Murphyd Posted January 29, 2009 Posted January 29, 2009 Your killing me Smalls! That would be "you're". Can I have the pedantic medal now? ;) /duck -- Murphy
ericinexile Posted January 29, 2009 Posted January 29, 2009 (edited) Same way as in the Air, with the pitot tube.. Negative GhostRider, The PVI uses an INS which means that, once the alignment process begins, it accounts for every acceleration experienced by the aircraft. Once airborn, it can calculate windspeed and direction based on known performance data, air-data, and groundspeed. This calculation is simply not possible on the ground. I think the right answer is that the PVI indications are primatively scripted under DCS and not all logic is realistic. Smokin' Hole Edited January 29, 2009 by ericinexile Smokin' Hole My DCS wish list: Su25, Su30, Mi24, AH1, F/A-18C, Afghanistan ...and frankly, the flight sim world should stop at 1995.
GGTharos Posted January 29, 2009 Posted January 29, 2009 Air data in the PVI is stored 'ahead of time' IIRC. I'll have to check the manual to confirm though. [sIGPIC][/sIGPIC] Reminder: SAM = Speed Bump :D I used to play flight sims like you, but then I took a slammer to the knee - Yoda
SaintJ Posted January 29, 2009 Posted January 29, 2009 That would be "you're". Can I have the pedantic medal now? ;) /duck -- Murphy You know, I went to lunch and wondered if I got the "you're" right. I log back in to correct it and what do you know, you did it for me! Go Go Grammar police. Everybody loves ya (you)
congo Posted January 29, 2009 Posted January 29, 2009 You know, I went to lunch and wondered if I got the "you're" right. I log back in to correct it and what do you know, you did it for me! Go Go Grammar police. Everybody loves ya (you) Geez Man the GoGo Grammar Police. Where are they playing. GG you still muck around over at the Steel Beasts site.
congo Posted January 29, 2009 Posted January 29, 2009 Sorry but this is just wrong, you move 100 knots but the air particels are also moving towards you with 25 knots in our example, and 100 + 25 is 125. You can test this when you are standing on the ground, your Airspeed will show 0 ground speed + the wind from ahead. Your airspeed indicator will never show groundspeed. It will just indicate airspeed which is the air flowing around the aircraft.
SaintJ Posted January 29, 2009 Posted January 29, 2009 Sorry but this is just wrong, you move 100 knots but the air particels are also moving towards you with 25 knots in our example, and 100 + 25 is 125. You can test this when you are standing on the ground, your Airspeed will show 0 ground speed + the wind from ahead. This is incorrect.
GGTharos Posted January 29, 2009 Posted January 29, 2009 No, your air speed will show your *air speed*. Not air speed + ground speed. [sIGPIC][/sIGPIC] Reminder: SAM = Speed Bump :D I used to play flight sims like you, but then I took a slammer to the knee - Yoda
Frederf Posted January 29, 2009 Posted January 29, 2009 The airspeed indicator does not function at less than 50 kmph. It is really asking for confusion to say "We have a ground speed of X and there is wind Y so our airspeed is Z." That seems to hint that ground speed and wind combine to cause airspeed when it's the other way around. Ground speed is the result of airspeed and wind. Just imagine this argument: "I am swimming in a river at 3 mph ground speed and the river is flowing against me at 40 mph. I must be swimming at 43 mph through the water!" It's just silly to assume ground speed first.
ericinexile Posted January 29, 2009 Posted January 29, 2009 (edited) Sorry but this is just wrong, you move 100 knots but the air particels are also moving towards you with 25 knots in our example, and 100 + 25 is 125. You can test this when you are standing on the ground, your Airspeed will show 0 ground speed + the wind from ahead. This is incorrect. An airborn object does not "feel" the movement of the airmass that surrounds it. The exception is the localized shear that you feel as turbulence. Right now you are sitting (presumably) in front of a computer but moving thousands of miles an hour through the solar system. You don't feel that movement because you are part of it--riding through space on a blue and green rock. Almost the instant your skids, wheels, or floats, leave the surface of the earth, wind ceases to have anything to do with your airspeed*. Smokin' Hole *But what about windshear you say. Well yes, all objects have mass and therefore inertia and are unable to react instantly to changes in air velocity. The more the mass the more this holds true which is why large airliners suffer from airspeed loss and gain in windshear and smaller aircraft do not. But it is simpler (and usually truer) to just picture yourself as part of the airmass. Edited January 30, 2009 by ericinexile Smokin' Hole My DCS wish list: Su25, Su30, Mi24, AH1, F/A-18C, Afghanistan ...and frankly, the flight sim world should stop at 1995.
