Some "expert" being interviewed on CNN claimed the glide ratio on the 777, zero power, from 30,000 was 90-100 mikles. I find that hard to believe, anyone?

Jim

read somewhere that the glide ration of a 747 was between 15 and 17 to one.

Given that, I don't find it so hard to believe.

At 15:1 that'd be 85 miles or so from 30k.

I remember an A330 flying from Toronto>Lisbon that had a catastrophic fuel loss accident (Cracked line in the feed to #2)

lost #2 at 135nm and #1 at ~65nm.

and managed to glide it to a safe landing at Lajes

Though with the loss of both engines they were also without primary hydraulics so had to land without Flaps, spoilers or a properly working brake system.

They had to do a 360deg turn and a series of S-turns to dump excess altitude, and blew all eight main gear tires on touchdown, but other than a few injuries while evacuating the aircraft and structural damage to the landing gear they made it.

As the saying goes any landing you walk away from is a good one.

a superb landing is one where the airplane is re-useable.
(Even if you have to sell it at a scratch & dent sale)

They had altitude, airspeed and an idea that proved correct.
Lack any of those three things and you are basically fucked.

But in any event their landing, however rough, was preferable to any available alternatives.

The Longest Glide ever by a non-glider aircraft was actually done by a B747-236B.

British Airways Flight 9 on route from London to Melbourne when they lost all four engines at FL370 and glided down to FL135 before they managed to restart the engines. Volcanic ask and Jet engines shouldn't be mixed.

quote:

Originally posted by Jim Kobe:
Some "expert" being interviewed on CNN claimed the glide ratio on the 777, zero power, from 30,000 was 90-100 mikles. I find that hard to believe, anyone?

Jim

Nope it's not BS that is just about exactly correct. Most commercial airliners have about a 3 to 1 decent rate so figure just over 3 miles glide for every 1,000' of altitude lost. the 777 actually does a bit better than that. I'd give it closer to 120 miles in 30,000 feet of altitude lost. In the 777 you figure a power off decent of 4 to 1 because it has such an efficient wing.

quote:

Originally posted by surestrike:

quote:

Originally posted by Jim Kobe:
Some "expert" being interviewed on CNN claimed the glide ratio on the 777, zero power, from 30,000 was 90-100 mikles. I find that hard to believe, anyone?

Jim

Nope it's not BS that is just about exactly correct. Most commercial airliners have about a 3 to 1 decent rate so figure just over 3 miles glide for every 1,000' of altitude lost. the 777 actually does a bit better than that. I'd give it closer to 120 miles in 30,000 feet of altitude lost. In the 777 you figure a power off decent of 4 to 1 because it has such an efficient wing.

Just wondering about your math

Wouldn't 3 miles for every 1000' of altitude be an 18:1 glide ratio?


The Space Shuttle which everyone described as "Flies like a brick" had a 1:1 Glide ratio while at speed and altitude and a 4.5:1 ratio on approach.

The Gimli Glider, a 767-200 demonstrated a ~12:1 Glide ratio

Allan,

I am not speaking in glide ratio of miles to miles I am figuring feet to miles. That is how we figure a descent distance. Altitude needed to lose x 3 plus 1 mile per 10 kts of speed loss and plus or minus 1 mile for each 10 kts of head wind or tail wind.

So if I am cruising at 35,000 feet and I have a waypoint that I am cleared to cross at 10,000 feet and 250 kts. I need to loose 25,000 feet using the 3 to 1 formula and slow from 300 to 250 kts I figure 25x3=75 miles plus 5 miles to slow from 300 to 250 kts. So I need to start down about 80 miles from my altitude crossing point.


I don't know where they came up with the 12 to 1 number on your example. It could have to do with winds or speed flown. I can tell you this however, the 3 to 1 figure I just explained works on just about any jet transport ever built. It worked for me again just a couple of hours ago in a 767.

So the answer to the OP is that yes a 777 glides about 120 miles in 30,000 feet.

God, I love it when yous guys talk "tech"!

And yes Allan that works out to an 18 to 1 glide ratio in miles but remember that is with the engines running at idle thrust which provides some forward thrust. With engines shut off the glide will be somewhat reduced.

"Rule of thumb" only works for those familiar with your units of measure...

"What's a thumb?"

on the Gimli Glider 767 that ratio was calculated by what the plane actually did to put down where it did.

I'm sure they could have glided further to some off runway crash site...

but as I like repeating, any landing where the aircraft is re-useable is by definition a superb landing.

the Gimli Glider was FLOWN from the incident site and returned to service.

Allan, I feel as though I am speaking at a level above your capability of understanding? I explained to you the industry standard formula for figuring a descent distance in miles and converting that from feet descended to miles covered. It is not a rule of "thumb" it is how we as professional airline, cargo, charter, corporate and military transport pilots calculate a descent distance.

