Basic Helo flying info

[ArcherII]

Here in a couple of days (whenever this mid-March winter storms decides to pass by) I'm planning on getting a helicopter demo in an R22.

1/2 hour ground, 1/2 hour flight.

To make out the most out of my 1/2 hour of flight, and learn the most about helicopters.

All I know right now is that the cyclic controls the rotor tilt and the collective controls the pitch and MP, and that you vary the pitch to produce more or less lift.

I would like to confirm some of this and learn more...

so if any of you are Helo instructors or if you know any website that has some good info, or if you fell like explaining some of here, then please do so. I would greatlly appreciate it.

Oh, and I'm fixed wing pilot, I know a little about flying those.

Archer

browsing google I found www.helis.com

they have a pretty good introductory section on helicotper principles.

The one thing that I still don't understand is, is there a throttle control on the collective? Can you change the throttle setting or do you just change the collective pitch of the rotor blades?

It seems helicopters are the opposites of Constant Speed piston airplanes.

In those, you set an RPM using the prop lever, and the governor changes the pitch to maintain RPM for a given MP setting (which you adjust with the throttle lever).

It seems in helis it's the opposite,

you set the RPM with the MP (throttle), and the governor changes engine torque for a given collective pitch setting.

So in planes you set the MP, and the governor changes pitch to maintain RPM.

IN helis you set the pitch, and the governor changes MP to maintain RPM.

Correct me if my understanding is wrong

Archer

[Heliport]

ArcherII

These two sites are useful:
FAA Flight Instructor's Handbook (http://www.dynamicflight.com/avcfibook)
Helicopter tutorials (http://www.fas.org/man/dod-101/sys/ac/docs/poh/index.html)

If you want to buy a book, I'd recommend:

The Helicopter Pilot's Handbook by Phil Croucher, ISBN 0-9681928-3-1, published by Electrocution
or
Cyclic & Collective by Shawn Coyle, ISBN 0-9726368-0-3 published by Helobooks

I wouldn't usually recommend the second book for someone who's not yet taken a trial lesson but, given that you know quite a lot already, it's worth considering. It's commonly known as the 'helicopter pilots bible'.

Book reviews here (http://www.pprune.org/forums/showthread.php?s=&threadid=82123&perpage=40&pagenumber=1)

[Ascend Charlie]

For your trial flight, remember this:
An aeroplane is dynamically stable, and wants to fly. It will only crash if the pilot makes it crash.

A helicopter is dynamically unstable, and wants to crash. It will only fly if the pilot makes it fly.

The differences you will see are:
1. You set an attitude, and you have to work to keep it there - no effective trim, and it wants to diverge.

2. Attitude is airspeed, power is rate of descent (or climb, or level)

3. Rotor is kept at 100% by the governor and throttle. Pull in power, the revs want to droop, governor or pilot adds throttle to keep revs up, MAP goes up.

4. Almost no feel to the cyclic stick (depending on R22, H300, B47) so it is really easy to overcontrol.

5. DON'T LET IT GO!

6. In forward flight, pedals control balance (skid ball / piece of string) but in the hover, balance is irrelevant, and pedals control where you are pointing.

You will start your flight with the instructor taking off into forward flight, and you following through lightly. Once airborne, he will get you to control the cyclic to hold the attitude / airspeed steady, then try some gentle turns, speed changes etc.

Next is the collective on its own, making some power changes. Then the pedals, keeping in balance while he changes the power. Then collective and pedals together, then all three. He will take over when you lose it.

Back into the circuit for some hovering, starting with pedals to make the nose point at some object; then collective, to hold height steady, then collective and pedals together.

Second last is cyclic, and don't be too upset when you lose it within 5 seconds. The aim is just to hold the attitude steady - don't worry about ground position, it will follow eventually. If you can correct a wrong attitude and get back to a level attitude, you have grasped the basics of hovering. Lastly, he gives you the lot in the hover, and you will lose it fairly quickly.