congo Posted January 29, 2009 Posted January 29, 2009 (edited) An airborn object does not "feel" the movement of the airmass that surrounds it. The exception are the localized shear that you feel as turbulence. Right now you are sitting (presumably) in front of a computer but moving thousands of miles an hour through the solar system. You don't feel that movement because you are part of it--riding through space on a blue and green rock. Almost the instant your skids, wheels, or floats, leave the surface of the earth, wind ceases to have anything to do with your airspeed*. Smokin' Hole *But what about windshear you say. Well yes, all objects have mass and therefore inertia and are unable to react instantly to changes in air velocity. The more the mass the more this holds true which is why large airliners suffer from airspeed loss and gain in windshear and smaller aircraft do not. But it is simpler (and usually truer) to just picture yourself as part of the airmass. Finally some sanity on the subject of airspeed. It never ceases to amaze me the misconceptions that exist around this subject. Edited January 29, 2009 by congo
krac Posted January 30, 2009 Posted January 30, 2009 (edited) Gee, to my unlearned brain it sounds an awful lot like congo and Pfadfinder were saying the same thing - albeit congo's was probably the correct way of *saying* it. One was saying "if you are travelling at a groundspeed of 100 into a headwind of 25, the air rushing over your craft is going to be read as 125" The other was saying "if the air being read rushing past your aircraft is 125, and you're travelling into a headwind of 25, your groundspedd will be 100." Congo's was the second, and makes more sense since all aircraft have airspeed indicators, and for the interests of energy and stalls etc that's what's important. For traveltime though, you're more interested in groundspeed so... you know. Each to his own? Edited January 30, 2009 by krac
krac Posted January 30, 2009 Posted January 30, 2009 If my previous post is actually correct... what happens if there is a tail wind blowing at 100, and a jet aircraft flys at a ground speed of 100 also... so the ground speed is 100 but airspeed is zero. Does it stall?
luke88 Posted January 30, 2009 Posted January 30, 2009 An aircraft flying at sea level on a standard ISA day at 100 knots indicated airspeed with 0 wind will show a ground speed of 100 knots. An aircraft flying at sea level on a standard ISA day at 100 knots indicated airspeed with a 10 knot headwind will show a ground speed of 90 knots. An aircraft flying at sea level on a standard ISA day at 100 knots indicated airspeed with a 100 knot tailwind will show a ground speed of 200 knots. Just to complicate matters, there also comes into effect the thickness of the air itself. As you increase altitude (or temp for that matter) the air becomes thinner and as a consequence you go faster along the ground for a given airspeed than you would down low. This is why jets go high. A jetliner at 35,000 ft could have an IAS of 250K but be doing 450 along the ground. An airplane's wing doesn't know how fast it is travelling along the ground. It only "feels" the medium its travelling through.
Frederf Posted January 30, 2009 Posted January 30, 2009 There's the fun difference between IAS, CAS, and TAS. Indicated airspeed is what the gauge says, Calibrated airspeed is what the gauge should say with some correction (I forget), and True airspeed is how fast you are moving through the atmosphere. IAS and CAS are usually pretty close together but at higher altitudes CAS and TAS can be wildly different due to the low density of the air up there. I still like the difference between airspeed and groundspeed expressed in the cause and effect order. Airspeed causes groundspeed and not the other way around. It's the difference between "the sun came up because it's sunny" and "it's sunny because the sun came up."
AlphaOneSix Posted January 30, 2009 Posted January 30, 2009 Gee, to my unlearned brain it sounds an awful lot like congo and Pfadfinder were saying the same thing They are. The difference, as it seems to me, is that each is leaving just enough ambiguity in their statements that the other is able to interpret something said as being incorrect. It would be just as simple to interpret each message another way, which results in both of them saying the exact same thing but with different words.
