Moderators: richierich, ua900, PanAm_DC10, hOMSaR

 
gopal
Topic Author
Posts: 168
Joined: Thu Jun 03, 1999 3:05 am

2 Vs 4 Engines Debate

Tue Jan 20, 2009 3:23 pm

Do the incidents with regard to US 1549 and BA 38 highlight the inadequacies of the 2 engine model ? Will the fervent supporters of the 4 engine model for most airplanes get a lot of support from these incidents ? The 2 engine model is based on the premise of a Infinitesimal probability of inflight failure of both the engines in a modern jetliner. Do these two incidents point towards a greater possibility of this happening ?

Would it be fair to state that this incident could have happened in a densely populated metropolis in Asia. Many airports in Asia have densly populated colonies surrounding airports thus increasing the bird menace. These cities do not have big bodies of water or open space for a safe ditching/crash landing.
 
User avatar
JerseyFlyer
Posts: 1588
Joined: Fri May 25, 2007 7:24 pm

2 Vs 4 Engines Debate

Tue Jan 20, 2009 3:24 pm

4 engines 4 flying into flocks of geese!
 
lowrider
Posts: 2542
Joined: Wed Jun 30, 2004 3:09 am

2 Vs 4 Engines Debate

Tue Jan 20, 2009 3:30 pm



Quoting Gopal (Thread starter):
Do the incidents with regard to US 1549 and BA 38 highlight the inadequacies of the 2 engine model ?

No.

Quoting Gopal (Thread starter):
The 2 engine model is based on the premise of a Infinitesimal probability of inflight failure of both the engines in a modern jetliner. Do these two incidents point towards a greater possibility of this happening ?

They remain fleetingly small. How many flights of two engine aircraft occurred with incident during the same time period?

Quoting Gopal (Thread starter):
Will the fervent supporters of the 4 engine model for most airplanes get a lot of support from these incidents ?

No. I like 3 and 4 engine aircraft as much as ( or more ) than most, but two crashes with unrelated causes are not going to shift design or purchase priorities.
Proud OOTSK member
 
User avatar
Francoflier
Posts: 5644
Joined: Wed Oct 31, 2001 12:27 pm

2 Vs 4 Engines Debate

Tue Jan 20, 2009 3:41 pm



Quoting Gopal (Thread starter):
Will the fervent supporters of the 4 engine model for most airplanes

I don't think there are such people. Maybe a few extremists... But I doubt even the harshest of those extremists would doubt that the idea of making a 4 engines replacement to the A320/737 is a good one.  Wink
I'll do my own airline. With Blackjack. And hookers. In fact, forget the airline.
 
MCIGuy
Posts: 1445
Joined: Sun Mar 26, 2006 8:15 am

2 Vs 4 Engines Debate

Tue Jan 20, 2009 3:42 pm

Besides what's already been stated, if this incident had happened with a four engine airliner the result probably wouldn't have been as good. Two more engines would have greatly increased the chances that a wing would have been torn off and/or it would have cartwheeled.
Airliners.net Moderator Team
 
ac788
Posts: 39
Joined: Mon Jan 19, 2009 4:57 am

2 Vs 4 Engines Debate

Tue Jan 20, 2009 3:51 pm

British Airways Flight 9, also known as the Jakarta incident, comes to mind in this debate.
The aircraft lost all four engines by flying through a cloud of volcanic ash.

For anyone who hasn't seen the "Mayday" episode of this incident I recommend it.
 
RussianJet
Posts: 5983
Joined: Sat Jul 21, 2007 4:15 am

2 Vs 4 Engines Debate

Tue Jan 20, 2009 3:53 pm



Quoting Francoflier (Reply 3):
I don't think there are such people. Maybe a few extremists... But I doubt even the harshest of those extremists would doubt that the idea of making a 4 engines replacement to the A320/737 is a good one.

