|
Platystemon posted:This is going to sound trivial, but if you take the “put a wing on it to take weight off the wheels” idea to its extreme, you end up with an æroplane. hold on a minute though... if you take a fully loaded dreamliner and fly it across the world, or drive the same number of people the same distance in the corresponding number of SUVs, which uses less fuel? Not really related to the discussion of lift and drag, but still... PT6A posted:I can say with 100% certainty that the last thing I want in a ground vehicle is anything taking weight off the wheels. Yeah I had a feeling this was the case too. Cheers. e for snipe: 
Bucky Fullminster fucked around with this message at 04:22 on Oct 25, 2018 |
#
?
Oct 25, 2018 04:17
|
|
|
|
| # ? May 17, 2024 23:30 |
|
|
Last I checked, which was admittedly a while ago and not rigorously, the average airliner (average loading) and sedan (certified single occupant) worked out to similar figures for grams of carbon dioxide per unit distance. SUVs would lose to a laden 747.
|
|
#
?
Oct 25, 2018 04:22
|
|
|
Hobo Erotica posted:hold on a minute though... if you take a fully loaded dreamliner and fly it across the world, or drive the same number of people the same distance in the corresponding number of SUVs, which uses less fuel? SUVs aren’t designed to be fuel efficient like planes are though. A lot of effort goes into making planes fuel efficient, at the expense of pretty much everything else except safety. Design of consumer road vehicles is more focused on marketing than fuel efficiency. Gotta have those heated seats and spoilers. Per pound mile, semi trucks are probably more fuel efficient than planes. They’re certainly cheaper.
|
|
#
?
Oct 25, 2018 04:25
|
|
|
WINGS ON CARS 
|
|
#
?
Oct 25, 2018 04:37
|
|
|
FrozenVent posted:SUVs aren’t designed to be fuel efficient like planes are though. A lot of effort goes into making planes fuel efficient, at the expense of pretty much everything else except safety. From https://www.washingtonpost.com/outlook/five-myths/five-myths-about-air-travel/2017/06/22/ffb9357a-553a-11e7-b38e-35fd8e0c288f_story.html "At a transatlantic distance, a 525-seat Airbus A380 has an efficiency of 74 miles per gallon (mpg) per passenger, while the brand-new 168-seat Boeing 737 MAX 8 reaches 110 mpg per passenger." The 4WD Escalade gets 21 mpg on the highway, but also seats eight, which puts it at 168 mpg per passenger. Consumer vehicles are designed to hit fuel efficiency targets, with the caveat that those targets are regulatory and not driven by customers that need to save every penny on fuel possible to even hope of turning a profit.
|
|
#
?
Oct 25, 2018 04:37
|
|
|
Additionally, a common dumb theme is the idea that spoilers are nothing but downforce rather than an item that smooths out aero drag.
|
|
#
?
Oct 25, 2018 04:45
|
|
|
Hobo Erotica posted:Cool, thanks heaps guys, kind of what I suspected. Hydrofoils are useful because big buoyant hulls create a lot of drag through the water. If you can create a water wing that lifts those hulls out, you're trading a colossal amount of hull drag for a much smaller amount of drag on the wing; then the same thrust, either from wind or a propeller, can push the boat to much higher speeds. Air drag is negligible in comparison. Cars are a different story. Above about 40 mph, air drag is the dominant force acting to slow the car down, and it increases quadratically. Any drag you add via protuberances is only gonna make that worse, and as others said, "tire drag" is negligible, and reducing it by lifting the car up has other, severe consequences. The ideal car shape for fuel economy is a lift-neutral symmetric airfoil like you see on solar challenge type cars. These, though, present some minor impracticalities for a commuter car. https://www.youtube.com/watch?v=KZNh3vRH228
|
|
#
?
Oct 25, 2018 05:15
|
|
|
dupersaurus posted:Wings create a lot of drag. They work for race cars because the increase in speed they provide in turning more than makes up for the lost top speed in the straights (and/or prevent the car from taking off in the wind) You could always build a car with variable airfoils, allowing you to angle them to increase downforce when cornering but return them to a low-drag configuration for additional straight-line speed. All of the racing organizations have banned variable airfoils because the cars that use it are too fast.
|
|
#
?
Oct 25, 2018 05:53
|
|
|
There's some very good reasons why lift is bad and not something you want on a road vehicle. Here is one graphic example:
|
|
#
?
