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The Gimli Glider  
User currently offlineIndian_flyboy From , joined Dec 1969, posts, RR:
Posted (12 years 2 weeks 5 days 5 hours ago) and read 4261 times:

Hi Guys ,

I believe , most of you would have definitely heard of the gimli glider , for those who don't it's a 132 tonne glider based on a complete B762 frame without any fuel. Capt Bob Pearson , hats off to the genius who saved 69 lives by sheer presence of mind , did a maneuver called the sideslip to slow the aircraft and the decent rate down to a point where the a/c could land safely . I wanted to know what exactly is the physics behind a sideslip .

This is what I believe , momentum carries the aircraft in a straight line eventhough the nose is pointing in a different direction , but since the wings are not in the direction of the flight , wouldn't the lift decrease hence increasing the rate of decent and the speed ? I know I am going wrong somewhere here , if a B762 can be brought down safely with a sideslip any damn aircraft could be (atleast theoretically ) .
Can any one out there help out ? Anyone actually tried sideslipping ?

Skipper, if you are reading this , would really appreciate something from you ...I was wanting to put this out for your usual expert advice, but read that you decided to get out of this forum :-( , ofcourse no disrespect to anyone else on this forum.

Regards



21 replies: All unread, jump to last
 
User currently offlineXFSUgimpLB41x From United States of America, joined Aug 2000, 4200 posts, RR: 37
Reply 1, posted (12 years 2 weeks 5 days 5 hours ago) and read 4240 times:

A foward slip (the actual term what what the captain did-a side slip is like what you do for a crosswind landing) is basic practice from your private pilot onward. The only time ive ever heard of an airliner do that is in this case. Basically what you are doing is kicking the rudder all the way in to make the airplane point sideways and then adding whatever aileron necessary to make the airplane track along the centerline of the runway. The aileron gives a certain bank angle necessary to add the horizontal lift component that gifts enough lateral force to allow the airplane to continue tracking the desired direction. The rudder gives the airplane a less than optimal track through the air which increases drag so much that the airplane drops quicker without gaining airspeed.

I really hope that made sense.  Smile



Chicks dig winglets.
User currently offlineZionstrat From United States of America, joined Apr 2001, 226 posts, RR: 0
Reply 2, posted (12 years 2 weeks 5 days 4 hours ago) and read 4209 times:

There's an interesting thread on Pprune started by an alleged 737 pilot who claims to slip regardless of SOPs- Here's the thread-

http://www.pprune.org/forums/showthread.php?s=&threadid=60806&perpage=15&highlight=side%20slip%20and%20forward%20slip&pagenumber=1


User currently offlineRick767 From United Kingdom, joined Jan 2000, 2662 posts, RR: 51
Reply 3, posted (12 years 2 weeks 5 days 3 hours ago) and read 4174 times:

Zionstrat.

That post was started by a "pilot" who also said:

"I'm not interested in the opinions of pilots who keep their bank limiter set to 10 degrees in the traffic pattern and who don't know the difference between a Forward Slip and a Side Slip. Who consider a standard rate turns, "S" turns and "360's" to be the realm of aerobatics. Who "**** their pants" with the loss of their FDs. You guys can "kiss my @$$"."

Make of that what you will. He may advocate forward-slipping a 737-800 within 1,000ft of the ground just to make the runway, but unless I was about to crash by overshooting a field, I wouldn't.



I used to love the smell of Jet-A in the morning...
User currently offlineZionstrat From United States of America, joined Apr 2001, 226 posts, RR: 0
Reply 4, posted (12 years 2 weeks 5 days 3 hours ago) and read 4170 times:

Rick767-
Agreed 100%- Note my use of 'alleged' and 'claims'-

I actually get a kick out of trying to figure out which ones are media and which ones are 13 year olds- But I think the pros came out enforce in this thread Smile

Back to the original topic, I probably pitch the book "emergency in the cockpit" about once a month, but wanted to suggest it again as a great source of Gimli info.


User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 5, posted (12 years 2 weeks 5 days 2 hours ago) and read 4147 times:

Hi guys.

I remember my father and I picking up my mother at Toronto's Pearson Intl (YYZ) about a year ago after she arrived from Florida on the famous Gimli Glider. She thought it was neat when I told her she was flying on C-GAUN. She remembered the incident over Manitoba.

