Is this really a 787's peak performance. And why don't they make it?

[Arugela]

I'm assuming this could be a joke. But you never know. Why would they not make this if it was true.

[mikegarrison]

It's either a joke or something made by somebody who has no idea what they are talking about.

Let's quickly look at the worst problems:

1) Too many engines. It's well known that two engines is the correct number. More engines are only used when the technology or the design does not support two engines with enough thrust. For instance, the newest 777 and A350 planes are heavier than the original 747s, but only use two engines because engines now have enough thrust for this.

2) Too many wings. One wing with more span gives the same lift with half the drag. (KSP lies to you about this.) You do need pitch control, so usually planes have control surfaces at either the nose or the tail. But you don't need both.

3) Putting a vertical stabilizer in the center of the plane is useless drag. You want it at the tail, as far back as possible. That way it has the biggest possible lever arm so you can make a smaller vertical stab.

Edited October 10, 2019 by mikegarrison

[kerbiloid]

And why the main wing looks backwards.
It should be like this

Spoiler

 

[Guest]

Aircraft designers have a saying: if it looks nice, it'll fly nice. Generally, what you want is minimum lifting surfaces and other protrusions for what you need to do. That's why aircraft look the way they do. The guy who made that picture is either joking, misinformed or plays too much KSP (that said, this design wouldn't work all that well in KSP, either).

[sh1pman]

@mikegarrison also, from the looks of it, the CoL is in the front (from forward wings), and CoM is way back (from the engine inside the tail fin). That’s probably not ok. 

[magnemoe]

15 hours ago, mikegarrison said:

It's either a joke or something made by somebody who has no idea what they are talking about.

Let's quickly look at the worst problems:

1) Too many engines. It's well known that two engines is the correct number. More engines are only used when the technology or the design does not support two engines with enough thrust. For instance, the newest 777 and A350 planes are heavier than the original 747s, but only use two engines because engines now have enough thrust for this.

2) Too many wings. One wing with more span gives the same lift with half the drag. (KSP lies to you about this.) You do need pitch control, so usually planes have control surfaces at either the nose or the tail. But you don't need both.

3) Putting a vertical stabilizer in the center of the plane is useless drag. You want it at the tail, as far back as possible. That way it has the biggest possible lever arm so you can make a smaller vertical stab.

Is two engines better than one if we ignore engine out safety? Yes putting engines below the wings reduces stresses I belive. 
3 and 4 engines was also used because safety concern with 2 engines with engine out over oceans. 
This is mostly solved now but the 380 has 4 engines as its so huge. 

[Arugela]

2 hours ago, Dragon01 said:

Aircraft designers have a saying: if it looks nice, it'll fly nice. Generally, what you want is minimum lifting surfaces and other protrusions for what you need to do. That's why aircraft look the way they do. The guy who made that picture is either joking, misinformed or plays too much KSP (that said, this design wouldn't work all that well in KSP, either).

I'm pretty sure I made that before. It's perfect for messed up COM. It allows lift on the front nose to get off the runway earlier! >< Rear weighted engines help with COM coming back farther. Although most of the engines are centered. It's a bit like my current cargo vessel too.

2 minutes ago, magnemoe said:

Is two engines better than one if we ignore engine out safety? Yes putting engines below the wings reduces stresses I belive. 
3 and 4 engines was also used because safety concern with 2 engines with engine out over oceans. 
This is mostly solved now but the 380 has 4 engines as its so huge. 

I think some of them have rear engines for odd airflow issues(or advanced airflow intakes) and efficient cruise and other odd solutions. Or better power from odd positioning compared to all wing positioned or something. Also taxi fuel potentially. I forget. I've seen stuff on this before.

Edited October 11, 2019 by Arugela

[mikegarrison]

7 minutes ago, magnemoe said:

Is two engines better than one if we ignore engine out safety?

Well, but you can't ignore engine-out safety.

Besides engine-out issues over water, three and four engines were used on large planes simply because you couldn't make engines with enough thrust back then. Now you can.

Edited October 11, 2019 by mikegarrison

[magnemoe]

1 minute ago, mikegarrison said:

Well, but you can't ignore engine-out safety.

You can in some settings, like an UAV who has one engines, most fighter planes has one engine same with small propeller planes, the fighter plane has an ejection seat and the propeller plane has so low landing speed you can land everywhere. 

