Wary of updrafts
 

Anyone ever been caught out by a powerful updraft ? I was flying level with a South of England cliff line last year, and for a good couple of minutes, the manifold pressure dropped, the controls become very light and a heavy whine started from somewhere behind me. Fearing the worst, I made a precautionary on a remote part of the cliff top and checked the aircraft over. After finding no problems and calling the office, I determined that the vertical updraft being forced up the cliff face was so powerful, it was windmilling the rotor and offloading the engine and gearbox torque. Does this sound like a load of old claptrap or is it a common occourence when mountain flying etc ?

TFS

Claptrap.:E

Old or new, you take your pick:=

Robbies always make a strange whine, that’s them running...:ok:

Paragliders will float on this lift for hours.
If the cliff/hill has a smooth profile and the wind is off the sea (steadier then from the land) then the lift can be equally stable.
Hence:
Is it normal ? - Yes (dependant on conditions)
Will it put you close to autorotation ? - The wind would need to be very strong to do this but your power required for level flight will certainly reduce.

Where does it say he was flying a Robinson?

Whining sound? Coulda beena Gazelle

TFS

Did you lower the collective to maintain level flight as this is the only way you can off load the rotor. if you don't lower the collective then you will just soar on the up draught.

I have had a Wessex 2 in autorotation while cliff winching on the N Devon cliffs. The winch op wanted "down 1" and the only way I could descend was by slightly yawing the helicopter as the collective was on the down stop!!

When in the Scottish moutains one always tried to fly on the updraughting side of the features as it was far more pleasant than flying in the downdraughts:ok:

HF

Well - I noticed because I was trying to maintain level with the clifftop - I noticed myself pushing the collective down at first to remain parallel, and then the whine started ( And no I didn't have the wife with me ! ) The aircraft was most likely the 300 CBi varient. Nothing like this has ever happened to me since. When I told the governor back at the hanger, he said it was feasible and happened in the Jetboxes all the time.


TFS

My instructor once took a Robbie into the mountains and at one time was hovering with 11" MAP (grown-ups, the usual figure is more like 22-23").

Helicopter Red Eye


Which model of Gazelle has a manifold pressure gauge?:D

Wowsers, you guys hill soaring now too? :ok: Hint, if you want to find lift look for the sharply defined clouds: cumulus for thermal; lenticular for hill wave. In general air mass going up causes some kind of cloud formation if there is enough moisture content. Word of caution: beware the rotor systems over sharply defined vertical land features, you could find yourself pointing the wrong way up...

Please keep an eye out for gliders! I still have pals doon sooth, and i wouldn't want to incur their wrath...

Mart

Soaring and Vortex
 

XC middle of summer strong well defined Cu's and in cruise travelling through these thermals regularily dropping MP to 15' or below (in a CBi) to maintain level flight. Never heard any whining.

I had this discussion with an instructor: But here is a question for the knowledgable: Say you take off from this cliff face and as you depart to the windward cliff face and encouter the ridge and thermal lift there... if it is strong lift (Say 1000 FPM+) can you enter Vortex Ring with no actual descent occuring?

Just remember things tend to equalise in the air (apparently Newton had somehting to say about such things) - if air is going up that strongly, somewhere it is going down just as strong.

Texdoc,

It most certainly is, assuming you have all 3 factors of Vortex Ring happeing at the same time. The upflow air gives the same effect of a high rate of descent, now you just need to reduce the speed to nil and as long as your using some power......

The updraft does however need to be coming pretty much straight up at you, 99% of the time updrafts help us of course, as long as there is some horizontal component to the airflow, vrs straight up.

Hummingfrog,

I have been in that same situation many times (with a drill on a longline, not a guy on a winch). Hovering with 3000 lbs on the end of the line and using half the power it normaly takes me to hover with zero weight on the line. It may all feel good and stable with the collective on the floor...till you pull in some power...it gets real ugly real fast that close to the ground!

So for all you Ppruners out there....there you are....hovering just out from the edge of the cliff...dam power sure is low...hmmm.....airspeed reads zero..time to think a bit harder about that backdoor you have left open(you did leave yourself a way out right?) Ok...you know you can fly away from this by dropping the pole and moving away from the cliff if need be....collective is still really low...time to pull a bit of power and see what happens. As soon as you pull the bottom drops out. So you lower the pole and head away from the cliff, just like you planned. Assuming you had made provisions for this possibility in the first of course...

