Comments on: “My wife, my children, and the nation of Romania.” http://dansdata.blogsome.com/2008/02/03/my-wife-my-children-and-the-nation-of-romania/ the blog that is not dansdata.com Thu, 28 Aug 2008 19:43:51 +0000 http://wordpress.org/?v=1.5.1-alpha by: swalve http://dansdata.blogsome.com/2008/02/03/my-wife-my-children-and-the-nation-of-romania/#comment-2048 Thu, 07 Feb 2008 09:55:50 +0000 http://dansdata.blogsome.com/2008/02/03/my-wife-my-children-and-the-nation-of-romania/#comment-2048 The mythbusters airplane thing depends on the following: airspeed versus ground speed. The mythbusters airplane thing depends on the following: airspeed versus ground speed.

]]> by: jaws_au http://dansdata.blogsome.com/2008/02/03/my-wife-my-children-and-the-nation-of-romania/#comment-2045 Wed, 06 Feb 2008 23:15:32 +0000 http://dansdata.blogsome.com/2008/02/03/my-wife-my-children-and-the-nation-of-romania/#comment-2045 Actually the comment about African or European helicopters is quite true... though more American or Russian helicopters. American helicopters rotate anti-clockwise (looking from above), Russians the other way. Europeans are split, even within the same company :) The ultimate helicopter on a turntable question though would involve one of the Russian twin-rotor designs... I've no idea if the lift of just one rotor would be enough to get it off the ground, despite the turntable. Actually the comment about African or European helicopters is quite true… though more American or Russian helicopters. American helicopters rotate anti-clockwise (looking from above), Russians the other way. Europeans are split, even within the same company :)

The ultimate helicopter on a turntable question though would involve one of the Russian twin-rotor designs… I’ve no idea if the lift of just one rotor would be enough to get it off the ground, despite the turntable.

]]> by: Daniel Rutter http://dansdata.blogsome.com/2008/02/03/my-wife-my-children-and-the-nation-of-romania/#comment-2033 Tue, 05 Feb 2008 23:53:39 +0000 http://dansdata.blogsome.com/2008/02/03/my-wife-my-children-and-the-nation-of-romania/#comment-2033 In the real world, aircraft wheel friction is slight enough that it's left as a constant for runway length calculations, for <b>all</b> rolling speeds of a given aircraft. So whether a given plane is minimally loaded and taking off at sea level (and can thus take off at a low speed) or stuffed to the gunwales with passengers, fuel and cargo and taking off from a Himalayan airfield (and thus needs to be rolling so fast that its tyres are approaching their rotational speed limit), wheel friction is given the same low value. This is fair enough, since wheel friction is very small at taxiing speed and increases directly with speed, but air resistance increases with the square of a vehicle's speed. So the faster you go, the <b>less</b> important wheel friction is, as long as no bearings have seized and no tyres have blown. In the real world, aircraft wheel friction is slight enough that it’s left as a constant for runway length calculations, for all rolling speeds of a given aircraft.

So whether a given plane is minimally loaded and taking off at sea level (and can thus take off at a low speed) or stuffed to the gunwales with passengers, fuel and cargo and taking off from a Himalayan airfield (and thus needs to be rolling so fast that its tyres are approaching their rotational speed limit), wheel friction is given the same low value.

This is fair enough, since wheel friction is very small at taxiing speed and increases directly with speed, but air resistance increases with the square of a vehicle’s speed. So the faster you go, the less important wheel friction is, as long as no bearings have seized and no tyres have blown.

]]> by: sockatume http://dansdata.blogsome.com/2008/02/03/my-wife-my-children-and-the-nation-of-romania/#comment-2032 Tue, 05 Feb 2008 23:18:46 +0000 http://dansdata.blogsome.com/2008/02/03/my-wife-my-children-and-the-nation-of-romania/#comment-2032 Oh, of course there's also the version where the plane is being kept stationary relative to the airmass around it, while the treadmill moves under it at takeoff speed, but the version of the question I read specifically stipulated that the plane was using its engines and the treadmill surface was moving with exactly the opposite velocity to the plane. Oh, of course there’s also the version where the plane is being kept stationary relative to the airmass around it, while the treadmill moves under it at takeoff speed, but the version of the question I read specifically stipulated that the plane was using its engines and the treadmill surface was moving with exactly the opposite velocity to the plane.

]]> by: sockatume http://dansdata.blogsome.com/2008/02/03/my-wife-my-children-and-the-nation-of-romania/#comment-2031 Tue, 05 Feb 2008 23:10:35 +0000 http://dansdata.blogsome.com/2008/02/03/my-wife-my-children-and-the-nation-of-romania/#comment-2031 (The treadmill accelerates instantaneously, or at least on a timescale far shorter than that required for the plane to take off, I should add.) (The treadmill accelerates instantaneously, or at least on a timescale far shorter than that required for the plane to take off, I should add.)

