Helicopter ground resonance

[Old Farang]

Slow news day. This phenomena only occurs in helicopters with fully articulated rotor systems, and more often those with 3 main rotor blades.
In small helicopters, such as the Hughes 300 shown here, the onset is very rapid and requires instant response from the pilot.

As an aside: the comments mention the oleo struts in this case MAY have contributed to the event. During my training I did some time on these particular machines (I do NOT like them). With an instructor on board one day approaching to land he noticed that one landing skid was hanging down lower than the other. The bloody oleos on one side had slipped apart, a bit like a car shocker that has a screwed in end cap on it, allowing the skid to hang down. After some discussion it was decided that ONE of us would have to get out and try and put the offending strut(s) back in place!
As he was the better pilot, guess who drew the short straw! So while he kept the helicopter in a steady hover out I went and managed to put the bloody thing back in place, and he landed without a problem! I dread to think what may have happened if he had not noticed the skid hanging low.


https://www.youtube.com/watch?v=SPHoumJvVtQ


https://www.youtube.com/watch?v=IN2Bw79KK80

[Tins]

In small helicopters, such as the Hughes 300 shown here, the onset is very rapid and requires instant response from the pilot.



I believe my instant response would be not to get in the damn thing in the first place. I have seen similar footage before, but had no idea that it was caused by engineering seeking a problem rather than a solution.
OF, do such birds require separate endorsement? Seems to me that a higher level of training would be required.

[Old Farang]

I believe my instant response would be not to get in the damn thing in the first place. I have seen similar footage before, but had no idea that it was caused by engineering seeking a problem rather than a solution.
OF, do such birds require separate endorsement? Seems to me that a higher level of training would be required.


had no idea that it was caused by engineering seeking a problem rather than a solution.
Ah, rather the other way around. The problem is induced by the pilot (mostly), the C of G of the rotating mass gets displaced and the engineering attempts to rectify it.


do such birds require separate endorsement? Seems to me that a higher level of training would be required.

All helicopters require an individual endorsement, as compared with group endorsements for fixed wings. Ground resonance is covered in theory studies, but as you cannot demonstrate it, even in an incipient stage, some folks just don't get it!

[Hugh Jars]

Wouldn't have liked to be sitting in the back of the CH-47 when the rear mast came off. I think that one was flight testing/demonstrating ground resonance, wasn't it?

[Old Farang]

Wouldn't have liked to be sitting in the back of the CH-47 when the rear mast came off. I think that one was flight testing/demonstrating ground resonance, wasn't it?

Yeah, not sure just what they are up to there, John. After all, they are probably Americans! What I first thought were test monitoring lines running off, a closer look at the lines show they may just be tether lines to prevent it flying off into the ether by itself.

But I do think it was some type of testing, and I doubt that anyone was on board.

[Tins]

Wouldn't have liked to be sitting in the back of the CH-47 when the rear mast came off. I think that one was flight testing/demonstrating ground resonance, wasn't it?

Had a couple of rides in a Chook back in the day. Didn't know a thing or I might have risked being disciplined for disobeying a lawful command.... I was silly enough to ask the crew about its auto rotational capabilities. Got told that the "****er has all the auto rotational capability of a housebrick". I look back in horror...

[Old Farang]

Had a couple of rides in a Chook back in the day. Didn't know a thing or I might have risked being disciplined for disobeying a lawful command.... I was silly enough to ask the crew about its auto rotational capabilities. Got told that the "****er has all the auto rotational capability of a housebrick". I look back in horror...

They were just rattling your chain mate!

[Hugh Jars]

Had a couple of rides in a Chook back in the day. Didn't know a thing or I might have risked being disciplined for disobeying a lawful command.... I was silly enough to ask the crew about its auto rotational capabilities. Got told that the "****er has all the auto rotational capability of a housebrick". I look back in horror...
I went for a ride in a Huey when on a promotion course in Amberley with the ATC cadets, way back when. The loadmaster sat me at the left door gunner position, which had the best view in the house.

I was lucky and had a helmet and headset on, and could hear the crew talking over the intercom. We spent most of the flight chasing roos at treetop level. When the captain announced his intent to do a practice autorotation, I had no idea [bigsmile]

When the engine spooled down I got the idea[bawl]. My life flashed before my eyes, but of course the manoeuvre was well executed.
It was one of my most memorable flights as a sprog in a Service aircraft [biggrin]
Sadly, the crew were lost in a prang a few months later. I was shocked to read it in the RAAF News.

