Why do Dassaults have 3 engines?

[tuna hp]

Why does Dassault still design 3 engine planes when from everything I read about airplane design, 2 engine configurations are cheaper and more efficient?

From a safety standpoint, I have read a lot of arguments that 2 engines are just as safe. You're less likely to lose an engine to begin with, and at least with the old airliner trijets, you couldn't maintain altitude with 2 engines out anyway. Are Dassaults designed to maintain altitude with 2 engines out? With 2 engines out could they attempt a landing and climb out of it if they needed to?

The question about the choice of 2 or 3 engines has really captured me because everything I read about airliners choosing 2 vs 3 vs 4 engines says that 2 engine designs are more fuel efficient (lot of reasons: higher bypass ratio, less tip spacing loss relative to thrust, less internal drag compared to thrust, less nacelle drag) and lighter (2 engines will be lighter than 3 that make the same thrust, airframe design can be lighter), and better takeoff performance (because of higher max thrust).

And yet I look at the trijet Falcons and compare them to other planes in their weight and range classes and the Falcons always win in both fuel consumption and runway performance. Sometimes by large margins. How is that? Is it only because Falcons also typically have the smallest cabins in their class?

Or is it for some more interesting technical consideration in choosing between 2 and 3 engines? I completely understand that if you wanted X total thrust, it would be more efficient to get it out of 2 engines than 3. However, from what I have learned the dominant factor in figuring out the thrust that you need for an airplane is the regulation that mandates that a plane must be able to lose its most critical engine at its most critical point in takeoff and still be able to complete it. So say that this amount of thrust needed is A, then a bijet needs 2A total thrust while a trijet only needs 1.5A total thrust. A little less actually because the bijet will get more drag off the dead engine and the vector of its thrust will be farther from the planes center of gravity so plane has to waste more power trimming. Could this single consideration mean that when you take into account this regulation that trijets are actually more efficient than bijets?

And what about takeoff performance? Planes like the Global Express and G550 destroy the Falcon 7X in thrust to weight ratio, and yet the Falcon only needs 5,500' of runway compared to 6,000' or 6,300'. What could possibly be the reason for this? Only wing design? That seems doubtful to me, because a wing that so completely dominated others in low speed lift would also have to perform more poorly at high speeds and yet the 7X gets maximum efficiency at M.80, can fly somewhat efficiently at M.85, and an article in flying magazine claims that they took the plane up to M.93. Just as fast as those other planes. I don't know anything about turbine or airplane design but I know that for turbochargers in cars, smaller turbines spool up much faster. Could this mean that trijet designs have an inherent advantage in takeoff performance? Do they?

[wondering]

Another advantage: More direct routings when compared to ETOPS limited twin engine aircraft.

And dont they just look beautiful :)

[Arkwright]

The Falcon 900 EX has similar range and speed to a G4, but uses a LOT less fuel! :ok:

We practice single-engined go-arounds, (yes, thats TWO engines failed with 1000' AGL DA), on the recurrents.

The performance manual has data on two engines operating departures. :D

And yes, they do look beautiful! :E

[capt.sparrow]

yet the Falcon only needs 5,500' of runway compared to 6,000' or 6,300'. What could possibly be the reason for this?

Leading edge slats. Allows low speed arrivals/departures but high speed wing for cruise.

[Pugilistic Animus]

ETOPS =extended operations in the US applies to three/four engine jets, but that's only if they are operating more than 180 minutes from a suitable alternate

[tuna hp]

Another advantage: More direct routings when compared to ETOPS limited twin engine aircraft.

And dont they just look beautiful

They are by far the best looking jet, but I'm pretty sure that ETOPS doesn't apply to privately operated planes (probably including fractional operators) and does it even apply to charter operators?

We practice single-engined go-arounds, (yes, thats TWO engines failed with 1000' AGL DA), on the recurrents.

So Dassault does in fact take advantage of their 3 engine design to give a safety advantage. That is very interesting. I was reading an article comparing different number of engines and the probabilities of losing engines. If the probability of losing any single engine is P, then on a twinjet the probability of losing 2 engines is p^2 and on a trijet its 3p^2... 3 times as high. I also know that the central engine on the 7X has fewer redundant systems than the outside engines and what twinjet engines would have. In this equation that would make P higher in the trijet. But if the plane can operate safely on 1 engine then thats still probably a big safety advantage.

Leading edge slats. Allows low speed arrivals/departures but high speed wing for cruise.

The Gulf doesn't have the leading edge slats but I believe that the Bombardier does and it still requires 6000'. So you don't think that there's anything inherent to the 3 engine design that would aid runway performance? Dassault trijets have always been known for their runway performance, but then if you look at the performance of their Falcon 2000 twinjet its nothing special at all. Does Dassault simply coincidentally engineer its trijets' wings for good runway performance or is there something inherent to having 3 engines? Thats what I'm trying to find out. I have a guess that more smaller turbines could produce more thrust early in the takeoff run but I could be way off.

[Pugilistic Animus]

those operating under 135 rules:)

[tuna hp]

those operating under 135 rules:)

What? If they are operating under part 135 then they need to follow full ETOPS? Without special maintenance programs they have to stay within 60 minutes of a diversion, and with ETOPS certification they still have to stay a max of 180 minutes? Would a normal American bizjet charter operation have to operate part 135 / follow ETOPS? If so, is it something that everyone does and they all have the 180 minute clearance or is it something that is very rare?

[tuna hp]

The Falcon 900 EX has similar range and speed to a G4, but uses a LOT less fuel!

