Helicopter Wake Turbulence

[helispotter]

I recently viewed an episode of "3 Minutes of Aviation" and was surprised to see the impact the wake turbulence of a UH-60 Blackhawk had on control of a Pilatus PC-12 apparently attempting a landing:

https://youtu.be/FiB8Ya6mbqw https://youtu.be/FiB8Ya6mbqw

I wondered if this topic had been discussed on PPRuNe and it has, but under a title where it isn't obvious: https://www.pprune.org/rotorheads/649520-sar-pilot-crew-training.html

That thread has a good video of a BEA presentation on the risk of helicopter wake turbulence with examination of the fatal accident of a paraglider when its canopy collapsed after encountering wake turbulence. You can understand a paraglider being sensitive but a Pilatus PC-12 is hardly a small aircraft.

Then I found a video of a Cessna 120 accident while attempting to land behind a UH-1 Huey which is is embedded within:

https://www.avweb.com/multimedia/best-of-the-web-surviving-a-rotorwash-crash/

Within this item there is footage of a Cirrus SR-20 crashing on attempt to land some 30 seconds behind a departing UH-60 Blackhawk helicopter at Fort Collins, Colorado:

The dangers of flying through rotor wash - FlyTime.ca (https://www.flytime.ca/dangers-flying-rotor-wash)

I was also reminded of old one page articles on helicopter wake turbulence that appeared in Aviation Safety Digest 104/1978 (page 11) and 121/1984 (page 3):

https://www.atsb.gov.au/sites/default/files/media/5774800/asd_104_78.pdf

https://www.atsb.gov.au/sites/default/files/media/5774817/asd_121_84.pdf

Makes me wonder if this is a more common issue?

[XA290]

The wake turbulence off a large helicopter is significant. It is not as predictable as that off a fixed wing aircraft but it is foolhardy in the extreme to get too close in something small.

see below:-

https://assets.publishing.service.gov.uk/media/5422f94de5274a13140006ed/1-1993_G-BPJT.pdf

[POBJOY]

It seems this 'situation' is always a surprise to those who may not have experienced it before.
At a licensed airport ATC would normally require landing traffic to be separated by several minutes from a large Rotary movement for very good reasons.
When we operated Islanders to St Marys IOS back along, the other main user was the S61 from PZ which put out a hefty rotary wash and was best kept at a safe distance (or upwind of it).
In fact St Marys ATC would not allow an approach by fixed wing for several minutes to keep matters safe.
We would sometimes 'encounter' the S61 effect enroute and that was enough to keep you 'aware' of a regime that is best avoided.

[ericferret]

This issue has been around for a long time.

https://assets.publishing.service.gov.uk/media/5422f94de5274a13140006ed/1-1993_G-BPJT.pdf

[[email protected]]

A large helicopter (say S-92) can be moving up to 12 tons of air constantly (UH 60 up to 10 tons) and in the hover or slow speed flight that is concentrated into quite a small area.

All helicopter pilots should know to keep clear of FW, especially light ones when hover taxiing as they are easy to blow over.

A light FW on final approach is very vulnerable to rotor downwash.

Helicopters are much more tolerant of FW wake turbulence generally.

[JimL]

Apropos not quite this subject - here is a paper that addresses Rotorwash; in the table, the comparative figures are shown:

https://www.dropbox.com/scl/fi/1ii5tbxb6smszqbt9u5qv/Rotorwash-Heliport-Guidance.pdf?rlkey=g57rxpq8u23jn0ldcj7zd7t0h&dl=0

Jim

[JohnDixson]

Hello Jim- your chart included the 53E and 101 and Mi-26, but where is the V-22?

[76fan]

helispotter: https://www.atsb.gov.au/sites/defaul...asd_121_84.pdf (https://www.atsb.gov.au/sites/default/files/media/5774817/asd_121_84.pdf)

Thread drift but I particularly liked "The good olde days ..."

and the preliminary accident report on the Bell 47 on the 24th March. I do hope he survived after all that!

[60FltMech]

Hello Jim- your chart included the 53E and 101 and Mi-26, but where is the V-22?

John,
V-22 is listed on the table above SH-60(paired with AW609), 139kts velocity of downwash must make for exciting ground ops for anyone standing underneath.