AlphaOneSix Posted January 30, 2009 Posted January 30, 2009 If my previous post is actually correct... what happens if there is a tail wind blowing at 100, and a jet aircraft flys at a ground speed of 100 also... so the ground speed is 100 but airspeed is zero. Does it stall? No, because it already stalled a long time ago! But I see you point, if you have a 100 knot tailwind and show 100 knots of ground speed, your airspeed is 0. So unless you're in a helicopter, your goal should be to never encounter this situation. ;)
congo Posted January 30, 2009 Posted January 30, 2009 (edited) If my previous post is actually correct... what happens if there is a tail wind blowing at 100, and a jet aircraft flys at a ground speed of 100 also... so the ground speed is 100 but airspeed is zero. Does it stall? Aircraft do not fly by groundspeed , they fly by air passing over the wing which is airspeed. The above situation you describe is virtually impossible except for a Helicopter and then you would still have the air passing over the rotor blade because of rotation. In this situation airspeed and rotorspeed are one and the same. The flight of all aircraft (Airplanes,Helicopters,Gyrocopters is dependent upon airspeed, Ballons are dependent upon buoyancy. Airships use a little of both. Edited January 30, 2009 by congo
congo Posted January 30, 2009 Posted January 30, 2009 Sight the ambiguity of my statements. They are. The difference, as it seems to me, is that each is leaving just enough ambiguity in their statements that the other is able to interpret something said as being incorrect. It would be just as simple to interpret each message another way, which results in both of them saying the exact same thing but with different words.
congo Posted January 30, 2009 Posted January 30, 2009 (edited) So there is difference between air and ground speed? How’s that? For ground speed we take in account the vertical speed too? No vertical speed is measured by the VSI ( vertical speed indicator ) or in sailplanes a variometer. Which tells you the speed you are either going up or down. Usually in american aircraft it is read as feet per minute. In sailplanes they are usually combined with an audible warning on the positive side so it will chirp as you go up. This will help you realize when you are in up moving air. And yes there is a difference between air and ground speed on windy days or flying in the jetstream. On a zero wind day thay are pretty much the same. Edited January 30, 2009 by congo
AlphaOneSix Posted January 30, 2009 Posted January 30, 2009 Sight the ambiguity of my statements. You weren't the one being ambiguous. Pfadfinder was, and you interpreted his comments in such a way that made you see him as incorrect. Interpreted another way, he was right.
congo Posted January 30, 2009 Posted January 30, 2009 (edited) You weren't the one being ambiguous. Pfadfinder was, and you interpreted his comments in such a way that made you see him as incorrect. Interpreted another way, he was right. A16, I dont know any other way to interpet this: Airspeed is the speed of an aircraft relative to the air. So there is a difference if the air surrounding me is moving ahead me or from the side or from behind. If im moving with the air my airspeed is in relative to my groundspeed lower than when i moving against the air. Sounds to me like he is saying that if he is moving with the air his airspeed is lower than if he is moving against the air. Maybe something is lost in translation. The only thing Im saying that if your airspeed is 100 knots it makes no difference if there is a headwind or tailwind your airspeed is still 100 knots whether you are flying upwind or downwind or crosswind. I guess the way to state it would have been: If i'm moving with the air my grounspeed is higher and if i'm moving against the air my ground speed is lower. Edited January 30, 2009 by congo
Pfadfinder Posted January 30, 2009 Posted January 30, 2009 Maybe something is lost in translation. I think that was the problem ;) I had really problems to say what i wantet to say in english. But the answer from the opener has been answered so evrything is good :) Lt. Jake Grafton: "Fighter pukes make movies. Bomber pilots make... HISTORY!"
congo Posted January 30, 2009 Posted January 30, 2009 I think that was the problem ;) I had really problems to say what i wantet to say in english. But the answer from the opener has been answered so evrything is good :) No problem, what is your native language.
AlphaOneSix Posted January 30, 2009 Posted January 30, 2009 For example you fly with 100 km/h against the wind direction and the wind blows with 25 km/h, then your ground speed shows 100 km/h and your air speed shows 125 km/h. This seems to be the ambiguous text. To me, I assumed that the the first mention of "100 km/h" is referring to ground speed, which makes the rest of the text make more sense. The ambiguity is that it is unclear if the first speed mentioned was airspeed or ground speed.
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