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cirrus sr22

Old 3rd Nov 2011, 23:56
  #301 (permalink)  
 
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Originally Posted by BackPacker View Post
Mmm. My gut feeling tells me that that might be a bad thing actually. If you have a partially deployed chute slowing you down, it may (will?) slow you down below stall speed so you lose wing lift. But at the same time the chute is not fully deployed so it may not fully cushion the vertical speed. Additionally, it will take time for the aircraft to dangle backwards, vertically below the chute so initially there may be an increase of vertical speed. In an EFATO scenario, that might just happen to be the point where you hit the ground.
You are asking excellent questions. Well done.

However, it is important to realize that "it will take time" requires just 8 seconds to completely eliminate all forward velocity after activating CAPS and achieve a level attitude under canopy.

Rapid deployment was a design criteria enabled by the ballistic rocket extraction of the parachute into the slipstream. Very effective. Very short time period. Think about how short 8 seconds can be in an emergency response!


Cheers
Rick
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Old 4th Nov 2011, 00:21
  #302 (permalink)  
 
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That's pretty impressive. So what's the minimum altitude for succesful CAPS deployment in an EFATO situation, assuming more or less level flight? About 500' or so?
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Old 4th Nov 2011, 00:26
  #303 (permalink)  
 
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Originally Posted by Backpacker View Post
In addition to this, somebody mentioned that if you're sitting more or less upright, and are properly strapped in, your body can sustain 50G in the horizontal, but only 15G or so in the vertical, because your spine is relatively weak in compression. I haven't done the sums (and they would depend on the size of the horizontal and vertical crumple zone anyway) but based on this it may well be that crashing horizontally into something at stall speed is more survivable than crashing vertically into something under a partially inflated chute. (But I'll take a fully inflated chute over an unrecovered spiral dive any day!)
What forces are survivable are subject to experimentation. What forces are experienced in an airplane crash are empirical.

And you don't really want to be in a crash where the forces exceed survivable limits.

First, consider crashing at stall speed. For calculation purposes, the Cirrus SR22 stall speed is 59 knots. FYI, observable airspeeds in a Cirrus spin have been consistently 100 knots and spiral descents are often in excess of 180 knots. In comparison, under canopy the vertical descent is 17 knots (1700 fpm, 20 mph, equivalent of a 13 foot drop).

If you hit something, the energy dissipated is related by the square of the velocity. Hence, the impact at 59 knots stall speed has 12 times more energy to dissipate. (FYI, those other speeds have 34 and 112 times more energy.)

Ah, the claim is made that the human body can withstand greater horizontal forces than vertical forces. Except, ground impacts are rarely one-dimensional and consequently the human body is subjected to significant forces in other dimensions. And there is the problem of restraints failing at higher than specified forces. The current restraint specification is 26G forward deceleration.

For me, I would much, much prefer to activate the CAPS parachute a few seconds earlier and descend vertically under a fully inflated parachute than risk a higher energy impact.

Cheers
Rick
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Old 4th Nov 2011, 00:35
  #304 (permalink)  
 
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Originally Posted by BackPacker View Post
That's pretty impressive. So what's the minimum altitude for succesful CAPS deployment in an EFATO situation, assuming more or less level flight? About 500' or so?
Yes, 500' AGL is a convenient rule of thumb.

Flight instructors involved with the Cirrus full-motion simulators and the Cirrus Pilot Proficiency Program (CPPP) have established two altitudes for loss of engine power on takeoff and the following guidelines based on the viability of the CAPS parachute system:
  • Below 500' AGL: NO CAPS!
    Plan a departure briefing with options to land straight ahead
  • Above 500' AGL: CAPS NOW!
    Immediate action is required due to the observed delay in recognizing an emergency and then taking action, before the aircraft descends below a viable altitude for using CAPS
  • Above 2000' AGL: CONSIDER CAPS!
    Note that this is higher than pattern altitude, and it provides sufficient altitude to make choices, but stay alert for descent through 500' AGL when CAPS may be a better choice than an off-airport crash.
These procedures are accompanied by guidance on developing a departure briefing. What altitude is 500' AGL? 2000' AGL? What are my options below 500' AGL? Where will I be if I climb at Vy to 500' AGL? How can terrain affect my options? Etc.


Cheers
Rick
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Old 4th Nov 2011, 14:18
  #305 (permalink)  
 
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If you hit something, the energy dissipated is related by the square of the velocity. Hence, the impact at 59 knots stall speed has 12 times more energy to dissipate. (FYI, those other speeds have 34 and 112 times more energy.)
Just out of curiosity (and boredom) I decided to look up the relevant formula, plug in these numbers and see what I got.

v1^2 - v0^2 = 2ad, where:
v1 = initial velocity
v0 = terminal velocity
a = acceleration
d = distance travelled

In the vertical descent under a canopy case (17 knots as quoted = 8.75 m/s), my estimate is that the "crumple zone" is 0.5m - essentially the height of the landing gear. Assuming that the crumple zone crumples evenly, you are confronted with an acceleration of 76.56 m/s^2 or 7.6G. Very survivable, as multiple CAPS deployments have shown.

