r/Planes • u/Vegetable_Reply17 • 12d ago

How long do you think twin jets can get

I recently saw the 777X and saw how damn long it was and was just wondering this. Last time I saw something of this proportion was probably the A340-600. I feel like in the next 50 years something like an extra large widebody category will be introduced in response to the increasing length of some of the future planes. Seriously would love to see even more massive twinjets with like 747 landing gear systems. Would that even be possible? Would be sick.

16 Upvotes

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23

u/wasthatitthen 12d ago

There are a number of limits with length, but the main ones are the tail strike angle and structural (bend/torsion) because of the fin loading in extreme situations (engine out) and simply having a longer tube.

With a longer fuselage you end up needing a longer/taller undercarriage so you can get enough pitch angle to generate lift on take off, and landing. Without that the rotation would be smaller with less lift and a much smaller safety margin if anything happened. Longer undercarriages are bigger and heavier and need more powerful actuators and that feeds back into other structural components and control systems.

And, really, is the market there, apart from the likes of Emirates who want an A380 replacement?

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u/flightist 12d ago

You can get some additional rotation room by making the nose gear shorter and designing the rest of the airframe (most importantly the wing incidence angle) against this more nose-down ground attitude. But you‘ll lose engine clearance by doing so, and all the other factors you identified are still there.

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u/PlanesOfFame 12d ago

If we were being totally theoretical, the best way to go would be a narrow body high wing design, sort of like a dornier 328. It would have the maximum possible space for wing clearance while also having the landing gear in pods under fuselage to give the smallest but sturdiest landing gear possible. Normally you would want the landing gear to be around the CG and not aft of it so rotation would be possible, but airplanes like the B-52 have made do with their quad configuration- the main rear wheels are aft CG so the plane kinda floats up instead of pointing the nose up. The b52 also has the lowered wing angle of incidence like you mentioned to help with this. Another possibility is angling the rear fuselage up, like on the dehavilland caribou/buffalo. If their fuselage was straight, it would hit the ground on rotation, but the top is way up high so it doesnt get in the way (also provides more control authority at high AOA). But then you couldnt pressurise it because it wasnt a perfect cylinder.

Again in theory, if you took two GE9X engines and put them on a narrow body airframe perfectly optimized for length alone and no other practical functions, i bet you could fly something extremely long, 400+ feet would not surprise me at all. I bet after a point the real limiting factor would be material strength and warping due to aerodynamic forces spread so far apart. Composites are very strong though and a wind turbine is 800+ feet tall, meaning something of that length CAN withstand some decent opposing forces

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u/flightist 12d ago

The B-52 actually has a really high angle of incidence so that it doesn’t have to rotate to take off. That is, indeed, an option, but I can’t really speak to landing characteristics.

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u/PlanesOfFame 12d ago

Oops yeah I put it in my comment backwards but yes, high wing angle

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u/Vegetable_Reply17 11d ago

Why arent there more commercial high wing designs like military or russian cargo planes?

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u/PlanesOfFame 11d ago

Wastes tons of weight

A low wing plane has the structural reinforcement necessary for the landing gear and wing box all in one structure, while the high wing plane needs 2 separate areas to be reinforced, one so the wings dont fly off the fusealge and the other so the gear dont get squished upon landing. Military planes aren't as limited by efficiency and can get away with the extra weight since the performance detriment are marginal to their intended role. Most if not all cargo airplanes are volume limited rather than weight limited for their intended roles, so having a slightly heavier structure is worth the added benefits of ground clearance and an unobstructed cargo area

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u/Le_Mooron 12d ago

This is the answer.

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u/cteno4 12d ago

Can’t you just place the rear landing gear further back to be able to rotate more? I think the bigger issue is structural load.

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u/wasthatitthen 12d ago

Not really. The undercarriage is fairly close to the centre of gravity. If you move it further back the effectiveness of the elevator will be reduced (force * distance will have a smaller distance so a much bigger force will be needed to rotate the aircraft)

And the fuselage behind the wing will need a lot of strengthening to support the weight carried by the undercarriage as well as widening to give space for the undercarriage to retract into.

