PPRuNe Forums

Go Back   PPRuNe Forums > Aircrew Forums > Rotorheads
Forgotten your Username/Password?

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


Reply
 
Thread Tools
Old 11th Jan 2010, 19:02   #1 (permalink)
 
Join Date: Apr 2007
Location: Center of the Universe
Posts: 596
Cobham/Chelton HeliSAS

Wondering if anyone has insight/opinions re this product? Recently issued STC for R44 and TSO'd, with STC for 206 and 407 said to be in the works for first half 2010. Here are some links which provide a fairly comprehensive description and demo:


http://www.helisas.com/UserFiles/Fil...alOverview.pdf







Thanks,

EN48
EN48 is offline   Reply
Old 11th Jan 2010, 21:23   #2 (permalink)
 
Join Date: Mar 2003
Location: the hills of halton
Age: 61
Posts: 722
I never heard low cost and military in the same paragraph before . I wonder What the installed cost is , what percentage of deliverd R44 have hyd coost ?.
widgeon is offline   Reply
Old 11th Jan 2010, 23:16   #3 (permalink)
 
Join Date: Apr 2007
Location: Center of the Universe
Posts: 596
Quote:
I wonder What the installed cost is ,
Cobham has been quoted in the press IIRC as saying that the cost for an R44 is expected to be in the $55,000 to $65,000 area. I have seen estimates for this system in turbine helicopters which are higher than this. "Low cost" is no doubt in reference to other helicopter autopilots, not absolute cost. While perhaps not economic for a privately owned R44, it may be appropriate for an R44 used in law enforcement, ENG etc. And for a 206 or 407, which seem to be on the certification agenda, an installed cost of $75,000 to $100,000 may be reasonable given the alternatives, provided it performs as advertised.

Last edited by EN48; 12th Jan 2010 at 11:24.
EN48 is offline   Reply
Old 12th Jan 2010, 09:54   #4 (permalink)
 
Join Date: Mar 2003
Location: the hills of halton
Age: 61
Posts: 722
That does sound like a good price ( sorry for my spelling ) my recollection of the SFIM was that the computer alone cost close to that price. The demo tape is impressive though.But as my phone now has more computing power than my first computer this sounds reasonable.
widgeon is offline   Reply
Old 12th Jan 2010, 11:47   #5 (permalink)
 
Join Date: Dec 2001
Location: Philadelphia PA
Age: 64
Posts: 1,806
I flew an early prototype at least 5 years ago with Roger Hoh, the developer. The article appeared in Helicopter World, I believe. Anyone who wants to pm me can have the draft of the report.
I was impressed - it was designed to work best in forward flight, but actually made hovering slightly easier as well. Well thought out - but then again you'd expect that from Roger, who wrote most of the new military handling qualities specification for helicopters.
Without droning on, during a long transit from one airport to another (including liftoff and touchdown and transition to and from cruise), I needed to press the trim release a total of 5 times. The device moves the stick, and in the light turbulence encountered, it moved the stick about half a second before I would have made the same correction.
Nice to see they have it approved! Just wish it hadn't taken so long.
Shawn Coyle is offline   Reply
Old 15th Jan 2010, 01:37   #6 (permalink)
 
Join Date: Jul 2002
Location: Lost in thought
Posts: 79
I think it's a great idea that someone has put a low-cost autopilot system for helicopters on the market. I think it is a great pilot aid for VFR flight. But ironically, the one thing this system is NOT is a "SAS." The name choice is most unfortunate because it is misleading.

The reason the Chelton/Hoh system is low cost is because it uses "parallel" actuation only. That means it works in parallel on the controls, applying force through a spring. It's like having someone in the other seat on the controls applying force to correct your flying. But other than the sensation of spring force back to the pilot, there is no real assistance to stability when the pilot is on the controls.

A true Stability Augmentation System (SAS) or in some cases a Stability and Control Augmentation System (SCAS) works in "series" with the controls and adds or subtracts from the pilot's control inputs in order to augment the stability or boost the control input as the flight situation demands. For example, in turbulence a governed power system will increase and decrease power which in some helicopters leads to tail wag. A true SAS or SCAS system will detect the power changes, see the wag, and put in the corrective yaw control before the pilot even notices. And all this happens without the pedal positions ever moving. A true SAS or SCAS does this same thing on pitch, roll and yaw and actually improves the flying behavior of the helicopter. It can fix handling quality problems like the power/attitude to airspeed/altitude relationship. This is especially important when you are trying to meet the stability requirements specified in Appendix B of the FAR 27 and 29 for IFR.

