Military Training Wrong ... ?
 

CRAB (and other mil-bible die hards)... just a side question : Do the military still teach (wrongly) that recirculation at cliffs results in attitude change TOWARDS the cliff?

Joe,

I have been in for 19 years of which 11 have been as a QHI and I have never been taught or taught others anything other than the fact that recirculation can occur when hovering next to any obstruction. The AP 3456 (Mil-Bible) does not claim an attitude change occurs in the direction of the obstruction - where were you taught this idea?

I learnt to fly way before that - so maybe they corrected it already! But I thought I saw it in some relatively recent(15-20yrs) CFS notes (... maybe only the Navy?)

Joepilot - are you just an anti-christ, or do you just like antaganising real pilots?!!!
Think basic PofF =- when hovering next to any building, cliff, wall etc, where will all the downdraught go from the side of the disk nearest to the obstruction? - It must go up then fed back into the disc along with normal downdraughting air thereby increasing the induced flow on the side of the disc nearest the obstruction - basic P of F again increase in induced flow = decrease in lift = aircraft drifts into obstacle because the other side of the disc remains unafected thereby producing more lift than the other side hey presto A/C drifts into cliffs

A/C only drifts into Cliffs - if pilot does nothing about it....that's why we have a Siclik ....most pilots look at the cliff and decide not to fly into it..... :) Forget about the P of F

Loss of lift on the side of the disc nearest the cliff yes. But what about gyroscopic precession?

Are any of these guys really pilots ??? unbelievable - I hope that passengers dont clap eyes on this thread.
:rolleyes:

[This message has been edited by SARcastic (edited 22 January 2001).]

Thats what happens when you mix wannabees with the real thing............

To: Joe Pilot

This is taken verbatim from the FAA Rotorcraft Flying Handbook. “ When flying an approach to a pinnacle or ridgeline, avoid the areas where downdrafts are present, especially when excess power is limited. If you encounter downdrafts, it may become necessary to make an immediate turn away from the pinnacle to avoid being forced into rising terrain”.


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The Cat

OK, just for the hell of it...
If close to an obstruction air will be recirculated to the disc as induced flow moves up the side of the obstruction. This will happen in proportion to the height and density of the obstruction (trees with space in between would cause less recirculation than solid walls). Gyroscopic precession (I know at least one person who will like this !) will carry the effect of loss of thrust (lift if you like)90 degrees on.

So - Obstruction on Helis. right with anti clock rotor = Front of disc or skids lower, etc. Most recirculation is generally quoted as happening around one third of the rotor diameter away from the tips and that's close enough for most.

BUT this change in attitude is only good for the recirculation at the tip area of the disc. If the disc gets closer to the obstruction more of it is affected. If half of the disc is affected the loss of thrust is still precessed, but now the blade over the tail(still obstruction on the right) will become low TOWARD the obstruction as well. End effect = disc low at front and to the right.

This is why some exam Q's I have seen include this as a correct answer. It is one of those 'paper correct' theory things that means little in the real world.

We'll all be close enough to an obstrction to have a slight change in hover attitude at some time or other, depending where we operate from, but as for the 'sucking in' of the Heli to the obstruction I have heard quoted, I beleive it to be impossible as the disc would have to be so close for 1/2 of it to be affected in such a way (or already be buried IN the obstruction!) if 1/3 of the diameter is accurate.

Yes, agreed fully. Common piloting sense is one thing and answering an exam question that has little relevance to flying is another. No pilot is going to get so close to an obstruction that it becomes 'sucked in', if it is possible at all. I'm sure all will give the maths a think and maybe arrive at the conclusion I did - For the aft blade to be affected by 1/3 of rotor diameter max. recirculation whilst it is 2/3rds of the radius away from the obstruction, it will have already struck the obstruction?

SPS, sometimes disenhchanted with having to teach one thing for the student to pass exams and another to put it right afterward.

Sure it's a bit theoretical ... but it does help pilots understand what is happening with their rotor disc...

Blades on the 'cliff' side experience more ind. flow ... and therefore flap down in that half ... therefore they are lowest by the end of that half ... therefore the attitude WOULD NOT change towards the 'cliff', but Parallel to it (some people call this gyroscopic precession).

The attitude does not change however because the pilot uses the cyclic to maintain the desired attitude.
CLEVER BIT:
- in doing so he is running more Pitch on the 'cliff' side (to combat the higher ind. flow) ... and a slightly increased collective ... and so just MORE POWER!

