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Flare on normal landing


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#1 octagon

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Posted 22 August 2018 - 13:44

All the instruction for normal landings that I've seen says to fly straight in to the landing spot with a certain glide slope, bleeding off airspeed smoothly, to arrive at a hover above the spot with zero forward speed. I'll be at about 45-50kt when turning final.

 

Why not fly the entire approach at 65 knots and flare at the end? Specifically I'm thinking that at 65kt one could enter auto-rotation and land safely if the engine should quit?



#2 RisePilot

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Posted 22 August 2018 - 14:57

While a myriad of flight techniques can get you to the ground safely, outside of training most helicopter landings are made to a specific spot.

 

Zooming in at 65kts makes an assumption that you will always have a large unobstructed landing area with an extended safety buffer zone - not the case with most LZs.

 

Best idea is to keep the machine in ETL as long as you can and watch your VSI.


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#3 Discap

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Posted 22 August 2018 - 17:52

Don’t forget that settling with power is an inertia event (not to be confused with vortex ring state). So if you are coming in hot then you need lots of power to slow down.
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#4 Azhigher

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Posted 22 August 2018 - 18:52

Which do you suppose is more likely to happen: 

1. An engine failure on short final.

or

2. You're burning into an LZ and you f*ck it up and hit something.

 

At least that's what I was asked back flight school. 

 

Fwiw when I was young and dumb I got low rotor RPM in an Astar doing just what you described. Burning it into an LZ, flare, bring in power and... low rotor horn. That was enough for me, now I take it easy. In the end, fly it however ya want. (Or your employer allows)


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#5 Eric Hunt

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Posted 22 August 2018 - 19:47

Coming in hot and then flaring will mean your rotor RPM will be trying to go very high.

 

Your engine governor will see this and drive the engine to as low as it can go.

 

Suddenly you suck on the lever big time, and the engine has to go from almost idle to perhaps full power in a second or two - doesn't happen. Splat.


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#6 r22butters

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Posted 22 August 2018 - 21:14

 
Why not fly the entire approach at 65 knots and flare at the end? Specifically I'm thinking that at 65kt one could enter auto-rotation and land safely if the engine should quit?


,..because that would be boring!

Hang it on the edge of ETL and come in slow and steep,...that's how butters likes it :)

Though come to think if it, sometimes I do back it down to about 40, dump the collective and come in nice and quiet like. Then near the end I flare a bit and finish off with an airtaxi to my spot, but that's only when I'm making a 180 approach close in from downwind and I have quite a ways to go before my parking spot. That's fun to do, but only because I'm turning as I descend :D
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#7 Bonzo828

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Posted 23 August 2018 - 10:12

If you ever fly passengers and depending on your mission, most don't like a 65 knot approach with an aggressive flare at the bottom.  Have you ever watched a HEMS approach?  Most commercial operators are going to want slow and controlled.


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#8 Wally

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Posted 23 August 2018 - 11:06

All the instruction for normal landings that I've seen says to fly straight in to the landing spot with a certain glide slope, bleeding off airspeed smoothly, to arrive at a hover above the spot with zero forward speed. I'll be at about 45-50kt when turning final.

 

Why not fly the entire approach at 65 knots and flare at the end? Specifically I'm thinking that at 65kt one could enter auto-rotation and land safely if the engine should quit?

 

There is a difference between the training world and the real world, even in required operator line pilot recurrent training events.

Training for initial certification is very broad but generally designed to teach a potential pilot what the basic approach should include, types of basic approaches, planning that approach and then flying the specific type of approach with appropriate control adjustments to maintain the steep, shallow, normal approach; resulting in an approach to the ground with no run-on, some run-on, running on above x-speed, etc' etc. etc.

The training scenario is controlled, with optimal conditions, some challenges, etc. etc. etc.

The training scenario will require the approach be flown to resemble some defined routine.  None of that, or very little of all the conditions will apply in the real world- helicopters routinely operate in order to place, remove stuff from more or less improvised landing places.  The pilot should have the skills to adapt to immediate requirements, or the judgement to seek another answer....

 

Which is all a long way to getting to the point of your particular question- if not "A" then it must be "B"!  There isn't a one size fits all answer, every parameter on an approach is on a scale, airspeed on approach, approach angle and path, approach air speed- everything, even where the wind is versus any part of the approach, even the termination.

 

Fast approaches are much harder to control and involve greater risk to do... what?  You're not taking fire on the approach, are you?  Do you think the screaming approach protects against mechanical failure?  It is taught as an answer to some mechanical issues, yes, but one is at much greater risk with big power changes inducing the failure than the risk otherwise.