So a helicopter autopilot with "true" SAS will have fast-moving series actuators to improve handling and stability, and slower-moving parallel actuators to control the helicopter when the pilot is off the controls. The SFIM autopilot mentioned (which became SAGEM and now SAFRAN) has a basic 2-axis autopilot (pitch and roll parallel trim actuators) with a 3-axis SAS (pitch, roll, and yaw series actuators) So this system provides a true SAS. To that you can add a yaw damper computer with another parallel actuator on the pedals. To that you add a flight director computer for coupled ILS and the like. (In true SAGEM fashion, the intent seems to be to sell as many boxes as possible.) This causes it to be a somewhat overpriced system with a more-complex-than-necessary installation. But it is a more capable system.

IFR Helicopter autopilots like those in the S-76 and 412EP usually require 2 sets of series actuators on each axis driven by independent computers. (That means the system has 6 series and 3 parallel actuators) . Each of the flight control computer uses a separate set of flight sensors. This is because the series actuators operate rapidly enough so that if something went wrong, they could turn the helicopter "dirty-side up" before the pilot could notice it and grab back the controls. So you need a second system, just as powerful as the first that will immediately add or subtract control input in the opposite direction to keep the helicopter "dirty-side down." This is called "fail passive" operation.

4-axis autopilots add a 4th trim actuator on the collective. 4-axis autopilot allow you to couple both a speed and a vertical mode (like glideslope) at the same time. This is really nice for the new WAAS steep helicopter approaches where you want to have the glidelope on collective and speed on pitch.

But back to the "HeliSAS" system: It is a 2-axis (pitch and roll) parallel-actuator only autopilot system. (2 faster moving actuators than traditional trims as I understand it). It can fly the cyclic when you need it, and nudge in corrections to your hand flying when you are on the controls. In a lot of cases, that's good enough and it's a handy aid to have. Unfortunately all these systems are called "Autopilots" and the word SAS in the name doesn't mean you are getting one. Be sure you know what you need and what you're getting.

Last edited by Avnx EO; 15th Jan 2010 at 01:54.
Avnx EO is offline   Reply
Old 15th Jan 2010, 19:06   #7 (permalink)
 
Join Date: Apr 2007
Location: Center of the Universe
Posts: 596
Quote:
Be sure you know what you need and what you're getting.
Thanks for the lesson, Avnx. Very useful. I am in the process of equipping a new B407 (VFR only) and have made inquiries about certified SAS/autopilots for this helicopter. AFAIK to date, the only other candidate is a SAGEM/SAFRAN unit marketed through a Bell subsidiary. The informal feedback I have been getting on this unit can be summarized as follows: expensive ($200,000+), unreliable, poorly supported (at least in the US). Wondering if this is substantially correct and if there are other alternatives STC'd for the B407?
EN48 is offline   Reply
Old 16th Jan 2010, 01:48   #8 (permalink)
 
Join Date: Dec 2001
Location: Philadelphia PA
Age: 64
Posts: 1,806
Avnx EO:
There is no officially designated definition for what constitutes a SAS. I've used an academic definition in my book (and flight test lectures) to help students understand what the various terms may mean.
But every manufacturer is free to call their system whatever they want.
This system combines the series and parallel actuators into one system (wish I knew exactly how they did this - must be pretty clever).
It's an object lesson to all of us to make sure you know what the terms mean and how the system operates.
Shawn Coyle is offline   Reply
Old 16th Jan 2010, 02:27   #9 (permalink)
 
Join Date: Jul 2002
Location: Lost in thought
Posts: 79
Actually AFAIK, the "Bell Subsidiary" picked up the SAGEM/SFIM STC as part of the package deal when HAS went bankrupt (i.e. they didn't specifically go out and choose that system.) My understand is that the Chelton/Hoh system is not yet certified on the 407. And If I were them I'd do the 206 first before biting off the 407. The 407 is likely to be a bit of a challenge because of the control responsiveness compared to a 206 or R44.

