Aerodynamic optimization for towing 2.53 m width and 4 m height obejcts

[HaulingAss]

What is the minimum tongue weight? What Is Proper Tongue Weight?
For conventional trailers with ball-mounted hitches, proper tongue weight is roughly 10 to 15 percent of the total loaded trailer weight.

GMC Life - Tongue Weight Is Key To Safe Towing
https://www.gmc.com/gmc-life/trucks/why-tongue-weight-is-important-for-safe-towing

The tongue weight rule of thumb of 10-15% of the load weight was developed by trial and error over many years using a variety of non-optimal towing solutions. It is not a hard rule of physics that stability requires 10-12% tongue weight.

The Cybertruck chassis will be very rigid in contrast to typical trucks that have a ladder frame and are essentially a giant spring when loaded near capacity. The springiness of a ladder frame is what has caused many experienced tow drivers to recommend such high tongue weights. The Cybertruck will likely tow beautifully with 7-8% tongue weight. Some testing may be required at lower tongue weights to determine the limiting factors.

I don't think this has a lot of importance to this particular application, but I wanted to broach the subject so people can realize that the Cybertruck will have very different (better) tow dynamics from traditional trucks with springy ladder frames.

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[rr6013]

Assuming 1% rolling resistance, Cybertruck loaded to 3500 kg, trailer 3500 kg

Specifying a maximum claimed pulling capacity of Cybertruck with a 50/50 weight distribution CT–Trailer loaded is a category of haul called “heavy haul”. Heavy haul is a load that is either high, wide, heavy or ugly. Specially built equipment is necessary to haul loads at maximum capacity.

In your case, you are at least “heavy”. Too heavy on the truck! The piece of equiment used to equalize load distribution over multiple axels you will need to build is called a “jeep”. Not the 4x4 kind.

You will mount a 5th wheel in the bed of the Cybertruck. Don’t be rigid about this 5th wheel following convention i.e. bottom plate under a trailer pin(shown above) Smaller trucks do better inverted running a 5th wheel mounted upside-down to the jeep gooseneck. And a pin fixed to a center plate in the bed of the pickup.

Your jeep will gooseneck back to a load bearing axel which pulls the trailer, also a gooseneck. Imagine your jeep as a ½ scale to the picture above. Tires will be at least 20” truck tires to adequately dissipate heat.

Stay with a single axel to keep it simple, easy to backup and maneuver. Get an engineer to load calc your design to keep from over building beyond your needs.

Or get a Unimog.

 

[Ogre]

I don't think this has a lot of importance to this particular application, but I wanted to broach the subject so people can realize that the Cybertruck will have very different (better) tow dynamics from traditional trucks with springy ladder frames.

Nice post. I’d add that 4 wheel steering also increases trailer safety significantly. Not sure how that would affect this part of the equation, but it definitely helps out in general.

 

[JBee]

The tongue weight rule of thumb of 10-15% of the load weight was developed by trial and error over many years using a variety of non-optimal towing solutions. It is not a hard rule of physics that stability requires 10-12% tongue weight.

The Cybertruck chassis will be very rigid in contrast to typical trucks that have a ladder frame and are essentially a giant spring when loaded near capacity. The springiness of a ladder frame is what has caused many experienced tow drivers to recommend such high tongue weights. The Cybertruck will likely tow beautifully with 7-8% tongue weight. Some testing may be required at lower tongue weights to determine the limiting factors.

I don't think this has a lot of importance to this particular application, but I wanted to broach the subject so people can realize that the Cybertruck will have very different (better) tow dynamics from traditional trucks with springy ladder frames.

What exactly is a "springy" ladder frame and how does it effect trailer tracking from a single point hitch? Do you mean poor suspension?

Rigidity is good, but poor suspension setup is much worse. Also the CT will have less rear overhang to the hitch, so a shorter lever arm will help to keep the trailer in line.

 

[founder]

To clarify the requirements: It should be possible to drive with EU B+E driving license
This means the total weight of the car can be 3500 kg,
the total weight of the trailer can be 3500 kg.

Maybe EU increases the maximum total weight to 4250 kg, but this decision is in the future.
Discussion about this is end of 2022.

One segment is 2.53 m width, 5.35 m long and 3.43 m height.
The height is only possible, because the trailer is only 0.55 m height.
This is possible by 3 axles with 10" wheels.
So the segment on the trailer is just bit less than 4 m height.

A truck is no option because
1.) Could only transport 2 segments, total length of a vehicle restriction.
2.) The trailer is necessary to position the house segment at the construction ground.

I found in the 18 answers nothing about aerodynamic optimizations.

 

[JBee]

To clarify the requirements: It should be possible to drive with EU B+E driving license
This means the total weight of the car can be 3500 kg,
the total weight of the trailer can be 3500 kg.