The biggest risk is allowing for error in your technique- one gets too low, too fast, 'behind the bucket' the decel is a significant increase in tail rotor strikes.  It's also more difficult to be precise in your skid placement while you're dealing with pitch attitude, approach angle, power and speed adjustments in the last seconds where precision is everything.

Oh, and the power thing is a very real issue- even with careful calculations of weight and power and a hover check at altitude prior to approach initiation, it's a all a guess as to how much power is available and how much you'll need to terminate as planned.   A slow approach gives you time to evaluate, adjust or abort.  It's real exciting (and dangerous) to discover that you don't have the power available to do whatever you planned in the low and slow part, but much easier to abort than after a high speed approach and aggressive decel.

The power issue carries into turbines (other governed engines, maybe?) if you're maneuvering aggressively in the last seconds- turbine wind-down does indeed occur in which the engine maintains rotor during the airspeed decel, but the gas producer drops below the ability to recover significant power as quickly as you need.  It takes time to move from 90% to 100% NG.  The NR goes from you maintaining high green to out the bottom as you pull pitch to avoid impact.  Been there, did that, and fortunately had altitude around the intended point of landing to fly out of the situation, nursing pitch to get back into the green.....

Those are big issues. Add that the wind is an uncontrolled, variable and critical commodity in your approach. If it's not where you really need it to be exactly when you need it to be, you need to be able to adjust.  If the wind is in the wrong place when you pull pitch after, or worse yet, during an aggressive decel, you could find yourself in the dreaded vortex ring state without time and altitude.

 

The best approach has no pitch attitude or power changes after you align with your termination point, or minimal changes.  Perfect is NO CHANGE in pitch, power, yaw or roll- you roll out at wto, three hundred, 50-65 knots and just slide down the wire to a zero airspeed or run-on speed.  Besides being the easiest, most recoverable method, it allows you time for your low recon, a chance to see what's going to be a factor at termination.  I hear "Oh, I do a really good high recon first!"  A pilot seldom hits an obstacle seen in the approach...

 

Slow and boring is how you get old.


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Just a pilot (retired, so I have a LOT of time)...


#9 Nearly Retired

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Posted 23 August 2018 - 12:08

Back when I was young and stupid...okay younger and stupider, my collective used to have two settings: Full-up and full-down.  Every takeoff was at full power and every approach was a simulated autorotation.  I nearly got run-off my first job assignment in the Gulf o' Mexico because I was scaring the guys so bad.  They mentioned it, I back off a bit, and I spent the next thirteen years refining my technique.

 

Now, like Wally above, I fly like an old lady.  (Unlike Wally, I do not dress like an old lady however.  But let's not go there.) I fly slow, stable approaches.  If I'm in the shaded area of the H/V curve, so what, I do not care.  Everyone else above has noted the reasons for this, and they are correct.  I fly so slowly now that one day I took me 90 year-old mum up for a helicopter ride and as we were coming back in she said, "Come ON...what is this, OGE hover practice??  Even I fly faster approaches than this!!" 

 

And I was, like, oh well...

 

You can fly fast, autorotative approaches all the time.  I'm living proof of it.  But your judgment, technique, timing and execution have to be exquisite.  Every time.  And I realized that I couldn't guarantee that I could be *that* good.  YMMV.


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#10 octagon

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Posted 23 August 2018 - 12:09

Thanks for the thoughtful responses, it'll take me some time to ruminate and absorb. I'm trying to develop my intuition for balancing different risks.



#11 johnnyb

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Posted 02 September 2018 - 17:48

Why not fly the entire approach at 65 knots and flare at the end? Specifically I'm thinking that at 65kt one could enter auto-rotation and land safely if the engine should quit?

 

You ask a good and interesting question. You got some long-winded and albeit some not really relevant answers, I don't think the real issue has been addressed. Let me try.

 

The main, no the ONLY purpose of your flare, at the end of your approach (under power), would be to reduce your speed.

In a power OFF situation, after you lost your engine, in addition to slowing down, the main purpose of the flare is to increase rotor RPM, to store energy to be sacrificed later for lift.

Very different.

 

So, to flare at the end of a high speed power on approach and then utilize it for RPM in a sudden power off situation will do you no good.

In a power on situation, the wind is flowing downward through the rotor system, even in a flare.

In a power off situation, during an auto, the wind is flowing upward through the rotor system

When you transition from a power on to a power off situation, you need time for the flow of air to change from the top down to the bottom up. This does not happen in an instant. You'll need time which you won't have.

