FireHawk Blade Strike

[Cyclic Hotline]

Interesting event and response.
https://fireaviation.com/2020/08/07/la-county-s-70a-firehawk-helicopter-suffers-a-rotor-strike-during-training/

[industry insider]

Very interesting response. Hard to see the area from the video but not what I would have done.

[BigMike]

It stuns me that they flew it away... How do you know it is not going to come apart...
Looks like a large enough clearing they pass at -15 sec on the video.

[OvertHawk]

They may well have had no choice but to fly away from the location where they had the strike - a forced landing at that spot may have been impossible. But as Mike says they do seem to have passed potentially useable forced landing grounds.

That said - None of us were in the seat seeing what they saw and felt. It's all well and good to say that there's a landing spot in a video we've watched several times - it may not have been what they saw or they may have been past it by the time they saw it.

Either way - Glad they got it down in more or less one piece.

[BigMike]

Maybe, but wouldn't you be looking for the nearest spot the moment you lifted from the strike? How do you know the blade is not about to let go...

[nomorehelosforme]

The first open area they flew over where cars are parked has a wire strung through the middle of it so that probably wasn’t a great option for landing! That noise is horrible they must have been sh**ing themselves, Glad they got it down safety could have been a whole different story.

[Two's in]

Very similar to this discussion:

https://www.pprune.org/rotorheads/634074-qg-air-aw139-blade-strike.html

[OvertHawk]

Maybe, but wouldn't you be looking for the nearest spot the moment you lifted from the strike? How do you know the blade is not about to let go...

In truth i imagine i'd be concentrating on escaping from an area where a crash would men death. By which time i'd then probably have overshot the are you suggest as perhaps being suitable

My point is that what appears suitable to us in our armchairs viewing from a different perspective and with the benefit of time and hindsight may well have seemed different to those who were at the pointy end at the time.

A little professional courtesy to fellow aviators is due here methinks.

[gulliBell]

Can somebody explain to me what the training value was in what they were doing? Particularly in the fire fighting context.

[roscoe1]

In the early 80s, our corporate flight department had a 222. This was just as the awful problems with the PT wheels and bearings on the LTS 101 were in full bloom. One rainy night, the chief pilot executed 2 missed approaches all the while a red ( not the yellow engine chip light but the red one) was glaring at him and the co-pilot was getting more and more adamant about wanting to bust minimums due to an emergency, which it surely was. CP also would not roll back the sick engine as the FM demanded. They did get on the ground the 3rd time. The next morning, maintenance went out and pulled the chip detector for the #3 bearing and it looked like one of those jokes they do jn the shop when they drag a magnetic chip detector through the drill press shavings and show the boss. The DOM said we'd have to find a hangar to change the engine. The bad judgement didn't end there. The next day, unbeknownst to anyone, the CP fired up the "good engine" and did a rolling takeoff, flew back to base OEI and swears he didn't pull the guts out of it landing on the company base pad.

I think if all the LA pilot might have done is fly past a marginal landing spot but get on the ground as soon as they could after that, he deserves lots of slack. A plastic bag, even a small one stuck on a rotor blade makes a gawd awful sound. I'd love to see what the damage actually was and hear whether or not the crew was experiencing severe vibrations or changes in control. Given it's public use, I doubt we will unless LA County decides it is a learning experience and lets the rest of us in on it. In my experience, if the video had not been made and there were no ground witnesses, we probably would not be hearing about it. The pilot may not deserve a medal but I'm sure they deserve to have no guilt beyond maybe hitting the rock in the first place. His snorkel wasn't extended and I wonder what they were doing in such a tight spot.

[megan]

A single engine ferry can not be called "bad judgement" in and of itself. Have seen it done with a stranded S-76 on an oil rig with the approval of the regulator, not putting words into John Dixons mouth, but think Sikorsky gave a thumbs up as well - corrupted between the ears hard drive I'm afraid, was a very long time ago.

[SuperF]

Having been in a situation where i thought it best to land as soon as possible, i can guarantee you that when you have the A/C slowly descending towards what looked like a suitable landing spot, there was no way i was going to dump the collective, and rip off a big flare at the bottom to land somewhere closer. My thinking at the time was, it hasn't flown apart yet, if i don't change anything, hopefully it holds together until i grease it on...