Indeed, four engines would be silly. Personally, I favour the six engine model.  duck 
✈ Every strike of the hammer is a blow against the enemy. ✈
 
na
Posts: 9812
Joined: Sun Dec 12, 1999 3:52 am

2 Vs 4 Engines Debate

Tue Jan 20, 2009 3:53 pm



Quoting MCIGuy (Reply 4):
Two more engines would have greatly increased the chances that a wing would have been torn off and/or it would have cartwheeled.

No. The outer engines are above belly level in flight. I would say on a twin with very big engines, like a 777, the chances would be highest for cartwheeling as their massive weight would be decisive.

Quoting Gopal (Thread starter):
Do the incidents with regard to US 1549 and BA 38 highlight the inadequacies of the 2 engine model ?

To some extent yes. Chances are higher not all egines might have been effected on a quad and the airplane would have a much better chance to reach an emergency airport.
 
ac788
Posts: 39
Joined: Mon Jan 19, 2009 4:57 am

2 Vs 4 Engines Debate

Tue Jan 20, 2009 3:54 pm



Quoting RussianJet (Reply 6):
I favour the six engine model.

Haha and who doesn't?? You've gotta love the Mriya!  Smile
 
lhr380
Posts: 2453
Joined: Thu Jan 15, 2009 5:39 pm

2 Vs 4 Engines Debate

Tue Jan 20, 2009 3:58 pm

Regarding the BA incident, the same thing would have happened to a 4 engine aircraft that happened to the BA flight as the cause affected all the engines.
(The views on this site are my own and no one elses)
 
MCIGuy
Posts: 1445
Joined: Sun Mar 26, 2006 8:15 am

2 Vs 4 Engines Debate

Tue Jan 20, 2009 4:04 pm

Quoting Na (Reply 7):
No. The outer engines are above belly level in flight. I would say on a twin with very big engines, like a 777, the chances would be highest for cartwheeling as their massive weight would be decisive.

Apples to oranges. Review the video of the landing, it spun sideways almost immediately after contact, presumably when the engine was sheared off. A little more airspeed and that would have been really ugly. Regardless of what a 4-holer does in level flight, one wing will dip more on contact with water and both engines on that wing will dig in.

PS> The outboard engine will also put greater stress on the wing root because of the longer moment arm.

[Edited 2009-01-20 08:07:19]
Airliners.net Moderator Team
 
na
Posts: 9812
Joined: Sun Dec 12, 1999 3:52 am

2 Vs 4 Engines Debate

Tue Jan 20, 2009 4:07 pm



Quoting MCIGuy (Reply 10):
Regardless of what a 4-holer does in level flight, one wing will dip more on contact with water and both engines on that wing will dig in.

But the momentum of one huge twin engine will be much higher than the smaller ones on a quad.
 
nomadd22
Posts: 1572
Joined: Fri Feb 22, 2008 7:42 pm

2 Vs 4 Engines Debate

Tue Jan 20, 2009 4:33 pm

The reasoning wasn't that a two engine failure was exceedingly improbable. It was that anything that caused both engines to fail would probably cause all four engines to fail. This incident did disprove that. It was an incredible coincidence that two geese would enter both engines in at the exact same time. (If that's what happened). A four holer would have probably had two engines left.
The problem is, there have been several incidents where single engine failures have caused enough damage to bring down the airplane on three and four engine jets, so more engines aren't really increasing your odds.
At least, that's what my brain says. The fact that I was on a C-130 that lost two engines for unrelated reasons kinda makes my gut say otherwise.

[Edited 2009-01-20 08:36:48]
Anon
 
User avatar
SEPilot
Posts: 5680
Joined: Sat Dec 30, 2006 10:21 pm

2 Vs 4 Engines Debate

Tue Jan 20, 2009 4:35 pm



Quoting Na (Reply 7):
No. The outer engines are above belly level in flight. I would say on a twin with very big engines, like a 777, the chances would be highest for cartwheeling as their massive weight would be decisive.

