Originally posted by WeRpeons
reply to post by waynos
So explain this to me without being so denigrating.
I simply pointed out your lack of understanding of this topic and was not denigrating in any way. Pardon me for not writing a fuller explanation in
that post, but I've written it out so often for it simply to be ignored as inconvenient that I now wait to be asked.
I understand how atmospheric conditions can change how contrails expand. I am relating what I have never observed in all my years growing up
and playing outside as a young boy all day from morning until the street lights came on. You can't tell me that the kind of contrail grids people are
seeing today existed back in the 60's and 70's. Sure, I've observed contrails crossing each other in the past, but nowhere near the amount nor the
expansive appearance I've seen today.
This would be correct. As you say, you saw contrails crossing in the past. This was the beginning of what we have today. If you go back to the 1970's,
for instance, quite apart from there being fewer aircraft than there are now, the nature of the worlds air fleets was also very different. I will
assume you know the engine terms I am going to use here, if not you can look them up or ask. High Bypass tubofans, the sort that, under the right
conditions, leave long thick trails behind high flying aircraft, at that time powered ONLY the very largest, widebody jets. These were the Boeing 747,
McDonnell Douglas DC-10, Lockheed TriStar and Airbus A300B.
These aircraft were new then, the 747 was the first of them, entering service in 1970, DC-10 and TriStar followed in 1972 and the A300B in 1974. They
would not be widely seen in service until about 1977-79 Most airlines still operated older types such as the 707 and DC-8 on their long range routes,
these were powered by turbojets or non high-pypass turbofans of an older generation and even though they did create contrails (possibly the ones you
observed) they were less visible than now, and of course far fewer. But that is only part of it.
The far more populous fleets were made up of short range aircraft. These included the early model 737, DC-9, BAC One Eleven and Sud Caravelle, for
example. These were powered by turbojets and flew shorter routes at lower altitudes, then below those there were the regional airliners, Vickers
Viscount, Lockheed Electra, Convair 340 etc down to the smaller 30+ seaters like the DC-3 (still in wide use at the time) HS.748, Fokker F.27 etc
which were all propeller driven and flew even lower, mostly not leaving any sort of trails at all.
Fast forward to the 1990s and ALL these propeller and turbojet driven airliners are gone, there are some modern turboprops such as the Dash 8 and ATR
series still doing well, but basically every single size of airliner from 50 seats up to 850 is served by an aeroplane powered by high bypass turbofan
engines and flies at higher altitude in the more rarefied air, because this is what costs least and generates most profit. The result is masses of
trails all over where there were previously very few. But they WERE there.
The vapor trails today expand at a much quicker rate and their is definitely a concentrated effort and planned spacing between the trails.
This is an assumption, The reason the trails expand so much more is because they contain so much more water, due to the nature of the high bypass
engine which compresses the ambient air without it going through the engine core and burning in order to augment thrust without using more fuel. While
burning fuel itself creates water, the sudden depressurisation of this bypass air aft of the engine simply adds to that (think of the effect when you
pull ring-pull on a can of pop and the mist that is created, but multiplied and sustained. An aeroplane would not be able to replicate this effect by
carrying something it sprayed, there would be too much volume required. Indeed, it could be said that without the invention of HBPR engines the trails
now would be even more vast as so many more engines would be required and they would burn so much more fuel to power the size of aircraft that now
By way of an example, the Saro Princess was powered by TEN Proteus engines and did not sell, only one ever flew. A projected airliner by the same firm
called the P.192 which was slightly larger than the Airbus A380 would have required 24 RR Conways (4 of the same engine powered the 707) todays A380
manages with 4 R-R Trents, this is the scale on which engines have developed. Here is a thread I made some time ago about that Saro project.
Please, don't try telling me it's because there are more planes flying today. Were not talking a limited amount of space for flights like a 4
lane highway. Atmospheric conditions haven't changed that would make contrails appear any different today as they did in the past.
As I said, more planes is only part of the explanation. See also engine and altitude changesfor all classes as described. The atmospheric conditions
dont need to have changed, this is a common claim and supports what I was saying about not fully understanding.
Oh, and regarding your mention of airports, which is what prompted me in the first place. Because of the conditions required for contrails, unless it
is particularly and unusually freezing cold where you are, no trail you spot over your head will have anything to do with aircraft landing and taking
off at any airport near you.
edit on 5-1-2013 by waynos because: add link