Oct 25, 2018 06:04
|
|
|
Well I definitely came to the right place.
|
|
#
?
Oct 25, 2018 06:23
|
|
|
Videos of racecars getting lift are unreal. https://www.youtube.com/watch?v=nkcGPf-fLV0 It’s like God sneezed.
|
|
#
?
Oct 25, 2018 06:32
|
|
|
Hobo Erotica posted:Is there a reason we don't see what's basically a wing on the top of a car? Like instead of roof racks, a flat (ish) platform in the shape of an aerofoil, slightly raised above the roof? Would it provide enough lift to improve fuel efficiency, or would it provide too much lift and make them less controllable? Would the downward force of an upside-down one help at all? Or would none of them really do anything?  O Mother of Perpetual Downforce, grant that I may ever invoke thy most powerful name, which is the safeguard of the driving and the salvation of the quarter mile time. O Purest Bernoulli, O Sweetest Bernoulli, let thy name henceforth be ever on my lips. Delay not, O Blessed Cessna Wing Section, to help me whenever I call on thee, for, in all my needs, in all my races I shall never cease to call on thee, ever repeating thy sacred name, Bernoulli, Bernoulli.
|
|
#
?
Oct 25, 2018 06:46
|
|
|
Hobo Erotica posted:Is there a reason we don't see what's basically a wing on the top of a car? Like instead of roof racks, a flat (ish) platform in the shape of an aerofoil, slightly raised above the roof? Would it provide enough lift to improve fuel efficiency, or would it provide too much lift and make them less controllable? Would the downward force of an upside-down one help at all? Or would none of them really do anything? Here you go, the Thule Wingbar roof rack.  Doesn't add lift (which as mentioned will add drag) but supposedly isn't as draggy as normal racks. Somehow, my normal sensible car forum answer feels tame and inadequate.
|
|
#
?
Oct 25, 2018 07:03
|
|
|
Ola posted:Here you go, the Thule Wingbar roof rack. Funnily enough I think this brings us back full circle to where I started, I was looking at these last night, and remembered hydrofoils (and spoilers) then thought 'hold on, what if... would that... or would it...' Then you guys came out and just answered the poo poo out of everything, was really interesting, so thanks everyone again.
|
|
#
?
Oct 25, 2018 10:35
|
|
|
Hobo Erotica posted:Is there a reason we don't see what's basically a wing on the top of a car? Like instead of roof racks, a flat (ish) platform in the shape of an aerofoil, slightly raised above the roof? Would it provide enough lift to improve fuel efficiency, or would it provide too much lift and make them less controllable? Would the downward force of an upside-down one help at all? Or would none of them really do anything? Lift doesn’t make you more efficient, it just reduces the forces acting on your tires so you can’t steer or brake properly and you die. You make a car use less energy by reducing drag. Which people do; the reason Teslas have such good range is that their designs are very low drag. Upside down wings create downforce. Here is a handy history lesson I wrote on the topic recently: https://arstechnica.com/cars/2018/09/how-a-day-driving-high-downforce-cars-at-vir-taught-me-im-ok-being-slow/ drgitlin fucked around with this message at 14:07 on Oct 25, 2018 |
|
#
?
Oct 25, 2018 12:42
|
|
|
mlmp08 posted:Additionally, a common dumb theme is the idea that spoilers are nothing but downforce rather than an item that smooths out aero drag. A wing != spoiler.
|
|
#
?
Oct 25, 2018 12:43
|
|
|
Finger Prince posted:There's some very good reasons why lift is bad and not something you want on a road vehicle. Here is one graphic example: Didn't Mark Webber do it twice?
|
|
#
?
Oct 25, 2018 13:06
|
|
|
drgitlin posted:A wing != spoiler. This is what I came here to post. Wings are designed to generate downforce. Spoilers act just like the spoilers on an aircraft, spoiling the lift created by the body of the car. Look at the silhouette of a regular sedan or coupe from the side. Flat on the bottom, with a large bump at the top. It basically IS a wing. This is why factory active spoilers became a thing on certain Porsche, Audi, Chrysler, Tesla, and other vehicles, to reduce body lift at speed. Due to the disruption of lift, a properly designed spoiler also reduces overall drag, if the parasitic drag of the spoiler itself is lower than the induced drag of the body lift it is spoiling. I really wish there was a race class that allowed active aero, because it’s cool as gently caress.
|
|
#
?