I doubt that. The point is to keep the nose up so that the aft fuselage contacts first; hopefully by the time that the engines hit there will not be enough energy left to cartwheel, although it may spin like the A320 did.
Let's keep this in perspective. When was the last time that a plane crashed because of bird strikes? The only one I remember was back in the early 60's, and it was a four engined plane IIRC. What is most surprising about this accident is that it happens so rarely. Adding more engines because of an event that happens once in 40 years is just silly, especially because it adds only a very small margin of safety; if there are enough birds to kill 2 engines there is a better than even chance that they can get all of them.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
RussianJet
Posts: 5983
Joined: Sat Jul 21, 2007 4:15 am

2 Vs 4 Engines Debate

Tue Jan 20, 2009 5:35 pm



Quoting SEPilot (Reply 13):
When was the last time that a plane crashed because of bird strikes? The only one I remember was back in the early 60's,

Ryanair 738 at Rome Ciampino a few months back also had double engine trouble owing to multiple bird strikes, but fortunately made the airfield.
✈ Every strike of the hammer is a blow against the enemy. ✈
 
OPNLguy
Posts: 11191
Joined: Tue Jun 15, 1999 11:29 am

2 Vs 4 Engines Debate

Tue Jan 20, 2009 5:39 pm

Having 4 engines (versus 2) doesn't necessarily ensure one can still avoid 5149's situation, and a good example of that is the USAF -135 that crashed near Fairbanks AK some years back.
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
ikramerica
Posts: 15104
Joined: Mon May 23, 2005 9:33 am

2 Vs 4 Engines Debate

Tue Jan 20, 2009 6:07 pm



Quoting Nomadd22 (Reply 12):
This incident did disprove that.

How so? Please show us how this is disproved.

Do you know that a 4 engine BAE146 would have only lost 2 engines to geese and not four? I can't see how you can know that…

Now, would tail mounted engines have been as susceptible to a double bird strike? That is a different question entirely.
Of all the things to worry about... the Wookie has no pants.
 
User avatar
SEPilot
Posts: 5680
Joined: Sat Dec 30, 2006 10:21 pm

2 Vs 4 Engines Debate

Tue Jan 20, 2009 6:21 pm



Quoting RussianJet (Reply 14):
Ryanair 738 at Rome Ciampino a few months back also had double engine trouble owing to multiple bird strikes, but fortunately made the airfield.

Yes, this has happened a number of times. The only other crash that I know of that was caused by birds was in Boston in 1960 when a Lockheed Electra flew into a flock of starlings. And that was a 4-engined plane at that. After searching I discovered another crash due to bird strikes; this one was a Vickers Viscount (UA 297) in 1962, also a 4 engined airliner. But this one crashed because the bird in question took out the horizontal stabilizer.

Quoting OPNLguy (Reply 15):
Having 4 engines (versus 2) doesn't necessarily ensure one can still avoid 5149's situation, and a good example of that is the USAF -135 that crashed near Fairbanks AK some years back.

I have searched for this one and cannot find it. Do you have any more info on it?
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
taxpilot
Posts: 66
Joined: Fri Sep 01, 2006 8:29 am

2 Vs 4 Engines Debate

Tue Jan 20, 2009 6:43 pm



Quoting OPNLguy (Reply 15):
Having 4 engines (versus 2) doesn't necessarily ensure one can still avoid 5149's situation, and a good example of that is the USAF -135 that crashed near Fairbanks AK some years back.

Correct. An E-3A (B 707-320) was lost in an accident on 22 September 1995 at Elmendorf AFB, Alaska. All 24 crewmembers were killed in the accident. The USAF accident investigation report concluded that the accident was directly caused by the ingestion of Canada geese into No. 1 and No. 2 engines. The ingestion of the geese into the aircraft's engines caused a loss of thrust that rendered this aircraft incapable of controlled flight.
 
Rj111
Posts: 3007
Joined: Wed Sep 08, 2004 9:02 am

2 Vs 4 Engines Debate

Tue Jan 20, 2009 7:26 pm

It will always be slightly harder to get birdstrikes in 4 engines as supposed to 2. You can't really deny that. You could argue however, that a smaller engine is more likely to be fatally damaged by a bird. In this situation, and in most where it's dense enough to lose two, it sounds like a quad would have suffered the same fate.