An idea of mine, have an hybrid plane, you have an battery, two electrical engines with propellers you can fold in or redraw into the wing after takeoff, you also have jet engine(s) but they don't run on full power during standard takeoff to reduce noise, you can still take off from an short runway as you have lots of power.  
As you speed up you stove the propellers and the jet engine take over part of it job might be to recharge the battery but this depend on flight profile. 
I see this as an very nice design for stuff from island jumping to airports inside cities to hubs. 
Now do you want one or two jet engines here ?

[Guest]

Also, single engine for jets presents mounting issues. Generally, that means housing it in or on top of the tail, which has its problems, in contrast to an underwing mount, which is optimal for several reasons. A single engine this powerful would also be very big, probably causing further layout problems.

[mikegarrison]

10 minutes ago, magnemoe said:

You can in some settings, like an UAV who has one engines, most fighter planes has one engine same with small propeller planes, the fighter plane has an ejection seat and the propeller plane has so low landing speed you can land everywhere. 

An idea of mine, have an hybrid plane, you have an battery, two electrical engines with propellers you can fold in or redraw into the wing after takeoff, you also have jet engine(s) but they don't run on full power during standard takeoff to reduce noise, you can still take off from an short runway as you have lots of power.  
As you speed up you stove the propellers and the jet engine take over part of it job might be to recharge the battery but this depend on flight profile. 
I see this as an very nice design for stuff from island jumping to airports inside cities to hubs. 
Now do you want one or two jet engines here ?

OK, well I assumed that the setting we are talking about is 14 CFR Part 25, Airworthiness Standards for Transport Category airplanes. I think all Part 25 airplanes must be multi-engine.

There have been designs proposed for electric/hybrid airplanes. See, for instance, https://zunum.aero

(But FYI Zunum recently ran out of startup cash and is, AFAIK, essentially dead.)

[YNM]

5 hours ago, magnemoe said:

Is two engines better than one if we ignore engine out safety?

There are other reasons - a single engine would have to be placed on the fuselage, and as such wouldn't be well-suited for passenger planes which needs lots of space. Works very well for fighter jets though.

 

There's also a reason why engines on passenger planes tend to be placed beneath the wing, and the wing beneath the cabin - it means a quieter cabin. An engine on the tail means noisy rear cabin - fine if it's only cargoes there.

5 hours ago, magnemoe said:

An idea of mine, have an hybrid plane, you have an battery, two electrical engines with propellers you can fold in or redraw into the wing after takeoff, you also have jet engine(s) but they don't run on full power during standard takeoff to reduce noise, you can still take off from an short runway as you have lots of power.  
As you speed up you stove the propellers and the jet engine take over part of it job might be to recharge the battery but this depend on flight profile. 
I see this as an very nice design for stuff from island jumping to airports inside cities to hubs. 
Now do you want one or two jet engines here ?

Takeoff noise can be reduced by simply expediting ascent. New, higher-bypass-ratio engines also help.

Landing is much more difficult, however.

 

Edited October 11, 2019 by YNM

[Meecrob]

Another thing to keep in mind with the 1 engine vs 2 engine debate is accessories that are run off the engine. With one engine you only have one main (non-backup/non-redundant) source for electricity, hydraulics and bleed air.

[mikegarrison]

9 minutes ago, Meecrob said:

Another thing to keep in mind with the 1 engine vs 2 engine debate is accessories that are run off the engine. With one engine you only have one main (non-backup/non-redundant) source for electricity, hydraulics and bleed air.

Unless you have an APU.

[Meecrob]

Haha, of course you are right, @mikegarrison. However, aren't some APU's on transport category aircraft unable to start their APU in flight? And if I'm remembering that correctly, is it a design choice by the manufacturer, or a limit of the APU?

[mikegarrison]

27 minutes ago, Meecrob said:

Haha, of course you are right, @mikegarrison. However, aren't some APU's on transport category aircraft unable to start their APU in flight? And if I'm remembering that correctly, is it a design choice by the manufacturer, or a limit of the APU?

Older APUs often could not be started above about 15K (the height of the highest airports). But these days, AFAIK, all modern APUs are rated to be startable over the full flight envelope of the airplane.

