Difference between revisions of "3161: Airspeed"
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(Undo revision 389950 by Mathmaster (talk) I cannot comprehend what further details there could be about travelling mineshaft by balloon. Big balloon. Narrow mineshaft. Which is mentioned.) |
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==Explanation== | ==Explanation== | ||
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In the comic, [[Megan]] and [[Cueball]] are trying to break the record for {{w|airspeed}} in a {{w|hot air balloon}}. Cueball's exclamation "yessss!" suggests that they achieved it when there was a slight variation in conditions that allowed them to briefly reach 2 miles per hour (roughly 3.2 km/h, or 0.9 m/s), which would not seem particularly impressive to most people as it is even slower than typical human {{w|Preferred walking speed|walking speed}}. | In the comic, [[Megan]] and [[Cueball]] are trying to break the record for {{w|airspeed}} in a {{w|hot air balloon}}. Cueball's exclamation "yessss!" suggests that they achieved it when there was a slight variation in conditions that allowed them to briefly reach 2 miles per hour (roughly 3.2 km/h, or 0.9 m/s), which would not seem particularly impressive to most people as it is even slower than typical human {{w|Preferred walking speed|walking speed}}. | ||
Revision as of 00:52, 1 November 2025
| Airspeed |
 Title text: Carefully maneuvering the balloon down a mineshaft in an effort to break the OTHER altitude record |
Explanation
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This is one of 52 incomplete explanations: This page was created by a HOT AIR ROBOT. Don't remove this notice too soon. If you can fix this issue, edit the page! |
In the comic, Megan and Cueball are trying to break the record for airspeed in a hot air balloon. Cueball's exclamation "yessss!" suggests that they achieved it when there was a slight variation in conditions that allowed them to briefly reach 2 miles per hour (roughly 3.2 km/h, or 0.9 m/s), which would not seem particularly impressive to most people as it is even slower than typical human walking speed.
Airspeed is the velocity of an aircraft relative to the air it's flying through. This differs from ground speed, which is the velocity relative to the ground below, because it is adjusted for the speed of wind around the aircraft. Most powered-flight airspeed records (from human-powered aircraft to rocket-planes) are made with reference to the attained passage through the air, both because it is traditionally easier to establish from within the craft itself, and in order to disregard either assisting or opposing winds at the flying altitude. Ground speed is usually what passengers care about, since it relates to how soon you'll reach your destination.
Unlike airplanes, helicopters, autogyros and dirigibles, though, untethered hot air balloons are pushed by the wind itself[circulation needed] and don't have any other form of horizontal propulsion (changes in the heated air in the balloon allows vertical propulsion due to positive or negative buoyancy, but this is specifically disregarded by the wording used in the comic). This means that their airspeed is normally very close to zero. It may differ occasionally if the wind changes suddenly, in velocity or direction, as it will take a few seconds for the balloon to overcome its inertia. If the wind drops the balloon may coast a bit at the higher speed, but a large balloon will have plenty of drag, so it will not take long to match the new wind speed.
An additional possibility is that it is straddling a significant wind-shear layer that affects the upper parts of the balloon differently from the lower parts, but this does not appear to be the case here, especially as the "level flight" stipulation would seem to disqualify the particularly vertically-turbulent conditions (updrafts and downdrafts) that would accompany this. Away from ground level and the effects of undulating terrain or ground-based structures (and assuming no large powered aircraft have themselves passed nearby, locally disturbing the air), the laminar nature of the air means the airflow tends to more gently transition at the height of a balloon.
Airspeed is useful to aircraft designers and pilots, since it reflects how much power is needed, and the aerodynamic behaviour of the lift and control-surfaces. When you're flying in the same direction as air movement (a "tailwind"), you get more ground speed from the same airspeed, because the wind is boosting your speed; conversely, when you have a headwind, you'll either have lower ground speed with the same engine power, or you'll need more power to get the same ground speed. Prevailing winds in the middle latitudes tend to flow eastwards, which explains why west-to-east flights are often quicker than the corresponding east-to-west flights for such air-commerce as the trans-Atlantic routes between the US and Europe.
A more common record that people try to achieve with balloons is altitude; at this time the current record is 69,850 feet (21,290 m), set in 2005. The title text suggests achieving a negative altitude record by allowing the balloon to descend down a mineshaft. This could just be in relation to the height of the land in the immediate vicinity of the mineshaft, but could also be with respect to mean sea level, similarly avoiding direct comparison against the ground. With the typical width of a properly inflated balloon being greater than a typical mineshaft, it could be a logistical challenge to make a controlled descent (unless an open pit mine were to be considered a mineshaft — the Bingham Canyon Mine reaches a depth of 1210 m).
Hot air balloons have been referenced previously in the comics 3153: Hot Water Balloon and 2940: Modes of Transportation.
Transcript
- [A hot air balloon is shown with its six vertical panels alternating in black and white. Megan and Cueball are riding in the basket, with Cueball looking over the side and down while Megan looks at something inside the basket, also looking down.]
- Megan: 0 MPH... 0 MPH... Ooh, 1 MPH with that last gust... 0 MPH... 1 MPH... 1 MPH... 2 MPH!!!
- Cueball: YESSSS!