As for the ditching, i would have thought the quad would have handled better. The reason, is that the engines would have hung relatively higher to the body, then see the principal of leverage. That's just pure speculation though.

Way too rare an occasion to design for though.
 
ikramerica
Posts: 15104
Joined: Mon May 23, 2005 9:33 am

2 Vs 4 Engines Debate

Tue Jan 20, 2009 8:00 pm



Quoting RJ111 (Reply 19):
It will always be slightly harder to get birdstrikes in 4 engines as supposed to 2.

True, but this event didn't prove or disprove anything re: 4 engines, because there is no way to know if all 4 engines would have been hit by birds, or if 3 of 4 would have, not to mention that 4 engine planes can't do much on 1 engine anyway, or even 2.
Of all the things to worry about... the Wookie has no pants.
 
nomadd22
Posts: 1572
Joined: Fri Feb 22, 2008 7:42 pm

2 Vs 4 Engines Debate

Tue Jan 20, 2009 8:17 pm



Quoting Ikramerica (Reply 16):
How so? Please show us how this is disproved.

Do you know that a 4 engine BAE146 would have only lost 2 engines to geese and not four? I can't see how you can know that…

Now, would tail mounted engines have been as susceptible to a double bird strike? That is a different question entirely.

I'm not claiming to be psychic. Like everything else in life, I can only guess the odds. And I don't believe the odds favor a third strike just because two happened. You have hundreds of single engine failures without a second engine getting hit. You'll probably have hundreds of two engine strikes on a four holer for everty time a third engine gets hit.
I said this situation disproved the theory that separate causes will probably never cause both engines on a twin to fail. The causes were definitely related, but it was two different birds, or bunches of birds.
Anon
 
Viscount724
Posts: 19316
Joined: Thu Oct 12, 2006 7:32 pm

2 Vs 4 Engines Debate

Tue Jan 20, 2009 8:26 pm



Quoting TaxPilot (Reply 18):
An E-3A (B 707-320) was lost in an accident on 22 September 1995 at Elmendorf AFB, Alaska. All 24 crewmembers were killed in the accident. The USAF accident investigation report concluded that the accident was directly caused by the ingestion of Canada geese into No. 1 and No. 2 engines.

In July 1996, less than a year after the Alaska E-3A crash, a NATO E-3A was also written off in a non-fatal overrun accident in Greece after ingesting birds. Photos of the NATO aircraft below.





 
lhr380
Posts: 2453
Joined: Thu Jan 15, 2009 5:39 pm

2 Vs 4 Engines Debate

Tue Jan 20, 2009 8:32 pm



Quoting Viscount724 (Reply 22):

During my short stint in the RAF, there were a lot of pics of this around the briefing room, I always had a look and could not see what how the crash happened, or get any info on it. 4 years later here it is  Smile
(The views on this site are my own and no one elses)
 
Rj111
Posts: 3007
Joined: Wed Sep 08, 2004 9:02 am

2 Vs 4 Engines Debate

Tue Jan 20, 2009 8:49 pm



Quoting Ikramerica (Reply 20):


Quoting RJ111 (Reply 19):
It will always be slightly harder to get birdstrikes in 4 engines as supposed to 2.

True, but this event didn't prove or disprove anything re: 4 engines, because there is no way to know if all 4 engines would have been hit by birds, or if 3 of 4 would have, not to mention that 4 engine planes can't do much on 1 engine anyway, or even 2.

1 not a lot. But 2 would drastically increase your "glide" range.
 
gopal
Topic Author
Posts: 168
Joined: Thu Jun 03, 1999 3:05 am

2 Vs 4 Engines Debate

Tue Jan 20, 2009 8:50 pm

Twin or Quad, it looks like safety technology to avoid bird ingestion into engines needs to be developed. Skies are getting crowded, human population/settlements around airports is getting denser, which will increase the probability of bird hits to airplanes.

Sensors could be added to the fuselage/engines to detect birds/solid objects when they are several feet away from impact. These could be deflected either mechanically or by means of a blast of compressed air from the fuselage.
 
ikramerica
Posts: 15104
Joined: Mon May 23, 2005 9:33 am

2 Vs 4 Engines Debate

Tue Jan 20, 2009 9:05 pm



Quoting RJ111 (Reply 24):
But 2 would drastically increase your "glide" range.

