Cybertruck frame in scrap yard shows no midgate and other details

[HaulingAss]

4 years in and we are still arguing about what the SS does, if there is an exoskeleton, what even is an exoskeleton, if it doesn't have an exoskeleton then what is it, where is the load being carried, etc.

I can't wait till we start getting deliveries so we can start talking about actual experiences instead.

I know, crazy, huh? If you review these many disruptions, you will see they can all be traced back to the fact that @JBee doesn't understand that the skin, on a skinned structure, can re-distribute the load forces more evenly back into the underlying structure.

That's the only thing that explains why he's always asking for a load path diagram to show how the skin of the exoskeleton is load bearing. That's what every disruption comes down to, this one fundamental misunderstanding about how the skin of a skinned structure functions. I suspect that, even when the Cybertruck is out, he will insist he was right all along.

It matters little to me, except that I don't like to see others misled by his continued insistence.

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[JBee]

I know, crazy, huh? If you review these many disruptions, you will see they can all be traced back to the fact that @JBee doesn't understand that the skin, on a skinned structure, can re-distribute the load forces more evenly back into the underlying structure.

That's the only thing that explains why he's always asking for a load path diagram to show how the skin of the exoskeleton is load bearing. That's what every disruption comes down to, this one fundamental misunderstanding about how the skin of a skinned structure functions. I suspect that, even when the Cybertruck is out, he will insist he was right all along.

It matters little to me, except that I don't like to see others misled by his continued insistence.

Ditto dude.

Misinformation is a strong force with you, especially when you shoot from the hip to make a point.

Btw, I'm glad aircraft fuselages still flex at least as well as you!

But it might be time to go to back to school, then take a course to get a structural engineering degree, then build a exoskeleton bridge, and get over it. ?

Once you do that, you'll be able to make a pretty load path diagram in pink, just for little ole me.

 

[Stuck4ger]

This is false. Airplane wings are purposefully designed to have "serious amounts of flex" in a horizontal direction and as little twisting flex as reasonably feasible. The flexy nature of the wings acts like a suspension for a plane flying through turbulence. Airplane fuselages, while they do unavoidably flex a small amount under peak landing loads, are actually designed to be rigid, relative to the wings, because it's important for control of the airplane in flight, particularly when taking off and landing, that the horizontal stabilizer does not change attitude, relative to the wings. A flexible fuselage would have the effect of unintended control inputs which would be undesirable in all situations.

Even though the fuselage skeleton is designed to be the rigid main structural load carrier, aluminum aircraft skin panels often bear critical stress. I know of aircraft that cannot be towed without certain fuselage panels in place.

 

[JBee]

Even though the fuselage skeleton is designed to be the rigid main structural load carrier, aluminum aircraft skin panels often bear critical stress. I know of aircraft that cannot be towed without certain fuselage panels in place.

Completely agree that many aircraft are a stressed skin structure.

But CT is not an aircraft, nor a stressed skin structure.

 

[FutureBoy]

The argument about the skin has me stressed. Does that count?

 

[Mini2nut]

A Vietnam resident recently completed a wooden replica of the Cybertruck including a CyberQuad.

https://carbuzz.com/news/running-tesla-cybertruck-wooden-replica-shows-impeccable-build-quality

 

[FutureBoy]

A Vietnam resident recently completed a wooden replica of the Cybertruck including a CyberQuad.

https://carbuzz.com/news/running-tesla-cybertruck-wooden-replica-shows-impeccable-build-quality

Can we see the back seats? And does it have a midgate?

 

[PilotPete]

No, fuselage flex is real and is most noticeable on long slender fuselage like 757/MD80 etc. It wiggles like a pool noodle. Steady state attitude control is why they invented trim and many larger aircraft are FBW anyway, and there pilots only interact with control surfaces through computers that calculate moment to moment changes. (Even my 3kg evtol 120km range UAV has this)

F35 and F22 are actually "unstable airframes" that cannot fly without FBW, this is what gives them both their manoeuvreability and efficiency for range, because any naturally balancing wing induced forces, come at a cost to flight performance. Also a big reason why F35 was delayed.