Maybe EU increases the maximum total weight to 4250 kg, but this decision is in the future.
Discussion about this is end of 2022.

One segment is 2.53 m width, 5.35 m long and 3.43 m height.
The height is only possible, because the trailer is only 0.55 m height.
This is possible by 3 axles with 10" wheels.
So the segment on the trailer is just bit less than 4 m height.

A truck is no option because
1.) Could only transport 2 segments, total length of a vehicle restriction.
2.) The trailer is necessary to position the house segment at the construction ground.

I found in the 18 answers nothing about aerodynamic optimizations.

Did you miss my post on the first page? I think that was all about aerodynamic optimisations?

https://www.cybertruckownersclub.co...width-and-4-m-height-obejcts.5655/post-117840

On your weight restrictions: it is questionable if at all the Cybertruck will be allowed to be driven with a car license in the EU, as the 1500kg payload would be on top of about 2500-2700kg CT empty weight, meaning the Cybertruck GVM is over 4000kg. SO that might be the first issue you need to get over, once it makes it to the EU.

What is the empty weight of your trailer?

 

[founder]

Excuse, I really missed Your post.

I thought of something like the slope plate at the Cyberdruck and something inflateable behind the transported house segment .
With drag cw=0.5 the consume at 90 km/h would be about 68 kW.

It is possible to register a car with less maximum weight.
So I had once a Citroen Jumper van registered for 2800 kg maximum allowed weight.
Could have been also 3250 kg, but severe restrictions in Germany, when more than 2800 kg at this time.

When the CT would have 2700 kg empty weight, no problem to register to 3500 kg maximum allowed weight. 800 kg payload are good enough.

The empty weight of the trailer will be about 800 kg.
The trailer must have electric motors to be positioned on the construction ground and something to push up the house segment from 0.55 m to 0.7 m above ground.

 

[JBee]

Excuse, I really missed Your post.

I thought of something like the slope plate at the Cyberdruck and something inflateable behind the transported house segment .
With drag cw=0.5 the consume at 90 km/h would be about 68 kW.

It is possible to register a car with less maximum weight.
So I had once a Citroen Jumper van registered for 2800 kg maximum allowed weight.
Could have been also 3250 kg, but severe restrictions in Germany, when more than 2800 kg at this time.

When the CT would have 2700 kg empty weight, no problem to register to 3500 kg maximum allowed weight. 800 kg payload are good enough.

The empty weight of the trailer will be about 800 kg.
The trailer must have electric motors to be positioned on the construction ground and something to push up the house segment from 0.55 m to 0.7 m above ground.

No Worries.

We had the same discussion in another thread about the EU 3500kg weight limit, and came to the same conclusion that you can register it with a lower gross weight.

For moving around on site without the CT attached you could use a caravan mover you can source from here, just be careful with the weight rating:

https://caravanmovershop.eu/

Hopefully, the CT will have a reversing assist using the FSD and cameras to locate the trailer. That should make moving it on site much easier, to the point you might not need the trailer motors. Another version is to have hub electric motors, but then you also need dedicated batteries and speed controller etc. which reduces the payload and would cost more as well.

To lift the trailer air suspension bags on the trailer would probably work best to lift 150mm, if the suspension has enough travel. Alternatively there are also pneumatic carjacks that can support that sort of weight, without being too heavy themselves.

 

[rr6013]

Least problem to solve is aerodynamics, time, speed and truck. As none solve the end-result siting dilemma at delivery. Envisioned as a jack up problem into place is your structure a component to a larger structure? Constraints?

Assuming the structure can support its own weight, i.e. ocean container, the final resting place can be accomplished several ways. Roll-off style, skid style, jack style, crane style or excavator style. Which do you prefer?

House movers work the siting problem in reverse. A structure is transported to site then jacked down into place. A trailer deck ht. will be 16-30” above ground depending on weight of structure. So they excavate a mound above foundation ht. Drive up onto mound, install jack supports then drive trailer out from under structure. Finally, jack down structure onto foundations.

 

[HaulingAss]

What exactly is a "springy" ladder frame and how does it effect trailer tracking from a single point hitch? Do you mean poor suspension?

Rigidity is good, but poor suspension setup is much worse. Also the CT will have less rear overhang to the hitch, so a shorter lever arm will help to keep the trailer in line.

"Springy" is a highly technical term for the opposite of "rigid".

Sheesh!

A ladder frame is a traditional truck frame. They are designed to flex rather than crack and break. If you have taken these off-road you are aware of how much the frame can twist and deflect just from static loads on uneven ground. Dynamic towing loads are much higher. When a heavy trailer is attached to the rear-most point of a ladder frame it is usually a significant distance behind the rear axle and the side forces applied to this point from the normal motion of the trailer being towed are high enough to deflect the chassis laterally. This energy builds up in the ladder frame and then is released (for every action there is an equal and opposite reaction). A ladder frame does not dampen the energy much and every frame has a natural frequency or resonance that it responds to. This is the source of that most dangerous towing condition, often called "trailer sway".