I know and I'm desperately curious to find out how :ok:

[poss]

I don't know if the Dassault is an example of this but I read somewhere that some tri engined a/c use the 3rd engine, mostly, for take off... perhaps what I read was utter crap, as I say I cannot confirm the source as it was a while ago.

[Pugilistic Animus]

no private jets can do 91 if they want

but if you decide to use the benefits of etops flight then you will have to pay the associated costs; if you don't want to stop for refuelling in Kiribati with the canibals:}

[Red Goose]

Why do Dassault's have 3 engines?

Pax feel better with 3 engines when coasting out at FL370 overhead Seattle on the way to Maui (so do I!)

yet the Falcon only needs 5,500' of runway compared to 6,000' or 6,300'. What could possibly be the reason for this?

Two-engine aircraft are much more limited in the 2nd segment climb perf than three-engine aircraft.

The Falcon 900 EX has similar range and speed to a G4, but uses a LOT less fuel!

It's also about 10 tons lighter!

My simple thoughts about it,

Red

[tuna hp]

Two-engine aircraft are much more limited in the 2nd segment climb perf than three-engine aircraft.

Why do three-engine aircraft with lower maximum thrust than two-engine aircraft getter better second second climb performance? Do you mean with one engine out? I don't know much about airplanes or flying: would that takeoff distance (5500') be calculated based on how fast the plane must get going before it leaves the ground in case it loses an engine?

It's also about 10 tons lighter!

Yeah how the hell does Dassault build its planes so lightly?

G450
Range: 4450nm
Cabin Volume: 1525 ft^3
Basic Operating Weight: 43,000 lbs
MTOW: 73,900 lbs

900EX
Range: 4500nm
Cabin Volume: 1264 ft^3
Basic Operating Weight: 24,700 lbs
MTOW: 48,300 lbs

Same range, roughly same speed and altitude performance, and the G450 has only 20% more cabin volume, why the hell does it weigh 75% more? And Dassault cabins are supposed to be the quietest even with the engine right behind it so I know that they aren't skimping on insulation...

[Red Goose]

Second segment climb (from gear up to 400ft above ground, 2.4% climb gradient for 2 engine aircraft, 2.7% for 3 engine aircraft), a certification requirement, is more limiting on 2 than 3 engine aircraft. This is simply due to the fact that with a 3-engine aircraft, with one engine out, you only lose 1/3 of your thrust (more drag, true, but you're still doing better!), and that counts for take-off performance.

how the hell does Dassault build its planes so lightly?

Probably, because they are used to building fighters, where every pound counts.
As an example, Cessna and Dassault developed the Citation X and the Falcon 2000 at the same time.
Cessna realized their aircraft was heavier than expected, so they had the power of their engines increased.
Dassault found out their aircraft was performing better than expected, so they had there engines de-rated.

[Arkwright]

Dassault trijets have always been known for their runway performance, but then if you look at the performance of their Falcon 2000 twinjet its nothing special at all.

Dassault Falcon 2000 (two engines) only has outboard leading edge slats. Falcon 7X and 900 (three engines) have both inboard and outboard slats.

[Red Goose]

Dassault Falcon 2000 (two engines) only has outboard leading edge slats. Falcon 7X and 900 (three engines) have both inboard and outboard slats.

And that increases the Vref, at similar weights, by 4 knots.
Take-off performance is not affected that much, though.

[Paradise Lost]

It's all been said now....G4 is 10 tons heavier= worse fuel burn.
Pax prefer 3 engines.
Second segment climb better with just 33% loss of power.
Short field performance due to a slatted wing.
......and they DO look good too........

[tuna hp]

Second segment climb (from gear up to 400ft above ground, 2.4% climb gradient for 2 engine aircraft, 2.7% for 3 engine aircraft), a certification requirement, is more limiting on 2 than 3 engine aircraft. This is simply due to the fact that with a 3-engine aircraft, with one engine out, you only lose 1/3 of your thrust (more drag, true, but you're still doing better!), and that counts for take-off performance.

Yes but if you compare the Dassaults to their competitors they have engineered the planes to take advantage of this. They have significantly lower thrust/weight ratios to begin with. After losing an engine and 1/3 of their power their thrust/weight ratio is still within 10% of a gulfstream losing one of its engines since the gulfstream has so much more thrust to begin with. If Dassaults started with higher maximum thrust maybe that would change their efficiency and they wouldn't be as economical relative to the other planes.

My basic questions about 2 vs 3 have not really been answered.

-Suppose that you would engineer a trijet to have 80% of the total thrust you would have engineered a twinjet to have assuming you were making a plane with roughly the same characteristics. Is the plane heavier with 2 engines making X thrust or 3 engines making .8X thrust? Assuming an S-duct layout like the Dassaults

-Is there something about engines operating closer to their maximum rating being more efficient? If you are making a twinjet and a trijet with the same characteristics, is it going to get better cruise economy with 2 engines that produce Y cruise thrust out of X maximum thrust or the trijet that needs about the same Y thrust to cruise out of .8X maximum thrust?

-What are some of the performance tradeoffs between having 3 smaller turbines versus 2 larger ones? If you have a plane that needs 50 "thrust" for takeoff, then the twinjet needs 50 thrust per engine and the trijet needs 25. So the twinjet engines will be twice as powerful. I know for example that the twinjet engine will be more efficient in terms of energy used per lb of thrust produced. Will the smaller engines spool up to their higher thrust levels faster? Is it significant enough to effect takeoff performance? What are the other tradeoffs?