Accordingly, both fuselage and wing flex (which admittedly is more by design) are controlled by active attitude control. (Along with stall prevention, auto throttle etc)

JB,

I’m sorry, but you are a touch off on most of this. There is no such thing as “inverted trim”. The standard configuration for aircraft in which the tail produces a downward force has NOTHING to do with steady state flight, and EVERYTHING to do with upset recovery. This is the CG envelope which comes with the PART 23 and 25 certification. The only planes I can think of off the top of my head (civilian) that got around this are the Piaggio 180 and the Beech StarShip.

Yes, the stability of military fighters is nonexistent by design, because stability and maneuverability are in opposition. FBW fixes all that. But the design has nothing to do with range, nor the CG envelope. And when it comes to fighters, the range really sucks. The F22 range is all about “super cruise”, which is the ability to fly at lower supersonic speeds without afterburner. The big military cargo aircraft (C5/141/17/130) all use positive stability, regardless of flight control systems. Even the big A350 and B787 are positively stable regardless of their flight control systems. The B747 can go aft CG in cruise (only) for efficiency, even with the standard old school hyd-boost manual controls.

The B1 can get in an aft CG configuration (only happened once that I’m aware of) by a fuel transfer failure. When you sweep the wings, the fuel has to be transferred aft to maintain within the CG envelope. If you are unable to transfer back forward, then you can’t ”unsweep” the wings without being so far out of CG, the plane is virtually unflyable. So you land around 250kts with the wings swept. In that case, it helps to have a 10 mile long dry lakebed runway.

 

[JBee]

JB,

I’m sorry, but you are a touch off on most of this. There is no such thing as “inverted trim”. The standard configuration for aircraft in which the tail produces a downward force has NOTHING to do with steady state flight, and EVERYTHING to do with upset recovery. This is the CG envelope which comes with the PART 23 and 25 certification. The only planes I can think of off the top of my head (civilian) that got around this are the Piaggio 180 and the Beech StarShip.

Yes, the stability of military fighters is nonexistent by design, because stability and maneuverability are in opposition. FBW fixes all that. But the design has nothing to do with range, nor the CG envelope. And when it comes to fighters, the range really sucks. The F22 range is all about “super cruise”, which is the ability to fly at lower supersonic speeds without afterburner. The big military cargo aircraft (C5/141/17/130) all use positive stability, regardless of flight control systems. Even the big A350 and B787 are positively stable regardless of their flight control systems. The B747 can go aft CG in cruise (only) for efficiency, even with the standard old school hyd-boost manual controls.

The B1 can get in an aft CG configuration (only happened once that I’m aware of) by a fuel transfer failure. When you sweep the wings, the fuel has to be transferred aft to maintain within the CG envelope. If you are unable to transfer back forward, then you can’t ”unsweep” the wings without being so far out of CG, the plane is virtually unflyable. So you land around 250kts with the wings swept. In that case, it helps to have a 10 mile long dry lakebed runway.

Note I said "invented" not "inverted" trim.
I think this lead to some misinterpretation of my comments.

Canards, like the Piaggio/Beechcraft/EZ have two sets of wings that produce lift. (Piaggio has an additional tail) The downwards force created by the tail in conventional aircraft is not lost on me.

But the context of my comment was fuselage flex upsetting attitude control and what methods of control there are to offset it, being trim and FBW.

On your comments regarding efficiency, I agree that fighters are not efficient, mostly due to their low aspect ratio wings, which in turn are required for maneuverability and roll rate etc. Supercruise, or most forms of supersonic flight aren't either, and is why many of the lesser F# aircraft have only supersonic capabilities for minutes and not hours using afterburner.

Basically my comments were trying describe the benefits of FBW, and how that affects aircraft design. Note I didn't say passenger aircraft are unstable designs, rather my comments were limited to F22/F35. From a liability proposition I don't think we'll see many unstable passenger aircraft designs, but military aircraft are not passenger aircraft, so are designed with other constraints in mind.