[farmerben]

On 10/10/2019 at 7:45 PM, magnemoe said:

Is two engines better than one if we ignore engine out safety? Yes putting engines below the wings reduces stresses I belive. 
3 and 4 engines was also used because safety concern with 2 engines with engine out over oceans. 
This is mostly solved now but the 380 has 4 engines as its so huge. 

 

I think putting engines in the wings reduced vibration and noise in the passenger compartment.  Stress forces on the air-frame are greater, but it's worth it.  3 engine was popular in commercial flight for a long time because of engine out issues.  Putting the engine in the tail involves more torque issues than putting it inline with the fuselage, so they have to compensate with trim as circumstances change.  Maybe they didn't want to redesign the air intakes to put it inline.  

 

Burt Rutan's Catbird

Having an oversized Canard and tail is good for short take off and landing, and especially water takeoff.    Variations of this are used in most of my best KSP sea planes.  The tail does primary pitch control.  The canard only uses the deploy control and the authority limiter.  Deploy canard to 100% throws the center of lift forward of the center of mass and lifts the plane out of the sea.  Then I use the authority limiter of the canard to adjust trim, which changes with speed when you have three lifting surfaces at different angles.  

Adding more tail elevons allows the addition of more canard which allows more aggressive pitching and low speed climb.  

[mikegarrison]

4 hours ago, farmerben said:

I think putting engines in the wings reduced vibration and noise in the passenger compartment.  Stress forces on the air-frame are greater

Did you mean "in" the wings or attached to them?

Anyway, no. Putting weight on the wings actually reduces the stresses on the structure. All the weight has to eventually get transmitted to the wings, because it is the wings that lift the airplane. The more weight you actually put on or in the wings, the less weight that you have to put into the rest of the airplane and then carry to the wings anyway. This is why most wings are "wet" -- it's the best place to stick the fuel, because the weight of the fuel can be carried directly by the wings and doesn't have to be brought to them.

Similarly, putting engines on the wings lightens the structure of the airplane.

The main reason not to put the engines under the wings is because then you need taller landing gear. This is why many small jets (especially bizjets) put the engines elsewhere. The like to have very short (and light) landing gear so that they can also use the door as stairs.

[kerbiloid]

51 minutes ago, mikegarrison said:

The more weight you actually put on or in the wings, the less weight that you have to put into the rest of the airplane and then carry to the wings anyway.

Who needs the rest when there are wings.

Spoiler

 

[mikegarrison]

32 minutes ago, kerbiloid said:

Who needs the rest when there are wings.

Well those designs have their own issues. Suffice to say there are many reasons why the flying wing is a very rarely-used specialty airplane.

[kerbiloid]

1 hour ago, mikegarrison said:

Well those designs have their own issues. Suffice to say there are many reasons why the flying wing is a very rarely-used specialty airplane.

Different flight profiles need different craft designs.
(For a VTHL spaceplane the best is probably a flying sneaker like Spiral/Bor/Dreamchaser.)

Edited October 13, 2019 by kerbiloid

[YNM]

21 hours ago, mikegarrison said:

these days, AFAIK, all modern APUs are rated to be startable over the full flight envelope of the airplane.

Plus a ram air turbine.

9 hours ago, kerbiloid said:

Who needs the rest when there are wings.

Passengers want windows, though.

Plus, large wingspans are not very good. There's a reason they have to fold the 777X wing.

Also, so far airplanes put their fuel tanks on the wing and their load on the fuselage - putting the passenger cabin on the wing means now they share the exact same structural part.

Edited October 13, 2019 by YNM

[kerbiloid]

39 minutes ago, YNM said:

Passengers want windows, though.

Anyway nothing except sky above and clouds below. Screensaver is enough.

[Guest]

Actually, it's not that passenger want windows, it's that they want emergency exits. Flying wings have trouble with that, FAA requires that emergency exits do not require climbing to get to them, and that they're a certain distance from all passengers, which is pretty much impossible to realize in a flying wing. The only exits possible are to the front, back and upwards, the latter don't count according to FAA definition, and the former will leave most passengers too far away from them.

It's not a problem with bombers, since the crew has ejection seats, anyway.

Edited October 13, 2019 by Guest

[Commodore_32]

I know!! I have the answer!! The plane is:

Spoiler

B787/Eurofighter Typhoon/DC-10!!!!!!!!!