Wikipedia:Reference desk/Archives/Science/2024 April 2

= April 2 =

Why does the green channel die first and blue last?
A bar I frequent has a number of flat-panel TVs (I'm not sure whether they're LCD or OLED) that can only display the blue channel. A few weeks ago I saw some that also had a working red channel, but no green. I would've assumed the cause was damaged or loose cables, but tonight I was told the owner -- who's described by the staff I've spoken to as a penny-pincher -- is replacing the screens themselves. Why is it that these dying screens never have a working red or green channel without a working blue, or green without the red? Neon Merlin  06:14, 2 April 2024 (UTC)


 * There are too many variables here to consider, including not even knowing if they are LCD (which tend to have a back-lighting and get color through layered color filters) and OLED (which can use white OLED and color filters, or colored OLEDs directly and no color filter). The issue could also be loose or bad cables. In my personal experience, "penny-pinchers" are more interested in what they perceive as the quick and cheap fix rather than actually finding the root cause of a problem. Paradoxically, this can result in taking things become more expensive than necessary as 1) they might have to try multiple solutions to fix a problem when it could have been a single solution if they'd taken the time to look for a cause 2) they find a quick solution that "works" (e.g. new TVs), and so don't bother to see if something actually cheaper might have worked better 3) there solution is just waiting for the next breakdown and will have to be repeated again and again (e.g. buying a cheap TV model with a fast dying color filter that needs replacing ever year instead of a TV costing 1.5 times as much, but lasts 5 years).
 * Additionally, we would need more information on specific TV models. Are all of the screens at the bar the same make and model, or at least general model (i.e. 55 inch and 65 inch versions of the same TV)? In that case, it could be as simple as that model TV had a defective color filter all on the same color channel, or a defective signal line for that color channel. Or, it could be something else entirely. --OuroborosCobra (talk) 17:45, 5 April 2024 (UTC)

Why are there no vertical VTOL jetfighters as far as I know?
Wouldn't it be better to just make a Harrier that can or must take off and land on its tail? It could still thrust vector and fly horizontally just not hover horizontally. How often is hovering horizontally more than just cool but not militarily needed? Over 1 thrust-to-weight ratio is really gas guzzling, and extra nozzles that are only used for extra redirection exhausts seems like unnecessarily weight. Sagittarian Milky Way (talk) 21:50, 2 April 2024 (UTC)
 * All VTOLs are vertical; you presumably mean "tail-sitter" aircraft. There have been several, mostly prototypes. The Ryan X-13 Vertijet might be of interest.--136.54.106.120 (talk) 23:59, 2 April 2024 (UTC)
 * More vertical than the Harriers that go straight up in horizontal orientation. Sagittarian Milky Way (talk) 01:35, 3 April 2024 (UTC)
 * So it seems they tried but too many problems. Sagittarian Milky Way (talk) 01:53, 3 April 2024 (UTC)
 * One technical issue it seems with early designs of tiltrotor aircraft was that with more upright designs, like with having the entire wing body tilt up (with the engine bodies fixed to the wing), a big problem is any wind on the runway or during takeoff could cause damage or even knock the thing over. If part of the appeal of VTOL and STOVL aircraft is being able to work from non-optimal infrastructure, then a launching platform for a tail-sitter jet would need both to manage air intake as well as shield the structure from the wind. I don't know whether that's significantly more involved compared to maintaining a small airfield, or a flight deck on an aircraft carrier, say. SamuelRiv (talk) 04:40, 3 April 2024 (UTC)


