Density altitude is the biggest factor in aircraft take off on a given runway length, temperature, and altitude. I know this from firsthand experience as I used to be a private pilot – until my hearing got so bad that I decided I was a danger to myself and others. This study published in the Bulletin of the American Meteorological Society claims the number of days with a density altitude issue at some airports will increase per RCP model scenarios in 2050-2070. Of course they are assuming that the RCP models produce an accurate output, and that airplanes of the 2050-2070 era have the same airfoil efficiency and takeoff power of today.
Climate change and the impact of extreme temperatures on aviation
Department of Earth and Environmental Sciences, Columbia University, New York, NY 10027, USA.
Abstract
Temperature and airport elevation significantly influence the maximum allowable takeoff weight of an aircraft by changing the surface air density and thus the lift produced at a given speed (Anderson 1999). For a given runway length, airport elevation, and aircraft type there is a temperature threshold above which the airplane cannot take off at its maximum weight and thus must be weight restricted. The number of summer days necessitating weight restriction has increased since 1980 along with the observed increase in surface temperature. Climate change is projected to increase mean temperatures at all airports and significantly increase the frequency and severity of extreme heat events at some (Scherer and Diffenbaugh 2013; Donat et al. 2013; IPCC 2012). These changes will negatively affect aircraft performance, leading to increased weight restrictions especially at airports with short runways and little room to expand. For a Boeing 737-800 aircraft, we find that the number of weight restriction days between May and September will increase by 50-200% at four major airports in the United States by 2050-2070 under the RCP8.5 emissions scenario (Moss et al. 2010). These performance reductions may have a negative economic effect on the airline industry. Increased weight restrictions have previously been identified as potential impacts of climate change (National Research Council 2008; US Global Change Research Program 2009), but this study is the first to quantify the effect of higher temperatures on commercial aviation. Planning for changes in extreme heat events will help the aviation industry to reduce its vulnerability to this aspect of climate change.
so why not fly at night when it is cooler?
As far as that goes, aren’t we all going to be living in northern Canada and Siberia by then? You know, climate refugees?
Once there’s no more ice covering Antarctica, we could build a big humming airport there.
Glancing at the periodic table, won’t all that extra CO2 INCREASE the air density? /SARC
There are 5 major airports at heights above 4000 m.
http://en.wikipedia.org/wiki/List_of_highest_commercial_airports
At this altitude, air pressure and hence lift, is less than 60% of that at sea level.
“Global warming” has produced a warming of 0.8 degrees in the past 111 years since the first powered flight. This would result in a reduction in lift of 0.3%. This is ridiculously trivial compared to the 40% reduction in lift at some airports.
To bolster sagging support for the Democrats, Pres BO will shortly announce a program to land a Presidential hopefull on the sun and return her, “by the end of this decade”. When questioned about technical details likely to plague the mission, sources close to the Pres replied “we will send her at night.”
Oh, my these people are creative at finding more things to be alarmist about.
They narrowly focus on one subject, evading benefits of warming (including fewer icy runways?).
What was the payload of airline flights out of DEN and MEX in 1936?
There are models for everything. Unfortunatly there aren’t good it-educated systemprogrammers among the AWG belivers….
Where have all the money gone?
How do they takeoff at Las Vegas on a hot day even now when the temps are 100+F? Are we to assume the temperature will be in the 90’s and 100’s everywhere and every day in the future and all from a 0.1C rise in the global mean?
Some Boeing 737-800 data for you. Ok, so let’s choose some different runway lengths.
2,400m, which is quite short for a 737-800.
Max t/o weight: … 30º = 76.6t … 38º = 73.0t.
Or about 450 kg per degree centigrade.
2,800, with is nice for a 737-800.
Max t/o weight: … 30º = 82.5t … 38º = 78.5t.
Or about 500 kg per degree centigrade.
Max t/o weight of the 737-800 is 79t. So if the temperature increases by 2 degrees, you will lose a tonne of weight – but only if the runway is very short. If the flight is less than 6 hours, you would never take off with max weight anyway. 75t is more than enough, for a 4 hour flight.
So how many airports will this temperature increase effect? How many US airports have runways less than 2,800m long? Not many, I imagine.
.
But what this report fails to mention, is that two degrees of temperature increase could easily be overcome, if Boeing got off its fat rear-end and designed a new aircraft. The original 737, had four engines…..
