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please all MZ2 Mosquito owners... Reply
#31
Not following, the heat build up on the engine is proportional to the load requirement – you have to burn more btu’s for a heavy load vs light – if the requirement is reduced entering into an auto the btu’s requirements reduce (roll the throttle off to maintain the rpm) and then so does the cooling, fuel, oil, requirements - the rpms may remain the same but the energy to keep them there is reduced as is the heat transfer requirement
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#32
Hi Skeeter,
If you guys are not having any problems with EGT's rising during sustained midrange descents, everything is fine and your midrange jets are correct.

Now...if someone has a Mosquito that has needle jets in for 5000' density altitude, and they take it to Sun-N-Fun on a trailer, where density altitude is only 900', and do a sustained descent, the EGT's are going up and they run the risk of seizing the enine.

THE IMPORTANT TOPIC OF THIS WHOLE THREAD IS**** JETTING TABLES FOR THE BING CARBURETORS, THAT WERE DEVELOPED FOR FIXED WINGS, WILL NOT CALL OUT THE CORRECT MIDRANGE NEEDLE JETS FOR A HELICOPTER****
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#33
marcher07 - 2/22/2011 11:00 PM

Not following, the heat build up on the engine is proportional to the load requirement – you have to burn more btu’s for a heavy load vs light – if the requirement is reduced entering into an auto the btu’s requirements reduce (roll the throttle off to maintain the rpm) and then so does the cooling, fuel, oil, requirements - the rpms may remain the same but the energy to keep them there is reduced as is the heat transfer requirement

Everything you say here is 100% correct. Now think about what is happening? Only in a helicopter. The piston rings are scraping up and down the cylinder walls with very little oil. The engine could be on the work table and not even running or making heat.

Only in helicopters, you must have the midrange quite a bit richer than you would a fixed wing to get enough oil where it needs to be.

Would you want your engine on the work table, with the spark plugs out, hooked up to an electric motor and spun at 6,200 rpm for 1 minute with no oil (or inadequate oil) on the cylinder walls?
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#34
Bryan
RE: “Only in helicopters, you must have the midrange quite a bit richer than you would a fixed wing to get enough oil where it needs to be” I’m not seeing why the specific airframe mounts matters, the dynamics of an engine going from full rpm to anything less, down to idle are the same. If I reduce the power requirement, and demand I’ve reduced the BTU’s that were required and therefore I’ve reduced the fuel / cooling requirements proportionally. The engine doesn’t stop sucking in fuel and oil when you go to idle the difference is in the power demand and BTU requirements to support the demand, when they change so does the cooling requirement. My take would be if you don’t see an increase in temps throughout the range then you’re in the ballpark and ok. Anyway I think we beat this one to death with the different perspectives – Skeeter – there are no issues that I know of, this has been a discussion on theories and perspectives of operation and jetting not specific to any incidents -
M
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#35
Bryan
RE: “Only in helicopters, you must have the midrange quite a bit richer than you would a fixed wing to get enough oil where it needs to be” I’m not seeing why the specific airframe mounts matters, the dynamics of an engine going from full rpm to anything less, down to idle are the same. If I reduce the power requirement, and demand I’ve reduced the BTU’s that were required and therefore I’ve reduced the fuel / cooling requirements proportionally. The engine doesn’t stop sucking in fuel and oil when you go to idle the difference is in the power demand and BTU requirements to support the demand, when they change so does the cooling requirement. My take would be if you don’t see an increase in temps throughout the range then you’re in the ballpark and ok. Anyway I think we beat this one to death with the different perspectives – Skeeter – there are no issues that I know of, this has been a discussion on theories and perspectives of operation and jetting not specific to any incidents -
M
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#36
I have to agree with Byran on this matter and think he has a very valid point. I know there are a lot of things going on landing the helo and concentraion level is high to make a safe landing, but what if you have your fuel tanks plumbed,with a 2 way valve, to where you could choose left/right fuel delivery to engine. Mix fuel in one tank, let's say 40:1 or lower if you wish for decents and the other tank 50:1 for normal operation, switch valve to tank with higher oil ratio just before you start your decent, than switch back to normal operating tank after landing. I know this would cut down on normal flying time, but would this help Byron's theory of oil starvation on decents theory. Stick with Byron on this matter...I think he is on to something that puts the engine in danger of seizure and xtra wear on rings and rod bearings. Just because we haven't had any engine seizures on decents, I think there is a high risk factor of it happening after hearing Byron's explanation. Joe
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#37
I don't know where the choke is located, but if you could somehow install the choking option somewhere in the cockpit of the aircraft , you could apply partial choke on descents, that would certainly enrichen fuel flow to engine......just another thought I had.
Joe
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#38
I would appreciate if Mr. Uptigrove and/or Mr. Junkin would either tell me that the point of this thread (Not Using Published Fixed Wing Tables to Select Needle Jets)
is valid for the MZ engine or not.

I DO NOT want to present incorrect information here, but I do enjoy sharing lessons I have learned over the years, especially flying 2-strokes.

Humbly,
Bryan Cobb
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#39
There might be another way to look at it in rotorcraft. If when on the ground with the rotor rpm at 100% and flat pitch and the EGT's look safe , you might not have a problem with the sustained descents causing overly lean situations, it is normal for some increase in temps. reducing engine RPM (like practicing autorotation from pattern altitude) may cause the EGT's to increase if jetting isn't quite right . It's not so much the heat but the reduced lubrication during that period. That is why we monitor the EGT's and get to understand exactly what it means..
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#40


xel2 - 2/23/2011 12:20 PM

I have to agree with Byran on this matter and think he has a very valid point. I know there are a lot of things going on landing the helo and concentraion level is high to make a safe landing, but what if you have your fuel tanks plumbed,with a 2 way valve, to where you could choose left/right fuel delivery to engine. Mix fuel in one tank, let's say 40:1 or lower if you wish for decents and the other tank 50:1 for normal operation, switch valve to tank with higher oil ratio just before you start your decent, than switch back to normal operating tank after landing. I know this would cut down on normal flying time, but would this help Byron's theory of oil starvation on decents theory. Stick with Byron on this matter...I think he is on to something that puts the engine in danger of seizure and xtra wear on rings and rod bearings. Just because we haven't had any engine seizures on decents, I think there is a high risk factor of it happening after hearing Byron's explanation. Joe


This soulution won't work, someone pointed out to me that this helicopter only has one fuel tank........scratch this solution.
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