Oct 25, 2018 13:25
|
|
|
Humphreys posted:Didn't Mark Webber do it twice? IIRC after the second time they immediately pulled that car type from the race.
|
|
#
?
Oct 25, 2018 14:28
|
|
|
drgitlin posted:A wing != spoiler. Right, but until the heat death of the universe, you'll have people yucking it up about spoilers on FWD cars without realizing how dumb it is.
|
|
#
?
Oct 25, 2018 14:29
|
|
|
FrozenVent posted:SUVs aren’t designed to be fuel efficient like planes are though. A lot of effort goes into making planes fuel efficient, at the expense of pretty much everything else except safety. Amusingly, just last week, I did the math on this. A 737, carries passengers at about 110mpg. Per person. Semi trucks... lets do that math, real quick like. They get 6-7 mpg loaded. (IIRC..) And can carry 45000lbs. Figuring 225lbs per passenger, between luggage and bag-o-meat. You get 195 passengers. Well... you're not putting 195 people into a 45' trailer. That works out to something like 1170mpg, per person. However, that's litteral cattle seating. Something more reasonable is like a 58 passenger motor coach. That's more like 350mpg. With vaguely similar comfort to an airliner. and if the trip is less than 300 miles, you might even get there sooner! Fuel economy gets positively stupid once you get into trains. They're something like an order of magnitude better than planes. And then there's boats. :-) Which trumps them all. What's really impressive, is that airliners get that 100+mpg per passenger, at 400mph. drgitlin posted:Lift doesn’t make you more efficient, it just reduces the forces acting on your tires so you can’t steer or brake properly and you die. You make a car use less energy by reducing drag. Which people do; the reason Teslas have such good range is that their designs are very low drag. Nice article. I've recently started r/c car racing. Between low CG, and downforce, they do something like 6-8g's in the corners. It's brain bending. https://www.youtube.com/watch?v=ZiChT2jyDes Nerobro fucked around with this message at 15:22 on Oct 25, 2018 |
|
#
?
Oct 25, 2018 15:18
|
|
|
Nerobro posted:What's really impressive, is that airliners get that 100+mpg per passenger, at 400mph. That's the important part. I'm not cramming into a loving bus and slowpoking across the country, I have things to do.
|
|
#
?
Oct 25, 2018 15:46
|
|
|
Platystemon posted:Videos of racecars getting lift are unreal. https://youtu.be/pChX7tARscw
|
|
#
?
Oct 25, 2018 15:49
|
|
Bad Angus! Bad!
|
Nerobro posted:Amusingly, just last week, I did the math on this. Interestingly, a 45' trailer is roughly equivalent to a CRJ-200 for cabin dimensions. The CRJ is 40' long in the cabin, but that extra 5' on the trailer you could allot to cargo/baggage. CRJ can squeeze in 50 pax in a pinch, and it needs to have some of that space dedicated to flight attendant/galley and toilet.
|
|
#
?
Oct 25, 2018 16:14
|
|
|
HookedOnChthonics posted:
fuuuuuuuuuuuuuuuuck i think i actually got the season's pass for that game too
|
|
#
?
Oct 25, 2018 16:47
|
|
Pimp My Bomber: B-17 Edition is out
|
Finger Prince posted:Interestingly, a 45' trailer is roughly equivalent to a CRJ-200 for cabin dimensions. The CRJ is 40' long in the cabin, but that extra 5' on the trailer you could allot to cargo/baggage. CRJ can squeeze in 50 pax in a pinch, and it needs to have some of that space dedicated to flight attendant/galley and toilet. That closely matches the bus passenger situation too. Still 400mph versus 55. Cessna 172: 131 knots, 8gph. So going to "car numbers" 150mph, 8gph. That's 18.75mpg. With 3 "real" people on board, we're only at 56mpg.
|
|
#
?
Oct 25, 2018 17:32
|
|
|
Nerobro posted:
If it's completely full, which they rarely are. A Prius with 4 people in it is180 mpg and it takes you door to door. Not transatlantic though.
|
|
#
?
Oct 25, 2018 17:57
|
|
|
The 737 may be carrying cargo too which helps in the calculation.
|
|
#
?
Oct 25, 2018 17:58
|
|
|
Ola posted:If it's completely full, which they rarely are. A Prius with 4 people in it is180 mpg and it takes you door to door. Not transatlantic though. I don't know how much you fly but I do, more than I wished, and it's rare that you get on a half-empty plane these days.
|
|
#
?