No doubt. The plane might have made it to EWR. But it also might have made it to Teterboro like they were considering, and then run off the runway onto Route46 and burst into flames…
Of all the things to worry about... the Wookie has no pants.
 
nomadd22
Posts: 1572
Joined: Fri Feb 22, 2008 7:42 pm

2 Vs 4 Engines Debate

Tue Jan 20, 2009 9:16 pm

There's no way to know if the crew wouldn't be kidnapped by aliens either. If you're going to depend on proving negatives, you're in for a long wait. The evidence for multiple engine failures from bird strikes isn't lacking or hard to understand. Even if you fly into a large flock, the odds are very slim you'll suck up two birds. Hence my previous reference to the fact that there are hundreds of single engine failures for every dual failure caused by birds. Saying that those odds don't mean anything because "You can't prove birds wouldn't take out three engines" is ridiculous.
And four engine planes can generally fly across the ocean on two engines if they want. They just can't take off in the prescribed distance or climb very well. That's why BA doesn't consider a single engine out on a 747 anything to worry about.
Anon
 
ikramerica
Posts: 15104
Joined: Mon May 23, 2005 9:33 am

2 Vs 4 Engines Debate

Tue Jan 20, 2009 9:22 pm



Quoting Nomadd22 (Reply 27):
Saying that those odds don't mean anything because "You can't prove birds wouldn't take out three engines" is ridiculous.

It's far from ridiculous.

For a twin to have a two engine failure due to birds, it means the flock was on both sides of the plane. The odds of 3 or 4 engines out in this situation on the SAME SIZED AIRCRAFT would be pretty high, because we are talking about a very large flock of birds.

This is not the same thing as two engines on the same wing of a quad going out. In that situation, it is very likely that only one engine of the twin would go out.

It takes far more data than what you are claiming to come to any conclusion.

We would need to know how many twins have ever had both engines taken out completely by birds, how many quads have had 2 engines on one side, how many quads have had 2 engines but not on the same side, etc. Then we'd have to know whether wing mounting is more likely to lead to multiple strikes than tail or fuse mounting, etc.

It's not simple enough to say the odds would keep going down exponentially from 2 to 3 and 3 to 4...
Of all the things to worry about... the Wookie has no pants.
 
nomadd22
Posts: 1572
Joined: Fri Feb 22, 2008 7:42 pm

2 Vs 4 Engines Debate

Tue Jan 20, 2009 9:50 pm

Have you ever seen a formation of geese? A tiny one is wide enough to stretch the width of a plane. Some of them are miles long.
Now you're making me think. I hate that. I hope you're happy.
Geese aren't disorganized masses like pigeons or soccer fans. They like to stay in line. Or, two lines of a V if you like. If the plane hit one of those lines oriented along the direction of the planes flight, I could see how it might sweep up a lot of birds.
But I'd still bet Euros to donuts that the odds of three engines getting trashed are about one percent of the chances of two getting stalled.
Maybe they should just fly 777s. You could throw an ostrich into one of those suckers without stalling it.

[Edited 2009-01-20 13:57:49]
Anon
 
User avatar
SEPilot
Posts: 5680
Joined: Sat Dec 30, 2006 10:21 pm

2 Vs 4 Engines Debate

Tue Jan 20, 2009 9:52 pm



Quoting Ikramerica (Reply 28):

We would need to know how many twins have ever had both engines taken out completely by birds,

From my research the answer is one. More have had birds in both engines, but have not lost all power in both. And it appears that more quads have crashed due to birds than twins.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
Rj111
Posts: 3007
Joined: Wed Sep 08, 2004 9:02 am

2 Vs 4 Engines Debate

Tue Jan 20, 2009 9:58 pm



Quoting Ikramerica (Reply 26):


Quoting RJ111 (Reply 24):
But 2 would drastically increase your "glide" range.