If it works on the 407, I think the Chelton/Hoh might be a smart buy. As long as you keep in mind its limitations. But until it's certified for the 407, I'm a skeptic when it comes to what people promise in autopilots. Marrying autopilot to airframe is an artform. Just because it works on one model doesn't mean it will perform anywhere near the same on another. I've seen people stuck with a non-working, uncertifiable system and a half disassembled aircraft. (The HAS-promised 427 autopilot based on the 407 SFIM/SAGEM is a classic example of that.)
Avnx EO is offline   Reply
Old 16th Jan 2010, 02:56   #10 (permalink)
 
Join Date: Jul 2002
Location: Lost in thought
Posts: 79
Shawn... it can't be a "series" actuator unless its in "series". I've seen the installation and it is a parallel actuator (they don't cut the control tubes to put in the actuator.)
I've also heard that same statement: that they "combine" the series and parallel actuators into one. That's a bit of an overstatement. You can't apply a series input with a parallel actuator.... by definition. What I understand they are doing is using a fast-moving parallel actuator that is limited from large authority over-travel by clever monitoring. This allows the system to be responsive enough for the fast and fine control movements in small scale (like those traditionally done by a series SAS actuator) but then still use the same actuator for the long-travel slower positioning one needs for trim centering.

This is a truely cost-effective and clever way to do a hands-off system. But other than the nudges it gives you in parallel to your own actions, there is no handling quality improvement to the extent you get with a true SAS with the pilot hands-on.
Avnx EO is offline   Reply
Old 16th Jan 2010, 03:44   #11 (permalink)
 
Join Date: Jul 2002
Location: Lost in thought
Posts: 79
One more thing....
Quote:
There is no officially designated definition for what constitutes a SAS
If I go to AC 27-1B Appendix B section b(6) Stability Augmentation System it states:
Quote:
If a SAS installation stabilizes the rotorcraft by allowing the pilot to "fly through" and perceive a stable, well behaved vehicle, it qualifies as a SAS...
That's the FAA's definition of a SAS per the advisory material, and it is pretty clear to me that it applies to the "hands on" flying behavior. And in order for the pilot to perceive something different than the rotorcraft's natural, (usually unstable) control behavior, you have to break the direct link from the pilot to the control and add or subtract input as required. That's certainly most people's understanding of what constitutes a SAS.

I'm not saying its a bad system. But if it's primarily a hands-off system, it's a clever autopilot - not a SAS.
Avnx EO is offline   Reply
Old 16th Jan 2010, 12:45   #12 (permalink)
 
Join Date: Apr 2007
Location: Center of the Universe
Posts: 596
Quote:
And If I were them I'd do the 206 first before biting off the 407. The 407 is likely to be a bit of a challenge because of the control responsiveness compared to a 206 or R44.

According to press coverage, this is the plan. Cobham/Chelton has announced that they will do the 206 first, followed by the 407. The link in my first post to the Technical Description of this system actually shows photos of the servos installed in a 206.

Here is an excerpt from a recent press release:

"Previously, Cobham has received a Supplemental Type Certification (STC) from the FAA for HeliSAS use in a Robinson R44 helicopter, which the Company announced on 23 November 2009. Cobham is in the process of achieving HeliSAS certification for use on the Bell 206, Bell 407, Eurocopter AS350, and the U.S. Navy's Bell-made TH-57 helicopters"

Your point about being wary until it is certified on the 407 is well taken, as aviation is full of missed expectations.

Another Cobham/CHelton press release:

News
October 19, 2009 (MINERAL WELLS, Texas) Cobham Avionics announces that HeliSAS certification activities have begun on the Bell 206B and 407 helicopter models. Cobham is partnering with Edwards & Associates, Piney Flats, TN, for HeliSAS installation and certification on the Bell rotorcraft. The two-axis VFR STC program on both of these models is currently in the flight testing stage at Edwards, and early B206B results have been positive. In addition, HeliSAS components are being fitted on the B407, which is expected to be in flight test by early December.
FAA certification on the B206B is anticipated in January, 2010 with the B407 to follow by April. Cobham Avionics has also plans to introduce HeliSAS on the Eurocopter AS 350 models and EC 120 later in 2010.

