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Less Rpm=more Lift

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I think some folks are confusing engine oil pressure with the oil pressure measured within a torque-sensing component of the drivetrain. As an example, 212/UH-1Ns and other PT6T-powered helos have individual engine output torque (from the Nf/N2 section) measured by torque-sensing meters for each power-section output shaft within the combining gearbox. As the units are contained within the CBox, the working medium is the CBox's lubricating oil, not the engines' oil. The two electrical output signals are added together to provide a total torque output indication. The 412 has the same system to report individual engine torque as well, but as GWK notes, there is an electro-mechanical mast-torque transducer contained within the lower mast shaft that is independent of any oil system on the aircraft.


On topic, there are a number of helicopters whose rotor system may be more "efficient" (read less fuel burned for a specific power setting) at less than 100% Nr, however, "efficient" and "maximal lift" are not necessarily the same thing. Huey's could be beeped down enroute for lower fuel burn, same with 412s (97% Nr, per the FM), but you would always beep back up to 100% when landing or manoeuvring.


You can't go wrong operating the aircraft per its FM.




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Yes thank you, to specify i was talking about the as350 and b206series, same goes for ec120 and ec130, the original topic was about the 204/205 which displays a reading in PSI. As for anything else, i don't know. Some use electomech and some use optical sensing.


The EC130 actually slows it's own rotor down in cruise flight but will increase again during any higher power setting, again only for CRUISE. Most important point is that you keep it within the limits of the flight manual..


I have never heard of an N1 torque sensor.

Wet lines to the gauges are still widely used as they are more reliable albeit sometimes messy.



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I do beleave the 204 with a T53-11 would droop off and you could continue to pull as long as no limitations were exceeded. When the -13 engine was installed with more N1 available the engine did not droop as much. I have flown 204 with the -11 and never would never beep RPM to lift more. The AC would how ever droop at Higher density Altitudes and when that happened I would reduce Collective and try something else. This is one reason a power check prior to landing on your recce is so important. My 2 cents worth, be safe, fly smart.

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I hope I can help with some scientific information here.


Has anyone ever noted that helicopters are horsepower limited at the transmission but the engine power is measured in torque?


Horsepower is basically a formula that is Torque X RPM with a constant factored in (I don't feel like searching for it right now).


Reduce your RPM and at 100% Torque you are not giving the transmission maximum horsepower.


On the old 204's with the dash 11 engine some pilots found that if they were reaching max N1 they could beep down to 97-98 N2 and the N1 was lower at 100% Torque or in effect they could now pull max Tq without hitting max N1. In reality they were simply asking the engine to produce less horsepower (Torque X RPM) so they were not actually getting more power. Whether the blades become more efficient is moot as it is a fact that you have less horsepower.


If you want to understand this more then simply perform a power check at 100% N2 and again at 97% N2 and then check your numbers. You will find that the N1 is lower.


I hope this is helpful and if it is not understood I will endeavour to find more a more detailed answer.


By the way - I am right.

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... by the way - FREDDIE is right too!




Ah, but with a lower rpm there is less lift. In order to create the same lift, one must increase the blade angle which also requires more torque to overcome the extra drag.

A good example is with a left jam pedal, if you lower the rpm you start to sink without correcting the yaw. Its only when you lift collective that the yaw will start to disipate. Also due to the higher torque required to drive the blades due to the extra drag. Try it some time with a left jam pedal.


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When setting the RPM for a 350 with a lycoming the only thing that matters is how well you get along with your engineer :D ...especially in the shoulder season when the temperature can change up to 20 C or more throughout the day.


Joking aside I've found with D's (symetrical blades), B2/D2/FX2 (asymetrical blades) that if you want maximum lift always have the RPM at maximum end that the flight manual allows and not just within parameters. ie a straight D is 385 +1 -5. Trust me...you want that thing at 386.


Fly Safe




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Low timers (and high timers if you have forgotten) remember just because you can beep the RPM down doesn't mean that you can beep it back up when required- about 5 years ago a certain "beeping" kind of pilot ended up in a logging slash with a fully loaded Jet Ranger swirling around in the small trees at 95% or so N2 with a broken wire to the actuator. Lucky he wasn't trying to land in the mountains.

I have had 2 failures of linear actuators (or wiring to them) in my career- fortunately Bruce Payne- VIH chief pilot at the time always told us not to #### with it or he would have our thumbs removed. Good advise- thanks Bruce.


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