Less Rpm=more Lift

[Freefall]

Lower rpm means you have to have higher angle of attack to get the same amount of lift. Higher angle of attack creates more drag, which requires more power from the engine to force the blade through the air.

 

I just don't see how a lower rotor rpm could ever generate more lift. It would certainly make your torque go up though.

[Heliian]

Here's the answer to your question.

 

When you beep down the rotor, you are also slowing the engine. The torque pressure is a derivative of engine oil pressure so less oil pressure into the torquemeter piston, the less oil pressure coming out and to the gauge=more room on the gauge. Most engines will maintain a set oil pressure with minor fluctuations of engine speed, but the older ships probably didn't maintain as well. Therefore, as long as your oil pressure stays the same, you're not going to get any more "torque" by beeping it down, all you are doing is slowing the rotor and putting more stresses on the aircraft. the "beep" switch is there to provide you with an adjustment to compensate for temperature and pressure changes(ambiant) so that you can keep it at 100%. Read the Flight Manual and know your droop limits instead of chasing it around all the time.

 

Leave it at 100% and if you can't get off the ground you are doing something wrong. Get a more powerful machine or do 2 trips. You look like an *** when you wreck an overloaded aircraft, not to mention the resultant serious injury or death.

 

Hope this explains it well enough

 

I

[gwk]

For the 204B and the 205B, with the standard blades, reducing RRPM by about 2-3% is supposed to provide you with more lift.

By reducing RRPM, you can then increase your TQ back to it,s original setting by increasing your collective, increasing the angle of attack on the blades, and increasing lift, or so the theory goes.

It only works on symetrical blades for lifting, not asymetrical blades which are designed to work best at 100% RRPM, like the 212.

With the 412, we reduce RRPM in the cruise to reduce vibrations, increase speed (about2-3kts), and improve fuel economy.

I would not expect a AS350 to perform better at a lower rpm, if you could, because the blades are designed to be most efficent at 100% RRPM.

If you remember, next time your up close to a 204 or 205, look at the blades, specifically the ends, an you will see what I mean be being symetrical, the top and bottom look exactly like a mirror image of each other.

 

[Outwest]

In helicopters........RPM = life

 

What this should say is " RFM approved RRPM =life" Too much RRPM can be just as fatal as too little. All helicopters have a critical RRPM value that if allowed to drop below it is impossible to recover. As I said the S61 is 72% and I believe the R22 is very critical in this area.

 

Do not misunderstand me, I'm not for a minute suggesting anyone should intentionally lower RRPM in an attempt to pickup a heavy load.

 

I merely stated that it is possible that some rotor systems may perform better at less that the standard cruise RPM. This will be clearly stated in the RFM of that particular a/c. If you are doing something not advised in the RFM, you are now a test pilot and on your own.

 

Again, designers make compromises in high lift vs high speed. Think about a Piper Cub and an F5. The Super Cub can probably get airborne with about 30 kts flowing over the wing, but 100 kts is about the top speed. The F5 can do 600 kts but needs 150 kts to get airborne. All about the wing design and don't forget we are flying rotary wing a/c.

 

My point in this whole post is, do not assume that lower, or higher RRPM for that matter, than recommended by the manufacturer will make the helicopter do something it was not designed for.

 

Operate within the limits of the RFM and you will live a long an healthy life.

 

 

[Outwest]

The torque pressure is a derivative of engine oil pressure

 

OMG!!!

 

Please don't post things that are so obviously false.......

 

Engine oil pressure has absolutely nothing to do with torque!!!

 

Torque is a measure of power being applied to move an object that is resisting that power. How it is measured is done in many ways.

 

It is true that oil pressure is used in torque indicating systems but only as a means of relaying that info to the cockpit. Helical gears, mast bending, etc, etc are the real indicators of torque applied.