[ring gear]

Before we arm-chair critics throw too many stones in this incident, the B'Hawk blade design does have some very well thought out features making it a fantastic utility machine....combat or peacetime.

As mentioned in UH60 Bad Blade https://www.pprune.org/rotorheads/552421-uh-60-bad-rotor-blade-2.html#post8780694.........John Dixson sheds some additional light on the original design concepts and considerations worth reading. Fortuitously, this thread has just surfaced yet again on another issue for ease of reference just below.

I think some of these design features do need to be considered when flying our machines...this is one of the many elements euphemistically called "experience" but so many people fail to understand...its not all about the number of flying hours necessarily, but what you understand about the machinery you are flying and responsible for. In many of our careers we are called upon to make "valued judgments". It used to be called "captaincy"....a concept which seems to be disappearing into the distant past as we seem to be overtaken be the need to fell more trees to create an A4 "risk assessment" sheet before every flight.

The B'Hawk tip cap is a very light composite structure providing an aerodynamic cover and extension, almost 12inches out from the main blade structure and in particular, it's span tip weights. It is quite conceivable that the tip cap could well have been shattered and flailed in the slipstream, making that ever familiar whoosh/whoosh or slap/slap sound that those of us who have experienced - or the rest of you that will experience it, will hear when you pick up a plastic bag/material or palm frond or other soft material on the blade. It certainly sounds like it on the video sound track...quite impressive.

If the Tip cap is simply shattered and flailing in the slipstream, it is quite conceivable that there would be minimal change in lateral vibration - even if the Tip cap disappeared totally. Providing the main structure and in particular the span tip weight package was still in tact.

You will notice the B'Hawk tip cap is attached with quite a number of flush screws to the main blade structure. See the link below and see a more detailed picture of the blade and tip cap structure. Note the extend the Tip cap extends beyond the main blade structure. The link below may shed some light on both the tip cap and the effects of rotor blade balance.

https://www.rwas.com.au/blade-balancing/

Perhaps going lower and completing a landing in situ would have resulted in far greater and more catastrophic damage,...difficult to say from the camera angle and field of view presented in the video.

[JohnDixson]

Ring gear makes the main point, i.e., that the tip weights are not in/on the tip cap but at the outboard structure where the tip cap is mounted.

Somewhere out there some 60 pilot has smashed a tip cap into a tree I’d guess, but not I. One day tho’ I was sitting in the front seat of the S-67 making part of that movie one can find on line. This part didn’t make the final cut: we’re flying down the shoreline of the lake on the West Point Reservation and Kurt ( Cannon-S-67 Project Pilot and a great one ) cut it a bit close to the treeline and whacked a decent sized limb. Created a significant 1P ( mostly vertical ) and track problem, but otherwise allowed flight. Found a large unoccupied parking lot and had a spare blade delivered from Stratford. That tip cap was a mess and not doing anything good at all, aerodynamically.
( there was a slightly humorous angle: when we hit the tree, Kurt said immediately on the ICS “ what was that “ . His loyal copilot responded “ you hit that damn tree back there, Kurt”. Kurt hadn’t had the advantage of being in the Army for the SE Asia Games. Courtesy of the Army, I had some experience in that area ).

[bellfest]

The best thing about that footage is the damaged blade noise demonstrating how slow individual blades revolve in a multi bladed aircraft....... seems way faster usually.
Poor buggers must have got a hell of a fright.

[Blackhawk9]

Seen blade strikes when I was on Black Hawks, usually not a big deal , tip trashed , blade sent away for insp and repair , the blades were made to take hits from 23mm cannon, hitting a tree with tip not in the same class, years ago a blade strike on a Bell was only a major issue if you found damage , now Bell call it a sudden stoppage requiring a major insp , had a 212 just touched a branch but ripped off the blade end cap , under the current insp criteria that would require major insp and work, back then it was just screw on a new blade end cap.

[blackdog7]

Although the camera angle can be deceiving, what terrible management and operation of a $15 mill machine.All involved should be **** canned.

