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Vortex Ring Advise?


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VR;

 

That a/c had a bleed valve tach box failure, this was not detected for two years due to everyone thinking that the pilot had vortex ring. The truth came out when the company which bought the wreck went to overhaul the tach box and found that a diode had burnt out. If the driver had had some gauges in the floor he would have be able to tell that the bleed valve had not closed and topped the engine which caused the low rotor problem. He thought that his engine had failed like had happened not too long before to a sister ship, lowered collective and pulled at the bottom, walked away sans helicopter. Shoulder harness and helmet saved his life, floor of cabin buckled, cabin roof broke open, was not pretty. His story was true and no one would believe him, I did because I was there to do the investigation, he had dropped one of the bags already and was heading off to drop another when the rotor rpm decayed, pretty hard to get into VR state on takeoff over flat terrain. The bags were all on top of each other but there was one that was not hooked to carousel and under all the rest, showing that infact he had released one bag. Kodiak data showed average rate of descent on final to be under 300 fpm as well. Seemed like no brainer to me but the investigation was dropped as was easier and cheaper to blame the pilot for VR state. Lesson-do not stop the investigation unless you are COMPLETELY satisfied with the results.

 

sc

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It is good to finally hear the accurate data there Skully! All these years the experts were dictating Vring! As per the other topic - maybe our TSB investigations need to be more through and processed a little faster to get need to know info out to the rest of the operaters for a life saving, insurance reducing benifit to all involved! They are short staffed as we all are but maybe this is where Ottawa shoud put in some extra effort!

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Keep the disc loaded on approach and keep it under 500fpm. If you don't....wellll "it's a long alley without trash cans". Allouettes II & III will tell you before you get into VR unless you are legally deaf.........Bells don't.

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OK,

My input on how to get into it:

Fly into wind at HIGH height (2000-3000 AGL), slow down, with slight power on, when about 30 KIAS turn downwind and watch yourself go down! You don't need to actively slow down any, as the turn will do that for you, and when you are downwind, you WILL go down (if you have any wind at all). Its out of Shawn Coyle's book, Cyclic and Collective.

 

It works! Almost scared the #### outa' me! :D

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There is another scenario to watch for, sometimes in seismic you are required to move equipment downwind, not an issue for the astar but have heard that if the wind is strong and can push your vortices ahead of the aircraft and you settle into them the vortex ring state that you enter is extremely fast and violent. Have never had the pleasure but know some who have and say that normal VR state is a gentle #### cat compared and you slow WAY down after that.

 

 

 

sc

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Skully.....I have had that happen in a 407.... had my head up my ***, moving from one line to another, about to overfly the first drop. Did a tight 180 degree turn with lots of peddle so's not to loose sight of the flag and did a flat "skid" of sorts. (the flight path was level, disk was tilted) It was very sudden, definatly not a downwind/mushing lack of power kinda thing. That was the first and last time for that one! I was a bit downwind when I started the turn ..(it was off my 7 or 8:00 I think)...still not sure if it was because I had air coming in through the top of the disk (downflow) or if I was skidding enough to have air effectivly hitting me from below (upflow)

 

DMNH

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  • 2 weeks later...
Anyone ever get into it in an S76?

Part of my training at Helijet included a demonstration of vortex ring state, at night over the water between Boundary Bay and the Gulf Islands. Scared the crap out of me.

 

The night autos in Abbotsford were fun in comparison.

 

RH

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That a/c had a bleed valve tach box failure, this was not detected for two years due to everyone thinking that the pilot had vortex ring. 

 

His story was true and no one would believe him, I did because I was there to do the investigation.

 

Lesson-do not stop the investigation unless you are COMPLETELY satisfied with the results.

 

sc

I don't think it's quite true that no one believed his story. There were certain elements that didn't make sense but I believed that something had gone wrong. As you may recall SC, I convinced that former Royal Navy insurance investigator of that fact (you remember the guy...his name was Ian but FN kept introducing him to everyone as "John"...at which time Ian would produce a card that said "Ian" in large letters...but FN failed to notice this...that was repeated at least 10 times over 2 days...and then, finally, Ian was walking down the hall with FN chasing him yelling "John! John!" CU and I couldn't stop laughing).

It was the input of Bob Waldron and the acquiesence of the parent company (which simply wanted the cheque...of course the company entered bankruptcy protection within a couple of days of this incident) that resulted in a "Pilot Error - Case Closed" situation. The final report I wrote specifically denied the possibility of Vortex Ring...so I'm not quite sure who you think should have kept investigating (you've hurt my feeling slightly). When they told me the engine "ran fine" in the test cell, as if that was a surprise, I knew no one was listening. The engine was "running fine" on the ground and had to be shut down by the pilot...so where's the surprise that it ran in the test cell? You may also recall that I told you last year that I was theorizing it was the bleed valve and that's when you told me about the diode in the tach box...but, to paraphrase Sherlock Holmes, "have you considered the dog barking in the night Watson?"

 

As for Vortex Ring in general, there is an excellent thread on this subject on PPRUNE. The input of Nick Lappos and Shawn Coyle is spectacular. They are in agreement, for instance, in denying the possibility (or at least the "likelihood") of entering VR at a low rate of descent such as 300 fpm. Although I don't agree with everything they say (some of it seems contrary to my personal experience)...the raw data is excellent. Many pilots do not know that VRS begins near the mast. When the induced downward velocity of air through the disc is exceeded by "upflowing" air (whether from a ROD or from "upflow"), the air begins to recirculate. This explains why a "light" helicopter does, in fact, get into VRS more easily than a "heavy" one (at least that has been my experience with 500's and Astars). Windtunnel tests (I have read the results...I don't have any personal involvement in that kind of thing) have shown that in all cases of VRS the mainrotor continues to produce lift. BUT, when the air through the centre of the disc stalls out a portion from the mast to outboard, and this combines with the ever-present "Wingtip Vortices", there (in most cases) isn't sufficient lift to support the weight of the helicopter. This also explains why a light, falling helicopter stops, almost magically, in a low hover...if you're lucky enough to have a nice, flat spot under you that is! Not for the squeamish in any case...and I'm way too squeamish. :shock:

 

HV

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