John R.

[Old Farang]

I have flown a Huey (while working offshore), but I am not endorsed on them. Auto rotations (successful ones!), depend a lot on the inertia in the rotor system. It is said of the Huey that there is enough inertia in the rotor system that; if sitting on the ground at flight idle you cut the engine it is possible to lift off the ground and turn a full circle and land again without damage.

The first helicopter that I owned was a Robinson R22. A very low serial number and one of the first imported into Australia.
Now that DID auto like a brick! It had about as much inertia as a paper bag. So much so that one of the first mods carried out by the factory was to install weights in the tips of the main rotor blades. (from Serial number 200 on if I recall correctly).

That did improve it, but it was still a delicate manoeuvre! It was also very easy to overspeed the rotor system, so it took a LOT of practice to become proficient.

[Tins]

I have flown a Huey (while working offshore), but I am not endorsed on them. Auto rotations (successful ones!), depend a lot on the inertia in the rotor system. It is said of the Huey that there is enough inertia in the rotor system that; if sitting on the ground at flight idle you cut the engine it is possible to lift off the ground and turn a full circle and land again without damage.



With a rotor diameter of nearly 15 metres there would be a fair bit of inertia...

[350RRC]

I have flown a Huey (while working offshore), but I am not endorsed on them. Auto rotations (successful ones!), depend a lot on the inertia in the rotor system. It is said of the Huey that there is enough inertia in the rotor system that; if sitting on the ground at flight idle you cut the engine it is possible to lift off the ground and turn a full circle and land again without damage.

The first helicopter that I owned was a Robinson R22. A very low serial number and one of the first imported into Australia.
Now that DID auto like a brick! It had about as much inertia as a paper bag. So much so that one of the first mods carried out by the factory was to install weights in the tips of the main rotor blades. (from Serial number 200 on if I recall correctly).

That did improve it, but it was still a delicate manoeuvre! It was also very easy to overspeed the rotor system, so it took a LOT of practice to become proficient.

i learnt about all these concepts from reading 'Chickenhawk' and remember the author was horrified that Cav trainee pilots stopped being 'inducted' into the experience of a real auto-totation by their instructors.

From memory Mason became an instructor and did it anyway. Rule 1 was something like 'flatten the pitch with the collective' to keep the blades spinning and the rotor disc acting like a wing.

great book, DL

[p38arover]

I went for a ride in a Huey when on a promotion course in Amberley with the ATC cadets, way back when.

I won Dux of Qld Squadron (I still have the trophy) in the ATC at Amberley in 1964 and was offered a ride in a Canberra. I didn't get the ride as I was sick. [bigsad]


Q.U.S.Q.N.A.T.C. 1964
Presented to Cpl Beckett, R.L.
From the staff of 18 Flight

Yes, all those full stops are there in the inscription :) )

I have one other trophy I've kept - presented by Arthur Gorrie who owned a hobby shop in the Gabba, for my control line model of a N.A. B25 Mitchell bomber.

Getting back to helicopters, I have an RC flying model of the Iroquois and several other RC helos. A pic from around 1988 - I wish I was still that slim! (Hirobo Falcon 505 with an OS 40FSR-H (6.5cc) and tuned pipe, radio Futaba FP-5JH helicopter radio.)

170865

[Saitch]

Years ago, we were using a Bell, Jet Ranger in mountainous areas for access to several mountain peaks. Now, even though auto-rotation looks a bit dodgy, I reckon I'd still take my chances, rather than lug 25-30kg of gear up the mountain on foot and then have to descend with same, sometimes after dark.[biggrin]

I must say that it took a bit of getting used to when, on hitting a decent downdraught, the rotor blades would stop making noise for a bit and then slowly start 'Chunk, chunk, chunking' again when catching air.
It was a quick education on 'Mountains and Air Currents'.

[Hugh Jars]

Ron,
I never achieved any awards during my time. Nevertheless, it really shaped me as a person and instilled values I use to this day.

I went back as a PLTOFF instructor in the 90s as the Supervising Grade 1 for NSWSQN Flying Training unit. My boss (SOFO) was funnily enough a PLTOFF I met on that same promotion course at Amberley in 1975. When he joined he was a Qantas cadet starting his flying career, and when I met up with him again, a Senior Captain on the B744.

The most rewarding memories during my time as an adult was sending kids on their first solo flights - many times on their 16th birthdays. Some I have interviewed for flying jobs years later. Great memories.