[Gordy]

Although the camera angle can be deceiving, what terrible management and operation of a $15 mill machine.All involved should be **** canned.
You have never made a mistake? You do not know the circumstances and you are blaming a fellow pilot and asking for his dismissal, and likely would not get another job... Way to support your peers.......

[JohnDixson]

The photography is very limiting, but the stills and the video “seem” ( to me anyhow ) to indicate the right hand crewman is looking down, i.e., we are seeing the top of his helmet. Wonder what was going on below that had his attention, rather than rotor clearance issues ( that is, if my interpretation of the photos and video is correct ) ?

[[email protected]]

Agreed John - no scan to the tips or tail, just fixation on talking the wheels down it appears. I'm sure the surface was tricky to land on amongst the rocks but rotor clearances are day one, week one at crewman school.

[ring gear]

Well spotted JD.
The object in the RHS Crewmen’s window (looks like a helmet, but doesn’t move), appears to be fixed in the vertical position. The amazing thing is that it doesn’t appear to move throughout the video – even after the impact. It appears totally transfixed to the vertical position for whatever reason with no evidence of any sort of a clearing scan whatsoever as Crab said. – very strange. Even after the impact and the camera resumes the aircraft in the field of view during its climb out, the “helmet” appears to be fixed in the vertical position. This would seem very strange given that most people instinctively move there eyes to observe any sudden loud noise which was clearly evident at and post impact. Not seen in this case.


For bellfest : Nr 258rpm – but probably a little less on this occasion due to the sudden increase in rotor drag due to the shattered rotor tip/s ;) (I know,….. the FCU would have maintained 100%Nr….just couldn't resist it):}.


For BlackHawk9: Yes, had one blade flex down and take a clip out of the T/R Intermediate gearbox fairing once…perhaps that's why Sikorsky designed it to be sacrificial??:O No damage to the tip cap on that occasion but a different story for the IGB fairing. And many others that we are all aware of ..thank heavens they were all in B’Hawks!:)

Perhaps the reason Bell has the requirement for a “Sudden Stoppage” inspection is that like the CH47 and many other blades of that generation (AS322, AH1, etc), they all had full length spars running right to the tip. With the Span tip weight pockets located in and around the spars ie the main blade structure went right to the tip. There were no sacrificial components designed to dissipate energy in event of sudden impacts. I think you will find the B212 will be not unlike the B204/205 with a “D” spar right to the tip. The Span Static weight pockets will be located immediately behind the rotor tie down eyelet. You will see an example of this in the link posted earlier and below of the UH1 tip. Go down to "Static/OEM Blade Adjustments" to see a diagram and pics of various tip caps and rotor structures including UH1/Ch47/As322/others.

https://www.rwas.com.au/blade-balancing/

As you would know (and many others who have the pleasure of some UH1 experience), who hasn’t experienced the “thwack-thwack” as the tips gently hit the soft green mangrove leaves along Shoalwater Ck while your crewman tries to retrieve some crab dilly pots out of the water with a fire rake? :ooh::) No harm with soft impacts...rotor blades can be quite surprisingly robust and damage tolerant.

If you do have a significant blade strike (i.e. take the blade end cap off) in these earlier full length structures, the energy from the impact will travel down the load path through the Transmission and drive train components. The sudden impact forces has the potential to cause stress damage to various components in along this drive train.

I’m sure you will be familiar with these in any case BlackHawk9. But others may not.

The B412 for example, does not have its spar (fibreglass) run all the way to the tip. It's Tip cap however is only relatively small and not sacrificial. Its big disadvantage is that the tip cap is a bonded fairing and houses its Static Span weights in the form of lead pellets or beads. They are inserted in the top through a very small flush mounted Allen bolt. The lead pellets then get deformed under centrifugal force to solid mass. The only way you can adjust these is to physically debond the tip cap. It is subject to a tip strike, it is highly likely to loose all the Static Span moment arm balance weight and set up quite a significant lateral…not a very clever design.

Other examples of sacrificial design features for rotor blade strikes are seen on the Bk117. The vertical fins have sacrificial segments designed to shear away without causing structural damage to the main fin and leaving still an aerodynamic surface. This enables a pilot to recover the machine back to maintenance rather than leaving it parked up in a paddock. A clever design feature to overcome a different design flaw which was later rectified on the 145 models.

