Asymmetric Aircraft

[Green Baron]

He, that's me peeling off the swastika

Edited January 3, 2018 by Green Baron

[kerbiloid]

Btw are there many examples of four-engine planes still flying having lost both engines from one side?
Having lost the outer engine without switching off the opposite one?

While airbuses with two engines close to the fuselage can fly with one engine.

Spoiler

55 minutes ago, Green Baron said:

He, that's me peeling off the swastika

Had to zoom to see it.

 

Edited January 3, 2018 by kerbiloid

[Green Baron]

58 minutes ago, kerbiloid said:

Btw are there many examples of four-engine planes still flying having lost both engines from one side?

 

  Hide contents

Had to zoom to see it.

Of course it depends on the moment of the engine out, worst case is usually just after passing v1 during take off run.

Besides military stuff, there are B747, A340 and A380 and a small one Avro something flying these days. Any more ? JAR/FAR part 25 states the airworthyness criteria for commercial airliners, but i don't know them by heart :-). I think a four engine commercial aircraft must pass your scenario, in principle. But usually, if such a thing really happens, the sweat running from the crews foreheads might locally influence physics at that moment .... :-/

 

Zoom to see: we all don't get younger ;-)

 

Edit: praise the search engine (all except google), here you go:

https://aviation.stackexchange.com/questions/11582/can-the-airbus-a380-safely-fly-with-two-engines-out-on-the-same-wing

Edited January 3, 2018 by Green Baron

[DDE]

1 hour ago, kerbiloid said:

Btw are there many examples of four-engine planes still flying having lost both engines from one side?
Having lost the outer engine without switching off the opposite one?

I recall an early AC-130 almost making it home with loss of both port engines.

[Green Baron]

To clarify: yes, an airliner must fully demonstrate controllability during level flight, approach and landing. This includes banking and turning against the full thrusting engines on the other side. It must be able to safely take off in case of a failure on one side when passing v1.

The difference in thrust between a two engine airliner and one with four engines is about the same on a failure on one side. The lever of the four engine one is worse since one engine is farther out. This must be compensated with a higher speed to maintain controllability.

Since an airliner in such a case usually touches down with a much slower speed than the minimum control speed necessary for turning against the full thrusting good engines, a go around with two engines on one side might be difficult.

Hope that clarified things.

Edited January 3, 2018 by Green Baron
papperlapapp

[mikegarrison]

The rules for engine out are the same no matter how many engines a multi-engine plane has -- you have to consider the effect of the loss of the "critical engine", which is whatever engine would produce the most adverse control issues. You do not have to consider the loss of more than one engine.

But of course, if more than one engine is lost, the pilot will still try to keep the plane under control as best possible.

The B-36 had 10 engines (six turning and four burning) and routinely lost more than one engine per flight because they were all very unreliable.

[wumpus]

3 minutes ago, mikegarrison said:

The rules for engine out are the same no matter how many engines a multi-engine plane has -- you have to consider the effect of the loss of the "critical engine", which is whatever engine would produce the most adverse control issues. You do not have to consider the loss of more than one engine.

That's fine for the airplane, but how about the pilot?  Isn't the license a pilot needs for a single engine easier to obtain than one for n-1 engines?

You would think it would be the other way around (considering the difficulty of performing a deadstick landing on arbitrary landscape), perhaps there are enough nations where such rules work that way.

[mikegarrison]

2 minutes ago, wumpus said:

That's fine for the airplane, but how about the pilot?  Isn't the license a pilot needs for a single engine easier to obtain than one for n-1 engines?

You would think it would be the other way around (considering the difficulty of performing a deadstick landing on arbitrary landscape), perhaps there are enough nations where such rules work that way.

I'm not a pilot. I know more about the design end of the business than the piloting end of the business.

[PB666]

29 minutes ago, mikegarrison said:

The rules for engine out are the same no matter how many engines a multi-engine plane has -- you have to consider the effect of the loss of the "critical engine", which is whatever engine would produce the most adverse control issues. You do not have to consider the loss of more than one engine.

But of course, if more than one engine is lost, the pilot will still try to keep the plane under control as best possible.

The B-36 had 10 engines (six turning and four burning) and routinely lost more than one engine per flight because they were all very unreliable.

If you run a piston engine to FL500, viability, is no longer a fathomable quality.

IAS of a craft at FL500 is 43.3% of ground speed. If the Ne of the engine is say 400Mph, the highest IAS it could fly at 150 kts at 50,000

Po = 101,325 kg/square meters. at FL500 its 19,000 kg/square meter. 

 

21 minutes ago, wumpus said:

That's fine for the airplane, but how about the pilot?  Isn't the license a pilot needs for a single engine easier to obtain than one for n-1 engines?

You have to be checked out on every plane you fly, but if the plane is dramatically different from your experience level, it might be hard to insure.

THis discussion has gone into never-never land.

