View Full Version : FI Revision (Ex4. Effects of controls)
4th Dec 2005, 14:49
Thanks to everybody that answered my previous revision question. I do hope I am not boring everyone with my questions. I think that revision of a topic is good for everyone.
Anyhow, I now have some Qs about Ex 4.
Please also refer to the book I mentioned in my previous thread. ( http://www.rnk.co.uk/himan/documents/Exercise_4.htm )
1. Ex 4. My original notes state that cyclic forward, yaws left. Does it? The notes in the link above make no mention, so to be safe, I have left them off my re-write.
2. Ex 4. My original notes state that raise collective lever, RRPM decrease. However, book (link above) states RPM increase, though book mentions throttle and correlator. I assume that my original notes are correct.
3. Anybody that has done the AFI course with Mike Green might be able to help me on this one...
"1. Further effect of Lever and Throttle" then a picture of an airfoil, with "Lift" (over airfoil), "Weight" (below airfoil), "Thrust" (at leading edge), "Drag" (at trailing edge) then "(Autorotation)" against the picture.
Now, I don't quite know what I mean with this. Is this supposed to be the vector diagram with Plane of Rotation, Axis of Rotation, Angle of Attack, Relative Airflow, Left, Drag, Total reaction etc???
Also, I have...
4. Cyclic Right Trim
6. Carb AC Temp Control
7. Low RRPM Warning
and no explanation at the side of them. I am assuming that these are just pointers that I discuss in the classroom.
Thanks again for your help.
4th Dec 2005, 14:52
That guide is only one source, scan a few others on the same subject to fill in the holes.
I can recommend about 20 better sources, Shawn, where are you when we need you! Shawn's Book:
Here is a page from the old FAA Handbook discussing controls and throttle, it is simpler and more direct that the one you are slogging through:
Here is the entire document:
I must say that the idea of drawing angles on airfoils as a way to truly understand anything about helicopters is simply awful. The rotor behaves as a rotor, a big one piece thing that developes thrusts and eats power. Unless your exam has diagrams of airfoils on it and asks you to show how all the thingies are flipping all over it, I would stick to understanding how the rotor reacts.
I know I will face a zillion guys who swear by the airfoil diagram, and I wish we were all in a pub so we could slog it out with a black board. I guarantee you that except for delta3's magical computer (and its bigger brother at Sikorsky), almost nobody knows much about the angle of attack on rotor blades. Having been chief R & D test pilot, I had to sit in that simulator and explain how the real helo didn't do that, and it was always the poor way the model characterized what the blade airfoil was experiencing. I can take any helo model and pull to near stall and drive it to ridiculous results, usually in about 20 seconds.
6th Dec 2005, 11:03
who swear by the airfoil diagram
...because it's a simple way for simple instructors to explain to simple students simplely how POF works(or is thought to work!).
6th Dec 2005, 11:30
I read your original reply, but hadn't realised you had editted it since.
I have the Basic Helicopter Handbook already.
I understand where you are coming from. The book in the link has way too much information, but it is the only one that I can find that covers the syllabus that I have to teach.
I have to be able to prepare a board brief for the JAA PPL syllabus. I will be expected to draw the blade vector diagrams, but I am not sure if that is what is expected in Exercise 4. Also, I have information in my own original notes that don't appear here, such as a yaw when the cyclic is moved forward. Is this an ommision in the book or have I got confused. (An example, Some of my notes for some reason said that increase collective, nose yaws left, which on an R22 is actually wrong, yet I put it on my board brief (I couldn't understand myself why the nose (supposedly) yaws left, but it was in my notes, so that is what I used))
For the test, I have to be able to demonstrate I know the knowledge particular to the chosen exercise. This is usually much more information than would be presented to an actual student.
Because of my board brief incident, I wish to ensure that my notes are correct, with all relevant information for the exercise in question, hence my questions. Simply reading fact books with no bearing to lesson content won't really help me I don't think. Whilst the theory is useful, I have to follow the course structure.
6th Dec 2005, 12:40
1. MG made a point about this in my instructor test. His point is that with cyclic forward & no power change the acceleration causes the vertical stabiliser to work harder, which means that you're likely to be holding too much left pedal, hence yaw left. He feels that when you are later teaching straight and level in Ex. 6 this effect outweighs the additional torque reaction due to increased power therefore no net left pedal requirement on acceleration in straight and level.
2. Depends which part of the collective travel you're talking about. Your notes describe governor off behaviour at cruise power setttings, the book is talking about lifting the collective from flat pitch on the ground. The difference between the two is due to the imperfect correlation.
3. The purpose of the further effects of lever & throttle section (gov off) is to show intially the rpm droop as you move below the correlator range, then needle split and rising rpm, and finally lever control of the rpm in auto. The diagram you have described doesn't sound especially helpful in this context, and anyway, extensive aerodynamic lectures are a bit premature for ex 4 - your student will have a head full of bees before you go flying if you labour that.