]]> by: sockatume http://dansdata.blogsome.com/2008/02/03/my-wife-my-children-and-the-nation-of-romania/#comment-2030 Tue, 05 Feb 2008 23:07:29 +0000 http://dansdata.blogsome.com/2008/02/03/my-wife-my-children-and-the-nation-of-romania/#comment-2030 Having evaluated pretty much all of the possible interpretations, I think the plane's going to take off the conveyor belt except in two scenarios: You specifically design the plane's wheels so that the resistance to rotation (i.e. grip to the tarmac + friction in bearings) is on the order of the thrust from the engines at all treadmill speeds. In this instance either the plane doesn't begin moving at all because there's too much drag on the wheels, the wheels get worn flat from being dragged across the tarmac and it takes off anyway, or the wheels wear through and the plane crashes. If you idealise the treadmill so that it accelerates to exactly match the plane speed <i>as measured by the rotational speed of the plane's wheels</i>, but do not also stipulate that it and the plane are indestructible, then the plane and/or treadmill will be destroyed instantly the moment the plane achieves nonzero speed: (treadmill speed) = (wheel speed) = (treadmill speed) + (plane speed) Where (plane speed) &gt; 0, (wheel speed) &gt; (treadmill speed), treadmill accelerates to infinity. In all of the other (i.e. reasonable) interpretations, there's nothing to stop the plane taking off. However it's more fun to come up with unreasonable interpretations. Having evaluated pretty much all of the possible interpretations, I think the plane’s going to take off the conveyor belt except in two scenarios:

You specifically design the plane’s wheels so that the resistance to rotation (i.e. grip to the tarmac + friction in bearings) is on the order of the thrust from the engines at all treadmill speeds. In this instance either the plane doesn’t begin moving at all because there’s too much drag on the wheels, the wheels get worn flat from being dragged across the tarmac and it takes off anyway, or the wheels wear through and the plane crashes.

If you idealise the treadmill so that it accelerates to exactly match the plane speed as measured by the rotational speed of the plane’s wheels, but do not also stipulate that it and the plane are indestructible, then the plane and/or treadmill will be destroyed instantly the moment the plane achieves nonzero speed:

(treadmill speed) = (wheel speed) = (treadmill speed) + (plane speed)

Where (plane speed) > 0, (wheel speed) > (treadmill speed), treadmill accelerates to infinity.

In all of the other (i.e. reasonable) interpretations, there’s nothing to stop the plane taking off. However it’s more fun to come up with unreasonable interpretations.

]]> by: Odeen http://dansdata.blogsome.com/2008/02/03/my-wife-my-children-and-the-nation-of-romania/#comment-2029 Tue, 05 Feb 2008 17:49:41 +0000 http://dansdata.blogsome.com/2008/02/03/my-wife-my-children-and-the-nation-of-romania/#comment-2029 African or European helicopter? African or European helicopter?

]]> by: Daniel Rutter http://dansdata.blogsome.com/2008/02/03/my-wife-my-children-and-the-nation-of-romania/#comment-2025 Tue, 05 Feb 2008 08:57:24 +0000 http://dansdata.blogsome.com/2008/02/03/my-wife-my-children-and-the-nation-of-romania/#comment-2025 Personally, I agree with those who say the phenomenon that <b>really</b> needs to be investigated is whether a helicopter can take off if you put it on an enormous turntable. Personally, I agree with those who say the phenomenon that really needs to be investigated is whether a helicopter can take off if you put it on an enormous turntable.

]]> by: ambler http://dansdata.blogsome.com/2008/02/03/my-wife-my-children-and-the-nation-of-romania/#comment-2021 Mon, 04 Feb 2008 23:29:38 +0000 http://dansdata.blogsome.com/2008/02/03/my-wife-my-children-and-the-nation-of-romania/#comment-2021 If a stationary plane takes off in an airfield and there's no one to see it lift... can it really fall? If a stationary plane takes off in an airfield and there’s no one to see it lift… can it really fall?

]]> by: Popup http://dansdata.blogsome.com/2008/02/03/my-wife-my-children-and-the-nation-of-romania/#comment-2020 Mon, 04 Feb 2008 23:29:13 +0000 http://dansdata.blogsome.com/2008/02/03/my-wife-my-children-and-the-nation-of-romania/#comment-2020 There was a time when in Sweden you could, under some conditions, have a marginal tax of <b>102%</b>, which kinda is what you're asking for. It happened to a famous <a href="http://en.wikipedia.org/wiki/Astrid_Lindgren">author</a> of children's books, e.g. Pippi Longstocking) who was outraged and wrote a highly publicised <a href="http://en.wikipedia.org/wiki/Pomperipossa_in_Monismania" rel="nofollow">story</a> about it. The finance minister tried to get snarky, and in the end it resulted in the fall of the social democratic government for the first time in 40 years. There was a time when in Sweden you could, under some conditions, have a marginal tax of 102%, which kinda is what you’re asking for.

It happened to a famous author of children’s books, e.g. Pippi Longstocking) who was outraged and wrote a highly publicised story about it. The finance minister tried to get snarky, and in the end it resulted in the fall of the social democratic government for the first time in 40 years.

]]>