Last edited by EN48; 16th Jan 2010 at 14:22.
EN48 is offline   Reply
Old 11th Feb 2010, 04:21   #13 (permalink)
Probationary PPRuNer
 
Join Date: Feb 2010
Location: California
Age: 36
Posts: 1
You obviously know a thing or two about autopilots... but this IS a SAS. You definetely have to demo this one. You WILL be impressed.
MATLABer is offline   Reply
Old 11th Feb 2010, 11:36   #14 (permalink)
 
Join Date: Sep 2002
Location: in the office
Age: 34
Posts: 39
I contacted Cobham/Chelton after they received the FAA STC for the R44 and was told they weren't currently considering EASA certification, then a week or so ago I contacted them again for another R44 customer and was told that due to insurance issues the equipment was not currently being sold for R44's. I'm not quite sure what the state of play is.
Tallguy is offline   Reply
Old 11th Feb 2010, 14:35   #15 (permalink)
 
Join Date: Apr 2007
Location: Center of the Universe
Posts: 596
Quote:
I'm not quite sure what the state of play is.
Cant comment on the status of HeliSAS for thr R44, or EASA cert status. Re the 206 and 407, Cobham has announced previously that they are working jointly with Edwards & Associates (Bell subsidiary) on the 206 and 407 STC's. I have spec'd this on a new 407 currently being completed for delivery June, subject to the STC being complete. Look for more specific info at HAI next week. Am being told by some insurance types that this system may be seen as a safety device which might result in lower premiums for acft so equipped.
EN48 is offline   Reply
Old 11th Feb 2010, 21:24   #16 (permalink)
 
Join Date: Dec 2008
Location: Las Vegas
Age: 27
Posts: 6
Is Chelton a common FMS ? In one of my classes at Embry-Riddle we learned to use Chelton, I thought it was great but don't know when I will ever use it.
DeltaFoxy is offline   Reply
Old 23rd Feb 2010, 23:12   #17 (permalink)
 
Join Date: Apr 2007
Location: Center of the Universe
Posts: 596
Quote:
Is Chelton a common FMS ?
Depends on what the meaning of "common" and "FMS" is. The Chelton (now Cobham) Flight Logic system is AFAIK the only FMS STC'd (and appropriate) for installation in light helicopters. However, one doesnt find all that many installed. There are other glass panel displays installed even more rarely (Sagem now and Garmin G500H once certified) but these dont fit the common understanding of what constitutes an FMS as these require a separate (not integrated) navigation system, usually a GPS such the Garmin 430/530. Some may consider the 430/530 a reduced function FMS, but these are more properly called GPS navigators IMO.
EN48 is offline   Reply
Old 24th Feb 2010, 12:28   #18 (permalink)
 
Join Date: Nov 2004
Location: London
Posts: 393
I fly the Chelton EFIS system in a fixwing. It's a very good piece of kit however there is a lot of button pushing. Updates are done through Jeppesen and are very easy, the terrain and obstruction database I find useful when landing at smaller airports often in mountainous terrain decending IFR. So I imagine it would be very good also in a helicopter when flying in marginal conditions.
nouseforaname is offline   Reply
Old 10th Apr 2010, 16:50   #19 (permalink)
 
Join Date: Apr 2007
Location: Center of the Universe
Posts: 596
I had an opportunity to fly a B407 with the Chelton HeliSAS this week. Quite impressive and a definite safety enhancer. We tried a number of extreme attitude manuevers and found that the system returned the helicopter to straight and level with no drama by simply releasing the cyclic. Handles a coupled approach nicely, which may be useful for IIMC encounters. I have no other experience with helicopter autopilots, but do have substantial airplane AP experience and the HeliSAS seems quite comparable to AP's used in light SMEL airplanes.
EN48 is offline   Reply
Old 11th Apr 2010, 03:51   #20 (permalink)
 
Join Date: Mar 2008
Location: Indiana
Age: 57
Posts: 43
That's very cool. I have been talking to them for the last 6 months about getting the whole system put in my Eurocopter EC130, but i can't get them to give a price or tell me how long it would take. It looks like a great system and I love the Chelton in my Enstrom. I was hoping to put it in the EC 130 and add the autopilot. I think now, i am going to do the new Garmin G500H and give up on the Heli-SaS...now I have to wait on the darn stc for the Garmin.
chucksweet is offline   Reply
Reply
 
 
 


Thread Tools


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT. The time now is 19:39.


vBulletin® v3.8.7, Copyright ©2000-2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
1996-2012 The Professional Pilots Rumour Network