Edited January 3, 2018 by PB666

[Green Baron]

1 hour ago, wumpus said:

That's fine for the airplane, but how about the pilot?  Isn't the license a pilot needs for a single engine easier to obtain than one for n-1 engines?

A pilot is licensed either private (mostly VFR), commercial (may fly for money, e.g. the boss of a firm), or airline transportation (may fly commercially scheduled flights). If you want to look up the details: PPL, CPL, ATPL, according to what the rules say (FAR for America, JAR for Europe, but they don't differ much and the one can fly in the other's garden).

Besides these three licenses (plus supplemental ratings for IFR, instrument landing, long range, etc. pp. which can be really expensive !) there are the type ratings for different aircrafts. Automatic is that for a simple aircraft with a fixed prop and gear during basic PPL, with which you must start. So-called complex aircraft (variable prop, retractable gear) and multi-engine is a different rating, usually done on a small two propeller engine thing like a Piper Seneca or so. Having mastered that you have to rate yourself for the craft you want to fly (e.g. Dash 8, A320, B737, and so on) and keep and renew that rating (besides health checks) if you want to fly somebody else around.

So, in principle, you can fly an A380 with a PPL, if it is your plane and you only fly privately. But few do such a thing. Idk, a few actors fly privately jets ...

That's it in very brief, but there may have been changes in the past 20 years :-)

Edit: yes, things have changed. Wikipedia says that instrument and complex aircraft are requirements for ATPL.

Edited January 3, 2018 by Green Baron

[Green Baron]

56 minutes ago, PB666 said:

If you run a piston engine to FL500, viability, is no longer a fathomable quality.

I assume you mean FL50 :-) Flight level 500 is right in the stratosphere, even for jets unreachable (Concorde !), execpt a few military ones ...

Edited January 3, 2018 by Green Baron

[Nuke]

 

On 1/1/2018 at 3:14 PM, Racescort666 said:

Regarding asymmetric aircraft, if there is a specific need for it sure, but being different to be different is ridiculous. In aerospace function always preceded form. That being said, Burt Rutan is kind of a hack and makes something conventional overly complicated.

For the case in point: why design a complicated asymmetric aircraft when you could design half of one and just mirror it and save yourself a lot of design time and headache? It makes everything from testing to manufacture easier and less expensive.

i really dont understand the hate for burt rutan and his boomerang. its just a one off test aircraft built to test a different configuration. the test was successfull enough that the plane was made part of the scaled composite airforce. it was used as a chase plane for the testing of space ship one and its successor. he was building all composite aircraft back in the '70s doing kit planes trying to sell the idea of all composite aircraft. they have produced some really out of the box (and quite sexy, see proteus, starship, etc) aircraft designs over the years while everyone else builds the tried and true saussage with wings design. i like where other people write the idea off as insane, he builds an airplane. 

 

Edited January 3, 2018 by Nuke

[Racescort666]

The Starship may have looked cool but it was a huge disaster and aerodynamically a turd. 

[Nuke]

On 1/1/2018 at 11:37 PM, Green Baron said:

I'd like to see the weight & balance sheet of that Rutan-insect. Is it principally different from a symmetric aircraft ?

Also, does the asymmetry add a level of complexity to the procedures in case of an engine failure ? Like, fails the right engine: pray to Ra, fails the left engine: pray to Ishtar ?

Well, organisms aren't always symmetric as well, though all the flyers are, i think.

i think it just has more roll trim authority than a typical aircraft. i know the baggage compartment is in the unmanned boom. in situations where no baggage is used ballast can be used instead. i googled this which is a step by step abstraction of the design process. 

Edited January 4, 2018 by Nuke

[mikegarrison]

53 minutes ago, Racescort666 said:

The Starship may have looked cool but it was a huge disaster and aerodynamically a turd. 

I've got friends who work in the bizjet business and the Starship is a classic case study of a really bad idea (for its intended market, anyway).

[Zeiss Ikon]

18 hours ago, kerbiloid said:

Another plane has two engines sitting far from each other and from the plane axis.

If one of them is off, the lever arm is long, so its torque will be higher, and you even probably can't force engine, maybe even have to set low thrust.
It's very possible that it would be safer to switch both engines off and fly/land like a sailplane.

You picked a rather poor "bad example" -- the P-61 was very capable with an engine out, in some ways better than a P-38 (though otherwise, it was far inferior in performance -- but as a night fighter, it was built to different goals): "Full control could be maintained on one engine—even when fully loaded. It could be slow-rolled into a dead engine, a maneuver that was devastating on the Lockheed P-38 Lightning."  Twin engine aircraft (other than push-pull designs like the Cessna 337 Skymaster, aka "Mixmaster") generally have lots of rudder trim authority, specifically to allow operating a single engine at maximum power without an uncontrollable yaw response.

Engine out procedures for twins generally run similar to this: identify dead engine (it's the one opposite the floored rudder pedal), feather dead engine (turning propeller blades edge on to the air, which reduces drag), trim for straight-ahead flight, then fly normally (likely at higher than cruise throttle on the good engine) while declaring an emergency and landing at earliest opportunity.