No doubt. The plane might have made it to EWR. But it also might have made it to Teterboro like they were considering, and then run off the runway onto Route46 and burst into flames%u2026

More options are never bad though.
 
RussianJet
Posts: 5983
Joined: Sat Jul 21, 2007 4:15 am

2 Vs 4 Engines Debate

Tue Jan 20, 2009 10:00 pm



Quoting SEPilot (Reply 30):
From my research the answer is one. More have had birds in both engines, but have not lost all power in both. And it appears that more quads have crashed due to birds than twins.

How many six-engined planes have crashed because of birdstrikes? I believe it's none, so in a particularly specious piece of reasoning I'm going to say that this is definitely the safest configuration in respect of birds.  silly 
✈ Every strike of the hammer is a blow against the enemy. ✈
 
nomadd22
Posts: 1572
Joined: Fri Feb 22, 2008 7:42 pm

2 Vs 4 Engines Debate

Tue Jan 20, 2009 10:04 pm



Quoting RussianJet (Reply 32):
How many six-engined planes have crashed because of birdstrikes? I believe it's none, so in a particularly specious piece of reasoning I'm going to say that this is definitely the safest configuration in respect of birds. silly

Ha! We B-52 folks scoff at your six engines. *scoff*scoff*
Anon
 
bravogolf
Posts: 360
Joined: Thu Apr 21, 2005 6:18 am

2 Vs 4 Engines Debate

Tue Jan 20, 2009 10:18 pm

OK To take care off all possibilities 2 engines on the wing and three in back.
 
aviationfreak
Posts: 1071
Joined: Sun Nov 09, 2003 9:01 am

2 Vs 4 Engines Debate

Tue Jan 20, 2009 10:25 pm



Quoting Na (Reply 7):
No. The outer engines are above belly level in flight. I would say on a twin with very big engines, like a 777, the chances would be highest for cartwheeling as their massive weight would be decisive.

If I'm not mistaken engines are designed to break off in this kind of situations. Hence both engines of US1549 where on the bottom of Hudson river.

Sander
I love both Airbus and Boeing as much as I love aviation!
 
nomadd22
Posts: 1572
Joined: Fri Feb 22, 2008 7:42 pm

2 Vs 4 Engines Debate

Tue Jan 20, 2009 10:46 pm



Quoting Aviationfreak (Reply 35):
If I'm not mistaken engines are designed to break off in this kind of situations. Hence both engines of US1549 where on the bottom of Hudson river.

Sander

That turned out to be a false report the media ran with. One engine is still on the plane.
Anon
 
AFGMEL
Posts: 190
Joined: Wed Jul 18, 2007 8:39 am

2 Vs 4 Engines Debate

Tue Jan 20, 2009 11:19 pm

Those who know more than me can contradict me, but I am pretty sure that a four holer that flies into a flock of birds could lose two engines on one side. Not sure a heavily laden aircraft could handle that just after take off.
B 727-44/200 732/3/4/8/9 767-3 742/3/4, 772/3, A319/20/21 332/333 342/3 , DC3/4/10, F28/50/100, ATR72
 
jbernie
Posts: 206
Joined: Wed Jan 10, 2007 10:09 am

2 Vs 4 Engines Debate

Wed Jan 21, 2009 1:24 am

Maybe they should be looking at some kind of afterburners for take off so that you at least always get roast bird as a result  Smile

If a twin loses one engine to birds then it is possible that if it was a quad in that situation it would lose two engines, like wise with the US Airways flight, as it lost both engines to birds then it is quite likely that had it been a quad it would lose four engines.

As much as we try and reduce the risk in all situations it is not possible to have zero risk 100% of the time, think of the Mythbusters show, how many time do they try to test a scenario where they have documented & verified evidence that an event occured, yet they are unable to repeat the event because they not able to replicate the event to 100% accuracy. All you need is to have a freak occurance that can't easily be replicated and all that hard work goes out the window.
 