[DA50driver]

Assume you need 100 units of power to maintain level flight. If you have three engines that produce a total of 300 units you have 200 units available for climb. (Excess power available for climb). If you have two engines that produce a total of 300 units and one stops delivering power you are down to 150 units of power, in a three engine airplane you still have 200 units left. (50 units more, or 100%). This is simplified greatly, but it is the concept.

It is all about the percentage of power loss. This also affects runway performance numbers for take off. You get to see the end of a lot of runways in three and four engined airplanes, as opposed to 2 engine airplanes that rotate at a much earlier point due to the requirement to cross the end of the runway at 35'.

I spent a lot of time in the Falcon 900EX, I loved the airplane. It handles like a dream and it has redundancies that make the cold, dark Atlantic look a lot less intimidating:) I am currently flying a Gulfstream 450, which has as much power in one engine as the 900 had in 3. It is also a great airplane, very comfortable, spacious and built like a tank. Prior to the 450 I flew the Gulfstream 5, which has a different wing than the 450. The 5 had runway performance numbers close to that of the 900 for the same stage lengths. (4000' of runway is plenty for flights up to 6 hours).

The cruise power setting in a Gulfstream is approximately 82% power, giving a total fuel burn of approximately 2500lbs/hr. In the 900EX the power was in the low 90% range with a total fuel burn of 1900lbs/hr at mach .80. (you can cruise faster in both, but .80 seemed like a good trade off for speed vs. fuel burn).

They are all great airplanes, just different. The Gulfstream crowd refer to the engines on the 900 as hair-driers by the way.

[tuna hp]

Thanks for the details, DA50driver.

This also affects runway performance numbers for take off. You get to see the end of a lot of runways in three and four engined airplanes, as opposed to 2 engine airplanes that rotate at a much earlier point due to the requirement to cross the end of the runway at 35'.

Thats very interesting I didn't know that. That would seem to give 3 and 4 engine planes an inherent takeoff advantage when you include following regulations. Is that a significant difference in actual takeoffs?

The cruise power setting in a Gulfstream is approximately 82% power, giving a total fuel burn of approximately 2500lbs/hr. In the 900EX the power was in the low 90% range with a total fuel burn of 1900lbs/hr at mach .80. (you can cruise faster in both, but .80 seemed like a good trade off for speed vs. fuel burn).

Those percentages are what I was trying to articulate. Twinjets cruise at lower power percentage because they have higher maximum power/ weight ratio. Do turbofan engines operate significantly more efficiently at either 82% or 92%? From what I know intuitively about engines, the higher the pressure ratio of the combustion, generally the more efficiently it operates. If both a small turbofan and a big turbofan were built to the same level of technology and could operate at the same maximum pressure ratio, then the twinjet operating at 82% should be working at a lower pressure ratio than the trijet at ~92%. I wonder if that is significant to efficiency differences between twinjets and trijets.

Also thats relevent to your example of the twinjet and the trijet that both need 100 units of power to maintain flight. A twinjet would need to produce at least 200 but I trijet should be able to do it with 150. So if you do it with the smallest engines possible, then with 1 engine out both planes will have the same performance (100). I know that falcons are engineered to be able to fly on 1 engine, but isnt the real relevant aspect that they have to be able to complete a takeoff run on 2 engines? I don't know if the takeoff run requires more than twice as much power as maintain level flight... but my point is that with all engines, twinjets have higher thrust/weight ratios than Falcons. Yeah they beat Gulfstream thrust/weight ratios with one engine out, but not by 33% as in your example, I think its actually under 10%. If Falcons had the same all-engine thrust/weight ratio as Gulfstreams I imagine that they would have to be much less efficient.

[CL300]

It is all about aerodynamics, the exhaust of the third engine and the design of the tail section induce a laminar flow with virtually no parasite drag. The work on the Falcon 2000 for the computation of the area_ruling that governs the aft fuselage was horrendous.
Therefore, with the the same amount of thrust you are saving around 30%, just in aerodynamic excellence. On a Falcon you do not have unnecessary feathers.

Now a cabin size stand point , the 7X could have been better, but since the fuselage certification is a big chunk in a program; Dassault is still using the grand fathers rights of the Falcon 20 certification....only 40 years old...bugg_er.

Now they want to go all electrics...a twin-engine electric...;sounds like a R/C model...:rolleyes:

[tuna hp]

It is all about aerodynamics, the exhaust of the third engine and the design of the tail section induce a laminar flow with virtually no parasite drag. The work on the Falcon 2000 for the computation of the area_ruling that governs the aft fuselage was horrendous.
Therefore, with the the same amount of thrust you are saving around 30%, just in aerodynamic excellence. On a Falcon you do not have unnecessary feathers.

Yeah I knew that was an advantage of the 3 engine layout... thats the sort of thing that I was trying to figure out. It is generically said that 3 engines are heavier than 2 larger ones, but if you can save 10 feet or more in necessary fuselage tapering AND still come away with better aerodynamics, then who knows. I suppose its an extremely technical question. I would love to pick the brain of a dassault engineer for an hour, ha.

All electric? I don't see how thats possible in long range planes.

[CL300]

The name of the pepole you want to speak with is CATIA; with a couple of bundles for aeroynamic and visco elasticity modules. Aera ruling is more trial and errors than a true science, nethertheless results are proven indeed...

For the electric gizmo; they only speak about flight controls, brakes, etc.. Not the engines...It was initially Rolls Royce, but apparently some last minutes with the silvercrest (snecma) are giving a new deal.... Let us see what comes out of the box... Hopefully it won't have winglets....:{

[galaxy flyer]

Over oceans or remote areas, three or four engined planes do not have to divert upon loss of an engine, they can continue on 2/3 to their destinations, if 1/2 cruise ceilings are above the terrain and no other system emergency dictates a divert. ETOPS or not, an engine failure on a twin over water or Siberia has a real problem. See numerous threads about BA going on three from LAX to LON, Manch, actually.