Very elegant really...

Swerve: is that a revelation to you?
Eden: Spot-on , agreed
Helisphere: Yes! (but no need to hide behind the term Gyroscopic Precession)
SARcastic: Just curious... do you mean it's a tedious subject?(agree) Or did/do you dissagree with the assertion?
Purple: Expand please.. (see above)
Lu: Missed the point...

SPS: Approximately correct. the hole in your arguement is (for your orientation) to treat the 'extra' ind. flow over the tail, on getting closer, as different from that at the front. - or in your language; 'the SUM of the precessions of blades experiencing increased ind. flow (the right hand half still results in a low point over the front...' -

To: All

Here is a theory that will really get you to thinking. Assuming the pressure differential between the cliff side of the rotor and the opposite side of the rotor. If there is a differential of pressure between the sides of the disc there is a differential of pressure on the fuselage and the greater pressure is on the side of the fuselage away from the cliff. Nature being what it is, the pressure differential acting on the fuselage will push the helicopter towards the cliff in order to compensate for the differential. The closer to the cliff the greater the differential and the greater the sidward force.

Don’t laugh or, I’ll have to use rocket science. If you have ever seen a large liquid propellant rocket engine you will have noticed circumferential rings around the nozzle. These rings give stiffness to the bell and help maintain the shape of the engine. Sometimes, during the start of the combustion at sea level the gasses can’t fully expand which creates a pressure differential between the inside and the outside of the bell. This is called Jet Separation, This pressure gradient can be so strong as to shift the engine sideways and force the control servos up into the structure or, it could cause the nozzle to collapse. The rings increase the resistance to collapse by altering the hoop stresses on the nozzle. I am not sure but the Space Shuttle Lox / Hydrogen engines may have a two stage hydraulic system to allow the engine movement but the force is attenuated by a spongy servo. Next time they show a closeup of the engines you can see them move at ignition start.

The same is true for aircraft wings on aircraft flying in close formation and the wings overlap. The air between the wing tips increases in speed due to the venturi effect and causes a low pressure. The result is that the wings “lock”. These illustrations prove that pressure acting over a large surface can generate a great deal of force and in this case move the helicopter, which is a free body in space into the cliff.


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The Cat

[This message has been edited by Lu Zuckerman (edited 23 January 2001).]

[This message has been edited by Lu Zuckerman (edited 23 January 2001).]

Lu, the clue in your quote from the FAA is "downdraught" - this is not recirculation but turbulence on the lee side of a mountain feature where the air is going downwards and takes the aircraft with it - standard reaction is to turn away from the obstacle(high ground) and establish a maximum rate climb configuration. Then you wait (and pray)that the severity of the downdraught really does reduce as it nears the ground!
Your rocket science sounds like COANDA effect which the NOTAR aircraft use to exploit pressure differentials on opposite sides of the tail boom to produce anti-torque thrust in the yawing plane. They enhance it by blowing air down the inside of the tail boom and out through a slot along it's length. Fine yaw control is achieved by installing a movable bucket on the end of the tail to direct the remainder of the air in an appropriate direction.
Back to the cliffs and the Vortex ring thread highlights how recirculation around the tip vortex causes a loss of lift which in this case would be on the side nearest the cliff. Nice theory, never seen it practice and I have hovered close to a lot of cliffs.

It basically just costs a little power. So it is rarely noticed ...

Lu:

Your analogy of fixed wing flying in close formation is not quite right. The resultant pressure differential actually causes the trailing A/C to fly away requiring a trim change into the lead aircraft (ie. echelon right requires trim left).

Quite apparent when your doing a tight (wing overlap formation) at 120/3 and 240+ knots. (BTW 120/3=120 degrees of bank and 3G).

Cheers, OffshoreIgor http://www.pprune.org/ubb/NonCGI/eek.gif


[This message has been edited by offshoreigor (edited 23 January 2001).]

Don't know about COANDA.... but if you're blowing too much air anywhere it was probably the CORIANDER effect of too many PHALL blowouts and the resultant application of STOKES LAW to the viscous fluid deposited thereof.

Ooooooeeer - nothing like a flying suit full...suits you sir! :)

To: Offshoreigor

What do I know, I saw it in the movies and on TV. In one case the wings locked and on another the pressure on top of the wing was used to support the wing of another aircraft. Do you think they used artistic license to make the movies more interesting?