Now the horizontal arrest, where you fly the aircraft to a crash landing at stall speed (59 knots as quoted = 30 m/s). Assuming a "crumple zone" of 1m (essentially the engine compartment), you get an acceleration of 450 m/s^2, or 45G. Ouch.

But the latter is assuming you essentially hit a concrete wall at stall speed, and all you have to arrest your speed is the crumpling engine compartiment (which probably is not an all that good crumple zone to begin with). If you land in something that has a little more "give", like bushes, crops or something similar, and assume a landing distance of 10m, the acceleration goes down to 45 m/s^2, or 4.5G. Not bad actually.

So I'm not entirely sure if I agree to the "CAPS NOW" notion of EFATO between 500' and 2000'. It would definitely depend on the terrain below.

On the other hand - this discussion does show the benefit of CAPS. It gives you a choice in situations like this which other airframes don't give you. But in an emergency situation you can't spend a lot of time deciding what to do. So creating a contingency plan as part of the departure briefing, like you suggested, is the best course of action. And that should take into account the terrain.

Last edited by BackPacker; 4th Nov 2011 at 14:55.
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Old 4th Nov 2011, 14:51
  #306 (permalink)  
 
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A little while back I looked through the NTSB databases on forced landings for LongEZs and VariEze's. It appeared that any forced landing onto unimproved terrain had a good chance of killing the occupants. Alas, I don't recall the percentage. Slower-stalling aircraft like STOL taildraggers, had a much better safety record, unsurprisingly. I'm assuming, of course, that there haven't been lots of unreported LongEZ forced landings.

I'd be interested to see more figures regarding stall speed and forced landing survivability, and I'd have thought it would help in deciding when to pull the handle.
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Old 4th Nov 2011, 15:07
  #307 (permalink)  
 
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In the vertical descent under a canopy case (17 knots as quoted = 8.75 m/s), my estimate is that the "crumple zone" is 0.5m - essentially the height of the landing gear. Assuming that the crumple zone crumples evenly, you are confronted with an acceleration of 76.56 m/s^2 or 7.6G. Very survivable, as multiple CAPS deployments have shown.
Possibly conservative as Cirrus say there is an additional crumple zone between the seats and the belly. Moreover to compare like with like you are assuming the landing is on solid terrain in one instance (with CAPS) but through bushes etc in the second (without CAPS). A Cirrus landing under CAPS onto a hedge will enjoy the same benefits as a FL through a hedge. Finally the energy vector is preferable vertically than horizontally as previously discussed.

All in all I agree it is academic however. The evidence is many FL are very successful and with some luck that you dont hit anything too solid they will probably work out fine but without luck the outcome is poor. With CAPS the outcome is more heavily weighted in favour of the occupants across a range of landings, the weighting improving at night or with low cloud where a conventional FL becomes more of a lottery.

So the argument in favour of CAPS is with CAPS you are pretty assured of a landing with 7.6G (to use your figure) or without CAPS between 45G and 4.5G without really knowing which card you will get dealt?

I quite like the idea of reducing the chance element as much as possible which is why I think CAPS a good idea all other issues aside the more especially if you intend to fly over a variety of terrain, at night or with low cloud.

I'd be interested to see more figures regarding stall speed and forced landing survivability, and I'd have thought it would help in deciding when to pull the handle.
I am not sure. With CAPS the pilot is going to make a quick assessment of whether he feels reasonably certain he can complete a successful conventional FL. I guess if there is an attractive field and the pilot is comfortable his skills are sound that might be the preferred option.

However, at the back of his mind he is also going to be aware for the above reasons that he is more assured of a successful outcome with a CAPS deployment.

I agree that the slower the approach speed (in types where CAPS might be installed other than Cirrus) the pilot will factor in the possibility of landing in a much smaller field or accept a landing site that he might judge unsuitable in a Cirrus.

Whenever I have asked a pilot to demonstrate a PFL I am conscious that their skills are more often not as sharp as they imagine. I suspect most FLs end up than being less than the perfect ones we imagine. However I am pleasantly surprised how often the outcome is reasonable. I have never been certain whether this says more about the performance of us pilots when push comes to shove or the resiliance of the human body and the aircraft we fly.

Last edited by Fuji Abound; 4th Nov 2011 at 15:25.
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Old 4th Nov 2011, 20:09
  #308 (permalink)  
 
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Originally Posted by Backpacker View Post
But the latter is assuming you essentially hit a concrete wall at stall speed, and all you have to arrest your speed is the crumpling engine compartiment (which probably is not an all that good crumple zone to begin with). If you land in something that has a little more "give", like bushes, crops or something similar, and assume a landing distance of 10m, the acceleration goes down to 45 m/s^2, or 4.5G. Not bad actually.
Not bad -- except for the consequences of having high energy!

