion chamber can only draw in enough air that is in conjuction to the chambers volume and all other air that is present after the compression stroke is exported to engines smog devices and is recirculated only AFTER being filtered. *All engines come off the assembly lines, be it an airplane motor or a vehicle motor, to draw the amount of air that it needs to run at opptimum performance. *Ram Air is a myth and don't try to throw "turbo" into the conversation because turbo is recircualted exhaust and still has unburnt fuel in the fumes. I think you are quite wrong. Ram air in fact gives us a half inch or so more manifold pressure, and that increases the total weight of the air-fuel mixture in the cylinder. Reduce your 'it doesn't matter argument to an extreme to see how it fails. As for turbos, the turbine is powered by the exhaust gasses coming from the engine, the exhaust gas itself is not reintroduced into the cylinders. The turbine itself could be powered by an electric motor, for that matter. That was the model for my tongue in cheek comment about using a shop vac to increase manifold pressure. The air going into the manifold has the same atmospheric weight as if it was outside the manifold, what makes it denser is the addition of fuel into the air/fuel mixture, unless the air is in a perfect vaccum it will not increase in pressure and most certainly not density and the turbos do reintroduce fuel back into the combustion mixture, If you've ever seen a read out of carbon emissions for a non turbo vehicle it still has enough unburnt fuel to power your vehicle for another 5% of your fuel consumption *and turbos IF powered by a motorized turbine are as useless as ram air because of the statement I made in my previous post. your intake is only as much as the volume of your cylinders * * * * * * Turbocharging can be set to two different levels: Turbonormalizing, which brings manifold pressure to sea level pressure; and boosting, which raises manifold pressures to more than 30" Hg. If an engine is boosted, the air density in the cylinder at the bottom of the intake stroke could be well above atmospheric. I'm sorry to keep disagreeing but, but the pressure in which(if you can call it pressure) goes through a manifold is increased by MAP sensors which measure atmospheric pressure and regulates air fuel mixture, it has nothing to do with "ram air" and I do agree that that the density of the air/mixture is increased by the vaccum caused by a piston at bottom dead center but we were talking about air before it reaches the cylinder and the speed of which it arrives to carburation. * * * * *Dan- Hide quoted text - - Show quoted text -- Hide quoted text - - Show quoted text -- Hide quoted text - - Show quoted text - let me try to explain myself better, the amount of air that is drawn into an engine is in direct coralation to cylinder volume and the cam shafts "lift and duration" A valve can only stay open as long as the cam lobe holds the lifter up, therefore only allowing as much air/fuel as was scientificly formulated for the cylinder. for instance, lets say you have two guys who are going to breath in deep, now even if you are blowing an air hose in their faces, they are only going to be able to inhale as much as there lungs will hold. *Now lets say they are inhaling pot and when they blow out its put into a "turbo", the turbine spins and sends the unused pot back to their lungs, but it's still only as much as they hold in their lungs(cylinder volume)- Hide quoted text - Billy , I think you are confusing volume ( which is certainly fixed) with mass of air. by increasing the pressure you increase the density and therefore have a higher mass of air for the same volume. higher mass of course means more energy for the same volume charge. Terry PPL Downunder |
#57
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Ram air
On Jun 4, 12:54*am, wrote:
On Jun 2, 9:45 pm, Billy Crabs wrote: let me try to explain myself better, the amount of air that is drawn into an engine is in direct coralation to cylinder volume and the cam shafts "lift and duration" A valve can only stay open as long as the cam lobe holds the lifter up, therefore only allowing as much air/fuel as was scientificly formulated for the cylinder. for instance, lets say you have two guys who are going to breath in deep, now even if you are blowing an air hose in their faces, they are only going to be able to inhale as much as there lungs will hold. *Now lets say they are inhaling pot and when they blow out its put into a "turbo", the turbine spins and sends the unused pot back to their lungs, but it's still only as much as they hold in their lungs(cylinder volume) * * * * * Air density in the cylinder is governed by its pressure and temperature. MUCH more air can be forced into the cylinder if the manifold pressure is boosted; this is the principle behind getting more power out of a given number of cubic inches. You need to do some studying on the matter. I have, and I teach this stuff in college. If you are teaching this stuff you might like to make use of the data I put together on the C172 takeoff and landing performance. it is in the form of an excel spreadsheet which shows the takeoff and landing distance as a function of density altitude at different temperatures. ( derived from the Cessna tables of distance vs pressure altitude and temperature. It clearly shows that the takeoff performance is not simply a function of density altitude which all of the flight training literature i have read and all my own training drummed in to me. And perhaps you could come up with a better explanation than decreasing air viscosity :) It is clearly engine related because the landing distance data do fall on the same curve of distance vs density altitude irrespective of temperature. The best explanation I have heard is that higher for a given density will get the air into the cyclinder faster ( ie you will just get closer to the equilibrating the pressure between the outside and the cylinder. Anyway the analysis can be downloaded from the following site ( this is an australian pilots forum called straight and level downunder). this link will take you direct to the download page. You are welcome to join the forum too but you have to register for that ( to keep the kooks out - or in depending on your perspective). but you dont have to register to access the download section. http://www.straightandleveldownunder.net/downloads.html Terry PPL Downunder |
