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#21
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Venting of Lycoming 0-290 D Engine
On Apr 30, 9:34 am, et wrote:
Ben Never knew these existed. Have you or anyone else tried it on a Lyc? Probably need a couple of intakes on opposite valve covers? Ed The valve rocker cavity vents through the 3/8" OD oil drain tubes back to the case. Not very big at all. If you used the covers as an air inlet, you might need all of them vented. Dan |
#22
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Venting of Lycoming 0-290 D Engine
On Apr 30, 11:28*am, wrote:
On Apr 30, 9:34 am, et wrote: Ben Never knew these existed. *Have you or anyone else tried it on a Lyc? Probably need a couple of intakes on opposite valve covers? Ed * * * *The valve rocker cavity vents through the 3/8" OD oil drain tubes back to the case. Not very big at all. If you used the covers as an air inlet, you might need all of them vented. * * * * * *Dan Is there any venting through the pushrod tubes? Maybe a side benefit with four vents, head and valve cooling? Great discussion! Ed |
#23
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Venting of Lycoming 0-290 D Engine
On Apr 30, 3:57 pm, et wrote:
Is there any venting through the pushrod tubes? Maybe a side benefit with four vents, head and valve cooling? Great discussion! Ed Nope. The pushrod tubes on a Lyc go only to the lifters. On a Continental the tubes are on the bottom rather than the top, and the oil drains through them so they also act as vents. Much bigger vents. Dan |
#24
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Venting of Lycoming 0-290 D Engine
Thanks to ALL for the useful information , I think my friend has decided
against using a small tube for crankcase venting , your suggestions probably saved him a lot of grief and possible danger , Thank You All Again , Phil Lohiser EAA 12873 "Phil" wrote in message ... Hello I have been helping a young fellow EAA member with the restoration of a EAA Biplane , he is using a rebuilt Lycoming 4cyl. , 125 H.P. 0-290 D engine in this plane and has a 3/8 " O.D. aluminum tube running from the firewall and exiting just ahead of the tailwheel , he wants' to keep the underside of this fabric covered plane as clean as possible , the vent elbow that exits the top forward area of the crankcase has an I.D. of approx. 5/8 " , he plans to put a reducer to make the step from 5/8 " I.D. to approx 1/4 " I.D. on the alum tube , this tube will go from the firewall to the tailwheel , the question is this , does the engine vent just relieve pressure and will the long narrow tube cause any problem ?, am not an expert in the dynamics of this of this area of the engine , any thoughts or help would be appreciated . Thanks Phil Lohiser EAA 12873 |
#25
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Venting of fuel tanks (Was Venting of Lycoming 0-290 D Engine)
On May 3, 10:30 am, "Phil" wrote:
Thanks to ALL for the useful information , I think my friend has decided against using a small tube for crankcase venting , your suggestions probably saved him a lot of grief and possible danger , Thank You All Again , Phil Lohiser EAA 12873 Over the years (since 1972, EAA 89913) I have read of a few accidents arising out of fuel tank venting issues. The "venting of Lyc crankcase" reminds me that sometimes homebuilders don't have adequate frame of reference when making changes to systems and end up getting hurt or dead, or at least busting up a nice airplane. A classic problem involves two or more fuel tanks, perhaps one in each wing, or maybe a main and a header tank. For certified airplanes having more than one tank, and the possibility of feeding from both tanks simultaneously, certification requires that the tanks have a common vent. They word it this way: "Airspaces of tanks with interconnected outlets must be interconnected." (FAR 23.975(4)) Howcome? Well, imagine a high-wing airplane with a tank in each wing, with the fuel flowing from each tank through aluminum tubing down through the fuselage to a tee where they join, then through a shutoff valve, and from there to the strainer and carb. Imagine, too that each tank has its own vent sticking out from under its wing. If there is any difference in pressure inside each tank, fuel will flow faster from the tank with the higher pressure. If the difference is high enough, the high tank will empty completely while the low-pressure tank will not flow at all, or even worse, fuel from the high tank will flow through the tee and into the low tank, overfilling it and spilling from its vent. When the high tank is empty, the engine gets nothing but air, and the flight is finished even though there's still a full tank on board. It's very easy to get uneven pressures from two separate vents. Vent shape, angle of tip, any minor disturbance if the air around it, will all affect its pressure. The Glastar had this separate- vent system and uneven flow was the order of the day. Interconnecting the top of the tanks of the one we had here fixed it. The Cessna 150 also has this system, but being certified, it has a single vent that feeds both tanks. The 172 has a "Both" position on its selector, and because of that it also has a single vent source. Low-wing airplanes with two tanks do not normally have a "Both" position because we're not relying on gravity flow, and if one tank happened to run a little faster than the other (flying one-wing-low, for example) the pump would be quite happy to suck air from the dry tank rather than fuel from the one with fuel in it. The low-winger has very little "head" between the tank outlets and the lowest point in the system (maybe even no head at all) where the high-wing airplane might have three feet or more. Sucking air from the tanks in the low- wing airplane become a problem. Vented fuel caps sometimes work well, sometimes don't. With wing tanks, the low pressure atop the wing can reduce tank pressure dangerously. Cessna uses check-vented caps in case of the main vent plugging up with bugs or ice, but those caps have specially-designed static ports on them to somehow reduce the suction. I flew an Aircoupe that had a similar setup, without the check valves and without any other tank vent, and fuel could be seen streaming off them when the tanks were full. They also had those specially-designed non-sucking cap vent ports but they obviously didn't work too well. Taylorcraft used a cap with a forward-facing scoop to use ram pressure. The cap could be installed backwards, though. Citabria has the single-vent two- tank tee system like the 150, with totally unvented caps that *look* like older auto or truck fuel caps, except that those older auto caps were vented. I found one of those auto caps on a Citabria we bought, and of course it had uneven fuel-flow issues. One cap was sucking, the other not, and the low-pressure tank was a little slower. The interconnected tank vent kept things from getting too far out of hand. Parking an airplane with full tanks in a hangar can be asking for trouble. If the day is cold, the fuel will be too, and it will expand considerably in a heated hangar and run out of the vents, creating an awesome fire hazard. If the airplane has the interconnected outlets (or the selector is on "Both") and the hangar floor is sloped and the vented wing is lower, fuel will cross-flow through the system and run from the vent. As the higher tank drains, the lower wing gets heavier and droops lower and the flow increases. I get VERY annoyed when I find full tanks in our hangar, even after all the prohibitions against it. We've had some very close calls with fire. Dan |
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