See link below – go down to a couple of paras where it describes Blade Flex.
https://www.rwas.com.au/tool-description/

Gordy: – Totally agree with ya….

[JohnDixson]

Ring Gear: Great post and educational/maintenance information re some new equipment that must be a huge help in use.

One comment re whirl towers, at least as promulgated within SA during my tour of duty: the purpose of the whirl tower was to be able to replace a blade in the field, adjust the push rod length as indicated, and expect that its 1P ( i.e., track and balance characteristics ) to be flyable safely. Not that the 1P levels would meet the Maintenance test flight criteria ( which were the same criteria used for production acceptance of new aircraft ), but that would allow safe flight with perhaps elevated 1P levels and safe until you could get it to a maintenance facility with the vibration gear, and make the necessary adjustments to get the blade within the MTF ( maintenance test flight manual ) limits.

[blackdog7]

You have never made a mistake? You do not know the circumstances and you are blaming a fellow pilot and asking for his dismissal, and likely would not get another job... Way to support your peers.......

I’ve made mistakes...and hear hear to all the old boys.
I can count on my one finger how many pads next to a cliff face that anyone should be landing on with your T/R towards upsloping ground. How did that approach look?
Great news that any spinning rotor system can clip off an end cap and keep on ticking.
Darwin would be proud.

[Blackhawk9]

"As you would know (and many others who have the pleasure of some UH1 experience), who hasn’t experienced the “thwack-thwack” as the tips gently hit the soft green mangrove leaves along Shoalwater Ck while your crewman tries to retrieve some crab dilly pots out of the water with a fire rake? https://www.pprune.org/images/smilies/icon25.gifhttps://www.pprune.org/images/smilies/smile.gif No harm with soft impacts...rotor blades can be quite surprisingly robust and damage tolerant."

Ring gear you used a fire rake , we carried a rock anchor to fish them out with the hoist and a couple of orange baskets in the back to put the crabs in before resetting the pots, Iroquois blades were like big whipper snipers, ah the good old days at Albat T Ross productions. have seen a few blades strikes on Black Hawks and Iroquois flying up Star Wars alley (fire breaks) in the pine plantations at Schoalwater Bay.

[ring gear]

For JD: Yeah, we were victim to the "pre-tracked" s70 blades when we first got them. This was when SA where whirl towering them late 80's early 90's. This would have been when you were there for sure, probably when you were CP there, my best guess. I think I have a couple of SA certificates with your signature on it back around those times. I believe it was SA who prevented us from actually adjusting the tabs originally at unit level. It actually tied our hands behind our back when it came to RTB. We had to turn off the "Tab" option on the CH8500, as SA would not allow us to bend them. Finally, after bashing our heads agains brick walls and being forced to accept decidedly "average" balance solutions, we gained approval to adjust Tabs. This made a vast improvement in ride quality and speed-to-solution of RTB because we could finally use ALL the adjustment mechanisms available.

As the article about whirl towers on the web site tries to show, even if a blade is "pre-tracked", it cannot correct a blade track for changes produced through increasing IAS....exactly when tab bending should be used and utilised - unless SA utilised a humungas wind machine to simulate a 80/120kts airflow...which I doubt strongly they did. A whirl tower can only confirm a blade in-track condition in a on-ground flat pitch flight idle condition and in a hover condition i.e. with pitch/collective applied to hover power equivalent condition. And then, the change in blade track during these 2 x different "power"/angle of attack conditions, the adjustment should be made using the DYNAMIC chord adjustment weights ...not the tabs.

So the original usefulness of the "pre-track" that SA were recommending back then is dubious and strongly debatable. But many things change over time as we begin to learn more and more about all sorts of things.

The creation of rogue rotor blades as described on the web site is what happens in real life. The helicopter community has lived with the phenomena since day one...but not many have understood the process. It has cost, and continues to cost the helicopter operators/industry a lot of wasted time and money.....needlessly. The new tooling does prevent the rogue rotor blade from occurring. It is game changing, as witnessed by many Defence forces who use it....just need to get those damn OEMs to agree and embrace the new paradigm and allow civil operators to use the same tooling that many militaries are so successfully using world wide. ;):}

I would love to have a discussion with you about your time there in SA and discuss some of the items on the web site with you....maybe we can make contact privately and open up a private chat via skype/messenger or some means to discuss these many issues. It would be great to discuss and get your thoughts on various item from the perspective of your extensive experience.