But you will find that flying a helicopter is the most fun you can have with your clothes on.:8

[ArcherII]

Ascend Charlie,

thanx a lot for the insight! Now I know what I should expect. I'm sure some instructors let you do more or less than others, so should I mention that I expect what you have just outlined? Seems a very good way to get a real good idea of how a heli flies.

3. Rotor is kept at 100% by the governor and throttle. Pull in power, the revs want to droop, governor or pilot adds throttle to keep revs up, MAP goes up.

Ok, gotta explain this a little more to me, I'm still confused. 100% of what?

So the MP can be changed manually OR by the governor?

See, in fixed wing you can't control the pitch manually, the governor does it, the pilot can't. What the pilot can do is control the MP.

Now, from my understanding, in a helicopter the pilot can control the pitch, and the governor controls the MP. But from what you are saying, both the pilot and the governor can control the MP...I find that a little confusing.


Also, just tell me, is flying a helicopter as hard as MS flight sim makes it look like?

I can usually fly the R22 "OK" in there...I have a very hard time usually holding position, especially "forward/backward" motion...

also transitioning from like a 40 knot forward speed to a hover without gaining or loosing a lot of altitude is pretty hard.

I guess I'll find out how hard it is when I get to do it myself...

I'm just afraid I might get addicted to it and have to find $10,000 somewhere...:D

Archer

[Whirlygig]

... and addicted you will be ;)

Another book that I can recommend is "Learning To Fly Helicopters" by Randy Padfield. I read it before I learned to fly and found it very readable and quite amusing in places.

Hope you enjoy it.

Cheers

Whirlygig

[boomerangben]

To get the best value from your half hour is to buy another half hour and make it a whole hours flight. In my experience, half an hour is not enough to get a real good go at flying a helicopter.

I would not worry too much about the throttle at this stage - your confusion basically boils down to different techniques required for different types. Let us know what you are going to be flying and then the advice here will be a little less confusing.

Food for thought:
Before starting my IR, I asked the instructor if there was any reading I should be doing to prepare. He answered by telling me to throw any books I have into the back of the cupboard and chill out. They would teach me all I needed to know.

If I was you, take the advice given here, but walk into the briefing with an open mind - you will get more from listening to your instructor on the day than you will trying to remember what you have read here. No critisim on ppruners, but I've had plenty of overly keen students who wouldn't listen because they thought they knew it all.

[Whirlygig]

Boomerangben,

I'm afraid I would disagree about the hour's flying for a trial lesson. There is SO much to take in, the concentration required and the muscles used, that after half an hour flying, you will be knackered.

....Archer.... well, I WAS.

So much so that after my half hour ended, I jumped out of the helicopter (a Schweizer so a little higher off the ground than a Robbo) and promptly fell over as my legs had gone to jelly.

Cheers

Whirlygig

[ShyTorque]

I agree with BoomerangBen to a greater extent.

My best advice is that on your first lesson, treat it just as a famil flight and enjoy it. If you try to analyse the theory of what is going on in too much detail, you won't actually get the best out of the flight. Keep your eyes out of the cockpit window. Get used to the strange new effects that you (as a plankie) will experience.

Just listen to the instructor's brief, take it at face value, then go out and do it. Keep it simple and save the deep and meaningful questions until after you get back.

Enjoy it (you will!) but you have been warned, you are about to begin taking the highly expensive and addictive drug known as Rotree. And be aware that you are going to get very frustrated having to ground taxy to the runway next time you want to fly a plane....:ok:

[rotornut]

Before I started training for my commercial license I carefully read the Hughes Helicopter course material. It's excellent stuff prepared by Jeppesen. However, when I was given the cyclic and told to try and hover, all the theory went out the door and the sweat poured down my face. It took a few more hours before I could hold it steady but it came very naturally.

Good luck!

[Flying Lawyer]

I support Whirlygig's recommendation of "Learning To Fly Helicopters" by Randall Padfield.

It's well-written, very readable and deals with technical aspects in a readily understandable way which is a good introduction to the 'manuals' which can sometimes be rather demanding for a beginner - especially if, like me, they don't have a natural flair for aerodynamics and physics.
I read it several times when learning to fly helicopters and found it very useful, often going back to it when the manuals became a little heavy. It's an enjoyable read.