FltMech

[212man]

30+ years ago, when I was based in Aberdeen flying offshore, I went to the local Flying Club to do a flight in a PA-28 with an FI to keep my PPL(A) valid. On short final, on an approach soon into the flight, we suddenly rolled abruptly to the right to what felt like 80-90 degrees, but was probably 60-70. I believe a combination of aerobatic experience in my early flying training (at competition level) plus the generally good reactions we have as RW pilots, was what stopped us becoming a smoking pile. I simultaneously applied full power, full left yoke and full left pedal and we regained our composure and I climbed away - with a very shaken but relieved looking instructor who looked across at me and said "thanks!" We landed after the next approach and terminated the flight early, for a strong coffee, and I got my logbook signed off anyway! The wake was from a 332 - probably one of my colleagues!

[RVDT]

Helicopters are more resilient but not always.

There was an incident here many years back with a Hughes 500C following a Fokker F27 on approach which apparently makes nasty wake with a flap setting in the mid range.

The helicopter was rolled to the point that the shortest way back was to carry on with a complete roll.

On landing the tailboom was found twisted by about 25-30 degrees.

[JimL]

Hi John,

Interestingly, it was the incident at Cambridge (the Addenbrooke's Hospital site) where the V22 rolled up the temporary surface and scattered it about (and of course the fatal accident at Derriford), that prompted me to put pen to paper.

Jim

[Less Hair]

It would be a great use of LIDAR and HUDs or augmented reality to visualize vortex ahead in the cockpit.

[helispotter]

helispotter: https://www.atsb.gov.au/sites/defaul...asd_121_84.pdf (https://www.atsb.gov.au/sites/default/files/media/5774817/asd_121_84.pdf)

Thread drift but I particularly liked "The good olde days ..."

and the preliminary accident report on the Bell 47 on the 24th March. I do hope he survived after all that!

Lots to contend with in "good olde days" but no helicopter wake turbulence! Accident report for VH-UTQ implies pilot survived after that epic trek for help.

[helispotter]

It would be a great use of LIDAR and HUDs or augmented reality to visualize vortex ahead in the cockpit.

The mind boggles that something like this might be possible, but a brief hunt around the web indicates researchers are delving into such matters, eg:

https://amt.copernicus.org/articles/13/6543/2020/

[jimf671]

There has been progressively more interest in this subject and other downwash issues at the ICAR Air Commission and related matters appear to be cropping up locally.

IIRC, at the 2012 Congress, someone came up with a map of downwash for a Boeing chinook and questions were asked about whether such maps existed for other types and what we could learn from these especially for any type of HEC/HHO ops.

At the 2022 Congress, there were several presentations (4 territories) about rescue of canopy sports casualties (paragliders, base jumpers and so on) including the problem of the persistence and complexity of wake turbulance around a possibly unrestrained canopy and also a presentation about mapping of downwash effects below an aircraft during hoisting ops. The knowledge base has clearly expanded hugely during the last decade. We need to not just keep up but be aware that a lot of others are still not keeping up!

Locally, ATC have started to push back against training involving hovering on an airfield. A typical location is about 150m from the main runway. Having a super-medium rotorcraft hovering 150m from a runway used by light GA through to small and medium sized airliners, with the prevailing wind scattering the effects along the entire length of the runway, might not be a good idea.

[ShyTorque]

It is difficult when ATC don’t want aircraft operating from their airfield.

[JohnDixson]

Sorry Jim-thought I posted an acknowledgement of my error, but didn’t push the “Post” button apparently.

The larger machines of course have a real chance to cause trouble in this arena. The CH-53 and CH-54 were just starting production runs when I signed on at Sikorsky and we did have a couple of embara$$ing examples.
The Japanese CH-53E presented an interesting case as they intended to be able to use it as a backup rescue vehicle, prompting a real live ( as in a human in a Mae West ) doing test program in Long Island Sound. Wasn’t mid summer either. The swimmer was a former USN Helo pilot who had left the USN to take a job in the 53 Program Office. Volunteered to be the swimmer and it took 30-45 minutes with him in the water, in what looked like a localized hurricane on the surface as the downwash would consistently push him away when they thought they had him. Tried changing altitudes and different approaches etc. I was flying our rescue S-76 and was about to call it off when they finally got him.