Anyways, XSFUgimpLB41x's explanation of how a pilot performs a forward sideslip and the aerodynamic results sounded good and clear to me.

>Indian-flyboy, the main reason why a pilot uses a forward sideslip while on final approach is because he can increase drag (by exposing the side of the aircraft to the relative airflow), and thus lose altitude, while maintaining his airspeed and power setting. Pilots of much older GA airplanes that don't have flaps (gliders included) would use this technique to control their glideslope angle.

Perhaps Capt Pearson of the Gimli Glider had to perform a forward sideslip or he would have overshot the old airstrip....which could have been disasterous!

The Glider then:
View Large View Medium
Click here for bigger photo!

Photo © Ted Quackenbush



The Glider now:
View Large View Medium
Click here for bigger photo!

Photo © Pierre Lacombe



Chris  Smile



"Just a minute while I re-invent myself"
User currently offlineDelta-flyer From United States of America, joined Jul 2001, 2676 posts, RR: 6
Reply 6, posted (12 years 2 weeks 4 days 16 hours ago) and read 4081 times:

The sideslip is a staple of glider pilots, as you always want to come in a bit high then lose altitude rapidly in the final moments before landing.

Pete


User currently offlinePositive rate From Australia, joined Sep 2001, 2143 posts, RR: 1
Reply 7, posted (12 years 2 weeks 3 days 19 hours ago) and read 4006 times:

I understand that Captain Pearson was an amateur glider pilot at the time of the Gimli incident. Maybe the success of the landing was due to this- what if a non-glider pilot was in command of that 767, would the outcome have been any different?

User currently offline9V-SVA From Singapore, joined Aug 2001, 1860 posts, RR: 8
Reply 8, posted (12 years 2 weeks 3 days 15 hours ago) and read 4036 times:

Hasn't the Gimli Glider been put in storage? Or it was returned to service in May?

9V-SVA



9V-SVA | B772ER
User currently offlineZionstrat From United States of America, joined Apr 2001, 226 posts, RR: 0
Reply 9, posted (12 years 2 weeks 2 days 7 hours ago) and read 3935 times:

Positive rate
I think you hit a major theme with Gimili- First everything went wrong, then everything went right- A near perfect case study of everything unexpected in one flight:

1. Approved flight although didn’t meet MEL
2. Mis calculated and mis dipped fuel- Twice!
3. Landed on a race strip that was crowded with people and vehicles.

1. Co-pilot remembered abandoned military base
2. Pilot had gliding experience
3. Nose wheel would not lock, causing it to collapse, keeping the 67 from rolling into vehicles and people.




User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 10, posted (12 years 2 weeks 2 days 6 hours ago) and read 3933 times:

"The sideslip is a staple of glider pilots, as you always want to come in a bit high then lose altitude rapidly in the final moments before landing."

Ehm, no. We are taught not to sideslip at all. We have airbrakes for controlling our glideslope angle. And when you pop the brakes, you're coming down steep and fast, no need whatsoever for slipping. If we want to get down even faster, we just increase our airspeed a bit. The only time we fly uncoordinated is when aligning with the runway just before touchdown in a xwind landing and in thermals, where a bit of slip makes it easier to center and seems to give a bit lower sinkrate (although opinions vary on this).

There were some gliders a couple of decades ago which had only a brake chute and no airbrakes. Those would be the exception.

Gliders in general do seem to slip and skid rather well, but it's not SOP, not necessary and not recommended. At least here, uncoordinated turns is part of the curriculum and there is probably no form of flying which will give you better "stick and rudder" skills, including understanding of slipping/skidding. You can't get lazy and take your feet off the pedals while turning like you can in many GA aircraft. That's probably why the Gimli Glider captain chose to refer to his glider flying when describing how on earth he came up with the idea of slipping to steepen the approach.

On a sidenote, I've personally done some crazy slips and skids on approach in B735, SF34 and B738 FFSs, great fun but, again, very much not recommended. Especially not with a load of SLF in back as they'll spill their drinks and vomit quite a bit, especially the ones in the rear end. It sure helped the notoriously slippery SF34 come down at a high rate though! Big grin Swept wings tend to create lots of roll moment when slipped due to the changed apparent lenght of the wings in the airstream. I also had an engine seize on me in the FFS right when I put on power to go around, due to a friendly instructor behind my back. The yaw created was all to easy to miss, but the roll moment was beyond what the ailerons could cope with. By the time I figured it out and got rudder in, it was too late. Way too late. Ouch. A very humbling experience indeed.