GF

[Rosbif]

It would be interesting to see if the the drag caused by the rudder counteracting the assymetric thust after failure of an out board would be more, or less than, the additional drag caused by the loss of laminar flow around the tail after the failure of the centre engine. In either case, there are scenarios in which completion of a flight with an engine out will burn very little, if any, extra fuel. (With the FA50, at least).

[merlinxx]

ETOPS = Extended twin engine ops (DA50, 900 & 7X not twins thus EROPS)
EROPS = Extended range ops (multi i.e. more than 2 engines)

[unablereqnavperf]

Well at the end of all this discussion it all comes down to one thing. Europeans design their aircraft,cars etc for the job they have to achieve using all the very best technology available or indeed develope technology for the the equipment. American design rules are as follows design something big enough to fit overweight people in along with their over-inflated ego's, design it larger than it needs be so that the machine helps to further inflate already overinflated ego, then discover that said machine won't fly. Solution put a bigger engine on it!! ( just like their poorly designed cars that the world no longer wants to buy).

Dassault builds some of the best machines in the sky, having flown their military products and civil products I speak for both. Beautiful to look at even better to fly and cost effective to operate. Subttle strong and capable something US designers can only dream of!:D

[NuName]

I do hope our American friends can forgive you for your unsolicited ruddeness, at least they can spell better than you.

[con-pilot]

American design rules are as follows design something big enough to fit overweight people in along with their over-inflated ego's, design it larger than it needs be so that the machine helps to further inflate already overinflated ego, then discover that said machine won't fly. Solution put a bigger engine on it!!

Really, you obviously never flew a straight Falcon 900. It could barely get out of its own way. How did Dassault fix it, installed more powerful engines.

That being said, I flew Falcon 50/50EX/900B/900EX and loved them. I also took a demonstration flight in a straight 900 at MGTOW, in the summer. We didn't buy it.

As for the rest of your remarks; well, there is just no accounting for rudeness, is there. :rolleyes:

Back to a civil discussion on the subject. We had a fly off between the G-IVSP and the 900EX. We chose the 900EX for one primary reason, the 900EX can, under winter temperatures/conditions in good weather go non-stop from Aspen, Colorado to London, UK. The G-IVSP could not under any condition.

Also flying trans Pacific routes, having that third engine was/is great peace of mind. (There's a lot of real dark water at night between Hawaii and Guam.)

[ollycopter]

I know its just my opinion but I always felt the falcons looked like old aircraft.. I totally agree their performance is impressive, but they are NOT beautiful machines.. The 7X is the best so far but it just longs slightly off somehow, and the 900 looks like a retarded tristar.. A little short fat eye sore :D

Global got a pretty machine, the 550 is still stunning and the 650 is just gorgeous..

[con-pilot]

Oh well, as they say, beauty is in the eye of the beholder.

Needless to say I disagree. Now, you take a Hawker 125, that's ugly for you. :p

[Flightdeckone]

Unablereqnavperf

Charisma bypass reversals are now available.:ugh:

[TURIN]

I do hope our American friends can forgive you for your unsolicited ruddeness, at least they can spell better than you.

And you too Probably. :ouch:;)



Back to the thread,

When the question "Why has 'abc' got 3 of them?" is asked, the chorus of replies is usually "'cos two's not enough and four's too many". :ok:

[con-pilot]

When the question "Why has 'abc' got 3 of them?" is asked, the chorus of replies is usually "'cos two's not enough and four's too many".

Well you know the old joke.

Why do you only fly four engine aircraft over the oceans?

Because they don't make five engine aircraft.

:ok:

[NuName]

TURIN
:confused: you think I'm rude too?:p Your allowed a spelling mistake when your being polite.

[DA50driver]

Because they could not find room for a 4th. The 900 is severely underpowered. Or maybe its just because my fat ass weighed it down? And I am not even an "American".

I used to listen to G5 pilots talk about the 3 hair driers mounted on the 900. It hurt my feelings as I thought quite highly of the plane. Now I totally understand what they were talking about. Need to change my name from DA50driver now I guess.

[con-pilot]

From what I understand there are no straight 900s anymore. I believe that they were all upgraded to 900Bs.

Could be wrong, wouldn't be the first time.

[His dudeness]

Well at the end of all this discussion it all comes down to one thing. Europeans design their aircraft,cars etc for the job they have to achieve using all the very best technology available or indeed develope technology for the the equipment. American design rules are as follows design something big enough to fit overweight people in along with their over-inflated ego's, design it larger than it needs be so that the machine helps to further inflate already overinflated ego, then discover that said machine won't fly. Solution put a bigger engine on it!!

Well, I´m european, fat and I hate the cramped cockpit of my sovereign.

And my peers are all sleek, otherwise the sov would be too small. Slight flaw in yer thinking, innit?

I´d vote for the best of both worlds, a Challenger 300, as room as I need it and as small as I want it if I´d have to clean it.

Still, the Falcons are the beauty queens...IMO

[leonard17F]

...to you all for these very useful infos.

[exitfirstright]

Readng this thread there are few 'facts'.

First a bit of History!
3 engines vs 2 is a long debated topic but the issue started with relaibility. Long ago aircraft generally had three engines - 727, Trident, DC10, L1011 then relaibility improved and one engine dropped off. But its not just engine relability its system relaibility/redndancy that is as crucial. Engines often fail due to systems!

