Go Back  PPRuNe Forums > Aircrew Forums > Rotorheads
Reload this Page >

Helicopter missing in the Med

Rotorheads A haven for helicopter professionals to discuss the things that affect them

Helicopter missing in the Med

Old 9th Jun 2020, 19:58
  #81 (permalink)  
 
Join Date: Feb 2015
Location: USA
Posts: 106
Originally Posted by Jack Carson View Post
Are there any other FBW S-92s in service around the world? Was the CH-148 Cyclone’s FBW flight control system certified by the US Government as well as Transport Canada? It appears that the lack significant accumulative experience on the system may be a contributing factor. Wasn’t there a similar incident with an NH-90 early on in it’s fielding.
I believe the only other fly-by-wire S-92 is N592SA, an early S-92 used as a fly-by-wire development article. Sometimes referred to as “S-92F”.
SplineDrive is offline  
Old 9th Jun 2020, 23:41
  #82 (permalink)  
 
Join Date: Feb 2001
Location: Sometimes here, sometimes there
Posts: 386
An FBW issue, or basic IAS awareness during a critical tactical manoeuvre at low level? I'm not sure if any pilot would restrict reaction purely due to VRS concerns, but lack of reaction to IAS loss early enough could easily result in an upset state and rapid loss of altitide.

Not quite the same scenario, but the Cormorant Alpha accident is always a chilling reminder how offshore visual flying can easily result in a tragic outcome.

https://assets.publishing.service.go...993_G-TIGH.pdf

Variable Load is offline  
Old 10th Jun 2020, 05:36
  #83 (permalink)  
 
Join Date: Apr 2000
Location: EGDC
Posts: 7,849
But that one happened at night in snow showers and 55 Kts of wind - not really comparable at all other than they flew into the sea.
crab@SAAvn.co.uk is offline  
Old 10th Jun 2020, 14:25
  #84 (permalink)  
 
Join Date: Mar 2007
Location: Hobe Sound, Florida
Posts: 739
Re Jack Carson’s post: there still aren’t detailed FBW regulations in either Part 29 or the attendant Advisory Circular. Therefore, if an applicant wants a certification, one goes the “ Special Conditions “ route, one fraught with minefields. Not impossible, of course, but it hardly adds anything of value to the process.

Re Post 73 and the link included. The impression provided by the article and its sources is uninformed with regard to the FBW subject.The S-92 FBW subsystem is supplied by BAE, who incidentally also supplied the FBW system for the V-22, 609, RAH-66, and 53K . And a list of FW aircraft.
SA also flew FBW systems on the X-2 and UH-60MU.

The first SA FBW system was the CH-54 rear facing pilot station in the 1960’s.
( Just for grins: local practice was that one did not get signed off as a Crane first pilot until demonstrating the ability to fly good traffic patterns while flying backward from the rear seat. Take-off from the ground to landing. ).
JohnDixson is offline  
Old 11th Jun 2020, 20:31
  #85 (permalink)  
CTR
 
Join Date: Oct 2007
Location: Texas
Posts: 145
Originally Posted by JohnDixson View Post
Re Post 73 and the link included. The impression provided by the article and its sources is uninformed with regard to the FBW subject.The S-92 FBW subsystem is supplied by BAE, who incidentally also supplied the FBW system for the V-22, 609, RAH-66, and 53K . And a list of FW aircraft.
SA also flew FBW systems on the X-2 and UH-60MU.
Funny that the article states that BAE supplies the FBW “system, or subsystem”. This is equivalent to the company supplying an engine’s FADEC being responsible for supplying the aircraft’s propulsion system. Not taking anything away from BAE, but they primarily only provide the FCCs. The system architecture and control law software falls under the primes. Actuation, power generation, etc, falls to other suppliers.

