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Old 06-05-2017, 11:29 PM   #71 (permalink)
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Yes

Quote:
Originally Posted by Angel And The Wolf View Post
But do not two tires on the same real or virtual axle track a corner with less scrub than two tires mounted one in front of the other? The author of post 51 stated the fourth wheel was to qualify the car as a four wheel vehicle.
Tandem axles do induce scrub, but it just does not matter significantly. A horse cart with a single pivot in the middle of the front axle has no scrub, and the very first steam car, le Oblissante, managed it, along with extreme steering angles customary then, by using elliptical chainwheels.


Last edited by Bicycle Bob; 06-05-2017 at 11:33 PM.. Reason: Trivia Bonus.
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Old 06-05-2017, 11:40 PM   #72 (permalink)
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I would like a nice little 40-50 MPG Prius C with AWD and a higher ground clearance..
Equipped with QR roof racks, trailer hitch for a small cargo rack (or my bike carrier).
For in-town use during snow storms and for hauling stuff when needed..

(My RAV4 AWD is giving me 22 MPG around town)..
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Old 06-06-2017, 12:36 AM   #73 (permalink)
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Quote:
Originally Posted by Bicycle Bob View Post
The biggest problem with roadable aircraft seems to be available lane width vs the wingspan needed for efficiency. Lifting bodies are nice and neat, but draggy without wing extensions.
This is absolutely true, beyond 6-7ft wide and the vehicle is quite unmanageable on the road, so it needs a form of folding geometry to establish a useful aspect ratio or it wont ever leave the ground without a pile of HP for thrust.

As soon as one does that, air circulation around the wing tips sees it as no different to the full wing span, even though the bulk of the area is the lifting body. The lifting body comprises more than enough area to feather the winglets within its form for road use for a profile more consistent with road use.

Another issue discovered by solar race cars whose body form is a sleek aerodynamic profile, is inland gusts of wind. Such cars crossing the Australian desert were at risk of destruction because the car was liable to leave the ground and flip. Assist crews would have to hop out of the support vehicle and hold the car on the ground to avoid annihilation.

Clearly your flying car wouldn't be likely to have a support crew, so some attention needs to be paid to that phenomena. The single rear wheel on a motorcycle like swing arm can control the bodies angle of attack between on road use and flying configuration.

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Old 06-06-2017, 01:06 AM   #74 (permalink)
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Originally Posted by Bicycle Bob View Post
I sure wish hydroplane designers would start with a stable ground-effect glider, and then add a water prop and rudder. Anything light and fast needs to be blowover-proof.
I separated this part because it is in my view a different set of issues. Apologies if Im straying too far off topic but I thought this to be important and still relevant to vehicles on road.

I suspect a significant problem here is one of aerodynamic balance. Consider the Volkswagen beetle dynamics, where the center of gravity is positioned just forward of the rear wheels, we know this because thats were the jacking point is to lift both wheels on one side of the car.



With the weight so far aft, the car is only ever going to be stable while traveling in reverse! Which is one of a suite of reasons why the car had a strong tendency to go backwards when it got loose in a fast turn. And while on the way around to assume a dynamically stable position, the car was in complete loss of control and apt to rollover with potential for catastrophe.

I would be checking if a hydroplanes was capable of being dynamically trim stable. Explained another way, dynamic stability requires that the center of the vehicles mass leads the center of the vehicles resistance, because without that there will be a strong propensity to flip should some occurrence upset the stability.


Last edited by sidecar; 06-06-2017 at 01:25 AM.. Reason: include image
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Old 06-06-2017, 03:14 AM   #75 (permalink)
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Quote:
With the weight so far aft, the car is only ever going to be stable while traveling in reverse! Which is one of a suite of reasons why the car had a strong tendency to go backwards when it got loose in a fast turn. And while on the way around to assume a dynamically stable position, the car was in complete loss of control and apt to rollover with potential for catastrophe.
A suite of reasons? Sweet!

The edge case would be the Tatra V8. You established the center of gravity, where is the center of pressure? Understeer can throw the back end of the car, but it can be controlled by the roll center height front/rear (anti-roll bars), tire cross-section and inflation pressure. This is called tuning.

And how will it ever be stable in reverse when the Ackermann effect kingpin inclination is bass ackwards?