0newair0
Posts: 436
Joined: Fri Jun 01, 2007 12:21 am

2 Vs 4 Engines Debate

Wed Jan 21, 2009 3:36 am



Quoting Nomadd22 (Reply 12):
The reasoning wasn't that a two engine failure was exceedingly improbable. It was that anything that caused both engines to fail would probably cause all four engines to fail. This incident did disprove that. It was an incredible coincidence that two geese would enter both engines in at the exact same time. (If that's what happened). A four holer would have probably had two engines left.

You cannot assume that if the plane had 4 engines that the flock of geese would have missed the "extra" 2 engines. So, this incident did not disprove anything.


(...I may be wrong but I believe it was indeed a flock of geese and not just 2 geese flying around.)
That's not how this works! That's not how any of this works!
 
tdscanuck
Posts: 8573
Joined: Wed Jan 11, 2006 7:25 am

RE: 2 Vs 4 Engines Debate

Wed Jan 21, 2009 5:57 am



Quoting MCIGuy (Reply 4):
Two more engines would have greatly increased the chances that a wing would have been torn off and/or it would have cartwheeled.

Cartwheeling is one thing, but engine forces should never tear the wing off because they pylons are mechanically fused to prevent exactly that occurrence. This doesn't mean the engines will or won't come off in a particular event, but they should always come off before they cause structural damage to the wing box.

Quoting Na (Reply 11):
Quoting MCIGuy (Reply 10):
Regardless of what a 4-holer does in level flight, one wing will dip more on contact with water and both engines on that wing will dig in.

But the momentum of one huge twin engine will be much higher than the smaller ones on a quad.

That actually works in the twin's favour. The engine is big, heavy, and going straight ahead. The force the engine imparts to the wing is related to the decceleration of the pylon, not the weight of the engine. And, since the engine is heavier relative to it's frontal area (i.e. drag) the deceleration on a big heavy engine should actually be lower.

Quoting Nomadd22 (Reply 12):
It was an incredible coincidence that two geese would enter both engines in at the exact same time. (If that's what happened). A four holer would have probably had two engines left.

Since it's an incredible coincidence for two geese to enter to engines at about the same time, it's *very* likely that there were a lot more than two geese. And, since the engines are running full bore at relatively low speed, that leaves a lot of birds around for the quad to vacuum up.

Quoting Gopal (Reply 25):
Twin or Quad, it looks like safety technology to avoid bird ingestion into engines needs to be developed.

Why? An event that we all know is extremely rare caused zero fatalities. Very low probability of occurence coupled with very low consequence. That doesn't sound like too much of a call to action.

Quoting Gopal (Reply 25):
Skies are getting crowded, human population/settlements around airports is getting denser, which will increase the probability of bird hits to airplanes.

How does that increase the probability of bird hits? Increasing human population around airports should drive birds away, not attract them.

Quoting Gopal (Reply 25):
Sensors could be added to the fuselage/engines to detect birds/solid objects when they are several feet away from impact. These could be deflected either mechanically or by means of a blast of compressed air from the fuselage.

The airflow into a running jet engine is *far* larger than any practical volume of compressed air that could be carried on board, so your ability to deflect an incoming bird that way is very limited. Mechanical or aerodynamic deflection (which requires a mechanical movement somewhere) would be the only practical option...but you're talking about fitting a complex and, probably, heavy piece of equipment to mitigate an extremely small risk with apparently low consequence. Hard to see how that would meet the cost/benefit hurdles necessary to get on the airplane or to require FAR changes.

Tom.
 
bond007
Posts: 4428
Joined: Mon Mar 14, 2005 2:07 am

RE: 2 Vs 4 Engines Debate

Wed Jan 21, 2009 8:55 pm

If you fly into a large flock of geese ... aren't you more likely to get a bird ingested into the engine, the more engines you have??

Of course, there are details like the surface area of the engine, and the airflow into a 4 engine aircraft, not being twice as much as a 2 engine aircraft ... but you get my point.

Jimbo
I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
 
tdscanuck
Posts: 8573
Joined: Wed Jan 11, 2006 7:25 am

RE: 2 Vs 4 Engines Debate

Thu Jan 22, 2009 3:30 am



Quoting Bond007 (Reply 41):
If you fly into a large flock of geese ... aren't you more likely to get a bird ingested into the engine, the more engines you have??

