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Helicopter Throttles  
User currently offlineUSCGC130 From , joined Dec 1969, posts, RR:
Posted (7 years 3 months 1 week 5 days 13 hours ago) and read 5218 times:

Given that helicopters have a twist-grip throttle on the collective, what's the purpose of the throttle levers that are commonly found on the overhead panel just aft of the windshield? What's the functional relationship between those and the one on the collective?

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User currently offlineUH60FtRucker From , joined Dec 1969, posts, RR:
Reply 1, posted (7 years 3 months 1 week 5 days 13 hours ago) and read 5212 times:

Quoting USCGC130 (Thread starter):
Given that helicopters have a twist-grip throttle on the collective, what's the purpose of the throttle levers that are commonly found on the overhead panel just aft of the windshield? What's the functional relationship between those and the one on the collective?

Well it's a throttle, which means it controls the flow of fuel to the engine.

But the difference between helicopters and airplanes, in a helicopter you do not use your throttle for any type of movement control. If you want to slow down, you do not decrease the throttle, like you would do in an airplane.

Helicopter throttles typically have three settings - off, idle, full.

For idle, you are typically either running up or shutting down the helicopter. You can also go to idle if you will be sitting on the ground, but still running the engines, for an extended time. And lastly, you would go to idle immediately, during a tail-rotor malfunction. In the UH-60 there are certain additional things that happen when you go to idle, but I really shouldn't talk about them.

You can also manually control the throttle during engine malfunctions. If an engine is malfunctioning, it may require you to either reduce the throttle, or bring it all the way back to idle.

But suffice to say, when your helicopter is healthy, and you're flying along, the throttle will remain at 100% for the duration of the entire flight.

-UH60


User currently offlineCTR From United States of America, joined Jul 2005, 303 posts, RR: 0
Reply 2, posted (7 years 3 months 1 week 5 days 2 hours ago) and read 5144 times:

Building on the information provided by UH60.

The rotor on a helicopter must operate within a narrow rpm band.

To slow and insufficient centrifugal force is applied to those long slender blades to keep them stable and prevent them from flexing to the point of failure.

To fast and the centrifugal force will rip the blades from from the hub and have them shooting out like a rock from David's sling.

Therefore helicopters use governors (either mechanical or electronic) to maintain the rotor at a constant rpm.

When a helicopter needs increased thrust to climb, pulling up on the collective lever increases the pitch of the blades. But the rpm remains constant.

When an airplane (with a jet engine or constant speed prop) needs to climb, the engines increase rpm.

Have fun,

CTR



Aircraft design is just one big compromise,,,
User currently offlineAirRyan From United States of America, joined Mar 2005, 2532 posts, RR: 5
Reply 3, posted (7 years 3 months 1 week 5 days 2 hours ago) and read 5136 times:

Quoting UH60FtRucker (Reply 1):
If you want to slow down, you do not decrease the throttle, like you would do in an airplane.

The H-46 I used to work on had a system that has since been modified (PMS: Power Management System) so it's not as labor intensive, but I believe that the pilots would actually have to beep the throttles up or down depending upon the posistion of the collective they desired; if you were straight and level and you wanted to climb you had to beep your throttles up with your thumb so you could keep the rotors spinning within that N1 arc, and vice versa. The guys who flew those kinds of birds back then were truly pioneers, what a pain in the @ss those things must have been!


User currently offlineH53Epilot From Israel, joined Mar 2004, 177 posts, RR: 2
Reply 4, posted (7 years 3 months 1 week 5 days ago) and read 5112 times:

Quoting USCGC130 (Thread starter):
Given that helicopters have a twist-grip throttle on the collective, what's the purpose of the throttle levers that are commonly found on the overhead panel just aft of the windshield? What's the functional relationship between those and the one on the collective?

Sorry no one above answered your question. The twist grip on the collective and the power control levers on the overhead panel on larger helicopters serve the same purpose and that's to control the rotor RPM. On the 53E, for example, there's no reason to have immediate control of each engine's input to the rotor RPM as there is with a single engine helo. In a 3 engine helo if you lose an engine it is much less of an emergency than if you lost the engine on say a Jet Ranger.
Going to idle immediately during a tail rotor malfunction as UH60 states above is not coompletely correct. There are quite a few factors which affect the aerodynamics of a helicopter such as forward airspeed (the 53E, for example, has a huge vertical stabilizer which acts as a weathervane during forward flight) and the severity of malfunction. The tail rotor malfunction may simply be a result of reduced thrust (binding controls) meaning a possible reduction in power applied to the rotor head or a complete loss of thrust (mechanical linkage failure) which is again off set by forward airspeed due to the vertical stab, weathervaning effect. Slow down with a loss of tail rotor authority and you'll need to have the second pilot reducing the power to the engines as relative rotor torque increases but not so much as to reduce rotor RPM and the vertical component of lift. If you change one variable, another two change.
By the way, a 3 engine out auto rotation in the H53E is a theory.