We don't use miles descended to miles covered because.....Wait for it.....Altimeters read in feet above sea level not miles above sea level. If you want to later figure a glide ratio in miles simply divide your altitude in feet by a factor of 6000 and re figure.

I'm not sure why you think that the Gilmi glider's ratio has anything to do with the OP's question? I've already explained to you that you need to add or subtract for headwind or tailwind, that the glide ratio will be different with engines running at idle thrust vs shut off. The fact that he had a 12 to 1 glide simply means this was the glide ratio needed to achieve an adequate landing spot on that day. It has NOTHING to do with the actual glide ratio capability of the airplane.

Hopefully I've provoked you into thinking a little bit today?

Hey SS.

It's been a few years now since I flew but your numbers are spot on. 3 miles for every 1,000 feet to descend, +/- depending on head/tail wind at 1 for 1. In other words, 10 miles per hour tail wind component, start 10 miles earlier. So yeah, 35,000' cruise, cleared to cross a fix at 10,000, with no tail/head wind, plan on beginning the idle descent at 75 miles. 35,000 less 10,000 gives 25,000 feet of descent. X 3 miles per 1,000 feet and you get 75 miles as the start point. A very basic concept used by every professional pilot I've ever flown with.

quote:

Originally posted by surestrike:
Allan, I feel as though I am speaking at a level above your capability of understanding? I explained to you the industry standard formula for figuring a descent distance in miles and converting that from feet descended to miles covered. It is not a rule of "thumb" it is how we as professional airline, cargo, charter, corporate and military transport pilots calculate a descent distance.

We don't use miles descended to miles covered because.....Wait for it.....Altimeters read in feet above sea level not miles above sea level. If you want to later figure a glide ratio in miles simply divide your altitude in feet by a factor of 6000 and re figure.

I'm not sure why you think that the Gilmi glider's ratio has anything to do with the OP's question? I've already explained to you that you need to add or subtract for headwind or tailwind, that the glide ratio will be different with engines running at idle thrust vs shut off. The fact that he had a 12 to 1 glide simply means this was the glide ratio needed to achieve an adequate landing spot on that day. It has NOTHING to do with the actual glide ratio capability of the airplane.

Hopefully I've provoked you into thinking a little bit today?

I understand perfectly well that altimeters measure feet and that you travel Miles.

I am just saying that you ASSume that everyone was familiar on a gut level with your "rule of thumb"

I wish you well trying to find an aeronautical engineering textbook that uses the phrase "Glide Ratio" the way you used it

I equally defy you to find one that doesn't use the phrase the way I used it.

Yes, I'm bandying semantics, get over it.

I have the distinct feeling that you are the one doing most of the misunderstanding.

Allan,

Plain and simple your arrogance over rides your ignorance on this one. I really don't know how much more of a simplistic explanation I can provide.

I explained to you how a glide ratio is figured in the cockpit IE how somebody actually uses that calculation in a real world setting while operating a jet aircraft. I explained to you how to convert those numbers to a standard miles to miles glide ratio, 18 to 1 but slightly better in a B-777 due to it's super efficient wing,BTW and yet again. I answered the OP's question with real world numbers no internet Google expert SWAG, REAL honest to god numbers. I flew the 777 for just on a decade and in addition was an instructor and check airmen on the airplane. I am flying a 757 transcon tonight then back again the next day, as I do on a weekly basis. Yet somehow in your mind I have a misunderstanding of what the glide ratio of transport category turbo jet aircraft is? Even though this is what I do for living? Even though I do this stuff real world day in and day out and have thousands of hours doing it?

Go figure.....

well my personal glide ratio, is that after a sufficient intake of johnny walker, i can glide for several miles to home, where i crash land, and the wife makes sure that there are no survivors

quote:

Originally posted by surestrike:
Allan,

Plain and simple your arrogance over rides your ignorance on this one. I really don't know how much more of a simplistic explanation I can provide.

I explained to you how a glide ratio is figured in the cockpit IE how somebody actually uses that calculation in a real world setting while operating a jet aircraft. I explained to you how to convert those numbers to a standard miles to miles glide ratio, 18 to 1 but slightly better in a B-777 due to it's super efficient wing,BTW and yet again. I answered the OP's question with real world numbers no internet Google expert SWAG, REAL honest to god numbers. I flew the 777 for just on a decade and in addition was an instructor and check airmen on the airplane. I am flying a 757 transcon tonight then back again the next day, as I do on a weekly basis. Yet somehow in your mind I have a misunderstanding of what the glide ratio of transport category turbo jet aircraft is? Even though this is what I do for living? Even though I do this stuff real world day in and day out and have thousands of hours doing it?

Go figure.....

You sir are the classic arrogant PILOT.

And you are using a technical term as a pilot would use it and you arrogantly ASSUME that everyone else in the world uses it the way you do.