Last edited by Senior Pilot; 11th Jun 2020 at 21:00. Reason: Fix quote
CTR is offline  
Old 11th Jun 2020, 21:40
  #86 (permalink)  
 
Join Date: Mar 2007
Location: Hobe Sound, Florida
Posts: 739
CTR, my rsponse was aimed at the impression given by statements in the article like;”Shawn Coyle, a former Canadian air force helicopter test pilot, said he found the decision to install FBW technology on the Cyclones curious, given the fact that the civilian version has a conventional hydro mechanical flight control system with stabilization and autopilot features.

To make the technological leap to fly-by-wire, where computers replace standard hydraulics and cables, is "expensive and took a lot of time to get right," said Coyle,”

Perhaps Shawn displays a prejudice re FBW controls and I’d opine that if he had the opportunity to be involved in the design and development flying associated with that task, he’d change his stance. Now, this could easily turn into a thread regarding the reasons why the industry is transitioning to FBW for mid sized vertical lift and larger, but this thread is about the accident and the data from the recorders is needed so that may allow a rumor net to kick into second gear.
JohnDixson is offline  
Old 11th Jun 2020, 22:11
  #87 (permalink)  
CTR
 
Join Date: Oct 2007
Location: Texas
Posts: 145
Originally Posted by JohnDixson View Post
CTR, my rsponse was aimed at the impression given by statements in the article like;”Shawn Coyle, a former Canadian air force helicopter test pilot, said he found the decision to install FBW technology on the Cyclones curious, given the fact that the civilian version has a conventional hydro mechanical flight control system with stabilization and autopilot features.

To make the technological leap to fly-by-wire, where computers replace standard hydraulics and cables, is "expensive and took a lot of time to get right," said Coyle,”.
John, my commentary was really directed at the reporters that write technically inaccurate articles and inaccurately quote pilots and engineers. For example, computers do not replace any hydraulic complexity in the Cyclone.

I once was giving a flight line tour to a group of executives and poi out a FBW aircraft that was being serviced. One of the questions I was asked was “Why is a hydraulic cart hooked up to a FBW aircraft?”
CTR is offline  
Old 12th Jun 2020, 00:10
  #88 (permalink)  
 
Join Date: Mar 2005
Location: Poplar Grove, IL, USA
Posts: 851
“Why is a hydraulic cart hooked up to a FBW aircraft?”
That is awesome.

The latest press really doesn't answer any questions. As a former FBW guy I'd like to know.
IFMU is online now  
Old 12th Jun 2020, 10:14
  #89 (permalink)  
 
Join Date: Oct 1999
Location: Nigeria
Age: 53
Posts: 4,665
Originally Posted by IFMU View Post
That is awesome.

The latest press really doesn't answer any questions. As a former FBW guy I'd like to know.
I know nothing about the CH-148, but have climbed in and over the S-92 FBW development aircraft, and looking at the top deck it retained the standard hydraulic actuators, SAS and mixing unit as I recall. The only bit missing was the control rods from the actual cockpit controls. I think the fundamental difference from FBW Fixed wing, that typically use Electo Hydrostatic Actuators or Electo-Mechanical Actuators, is that in an aeroplane you can gain significant weight and complexity savings by reducing/removing the hydraulic distribution system. Whereas, the hydraulic pumps in a helicopter are almost co-located with the control actuators (for the Main Rotor) so this benefit cannot be obtained. That said, I am interested to know why helicopters cannot also use EMAs as I'm sure the control loads and input frequency for an F35's flying controls must be comparable to that of a helicopter MR, and this would take away the need for the primary hydraulic pumps and the TR Servo hydraulic lines (with their attendant vulnerability).
212man is offline  
Old 12th Jun 2020, 14:24
  #90 (permalink)  
CTR
 
Join Date: Oct 2007
Location: Texas
Posts: 145
Originally Posted by 212man View Post
I am interested to know why helicopters cannot also use EMAs as I'm sure the control loads and input frequency for an F35's flying controls must be comparable to that of a helicopter MR, and this would take away the need for the primary hydraulic pumps and the TR Servo hydraulic lines (with their attendant vulnerability).
For comparable weight vehicles, rotorcraft use an order of magnitude more hydraulic power and fixed wing aircraft. There is an AHS paper on the 12,000 lb 609 tilt rotor that shows it requires more hydraulic power for flight controls then a 138,000 lb MD 90 commercial jetliner. For conventional helicopters, the hydraulic power requirements are about 5 to 1 compared to fixed wing aircraft. So no, comparisons to the high performance F-35 fighter actuator power requirements do not extend to rotorcraft.

