FireHawk Blade Strike
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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??
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?
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….
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??
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?
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….
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.
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.
Last edited by JohnDixson; 14th Aug 2020 at 21:27. Reason: add addressee
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.
"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? 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.
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.
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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!
...and so indicative of the "new" age of aviation. 
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!
...and so indicative of the "new" age of aviation. 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! ...and so indicative of the "new" age of aviation.
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!
...and so indicative of the "new" age of aviation. And just for you ring gear....obviously an old codger. Welcome to the new age.
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.
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.