I agree students should forget what they've read in the books and concentrate on what the instructor says/demonstrates. I suspect the reality is that >90% of people on trial flights will forget >90% of what they've read. However, I can't resist reading up in advance if I'm about to try something for the first time, even though I know I'll forget it all in the excitement of the moment. :D

[Aser]

I have also read "Learning To Fly Helicopters" by Randall Padfield before the course and I think it's the perfect book for the wannabe.
It's a good "overview":ok:

Regards.

[MightyGem]

Archer, re 100%. Some helicopters have the rotorspeed gauge(otherwise known as Nr) in percentage, some have it in Rotor RPM(RRPM). Depending on the aircraft the Nr should be at a certain percentage. You would think 100%, but it can be higher. The British Army's Lynx, for example, has a take off setting of 107% Nr.

[ArcherII]

I would not worry too much about the throttle at this stage - your confusion basically boils down to different techniques required for different types. Let us know what you are going to be flying and then the advice here will be a little less confusing.


I'll be flying an R22.

And about the preparation...I just don't want to stumble in there without a clue...it'll make the half hour ground more effective...and I'll actually be able to accomplish more flying in the air.

[Flingwing207]

Hi Archer,

If you are taking the R.22 intro in the USA, part of your ground will be some "awareness training" on low-"G" mast bumping and low-rotor RPM stall.

You've already gotten the explanation on what 100% Nr (rotor rpm, or RRPM) is, suffice to say that the slower the rotor is turning, the less tota lift it can produce, and the more power it takes to maintain constant lift. The R.22 Beta II runs at 104% on the tach, which is about 2650 engine RPM and 500 RRPM.

If the RRPM drops to 97%, the rotor takes more power, but the engine is also slowing (to around 2470 rpm), so it is losing ability to make power. Now 97% is no worry in the R.22, but it is where the low-rpm horn goes off. The R.22 will fly quite well at 90% RRPM, it will just have less power reserve. So 104% is better, because the rotor is more efficient, and the engine is more powerful!

On the other hand, 80% is not so good, as the power the rotor demands to provide adequate lift is now getting close to exceeding the engine's ability to provide that power. Once those curves cross, the RRPM will decay rapidly - BAD THING. This is one cause of low-rpm rotor stall, the other one being letting the RPM go too low in autorotation.

The good thing is that in the R.22, you have two tachs, a governor, a warning horn, and your own ears. The chances of an aware pilot getting into a low-RPM situation is very small.

Low-"G" is simple. If you are in cruise flight or a cruise climb and you push the cyclic forward rapidly (as you might do with an airplane to dive), the rotor system is unloaded. Imagine an airplane which was hanging from its wings by strings - you push the plane over and the wing descends faster than the fuselage - the strings go slack.

In the R.22, what happens is the tail rotor (still producing thrust) starts to roll the airframe to the right pretty quickly, while the rotor disk does not roll! The rotor hub, which is just on a simple teetering pivot on the rotor mast, will rapidly reach the limits of its travel and start contacting the rotor mast. A couple of thumps, and the mast will bend or fracture, neither being conducive to continued flight. Again, super-easy to avoid - don't push the cyclic forward rapidly in cruise flight or from a climb.

To add a bit to the flying advice offered by others, when you are flying the helicopter, first keep your eyes outside and away from the ground, especially while hovering. Use references 50' - 100' minimum. Don't think of control movements, just control pressures, especially with the cyclic. The Robbie is very sensitive to the cyclic and will start to move the instant you think about moving. So if you start drifting right, just think about stopping the drift, not moving the cyclic left - if you actually move the cyclic left, you will start going back and forth like a yo-yo as your movements will inevitably be exactly out of phase with what's required.

Instead, if you start to drift right, just put a slight bit of left pressure on the cyclic. As soon as the drift stops, relax the pressure.