User currently offlineUH60FtRucker From , joined Dec 1969, posts, RR:
Reply 5, posted (7 years 3 months 1 week 4 days 23 hours ago) and read 5102 times:

Quoting H53Epilot (Reply 4):
Going to idle immediately during a tail rotor malfunction as UH60 states above is not coompletely correct.

Well jeez, without writing a book on our emergency procedures and specifying all of the different possible scenarios... I gave the shortest and sweetest answer for the man.

But yes, H53E's far more expanded answer is correct: at higher airspeeds, you would not immediately attempt an auto rotation if you had a tail rotor failure.

In fact, depending on the type of malfunction, an auto rotation may be unnecessary, where the pilot may chose to perform a run-on landing. But the scenario I quoted was a low, or zero, airspeed helicopter who suffered total tail rotor failure.... like and RPG to the tail... or an unexpected encounter with a tall tree behind you! Where continued flight was not possible. The helicopter is going to yaw right, regardless of the airspeed. However, the slower you are, the more severe the yaw will be.

In the situation I was quoting, an auto rotation should be entered immediately. And I was wrong earlier, you don't idle that throttle(s), you bring it to "off". You also say a quick prayer, because it's about to get real ugly in a few seconds.

Quoting CTR (Reply 2):
The rotor on a helicopter must operate within a narrow rpm band.

To build off of what CTR said, if you encounter an increasing or decreasing RPM R situation, then some sort of manipulation of the PCL (in a UH60 it's not called a throttle lever, but a power control lever), will be required. The pilot will need to manually take control, and adjust accordingly.

And many engine problems may require you to adjust/retard the PCL/throttle on the effected engine.

-UH60


User currently offlineCorey07850 From United States of America, joined Feb 2004, 2528 posts, RR: 5
Reply 6, posted (7 years 3 months 1 week 4 days 20 hours ago) and read 5085 times:

Quoting UH60FtRucker (Reply 5):
To build off of what CTR said, if you encounter an increasing or decreasing RPM R situation, then some sort of manipulation of the PCL (in a UH60 it's not called a throttle lever, but a power control lever), will be required. The pilot will need to manually take control, and adjust accordingly.

The rotor setup on a helicopter seems to be really similar to a fixed wing plane with a controllable pitch prop... Does that mean I can fly choppers too?  Smile


User currently offlineLongbowPilot From United States of America, joined Jan 2005, 577 posts, RR: 4
Reply 7, posted (7 years 3 months 1 week 4 days 9 hours ago) and read 5023 times:
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Quoting H53Epilot (Reply 4):
Going to idle immediately during a tail rotor malfunction as UH60 states above is not coompletely correct.

WOW, I think we have a few type a personalities.

Look in the end everyone here is absolutely correct about their input.

The BIG picture.

Engines throttles, power levers, PCLs or whatever you call them are advanced to full, fly, or whatever you call it. Then most modern helicopters are equipped with a Fadec or Electronic unit that attempts to maintain 100% rotor RPM. To semi-quote a "Heli-Tac" article... and every rotor-head will agree. AS long as your ROTOR is in the Green, you have a chance of survival. Lose your rotor then the deck is horribly stacked against you.


User currently offlineUSCGC130 From , joined Dec 1969, posts, RR:
Reply 8, posted (7 years 3 months 1 week 4 days 9 hours ago) and read 5020 times:

Guys, I appreciate all your replies; they were all interesting. But I think my question was misunderstood, and that's my fault for the order in which I phrased it. Let me take another crack at it.

Given that each engine has its own overhead throttle, and given that aircraft movement isn't controlled with the throttles, where does the twist-grip throttle on the collective come in?

In other words, once the power of each engine has been set to "full" with the levers prior to taxi or takeoff, is the twist-grip on the collective a sort of "master" throttle that controls the power of all engines simultaneously through some sort of integration mechanism?

If the levers are set to idle, does that limit the power that can be selected with the throttle on the collective? And conversely, does advancing the levers to "full" enable a full range of power to be selected with the throttle on the collective? Theoretically, I mean -- whether or not one would actually want to?

