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I've often wondered why European trucks don't have some sort of mechanism to make them more aerodynamic when they're on the highways i.e. an inflatable nose. T

I've often wondered why European trucks don't have some sort of mechanism to make them more aerodynamic when they're on the highways i.e. an inflatable nose. The boxy design must cost a fortune in fuel

noja 5y ago
You have often wondered why trucks do not come with inflatable noses?
- jack_riminton 5y ago
  yes
SkyPuncher 5y ago
From my understanding, the drag caused by the flat back of the trailer causing a vacuum is much more impactful than the front shape. I believe a "pillow" of air kind of builds up in the front. It also looks like truck in EU are limited to 55mph. When I tow our trailer (just with a normal vehicle), there's minimal difference between fuel economy between 45 and 60. Significant drops come into play at higher speeds.
- colechristensen 5y ago
  Drag is proportional to the square of speed
  - SkyPuncher 5y ago
    Ah. Yes! I forget about this! In vehicles, there's a lot of additional, interesting factors at play - like engine efficiency.
    - colechristensen 5y ago
      Yes there will be many nonlinear factors which combine to a maximum efficiency speed, which can, to an extent, be chosen by design.
- reaperducer 5y ago
  From my understanding, the drag caused by the flat back of the trailer causing a vacuum is much more impactful than the front shape. I believe a "pillow" of air kind of builds up in the front. A lot of long-distance American tractor trailers deploy fold-out cones on their back doors to improve their aerodynamics while driving. They fold up for low speed driving and loading. Also, fold-out flaps under the trailer for the same reason.
  - mindslight 5y ago
    I've always wondered the reasons behind the regional difference in popularity of these. Trucks in the middle of the country seem to have them, trucks on the coasts seem to not. And you'd think longer haul trucks would be the most likely to have them, and so you'd end up seeing some on the coasts regardless. Is it something with state by state safety regulations, like prohibitions on protruding structures that aren't part of the main body? Or differently-defined overall length restrictions? Does a given long haul truck have them deployed in the middle of the country, but then they're removed before getting to the coastal states?
    - SkyPuncher 5y ago
      > I've always wondered the reasons behind the regional difference in popularity of these. There's an interesting mis-alignment of incentives. It comes down to who owns the truck vs the trailer. * Truck owner pays for fuel. * Trailer owner pays for the flaps. So, unless you own both the truck and trailer, there's little incentive for trailer owners to install them.
      - mindslight 5y ago
        That by itself isn't enough to explain the stark discrepancy though. Surely in the regions where tail flaps are extremely rare, there are still some operators that own both trucks and trailers.
HPsquared 5y ago
In terms of aerodynamics, a blunt nose isn't actually that bad - the real drag is caused by flow separation at the rear of the vehicle. It's far more important to have a gently tapered tail, to avoid a stagnant low pressure zone forming. Think a typical "teardrop" airfoil shape, they are blunt at the front and gently taper off at the rear. In fact most cars are more aerodynamic in reverse than they are going forwards for exactly this reason - on most cars the front end comes in more gradually (the hood portion comes in first, then enlarges to the passenger section) whereas the rear end is usually much blunter (to maximize storage space).
- alecst 5y ago
  Ok wow, that last point really fascinated me: > most cars are more aerodynamic in reverse than they are going forwards I tried to find more about it, but I could only find two sources. The first was a Mythbusters episode about a particular Porsche, and the second was a Top Gear episode about a different car. Can you point me to an article that substantiates this?
  - dboreham 5y ago
    https://en.wikipedia.org/wiki/Kammback https://en.wikipedia.org/wiki/Kammback https://en.wikipedia.org/wiki/Drag_coefficient https://en.wikipedia.org/wiki/Drag_coefficient
  - throwaway0a5e 5y ago
    He's BSing or just ill informed. If you taper properly before the flat cutoff a squared off back (Honda insight is the quintessential example) is fine because the real turbulence happens a few feet behind the vehicle. At speed a blunt (even if it's rounded) nose just isn't great no matter how you cut it but with careful attention to corners, shape transitions and whatnot you can mitigate that quite a lot (modern crossovers with their bulbous front bodywork make heavy use of this). This is a subject with a million gotcha's that add up to a lot. Be weary of anyone peddling rule of thumb solutions.
    - 5y ago
dtech 5y ago
Trucks are allowed to be a bit longer now (0.5m iirc), but only for aerodynamic measures. The first few trucks taking advantage of the new rules are on the road now, but it'll take a while before fleets have been replaced. The most effective aerodynamic changes are on the back though.
Melkman 5y ago
A blunt front isn't that bad for aerodynamics as long as it's rounded enough for the air stream not to separate. A lot more can be gained at the back of a truck. Like this: http://learntoflyblog.com/wp-content/uploads/2016/04/4-5.png http://learntoflyblog.com/wp-content/uploads/2016/04/4-5.png
seszett 5y ago
European trucks seem to generally have better fuel economy, but this might simply be because fuel economy isn't a focus of US manufacturers.
Snoozus 5y ago
It does, but the key heare is the length limitation. Spending 1m on a more aerodynamic shape means 1m less cargo space. So the fuel efficiency per cargo volume actually goes down.
froh 5y ago
Actually having a smooth undercarriage and a smooth transition from truck to trailer and some wind breaking fins reduce drag a lot. https://en.vda.de/dam/vda/publications/FAT-SCHRIFTENREIHE%20260/1384523963_de_344759559.pdf https://en.vda.de/dam/vda/publications/FAT-SCHRIFTENREIHE%20... And the front aerodynamics dépend more on the details than it's length. Some aerodynamic designs have shockingly steep fronts. https://en.m.wikipedia.org/wiki/Schl%C3%B6rwagen https://en.m.wikipedia.org/wiki/Schl%C3%B6rwagen

noja 5y ago

You have often wondered why trucks do not come with inflatable noses?