And I'm telling you however you use the term is UNIQUE to PILOT use of the terminology.

Engineers are quite content to keep ratios "Simple" by using as similar a unit of measure.

They are safely on the ground and don't need to take a shortcut with their math calculations, They are not moving at 3-6 miles per minute.

Your arrogance is defined by your inability to accept that others have a different point of view, I have conceded your point and explained myself several times.

An aerodynamic engineer uses the term the way I have previously (repeatedly) described.

you have a unique situational perspective but you REFUSE to accept other view points.

You use your rule of thumb the way you are comfortable using it, but it is not the way everyone OTHER THAN a commercial or military Jet aircraft pilot uses it.


I have no issue with your using it the way you do I just keep explaining why I and likely others who have remained silent, did not instantly understand your initial usage.

YOU DID NOT EXPLAIN YOUR UNITS OF MEASURE IN YOUR FIRST POST.

Remember WHO you are speaking to when you choose your terms. Not everone here is a jet transport pilot or even a pilot.

I doubt the majority of people on this subforum is a pilot, THREE POSTS before yours used ratios
that assumed equal unit of measure on both sides of the colon, and you suddenly drop in with your pilotese and insist your terms are correct, WHICH they are given your explanation and usage.

I assure you they are NOT in context with the previous conversation BEFORE you joined it.

I have personally made my living speaking the "different languages" that different flavors of engineers actually unconsciously speak which tends towards a culture of mis communication, which I see you are well entrenched in.

I am not arguing with you, even though you are a sanctimonious asshole. I'm explaining why I initially misunderstood you.

And you just don't get it, and I now believe this is entirely by choice.

This is called being obtuse.

Don't call me arrogant, it only proves you know how to MISuse the word.

Call me obnoxious if you like but before you do I feel obligated to tell you that you are also rather obnoxious.

Obnoxious is the word that people most often really want to use when they choose to misuse the word "Arrogant"

Now I am going back to the far more important job of arguing with my cellphone carrier about why they have not sent out the warranty replacement phone they said they were shipping via FedEx a WEEK ago!

quote:

And you are using a technical term as a pilot would use it and you arrogantly ASSUME that everyone else in the world uses it the way you do.

Actually shithead I explained it to you very clearly and converted it for you as well, multiple times.

quote:

YOU DID NOT EXPLAIN YOUR UNITS OF MEASURE IN YOUR FIRST POST.

Actually I did and I clarified and reexplained it for you in my 2nd 3rd 4th and 5th post. You were simply refusing to comprehend it.

From my first post...

quote:

Most commercial airliners have about a 3 to 1 decent rate so figure just over 3 miles glide for every 1,000' of altitude lost.

Basic math tells us that there are exactly 6,000 feet in a nautical mile. 6x3=18 so the very simple unit conversion works out to 18 to 1. Or 18 miles covered for 1 mile descended. This is the 6th time that I've converted those units for you now. You asked me to check my math. I did just that and broke it down for you in the most simple way possible. Yet you still got your panties in a wad.

So what is the problem here, really?

WOW! I imagine an MP standing at the conference room door must have heard the same intercouse of discussion between Patton and Monte, no?

quote:

Originally posted by jfromswk:
WOW! I imagine an MP standing at the conference room door must have heard the same intercouse of discussion between Patton and Monte, no?

As long as I get to be Patton I'm good with that.

quote:

Originally posted by surestrike:

quote:

Originally posted by jfromswk:
WOW! I imagine an MP standing at the conference room door must have heard the same intercouse of discussion between Patton and Monte, no?

As long as I get to be Patton I'm good with that.

+1

Geez guys, I started this one, didn't mean to piss youse guys off so much, Chill!

That would be Eisenhower. Really all this "simple" math is making my head hurt.

I remember being out at our local airport when I was younger; as a nice older twin (cessna?) was warming up for takeoff. I wondered outloud as to how far that thing would fly with only one engine? A mechanic there opined that it would make it all the way to the crash site.

I've never forgotten that statement; even if flying is the safest way to travel. That being said, I'm glad to know that a big commercial jet actually does have a glide capacity better than a rock as I had also heard.

My local cropduster always says, "Never run out of altitude, airspeed, or ideas at the same time". Seems like good advice.

quote:

Geez guys, I started this one, didn't mean to piss youse guys off so much, Chill!

Jim all I did was answer your question. Sorry....

Let's not confuse decent planning ratios of 3:1 or 4:1 with maximum glide distance. Clearly a B767 glided better than 10:1 and know that even a lowly Cessna 150 will go better than 7:1.

80+ miles is clearly doable with the B777 from 35000 feet at best lift to drag ratio speed.

f224

I saw you on TV the other night.

You did a great job.

Funny thing is I NEVER watch CNN. But I was channel surfing around to get the latest info on the missing plane, and there you were...