2. The Falcons engines are three lower powered - fact. Its got three Lear45 engines screaming their little heads off! The engines on the 900 (&7X for that matter) do not have an airline application which builds relaibility, lowers shutdown rates etc. Take for example the G4's Spey or the Challengers 604 CF34, the later having over 50 millions. The GV/GEX has the RR BR700 series also on an airliner - albeit defunct now.

3. Systems are probably more crucial. Check the latest level of redundancy in the hyrdaulics. electrics, fuel etc and the Falcon is lacking. Fine, set out for Maui in your 900 by all means but if these go you are as good as stuffed! The more recent aircraft have the redudancy of systems built in.

4. The infomation about the runway length/slats does not take account of the weights. Guess what the 900 is lighter - Falcon cheat with the interior - just look at the seats, small galley etc. Comparable approach speeds of the Gv and GEX prove this - GEX is 109kts and the GV is 129kts. Also you can get the GEX into & out of 4000ft. which is suicide in a GV!

Finally, Falcon have explianed to me with any satisfaction how if they have it right on the 900 and formerrly the F50 - both 3 holers, then are they wrong on the F2000 which was built to counter the 604, which is, yes you are right, a two holer....

Two is fine. Three is weight and maintenance costs.....:D

[con-pilot]

We purchased a 900EX after a great amount of research between the G-IVSP and the 900EX. We conducted a fly-offs between the two aircraft on trips that fit our trip profile. The fly-off were to see which aircraft could perform the following legs non-stop.

Oklahoma City-London/London-Oklahoma City. (Both aircraft could do this leg.)

Aspen-London. (Only the 900EX could do this leg and only when the OAT was -05 c. with good weather at Aspen. The G-IVSP could not do this leg no matter how cold the OAT was in Aspen.)

Aspen-Bogotá Colombia. (Both aircraft could do this leg, however, in the summer when the OAT was above, I believe 15c, the G-IV was unable to go non-stop.)

Plus a few others that both aircarft could do non-stop.

As the owner lived for the most part in Aspen and secondly in London, the non-stop Aspen-London leg was the most important to him. The only other two aircraft at the time that could go Aspen-London non-stop were the Global Express and the G-V, both of which were out of our price range. Therefore we chose the 900EX.

As for cabin size comparison it may interest you to know that the 900 has more space in the 'living' or passenger cabin area than the G-IVSP. This area excludes the galley and the aft lav. A small point and a small amount of square footage I'll admit. The size of the galley in the 900EX never caused us any problems.

One more point that was important to me and the other pilots was that loading baggage into the baggage compartment was a hell of a lot easier on our backs with the 900 verus the G-IV. A small thing admittedly and not something the passengers don't really care about, but was never the less a factor.

Other point, going across the Pacific Ocean having three engines, compared to the two, was a nice comfort factor to me at least.

Another point is that 900 was much lighter on the controls that the G-IV. The G-IV reminded me more of a 727, where the 900 flew more like a Sabre 40 or a Lockheed Jet Star.

However, in summation, I would have been just happy flying the G-IVSP if that been the aircraft the boss chose to buy. Both aircraft are great and again I would been happy flying either one.

[7xXx]

Good "hands on" feedback !:ok:

[Arkwright]

Existfirstright,

I may have to dispute some of your 'facts'!

Not sure about the 7X engines, but the 900 engines which you say have no airline history is somewhat incorrect. The Honeywell engines on the Lear 45 and Falcon 900 are in fact the core units from the McDonnell Douglas DC10/MD11 APU's. I know APU's don't have to be as reliable as the primary powerplants, but the BAe 146 and Chinook and others seem to manage OK!!

I'm no expert on Gulfstream's or Bombardier products, but the 900 does have two completely independent hydraulic systems with four hydraulic pumps..... how many other bizjets have four independent pumps?

[petdemouche]

At the same time, given the close proximity of the 3 engines, I'm not that convinced by the safety argument.
It's nice if one of the engines goes down (no fuel :rolleyes: ?), but if it's an uncontained failure, it would probably have been better to have just one engine, but on the other wing...no ?

Nice plane though.

[Time Traveller]

Chinook and others seem to manage OK!!

Hmm; not so sure about that!

Also, that engine had two major flaws which wouldnt necessarily show themselves in APU application - Rollback, and bleed air contamination.

[Arkwright]

Well, an uncontained failure between engines one and three on the 900 are no different than any other pylon mounted twin engined jets, with any failure debris having to puncture through the fuselage to get to the other side.

Most people don't realise that the centre engine on the 900 and 7X is mounted well aft of the other two. There is a large 'S' duct and nacelle entrance is not where the mid engine is mounted!!!!

Certainly the BAe 146 has had its fair share of contaminated air issues, but the DC10 APU was/could be used in flight to assist pressurization and bleed air to the cabin, so not sure there's much mileage in that argument?

[Time Traveller]

I'm not an expert on the subject, but I believe the contamination issues only arose when the engine was used as such, and not as an APU. There are some significant differences in extracting air from an APU versus an engine, plus of course, the exposure to engine air lasts a lot longer.

Rollback was an issue above F260 - not a factor thats going to become apparent as an APU!

[falconeasydriver]

The bigger issue in respect of the Honeywell engines in the 900EX and EASy's that I've flown, is the issue of engine runaway...and I believe a lear was "parked" into a hangar at some point thanks to this.
Never heard of the bleed air issue before, so thats a new one on me.
Lastly, the Falcon has 3 levels of redundancy when it comes to flight controls, 2 independant hydraulic systems, and manual reversion...a bit like a 737.