In your high speed approach, once you start your flare, and you lose an engine, you are going to hit the ground with high forward airspeed, and the flare will do nothing for you. In fact it will likely make things far far worse.

 

Try a few of those high speed approaches, with a flare and see how they work out for you.

Just keep in mind, you're flying a helicopter and once you get paid to fly you're almost always going to be shooting an approach to a "spot", not a runway. Those are for airplanes. Good luck.

 

PS: when i started teaching, I used to teach students to fly approaches and do autos to runways / taxiways...mainly because the flight school i started out at did it that way. I later on learnt the stupidity of this and changed to teaching students to fly to a spot.


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#12 octagon

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Posted 02 September 2018 - 18:33

I see the light, makes perfect sense.

 

- Generally you're landing on a spot, probably not a runway, so there isn't space to flare.

- Engine failure on final is a very low order of risk compared to me botching the flare and recovery.

- Engines are more likely to fail when large changes in power are required, and that's exactly what the flare demands.

- Shifting wind or miscalculation could mean that more power is required than is available to arrest the descent and terminate in a hover safely.

- Less opportunity to perform the low recon to feel out conditions on the approach.

- Passengers hate it.

 

Thanks! The question seems pretty silly now.


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#13 Nearly Retired

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Posted 03 September 2018 - 09:31

The only reason you'd ever want to make a fast approach in a helicopter is: 1) if someone is shooting at you; or 2) if you were afraid that the engine was going to quit.  But as johnnyb correctly points out, there is going to be some transition time between power-on and power-off flight.  And that takes time...time which you may not have.

 

That's why God invented the Height-Velocity Diagram.  It shows us dumb pilots the altitudes and airspeeds to avoid if you want to perform a safe landing after an engine failure.  And here is where I disagree slightly with johnnyb's premise.  If you stayed out of the shaded area all the way down, then...theoretically...it shouldn't matter if the engine quit at any point during the approach (or take-off, for that matter). 

 

However!  I think pilots sometimes ignore the fact that if the engine does quit on a "fast" approach, you WILL land short of your planned termination point...unless that approach is truly a simulated EOL.  If you have any power pulled at all, you're going to have to get the pitch down, and that's going to mess with your descent angle, no two ways about it.  So you better have good areas underneath you at all times during that approach.  

 

However, a good example of what johnnyb described can be found by watching the video of the 206B that crashed in Hawaii back in 2016.  That was basically an "engine failure" on short-final.  (I know, I know, it was actually an input driveshaft failure, but the end result was the same - loss of power to the main rotor.) 

 

The guy was at the bottom of the approach.  He was slow and had "some" (a lot of?) power pulled in.  When the drive to the main rotor went away, that ship plopped into the water like Rosie O'Donnell off the high-dive board.  At that point it probably would not have mattered much what the pilot did with the collective.  If he'd pushed it down, the ship would've descended faster.  If he'd pulled it up, the ship would've descended faster.  It was, truly, a no-win situation for him.  The only corrective action he could've tried was to quit the job a day earlier and avoid the accident altogether.  But that would've necessitated him seeing into the future, something we helicopter pilots aren't particularly good at.

 

Even if that guy still had some airspeed, the outcome would have likely been the same...unless he was well and truly autorotative.  Which...in hindsight...probably would've been a good idea.  I mean, he obviously knew that he had "some" kind of problem, which was the reason for the precautionary landing to begin with.

 

Luckily...thankfully...engines just don't quit so much anymore.  We're not over-stressing them and pulling every inch of what they're capable of producing.  And the materials they're made of have improved over the years.  And so the fear of an engine failure drops down a bit on the "List Of Things That Can Go Wrong!"  Especially on an approach.  Other factors must take priority.

 

The reason that some answers are "long-winded" like Wally's and mine are because flying helicopters is not simple.  There are a gazillion things to consider on every flight.  You can't make the same approach every time to every LZ.  (Even something as "simple" as selecting a cruising altitude is fraught with considerations.  Do you go high or stay low?  Do you go direct or take some other path?  There is no simple or easy answer.)  Wally flew out in the Gulf of Mexico at least as long as I did, and I got over 45,000 landings to offshore oil structures during my stint there (7,500 hours times 6 landings per hour on average), so I'm sure he got as many or more.  Consider that 45,000 number for a moment.  Do you think that he and I didn't get proficient in making a precision approach?  We had to.  There is no such thing as an "average" GOM pilot.  Experience is a good teacher.