They called it the 707:
http://www.air-and-space.com/20060302%20LAX/DSC_3524%20707-330B%20N88ZL%20front%20l.jpg
Which then became the 727:
http://cdn-www.airliners.net/aviation-photos/middle/4/1/1/1811114.jpg
And then became the 737:
http://skybotechnik.com/wp-content/uploads/2011/10/Boeing-737-800-e1319143021830.jpg
And is about to become the 737 Max:
http://cargofacts.com/wp-content/uploads/2011/08/622-Boeing737B.jpg
Yes, Boeing is going to be making an aircraft that is going to be in service for 100 years. Bravo for Boeing, that is 35 years longer than the interval between the first flight of the Wright Flyer and Concorde.
And the trouble is that this is the 707 cockpit:
http://www.geocities.ws/CapeCanaveral/Hall/6690/2-BEIRUT1N720JRB720cockpit-062.jpg
And this is the latest 737-800:
http://www.creativesimulations.com/737%20Cockpit.jpg
Hmmm, not a lot of change then. Ok, so there is a new wing and new engines, but this is still a 1958 design, still in production.
Just imagine if you went to the Chevy dealership to buy a car, and they had this in the showroom (1958 Impala):
http://4.bp.blogspot.com/_QlMkZ-ZvBAY/TJCK5gXjRTI/AAAAAAAAAdc/PWx7F-oBaoc/s1600/58impala.jpg
Or to the Ford dealership and they showed you this. (1958 Ford Custom 300):
Clearly, there is a great deal of room for improvement, in the small aircraft market. Improvements that will overcome a two degree temperature increase in a trice. And you can bet that if Boeing does not do this, and make an all-new design, then China will.
Ralph
Your aircraft pictures are missing the central processor.
That one between the pilots ears 🙂
China only counterfeits and reverse engineers stuff.
Hmm…. yes please to the cars. But the reality is that whilst the body shapes and interiors have changed, the engines have not necessarily kept up. Most engine blocks and heads are re-used examples from the fifties and sixties. They perform better due to engine management systems (due injection and so on).
Sorry, but that is completely wrong. In a few isolated examples, companies may be using old engine designs (Bentley perhaps?). The vast majority of new design car engines have precious little to do with their predecessors, easily eclipsing them in power, weight, size and efficiency. Even the ‘old’ Chev Smallblock has only the basic measurements the same – everything else is in different materials, to a different design, with drastically different results.
Actually, Bentley is now owned by Volkwagen, and uses a state-of-the-art VW engines. The normal engine of choice is the remarkable W12, which was made by fusing two V6 engines together.
http://www.indiancarsbikes.in/wp-content/uploads/2012/02/A-cutaway-of-the-W12-Petrol-Engine-on-an-Audi-A8-Copy.jpg
You have to understand that alarmists are not aware that species can adapt, especially humans, engineers, farmers, even over centuries.
I don’t know why you are all being so dismissive. When that fluffy white Global Warming piles up a metre deep on the runway, the planes simply can’t take off. And, as a result of Man Made Climate Change, that sort of thing is happening more and more frequently in the Northern Hemisphere.
But if they are worried about the warm type of Global Warming, perhaps they could find out how the airlines and the Flying Doctor manage in Central Australia.
What’s new?! My son regularly flies large aircraft out of Dubai all summer. That is HOT. He flies into all sorts of places with very different weather/climates. Good grief! The piece is full of the usual could/might scare stuff.
Heck, don’t give them too much grief about this… maybe some poor Grad Student managed to get his MS out of this!
I think that the authors of the paper are forgetting that aeroplanes and airports airports are not slaves of their genes and chromosomes as we and the whole natural living world are.
Therefore, if it does become a nuisance taking off and keeping to schedules etc. (assuming that significant warming is the cause,) – well – how long would it take aero industry to fit bigger flaps – more powerful engines – bigger wings etc to solve the problem?
It won’t be millions of years I assure you.
Once again the taxpayer has footed the bill for this nonsense.
Cheers
Roger
http://www.rogerfromnewzealand.wordpress.com
No worry. The IPCC referenced climate change models are primitive and erroneous. They fail to characterize water vapor (the largest greenhouse gas), clouds, solar effects, and aerosols, among others. For example the average of 44 recent models showed 2012 warming more than three times the values actually recorded by satellites that measure global temperature with an accuracy of plus-or-minus 0.01%. Additionally, the models did not predict the lack of warming in the last 18 years.