[Arkwright]

Well ditto, I'm no expert on this either, but I don't see why there is a difference in extracting bleed air from an engine just because its being used as primary power rather than auxiliary?

Which aircraft fitted with these engines suffered from 'rollback' issues then? I've certainly never heard of these major flaws you refer to!

There is certainly more protection from this with FADEC/DEEC when used as primary sources of power.

[Pilocol]

Hey, CON-PILOT I honestly hope you are talking about London (Canada) not UK. .. First ...
Second ... doubt on the Aspen - Bogota ...

Keep it safe .

[DA50driver]

I used to operate a GV out of EGTK, Oxford, England. Its about 4300'. Hardly even touched the brakes on that runway.

I think you have mixed the numbers for a G4 in there. 4000' would be tight for the 4, yet doable.

The Vref for a G5 is much lower than 129 at typical landing weights. I seem to recall 108.

[exitfirstright]

Please lets keep it sensible!! APU's are now powerplants, I dont think so.
As for the 146 well they had four engines and struggled to keep them all going. Three & Spare I recall my mate saying after flying one in Oz.

Falcon must be loving you for saying they have 3 x APU engines driving their fine aircraft. Also the Chinook came in for grief as the engines were - yes - unrelaibale! They are the engines in the original 146 - Lycoming ALF somethings... now there was a successful program, it nearly broke BAE.

As for the runway the Global needs 4139ft at ISA SL vs 5150ft for the 900EX for a 3,700nm mission.

Systems - I defy anyone to fly manual reversion at FL450.The Falcon has Dual Primary Flight Control Systems plus man. rev while the Global has three primary hydraulic. It also has 7 hydraulc pumps vs 4 on the 900 and 6 electrical vs 4.

One minor point while researching this topic the Flaocns range quote is at M.80 against M.85 for the Global.

The Global is simply more airplane and of course costs more money, there is mush more real estate down the back,

[NuName]

Comparing a Global to a 900 is daft, two different machines completely, and each wonderful in thier own way. Anyone that wants to knock the Falcons obviously has not flown them.

[7xXx]

Hey, CON-PILOT I honestly hope you are talking about London (Canada) not UK. .. First ...

What's surprising with a 900EX eastbound dear Pilocol ?...I remember a Mumbaï- Paris (France not Texas) wich was about 10h20min with the same type and more recently a KTEB-UUWW wich is around 4100nm with a EX..9H15...with everything required fuelwise and more...(Charter flight)

[falconeasydriver]

Systems - I defy anyone to fly manual reversion at FL450.The Falcon has Dual Primary Flight Control Systems plus man. rev while the Global has three primary hydraulic. It also has 7 hydraulc pumps vs 4 on the 900 and 6 electrical vs 4.


That is either a deliberate dig, or more likely one of the more idiotic statements I've read on PPrune in a long while.
First of all, why would you be at FL450 in a 900EX as in most configs you would struggle to get there unless you were on fumes, and secondly, why would you consider staying up there with two hydraulic systems failed?

I'm afraid your comparison is totally nefarious, 2 totally different aircraft for two completely different missions.
I'd love to see a GLEX get in and out of LCY for example, and then trott off to DXB.
You can happily fly at .85 all day long, trouble is your passenger will still arrive in DXB 30 minutes after the Falcon as they are going to have to get to LTN or STN...and thats going to take a minimum of 40 minutes.

2 very different aeroplanes with 2 different missions period.

:hmm:

[con-pilot]

Hey, CON-PILOT I honestly hope you are talking about London (Canada) not UK

No, I meant London, England. The 900EX/EASY can make that leg non-stop when the temperature is low enough, which it is most of the time in the winter, especially early in the morning. I've done it. (To be honest I've forgotten the actual temperature, it's been a while since I've thought about it.)

As for the 900EX/EASY cruising at FL450, it not a big deal. Admittedly one cannot go straight to 450 just after a maxi mun gross weight takeoff, however, you certainly can after cruising for a few hours at lower flight levels.

Same with the 50EX.

As someone already posted, you cannot compare the G-V or the Global Express to the 900EX/EASY. The G-IVSP, or whatever it is called now and the 900EX/EASY, yes.

Now as for DOC hourly cost between the G-IVSP and the 900EX/EASY, the 900 is lower due to the lower fuel burn on the 900, however, the difference is not that much. If I recall correctly it would take about ten years to see a real savings. One other minor point is that the 900 has lower airport usage fees because it is lighter than the G-IV/whatever.

As I previously posted, both aircraft are great and I would have been happy flying either one.

[tuna hp]

Wow I never imagined that this thread was going to be this enduring when I created it.

While the debate between the Falcon 900 and GIV is interesting, I think that they are two different planes designed at different times and with different philosophies and goals...

I'm wondering if any of the newer participants have insight towards my original question:

"Thinking theoretically/abstractly, what are the tradeoffs is performance characteristics between 2 and 3 turbine aircraft?"

For example, we all know that given the same level of technology, 2 engines are able to produce X pounds of thrust more efficiently than 3 smaller engines could. However, since airplanes only have to be able to complete their takeoff with one engine out, the 3 three engine plane needs less total thrust to operate, ceteris paribus. So which design choice (2 vs 3 engines) is fundamentally more efficient?

[galaxy flyer]

If 2 engines weren't more efficient, the B777 wouldn't be the most popular plane for int'l airlines. There are no 3-engine airliners anymore and the A380 is certainly the last 4-engine design we'll see.