While a ladder frame can be made as rigid as one would like, that would add a lot of weight that is not compatible with light duty trucks like the F-150 and the Silverado. The Cybertruck is not only light, but since the structural part of the frame is wider, outboard of the wheels rather than inboard, it will be naturally more rigid. It's simple geometry and leverage. Additionally, the material choice, cold-rolled steel, is naturally more rigid than mild steel. And the shorter lever arm that you mention (shorter rear overhang), will be an additional advantage.

The suspension plays into it as well because the suspension connects the frame to the wheels through the axles and the side loads are not always well controlled which allows the rear to go left while the front goes right. Leaf springs are incredible at handling huge loads but, on 1/2 ton trucks are often rather long (fore to aft) for ride comfort and suspension travel and this is less than ideal for towing stability because the springs allow a certain amount of twist and that is not damped by the suspension dampers. The Cybertruck will have beefy rods in the independent suspension controlling lateral loads and these will not store significant energy, unlike leaf springs.

A poor suspension that springs up and down with poor damping is not nearly as bad for towing as you think, except to the extent that they (poor suspensions) also tend to not control side loads very well. And of course, no one wants up/down oscillations while towing, if for no other reason, it's uncomfortable. But that motion is combatible with towing stability as long as side loads are well controlled, but they typically are not.

 

[Ogre]

I found in the 18 answers nothing about aerodynamic optimizations.

You seem to misunderstand what this forum is about.

This site isn’t a q&a site for engineering questions. Even if it was, your post is just too vague.

 

[JBee]

You seem to misunderstand what this forum is about.

This site isn’t a q&a site for engineering questions. Even if it was, your post is just too vague.

Why too vague?

He even done the basic aero calculation for you and provided the necessary info on the aerodynamics of the load.

Where else should he post a CT related question like this? Ogres r Us?

If you don't have anything to contribute then don't contribute at all, but otherwise that's just a plain rude thing to say to a foreign country first poster.

I wonder what happens when we all have CTs and are trying to figure out how to do things, if this will be the standard response here. I seriously hope not.

 

[Crissa]

"Springy" is a highly technical term for the opposite of "rigid".

Sheesh!

A ladder frame is a traditional truck frame. They are designed to flex rather than crack and break. If you have taken these off-road you are aware of how much the frame can twist and deflect just from static loads on uneven ground. Dynamic towing loads are much higher. When a heavy trailer is attached to the rear-most point of a ladder frame it is usually a significant distance behind the rear axle and the side forces applied to this point from the normal motion of the trailer being towed are high enough to deflect the chassis laterally. This energy builds up in the ladder frame and then is released (for every action there is an equal and opposite reaction). A ladder frame does not dampen the energy much and every frame has a natural frequency or resonance that it responds to. This is the source of that most dangerous towing condition, often called "trailer sway".

While a ladder frame can be made as rigid as one would like, that would add a lot of weight that is not compatible with light duty trucks like the F-150 and the Silverado. The Cybertruck is not only light, but since the structural part of the frame is wider, outboard of the wheels rather than inboard, it will be naturally more rigid. It's simple geometry and leverage. Additionally, the material choice, cold-rolled steel, is naturally more rigid than mild steel. And the shorter lever arm that you mention (shorter rear overhang), will be an additional advantage.

The suspension plays into it as well because the suspension connects the frame to the wheels through the axles and the side loads are not always well controlled which allows the rear to go left while the front goes right. Leaf springs are incredible at handling huge loads but, on 1/2 ton trucks are often rather long (fore to aft) for ride comfort and suspension travel and this is less than ideal for towing stability because the springs allow a certain amount of twist and that is not damped by the suspension dampers. The Cybertruck will have beefy rods in the independent suspension controlling lateral loads and these will not store significant energy, unlike leaf springs.

A poor suspension that springs up and down with poor damping is not nearly as bad for towing as you think, except to the extent that they (poor suspensions) also tend to not control side loads very well. And of course, no one wants up/down oscillations while towing, if for no other reason, it's uncomfortable. But that motion is combatible with towing stability as long as side loads are well controlled, but they typically are not.

A ladder frame isn't designed to flex - it's just not capable of not flexing. Flexing induces metal fatigue.

-Crissa

 

[HaulingAss]

A ladder frame isn't designed to flex - it's just not capable of not flexing. Flexing induces metal fatigue.

-Crissa

Not really true. They know it will flex and they design it to accomodate that. By distributing the flexing more evenly, and avoiding "hinge points", the metal fatigue can be minimized.

 

[JBee]

Deflection is inherent in any metal engineering design, you just don't go over the materials yield strength, and therefore stay in the temporary elastic deformation range, and not over into the permanent plastic deformation range, where it breaks.

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