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Van Horn blades
Read a TSB report that took issue with Van Horn blades (said they failed during an autorotation). I've flown them, they feel a little different than original Bell blades, but otherwise seemed good.
Anybody know more? TSB REPORT 2019 206 crash |
Originally Posted by malabo
(Post 11344744)
Anybody know more?
Van Horn Blade AD 2022-22-08 |
VHA News
We have had onset of severe vertical vibration in 206L1 with Van Horn Blades when lightly loaded and low fuel. Two separate machines and two different pilots. In both cases pilots described the vibration as severe enough to the point where they thought they had a major component failure. Van Horns statement "The resulting vertical hop can become very uncomfortable" is very understated. Both incidents reported to Van Horn and other operators have been experiencing same issues hence the release of the Van Horn statement. In the first occurrence pilot naturally dropped collective which made the vibration worse. As Van Horn subsequently stated using cyclic to offload the disc and the frequency of Nodal Beam interaction resolves the issue. It has reoccurred numerous time since on our aircraft in a similar configuration and operating environment (mountain, turbulent/rough air). Below a news article of another operator a few days ago. ASL |
See also the thread "Campbell River fatality 24th Sept 2019" started by John Eacott on 25 Sept 2019.
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As a side note VHA blades seem to be very "rigid".
They don't have the same flex in them as Bell OEM blades. Easy to Track and Balance with usually just some PCL change and no tab required. Maybe a bit of span weight only presuming chord alignment is good during initial assembly. Strange for composite blades which I would naturally assume would have more "flex" than OEM metal blades? Our pilots have been experimenting with the "vertical hop" when low on fuel and no pax during mainly mountain flying. Can anticipate it and cyclic will offload the vibration. Not a good situation to get into for a new operator with new newly installed blades. OAT approx 7 DA 11k'+ Low gross weight (single pilot and fuel). Rough air due to local environment. |
Originally Posted by Salusa
(Post 11352169)
As a side note VHA blades seem to be very "rigid".
They don't have the same flex in them as Bell OEM blades. Strange for composite blades which I would naturally assume would have more "flex" than OEM metal blades? Our pilots have been experimenting with the "vertical hop" when low on fuel and no pax during mainly mountain flying... The discussion of "vertical hop" gives me the feeling the composite blades might be experiencing some sort of natural frequency excitation as they do their 360 degrees through a massively changing inflow from advancing to retreating. That may just not have been the case with the less stiff OEM blades. Worth watching the slow-mo GoPro footage from Chuck Aaron of a flexing blade (along with cyclic pitch changes) on the Red Bull Bo105 (with rigid rotor head) at: |
Originally Posted by Salusa
(Post 11352169)
As a side note VHA blades seem to be very "rigid".
They don't have the same flex in them as Bell OEM blades. Easy to Track and Balance with usually just some PCL change and no tab required. Maybe a bit of span weight only presuming chord alignment is good during initial assembly. Strange for composite blades which I would naturally assume would have more "flex" than OEM metal blades? Our pilots have been experimenting with the "vertical hop" when low on fuel and no pax during mainly mountain flying. Can anticipate it and cyclic will offload the vibration. Not a good situation to get into for a new operator with new newly installed blades. OAT approx 7 DA 11k'+ Low gross weight (single pilot and fuel). Rough air due to local environment. |
Originally Posted by Rotorhead84
(Post 11352581)
I've been hearing for a while now that the van horns are actually beating the crap out of helicopters. Especially utility ships. Premature failure of transmission mounts, bearings, etc. 110% rumor but thats why the OH58 blades aren't out yet too stiff.
We are flogging out Transmission Restraint Bearings and Restraint Support Elastomerics at a rate I've not seen before. Lateral vibes at ground Idle also bad. Not a balance issue as vibe improves with RRPM and are fine at flight Idle and hover. Less than. 0.08 IPS. Nodal Beams look fine and hardly ever changed one in the past. Reckon the VHA blades don't work with the frequency on Nodal Beams when light or minimum collective applied. Utility work machines. 206L1 /C30P/VHA Main Rotor Blades. |
Rotorhead84 & Salusa: Interesting. Well if pilots can feel a worse 'vertical hop' under certain conditions, then most of the parts of the helicopter are likewise feeling this, so it wouldn't be surprising if components failing earlier than on helicopters that are not experiencing such vibrations (to the same extent).