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The Cat

Lu:

The term, wing overlap does not mean that the wings are on top of each other. It refers to the fact that the trailing aircrafts wingtip is inboard of the lead aircrafts wingtip.

If you were to look from directly above or below a formation such as the Snowbirds or Red Arrows, you would see this. Due to the fact that most spectators only ever see such a formation from the ground at an offset angle, the illusion of the wings being "locked" as you put it is observed.

Standard Mil training in Canada uses about three feet of overlap, ie a wingman would have his wingtip inboard of the lead by three feet and slightly below. The resultant vortice created by the lead requires that the wingman trim into the lead aircraft to maintain station.

Cheers, OffshoreIgor http://www.pprune.org/ubb/NonCGI/eek.gif

Joe - The hole in YOUR argument is that you can't spell argument....!! (:-])

Thatts tru abowt mosht werds...

To: Offshoreigor

What I was referring to, is when one wing was directly over the other and the closer they got the greater the pressure drop between them. The resulting pressure differential across the bottom of the lower wing and the top of the upper wing would force the two wings together or to use another term, the wings were locked together. The lock as I perceive it is not a mechanical lock but the wings are separated by a very high velocity airstream between the upper surface of the lower wing and the lower surface of the upper wing.

I don’t know what kind of car you drive but if it is a compact you may have experienced a similar condition when you passed near a semi trailer. The airflow between you and the semi speeds up the closer you get to the semi and this creates a pressure differential across your car and the semi. Since you are the lighter of the two, this pressure differential will force you towards the semi.

That is the effect I was describing relative to the helicopter and the cliff (obstruction).


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The Cat

To anyone taking this thread seriously:

SWITCH OFF THE COMPUTER, OPEN THE FRONT DOOR, WALK TO THE JOB SHOP, AND ASK IF THEY HAVE A LIFE AVAILABLE.

To the many that are not taking this thread seriously:

Isn't it not strange that the stick in front of you enables you not to hit the cliff????

To: EESDL

Like all threads by the time you get to the second page the thread has deviated from the original topic. As an illustration, check out the Military pilots forum under the CH 47 crash. Most of what has been stated in this thread is the theory that would cause the problem and in some cases (Joe Pilot) if the problem actually exists.

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The Cat

EEDSL:
Just tried that ... they said I already have one ...

I appreciate your sentiments tho' ... I'm only doing this as an 'exercise in boredom'...

Sorry Lu:

But if you truly believe what you say and I think you do. Then you are well and truly, "OUT TO FARKING LUNCH!"

You have now lost all credibility you may have had left. You have displayed once and for all your lack of knowledge in this and many other subjects. I have been very tolerant until now, as have other more qualified individuals, but your hollywood idolization of this thread and others is intolerable.

You continue to display the reaction time of a child or a clown, I don't know which. I have bitten my tounge many times in the past and watched as you ranted but this takes the cake.

Please, if you have any shread of self respect left, do not reply to this post as you will only make yourself out to be the true @rsehole you are.

Cheers, OffshoreIgor http://www.pprune.org/ubb/NonCGI/eek.gif

To: Offshoreigor

I will answer you because you unloaded on me without telling me what it was that was not correct. True, I have never flown a small aircraft let alone placed the wing of my aircraft under or over the wing of another but what I was explaining is based on scientific principles formulated by Messrs. Bernoulli and Venturi. A more practical example of pressure differential is the development of downforce on a Formula 1 or CART racecar. If it were possible to reverse the car / road relationship the down force (up force) would be strong enough to drive the car upside down until it either slowed down or it ran out of fuel and then it would fall off the road.

Although I have never flown the above described aircraft I have put a lot of miles on the road and I am very careful when I pass a semi trailer and especially when one is coming from the opposite direction and the closing speed is well over 100 MPH. At that speed the pressure differential is even greater and depending on conditions can either blow you away from the semi or suck you into it. All of this is due to a differential of pressure. Whether you want to believe that or not is your business.

If you were responding to my comments about seeing it in the movies and on television then it is obvious that you missed my post above.


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The Cat

Lu:

If you don't yet get it, see my post in reply to your drivel on "coreolis effect"

Keep talkin Lu, you're still not listening.

Cheers, OffshoreIgor http://www.pprune.org/ubb/NonCGI/eek.gif

PS. For a man who claims to have such a busy consulting schedule, I can't help noticing that all your posts occur between 08:00 and 17:00 in your time zone (Quebec). I on the other hand am in GMT + 8 hours Lu. You will note that the majority of my posts occur after normal working hours.