- [Caption below the panel:]
- Breaking the hot air balloon level-flight airspeed record
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must be a heated competition 79.78.17.137 21:34, 29 October 2025 (UTC)
- badum-tss! Barmar (talk) 22:17, 29 October 2025 (UTC)
- The record has been given an inflated importance. 82.13.184.33 10:58, 30 October 2025 (UTC)
It's actually worth noting that a quick google says that land speed records for hot air balloons are actually fairly fast, wikipedia claiming it clocks in at around 245 mph. Jet streams allow them to go pretty fast! 45.78.106.197 23:42, 29 October 2025 (UTC)
Airspeed is relative to the vehicle, and a balloon has no "front", so a gust in one direction is in theory indistinguishable from a lull in the opposite direction; both will appear as a momentary increase in airspeed until the balloon accelerates (in whichever direction) to match the local air movement. (I say "in theory" because if you consider your gusts and lulls relative to the overall movement of the airmass, it's plausible that one or the other will tend to be sharper.) The "gust that allowed them to coast", and the whole notion of "coasting", isn't really right. A non-zero airspeed means that the balloon hasn't re-stabilized with the local air movement, in whichever direction. In fact, "coasting", defined here as momentarily moving differently from the airmass as a whole, is actually an unlikely source of the 2MPH airspeed, because it requires that the balloon accelerate to match local air movement, before returning to the movement of the airmass as a whole. More likely is a localized change (a gust or lull), that causes the local air to be moving differently from the airmass as a whole, while the balloon is still moving with the airmass. Such a localized change might be present for a very small amount of time, not long enough to appreciably change the balloon's movement. But I'm not feeling like spending enough effort to distill that down into one sentence to update the explanation. Jordan Brown (talk) 23:59, 29 October 2025 (UTC)
You don't need a mine shaft to go for the minimum-altitude record, if you're measuring against MSL. Just make sure that your lines and your balloon are really strong, and your basket is really heavy, and your basket is water-tight, and go for Challenger Deep. Jordan Brown (talk) 00:21, 30 October 2025 (UTC)
3161 demonstrates a commonly held fallacy - the balloon has NO actual "airspeed" because it moves passively with the surrounding air mass; it has no method for generating lateral force on its own, to either vector add/subtract airspeed from the moving wind surrounding it. The balloon is never actually being "blown". This isn't just semantics - it has real relevance to powered aircraft flight. 2603:7000:9c07:5749:cfe:67ca:4e99:71f8 (talk) 01:38, 30 October 2025 (please sign your comments with ~~~~)/Aviator Joe, CFII
- Sure it does, transiently. It just can't cause itself to have a non-zero airspeed. An abrupt change in the movement of the local air - a gust, horizontal wind shear - would register as a non-zero airspeed, until either the local air goes back to matching the overall airmass (and the balloon), or the balloon accelerates (via drag) to match that moving air. Consider: you're cruising along in your airplane at an indicated airspeed of 100kt, and you get a 10kt gust from the front. Your airspeed indicator momentarily jumps to 110kt until the airplane restabilizes at an IAS of 100kt again, and then when the gust goes away the reverse happens; your IAS drops to 90kt for a while, then returns to 100kt. The exact same thing can happen in a balloon, except that the base IAS is zero - the balloon that you were passing as the gust hit you sees an IAS of 10kt as the gust hits it, then zero as it restabilizes, then 10kt in the opposite direction as the gust fades, then zero again. Jordan Brown (talk) 02:42, 30 October 2025 (UTC)
- Ah, but that is IAS. IAS increase in the situation you describe is an artifact of the measurement - transient increase in ram pressure on the Pitot tube. The actual airspeed of the balloon is zero (or close, if you neglect inertia/drag). I refer you to Chapter 5 of of "Stick and Rudder" 2603:7000:9c07:5749:cfe:67ca:4e99:71f8 (talk) 13:37, 30 October 2025 (please sign your comments with ~~~~)
- "...or close". And that's what the comic is saying. Agree/disagree?
- (Indented and 'unsigned' you, BTW. You don't need to do anything more to the above, but try to add the proper signing, and any useful indentation, in future edits...) 82.132.244.58 15:23, 30 October 2025 (UTC)
- "...if you neglect inertia/drag" Why would you neglect inertia and drag? Real balloons don't magically not have inertia and drag. If you get a sudden gust of wind, the inertia of the balloon will cause its speed to slightly lag the speed of the wind for a few moments. This is precisely what the comic is about Jeremyp (talk) 13:53, 1 November 2025 (UTC)
- IAS is what the airplane flies on; it's not a mere measurement error. Ram pressure on the pitot tube is almost always tied to ram pressure on the wings. If you think it's just measurement error, you need to explain that to your airplane when a nearby microburst gives you a huge tailwind, your IAS drops dramatically, and your airplane stalls. Jordan Brown (talk) 03:48, 8 November 2025 (UTC)
- Ah, but that is IAS. IAS increase in the situation you describe is an artifact of the measurement - transient increase in ram pressure on the Pitot tube. The actual airspeed of the balloon is zero (or close, if you neglect inertia/drag). I refer you to Chapter 5 of of "Stick and Rudder" 2603:7000:9c07:5749:cfe:67ca:4e99:71f8 (talk) 13:37, 30 October 2025 (please sign your comments with ~~~~)
Actually, there can be significant wind shear near the earth. If the basket is only a few feet above the ground, you can feel substantial “wind” because the ballioon, being higher up, is being pushed by a faster wind and dragging the basket through the lower, slower, air. If you mount your airspeed indicator on the basket, you can have a significant ‘speed’ relative to the air through which you’re being dragged. When I experienced this the first times, I said, “what the?” The pilot politely explained…… 73.162.95.226 (talk) 03:18, 30 October 2025 (UTC) (please sign your comments with ~~~~)
Couldn't one just break this air speed record by tying the balloon to the ground? --2001:638:807:507:4EB7:9F4B:6CF9:57A1 07:50, 30 October 2025 (UTC)
- Split the record into positive and negative value records? 2A02:2455:1960:4000:E0C5:65BB:8741:E289 07:56, 30 October 2025 (UTC)
- A balloon doesn't really have a front/back, so there's not really a positive or negative airspeed. 163.116.254.55 14:06, 30 October 2025 (UTC)
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