Van Horn blades

[malabo]

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 (https://www.tsb.gc.ca/eng/enquetes-investigations/aviation/2019/a19p0142/a19p0142.html)

[wrench1]

Anybody know more?
I haven't heard anything on the Van Horn B model blades but the L model MR blades had an FAA AD issued last month for delamination checks.
Van Horn Blade AD 2022-22-08 (https://drs.faa.gov/browse/excelExternalWindow/FR-ADFRAWD-2022-25030-0000000000.0001)

[Salusa]

VHA News (https://vanhornaviation.com/2022/03/22/206l-vertical-hops/)

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 (https://demerarawaves.com/2022/12/07/pilot-who-voiced-concern-about-unsafe-helicopter-dismissed-gcaa-confirms-chopper-grounded/)

[helispotter]

See also the thread "Campbell River fatality 24th Sept 2019" started by John Eacott on 25 Sept 2019.

[Salusa]

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.

[helispotter]

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...

Yes, my gut feeling was also that composite blades would be more flexible. But then I did a quick check of material comparative properties. Flexibility dictated by a parameter called Young's Modulus, or Modulus of Elasticity, "E". For Aluminium alloy, being the skin of a regular blade that is around 70 GPa. For unidirectional Carbon Fibre Epoxy Resin I see figures in the range of 135 to 183 GPa. So if the 'skin' of the composite blades has same thickness as alloy blades, it would have around double or more the stiffness. But I imagine the composite skin is much thicker than the alloy skin so stiffness of blades will be even more times that of the OEM ones.

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: https://www.youtube.com/watch?v=Pu48f7s5Ru8 (you can see when blade is in aft position when the tail boom / tail rotor sweep into view). Perhaps it would be worth VHA doing the same visualisation with some of their blades under the conditions described and then repeat visualisation with regular OEM blades as a comparison.

[Rotorhead84]

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.

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.

[Salusa]

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.

Interesting R84.

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.

[helispotter]

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/mod_label/intro/MC-F-011%20Vibrations%20Absortion%20%20System%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!

[[email protected]]

Aeroelastic tailoring was used to develop the Westland BERP blade.

[Salusa]

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