4. Cyclic right trim is just an opportunity to talk about when you use it, and to set up a demo in the air later.
5. Governor I was taught to leave to the end of the lecture, then you can go through all the items where rpm changed, and show that now rpm is governed and MAP changes as a result.
6. Carb temp - describe use and effects on rpm +/-gov.
7. Low rpm warning - as a lay up for when you cock up the auto demonstration (arf arf !).
My ex 4 also has a heading to cover rotor brake and mixture control for completeness.
Hardest lesson to teach IMHO, usually takes more than one flight, and I'm still not sure that cramming all this stuff in the students head at this stage actually has any benefit (other than insurance liability management !).
PS FWIW I've taken to doing this brief visually as three columns, primary effects, secondary/further effects, governor effects. eg. the first line across covers primary cyclic (speed & dir) secondary cyclic (airspeed and discloading), and governor swapping MAP changes for RPM changes during the airspeed and discloading demo.
6th Dec 2005, 13:07
If you learnt under Mike, you could be a good contact for me. I may direct some questions to you if you don't mind.
1. Ah, now I understand.
2. Confusion alert. This is where misreading something can lead to all sorts of problems. Aint aerodynamics wonderful and you can bend the rules through interpretation.
3. My picture is... (Airfoil leading edge towards thrust)
(Aarrgghhh. EDIT. Added dots to format picture. Ignore dots...)
<-------- (airfoil blade) --------->
If you learnt under Mike, do you have a similar picture. What would the picture be in relation to. To me, that is the 4 forces on an airfoil section.
Thanks for the other points.
My original notes have it in 3 columns, but not much supporting information.
It is a few years since I was taught and having no experience since has obvious brain fade.
6th Dec 2005, 18:05
I also did my instructor course with Mike Green. I pretty much agree with puntosaurus. With my original notes in front of me....
For moving the cyclic forward, I have
Nose down attitude
Yaw left (fin more efficient at higher speed)
The cyclic right trim, governor, carb heat control, and frictions, are simply other controls that you teach the student about, since this lesson is "Effects of Controls".
I have a similar diagram to yours, for explaining the "Further Effects of Collective Lever", ie the freewheel system. Lift, drag etc are the forces acting on the blade. My notes say, " Blade represents rotor disc. Must overcome drag, or blade slows down. So if raise lever, need to open throttle, and vice-versa. If engine stops, blades would stop as can't oppose drag. So lower lever to get rid of drag. Aircraft goes down. Freewheel system between engine and rotor allows you to disengage them. As aircraft descends, air coming up through disc keeps rotors turning, like a windmill. Energy stored in disc can be used to cushion landing."
Does that make sense at all?
I remember asking Mike if he really briefed students like this - the briefing as he did it is about 40 minutes I think. He said he did! Well, I tried to do it, just once. The student was obviously overloaded, and the CFI told me not to do it in that much detail as it confuses people. OTOH, I never got taught about the cyclic right trim as a student, and didn't use it for quite a while as a result.
I reckon you can brief about the main effects of the main controls, then on the way back to the field, take control and explain to the student about the cyclic right trim, carb heat control, etc. That way, you can do it all in one lesson. But I only have 70 hours total instructing time so far, so I'm hardly an expert.
Fanpilot, who are you doing the revalidation with? And would you let me know how it goes and what you have to do, please! Mine is due in April, and I'm starting to panic about it already. :( :eek:
6th Dec 2005, 18:46
MG did my test, I was actually taught by Mike Bill down at Redhill, and you're welcome to pm.
As Whirlybird says, I wouldn't sweat the diagram. As she also says, you're not going to tell your student why it autorotates at this point, just that the upward airflow through the rotor replaces the engine torque. So why make it complicated. I'm generally really crushed because I love the aerodynamics stuff (as an amateur I hasten to add) and yet I'm less and less sure it helps when teaching someone how to fly.
Re. 2 MB had a cunning diagram which is almost certainly wrong mechanically, but certainly helps to imprint the behaviour of the correlator on a student.
He drew the throttle cable as if it were wound clockwise (looking from the front) around the collective lever about six inches forward of it's pivot point. The twistgrip would therefore work as you'd expect but raising the lever would also open the throttle.
But because the collective moves in an arc its effect on the throttle in this configuration is a circular function not linear. If you draw it out (and my explanation has been OK) you can see that the movement would be relatively greater around 0 to 10 deg (from the horizontal) than say 40 to 50 degrees (ie a cosine function). Therefore the throttle overcompensates in the low range (<16") and undercompensates in the high range (> 21").
I'll admit it's not the simplest analogy, but it does work !
6th Dec 2005, 19:36
Hi PuntoSaurus and Whirlybird,
Thanks for your response. Yes, it does make sense, I have missed a minor detail off the diagram, "(autorotation)", so yes, I can understand it. I will have to put "instructor notes" with the diagram to explain to myself why I am using it.