Cheers,
Fred



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineWoodreau From United States of America, joined Sep 2001, 1043 posts, RR: 6
Reply 11, posted (12 years 2 weeks 21 hours ago) and read 3833 times:

Our designated examiner here for the glider license has the student demonstrate spoilerless landings, so in that instance a slip to a landing is required otherwise the glider would never get down on the ground in time, although I am at a loss to think if a reason why spoilers wouldn't work.

The instructor doesn't agree with the examiner's requirements to do a spoilerless and land on the runway numbers (at the end of the threshold), he thinks that's stupid and me thinks, it is kind of dangerous to do. So at least here we do teach the glider pilots to forward slip to lose altitude, although with spoilers it's not required for normal ops.

Cheers  Smile
Woodreau - KMVL



Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 12, posted (12 years 2 weeks 10 hours ago) and read 3819 times:

Hmm, is that actually in the written requirements or is it something the examiner does since it is something he has always done? Crossed controls on approach isn't something I'd consider a good idea as part of the training. In glass birds, it's not all that effective either IMO, it's not sliding a barn door sideways through the air as in the J3s and such... what are your trainers? Twin Astirs are the training aircraft here, club's got an old K8 as well but apart from that it's all glass.

I agree with you and your instructor, stupid and dangerous. You'll have to be awfully low on approach, right? I'd feel safe doing it at our field which doubles as an AFB meaning we can basically fly the entire pattern over the runway system and have 100+ meters landable grass before the treshold... but on a small field with trees and rocks under the approach? I wouldn't like it a bit.

It sure sounds like great fun though. Big grin

Cheers,
Fred



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineZionstrat From United States of America, joined Apr 2001, 226 posts, RR: 0
Reply 13, posted (12 years 2 weeks 2 hours ago) and read 3764 times:

Fred T-
I noticed your comment "Swept wings tend to create lots of roll moment when slipped" and thought this was a given and potential precursor to a snap roll?

I'm a GA type, but had always understood that the windward swept wing would get significantly more lift as the wing is closer to perpendicular to the apparent wind and that the leeward wing would loose lift rapidly due to the shadow of the fuselage.

Is this a case where you just have to keep IAS up, or is this not as big an issue as I had perceived?


User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 14, posted (12 years 1 week 6 days 22 hours ago) and read 3750 times:

Zionstrat,
in a snap roll, or flick roll to use another term, you put both wings near their stall AoA and then use rudder, and perhaps aileron opposite to the wanted roll direction, in order to stall one wing while keeping the other wing below the stall AoA.

When slipping a swept wing design, neither wing is stalled. You're correct that the cause of the roll moment is the upwind wing being more perpendicular to the direction of flight. Thus, the airspeed component perpendicular to the wing is higher for the upwind wing - and this airspeed component is what generates lift. Alas, the upwind wing creates more lift and you have a roll moment. This won't go away at a higher IAS. However, as IAS increases the fin will be more effective in keeping the aircraft aligned with it's direction of travel and any asymetrical effects will be less noticeable.

Not quite a flick roll. However, this effect sets the stage for another kind of rolling - the dutch roll.

Cheers,
Fred



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineZionstrat From United States of America, joined Apr 2001, 226 posts, RR: 0
Reply 15, posted (12 years 1 week 6 days 6 hours ago) and read 3710 times:

FredT-
Your reply is exactly why I love this forumn- Yes dutch roll makes much more sense- Thanks for the input-


User currently offlineCaptjetblast From Argentina, joined Aug 2001, 281 posts, RR: 0
Reply 16, posted (12 years 1 week 6 days 4 hours ago) and read 3716 times:

http://airsports.fai.org/aug2000/aug200004.html

http://www.frontier.net/~wadenelson/successstories/gimli.html



User currently offlineGodbless From Sweden, joined Apr 2000, 2752 posts, RR: 16
Reply 17, posted (12 years 1 week 5 days 4 hours ago) and read 3623 times:

This is a little off topic but does anybody here have information on how the got the "Gimli-Glider" out of Gimli?

Back in 1998 I went to Gimli and it was kinda cool to be there where 15 years earlier a 767 had landed without having a single drop of fuel but still leaving the plane without major damages.