Another aircraft with far larger separation between propellers (though the engines were buried inside the wing) was the Flying Flapjack -- a basic precaution avoided "engine out" problems: the propellers were geared together with an overrun clutch on each engine, so either engine could drive both propellers (the same thing is done with modern twin rotor helicopters, even with the V-22 Osprey, for similar reasons).

[Nuke]

1 hour ago, mikegarrison said:

I've got friends who work in the bizjet business and the Starship is a classic case study of a really bad idea (for its intended market, anyway).

i think the starship may have been a little too ambitious. its significant as a proof of concept for an all composite aircraft, if not as a marketable product. at a time when aircraft were mostly metal construction i think a plane made out of fiberglass and epoxy would have been a really hard sell, so they took the apple approach and made it look cool instead of fly well. form over function really is not a desirable trait in an aircraft, but its good if you are trying to prove a point and i think they made it. otherwise we wouldn't be using composites in production modern aircraft. 

[mikegarrison]

1 hour ago, Nuke said:

i think the starship may have been a little too ambitious. its significant as a proof of concept for an all composite aircraft, if not as a marketable product. at a time when aircraft were mostly metal construction i think a plane made out of fiberglass and epoxy would have been a really hard sell, so they took the apple approach and made it look cool instead of fly well. form over function really is not a desirable trait in an aircraft, but its good if you are trying to prove a point and i think they made it. otherwise we wouldn't be using composites in production modern aircraft. 

People who buy private airplanes want them to be fast (it's not) and have a long range (it doesn't). They don't care what it's made of, nor do they really care very much what it looks like.

Edited January 4, 2018 by mikegarrison

[Racescort666]

3 hours ago, mikegarrison said:

I've got friends who work in the bizjet business and the Starship is a classic case study of a really bad idea (for its intended market, anyway).

I used to work at Beech and the people who were around when it was built and they talked about how big of a headache it was. In a lot of ways, it was a regular airplane but there were definitely some serious flaws.

1 hour ago, Nuke said:

i think the starship may have been a little too ambitious.

That's a huge understatement. In regards to the Starship, my opinion of Burt Rutan stands. There were plenty of things that contributed to the Starship's failure but Rutan's attitude of being different for the sake of being different was something that could have easily been avoided. But then, the Model 2000 wouldn't have been be the Starship, it would have just been a replacement for the King Air as envisioned.

[S4qFBxkFFg]

In reply to those asking about the engine-out capabilities of four engined aircraft, the VC10 - https://en.wikipedia.org/wiki/Vickers_VC10 could, in most cases, maintain its altitude (or even climb very slowly) in the cruise on one engine.

It was designed for hot/high airfields, and usually would not even use full power for take-offs.

(Source was a member of the flight crew.)

[Van Disaster]

23 hours ago, S4qFBxkFFg said:

In reply to those asking about the engine-out capabilities of four engined aircraft, the VC10 - https://en.wikipedia.org/wiki/Vickers_VC10 could, in most cases, maintain its altitude (or even climb very slowly) in the cruise on one engine.

It was designed for hot/high airfields, and usually would not even use full power for take-offs.

(Source was a member of the flight crew.)

Was more a consideration of offset thrust than power - I seem to remember a 747 ended up in the grass recently because of FOD injestion on both engines on one side on it's takeoff roll, it hadn't even reached V1 & almost had an accident, apparently that is quite a hard situation to deal with. Admittedly there's no real rudder authority by then.

[softweir]

I know what FOF ingestion is, but can't find out what the acronym stands for? "Fluff Or Debris"?

[Racescort666]

6 minutes ago, softweir said:

I know what FOF ingestion is, but can't find out what the acronym stands for? "Fluff Or Debris"?

Foreign object damage

eta: or foreign object debris

Edited January 5, 2018 by Racescort666

[softweir]

4 minutes ago, Racescort666 said:

Foreign object damage

eta: or foreign object debris

Thanks. I ought to have worked that out, I'm just sloooow today.

[PB666]

2 hours ago, Van Disaster said:

Was more a consideration of offset thrust than power - I seem to remember a 747 ended up in the grass recently because of FOD injestion on both engines on one side on it's takeoff roll, it hadn't even reached V1 & almost had an accident, apparently that is quite a hard situation to deal with. Admittedly there's no real rudder authority by then.

747 cannot land if Vland (weight) is over 175 kts. So if on airborn it has to climb high enough to dump fuel otherwise its f_d.  Your typcal modern runway at large airports are designed with this in mind. IOW if you loose engine perfomance slightl  before v1 or even at v1 you pretty much are going to be sucking weeds. Damaged gear is better than gear collapse, gear collapse generally means airframe loss, at least the engine mounts will need service. For older 747 even sugnificant gear damage will mean retirement of airframe, so . . . . . .

If you loose two port or starboard engines on abort you also dont have thrust diverters, which means you are all brake and likely one or two tire fires on the hot side.