Barrel roll
in [Aussie Drivers]
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From: Noddy on 20 Jun 2010 08:45 "hippo" <am9obmhAc2hvYWwubmV0LmF1(a)REGISTERED_USER_usenet.com.au> wrote in message news:hvl0qb$u5s$1(a)news.eternal-september.org... > Could be interesting times then - he did promise to serve out his full > term! He'll be doing that any day soon I expect, and he'll probably break that one as well. -- Regards, Noddy.
From: Neil Gerace on 21 Jun 2010 00:33 On Jun 20, 7:19 am, Mickel <mic...(a)nospam.com> wrote: > The m on each side of the equation would cancel each other out. The mass is very relevant if you want the car to hold on to the surface of the tunnel. I think.
From: Doug Jewell on 22 Jun 2010 08:29 Neil Gerace wrote: > On Jun 20, 7:19 am, Mickel <mic...(a)nospam.com> wrote: > >> The m on each side of the equation would cancel each other out. > > The mass is very relevant if you want the car to hold on to the > surface of the tunnel. I think. Nope. As I previously posted: The downward force is weight which is mG. the upward force is centripetal force which is mV^2/r. The minimum speed at which the vehicle can complete the turn, is where the centripetal force balances the weight, or mG=mV^2/r. The m on both sides cancels out, and G is a constant (on earth it is anyway), so whether the vehicle can complete the manouvre or not is entirely dependent upon the velocity in relation to the radius of the curve. Doesn't matter if it is a hot-wheels toy, or a 4T truck, if the radius is the same the speed will need to be the same. Note that V in the equation is the angular velocity around the curve, not the linear velocity. The only part the mass will play, is in how easy it is to accelerate the vehicle to the required speed, and also how easy it is to turn the vehicle off the straight course and onto the curve. Once actually into the barrel roll though, mass is completely irrelevant to whether the vehicle stays on the roof or not. -- What is the difference between a duck?
From: veritas on 22 Jun 2010 08:56 On 20/06/2010 9:04 PM, Noddy wrote: Yeah at the other side of it - those three Russian pilots with eyes wide open knew what was going on, HUH. Descended, turned and placed the aircraft in a situation it was not designed for. The instruments were reading correctly. and they still didn't twig and they were seasoned pilots. You remember, the one that did every aerobatic manoeuvre known to man when they let the 14 YO boy at the controls before it spirally dived into the ground. No one had a clue what the aircraft was doing. They felt it in this case tho. A smooth pilot could fool an (eyes-closed) into thinking all was OK - Boeing test-pilot did it in a 707 and a PAX reported not knowing until looking out of the window to see the "ground" in the "sky". A ham fisted pilot, a bump from turbulence or a barrel roll - with your eyes closed you wouldn't give a clue as to what attitude the aircraft might be in. A smooth gradual entry it would not be felt! Even the grand old C180 goes over as smooth as silk.
From: Doug Jewell on 22 Jun 2010 18:26
veritas wrote: > On 20/06/2010 9:04 PM, Noddy wrote: > > Yeah at the other side of it - those three Russian pilots with eyes wide > open knew what was going on, HUH. Descended, turned and placed the > aircraft in a situation it was not designed for. The instruments were > reading correctly. and they still didn't twig and they were seasoned > pilots. > > You remember, the one that did every aerobatic manoeuvre known to man > when they let the 14 YO boy at the controls before it spirally dived > into the ground. > > No one had a clue what the aircraft was doing. They felt it in this > case tho. > > A smooth pilot could fool an (eyes-closed) into thinking all was OK - > Boeing test-pilot did it in a 707 and a PAX reported not knowing until > looking out of the window to see the "ground" in the "sky". > > A ham fisted pilot, a bump from turbulence or a barrel roll - with your > eyes closed you wouldn't give a clue as to what attitude the aircraft > might be in. > > A smooth gradual entry it would not be felt! Even the grand old C180 > goes over as smooth as silk. > Which is all completely irrelevant to the discussion at hand about a car performing a barrel roll. There are so many differences between an aircraft and a car that there is absolutely no point comparing the two. An aircraft is held in the air by the lift generated by the wings, and in some more powerful acrobatic planes the prop can also assist in providing lift. An aircraft has numerous controls that can alter the attitude of the aircraft. An aircraft in an acrobatic manouvre can gain and lose height as required. These capabilities mean that the pilot has a lot more scope to alter the perceived forces on a person within the plane. A car doing a barrel roll however has only 2 forces controlling it's vertical position - gravity and centripetal force from the curve. It's four wheels must remain on the surface of the tunnel at all times. It cannot arbitrarily gain or lose height. Therefore it MUST perform the manouvre such that at the top of the roll centripetal force >= gravitational force. By necessity this means at the start of the manouvre the force acting on it is greater. By necessity, the vehicle will have a variation of 2G between the top of the roll and the bottom. Simple physics. The driver may be able to reduce that slightly by changing the rate at which they turn in, but the changes will be slight. Sure if you had your eyes closed, you may not know you went upside down, but you sure as hell would know that it has done something extreme. -- What is the difference between a duck? |