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Old 19th Mar 2017, 01:34   #1 (permalink)
njk
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Settling with power

Hi Guys,

I knew that this topic would be brought up so many occasion but I couldn't find out solid explanation. My question is why we don't get "settling with power" during zero speed autorotation?
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Old 19th Mar 2017, 02:00   #2 (permalink)
 
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Vortex Ring Autorotation
may help you (I hope!)
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Old 19th Mar 2017, 02:02   #3 (permalink)
 
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No 'settling with power' in an Auto, cause You ain't pulling power
'Settling with power' is very different to VRS
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Old 19th Mar 2017, 04:45   #4 (permalink)
 
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Good grief....not again
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Old 19th Mar 2017, 10:46   #5 (permalink)
 
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Outwest - seconded
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Old 19th Mar 2017, 11:24   #6 (permalink)
 
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NJK, I think you may mean, "In zero speed auto when you pull the lever at the bottom".

The answer is if you still had a long way to go to the ground, the effects of VRS would be incipient as the descent continues, but the devil would steel your NR before the effect can fully develop.

If you have the throttle open in auto and the engine starts to drive to rotor as you raise the lever, if the descent continues with little or no airspeed then you will probably enter VRS dependant on the type of helicopter and its characteristics. Some like to enter VRS more than readily than others.

However, to be clear, with the lever fully down the blades will be in an autorotative state. As soon as the lever is raised they are no longer in an autorotative state.......generally.

VRS is only associated with high pitch on the blades and a reasonably high rate of descent with little or no airspeed. To be in autorotation you need minimum pitch on the blades.

So in practice you cannot be in both states at the same time.

Hope that helps a bit.
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Old 19th Mar 2017, 11:31   #7 (permalink)
 
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NJK, just some further food for thought. If you are thinking of trying this DONT without a good instructor sat next to you and DONT unless you have a lot of height above the ground before recover.

In zero speed auto, if you stuff the cyclic forward to get airspeed you may put the "pitched blades" in VRS before they can alter the attitude to gain airspeed and the situation will get nasty very quickly. You will enter the realms of the TP in a heartbeat.

In my opinion there is no real practical application for a zero speed auto. Better to look at an auto with minimum airspeed such as 40 KIAS, type dependant.

Better still, follow the instructions in your FM. They are there for a reason. They have been proven by the TP. If there is no procedure for a minimum speed auto in the FM THERE IS NO PROCEDURE, regardless of what others might tell you! Plan your flight path around the guidelines in your FM. Practice the procedures in your FM (with an instructor as required) and you should be OK.

One more issue. If you are hovering at height, zero airspeed and your single engine fails, you would immediately lower the lever and "push" cyclic for airspeed at the same time so a zero speed autorotation does not have time to develop, thus avoiding these nasty flight conditions.

Last edited by DOUBLE BOGEY; 19th Mar 2017 at 11:42.
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Old 19th Mar 2017, 12:51   #8 (permalink)
 
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DB, having taught high hover EOLs in the Gazelle, there is no need to push the cyclic forward - the nose drop from lowering the lever quickly can be quite alarming and you soon need aft cyclic although flapback will do some of the job for you.
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Old 19th Mar 2017, 13:00   #9 (permalink)
 
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Crab, seconded.

In a JetRanger or Squirrel too only the slightest check forward on the cyclic is enough, push the stick on a 206 and you'll be mast bumping in an instant.
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Old 19th Mar 2017, 23:51   #10 (permalink)
 
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Simply said, Vortex Ring State is the condition that occurs when the rotor is descending into its own down wash. In autorotation, the rotor is descending far faster than that, so that there is no downwash at all, there is up wash as the rotor is spun by the column of rising air around it.
In other words, VRS cannot possibly occur in an autorotation.

Also, VRS can only occur when the rotor is descending at 70% of the downwash speed, which is over 700 fpm for a robbie and 3000 fpm for a Black Hawk, and somehwere in between for most helicopters.
What people generally call VRS is usually where they are at near hover and unable to sustain a hover, so they fall through and descend.

Last edited by NickLappos; 20th Mar 2017 at 01:47.
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Old 20th Mar 2017, 05:53   #11 (permalink)
 
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Crab, I can't remember what my Army QHI taught us in the Gazelle. However, I clearly remember doing this from 500 feet hover in the 206 to support aerial filming qualification on my OPC some 25 years ago. We definitely had to "push" continuously to get the nose down enough to make a viable EOL at the bottom.