...and don't worry if you don't hover well or at all. As a CFI who has most of my hours in the Schweizer, I hopped into the R.22 after about six months out of it (with a factory IP), picked it up and almost immediately started going back and forth like a drunken boxer... :O

...I figured it out, but I think that IP was a bit worried for a moment!

And HAVE A BLAST! Flying a helicopter is truely something worth experiencing, as often as possible.

[ArcherII]

well flingwing,

I'll have to read your post a couple of times for it to sink in, but I get the jist of it.

I know from MS Flight Sim that helicopters are extremely "touchy"...don't know if that's the case in real life...or to what extent it is...but I get the general feeling that it is.

I've been on a helo once...it was a ride when I went skiing in the Alps...it was very amazing...just felt very wrong...not having wings stickign from the sides...and wondering how forward movement was kept...

the guy literally seemed to not move the cyclic...

I can't wait to try this out...might happen after tomorrow if the weather permits me flying TO the airport where the helis fly...as I don't have a drivers licence ;)

Archer

I just re-read your post and have a couple comments/qeustions

In the R.22, what happens is the tail rotor (still producing thrust) starts to roll the airframe to the right pretty quickly, while the rotor disk does not roll!

Now how exactly does the tail-rotor roll the helicopter? I thought the tail rotor only affected yaw...isn't the rotor right about the center of mass of the helicopter so it would not really produce any rolling moments? It would have to be higher or lower than the center of mass to cause a roll.

And when you push the cyclic forward, the disk is unloaded cause...you gain airspeed which helps the engine rotate the rotor?

And about the RPM/stall phenomenon...

does that have to do with the picth from the collective which causes variations in RPM (due to drag and load on the engine)...

so say youa re at 104% Ng (RRPM and engine RPM)...so you are good...you are hovering with a certain pitch on the blades (certain collective).

Now say all of a sudden you want to climb...pretty rapidly...so you increase collective...and thus all your blade rotors' pitch increases...they take a bigger bite from the air...inrease drag, increase lift.

Now increased drag means higher load on th engine which was at 104%...now say it dropped to 90% due to the load...the engine is loaded...

Now does this mean you can't possibly increase the Ng back to 104% anymore? or anymore than 90%? due to the drag from the pitch of the blades? So the engine can't do it anymore?

So obviously if this is the case...there is a limit, like you said maybe 80% where the RPM is very low...and the engine cant' take it anymore...

the thing is, I would think small pitch, 104% would produce same lift as 90% and larger pitch...

so I'm still a little confused I guess ;)

[boomerangben]

Archer,

all this is good stuff, but you are in danger of sitting the PPL helicopter theory course before even starting! If you are in a Robinson, the governor will maintain engine RPM and thus Rotor RPM automatically for you. Because Robinson's wisely derated the Lycoming engine, you will only get a small droop of RPM when you pull in power. Infact you will generally red line the Manifold Pressure before you get a low rrpm horn.

I personally think that you cannot be taught how to hover - it is a skill that can only be learnt by experience and it is some experience! Best tip I can give is rest your arm on your knee and hold the stick with your finger tips. Hold it in your fist and you will have the cyclic grip inprinted on your palm for a week.

Tail rotor roll is due to the tail rotor not acting in the same plane as the rotor head. That is why you see larger helicopters with the tail rotor on top of the tail fin.

Oh ****** you've got me doing it now!

Chill out, go out there and have a ball. But remember to leave all your fixed wing skills behind and watch out for the pedals. They are feather light in an R22 and I've had more trouble teaching Archer drivers than complete novices - the pedals in an Archer must be real heavy.

[Heliport]

ArcherII

The advice given by boomerangben and others is good. You've obviously learned a lot from the MS sim, but now you're going to fly the real thing - don't get too bogged down in the technical stuff at this stage. Concentrate on enjoying the experience of flying a real helicopter, and find out what the helicopter does when you move the controls - there's plenty of time to learn why it does it when you start your lessons.