(I'm not entirely unfamiliar with the way helicopters work. Even though I'm a C-130 type, I went through Aviation Machinist's Mate (AD) school in the Coast Guard in the days when everybody was trained for all aircraft, helicopters and fixed-wing both. I don't recall that the instructor of the HH-3F module went into any detail about this particular topic, whether I had the presence of mind to ask him to elaborate on it, or if I got a satisfactory answer if I did. Oh, and later on, I learned not to volunteer for for a flight that consisted of two hours of practice autorotations when I still had the remnants of a head cold.  Smile )


User currently offlineUH60FtRucker From , joined Dec 1969, posts, RR:
Reply 9, posted (7 years 3 months 1 week 4 days 8 hours ago) and read 5004 times:

Quoting USCGC130 (Reply 8):
Given that each engine has its own overhead throttle, and given that aircraft movement isn't controlled with the throttles, where does the twist-grip throttle on the collective come in?

Twist grip throttles mounted on the collective are typically only found on single engine helicopters. The throttle levers on the overhead panel are typically only found in multiple engine helicopters. Many attack helicopters have the throttle levers on a side panel, almost like a jet fighter.

So in the UH60, CH47, CH53, etc. there is no twist grip throttle on the collective, but instead throttle levers on the overhead panel. In the UH-1, OH-58, TH-67, MH-6, the throttle control is on the collective, and have no overhead levers. The AH-64 has the throttle control mounted on the left side panel. None of them have both a twist grip control and an overhead control lever. Doing so would be redundant, not to mention a twist grip on a multiple engine helicopter would not be able to individually control each engine.

Some might confuse the UH60 collective for having a twist grip - further down on the right collective shaft - but that's actually a collective friction. Twist it, and the friction on the collective increases or decreases.

Hope that cleared up your question!

Quoting USCGC130 (Reply 8):
I learned not to volunteer for for a flight that consisted of two hours of practice autorotations when I still had the remnants of a head cold.

Here's another tip - don't volunteer for command & control, or mission coordinator flights. Basically you go up high, slow to max endurance airspeed, and do race track patterns in the sky for 6-8hrs, while the mission commander sits out back and coordinates the battle. Talk about mind-numbingly boring... not to mention ass numbing!!!

-UH60


User currently offlineCTR From United States of America, joined Jul 2005, 303 posts, RR: 0
Reply 10, posted (7 years 3 months 1 week 4 days 6 hours ago) and read 4977 times:

All Bell helicopters, single AND twin engine have twist grip throttles on the collective.

Of the twin engine military helos this includes the AH-1 Whiskey Cobra, AH-1Zulu Cobra and the H-1Yankee.

Of the commercial twin engine helos this includes the 222, 230, 430, 427 and the newest Bell helicopter the 429 that is still in flight test.

To allow for independent operation of each engine there are two twist grips positioned end to end on the collectives. This allows the pilot to easily grasp both for simultaneous operation.

Why? Perhaps in a CH-53 with it's huge vertical fin and tremendous fuselage and main rotor mass is controllable following loss of it's tail rotor anti-torque thrust. But this is not the case in light and medium helos. Following the loss of the tail rotor thrust unless the pilot chops the throttle quickly yaw rate builds quickly. Chopping the throttles also requires reducing the collective rapidly to maintain rotor speed.

Until pilots come equipped with three arms, Bell light and medium helos (single and twin engine) will have throttles on the collective.

Have fun,

CTR



Aircraft design is just one big compromise,,,
User currently offlineUH60FtRucker From , joined Dec 1969, posts, RR:
Reply 11, posted (7 years 3 months 1 week 4 days 5 hours ago) and read 4963 times:

Quoting CTR (Reply 10):
All Bell helicopters, single AND twin engine have twist grip throttles on the collective.

Of the twin engine military helos this includes the AH-1 Whiskey Cobra, AH-1Zulu Cobra and the H-1Yankee.

Wow, that's really interesting. Whereas I have no experience with any of those helicopters (the Army got rid of the Cobra before I joined) I didn't know that. Cool.

So during run-up, does the pilot "roll" one throttle to initiate the first engine start, or are both throttles rolled on? Can you move both together as a whole, or do you need to move each throttle individually? During an auto, do you have to roll one throttle, and then quickly roll the other?

What about the RAH-66? I know the cockpit design was suppose to be revolutionary, including the controls. Know anything about how Sikorsky/Boeing designed the throttle?

Quoting CTR (Reply 10):
But this is not the case in light and medium helos. Following the loss of the tail rotor thrust unless the pilot chops the throttle quickly yaw rate builds quickly. Chopping the throttles also requires reducing the collective rapidly to maintain rotor speed.