Last edited by freebeard; 06-06-2017 at 03:53 AM..
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Old 06-06-2017, 03:35 AM   #76 (permalink)
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Quote:
Originally Posted by freebeard View Post
A suite of reasons? Sweet!
among the influencing factors was the swing axle of up to late 70's designs. This meant that the car tended to push on the now near sideways rear wheel, and by the attribute of the swing axle folding it under the car, reducing tyre contact patch and raising the rear of the car and therefore CG even higher, further degrading stability.

Should anything contact the most forward rear tyre at this instant causes a snap roll, even if the driver induces corrective steering it will matter not, the car is bluntly 'out of control'.

If one is lucky, the car will fully invert to traveling backwards, its most stable condition.

Quote:
Originally Posted by freebeard
The edge case would be the Tatra V8. You established the center of gravity, where is the center of pressure?
because I dont think there is any hope that the center of pressure or center of resistance is going to be anywhere near aft of the the CG, where it needs to be for stability.

Quote:
Originally Posted by freebeard
Understeer can throw the back end of the car, but it can be controlled by the roll center height front/rear (anti-roll bars), tire cross-section and inflation pressure. This is called tuning.

And how will it ever be stable in reverse when the Ackermann effect is bass ackwards?
I think the outrageous safety record of this car speaks for itself. I know these cars are still popular to this day, and I have owned a few myself. Im quite used to the arguments that somehow the data is wrong and these are cheap to run well 'engineered' cars. But a car that will kill you has no saving graces, its just lethal and unnecessary.
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Old 06-06-2017, 04:04 AM   #77 (permalink)
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Well, I just came back to edit Ackermann effect for kingpin inclination.

Quote:
...the swing axle of up to late 70's designs. This meant that the car tended to push on the now near sideways rear wheel...
....
I think the outrageous safety record of this car speaks for itself. I know these cars are still popular to this day, ... But a car that will kill you has no saving graces, its just lethal and unnecessary.
Wow... just wow.



Last edited by freebeard; 06-06-2017 at 04:13 AM..
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Old 06-06-2017, 05:32 AM   #78 (permalink)
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I'm constantly thinking/dreaming of the perfect multi-purpose vehicle that is both a wonder of reliability and fuel economy. To make things even harder, it should be both tiny and easy to park, AND spacious enough for a family of five, a huge dog and a lot of luggage. =Impossible? On top of that I live in Sweden where we have snow and icy roads in the winters so the inverted trike design I like a lot would be a realy bad design. The same goes for too narrow track width.

To maximize reliability you should actually have a dual engine design, perhaps even running on different fuels, like diesel/biodiesel and petrol/ethanol. Adding some sort of "light hybrid" can increase fuel efficiency a lot, and reduce the need for a much larger engine (-s) than what you need to keep cruising speed. With a parallel hybrid system you can still run the car on ICE's alone, with reduced performance. Such a hybrid system doesn't need so much of heavy, expensive and "enviormentaly hostile" batteries.

To cope with my "impossible" need for both a compact city car and a spacious multi purpose vehicle I'm thinking about a modular system that consists of front (drivetrain and driver cabin), a mid-section and a rear end. Both front and rear ends contain their own engine and light hybrid system. They can actually share the same physical design under the body, making it easier with spareparts.

The body should be narrow and long, with a rounded nose and tapered tail like an aircraft. The passengers are seated in tandem, all with their legs on each side of the passenger before them. Since I want a quite normal track width, the wheels will extend a bit out on the sides of the body, increasing drag. The gaps between front and rear wheels can be filled by low luggage boxes and we will end up with something that reminds of a long F1 racer. That design will also improve side impact safety.
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Old 06-06-2017, 06:03 AM   #79 (permalink)
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That sounds quite challenging, but anyway, since the seating arrangement would be quite similar to a motorcycle, eventually you should not disconsider a tricycle.
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Old 06-06-2017, 06:08 AM   #80 (permalink)
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Quote:
Originally Posted by cRiPpLe_rOoStEr View Post
That sounds quite challenging, but anyway, since the seating arrangement would be quite similar to a motorcycle, eventually you should not disconsider a tricycle.
there is also staggered tandem, which makes a shorter if slightly wider cockpit, but enables a rather better view forward with more elbow room for both driver and passenger.

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