jack_riminton 5y ago
yes

SkyPuncher 5y ago

From my understanding, the drag caused by the flat back of the trailer causing a vacuum is much more impactful than the front shape. I believe a "pillow" of air kind of builds up in the front. It also looks like truck in EU are limited to 55mph. When I tow our trailer (just with a normal vehicle), there's minimal difference between fuel economy between 45 and 60. Significant drops come into play at higher speeds.

colechristensen 5y ago
Drag is proportional to the square of speed
- SkyPuncher 5y ago
  Ah. Yes! I forget about this! In vehicles, there's a lot of additional, interesting factors at play - like engine efficiency.
  - colechristensen 5y ago
    Yes there will be many nonlinear factors which combine to a maximum efficiency speed, which can, to an extent, be chosen by design.
reaperducer 5y ago
From my understanding, the drag caused by the flat back of the trailer causing a vacuum is much more impactful than the front shape. I believe a "pillow" of air kind of builds up in the front. A lot of long-distance American tractor trailers deploy fold-out cones on their back doors to improve their aerodynamics while driving. They fold up for low speed driving and loading. Also, fold-out flaps under the trailer for the same reason.
- mindslight 5y ago
  I've always wondered the reasons behind the regional difference in popularity of these. Trucks in the middle of the country seem to have them, trucks on the coasts seem to not. And you'd think longer haul trucks would be the most likely to have them, and so you'd end up seeing some on the coasts regardless. Is it something with state by state safety regulations, like prohibitions on protruding structures that aren't part of the main body? Or differently-defined overall length restrictions? Does a given long haul truck have them deployed in the middle of the country, but then they're removed before getting to the coastal states?
  - SkyPuncher 5y ago
    > I've always wondered the reasons behind the regional difference in popularity of these. There's an interesting mis-alignment of incentives. It comes down to who owns the truck vs the trailer. * Truck owner pays for fuel. * Trailer owner pays for the flaps. So, unless you own both the truck and trailer, there's little incentive for trailer owners to install them.
    - mindslight 5y ago
      That by itself isn't enough to explain the stark discrepancy though. Surely in the regions where tail flaps are extremely rare, there are still some operators that own both trucks and trailers.

HPsquared 5y ago

In terms of aerodynamics, a blunt nose isn't actually that bad - the real drag is caused by flow separation at the rear of the vehicle. It's far more important to have a gently tapered tail, to avoid a stagnant low pressure zone forming. Think a typical "teardrop" airfoil shape, they are blunt at the front and gently taper off at the rear. In fact most cars are more aerodynamic in reverse than they are going forwards for exactly this reason - on most cars the front end comes in more gradually (the hood portion comes in first, then enlarges to the passenger section) whereas the rear end is usually much blunter (to maximize storage space).

alecst 5y ago
Ok wow, that last point really fascinated me: > most cars are more aerodynamic in reverse than they are going forwards I tried to find more about it, but I could only find two sources. The first was a Mythbusters episode about a particular Porsche, and the second was a Top Gear episode about a different car. Can you point me to an article that substantiates this?
- dboreham 5y ago
  https://en.wikipedia.org/wiki/Kammback https://en.wikipedia.org/wiki/Kammback https://en.wikipedia.org/wiki/Drag_coefficient https://en.wikipedia.org/wiki/Drag_coefficient
- throwaway0a5e 5y ago
  He's BSing or just ill informed. If you taper properly before the flat cutoff a squared off back (Honda insight is the quintessential example) is fine because the real turbulence happens a few feet behind the vehicle. At speed a blunt (even if it's rounded) nose just isn't great no matter how you cut it but with careful attention to corners, shape transitions and whatnot you can mitigate that quite a lot (modern crossovers with their bulbous front bodywork make heavy use of this). This is a subject with a million gotcha's that add up to a lot. Be weary of anyone peddling rule of thumb solutions.
  - 5y ago

dtech 5y ago

Trucks are allowed to be a bit longer now (0.5m iirc), but only for aerodynamic measures. The first few trucks taking advantage of the new rules are on the road now, but it'll take a while before fleets have been replaced. The most effective aerodynamic changes are on the back though.

Melkman 5y ago

A blunt front isn't that bad for aerodynamics as long as it's rounded enough for the air stream not to separate. A lot more can be gained at the back of a truck. Like this: http://learntoflyblog.com/wp-content/uploads/2016/04/4-5.png http://learntoflyblog.com/wp-content/uploads/2016/04/4-5.png

seszett 5y ago

European trucks seem to generally have better fuel economy, but this might simply be because fuel economy isn't a focus of US manufacturers.

Snoozus 5y ago

It does, but the key heare is the length limitation. Spending 1m on a more aerodynamic shape means 1m less cargo space. So the fuel efficiency per cargo volume actually goes down.

froh 5y ago

Actually having a smooth undercarriage and a smooth transition from truck to trailer and some wind breaking fins reduce drag a lot. https://en.vda.de/dam/vda/publications/FAT-SCHRIFTENREIHE%20260/1384523963_de_344759559.pdf https://en.vda.de/dam/vda/publications/FAT-SCHRIFTENREIHE%20... And the front aerodynamics dépend more on the details than it's length. Some aerodynamic designs have shockingly steep fronts. https://en.m.wikipedia.org/wiki/Schl%C3%B6rwagen https://en.m.wikipedia.org/wiki/Schl%C3%B6rwagen