In the UH-60, at a certain airspeed - which I assure you, is definitely attainable - the tail rotor is unloaded and the vertical fin provides stability control. In the event of a tail rotor failure, if you are at or above this speed, you will still have that yaw... but it will not be severe. However, the normal EP calls for the pilot to auto rotate.

If the control cable fail, the situation can also be controlled. The rotor is designed to go to a specific angle. You will be able to control the yaw and you must land at or above a certain speed.

BUT ANYWAY - even in the Black Hawk, the vertical tail can unload the tail rotor.

-UH60


User currently offlineJohnM From United States of America, joined Feb 2001, 348 posts, RR: 0
Reply 12, posted (7 years 3 months 1 week 4 days 2 hours ago) and read 4937 times:

A factor that makes aircraft such as the UH-60 a two pilot aircraft is the ceiling mounted PCLs. It's a bit of a problem to grab a handful of PCL (throttles) above the windshield while trying to manage a failure of tail rotor thrust, engine over/ underspeed, etc, and actually fly the sick bird at the same time. If a pilot in a UH-60 for example manually controls one of the engines, it is pretty much a full time job for one of the guys. This wouldn't be normal, but can happen when things break for real, and during check rides. The twist collective throttle of a Huey can be controlled in "emergency" governor position by a single pilot, and manage the entire situation with only a quick switch operation on the center console. Since the UH-1 is legal to fly with only 1 rated pilot, crew chiefs gets stick time during test flights, track and balance checks and such. So a UH-60 crew chief won't see any stick time. I think having only one rated aviator in front(of a UH-60) requires a big time waiver from way up there, however I've heard of a General officer doing just that and flying up front in a Hawk. I'm sure that's quite rare. Sorry, a bit off subject there.

The collective mounted throttle is very easy for an instructor pilot to be sneaky, and "roll" to the idle position at a hover, or at cruise. So everybody is surprised, except for the IP of course. Pretty hard to yank a PCL to idle without the other pilot seeing what is going on, so the element of surprise isn't quite as much fun. Also the UH-60 can usually fly pretty well (in MOST conditions) on only engine making noise, while a single engine aircraft is going to enter a high rate of decent ASAP, to autorotate.

If I understand your question, yes, the RPM of a turbine helicopter is "set" prior to takeoff, and will be maintained at the proper output speed to the transmission the entire flight. The UH-1 for example does this with the fuel control mechanically, and will maintain rotor speed according to the load placed on the engine in different modes of flight. More modern stuff, the -60 for example has an electronic control unit on the engine that will manage this, and even share the load with the other engine. The only time to mess with it in flight is for a fine adjustment, or if the electronic or mechanical governor screws up, and the pilot will have to constantly adjust the throttle up or down every time the load is changed on the engine, in other words, anytime a flight control position is changed. Other wise the engine can be oversped or not making enough power if the pilot isn't on top of his game. It can be a handfull in a single engine bird.

When the engine throttle is at "idle", it is milling over @ very low RPM, enough to sustain its self. I think that is "ground idle" position in the C-130 world, and our "fly" or "full open" position would relate to "flight idle" if my C-130 terms are correct.

I'm still amazed at the wild stuff that goes on to make a helicopter fly!


User currently offlineLongbowPilot From United States of America, joined Jan 2005, 577 posts, RR: 4
Reply 13, posted (7 years 3 months 1 week 3 days 13 hours ago) and read 4873 times:
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Quoting JohnM (Reply 12):
be sneaky, and "roll" to the idle position at a hover, or at cruise. So everybody is surprised, except for the IP of course. Pretty hard to yank a PCL to idle without the other pilot seeing what is going on, so the element of surprise isn't quite as much fun.

Not to mention the probability of an overtorque, because the good engine will attempt to compensate. Requires crew coordination before you do it. I wouldn't necessarily call it fun to roll a throttle off. It is an emergency many of us here would not like to experiance in a twin let alone a single engine aricraft.


User currently offlineCurt22 From United States of America, joined Jul 2007, 335 posts, RR: 0
Reply 14, posted (7 years 3 months 1 week 3 days 1 hour ago) and read 4810 times:

Quoting USCGC130 (Reply 8):
iven that each engine has its own overhead throttle, and given that aircraft movement isn't controlled with the throttles, where does the twist-grip throttle on the collective come in?

I think people are thinking TOO hard here...

Best explination I can provide is that helo's w/ overhead mounted throttle controls do not duplicate this conrol feature on the collective stick where they are found on other model helo's.

However...ALL helo's I'm familiar with do have engine "beep" control on the collective which offer limited engine trim control.


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