I am doing an FI(R) revalidation with Mike Green (shouldn't be a prob, even though I learned under Mike, this is a revalidation not an initial test), I guess not a full revalidation as I haven't had the opportunity to use my skills. This will be just like my original test, so it shouldn't be too much of a problem. (I did have a trial run, which I did the Ex 6 (in my last message) which didn't go too well).
If you are still FI(R), then if it is not for full FI, it should be very similar to your original test.
With your 70 hours, you will surely have had the opportunity to fine tune your notes. This is what I intend to do.
BTW. I read your thread as you were going through the course. You did yours after me and it did bring back memories of my own, though you had the opportunity to fly with another student. I was on me todd (on my own).
I will let you know how I get on. I am hoping to do it in the new year.
Thank you PuntoSaurus. I will take you up on that, and if Whirlybird is also offering, I will take that up as well.
I've now re-written ex 4, 5 and 6. It looks like Ex 7 could be a little awkward. For some reason, I have two sets of different notes. One of them appears to be the air ex. (see below). The other I think I wrote as an exercise in writing lessons while on the course.
Aim: TO teach the student how to enter and control the helicopter at a given airspeed and rotor RPM and recover to climb.
Airmanship: Hasel. Ground, W/V. Carb Heat, Verbal Warning, Rotor Limitations. 90-110%. Recovery height.
See pic 4.
1. Control RRPM
2. Speed Changes.(RRPM)
Increase Speed – RRPM Increase
Decrease Speed – RRPM Decrease
3. Disc Loading (RRPM)
Decrease Disk – Reduction in RRPM
Increase Disk – Increase in RRPM
Turns – Increase in RRPM
(a) 90Deg Turns
(b) 180Deg Turns.
Ex 7. Basic Autorotations
Aim: To teach how to enter and terminate a successful autorotation.
Airmanship. Lookout. Ts&Ps, HASEL.
On entry, a pitch down due to the horizontal stabiliser at the rear forcing the tail up.
During the autorotation, the airflow will be up through the blades, keeping them spinning.
On recovery, the helicopter will tend to pitch up, which slows the aircraft from an already slow speed. As power is being applied, a fast rate of descent, and slow airspeed, a Vortex Ring could result.
The helicopter flies with an Inflow Roll. That is the tendency for the aircraft to roll slightly to the right. Without power, the roll will be removed. The aircraft will roll to the left, unless corrected.
Pull on Carb Heat.
Lower the lever fully and close throttle. The tachs will split.
You will notice the helicopter will rotate to the left. Correct this with the right pedal.
Adjust attitude to keep the helicopter speed at around 60kts. This will look like the normal cruise attitude.
Raise collective slightly to keep the Rotor RPMs in the green.
About 300 ft before the minimum height for recovery.
Raise lever slightly to bring the needles together. Open throttle gently.
When needles join, then raise the lever and open the throttle until climb power is reached. Watch you don’t overspeed.
Apply forward cyclic to prevent nose pitching up and to maintain climb speed.
Maintain balance and heading with pedals.
Do these look familiar to anyone or am I totally on the wrong track?
6th Dec 2005, 22:01
Concerning your notes for Ex 4, I remember Mike Green was adamant that the diagram etc was for "Further Effects of Collective Lever" not "Auto-Rotation". He said you shouldn't be mentioning autos at that point, just explaining the freewheel system that comes into play when you fully lower the lever.
As for Ex 7, it sounds OK to me, except I don't think you say anything about closing the throttle, then during the recovery, opening it to join the needles, not just raising the lever. But it's a bit late now, and I'm tired, and I may have missed it in your post. I'll get out my notes when I have time and go over it properly.
Yes, you're welcome to contact me about any of this; it'll help me too. My 70 hours have been mainly trial lessons, so I'm fairly rusty on the other stuff too, though I took one student right through to first solo.
Are you attending a seminar too? You must be. I expect I'll have to do that too, unless I can manage to get 30 hours before April. Any recommendations?
I know the test should be straightforward, but I just dread tests, and the more I do, the worse it gets. Any cures for exam panic would be most welcome!
7th Dec 2005, 08:16
I hate tests too, especially this type where you are in an artificial environment.
Anyway, thanks for your offer.
I have already attended the seminar. I did mine down at Cranfield. I did it with eta.
examiners training agency
I learnt quite a lot and met quite a few pilots and contacts.
They have a problem though. As there are too few experienced heli pilots to lead the heli part of the course, the heli part will be few and far between, so if you can get it done sooner rather than later, you should be ok.
There is no test with this, though you do have to get up and do a safety brief on a particular subject. This was good. I learnt a lot. I enjoyed doing the brief, though in preparation of it, I did have the help of a very experienced (Ex RAF) heli pilot.
Good luck with building your hours or your flight test.