For BlackHawk9: Good old "StarWars Alley" ;):), we didn't have a rock anchor with us at the time. It had already been deployed in the dinghy we had deployed to Pine Mountain creek (through-load in UH-1), so we had to make do.

For Blackdog7: Your so anal! :rolleyes: ...and so indicative of the "new" age of aviation. :bored::(

[blackdog7]

For JD: Yeah, we were victim to the "pre-tracked" s70 blades when we first got them. This was when SA where whirl towering them late 80's early 90's. This would have been when you were there for sure, probably when you were CP there, my best guess. I think I have a couple of SA certificates with your signature on it back around those times. I believe it was SA who prevented us from actually adjusting the tabs originally at unit level. It actually tied our hands behind our back when it came to RTB. We had to turn off the "Tab" option on the CH8500, as SA would not allow us to bend them. Finally, after bashing our heads agains brick walls and being forced to accept decidedly "average" balance solutions, we gained approval to adjust Tabs. This made a vast improvement in ride quality and speed-to-solution of RTB because we could finally use ALL the adjustment mechanisms available.

As the article about whirl towers on the web site tries to show, even if a blade is "pre-tracked", it cannot correct a blade track for changes produced through increasing IAS....exactly when tab bending should be used and utilised - unless SA utilised a humungas wind machine to simulate a 80/120kts airflow...which I doubt strongly they did. A whirl tower can only confirm a blade in-track condition in a on-ground flat pitch flight idle condition and in a hover condition i.e. with pitch/collective applied to hover power equivalent condition. And then, the change in blade track during these 2 x different "power"/angle of attack conditions, the adjustment should be made using the DYNAMIC chord adjustment weights ...not the tabs.

So the original usefulness of the "pre-track" that SA were recommending back then is dubious and strongly debatable. But many things change over time as we begin to learn more and more about all sorts of things.

The creation of rogue rotor blades as described on the web site is what happens in real life. The helicopter community has lived with the phenomena since day one...but not many have understood the process. It has cost, and continues to cost the helicopter operators/industry a lot of wasted time and money.....needlessly. The new tooling does prevent the rogue rotor blade from occurring. It is game changing, as witnessed by many Defence forces who use it....just need to get those damn OEMs to agree and embrace the new paradigm and allow civil operators to use the same tooling that many militaries are so successfully using world wide. ;):}

I would love to have a discussion with you about your time there in SA and discuss some of the items on the web site with you....maybe we can make contact privately and open up a private chat via skype/messenger or some means to discuss these many issues. It would be great to discuss and get your thoughts on various item from the perspective of your extensive experience.

For BlackHawk9: Good old "StarWars Alley" ;):), we didn't have a rock anchor with us at the time. It had already been deployed in the dinghy we had deployed to Pine Mountain creek (through-load in UH-1), so we had to make do.

For Blackdog7: Your so anal! :rolleyes: ...and so indicative of the "new" age of aviation. :bored::(


And just for you ring gear....obviously an old codger. Welcome to the new age.

[Blackhawk9]

Ring Gear, when did the restrictions come in with T&B on the S-70, I was on them 88 till 92 and did the full range of adjustment, I had some smoooooth S-70 when I finished, was just looking at my old cheat book with all the T & B graphs ,1 x TR graph , 5 x MR graphs and 3 x graphs/charts to do cabin vibration absorber tuning, showed a young guy on Black Hawks all this stuff a couple of years ago and he said how did you do that if our computerised Vib gear is U/S we are grounded , I said old school old boys you had to know how stuff worked and work around it , something the "New Age" don't understand. Only ever used the concept of pretrack to do initials or to change a blade in the bush to fly you back to a maintenance place to T&B properly, I did the trials with RADS and 8500 in 89 and recommended RADS but the Army chose 8500 ???
I never had a Black Hawk die on me out bush/on a trip in 5 years , though what I did back then with U/S's wouldn't be allowed now.