I also echo the recommendations to read Randy Padfield's book "Learning To Fly Helicopters". He's an experienced professional pilot and instructor, and IMHO it's one of the best 'introduction to helicopters' books available.
ISBN: 0-07-157724-6

[ArcherII]

I'm about to graduate from Aerospace Engineering, so I blame that on my obsession with knowing the technical details behind everything.

Well, if the weather clears up at least a little, then the ride will be tomorrow :)

Archer

[Hilico]

One last point...MS Flight Sim is a lot harder than the real thing - basically down to the peripheral vision and feel in the real aircraft.

[Flingwing207]

I know from MS Flight Sim that helicopters are extremely "touchy"...don't know if that's the case in real life...or to what extent it is...but I get the general feeling that it is.
The control inputs and results in Flight Sim are fairly different from the real thing, especially the R.22. In the real thing, the controls are more sensitive, but you have a much better feel for what’s happening.
I just re-read your post and have a couple comments/questions
quote:
--------------------------------------------------------------------------------
In the R.22, what happens is the tail rotor (still producing thrust) starts to roll the airframe to the right pretty quickly, while the rotor disk does not roll!
--------------------------------------------------------------------------------
Now how exactly does the tail-rotor roll the helicopter? I thought the tail rotor only affected yaw...isn't the rotor right about the center of mass of the helicopter so it would not really produce any rolling moments? It would have to be higher or lower than the center of mass to cause a roll.
When you do a cyclic pushover, the nose goes down and the tail goes up. This puts the tail rotor’s thrust “line” above the CG – so the thrust rolls the helicopter. This is really only an issue with a 2-bladed rotor like the Bell 207, Huey, R.22, R.44 and so on.
And when you push the cyclic forward, the disk is unloaded cause...you gain airspeed which helps the engine rotate the rotor?
In this case, “unloaded” means the weight of the helicopter is not “hanging” from the rotor. The rotor is still taking power from the engine to turn it.
And about the RPM/stall phenomenon...

does that have to do with the pitch from the collective which causes variations in RPM (due to drag and load on the engine)...
The two most common scenarios for low-RPM stall are:

1 – Carb ice: The engine is losing it’s ability to make power, but the pilot doesn’t notice because the governor keeps opening the throttle to compensate. When the ice gets bad enough, the RPM starts to droop, and the helicopter starts to descend. If you’ve been sleeping at the sticks, you can still save it by lowering collective to maintain RRPM – as long as you have RRPM, you are alive, even if you are descending. If you have the altitude, you might be able to get the carb heat on before the engine stops, clear the ice, and continue on. If the engine stops, you autorotate to the ground.

However, if you ignore the CAT gauge and the decaying RPM and raise collective, it is as you said, the rapidly increasing drag will cause the RPM to droop rapidly, just like…

2 – Engine failure: The engine stops and the pilot does not lower collective to maintain RRPM. The rotor is slowing, the helicopter is descending, and…

…no matter how you got there, once you hit a critical combination of descent rate and low RRPM, you cannot recover, even if you bottom the collective. The angle of attack (and resulting drag) is just too great.
so say you are at 104% Ng (RRPM and engine RPM)... Now say all of a sudden you want to climb...pretty rapidly...so you increase collective...and thus all your blade rotors' pitch increases...they take a bigger bite from the air...increase drag, increase lift.

Now increased drag means higher load on th engine which was at 104%...now say it dropped to 90% due to the load...the engine is loaded...

Now does this mean you can't possibly increase the Ng back to 104% anymore? or anymore than 90%? due to the drag from the pitch of the blades? So the engine can't do it anymore?
In the R.22, the Nr will not drop until the governor has opened the throttle fully. If the rotor drag is still higher than the maximum power output of the engine, the Nr will droop. The only way to recover Nr is to lower the collective.