About a decade ago an attempt was made to install EMAs on a EH-101 for main rotor control. The HEAT project was appropriately named, since one major problem that halted further research was the inability to keep the actuators cool. Realize that with hydraulic actuator‘s, the cooling system comes for free.

Recently, under US Army FVL funding, Karem is developing an EMA rotor control using similar roller screw actuator configuration as HEAT. One significant difference however with the Karem design is the addition of pressurized oil circulation to each actuator to provide both lubrication and cooling. So the Karem EMAs will require hoses and pumps, same as hydraulic actuation ;-)

The biggest problem with EMA usage for rotorcraft swashplate control is the high probability of a jam failure mode. With linear hydraulic actuators, loss of fluid results in the actuator failing free to be back driven. This makes it easy to employ architectures with multiple cylinders either in parallel or series to provide redundancy. With EMAs, either rotary with gears or linear with screws, jam failure modes are very probable, and difficult to mitigate without adding considerable complexity and weight.

Remember on airplane you can have one actuator per surface, and multiple surfaces for redundancy. On a rotorcraft it is difficult to have multiple rotors for redundancy.

Hope my explanation makes sense.


CTR is offline  
Old 12th Jun 2020, 14:42
  #91 (permalink)  
 
Join Date: Oct 1999
Location: Nigeria
Age: 53
Posts: 4,665
Thanks CTR - that's great info!
212man is offline  
Old 13th Jun 2020, 10:36
  #92 (permalink)  
 
Join Date: Apr 2000
Location: EGDC
Posts: 7,849
Every day is a school day in aviation thanks CTR
crab@SAAvn.co.uk is offline  
Old 13th Jun 2020, 11:16
  #93 (permalink)  
 
Join Date: Mar 2007
Location: Hobe Sound, Florida
Posts: 739
Question, CTR: is that Karem project including higher harmonic control aspects?
JohnDixson is offline  
Old 13th Jun 2020, 14:59
  #94 (permalink)  
 
Join Date: Feb 2015
Location: USA
Posts: 106
CTR - good description of EMA challenges on rotorcraft. I was essentially going to say that on most applications I’ve studied, electrical main rotor actuation is heavier and often more complex than hydraulic. I’ve seen plausible electric actuation of tail rotor type applications where demands are lower.

Originally Posted by JohnDixson View Post
Question, CTR: is that Karem project including higher harmonic control aspects?
Yes, Karem’s rotor is rigid both in the flap-wise and edge-wise direction and they are going to attempt to use higher harmonic blade control to largely cancel the ludicrous levels of 3P such a three bladed design will generate, especially during non-axial flow flight. At least the primary driving blade harmonic is 2P, so perhaps more predictable and at a low enough frequency to for the system to respond to. Will definitely be a challenge, though... the state of the “force generator” that is being controlled is far more complex than a simple rotating mass like many current active vibration control systems. Now you have a latency and knowledge problem with understanding the aircraft vibrations, and a lack of precise force output knowledge with the “force generator” that doesn’t exist with a rotating mass system.
SplineDrive is offline  
Old 13th Jun 2020, 15:27
  #95 (permalink)  
CTR
 
Join Date: Oct 2007
Location: Texas
Posts: 145
Originally Posted by JohnDixson View Post
Question, CTR: is that Karem project including higher harmonic control aspects?
Yes. Karem has constructed a ground test stand and plans to test a rotor with IBC (Individual Blade Control). The EMA roller screws will be in the turning rotor frame of reference, requiring all electric power and cool fluid to pass through a slipring/ swivel.