But, unstable aircraft, like the super long range B2, are actually efficient too because of this, and the flying wing tailless design helps reduce radar signature too of course. This is only flyable with FBW at all.

This is because any control surface that does not create positive lift is a drag, and as such reduces range and efficiency in cruise.

Unstable aircraft all need FBW because pilots can't respond fast and accurate enough to changes. But that doesn't mean all FBW aircraft are unstable.

However, in saying that, the premise of increasing efficiency by using a "more" unstable aircraft configuration is not uncommon in airliners too, in that exactly how you described, by changing the CG aft, you reduce tail loading, which in turn reduces elevator control authority. Airbus also uses the CG shift in cruise configurations like this to reduce fuel burn as well, but obviously as you say all remain within a specified stability envelope.

Simply, the principal is that any stable aircraft is only stable because the configuration is such that "forces" are generated that provide stability. In flight these same forces consume energy to produce, and therefore, in most cases, reduce efficiency and range. How much efficiency is gained for F22/F35 by this is probably a state secret, but the principle still applies, hence my comment.

 

[Crissa]

It's kind of like the difference in trail between a motogp bike and a bagger. One is designed to emphasize being less stable - so it turns really well - the other is designed to emphasize recovery into stability.

Just because something flexes - and all materials do - doesn't mean it's desirable. The flex in trucks has allowed them to do some off-road-y things, but it also prevents them from being safer with heavier loads at speed.

-Crissa

 

[JBee]

It's kind of like the difference in trail between a motogp bike and a bagger. One is designed to emphasize being less stable - so it turns really well - the other is designed to emphasize recovery into stability.

Just because something flexes - and all materials do - doesn't mean it's desirable. The flex in trucks has allowed them to do some off-road-y things, but it also prevents them from being safer with heavier loads at speed.

-Crissa

Sort of?

Flex is only an issue if it creates a dynamically changing force that can't be compensated for by other means. In the case of unstable aircraft this is FBW. In the case of the CT it's the cast and cabin frame, and the suspension that compensates for changes in terrain and load.

A cable suspension bridge is a good example in how something can move and flex in some dimensions, but be rigid in others. Here in the below video even a relatively small sideways load can cascade into dynamic harmonics that can destroy the structure.



Similar in a vehicle, a high dynamic load, or tension between dissimilar structures can cause fatigue and structural failure. This can also occur with poorly placed or excessive loads.

In the case of any vehicle, the best structural compromise must be found to accommodate the changes in terrain, with the changes in vehicle load, to meet the specific performance the manufacture desires.

This doesn't mean in of itself that "rigid" is better than "flex", rather that a good vehicle structure design, has the right amount of both, for it's design constraints and specific goals.

The casts in the CT seem to be quite rigid in their design and connection to the cabin, and the casts themselves have much higher resistance to bending moments, meaning that the dynamic loads from the terrain will need to be dealt with by the suspension alone, as the cast's might otherwise be impacted because they resist flex. This means it will have fairly good driving dynamics on-road because the suspension alone can be designed to deal with the dynamics of changing loads, whilst the body structure remains the same.

However, because of this, the cast and cabin also need to be made with more structural mass and elements, because they will also cause higher dynamic loads at the points the suspension is connected to the cast, because the forces are not allowed to change the cast shape and "flex", like they would with a ladder frame chassis.

The point here is that neither the rigidity of a piece of glass, nor the flexibility of jello, is a good fit for the dynamic loads experienced by the vehicle, so a compromise of the right properties is required. In this case the cast is rigid, the suspension is flexible, but a more rigid suspension and more flexible frame can carry just as much load, "if" designed properly, like in a semi trailer, tipper, concrete truck etc.

So it's not simply a case of "rigid is better" and "flex is bad" when considering the whole design, rather it is important that the right parts of the design have the best possible structure to reach the desired goal. There's a lot of swings and roundabouts in engineering design.

 

[Crissa]

Weird that the example includes why you would want to limit flex for a heavy load, JBee.

-Crissa

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