Yes. However, the argument is basically about total engine loss, which requires two hits on a twin but four on a quad.

Tom.
 
bond007
Posts: 4428
Joined: Mon Mar 14, 2005 2:07 am

RE: 2 Vs 4 Engines Debate

Thu Jan 22, 2009 5:53 am



Quoting Tdscanuck (Reply 42):
Yes. However, the argument is basically about total engine loss, which requires two hits on a twin but four on a quad.

I understand, but if a 4 engine aircraft is twice as likely to get a bird in the engine, than a 2 engine aircraft ... simply because it does have more engines that a bird can be ingested into ... doesn't that make the chance of total engine loss the same  Wink

I know I'm assuming that the surface area of the engines is twice as much for this argument, which isn't true of course, since the engines on a 4-holer are generally smaller than those on a twin, but it must be at least 3 times the area perhaps?

If I'm trying to catch birds with a net, I'm twice as likely to catch one with 2 people and 2 nets, aren't I? Although I expect the answer is, no, not if the two nets are half the size of the single net!


Jimbo
I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
 
tdscanuck
Posts: 8573
Joined: Wed Jan 11, 2006 7:25 am

RE: 2 Vs 4 Engines Debate

Thu Jan 22, 2009 6:13 am



Quoting Bond007 (Reply 43):
I understand, but if a 4 engine aircraft is twice as likely to get a bird in the engine, than a 2 engine aircraft ... simply because it does have more engines that a bird can be ingested into ... doesn't that make the chance of total engine loss the same

Yes, at least in my opinion. I would consider running through a large flock of birds to be a common mode failure, and just as likely to take out a twin, quad, or trijet. It's probably not exact due to the details of engine placement and areas, but I suspect it's close enough as makes no difference.

Quoting Bond007 (Reply 43):
I know I'm assuming that the surface area of the engines is twice as much for this argument, which isn't true of course, since the engines on a 4-holer are generally smaller than those on a twin, but it must be at least 3 times the area perhaps?

Exhaust velocity is pretty constant across engine sizes (for commercial jets) so, to first order, total engine area should be roughly proportional to installed thrust. So, for the same MTOW, a twin will have about 50% more engine area than a quad. However, for the same total installed thrust the areas should be about equal.

Tom.
 
User avatar
HAWK21M
Posts: 30114
Joined: Fri Jan 05, 2001 10:05 pm

RE: 2 Vs 4 Engines Debate

Thu Jan 22, 2009 8:09 am

If the topic concerns bird strikes on Aircraft engines.....Would a Four Engined aircraft loosing both engines on one side at a critical phase in flight not be unstable to manuvere.
Secondly I feel We need to work out a solution to keep aircraft away from these Bird flock to avoid such Incidents.

regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
User avatar
Starlionblue
Posts: 20478
Joined: Fri Feb 27, 2004 9:54 pm

RE: 2 Vs 4 Engines Debate

Thu Jan 22, 2009 9:08 am



Quoting HAWK21M (Reply 45):
Secondly I feel We need to work out a solution to keep aircraft away from these Bird flock to avoid such Incidents.

Kill ALL the birds. ALL of them. Except chickens and ostriches and penguins. They can stay. Everyone else dies.

Problem solved. Tell Al Gore to send me my check now.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
User avatar
SEPilot
Posts: 5680
Joined: Sat Dec 30, 2006 10:21 pm

RE: 2 Vs 4 Engines Debate

Thu Jan 22, 2009 10:47 pm

The actual facts of the issue are that this is the first twin engined airliner that has actually crashed due bird strikes. Ironically, there have been at least 2 four engined airliners that have crashed due to birds, albeit neither of them were jets. There has also been at least two military quads discussed above that have crashed due to birds, so my conclusion BASED ON HISTORY is that twins are safer, especially considering that twins vastly outnumber quads in the fleet. Any arguments about probabilities should be tempered by the actual record.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler

Who is online

Users browsing this forum: Adispatcher, IAHFLYR and 48 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos