Helicopter Vortex wake.???

[helimutt]

Just out of interest, has anyone who flies light singles, ever experienced vortex wake when landing behind a medium twin helicopter?

Hypothetical situation:-
2 medium twin helicopters landing one after another with about 4 miles spacing between them. wind less than about 6kts. Light a/c follows to land behind them, spacing unknown. What are the chances of the light a/c being affected by the helicopter vortexes, if any?

[dont overfil]

A "heavy" helicopter sitting at the hold can spoil your whole day.
I'm sure one of the Aberdeen guys will be along shortly to give you some scary stories.
DO.

[M609]

Having done much of my flying from a RNoAF heli base with a certain JHC presence each year , I have some insight into this.

Yes, you will feel wake vortex from a medium helo like a Sea King or Puma, and was taught, and indeed felt that you should stay above the helos approach path if landing closer behind than say 3-4 miles.
From the tower I've seen a Grob get chucked around violently forcing a go-around when spacing up close behind a Sea King. Made him more aware about what "caution wake turbulence" actually means.

Smaller helos like the 412, Lynx etc not that bad, but you do feel their wake more than what their tonnage would imply. You will be affected if you turn in say 1-2 miles behind a 412, but not in such a way that it becomes dangerous IMHO.

[helimutt]

How about following an Sikorsky 76 type helicopter in a PA28. S76 is bigger than a lynx, smaller than a puma.

[silverknapper]

Recommended spacing for Jetstream 31 behind a Super Puma is 4 miles. Take from that what you will.

[Fuji Abound]

http://www.aaib.gov.uk/cms_resources.cfm?file=/dft_avsafety_pdf_501305.pdf

Something a bit larger is enough to kill you, sadly.

As I reported elsewhere the prop wash from an aircraft doing engine checks caused me a problem or two recently.

Anything running on the ground needs treating with caution.

[JW411]

See the thread above about a "C172 (sic) meeting its maker at Humberside".

[helicopter-redeye]

How about following an Sikorsky 76 type helicopter in a PA28.

Sensing guilt...probably was not you, but if you remember Roger's lectures , a helicopter creates a lot of WT relative to its size, especially in still air conditions.

[RatherBeFlying]

On final in a Citabria, noticed a couple Schweitzer 47s doing hover practice some 50 yards abeam the landing area into the x-wind. Made for an interesting landing:\

Once landing at the big airport beyond where a 747 was making a 135 degree turnoff to the taxiway and needed a bit of power to make the turnoff The wash was quite noticeable some 100-200' up.

[tmmorris]

Operating out of an RAF base with lots of big helicopters I am often warned 'Caution rotor downwash' but I've always kept well away - same drills as taking off/landing after a heavy e.g. take off before their rotation point and keep above their flight path, same on finals. I expect the Grobs do the same as I've not heard of any upsets.

Tim

[gasax]

It is a while since I operated from Aberdeen but ATC were very careful. A couple of incidents of light aircraft being blown over by taxiing heavy twins and some close calls make them much more aware than most ATC.

I recently flew into the wake of an S-92 in a very light aircraft - he was in the cruise doing about 120kts and light - it was a flight test, he went right and cut across my course and I did not climb fast enough. The turbulence was pretty intense although quite localised.
.
I would guess as the speed drops off the area of turbulence increases. Either way there is something about the turbulence from choppers than seems to make them pretty difficult for light aircraft. On a calm day 5 minutes plus seeems sensible. If you see an S-92 and are likely to cross its wake climb!

[Slopey]

Aberdeen ATC are pretty switched on about it - I departed a few weeks ago through the wake of a landing twin at the end of the runway, and on climb out we had a nice kick in the pants and decent chop even with a good few minutes spacing.

I always give them quite a wide berth if possible, and get off the deck well before where they were (albeit in a C172 so it's not too onerous).

[helimutt]

sensing guilt? No way. I fly what I fly. If someone flies something else over which I have no control and end up doing something wrong, it will never be my fault. Why should I feel guilty? i feel bad that someone was involved in an accident at the same airport I fly from.

I asked the question because the aircraft ended up on the right hand side of the rwy, at the threshold. the wind (very light )was just of rwy heading, from the left if I remember correctly on rwy 26. 2 S76's had come in within about 5 minutes of each other. I believe the fixed wing was close behind #2 S76.

?????

[gasax]

There used to be some really good video of helicopter wake turbulence on the net - cannot find it this morning IIRC it was done by NASA.

Anyhow the standard stuff about WT still applies and if the wind was very light then it would persist for a 'long' time. With two similar aircraft it is quite likely that the wakes interacted to some extent.

In Aberdeen most people 'know' to avoid the stopping or rotation areas on the runway where choppers have been - even after the usual interval the air is pretty rough - especially on still days.

[Captain Stable]

I've experienced very significant problems following a Puma into Aldergrove. I was flying a Turbine Islander, separation was about three miles.

I made the silly mistake of not noting where he landed, and I was intending to land long, so flew straight through where his vortex wake was strongest. :=

Went around, and lived to fly another day.

[Wycombe]

Back in the early '90's, a PPL instructor of mine at the time (an RAF heavy jet man) was killed in a dreadful accident at Oxford, after the PA28 he was instructing in encountered the wake turbulence from a departing S61 whilst on short final - it was British F1 GP day at Silverstone.

As a PPL u/t at the time it hit me hard and always made me very wary of heli-induced turb, especially as the place where I did a lot of my subsequent flying was at Blackbushe (intensive heli-ops, everything up to S92 size these days)....be careful out there!

[Sir Niall Dementia]

Wycombe;

I witnessed that as I was flying in the GP shuttle from there at the time. There was also the C172/Seaking accident at St Mawgan.

I fly rotary for a living and am VERY conscious of the potential for upset that my wake turbulence may cause. A lot of smaller airfields may not realise due to infrequent heli ops. Err on the safe side and give anything above a Twin Squirrel a good wide berth.

Also a lot of smaller airfields don't realise that our downwash can easilly upset a light aircraft when we are taxiing around. Parking us close to a flightline is a recipe for damage, either by the downwash banging control sufaces about or FOD being thrown around.

[md 600 driver]

i have also lost count of the smaller aeroplanes and microlights that park too close to the helicopter ,when you point it out to them they take it in had 2 flex wings park 10 foot either side of me once

[Captain Stable]

md600:-

Is there any chance that you could use punctuation, capital letters and grammar in order to make your posts intelligible, please?

[Sir Niall Dementia]

My helicopter mount is a medium sized twin. I was astonished recently when someone parked an R22 within 20' of me and then walked away without tying the thing down. The instructor was most put out when I asked him to tie it down as I was worried about blowing the main blades around.

If I had I suppose it could only have been a blessing to rotary flight:E

[Heliport]

Fuji Abound Something a bit larger is enough to kill you, sadly.
It could, but the incident in your link is not an example of it.

Extract from the AAIB report:

Conclusion

It was concluded that the Cessna crashed following a loss of control during an attempt to carry out a 'go-around'. The activity of the Sea King and the loss of control by the pilot of the Cessna were two distinct, and for the most part, unrelated events occurring at the same time. The plot constructed of the relative positions of each aircraft considered in conjunction with the rotor downwash trial established conclusively that the rotor downwash from the Sea King did not play any part in the Cessna leaving the side of the runway.


The possibility that the pilot of the Cessna was distracted by the actions of the Sea King could not be discounted. If that was the case, the option to stop on the runway by closing the throttle and applying the wheel brakes was available. The higher than normal speed maintained by the Cessna after landing was more likely an attempt to expedite clearing the runway than trying to take avoiding action. It is possible that expeditious runway clearance was either not to delay the departure of the Sea King or to reduce the time taken to travel to park at the Civil Air Terminal at the far end of the runway. The loss of directional control on the runway was attributed to the high ground speed and the attempt to carry out a 'go-around'. The go around was probably attempted to resolve the difficulties, experienced by the Cessna pilot, in maintaining directional control.



The outflow of air from the Sea King's downwash possibly affected the Cessna, when it became airborne and crossed vehicle access 'M'. The turbulence created by the downwash could have added to the Cessna pilot's control difficulties. It is also possible that the low speed and increasing high angle of attack of the Cessna as it rotated into the air may have caused the aircraft to stall and descend quickly after becoming airborne.





NB: The last para refers to what happened after the Cessna had gone off the side of the runway (on the same side as the Sea King was hovering), taking out a runway light as it did so and was bouncing over the grass.

[debiassi]

Large fixed wing or rotor, the effects can be deadly. Have a look at the following test. It makes you realise the unseen evil that lurks awaiting the unsuspecting pilot. A PA28 with a friend of mine ended up inverted at Humberside a couple of weeks ago due to the wake vortex from a departing helicopter leaving on runway 20 and he was landing into wind on 27. The westerly breeze blew the vortex towards the threshold just as the piper was approaching to land.
YouTube - NASA Airliner Wing Vortice Tests (http://www.youtube.com/watch?v=E1ESmvyAmOs)

[ShyTorque]

I think everyone who isn't used to helicopters tends to underestimate their downwash, full stop.

Quite recently I watched a pilot park a PA-28 directly adjacent to us, already parked on the helipad, in a 3 tonne helicopter, ignoring the other parking spots further away in the same row. The pilot was about to walk away, also ignoring the tie-downs nearby and her aircraft control locks. The only reason I can imagine she parked there was that it was the closest parking spot to the clubhouse. :hmm:

She seemed quite disgruntled when I walked over and politely advised her that it might be a good idea to at least put some tie downs on her aircraft's near wing, as we couldn't ground taxi and we were about to lift.

[XX514]

Here (http://www.aaib.gov.uk/cms_resources.cfm?file=/1-1993%20G-BPJT.pdf)is a better example of the dangers. I was closely involved with the initial investigation of this sad accident and, even with considerable experience of operating military fixed wing in an intense rotary environment, I was as surprised as everyone else at the effect of rotor downwash in this case.

[gasax]

Whilst looking for something pretty unrelated I came upon a report for the case which resulted from the incident reported above in the AAIB report at St Mawgans.

In essence the MOD lost the case and paid the relatives some £5M.

The quote is very simple and raises a variety of issues regarding how courts treat 'expert' reports

"Paton v MOD, £5 million settlement achieved the day before a 3 week Category A trial for a fatal claim arising out of an air accident, overcoming accident investigation reports by both the AAIB and the MOD which found the deceased to have caused the accident. Thought to be the highest award for a single fatality; "