 

You can only learn so much with an instructor sitting beside you, showing you his (or her) way of doing things.  A lot of what you'll learn will be picked up by trial and error, by watching accident videos and reading accident reports, and from watching (and listening to) the old guys like Wally (who I'm pretty sure is older than me) who've been doing this a long, long time without killing themselves.


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#14 r22butters

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Posted 03 September 2018 - 14:26

I guess you don't have to flare if you don't wanna?



Funny, that looked almost like a power on running landing in the 22 :D
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#15 Wally

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Posted 03 September 2018 - 17:23

Didjuh see anything normal in that video?  The 206 is a friendly aircraft, but...

 

No flare is the least of it:  airspeed at what- 30?  35 knots?  at the start of the video, slower than the Vx or Vy (my recollection) not a lot of energy to gain in the decel anyhow.

Then pitching the nose down, accelerating airspeed and rate of descent in the last 2-300 feet... towards min descent rate at touchdown to cushion with NR.

This ain't one to try without an experienced instructor, but you might want to think hard and learn some adaptive techniques for your next 'fo real, fo real' autorotation.

Flying isn't A or B, it's a 'spectrum' of factors to modify between A and B.


Just a pilot (retired, so I have a LOT of time)...


#16 Mikemv

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Posted 03 September 2018 - 17:40

Here is one we published with permission of Shawn Coyle.

 

http://www.ihst.org/...ghts/energy.pdf

 

Be educated before you attempt something different.

 

Then, be both current & proficient in what you are doing.


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#17 Eric Hunt

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Posted 03 September 2018 - 19:39

We used to do constant attitude touchdowns in the Hueys - aim/touchdown point is in the chin bubble, airspeed around 30Kt or less, go through the normal flare height, and when your backside starts biting the seat cushion, big initial pull on the lever. this stopped the descent and caused some forward motion,  we used what was left of the RRPM to cushion on. Usually only a demo and practice with the experienced instructors, then store it in the memory for when there is only a tiny hole in the trees and it is in about the right aim spot.


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#18 WolftalonID

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Posted 08 September 2018 - 11:14

Just as an example...some of the spots I land on are pretty small. Controlled approaches are always best. This is an offshore platform. Many on land locations can be just as tight but with trees, rocks, brush making it further confined. That and as many have mentioned...protect that tail.Attached File  D70DC181-7797-443A-9240-36E6D5590F5B.jpeg   162.81KB   11 downloads
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#19 octagon

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Posted 08 September 2018 - 11:23

I've been studying how professionals make approaches to drill ships and platforms, super interesting. How do pilots learn these kinds of specialized skills usually?



#20 iChris

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Posted 12 September 2018 - 11:50

I've been studying how professionals make approaches to drill ships and platforms, super interesting.

 

How do pilots learn these kinds of specialized skills usually?

 

Success in these kinds of specialized skills is neither magical nor mysterious. Success is the natural consequence of consistently applying the basic fundamentals. In any endeavor the mastery of the basic fundamentals is key.

 

You can practice shooting eight hours a day, but if your technique is wrong, then all you become is very good at shooting the wrong way. Get the fundamentals down and the level of everything you do will rise. 

 

The most important standard for an approach is maintaining a consistent angle of approach to the termination point. The collective controls the angle of approach. Use the cyclic to control the rate of closure or how fast the helicopter is moving towards the touchdown point. Maintain entry airspeed until the apparent groundspeed and rate of closure appear to be increasing. At this point, slowly begin decelerating with slight aft cyclic, and smoothly lower the collective to maintain approach angle. Use the cyclic to maintain a rate of closure equivalent to a brisk walk. 

 

At approximately 25 knots, depending on wind, the helicopter begins to lose effective translational lift. To compensate for loss of effective translational lift, increase the collective to maintain the approach angle. The increase of collective pitch tends to make the nose rise, requiring forward cyclic to maintain the proper rate of closure. 

 

As the helicopter approaches the recommended hover altitude over the intended landing spot, increase the collective sufficiently to maintain the hover. At the same time, cyclic to stop any forward movement while controlling the heading with antitorque pedals. 

 

Always keep in mind the increased inertia as a result of high rates of descent and forward speed near the end of the approach. That inertia must be arrested at some point. Near maximum power maybe need as a result of this increased inertia that must be overcome by lift (force) generated in the rotor system. 

 

Inertia defined as the tendency of objects to keep moving in a straight line at a constant velocity unless a force equal and opposite is applied to oppose that movement.


Edited by iChris, 12 September 2018 - 11:55.

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Regards,

Chris




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