It takes carefull planning to intentionaly put yourself (and crew) in a situation like that. Knowledge is the key of course, and it starts with knowing that your about to get into that situation in the first place.

Lots of fun and games!


DMNH
:O

DMNH,

Thanks. :ok: I was about to post what I remembered from what you said in a thread a bit back about vortex ring and updrafts, but it's far better coming from you. Wish you'd post a bit more often; you know loads of stuff from experience that's really useful for the rest of us...well, for me, anyway!

Flying an eye level recce on a pinnacle at 8,000', I was level at 40 mph in an autorotation with close to max Nr. It was exciting landing there since the helicopter didn't want to descend with power on, but once over the site needed max power.

It was a Jetranger.

VRS, power settling
 

Texdoc,

I don't think you will get into vortex ring state when ridge soaring a helicopter. To get into VRS, or power settling, you have to get the air mass under you moving down. In a ridge soaring situation strong enough to soar a helicopter, the mighty engine of nature is making that air go up. No little 300C is going to change that, nor a bigger helicopter. Plus, in a regular auto, you have a lot of downward velocity that needs to be arrested, and when you go to arrest it that's when VRS really can get you. In the ridge soaring case, you have no downward velocity.

-- IFMU

Many, many years ago, taking a 206 through the Rockies. Had overnighted in Golden, B.C. and the next day departed for Calgary, AB. Lovely day, if not a bit windy, no matter what level I flew at. Was thinking I might take a peek at shortening my route by going slightly more direct. Started to climb, when suddenly, things felt like I was REALLY climbing. Started lowering the pole........nothing. Kept lowering the pole........................nothing.

Eventually topped out at 11,400 feet, stayed there for a short bit when I noticed Calgary was now in view (if not far, far away). Began descending over the foothills, encountered the expected turbulence and finally managed to find some smooth air.

Interesting experience that I've yet to repeat again.

TFS
Sorry for sounding stupid but please tell me you know what aircraft you are flying in when you take off.:confused:

IFMU, I think you need to re-read about vortex ring, especially the bit about which way the air is moving through the rotor disc.

Banjo old bean...
 

The FBO has four 300's on it AOC - not all CBi's - I'm not dumb you know - I'll ask the missus - " darling, am I stupid.....darling?...darling....? "

TFS;)

MightyGem,

I have re-read the whole vortex ring state thing, also know to more simple minded people like myself as settling with power. When you get into VRS, the outer part of the rotor is still forcing air down, but there is upward flow through the center. Then you get the circulation between the outer downward part and the upward part. There is an excellent refresh of this material at http://www.copters.com/aero/settling.html .

I'm going to stick to my guns and say that when you get into VRS, the airmass is going down. Consider two of the ways you can get into it. First, a high hover, where you start to settle a little bit, pull in a little more power, settle a little more, and finally get into settling with power. The air under you, which normally obliges to hold you up, is going down. I think of it as walking up the down escalator. Yup, the airmass is mostly flowing from underneath through the rotor and out on top. But the column of air as a whole is sinking. The second method to get into VRS is a hot descent with an attempted arrest using lots of power. This can be especially bad with some tailwind, as it blows the wake in the same direction that you are going. Both of these cases are much different from the ridge soaring example for two reasons:

1) Ridge Soaring - no descent to arrest, lots of excess power. VRS - big descent to arrest, way behind the power curve
2) Ridge Soaring - the mighty engine of nature is making the airmass as a whole go up. VRS - The engine/rotor is making the local airmass under the helicopter go down

What can be more dangerous in the ridge soaring game is what Matthew Parsons described. I'm going to guess that over the site there was a change in wind, probably due to the local geography, that took away his ridge lift. So here he is, happily wafting down with no power, suddenly the updraft goes away and gravity takes over. If you don't anticipate it quickly enough you are going down rapidly. And, if you have blundered into some rotor, the airmass that was going up at 1000 fpm may now be going down at 1000 fpm. I have to confess that besides being a rotorhead, I'm also a plank driver, both of the silent type and the type that pull the silent ones up. The most negative G's I've ever pulled was from penetrating a rotor whilst flying a glider, several years ago and my head is still a little flat from where it hit the canopy.

-- IFMU

I can recall flying an A model Chinook with a sling load of howitzer ammo....about 13,000 pounds worth....with the Thrust Lever (Collective) full down....airspeed heading towards Vne....and the VSI was somewhere up about the peg....fortunately we flew out of that updraft into some sinking air....one learns about thunderstorms the hard way sometimes.:{