I love it. A reference citation in the first sentence of the abstract. One premise, with one reference, upon which the whole house of cards is stacked. Usually a no-no to cite in the abstract, in my memory.
It’s a good thing modern planes will be obsolete by 2050, replaced by aircraft with more efficient lifting surfaces, reduced drag, lighter weight, and more powerful, more efficient engines.
So planes will fly less and less carbon will be emitted into the air. Once again another negative feedback that has been ignored in the drive to make global warming as bad as possible.
The only reason that this becomes a crisis is because all of the government and ngo fat cats couldn’t then fly to some exotic location and sit in air-conditioning whilst whining about what other people are not doing about global warming.
I remain an optimist – I truly believe that one day the world’s leaders will wake up and realise that having these meeting where they crap-on about climate change, changes absolutely nothing (please excuse the Australianism).
In the meantime I suggest that only those people who can get there by bicycle, donkey, canoe or on foot should be allowed to attend and when they get there they should be allowed only to eat the equivalent of an average meal and sleep in crowded rooms, just like the vast majority of people in the world do. Until then they are just a bunch of utter hypocrites who have no right to say anything.
So I’m just not going to fly in and out of Denver in July. What’s the big problem?
Denver Airport (DEN) is a great example. That 0.7 degree C increase in global temperature (which has since abated) just about put them out of business. You may have noticed your airline tickets to The Mile High City included the disclaimer, “Invalid if Denver has a particularly hot day”. Whatta’ load! Thinner air means longer runways and that’s all it means. A plane that can fly at 40,000 feet can most certainly take off from any runway in the world regardless of ground temperature, if the runway is of sufficient length.
Move the thermometers away from the tarmac and jet engines.
That should lower the temp by 5degrees.
Then takeoff normally.
This is complete drivel. By 2050 we’ll have fission energy and anti-gravity. Then, we don’t need no stinkin airplane.
I wonder what is new or news in this. The aircraft flows through different temperature and wind regimes with space and time. Also aircraft differ in terms of temperature vs load. Accordingly the load to takeoff. At given place the temperature and wind regimes vary with seasons and cloud condition, etc.
Dr. S. Jeevananda Reddy
Couple of writers above have mentioned development and invention and new technology.
Lettuce “model” that progress between “now” and “the CAGW crisis” point 40 years from now in 2054 – only 40 years in the future!
So. Build me an airport in 1908.
(Hint: Only a very few planes in the world could carry passengers (first passenger went up with the Wright brothers) and that only for a few minutes of flight.) Steering was hard to do.
You would need:
A pasture. (And a fence to keep the cows out when you wanted to land.)
A tent for the mechanics. Their toolbox.
A can of gasoline.
Now. Build me an airport 40 years later. 1948. In Maine.
You would start with two 10,000 foot runways.
300 feet wide, of reinforced concrete 3 feet thick in the landing area.
Built of concrete for B-36 bombers, taking off with almost 800,000 pounds of aircraft and fuel for flights of over 24 hours duration.
You need hundreds of thousands of sq feet of concrete-paved taxiways, access ways, maintenance areas and parking pads.
10,000,000 gallons of fuel in a separate and secure tank farm.
500 more acres more for the weapons facility and its facilities.
Room and buildings and services for 4,500 military crew, maintenance and support personnel – plus all of their dependents and their services.
Hangers and tool cribs and machinist and services and part warehouses.
Yeah. No progress in aviation is possible in 40 years.
But, you see, the CAGW religion WILL require we kill millions worldwide very year using THIS PAPER as one of their excuses to cut carbon emissions to “prevent catastrophic global warming!”
When what is needed is a weight and power calculation ALREADY BEING DONE NOW for the few airplanes taking off in four airports worldwide for a few weeks each summer.
Maybe.
“… and that airplanes of the 2050-2070 era have the same airfoil efficiency and takeoff power of today. …”
One wonders how airlines cope operating from Saudi and Gulf State city runways in Summer then? Look at a heat map of that region in mid summer and it’s noticeably hotter than most other places on Earth, on any average summers day, and yet they still seem to manage to operate fully loaded A380s, 24/7, no problems at all.