CTR is offline  
Old 13th Jun 2020, 17:52
  #96 (permalink)  
 
Join Date: Feb 2015
Location: USA
Posts: 106
Originally Posted by CTR View Post
Yes. Karem has constructed a ground test stand and plans to test a rotor with IBC (Individual Blade Control). The EMA roller screws will be in the turning rotor frame of reference, requiring all electric power and cool fluid to pass through a slipring/ swivel.
CTR, a correction - the electrical power is generated in the rotating frame, not the stationary. This was done explicitly to avoid the reliability problems associated with sliprings. I suspect the oil cooling system is also contained in the rotating system... no real reason to pass it through a hydraulic coupling if the purpose is for cooling the electric actuators. There’s room for an oil cooler.
SplineDrive is offline  
Old 13th Jun 2020, 19:35
  #97 (permalink)  
CTR
 
Join Date: Oct 2007
Location: Texas
Posts: 145
Originally Posted by SplineDrive View Post
CTR, a correction - the electrical power is generated in the rotating frame, not the stationary. This was done explicitly to avoid the reliability problems associated with sliprings.
Splinedrive. I was basing my statement on the patents filed by Karem. So my statement may be out of date, having been based on earlier configuration.

I have not yet seen in a published application a configuration with generators and cooling in the spinner. I’ll do a search.....

https://patents.justia.com/patent/8235667

This is the latest I can find, and it’s back from 2009. Can you direct me to any later information? I have looked at power generation for IBC in the rotor under research I was doing. But the differential speed between the mast and the rotor required a heavy gearbox to get adequate speed for the generator. Would be interesting to see how he got around this issue.




Last edited by CTR; 13th Jun 2020 at 19:55.
CTR is offline  
Old 13th Jun 2020, 21:16
  #98 (permalink)  
 
Join Date: Mar 2007
Location: Hobe Sound, Florida
Posts: 739
Thanks, CTR-looks like higher harmonic control is headed for a real flight evaluation.
JohnDixson is offline  
Old 14th Jun 2020, 15:18
  #99 (permalink)  
 
Join Date: Feb 2015
Location: USA
Posts: 106
Originally Posted by CTR View Post
Splinedrive. I was basing my statement on the patents filed by Karem. So my statement may be out of date, having been based on earlier configuration.

I have not yet seen in a published application a configuration with generators and cooling in the spinner. I’ll do a search.....

https://patents.justia.com/patent/8235667


CTR, my understanding of the system is more recent than 2009, but I don’t have a source handy. I’ll dig around. The patent you linked didn’t really address where power comes from that I noticed.

Generating in the rotating frame does certainly add a gearbox, but a slip ring capable of the power levels and reliability levels required wouldn’t be simple or light, either. I fully admit that I could be remembering incorrectly.

Karem is doing some good research at full scale. I think it’s another significant stretch to integrate their rotor into a practical large aircraft, but they’re making good steps.

This thread has diverged pretty far afield from the CH-148 crash in the Med.
SplineDrive is offline  
Old 14th Jun 2020, 20:40
  #100 (permalink)  
 
Join Date: Dec 2000
Location: Arlington, Tx. US
Posts: 607
Originally Posted by JohnDixson View Post
Thanks, CTR-looks like higher harmonic control is headed for a real flight evaluation.
Real flight tests of a higher harmonic control was conducted by Hughes on a OH-6 in the early 80”s. Lot of pre-flight press and zero coverage post test flights. Those in the know indicated that the mechanical components between actuators and blade beat themselves to death in a very short period of operational time. Concept shelved as impractical.

Even with moving the entire thing to the rotating system, who thinks individual independent blade control is a good idea? There are so many failure modes the system safety assessment would be a nightmare (except for Boeing who doesn’t bother with such trivia). Any failure due to mechanical, wiring, electronic, or environmental (lightning) which results in the loss of pitch control to one blade is a catastrophic event which requires 1 in a billion level of reliability. So everything has to be independently triple redundant and impervious to common mode failure (lightning again). Concept impractical at the the most casual analysis.

Last edited by The Sultan; 15th Jun 2020 at 02:39.
The Sultan is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.