To me this means either you are temporarily unemployed or never had a real job in the first place.


[This message has been edited by offshoreigor (edited 24 January 2001).]

[This message has been edited by offshoreigor (edited 24 January 2001).]

I'll actually defend Lu here offshore. If you need someone to quote from a book or regulation, or quote a law of physics (doesn't mean he understands what he has read however) he's obviously got time to do so.

>>but what I was explaining is based on scientific principles formulated by Messrs<<

But when we go away into the real world of flying, piloting, (basically away from books, where possibilities exist of things not happening as planned, the uncertainty principle, etc.) He's lost.



[This message has been edited by RW-1 (edited 24 January 2001).]

To: Offshoreigor

“PS. For a man who claims to have such a busy consulting schedule, I can't help noticing that all your posts occur between 08:00 and 17:00 in your time zone (Quebec). I on the other hand am in GMT + 8 hours Lu. You will note that the majority of my posts occur after normal working hours.
To me this means either you are temporarily unemployed or never had a real job in the first place”.

If you look closely you might even find that some of the posts are made at 2.3.4.5.6:00 in the morning because I have another job that requires direct communication with a firm in Korea. Regarding my being at the computer during the daylight hours instead of at a real job, I am at my job. Although not on a contract at some firm away from Quebec I still do what in the modern parlance is called telecommuting or, in other words, I do my work and send it off via email. I also work on a retainer for two lawyers that are working on two different helicopter crashes. I also operate a business selling aircraft and helicopter models and I have been doing that since 1987. I represent the Korean firm as their North American Sales agent. They make some of the finest engineering models in the world. If you don’t believe me, type Model Masters Inc in the address box on your screen and hit the go button.

In reading the first paragraph above, it appears that you have run out of criticism about my theories or my technical statements and now you are questioning why it is that I am sitting at my computer when everyone else is out doing real work.

To:RW-1

On your website you show a birds eye view of your day to day -to-day work place. You tell everything about yourself but you don’t tell what it is that you do to earn the money to get your flight time. You know what I do, now, tell us all what it is that you do that has an influence on other peoples lives. If you say the building is a hospital and you are an EMT then I will apologize on this forum. But, be truthful.

Also, you only have a commercial helicopter pilots license but you come off in your high and mighty postulations as if you were one of those helicopter gods you talk about.





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The Cat

[This message has been edited by Lu Zuckerman (edited 25 January 2001).]

EESDL

I went along like you said, asked for a life but they misunderstood and gave me a lot of girly pictures...............

I get revenue from engineers who frequent my website :) (Why not get your own?)

Another fun attempt by Lu to elicit a response, or turn it into a pissing contest. Far be it for me to get caught up again in your neurosis.

I enjoy immensely the conversation at hand, and my previous post speaks for itself. Actually as an engineer, you should have caught a developing trend in certain responses to you, alas ...... again you miss the point of the post, at least you are consistant.

Have a good weekend now.

(Please make sure you respond as I expect you will, with yet another personal attack of some sort)



[This message has been edited by RW-1 (edited 25 January 2001).]

To: RW-1

You say I’m wrong not because you know I’m wrong but because other people say I’m wrong.

Your biggest bitch about my postings is because that I made some nasty (to you) comments about the Robinson Helicopters and I asked other individuals (you included) to perform a test that would only take 2-3 minutes of your flight time. I can understand your statement that I should perform the test and I would if I had direct access to a Robinson helicopter. Don’t you have the least bit of inquisitiveness to want to perform the test? After all, you said if I performed the test, you would think I was lying.

Regarding my having a website, I do. Print out Model Masters Inc in the address bar and hit the go button

Over

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The Cat

[This message has been edited by Lu Zuckerman (edited 26 January 2001).]

Dodgy to advocate amateur flight tests...

To: Joe Pilot

By your definition any pilot no matter how many hours in type would be an amateur if he/she were not certified as a test pilot. The test is simple and the maneuvers are performed every day as a part of normal flight. The only caution I had indicated was that if it is safe to do, don’t counter the transverse flow effect by adding left cyclic. Other than that, everything I proposed is performed by a Robbie pilot when he flies his helicopter. My test only deviates from what the pilot would normally do to counter the impreciseness of the controls and do the tasks under controlled conditions. Do you find fault with that?