Max


User currently offlinePPGMD From United States of America, joined Sep 2001, 2453 posts, RR: 0
Reply 18, posted (12 years 1 week 4 days 23 hours ago) and read 3599 times:

About Spoilerless landings in gliders: It's in the PTS if I remember correct and is a required manevuer. Now I do question his judgement to use the runway numbers as the aiming point, I think it would be best to land at a point part of the way down the runway. Its safer because it gives you a buffer zone.


At worst, you screw up and die.
User currently offlineJetguy From , joined Dec 1969, posts, RR:
Reply 19, posted (12 years 1 week 4 days 6 hours ago) and read 3577 times:

IMHO, slips, in flapless aircraft, should be relegated to the pilot's bag 'o tricks and should be used only when necessary to "save his bacon". Slipping an aircraft (especially a large one) in order to try to salvage a botched approach is not exactly what I'd call exemplary airmanship.

Slips have their place. They should be taught and they should be practiced, but as Fred correctly alluded to, they won't impress any non-pilot passengers you might have on board. As pilots we are used to (and sometimes even enjoy) the sensations associated with uncoordinated flight, but it is unnerving and frightening for most passengers. Again, it doesn't matter one bit how skillfully the maneuver is pulled off - if you've got passengers on board and you weren't in an abnormal or training situation when you did it you have blown it. You surely won't impress your passengers by doing it. Just my humble opinion.

I have nothing but respect for Captain Pearson and the skill that he demonstrated. My knowledge of the entire episode comes soley from what I've read and from the TV movie that was put out a few years back. (Of course, TV movies are noted for their technical accuracy.) It's the classic example of how an accident isn't caused by just one event, but by a series of events which form the chain that leads up to the actual event. Break just one of the links and the event is avoided. He did a dang fine job of handling the entire situation.

Along these same lines, I just returned from my 6-month recurrent at FlightSafety. On the last day, just for grins, my sim instructor, without warning, announced that I had contaminated fuel as he failed both engines ten miles from the airport. With the engines out, there was no hydraulic power for the airbrakes and the gear had to be blown down. I used flaps and slips to make the landing. (As a CFIG it sure would have been embarrassing not to have been able to put the airplane on the runway. Big grin )

From my perspective, The Gimli Glider episode only adds to the opinion that I have held for a long time - if I were king of the world I would make it a requirement for all pilots to have glider experience. The "feel" that you develop for flying will help you in all of the flying that you do in the future - regardless of the size of type of aircraft that you fly. The confidence that you develop in the ability to handle an engine failure will be invaluable.

Getting a glider rating is very easy - 14 year-old kids can solo gliders and you can get your PPL-Glider at 16. The cost is comparatively inexpensive and you can get a pvt or comm add-on rating at most glider operations in 2 to 4 days. Some things to think about.

Jetguy




User currently offlineYWG From Canada, joined Feb 2001, 1146 posts, RR: 2
Reply 20, posted (12 years 1 week 3 days 19 hours ago) and read 3547 times:

My dad works for Air Canada an at the time was sent out to YGM to service the plane. They eventualy repaired the damage an fairied it back into Winnipeg where it was made fully airworthy.

An on a side note about gliding, Gimli is the Regional Gliding School for the priare region for the Canadian air cadets, I'm staff there  Big thumbs up And I fly over that runway which is now a drag strip for cars, an I still can't see how a 767 landed there, but walking the runway everymorning before operations begins show's you the entire length, which respectivley is about 1.5km.



Contact Winnipeg center now on 134.4, good day.
User currently offlineJetguy From , joined Dec 1969, posts, RR:
Reply 21, posted (12 years 1 week 3 days 16 hours ago) and read 3535 times:

Geeze, I've really been having a bad day today. Once again I screwed up a post. In my post on this thread I wrote:

IMHO, slips, in flapless aircraft, should be relegated to the pilot's bag 'o tricks and should be used only when necessary to "save his bacon". Slipping an aircraft (especially a large one) in order to try to salvage a botched approach is not exactly what I'd call exemplary airmanship.

I should have wrote the following:

IMHO, slips, in aircraft equipped with flaps, should be relegated to the pilot's bag 'o tricks and should be used only when necessary to "save his bacon". . .

What's the first rule of flight instruction? Do what I mean, not what I say. Big grin

Oh well, that's what happens when I try to function on 3 hours of sleep. I'm off to bed now.

Jetguy


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