A friend of mine had the unfortunate experience of being a passenger in an R.22 where the pilot did just that. The helicopter was well past max gross so it wouldn’t pick up. The pilot pulled close to full collective all at once – the inertia in the rotor provided the added power to get the helicopter about 20’ in the air. But then there they were, with the Nr heading south and nothing to do but wait for the inevitable return to earth. The pilot compounded the error by not lowering the collective to attempt to gain some Nr so they could cushion the landing, so it was a hard landing indeed, followed by a rollover. Luckily, nobody injured.
So obviously if this is the case...there is a limit, like you said maybe 80% where the RPM is very low...and the engine cant' take it anymore...

the thing is, I would think small pitch, 104% would produce same lift as 90% and larger pitch...

so I'm still a little confused I guess
actually, it sounds like you get the idea – the higher the RRPM, the higher the airspeed over the rotor blade, so the less pitch/AOA is required, result? Higher RRPM = less drag for same lift.

[ArcherII]

When you do a cyclic pushover, the nose goes down and the tail goes up. This puts the tail rotor’s thrust “line” above the CG – so the thrust rolls the helicopter. This is really only an issue with a 2-bladed rotor like the Bell 207, Huey, R.22, R.44 and so on.

Wow, I can't believe I hand' thought of that...that makes complete sense...the rotor going above the CG of the heli when yhou push the cyclic down.

And I think I get the low RPM thing too now. I think what I was forgetting was that the R22 usually operates with excess power available. So say the pilot pulls on the collective ( increases pitch of blades, more drag, larger lift) the rotor RPM would normally go down. So the governor asks the engine to provide more manifold pressure, and since it has excess MP, it brings back the RPM to nomial. So now, you got higher pitch for same RPM...thus more lift...and the helicopter climbs.

Now where the trick is...is when you reach the limit of this excess engine power.

Say you are closer to the limit...and you pull on the collective (same stuff, higher drag, more lift) so lower RPM , and the governor asks the engine for more power to keep the RPM up. Well, in this case there is no excess power, so the engine CAN'T maintain rotor RPM, and thus it goes below 104% (the optimal...for lowest drag etc).

Well, if the pilot requires excessive collective, and the engine is at it's limit...then obviously the RRPM is going to plummet...and you are going to have an extremely low RRPM...that might not be enough for autorotation...thus you are screwed.

That's my understanding at the moment, which seems to make sense to me from a technical standpoint.

Archer

[Flingwing207]

You've got the idea!
:8

[[email protected]]

Archer, when the pilot demands more power (by raising the collective) than the engine can produce, the RRPM will decay - this is called "Overpitching" and should be demonstrated to all helicopter pilots. Don't worry about autorotation in this scenario, as soon as the lever is lowered, the engine will be able to cope again and the Nr will return to normal.

As for hovering - the key is in maintaining the correct hover attitude (a bit nose up and a bit left skid low for an R22). The required attitude will change depending on wind speed (more nose down to maintain position over the ground as the wind increases) and C of G (both lateral and fore and aft). As a plankie pilot you will tend to want to put the wings level - this will cause the helicopter to drift to the right quite quickly.

You should get given one control at a time - usually cyclic first to sort out the hover attitude, then the collective and last the pedals. It is best to then combine 2 controls (cyclic and collective or collective and pedals) before going for all 3 together. You have to learn to be logical and identify which control will correct the error you see in front of you. Unfortunately a helicopter will want to drift, yaw and climb all at the same time which is why it takes a while to be able to hover well.

Good luck and enjoy it.

[ArcherII]

well, it's not happening today as I had wished...weather is IFR still.

Yeah I read about the fact that helicopters will touch down on one wheel or skid first...since to counter the side force during hover a pilot must bank/move the cyclic to the left to maintain position and hover.

I understand this since that's exactly how you touch down with an airplane in a x-wind landing...one main gear, then the other, then the nose gear...due to the wind which imparts a side force on the aircraft that you have to counter by banking.

Same thing with a helicopter I gather...except the side force is produced by the tail rotor...which is producing thrust in one direction and thus needs to be countered...

Archer

[pilotwolf]

Whirlygig ...

I had same problem after I passed my private checkride - fortunately the examiner wasn't watching!

Oh and I ve a couple of hundred hrs, including time in the 206 - not much I know - but I ve never managed to fly it in MS Flightsim....

I can't get Heliport's first link to work...

Anyone else having problems?

PW