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The Cat

I must agree with Joe Pilot - whilst confessing to not actually reading in detail the full contents of this thread. The mere suggestion of testing anything whilst airborne is a wholly misguided philosophy best left to the shores of the North Americas. Lu - I have flown with American pilots and seen American ops up close and have been impressed and exceptionally unimpressed. Suggestions such as non-essentialin flight tests are irresponsible. You seem from your multitude of postings on pprune to have an opinion on a vast array of issues, unfortunately I feel you are maybe lacking in a shred of wisdom. Please don't reply to this and say the test is simple and not a flight safety issue - because I and many others will just laugh at you.

Up until now I felt fairly safe with some of your postings but this one has made me speak my mind.....the thought of some PPL running around in a Robinson 'test flying' when he should be doing many more important things makes me wonder what school of aviation created you. Please temper your enthusiasms in the future to cater for the broader base of all helicopter pilots - new and old.

Infact - now that you have raised such a point I suggest and hope that you will visit my thread 'B.O.L.L.O.C.K.' and add to the discussion.......one would hope...but it seems unlikely now that you have in the past brought pressure to bear on many a junior pilot to perform your enthusiastic luxury flying items....I and many others (I am sure) look forward to your considered response.

[This message has been edited by eden (edited 26 January 2001).]

To: Eden

Obviously by your own admission you do not know what the test is. If that’s the case I will tell you.

1) While on the ground determine the rigged neutral position of the cyclic stick.
2) Hover several feet over the ground. Do not counter any tail rotor translational movement.
3) Hover taxi the helicopter several feet over the ground by moving the cyclic straight forward with out moving the cyclic left or right of the rigged neutral center line. Which way is the helicopter flying?
4) If it is safe to do so fly forward without deviating from the rigged neutral centerline and do not correct for transverse flow. Once past transverse flow (about 20 knots) which way is the helicopter flying? I say that the helicopter is not flying straight ahead but it is flying 18-degrees to the left.

The test will prove me right or wrong.

Please tell me if you think this test is out of line and should only be performed by a licensed test pilot.


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The Cat

[This message has been edited by Lu Zuckerman (edited 26 January 2001).]

LU Z.... I stand by my original posting...you haven't even told me what you hope to achieve or wish to be observed..and I presume you wish something to be noted or absorbed by the said pilot as he flies these manouevres. The mere fact that you are asking any pilot to remove instinctive flying control inputs from his mechanical motor memory is asking him to do something extra-ordinary. This especially applies to junior PPL pilots. Now - as an instructor such flying is demonstrated to illustrate various flying characteristics, but we don't ask pilots to fly them...and I'm just an instructor!! So neither should you even suggest it. I think from my reply you now know how safe I think your tests are.

More importantly - are you going to add to the discussion on my thread and tell us how you have contributed to the big picture of communication in aviation or are you going to continue with theory, Laws of physics and engineering regs?

To: Eden

It is my contention that the design of the Robinson rotorhead is such that when rigging the helicopter the rotor is offset by 18-degrees from the lateral axis. This is as a result of the pitch horn leading the blade by 72-degrees and not 90-degrees like on a Bell two-blade rotor. Because of this offset it is my contention that the helicopter will fly to the left and not straight-ahead due to a precession of 90-degrees. You mentioned inbred instincts that the pilot would have to change in order to perform the test. These instincts are inbred in a Robbie pilot as he builds time and undergoes lectures from his instructors. In the process of his training the student and eventually the certificated pilot will develop the skills necessary to overcome the impreciseness of the Robinson controls.

It is my contention that the combination of the 18-degree offset and the impreciseness of control input is the root cause of the mast bumping rotor loss / rotor incursion accidents that have happened to the R22 and R44. The test is concieved to maintain a very precise cyclic movement in place of the present wandering of the cyclic in order to get the helicopter to properly respond. If the helicopter flies straight ahead when the test is performed then I am wrong but, If it flies to the left then I am totally vindicated as it will prove two points, The controls are imprecise and the helicopter flies to the left.

I hope this explains the purpose of the test.


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The Cat

It is so disappointing that you miss the point on so many separate occasions and I can now see why you attract such vociferous crticism. You fail to acknowledge or answer the point being made. I am obviously wasting my time and if there is any pilot out there who truly cares about Lu's 18 degrees (and his tests) more than flying the machine please publish a NOTAM when you fly and we can all watch out.

Not good Lu.

Surley you are wise enough to know that to advocate such things in a field which you are only just getting to grips with is just irresponsible ....

Sufficient tangled metal bears witness to the fact that your suggestion is bad ... therefore you are a danger.