At stall speed, are you not on the edge of control? Just a bit slower and you stall and lose lift and quickly lose altitude.

Here's what happened in a fatal accident with an experienced Cirrus pilot who apparently attempted to extend the glide after smelling fumes in the cockpit, diverted, did a power-off glide and stalled:


So, yeah, the best-case outcome can be "not bad actually."
But the worst-case outcome is deadly -- really bad actually!

In a review of all Cirrus parachute deployments, those within design parameters (below 133 knots airspeed and above demonstrated loss of altitude) have been survivable. Zero fatalities. No post impact fires.

Cheers
Rick
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Old 5th Nov 2011, 12:15
  #309 (permalink)  
 
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007Helicopter, I tried TAA, they were very helpfull and responded very quickly. Unfortuantely their PPL rate would be (approx) 368 per hour, which may be a bit over my budget :-(
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Old 5th Nov 2011, 16:52
  #310 (permalink)  
 
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Unfortunately it will be relatively expensive in a Cirrus, I cant think of anywhere else in striking distance of London. Rates are much more reasonable in the US even factoring in travel and other costs if you had the time and inclination do to a block training.
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Old 5th Nov 2011, 18:29
  #311 (permalink)  
 
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I wonder would the engine position have any relevance to the statistics of the Rutan canards v the STOL aircraft? Agreed of course, the slower the crash the less damage done but having a few hundred pounds of Lycoming going ahead of you has to be better than having the Lycoming trying to come through you.
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Old 9th Jan 2012, 19:24
  #312 (permalink)  
 
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Pair rescued off Bahamas coast after private plane plummets into the sea | Mail Online

Nice to see the chute doing exactly what it was designed to do and allow everyone to walk (sail) away afterwards!
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Old 9th Jan 2012, 19:32
  #313 (permalink)  
 
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Great result.
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Old 11th Jan 2012, 00:53
  #314 (permalink)  
 
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More info on the Cirrus parachute pull in the Bahamas last Saturday:
Early Reflections on CAPS Pull #32 by Dick McGlaughlin in the Bahamas

Cheers
Rick
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Old 1st Feb 2016, 17:14
  #315 (permalink)  
 
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I found this to be an excellent thread. I recently completed a checkout in a Cirrus SR-22 G1.

If anyone has any updated opinions on the Cirrus, they would be most welcome.
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Old 3rd Feb 2016, 00:25
  #316 (permalink)  
 
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Originally Posted by sternone View Post
There are a lot of lost of control accidents on landings in a Cirrus, do you have reason for that ?
I suspect that this statement from an instructor may be true, "It is my opinion and experience that the Cirrus BRS system attracts over-ambitious but under-skilled pilots whose spouses are placated by the BRS myth making the Cirrus the "doctor killer" of the current era."

Last edited by JammedStab; 5th Feb 2016 at 17:32.
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Old 8th Oct 2020, 16:25
  #317 (permalink)  
 
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I didn't want to start a new topic as this one is all about the SR22 and BRS:

One down today and thanks to BRS the two pax and a dog walked away from this 'landing'.
https://www.aviation24.be/miscellane...sdonk-belgium/

It's a petty (for the plane) they didn't make it to the smaller uncontrolled GA airfields right underneath the flightpath when trouble started at FL200. Instead they opted to divert to Brussels but it seems they where vectored for a looooong ILS approach, and came down 20 miles short. With hindsight, this option certainly worked for the occupants; the GA field alternative option, unfamiliar area with 1800-2000ft AGL broken ceiling & 6 nm vis., maybe nobody manning the A/G radio, etc. did not guarantee a safe (plane&pax) outcome either.
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Old 8th Oct 2020, 17:14
  #318 (permalink)  
 
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It is easy to be clever when looking on from a distance, I know very well. Still, I cannot help thinking EBBR was about the poorest choice possible for an emergency landing. Plus that, as stated above, there were plenty of alternatives at hand, EBBE Beauvechain to begin with. Depending on their location when "trouble" began, EBLG Liege and EBST Sint Truiden would also have been possible, both very quiet at the time of day, both with long hard runways. And while perhaps EBST radio might not be active, EBLG and EBBE certainly would.
Had they called a Mayday, or even Pan-Pan? In that case, EBST could certainly have been "woken up".

But the official accident report will explain it all, in a couple of years.

[[ later added ]] @above: perhaps the meaning was "it is a pity"? As the phrase stands, it looks a bit funny.

Last edited by Jan Olieslagers; 9th Oct 2020 at 10:09.
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