Oct 25, 2018 18:59
|
|
|
drgitlin posted:I don't know how much you fly but I do, more than I wished, and it's rare that you get on a half-empty plane these days. Domestic mainline in the US it’s a relief when there are ANY unused seats at all.
|
|
#
?
Oct 25, 2018 19:02
|
|
|
Ola posted:If it's completely full, which they rarely are. A Prius with 4 people in it is180 mpg and it takes you door to door. Not transatlantic though. Multiply it by 0.85 then? http://atwonline.com/airline-traffic/top-30-airlines-passenger-load-factor-year-date-july-2017
|
|
#
?
Oct 25, 2018 19:04
|
|
|
I know that it's common for an airliner to be quite full  Just saying it depends on the load factor and that a car easily beats an airliner. Ryanair has something crazy like 96% average load factor, but I'd rather drive transatlantic than fly with them.This wiki article has tons of fuel efficiency numbers and other interesting stuff. https://en.wikipedia.org/wiki/Fuel_economy_in_aircraft
|
|
#
?
Oct 25, 2018 19:12
|
|
|
Ola posted:If it's completely full, which they rarely are. A Prius with 4 people in it is180 mpg and it takes you door to door. Not transatlantic though. It's far more likely that that Prius is not completely full either, and most cars are operated as single occupant vehicles, so the theoretical per passenger economy is even less relevant in a car.
|
|
#
?
Oct 25, 2018 19:21
|
|
|
Finger Prince posted:It's far more likely that that Prius is not completely full either, and most cars are operated as single occupant vehicles, so the theoretical per passenger economy is even less relevant in a car. Commuting to work sure, but not going on holiday. A Prius with two people is 90 mpg, a 737 with 85% PLF is 93.5. A Tesla on the other hand...
|
|
#
?
Oct 25, 2018 19:27
|
|
|
Ola posted:A Tesla on the other hand... DNF
|
|
#
?
Oct 25, 2018 19:31
|
|
|
Nerobro posted:That closely matches the bus passenger situation too. Still 400mph versus 55. Unless you’re flying a Cutlass, no 172 is going to do 131ktas in level flight. 110 is a more normal cruise airspeed. So it’s a bit worse than that.
|
|
#
?
Oct 25, 2018 19:33
|
|
|
Ola posted:A Tesla on the other hand... Gets whompy wheels 10 miles into the trip and waits by the side of the road for a flatbed tow truck which carries it the rest of the way at 8-10mpg  vvv that guy you find in any troubleshooting thread for anything ever saying “Well mine works just fine” HookedOnChthonics fucked around with this message at 21:16 on Oct 25, 2018 |
|
#
?
Oct 25, 2018 19:34
|
|
|
Not much overlap with the EV thread I see. I've driven a Model S long range, it didn't have any problems and the comfort was great. Only problem was I had to stay sober. I would happily base the rest of my holidaying life on one, rather than airliners. I'd just like to go round the world first, then I can be green later...
|
|
#
?
Oct 25, 2018 20:01
|
|
|
Ola posted:If it's completely full, which they rarely are. A Prius with 4 people in it is 180 mpg and it takes you door to door. Not transatlantic though. True! But also at 60mph instead of 400. And "you're driving yourself". And.. the interior of Priuses are almost more hateful than the interior of a cheap airline. And the driving experience is everything driving shouldn't be. (I.. hate.. Priuses. I've driven three. They rank right there with a first gen FWD Impala for "driving this is punishment") a patagonian cavy posted:Unless you’re flying a Cutlass, no 172 is going to do 131ktas in level flight. 110 is a more normal cruise airspeed. I did not carefully vet my numbers. :-)
|
|
#
?
Oct 25, 2018 21:19
|
|
|
|
| # ? May 17, 2024 23:30 |
|
|
FrozenVent posted:The speed at which a spoiler starts to have a measurable impact is not a speed at which a vehicle should be operated on public roads. Germany says otherwise, and they're right. The first-gen Audi TT actually got recalled to add a spoiler because it generated enough lift to become unstable north of 100 MPH. https://www.nytimes.com/2000/02/20/automobiles/audi-offers-tt-fix-after-5-deaths.html
|
|
#
?
Oct 25, 2018 21:34
|
|