Dassault tried to claim that 2 was for "domestic" use and 3 was for overwater--worked until DA2000 customers wanted more range to go overwater.

GF

[galaxy flyer]

falconeasydriver

While the GLEX is not yet cert'd for LCY, I just ran a runway analysis and flight plan, LCY-DXB and it could do it, with NBAA reserves. Max TOGW today, dry runway was 81,000 lbs--straight climb to FL 430, step at 470 around Damascus

GF

[spannerbearer]

I only throw spanners at the things but does the 900 not have a greater range than the 2000 Galaxy flyer?

Also in defence of the TFE731 its been around in various formats for atleast 25yrs......Its a very reliable engine.


Garrett TFE731 - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Garrett_TFE731)

[Pilocol]

CON-PILOT and 7xXx ... Never ment disrespect ...
I never tought that the difference between B and EX was so great ... love to get my hands on an EX or in that matter a 7X ...

Done about 3K on the B although I love it, it is a bit limited in my missions ... most of the time I have 12 to 14 pax. for the long legs (That does not help) ... Done KMCO to LFMN once (Ferry) Nice flight .. even got a lightning strike out of Florida ...
One thing I have to add to this thread is that even though this 731s are reliable, they ask for a lot of care, they are not the most durable engines but they have giveN me a non stop 3K hours of truble free flights.
As one of you said, if you don't like the Falcons is becauce you have NOT flown one ...

Keep it Safe..

[tuna hp]

If 2 engines weren't more efficient, the B777 wouldn't be the most popular plane for int'l airlines. There are no 3-engine airliners anymore and the A380 is certainly the last 4-engine design we'll see.

Dassault tried to claim that 2 was for "domestic" use and 3 was for overwater--worked until DA2000 customers wanted more range to go overwater.

GF

Well the argument against that line of reasoning is that the commercial airframers' design experience, their production line, their worker expertise, etc, is with the classic tube-and-wings design. That there's a massive disincentive in developing a new s-duct airliner just in the fact that it requires very different structures to support the center engine, and different structures to maximize the benefits of the lighter outside engines. That since you're already investing billions in the new airplane design and are going to have to have it certified to extremely strict standards, there is a lot of interia towards sticking with the twinjet layout that the airframers have the most experience with.

I remember reading that Airbus applied for some sort of trijet patent in the '00s.

Also, there may be some disadvantage to the trijet design when the plane uses wing-mounted outside engines. With biz trijets, all the engine systems are in the same place. In commercial applications, the center engine is kind of in the middle of nowhere. The hypothetical is for business jets.

If twinjets are so much more efficient, then I don't understand how the Falcon 7X uses 30% to 40% less fuel than its direct competitors. That would imply incredibly poor design jobs by Gulfstream and Bombardier.

[galaxy flyer]

No, it would imply that Gulfstream and Bombardier designed larger planes that are heavier, greater cabin volume and longer range--the whole combination being heavier and, yes, less efficient. A 900 grossed out weighs about what the BOW is for an XRS. Big difference.

The 900 has greater range than a 2000 because it was designed that way, not because three engines are more efficient.

GF

[captainmorgan888]

The 2000EX and 900EX have almost the same airframe, and if we compare a 1000NM leg, the trip fuel, for the 2000 is 3915 lb vs 4150 lb in the 900. I would guss that most of the more fuel required by the 900, is because of the 2000 lb higher BOW.

Runway required for this leg would be 3370ft (2000) and 2795 (900).

[falconeasydriver]

Its really just a European/USA-North America difference in design philosophy, just like cars! In Europe, everything is designed with a VERY sharp pencil, across on the other side of the pond..they build bombers:}

[7xXx]

right...Bear in mind that the purpose of this thread wasn't to prove wich aircraft design is the best (Glex,GV..ect ) versus the Dassault 3 engines concept but just to expose and to learn a little more about what was behind that choice !

As for the "Bombers" from the other side of the pound...we owe you big time ! but it's another old story..:ok:

[galaxy flyer]

Just to refute the bombers analogy a bit. The Challenger 600 that overran the runway on take-off at KTEB--it went thru a steel fence, crossed a street, hit a car, punched thru a commercial brick building-the passengers and crew opened the main cabin door and evacuated. Taxi out for a 24 departure, you can see the brick repair work.

Something to "bombers"

GF

[Mark Malone]

When the Falcon 50 was designed there were limited choices and none in the thrust range for a two-engine airplane of this weight allowing long range.

Second, at the time three engines were considered the standard for overwater operations; think 707, DC8, 747, L1011, DC10.

Third, operating in third world countries gave the crew the 'option' of ferrying the airplane out on two engines at light weight if one engine was inop.

Obviously in 2010 with engine reliability so high, three engines is not much of a selling feature unless one is only interested in having two spares.

In a Gulfstream II/III/IV is was much less likely to lose one Spey than two Garretts.

One can always swing a conversation to their direction.....

[7xXx]

Mutt, please check your PM!

[tuna hp]

No, it would imply that Gulfstream and Bombardier designed larger planes that are heavier, greater cabin volume and longer range--the whole combination being heavier and, yes, less efficient. A 900 grossed out weighs about what the BOW is for an XRS. Big difference.

The 900 has greater range than a 2000 because it was designed that way, not because three engines are more efficient.

GF

So Gulfstreams are heavier than Dassaults and thats probably partly because of size/range and partly because Gulfstream design philosophy is to "build it like a tank" while Dassault is all about shaving weight. Dassaults have better residual values so I don't know how much more durable the "tank" Gulfs can be but I digress.