John R.

[p38arover]

John, you made it to a job I lusted after. Well done!

I'd have loved to be a pilot. I only got as far as sailplanes and one instructional flight in an R22.

I always wanted to join the RAAF even if I couldn't be a pilot but I was so short-sighted, I couldn't even read the first letter on an eye chart. I failed the RAAF medical and they said I wouldn't even get into the army. National Service comes along (Vietnam) and my eyes are suddenly good enough (I still failed the medical for other reasons).

If I go somewhere on holiday, I'll often take a local scenic heli flight. The most memorable was flying under the Golden Gate in the front seat of a Jet Ranger, then rising slowly level with the walkway to the surprise of pedestrians (a bit like would be seen in a movie).

Hint: if taking a scenic flight with one's wife, don't. Do the flights separately that way you'll both get the front seat. Couples sit in the back.

[Old Farang]

Wouldn't have liked to be sitting in the back of the CH-47 when the rear mast came off. I think that one was flight testing/demonstrating ground resonance, wasn't it?
According to Scruffy in the following video the Chinook was time expired and it was set up to test ground resonance.


(6) WHY HELICOPTERS GET GROUND RESONANCE - YouTube (https://www.youtube.com/watch?v=Lz1WfIrSPEg)

[350RRC]

If I go somewhere on holiday, I'll often take a local scenic heli flight. The most memorable was flying under the Golden Gate in the front seat of a Jet Ranger, then rising slowly level with the walkway to the surprise of pedestrians (a bit like would be seen in a movie).

Hint: if taking a scenic flight with one's wife, don't. Do the flights separately that way you'll both get the front seat. Couples sit in the back.

There is the old story of Ma and Pa who went to the County fair every year. There were always heli rides for 50 bucks.

Every year Pa was keen, but Ma said they couldn't afford it, 50 bucks is 50 bucks.

County fair came around again and they ended up over at the heli ride spot.

The guy running it said 'You two come every year for ages but you've never taken the ride'.

Ma says they can't afford it, 50 bucks is 50 bucks.

Heli guy says I'll take you for a ride and if you don't say anything it'll be free.

Ma says ok, so she and Pa get in the back seat and off they go.

The pilot flies around and does a few tricks but there is silence from the back. He tries a bit harder, but still nothing.

He lands and turns around and there is only Pa in the back.

Pilot asks 'Where is your wife?'

Pa says 'She fell out while you were mucking around'.

Pilot asks 'Why didn't you say anything?'

Pa just says '50 bucks is 50 bucks'.

[Old Farang]

John, you made it to a job I lusted after. Well done!

I'd have loved to be a pilot. I only got as far as sailplanes and one instructional flight in an R22.

I always wanted to join the RAAF even if I couldn't be a pilot but I was so short-sighted, I couldn't even read the first letter on an eye chart. I failed the RAAF medical and they said I wouldn't even get into the army. National Service comes along (Vietnam) and my eyes are suddenly good enough (I still failed the medical for other reasons).

If I go somewhere on holiday, I'll often take a local scenic heli flight. The most memorable was flying under the Golden Gate in the front seat of a Jet Ranger, then rising slowly level with the walkway to the surprise of pedestrians (a bit like would be seen in a movie).

Hint: if taking a scenic flight with one's wife, don't. Do the flights separately that way you'll both get the front seat. Couples sit in the back.

I have been on that flight Ron. Although I dont recall getting close to the bridge. It was operating from Fishermans Wharf area.

[p38arover]

I have been on that flight Ron. Although I dont recall getting close to the bridge. It was operating from Fishermans Wharf area.

I caught the flight from Sausalito, on the other side of the bridge - from here (I checked my photos): Google Maps (https://www.google.com/maps/@37.8785466,-122.5125988,137m/data=!3m1!1e3?hl=en-GB)

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I hope you realise I am bloody jealous of you! [bawl] :bat: I'd love to be able to fly choppers - or fixed wing.

[Old Farang]

I hope you realise I am bloody jealous of you! [bawl] :bat: I'd love to be able to fly choppers - or fixed wing.

I really enjoyed flying, both fixed wing and helicopters. For the helicopters it was a long hard and expensive experience, all totally destroyed in about 10 seconds by one idiots ego being much bigger than his abilities.
Lost my medical now, so all just memories. :twobeers:

[Grumbles]

Ron,

The most rewarding memories during my time as an adult was sending kids on their first solo flights - many times on their 16th birthdays.

I've often wondered if 16 year olds have the maturity/presence of mind to handle a real in flight emergency where the world is rapidly falling apart around them. 16 year olds can't solo drive a car but can fly solo...amazing really.

[ramblingboy42]

it is almost natural to fly

it is unnatural to drive a car

a good instructor will have a young person soloing in 10hours

there are very simple rules to flying

emergencies occur only when something causes one of the simple rules to be broken .

a bird never breaks flight rules.

[Old Farang]

I hope you realise I am bloody jealous of you! [bawl] :bat: I'd love to be able to fly choppers - or fixed wing.
I believe that you are a camera buff, Ron? Some of my most satisfying flying with a helicopter was photography flying. It was all commercial work and the need is to put the photographer in the right position, while maintaining a safe operation.

Some photographers are complete arseholes; mostly "media types" that honestly believe that they alone are the greatest people on the planet to ever wield a camera! I did both still camera work and video, although my old 2 bladed helicopter was not the smoothest platform for video work. A good photographer will outline what he is trying to achieve before take-off, and the clue to knowing that you putting him where he needs to be is no yelling from them while they are filming!

[p38arover]

Putting photographers and cameramen in position could be challenging. :thumbsup:

One group of pilots that impress are those who carry workers up to work on high tension power lines. Some of those lines are still powered. I have a lot of respect for the workers, too!

Actually, I think they are all mad!


https://www.youtube.com/watch?v=DPNK7bc2qvM

[Old Farang]

Actually, I think they are all mad!

As helicopter pilots, right from the start of training it is drummed into us to look out for, and STAY AWAY from ANY powerline!
Still, every year some poor bugger fly's into one with fatal results.

Many years ago ago I did some experimental work using IR camera's to survey some HT lines. The idea was not proceeded with, and although it would have been a lucrative contract, I was not really disappointed when it did not eventuate.

Maybe these nuts are even more insane:


https://www.youtube.com/watch?v=lcjhjna9jZE

[p38arover]

I thought about building my own chopper - but not like these:


https://www.youtube.com/watch?v=JNMHWwoAyzc

[350RRC]

As helicopter pilots, right from the start of training it is drummed into us to look out for, and STAY AWAY from ANY powerline!
Still, every year some poor bugger fly's into one with fatal results.

Many years ago ago I did some experimental work using IR camera's to survey some HT lines. The idea was not proceeded with, and although it would have been a lucrative contract, I was not really disappointed when it did not eventuate.

Maybe these nuts are even more insane:


https://www.youtube.com/watch?v=lcjhjna9jZE

I like the vid where they put patches over the hot spots in the wires. It ain't a 5 minute job.

DL

[superquag]

John, you made it to a job I lusted after. Well done!

I'd have loved to be a pilot. I only got as far as sailplanes and one instructional flight in an R22.

I always wanted to join the RAAF even if I couldn't be a pilot but

.

As a child I had a debilitating st-t-t-utttttter, which I rightly surmised would end my flying career (RAAF/ Fleet Air Arm) before it started... So I stayed on terra firma.

A couple of years ago I found a way to get that piece of paper, - alas, now a plastic and common credit-card sized thing... via Light Sports Aircraft. - Your Driver's licence "medical" is good enough. If I can do it (and step into a Robin and fly the beast...) - Any Senior Wind can !

No caption needed for the last pic... Every trainee pilot has had the same conversation with.... Satan.


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[Hugh Jars]

I've often wondered if 16 year olds have the maturity/presence of mind to handle a real in flight emergency where the world is rapidly falling apart around them. 16 year olds can't solo drive a car but can fly solo...amazing really.

The youngest I have taught was 11 years old. She took me by surprise, because she was getting through over double the sequences that an average adult would. We were effectively through all the emergency manoeuvres in about 7 hours, and would've soloed, had she been 16. I was disappointed she never pursued it as an older person, as she would've been a very competent pilot.

Younger people have minds like a sponge. They soak up the training content at an amazing rate. As an instructor, I had the legal responsibility to ensure all syllabus sequences are covered to an appropriate standard prior to sending them off on their own. One of which is being capable of handling an engine failure at any phase of flight and making it safely back onto the ground (not necessarily the airport).
A first solo (fixed wing) is only one takeoff, circuit and landing.
At that time, junior instructors did not have the approvals to send students first solo. Only grade 1 or 2's are approved.

John R.