 * In order to be vertical takeoff in any orientation, you need a thrust ratio to weight of over 1:1. That's just the physics of it; if you want to go straight up against gravity, you need to have more thrust pushing up on you than the weight from gravity pulling down. Doesn't matter if you are a Harrier or a Vertijet. Because of this, VTOL capable aircraft that have actually entered service (Harrier, Yak-38, and F-35) have always chosen a configuration that allows for STOVL (short take-off and vertical landing) instead. If your wings are providing at least some of the vertical force, then you do not need to have a 1:1 thrust ratio at takeoff configuration. For the Harrier, that means thrust vectoring where you have them partially angled downwards (but not completely), giving you forward thrust to get airspeed over the wings and vertical thrust to push you up before your wings have a enough lift to do so on their own.
 * By doing this, you can carry more fuel and more ordinance into the air than you could in VTOL. You don't need 1:1 thrust ratio on takeoff, so you can carry more weight that makes you heavier than 1:1, while still letting you takeoff from short carrier decks without catapults or hastily/quickly made short field strips. As a bonus, when you've completed your mission, you have a lot less fuel and ordinance on your aircraft, so now you do have a greater than 1:1 thrust to weight ratio. That means you can land on that short carrier or improvised landing strip without needing arresting cables/hook or a brakechute. You can just land vertically with your reduced weight. Every "VTOL" jet fighter that has ever gone into service has actually done almost all operations as STOVL, and not VTOL, for this very reason.
 * A tail-sitting VTOL aircraft doesn't have this STOVL option. They always have to takeoff vertically (or can only do horizontal with added external equipment and a long takeoff distance that defeats the entire point of having built this VTOL thing for rough conditions in the first place). A tail-sitting aircraft ALWAYS needs a greater than 1:1 thrust to weight ratio (where Harrier and F-35 do not), and therefore cannot carry as much fuel and ordinance.
 * Lastly, visibility for a pilot landing a tail sitter is terrible. It's very difficult to get things lined up for proper landings, make sure you are completely vertical in force balance (including things like sidewinds) and that your ground speed is actually zero. Think driving in reverse, without a good rear-view mirror, while moving at highway speeds or above, and being subject to crosswinds that you get to ignore in your car, and managing to back into your garage perfectly. Oh yeah, and while you are stopped, instead of nothing happening when you turn the steering wheel, you wildly move away from the garage and probably hit a tree. This has probably become less of a problem today with more advanced computer controls, but for most of the existence of jet fighters, that wasn't an advanced enough tool. Combine that with the limitations of not having STOVL capability, and there's no real good reason for a tail-sitter jet fighter. --OuroborosCobra (talk) 16:30, 3 April 2024 (UTC)
 * Of course it has to be >1:1 which is why I was wondering why they didn't skip the belly plumbing probably saving weight. I didn't realize the large area sum of the 4 levitators makes the Harrier levitate more efficient (makes sense though, helicopters levitate with large air fan(s), and they keep trying to raise airliner fan bypass ratio to save fuel).
 * So there's so many problems, one wonders why they test flew some instead of foreseeing a waste of money. I didn't know the F-35 was designed to VTOL. I knew it had enough thrust but not that it was a designed (probably rarely used) option. Sagittarian Milky Way (talk) 21:44, 3 April 2024 (UTC)
 * The Lockheed Martin F-35 Lightning II is a short take-off and vertical landing or STOVL aircraft. The Queen Elizabeth-class aircraft carriers were specifically designed for their vertical landing ability. Alansplodge (talk) 11:21, 4 April 2024 (UTC)
 * Only the F-35B variant. The F-35A is for ordinary runways, the F-35C for CATOBAR operations. PiusImpavidus (talk) 12:41, 4 April 2024 (UTC)
 * There could be a lot of reasons why pure VTOL "tail-sitter" designs like the Vertijet were test flown. Firstly is simply "did anyone have the idea yet?" VTOL in a horizontal configuration with vectored thrust (or even with dedicated lift engines separate from flight engines) and then transitioning from vertical to normal flight just might not have been much of an idea yet. I think it's pretty telling that we had several designs for pure VTOL before the Harrier and its Kestrel prototype (Bachem Ba 349 Natter, Convair XFY Pogo, Lockheed XFV, Ryan X-13 Vertijet, SNECMA Coléoptère), and basically none after the Harrier/Kestrel (outside of some UAV designs). Once VTOL with STOVL capability was possible, no one bothered with the disadvantages of just pure VTOL.
 * Second is material. In order to do things like the vectored thrust on the Harrier's Pegasus engine, you need some pretty good metallurgy and mechanics since you now are going to have the hot portion of the exhaust coming out of something that has to move around. The no longer "fixed" nozzles need to handle that, as does any part of the aircraft or fuselage that comes into contact with the hot exhaust. I have a feeling that these technical issues might be why the Soviet Yak-38 contemporary to the Harrier opted for dedicated lift engines rather than vectored thrust (with the disadvantage that outside of takeoff and landing, the dedicated lift engines are dead weight).
 * Third is flexibility. I've already gone over the advantages of having STOVL ability in your VTOL capable aircraft. Now, for some applications, those advantages might not matter as much (except for the extremely difficult landing). A dedicated point-defense interceptor aircraft would be a great application for dedicated VTOL, and that's where we saw designs like the SNECMA Coléoptère and the Bachem Ba 349. The thing is... that type of design basically can only do that one thing. It can be a point-defense interceptor. It can go up really fast, have some dedicated air-to-air weapons, and (hopefully) return to the ground with a living pilot. It can't do much else. It can't be easily adapted for interdiction or fighter-bomber roles or anything else. If you look at the history of Cold War and post-Cold War aircraft, you will see a lot of designs (often on paper only) for highly dedicated single mission aircraft, often interceptors... and you won't see a lot of them enter service. There are outliers, like the F-106, but for the most part, the military isn't spending its money on dedicated unitaskers. The F-104, for all of its problems, ended up often in roles where it was used for ground attack and not point-defense. The F-4, developed as a pure air-superiority fighter, ended up being a fighter-bomber with a greater bombload than a World War II B-17 heavy bomber. The F-16 was designed to be so pure an air-superiority fighter that much of the driving force behind it was "not a pound for air to ground," and has become one of the best strike, ground attack, and suppression of air defense aircraft of all time. Even the F-14 could carry bombs, and even the F-102 saw use with its IRST looking for campfires in Vietnam and attacking with rockets.
 * Pure VTOL aircraft, especially tailsitters, just can't be flexible like that. They are probably going to be good for only one thing, and that's not something the military usually wants to spend money on. The only aircraft exception to that is, well, helicopters. But their entirely different design allows them that flexibility, even as dedicated VTOL, that fixed wing VTOL does not. --OuroborosCobra (talk) 16:44, 4 April 2024 (UTC)