#58
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Ram air
"Billy Crabs" wrote let me try to explain myself better, the amount of air that is drawn into an engine is in direct coralation to cylinder volume and the cam shafts "lift and duration" A valve can only stay open as long as the cam lobe holds the lifter up, therefore only allowing as much air/fuel as was scientificly formulated for the cylinder. for instance, lets say you have two guys who are going to breath in deep, now even if you are blowing an air hose in their faces, they are only going to be able to inhale as much as there lungs will hold. Now lets say they are inhaling pot and when they blow out its put into a "turbo", the turbine spins and sends the unused pot back to their lungs, but it's still only as much as they hold in their lungs(cylinder volume) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Sorry, but no ()'s for your above post. Wow, what you don't understand about supercharging/turbocharging is "a bunch." In your above example, if one guy (instead of having an air hose blowing in his face) had a guy with twice the lung capacity giving him mouth to mouth recesitation as he was breathing in, and the guy blowing emptied his lungs completely into the "breathing-in" guy, that would be a better analogy to what a supercharger/turbocharger does. He is physically forcing more air into the guy than he could normally breath in, by forcing more air in throughout the intake stroke. Let's hope he has strong lungs, so they don't explode. That is what happens to engines that have extremely high boost running at high output, sometimes. They can't stand the extra kick provided by all of the extra air, gas, and resulting combustion. If the engine has a mass airflow sensor, that is how it knows how much extra gas to feed into the intake air. It can tell there is extra pressure, which gives the volume of air being passed though it (the sensor) extra mass. At _no time_ does a normal turbocharged/supercharged engine have already used combustion gas put back into the next (or any other) intake cycle. The only reason some engines have a feature like that would be for pollution control. -- Jim in NC |
#59
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Ram air
On Jun 3, 12:56 pm, "Ken S. Tucker" wrote:
Dan it was a trick question I asked you. It's the basic aerodynamic physics of the standard centifugal supercharger compressor operating principle. I tossed you a zinger, cuz you claimed to be a teacher in a college and I couldn't resist :-), don't worry about it, hardly anyone get's that one correct, and I hope you get a ha-ha-ah from it. The prop does not throw air outward. We've been over that one before. The air column actually narrows behind the prop, due to the lowered pressure caused by the air's acceleration. We can see it on cool mornings when the dew point is just below ambient temperature, and the vapor trails off the prop tips outline the periphery of the air column, showing it to be squeezing inward. A centrifugal super/turbocharger does it differently. The air is accelerated outward in the first place, not in an axial manner, and is directed into a divergent duct known as a diffuser, where it is slowed and its pressure raised. A different animal altogther, compared to a propeller. I mentioned, "dual phase superchargers" as a hint. Here's the answer: the ram-air pressure acquired at the prop tips is equal to the loss of pressure against the centrifugal force pushing air - via ducting - into the prop center that one obtains at the prop tips. "Dual-phase supercharger" is a misnomer. They were two-speed affairs, going to a higher gear ratio for higher altitudes. Dan |
#60
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Ram air
On Jun 4, 11:41*am, wrote:
On Jun 3, 12:56 pm, "Ken S. Tucker" wrote: Dan it was a trick question I asked you. It's the basic aerodynamic physics of the standard centifugal supercharger compressor operating principle. I tossed you a zinger, cuz you claimed to be a teacher in a college and I couldn't resist :-), don't worry about it, hardly anyone get's that one correct, and I hope you get a ha-ha-ah from it. * * * * * * The prop does not throw air outward. We've been over that one before. The air column actually narrows behind the prop, due to the lowered pressure caused by the air's acceleration. We can see it on cool mornings when the dew point is just below ambient temperature, and the vapor trails off the prop tips outline the periphery of the air column, showing it to be squeezing inward. * * * * A centrifugal super/turbocharger does it differently. The air is accelerated outward in the first place, not in an axial manner, and is directed into a divergent duct known as a diffuser, where it is slowed and its pressure raised. A different animal altogther, compared to a propeller. I mentioned, "dual phase superchargers" as a hint. Here's the answer: the ram-air pressure acquired at the prop tips is equal to the loss of pressure against the centrifugal force pushing air - via ducting - into the prop center that one obtains at the prop tips. * * * * *"Dual-phase supercharger" is a misnomer. They were two-speed affairs, going to a higher gear ratio for higher altitudes. There are also two stage systems Cheers |
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