 

 

[arctic_front]

I recall hearing from a few different sources that a 204B "can lift more than it can fly with"

 

The explanation for that I'll leave to the experts, but it must have some basis in fact. Why you'd want to lift something you can't go anywhere with is a mystery to me. My understanding is that the rotor can lift it.. but the T/R cant steer it. seems kinda pointless.

 

As for the statement from GWK, he is correct. However, the number of 205's in Canada with original blades is very small. Most have the 212 rotor system. A 212 rotor blade is a very different animal than a 204 blade. I will wager that there are many engineers/pilots who've seen 204/205 blades crack, shed bits and otherwise cause grey hair to appear. However, those blades were designed to take enemy fire in a war.. Was the 212 blade designed to be the same?... i think prolly not. apples and oranges.

 

One thing for sure, you never want to see 96% NR on anything with a 212 rotor system... unless you are very light and doing an engine vibe check

 

 

 

 

Outwest, however, is somewhat mistaken in practice, if not theory. Oil pressure inside the engine is how every turbine helicopter measures torque. They may do it in different ways, but it's entirely the measurement of engine oil pressure transposed to reflect rotor system load. Is that perfect? no.. is there a better method?... possibly. What does the industry use?... engine oil pressure.

 

 

 

 

[Crusty]

I recall hearing from a few different sources that a 204B "can lift more than it can fly with"

 

The explanation for that I'll leave to the experts, but it must have some basis in fact. Why you'd want to lift something you can't go anywhere with is a mystery to me. My understanding is that the rotor can lift it.. but the T/R cant steer it. seems kinda pointless.

 

As for the statement from GWK, he is correct. However, the number of 205's in Canada with original blades is very small. Most have the 212 rotor system. A 212 rotor blade is a very different animal than a 204 blade. I will wager that there are many engineers/pilots who've seen 204/205 blades crack, shed bits and otherwise cause grey hair to appear. However, those blades were designed to take enemy fire in a war.. Was the 212 blade designed to be the same?... i think prolly not. apples and oranges.

 

One thing for sure, you never want to see 96% NR on anything with a 212 rotor system... unless you are very light and doing an engine vibe check

 

 

 

 

Outwest, however, is somewhat mistaken in practice, if not theory. Oil pressure inside the engine is how every turbine helicopter measures torque. They may do it in different ways, but it's entirely the measurement of engine oil pressure transposed to reflect rotor system load. Is that perfect? no.. is there a better method?... possibly. What does the industry use?... engine oil pressure.

 

[gwk]

Artic front you are wrong on the tq oil thing. In the 412 the tq reading come from sensor located at the bottom of the transmission extending up into the bottom of the mast which measures tq or the mechanical twisting force applied to the main rotor. With the 412, tq measuring has nothing to do with oil which is significantly different from 212 and early 412 models,it stictly mechanical and electrical.

[Crusty]

Probably the best way to look at it is "critical flight" regime. If you are taking off, landing, OGE hover (slinging/bucketing), operating in the dead man's curve even with forward motion and so on, you are in a critical flight regime and that helo's engines/tranny will perform best while in that regime at 100% NR. The governors and torque control unit are rigged to provide optimum engine performance at 100% NR.

 

In a situation where you're beeped back and you are in a critical flight regime and should you lose an engine or if you have to roll an engine to idle (eg compressor stalls), beeping the other engine to max is required. But if you are in a situation where you've already beeped down to say 97%, you're well below the power curve and you are at great risk of drooping the rotor a lot sooner than you would ever want to (compared to the same scenario but you were running at 100% NR). Also, your N1 topping is optimum when that single engine running at 100% NR.

 

Beeping back provides you a small percentage of fuel flow benefit (reduced burn) for those long transits to your next fuel cache. Myself, I beep down only if I need that 2-3% fuel flow benefit in cruise.

 

Just my opinion.

[WTF_was_that]

The 407 has whisper mode, reduces RRPM in cruise. Haven't heard if anyone has this kit. Think it was another bell flop.