The 206L Noda-Matic nodal suspension system is likely still behaving much the same with either OEM or VHA blades as it is probably tuned to damp vibrations most effectively at the normal rotor blade passing frequency (which would be unchanged regardless of blade type and depends only on RRPM and number of blades). The VHA blades might be introducing vibrations at 'higher harmonics' which Noda-Matic isn't able to damp out. I found this set of university project slides on helicopter vibration absorption systems which gives a useful introduction to what is out there: http://ocw.upm.es/pluginfile.php/438...stem%20ARS.pdf Slide 7 suggests teetering rotors not great when it comes to rotor vibrations, another slide indicates the more blades the better when it comes to reducing vibrations, while slide 12 says it should be possible to design composite blades to achieve the desired bending and torsional rigidity. But I don't think any of that is trivial to get right! |
Aeroelastic tailoring was used to develop the Westland BERP blade.
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Severe tail wag on 206L at Idle with chord sweep above one point
Blades aligned string before install For lateral balance needed one point lateral sweep. Tailboom wagging like a cat on nip |
Interesting email from Van Horn this morning...
To our valued 206 Long Ranger Operators and Partners: This is an important update on Lightweight, High-Speed Vertical Vibration, and we appreciate both your attention to this message and assistance with relaying the information as widely as possible. Over the last 6 years, this issue has been reported to VHA and the FAA on only 15 aircraft out of an installed fleet of nearly 300. While most aircraft will likely never experience this phenomenon, it remains imperative for all pilots be aware of the conditions in which it may arise and the appropriate recovery method to apply if it is encountered. We have aggressively explored the issue over the past six months by conducting more than 60 instrumented flight tests using four different ships. The attached Service Bulletin, along with a forthcoming FAA-approved Flight Manual Supplement, represent The recovery method remains effective: DO NOT lower collective or enter an autorotation, but rather simply slow down and load the rotor; the vibration will cease almost immediately. The range of corrective actions has been expanded based on several aircraft configuration and maintenance items that have been identified as contributors. In some cases, the correction of one or more of the contributors has been sufficient to eliminate the vibration entirely. In all cases a significant reduction in severity and increase in the speed at onset has been achieved. I have first-hand experience of this 'vertical vibration'. The aircraft was configured with a single pilot, no passengers and less than 300lbs of fuel, typical of the configuration for others who have experienced the vibration. Describing what I experienced as a 'vibration' is a bit like saying Hitler was a 'bit naughty'! It was a violent vertical bouncing of the aircraft, accompanied by noises that I never want to hear in an aircraft again. There were a few seconds where I wasn't sure what the end result was going to be, it absolutely scared the hell out of me! I was running a GoPro looking inside the cockpit at the time so was able to provide footage to Van Horn. Ultimately, we removed the blades and sent them back. |
“I was running a GoPro looking inside the cockpit at the time so was able to provide footage to Van Horn.”
Can you share here? |
Can you share here? A couple of our pilots had reported what they thought was the onset of the 'vibration', both reported it at similar configurations. So I elected to take the aircraft out and see if I could replicate what they felt, I departed with 400lbs of fuel on board. Around the 300lb mark, a slight bounce became evident, you'll see me nod to the camera at the 00:11s mark to indicate I could feel something as I wasn't sure what the camera would pick up. The 'bounce' increased in amplitude so I applied lateral cyclic which, at the time, was a method to correct the phenomenon. The bounce did indeed reduce almost immediately, although it was still present. I continued on to see if it would develop again and this time would wait a little longer to see if it continued to increase in amplitude. I gestured again to the camera at 00:34s mark. When the bounce became uncomfortable, I tried the lateral cyclic again. This time the lateral cyclic had less of an immediate effect. Unfortunately, the video doesn't capture the sound properly as it added to the extremely unsettling feeling! |
Wow, that's horrible.
It reminds me of collective bounce I gave myself once in a longranger before I knew what I was doing |
Wow, that looks quite unnerving . Hard to ignore from Van Horns perspective I would imagine.
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Thanks for sharing that.... It may, in fact, give all drivers a heads up!!! That's why we share!!! :ok:
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I edited the swearing out of the last part of the video to protect any lip readers! :mad:
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Thanks!
When at Bell I troubleshot vibration issues across its fleet including the L and never had a report of,let alone experienced, anything like that with metal blades. |
I feel like it's only a matter of time before a tragic event happens, lawsuits to follow.
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