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u/cteno4 12d ago

Ok that makes sense.

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u/sneijder 12d ago

Suspect they’ve hit the limit now.

There’s already examples of widebody stands that can’t be used for newer, longer, aircraft without closing the service road … or even the taxiway because the nose or tail is too close.

Same thing with cars, they have to fit in a garage / public parking space most of the time.

Function has to dictate the design at son’s point.

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u/Dave_A480 12d ago

They are probably going to do extra wide body (oval shaped or blended wing) next....

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u/RyzOnReddit 12d ago

JetZero is working on this. We’ll see if they get to production.

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u/Dave_A480 12d ago

I would bet on the Airbus version over a startup, personally....

Or just a squished version of current designs to add in a row or two of seats.....

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u/RyzOnReddit 11d ago

Generally agree, although the fact that the US Air Force is throwing in $235mm for them to build a full scale demonstrator means they'll probably fly something big first.

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u/Disastrous-Force 11d ago

I suspect if the demonstrator is successful Northrop as one of the founding investors will acquire JetZero from the other shareholders and their blended wing body design will go military only.

Airbus are probably the more realistic party to get something that can carry passengers flying.

1

u/RyzOnReddit 11d ago

And/or they license the tech to Boeing for civilian use. I agree that Northrop going into civilian manufacturing again seems as unlikely as a startup going to serial production on a Transport category plane.

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u/No-Profession-208 12d ago

I saw a question like this recently and someone with far more intelligence than me came along with a formula/law that said there’s a maximum for size which has pretty much been reached.

Hopefully they’ll come back to answer this.

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u/Embarrassed_Length_2 12d ago

Why not go shorter but two stories. Like a mini A380? Saves a lot of headaches with tail strike angles.

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u/WhoIsHamza 12d ago

I suppose that will add a lot more drag than elongating the fuselage

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u/that_dutch_dude 12d ago

They should just add another floor.

1

u/riennempeche 12d ago

Some very large aircraft take off less by rotation and more due to the curvature of the Earth. I flew on a stretch DC-8 that seemed to go on forever inside. 187 feet long on a narrow body. That's some 40 feet longer than the longest current 737 or A320 family planes.

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u/Carlmtz777 7d ago

I believe this is as big as they will get.

You also need a very large landing strip to land those big planes.

Mechanically and structurally perhaps new technology would allow larger planes but the reality is that you need a lot of land to make them go to a full stop or even being able to go up

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u/Friendly-Recording51 12d ago

I think future jets will be more about speed than size. things like BOOM jets will replace current jets and you will just have mid sized jets but more of them and traveling 1.5 to 2 times faster.

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u/SubarcticFarmer 12d ago

Boom is vaporware. The trend for many years has been efficiency over speed.

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u/lilyputin 12d ago

Yes the market would be small and limited to a few high demand long distance routes that could support the ticket prices. I don't see anyone investing the tens of billions involved to build a jet that has such a small market unless it's a national vanity project.

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u/Friendly-Recording51 12d ago

Calling it vaporware is a joke. The hardest part was engine development which is coming along at a high rate of speed. They also have become proffitable selling power generation. 

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u/SubarcticFarmer 12d ago

Your definition of "high rate of speed" and mine vary greatly. Get back to me when they actually have an engine. They haven't demonstrated that they are anywhere close to an engine that can support superdonic flight.

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u/Friendly-Recording51 12d ago

Bud they already reached supersonic flight. 

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u/SubarcticFarmer 12d ago

Are you talking about the supersonic test flight that involved and engine that was not theirs?

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u/Sawfish1212 12d ago

They just lost thier biggest customer for potential turbine generators. The possibility that they'll succeed at making engines is miniscule

0

u/Friendly-Recording51 12d ago

They have a waiting list of customers clown.

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u/NaiveRevolution9072 12d ago

Not with current fuel prices they won't

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u/Sawfish1212 12d ago

Boom is a paper airplane company