Effect of a helicopter behind you?

[gerardflyagain]

Hello! After trying 2 get a PPL (A) 2 years ago and getting interrupted by life I'm back in the cockpit and determined to get it this time... I have a question: What effect can/does a helicopter behind you when in a circuit have?

This (https://www.skybrary.aero/index.php/Wake_Vortex_Generation_by_Helicopters) site talks about the effect of a hovering chopper, and a chopper that is ahead of you and moving forward. But I can't find anything on a chopper coming in behind you. Thanks.

[Sam Rutherford]

Um, none. Zero.

[9 lives]

A non effect would be that no matter how slowly you fly your circuit, the helicopter pilot can fly slower yet!

[gerardflyagain]

Thanks both.

[ShyTorque]

The afternoon rain never gets you wet in the morning.

[BackPacker]

There's just one real effect: You get nervous.

Apart from that, you need to understand that helicopters have different operating patterns and requirements. I'm not a helicopter pilot, but I know that although they can hover, they prefer not to do so. At least, not a few hundred feet of the ground. If their engine stops, they need altitude to first set up an autorotation, and then use the rotor energy to cushion their landing. So hovering a few feet above the ground is ok, and hovering maybe 500+ feet is also OK, but anything in between can be a problem. Furthermore, they can fly their circuit differently, and don't necessarily have to aim for the runway. It's perfectly OK for them to aim their final approach to a parallel grass area, and from there hover-taxi to the ramp. So they might just turn to base and final inside of you, and "land" parallel to you. And, of course, they produce quite a bit of wind when hover-taxiing, so you might want to hold on to the controls if they're doing it near you.

If you operate from a field that is also frequently served by helicopters, why not invite one of them over for a coffee and voice your concerns/ignorance. They'll be able to give you a lot of advice.

[Whopity]

A helicopter produces downwash equal to its weight. If you fly through it, it can have disasterous effects on a light aircraft, so treat it with respect. If the helicopter is behind you, it is unlikely to have any effect, but if its ahead or has crossed your path you need to allow sufficient time for the wash to sink. A colleague of mine was killed after a large helicopter flew over the runway he was landing on when his aircraft rolled in the downwash.

[rudestuff]

You're unlikely to find a helicopter behind you in a circuit: they are supposed to avoid the flow of fixed wing traffic.

[John Eacott]

BackPacker (https://www.pprune.org/members/167605-backpacker), to correct your assertion that helicopters need >500ft to autorotate we can autorotate from the hover all the way to the moon. Almost ;)

It is a matter of energy management from three sources: height, airspeed and rotor RPM (RRPM). The ideal is to arrive with zero airspeed at 5-10ft agl then sacrifice the RRPM to cushion the touchdown.

To the OP, a helicopter behind you in the circuit should have no effect whatsoever. Should you follow or cross a helicopter flight path then be aware of the tip vortices which can produce a noticeable bit of 'wake turbulence', but this is all dependent on the size and speed of the helicopter along with the size of the aircraft.

Whopity, where and when was the fatality that you refer to please?

[Sir Niall Dementia]

John Eacott;

1992 S61 vs PA28 at Oxford, 2 dead, I watched that one happen, Culdrose, In the 1990’s C182 vs Sea King, one dead 3 badly injured, one in the US, C152 vs S76, one of the 76 crew was one of my instructors at FSI, Humberside more recently PA28 vs S76.

1995 I was on approach to Aberdeen in an S61, a mate flying one of the BAF Viscounts hit our wake, he described it as being like trampled by Bigfoot. He was an ex-61 pilot and the near loss of control shook him a lot.

Helicopter wake is bad, and a lot of people don’t realise the speeds we do, joining down wind at base we’ll be slowing from 145kt in an S76, faster in some others, a PA28 might be doing 105 down wind, 65-75 on final at 11000+ lb it takes some slowing.

SND

[Pilot DAR]

Well, seeing as we've already drifted the thread, two things:

Yes, helicopters have an "avoid zone" of airspeed vs altitude for a safe gliding return for a landing. Fixed wing planes have an avoid zone too, it's just not published, and not taught. For helicopter pilots it's prime information during training, and in flight manuals. Ask yourself, like a helicopter, if you were flying your Cessna at 100 AGL, and 50 MPH could you enter a glide after a sudden engine failure, and accelerate to glide speed so as to be able to flare for a safe landing - before you hit the ground? No, a fixed wing plane won't do it either, just no one tells you, 'cause you're probably no supposed to be flying there. Sometimes helicopters have to, so it's published and trained.

And, yes, helicopters produce wake turbulence. It does change shape from the hover to cruise flight, though it's going to have the same negative effects on airplanes who might blunder into it, as would be the case of the airplane flying into the wake of another airplane.

Helicopter pilots may be given more direct traffic patterns, but be confident that ATC, and the helicopter pilot themselves are well aware of the burden of traffic avoidance (and the helicopter pilot has the better view!).

Helicopters have surprising similarities to airplanes in ways you would not expect.

[TheOddOne]

I was on final for the hard runway in a Cessna 150 when I was overtaken by a Squirrel going for the Northside grass. It seems from above that I had a lucky escape with just having a massive wing drop. I went around. I then had a 'conversation' with the 'lady' in the Tower who intimated that making it official would be very complicated for me. I then had to rush off to work. Later, I got a very friendly phone call from the Squirrel pilot and we had a nice chat and he agreed that whilst he wasn't going for the same runway as me, overtaking me had consequences he hadn't appreciated. I guess that Tower person had mentioned it to him!

BackPacker's comment is a good one - it's good to talk.
TOO

[Haraka]

Of course it works the other way as well. I know of a case when was in Germany when a German F104 (Starfighter) decided to phase a German Army CH53 by a close pass over the top.......
The rotor disk folded upward in chaos , with the inevitable 100% casualty result.

[Flyingmac]

Of course, in exceptional circumstances a strong tailwind could carry a helicopter's downwash forward and under a preceding fixed wing on approach. The fixed wing could descend into the resulting turbulent air pocket and suffer a very hard landing.

[ShyTorque]

Of course, in exceptional circumstances a strong tailwind could carry a helicopter's downwash forward and under a preceding fixed wing on approach. The fixed wing could descend into the resulting turbulent air pocket and suffer a very hard landing.

I'd be interested to see a mathematical explanation of that phenomenon.

[hoodie]

It's a bit contrived to discuss downwind approaches, isn't it? In practice you'd have a similar effect to a helicopter in front of the fixed wing during an into-wind approach - but that's not really the question asked.

Culdrose, In the 1990’s C182 vs Sea King,

Minor point, but that sad occasion was St Mawgan rather than Culdrose.

[rudestuff]

Yeah, you might want to rethink that one. A helicopter might be able to fly with -ve airspeed but I'm pretty sure an airplane can't!

[Sam Rutherford]

The lack of understanding about fundamental POF displayed by some here is a little scary!

Please, take a moment to analyse things.

Actually, the entire thread is ridiculous! (Sorry, but it is)

[Flyingmac]

I'd be interested to see a mathematical explanation of that phenomenon.

Just a daft response in the spirit of the original question.

[Haraka]

"The lack of understanding about fundamental POF displayed by some here is a little scary!

Please, take a moment to analyse things.

Actually, the entire thread is ridiculous! (Sorry, but it is)
Agreed Sam.
Perhaps some might have been more aware about avoiding their effect on a helicopter in front of them ( Particularly one parked on the ground?)

Hat ,Coat etc .........

[scifi]

The quote was... A helicopter produces downwash equal to its weight.
Yes but an airplane does the same. The only difference is that the helicopter may be several time heavier than the airplane. However the downwash will be in all radial directions from the helicopter.
We have mingled with rotary traffic before, but my worst 'upset' was when trying to taxi to the pumps, when a chopper did the same thing.
.
.

[9 lives]

However the downwash will be in all radial directions from the helicopter

In the hover, yes. In forward flight, the downwash will be very similar to that of an airplane, complete with vortexes.

[dook]

The lack of understanding about fundamental POF displayed by some here is a little scary!

Please, take a moment to analyse things.

Actually, the entire thread is ridiculous! (Sorry, but it is)

..……..:D:D

[custardpsc]

The Odd One - did your incident occur just west of London?? If it is where I think it is, I had a conflict with a helicopter there too ( circuit, not downdraft) and was flying with the sister of the lady in the tower, who was very diligent in filing a report form !

[meleagertoo]

Surely a helo in forward flight produces virtually no downwash? Wake turbulence certainly, but whether that is much if any more than a comparable weight f/w I don't know. Downwash in the hover is a totally different thing and in no way comparable to what happens in forward flight.The aerodynamics of hovering and forward flight are totally different.

[nevillestyke]

I'd be interested to see a mathematical explanation of that phenomenon.
The mathematical explanation would be that it's a Harrier.

[scifi]

I saw two Harriers take off in front of a crowd of spectators at RAF Sealand. They both blew 4 foot wide holes in the grass, with the divots going all ways.
.

[ChickenHouse]

Hello! After trying 2 get a PPL (A) 2 years ago and getting interrupted by life I'm back in the cockpit and determined to get it this time... I have a question: What effect can/does a helicopter behind you when in a circuit have?

This (https://www.skybrary.aero/index.php/Wake_Vortex_Generation_by_Helicopters) site talks about the effect of a hovering chopper, and a chopper that is ahead of you and moving forward. But I can't find anything on a chopper coming in behind you. Thanks.
It depends. Shall we assume the chopper started shooting at you already? If you dropped a bomb before it may be reasonable.

[Sam Rutherford]

Unsubscribed!

[tmmorris]

Hovering helicopters - avoid taxying past. Indeed I refused a taxy clearance recently as it would have taken me <100m from a hovering Puma. To be fair ATC took the point and asked him if he’d mind moving, which he did very shortly afterwards

[BackPacker]

Same here, only in my case it was a SAR helicopter preparing for a winch demonstration. They were already at winch height (what's that? Maybe 30 meters?) but not yet in position. Stopped, informed ATC and ATC kindly asked the heli to move a bit. Non-issue.

[treadigraph]

I was sitting in the back of a PA-28 while the pilot did the walk round, the door was partly open. A JetRanger hover taxied past at about 50', buffeting the aircraft and banging the door wide open. We then started and taxied to the pumps with the door closed - couldn't open it from inside. Fuel man opened it from outside; an engineer replaced a broken split pin somewhere in the latching mechanism, all dandy again. Glad the previous occupant hadn't topped it up after their bimble...

[gerardflyagain]

Thanks all. RIP to those mentioned who have died.

[meleagertoo]

You're unlikely to find a helicopter behind you in a circuit: they are supposed to avoid the flow of fixed wing traffic.

"Supposed.."?
Are they?

Maybe local guidelines suggest this but normally anyone can fly in the circuit.
The point is most times a helo does't want or need to conform with a f/w circuit and may well hinder aircraft behind as it comes to a hover on arrival so agreed it is usually best to avoid the f/w circuit but "supposed to avoid" is a bit strong, I think.
There are occasions when you need to/it is better to conform to a f/w traffic.

[Duchess_Driver]

@sam rutherford.

Sam, I’m more surprised that you’re surprised!

From an operational point of view dealing with any circuit traffic regardless of fixed or rotary or wherever it is in the circuit is something I’d expect a low hour PPL student to be asking.

There was a sign in an old crew-room which stated “The only stupid question is the one you don’t ask.” - As seasoned instructors we should be encouraging questions like this, then perhaps the level of knowledge would be far higher.

[Sam Rutherford]

The question was about a helicopter behind a plane.

The answer was 'none'.

If the other answers (to other questions) are to be kept, then perhaps the thread title should be changed to become a more general query about helis and planes in proximity?

[Mike Flynn]

This reminds me of a scenario a few decades ago.

Arriving at Andrewsfield flying a helicopter the guy on the radio replied G-XXX understand downwind cleared to land.

So landed downwind and hopped across the runway.

He was a bit annoyed thinking it was a fixed wing.