I don't do flapback! My hands have coped with that before my brain reacts so I am unaware that flapback is occurring. Hence the steady progressive push until the nose is down enough to accelerate. In the 206 I can't remember the nose down value but no need really as it was VMC procedure and more "feel" than numbers.

Like I said, stuffing the cyclic forward (or indeed, in any direction) is the root of all evil.

Anyhow, what do I know, I am just beginning to fly my B412 without the nose going the wrong way every time I move the collective after 12k hours of my MRH going the other way round my head had "hard wired" my feet to dance to a French tune! Don't even get me started on the standby AI which looks like a pissed scarecrow in a whisky glass! Or maybe the start procedure which involves 8 independent switch selections and the lottery of the motorcycle throttle thingies on the collective. Thus far I have achieved the "Holy Trinity" (open the first fuel valve, motor the second engine, open the first throttle but looking at second engine ITT, wondering why it won't start). Loads and loads of those pully-out things in the roof that make the electrics a randomised option also.
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Old 20th Mar 2017, 06:34   #12 (permalink)
 
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Ah, Double, you are opening some bad memories about 412/212 thingies, getting the wrong combinations of throttles, fuel valves, starter motors as you describe, and then leaving the starter motor running and not picking it up until you try to get the generator on line. Mumble,mumble...

NJK, read Nick's post. Settling with power, airflow is above the disk and energy is being added to push it down. Top to bottom.
Autorotation, air is coming from below the disk and energy is being extracted from it to make the blades turn. Bottom to top.
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Old 20th Mar 2017, 09:13   #13 (permalink)
 
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Can we just clarify -
Quote:
What people generally call VRS is usually where they are at near hover and unable to sustain a hover, so they fall through and descend.
is settling with power ie overpitching because there is not enough power to prevent Nr decay. Not VRS - the terms have been confused enough across the Atlantic and many times on these pages.
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Old 20th Mar 2017, 09:34   #14 (permalink)
 
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hey crab@SAAvn.co.uk

'settling with power' is when Your in a HOGE & either don't have the power available to hold height or You simply don't pull enough power; so the machine begins to descend vertically into it's down wash (generally at a slower pace). If You now pull more power, assuming you have more available then the descent will simply stop, as You are not in VRS. It may not be over pitching or Nr decay, you've reached your red line limit & can't pull more due to exceeding an engine or torque limit, a vertical descent begins If this is allowed to increase the vertical rate to well above 300fpm but more closer to 700+ with loads of power still on, without airspeed then You are definitely setting yourself up for a VRS situation
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Old 20th Mar 2017, 14:03   #15 (permalink)
 
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Vuichard technique for settling with power?

VF: You are aware this has been thrashed in the past, but as you say the difference between SWP and VRS is that the former is engine performance related and the latter is an aerodynamic phenomena. Neither the twain shall meet!
You are a naughty boy, stirring this up again.
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Old 20th Mar 2017, 14:28   #16 (permalink)
 
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DB.....the truth is finally out!

I heard most of your OEI experience resulted from the same techniques as you failed to start one before departing!
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Old 20th Mar 2017, 15:22   #17 (permalink)
 
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VF - no, settling with power is when you don't have enough power to achieve or maintain the hover OGE but continue to raise the lever, reaching an engine limit and decaying the Nr.

You could end up in VRS from this situation if you continued to pull as the RoD may increase to the point where you have 70% of your downwash speed but often the ground gets in the way first or the pilot transitions into forward flight.
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Old 20th Mar 2017, 16:18   #18 (permalink)
 
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Have to agree with crab on this one.

For example, you come into land at 9,000' and as you approach your landing spot, you settle due to reaching the limit of your power and settle to the ground. Hence "Settling with power".

Vortex ring state is an aerodynamic phenomenon caused by settling in ones own down wash. It requires a minimum of 300 fpm rate of descent. Therefore, (assuming one has done a good approach), one cannot get when hovering IGE.
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Old 20th Mar 2017, 21:12   #19 (permalink)
 
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The confusion will remain as long as the FAA uses the terminology "settling with power" for both conditions.
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Old 20th Mar 2017, 21:20   #20 (permalink)
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Power settling?


The original poster (njk) is invited to review the discussion on terms at the link.
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