My point is that if you do the math comparing the newest planes, the G650 has about a 12% higher thrust-rating to MTOW ratio than the 7X. So even being almost 60% heavier, with its 2 massive engine it has about 12% higher power to weight. Why can Dassault have less power and still perform? Because when you eliminate one engine from both, the 7X is left with a 10% higher thrust-rating to MTOW ratio than the G650.

So I'm thinking, can this phenomenon be key to a lot of the tradeoffs? For example, Gulfstreams are known for their low-sweep, no forward high lift device wings designed for climb performance AND ALSO engine out performance. They can stay in the air better with 50% of their power if they have a wing optimized for slightly slower speeds. However, obviously this costs them efficiency at normal cruise speed. The 7X, keeping 67% of its power with an engine out, with 10% better remaining power to weight than the G650, uses a more highly swept, faster wing. Is it possible that a reason that the Dassault wing can be more highly swept is because it doesn't need as much aerodynamic help from the wing in the case of an engine out?

These are the reasons that I'd really like to talk to a business jet engineer. 2 engines are inherently much more efficient than 3, but if the 2 engine plane has to produce more thrust, and it has to have a less efficient wing, and if it has to have more drag because an S-duct engine is more aerodynamic than any tailcone... then I can see how a 3 engine plane can be competitive.

Also, I know that there are many different design decisions that go toward Dassaults' great takeoff performance, but could smaller engines be part of it. One thing I know about cars is that smaller turbochargers spool up faster, and a turbocharger is just a form of turbine. Is it possible that smaller turbine engines on a plane spool up faster and start producing more of their thrust faster than larger engines? Could this have an effect on takeoff performance, or no?

[galaxy flyer]

Tuna HP

The answer is no, smaller engines are not faster to spool up; FAR 33 has standards that apply to all engines. In any case, spool up time, in this application won't change performance numbers.

Comparing Dassault and Gulfstream is not that easy. Dassault uses lots of high-lift devices that make the slow speed arena favorable to them-their speeds are probably about 15 knots lower than GLF at equivalent weights, as is Bombardier GLEX. The advantage of the 3-engine design is exactly as you say, loss of an engine is a 33% loss of power versus 50%. Wing design is pretty much independent of number of engines. GLEX, for example, has 35 degrees of sweep, high-lift devices and the same engines as the GLF with less sweep and conventional flaps. GLF operates about 15-20 knots faster in the runway performance, but field length is pretty close for the same mission. The GLEX would be about M.05 faster in cruise, but the GLF can do that at a bit higher fuel flow.

GF

[keithskye]

I may have missed it here on this thread, but has anyone addressed the climb performance under normal conditions, or a given set of conditions, when comparing the Falcons vs. the Gulfstreams and Bombardier products? I have only a few flights under my belt in the 900EX to use as a comparison, and nearly all of my 7500 hours of PIC jet time is split between the entire Challenger series and the G-III and G-IV. It seems to me that the Falcons and Challengers cannot begin to compete with a Gulfstream at max takeoff weights when it comes to climb and initial cruise speed and altitude. I cannot remember a day when I couldn't go straight to FL410 as my initial cruise altitude, and do at least M.80 when I got there, even at ISA plus a lot (I have several hundred Atlantic and Pacific crossings for comparison). Those are numbers that mean something to me, especially when there is weather to deal with (summer thunderstorms across the southern US and parts of the Pacific rim are no fun to get around when they can top 65K). I just love those Rolls Royce engines! If you check the failure rate history of the engines on Gulfstreams, it is a fraction of what you will find on other makes. And I for one think a G-III, G-IV or G-V is sexier than a Falcon any day.

Flame suit on!

~ Keith

[NuName]

I don't know how the Gulfstreams compare with the Falcon 3 holers on a engine out departure, 50% loss compared to 33%. I do know that I could retire to a life of luxury on the difference in purchase price, and or live in luxury on the difference in annual DOC's. I would love to fly a Gulstream, I think they are fantastic but I also love the Falcon.

[tuna hp]

The 2000EX and 900EX have almost the same airframe, and if we compare a 1000NM leg, the trip fuel, for the 2000 is 3915 lb vs 4150 lb in the 900. I would guss that most of the more fuel required by the 900, is because of the 2000 lb higher BOW.

Runway required for this leg would be 3370ft (2000) and 2795 (900).

Comparing the 2000 and 900 is definitely something that originally got me curious. You would think that it would be a great comparison considering that they have the same fuselage cross-section, same wing, and same general design sensibilities.

Your 1000nm numbers show the 900EX using 6% more fuel.
-It is 1,500 or 2,000 lbs heavier
-has a longer cabin that should add some drag (housing 20% more cabin volume)
-14.5% higher MTOW (carries enough fuel to fly 20% farther)
-It also is an older plane using even older engines first sold in 1972. The PWC engines on the 2000 didn't come out until the early 1990s.
-900 has much lower runway reqs

Seems to me that this is a very favorable comparison for the 900. Especially when you consider than 1000nm is a short leg for either of these planes, and shorter legs should favor the twinjets because of their faster climb.

[AviatorJack]

Because the french are just french?

[7xXx]

Just curious to know what do you exactly mean by that AviatorJack...?:)

[7xXx]

It also is an older plane using even older engines first sold in 1972
Not excatly right, for the 900Ex engines are 731-60 (Ex came up in 1995,new blades, more efficient but a little somehow fragile..) 5000 lbs of thrust compared to the TFE 731-5BR (4750lbs).

Yet you have to see, what range you would expect once you have done your 1000nm leg without having to refuel...