If density-altitude is a limiting factor for a flight the classic answer is to use a longer takeoff roll to rotate at a higher speed (i.e. you could just extend the runway a few hundred meters – solved), or else remove some payload weight (less passengers, less cargo or less fuel) then fly within the certification ISA>+20 limits in the AFM.
Some aircraft are actually limited by temperature, already, due to the black rubber anti-iceing boots on the leading edges of wings and empennage. Yes, the anti-ice boots are used just as much on hot days as well if there’s visible moisture on the climb-out. The air above is still very cold and ice will readily form in moist air (and hot air is on average always much wetter than cold air). The black rubber boots get so hot that if bleed air inflates them on the climb-out the rubber boots can be permanently deformed or else split, and require (expensive) immediate replacement. Which is why the boots are not used on new jets but many new turboprops still use them.
I seriously doubt density-altitude due to high temperature at sea level will ever be a flight limitation though, it has to be combined with actual altitude, such as ISA+30 conditions at a 6,000 foot elevation airport with a 3,000 foot runway. But even then the usual solution is to extend the runway and lift off at a higher speed. There is no insurmountable issue here, even if you were using 1950s wings and propulsion technology.
Examine graphs in any POH/AFM for a turbine aircraft and you can plainly see that density-altitude calculation is only a consideration for determining the appropriate takeoff distance and certified allowable weight.
There are downloadable phone or ipad apps for that calculation for most aircraft these days, it’s hardly a big deal. And it’s not a factor which determines a ‘go or no-go’ decision. It’s just something more that’s taken into account is all.
Verdict: density-altitude-induced-aviation-doom is yet another hyperbolic scare-campaign from climate-doomer dumb-dumbs.
These climate-doom schmartasses really should wait until they grow out of their nappy-wearing stage before they presume to enlighten people who’re several decades older and vastly more experienced with weather and climate, and how the world and technology really works. The young are supposed to learn from their older, not due to some sense of pontificating seniority, but simply because the older do actually know things which know-it-all students and 20-something post-docs still doesn’t know anything about – yet. And despite this clear indisputable total absence of real world life, work and community and political experience, the young fool then resolves to try to ‘educate’ these ignorant old fools, and tell them all about their pending doom. It’s the perpetual common-place error that happens every generation as students discover a few new and novel pet ‘issues’, and proceeds to self-appoint themselves as expert authorities and avidly adopts the Henny-Penny “the-sky-is-falling” tragi-comedy archetype, and sets about to militate and tirelessly warn the older about the great evils of their habits and complacency, and the sum of all diabolical foolishness, which they are here to put right.
Doncha love how they do that.
@ur momisugly Ralph
“Clearly, there is a great deal of room for improvement, in the small aircraft market. Improvements that will overcome a two degree temperature increase in a trice. And you can bet that if Boeing does not do this, and make an all-new design, then China will.” – Ralph
—
If you know all that which is within your post, then you should also know that airline boardrooms are constantly looking for lower drag lower fuel burn and operating costs per nautical mile, and are constantly changing aircraft as these improve, simply because the cost of fuel burned by an airliner dwarfs the cost of buying a new jet. This it is much more economic to constantly buy more efficient jets and to retire to the boneyard a jet that may be as little as ten years old – or less.
This happens all the time. Which is another way of saying, there is a powerful economic incentive for jet manufacturers to constantly improve and optimize and innovate their jet designs. There are massive differences in efficiency and cost per nautical mile between a 1950s 707 and a 2014 737.
You are assuming that the basic design need radical review and a total revolution in ideas, and presume that this has not in fact occurred. But it has, and that is why you have the current 737s and Airbuses. If it were possible to make a significant major difference to airliner efficiency (as opposed to incremental improvements we see), it would have already occurred.
The history of aviation is littered with the many attempts to design a better turboprop or jet airliner. Indeed people dis them, but turbo props are almost as fast and much more efficient than jets, but airlines simply won’t buy them. The Russian ‘Bear’ maritime patrol turbo-PROP aircraft has a max cruise speed of 510 knots(!!) with contra-rotating props. For contrast a Boeing 747’s maximum cruise speed is about 20 knots SLOWER that this ancient Russian turboprop! So now you know why the Russians keep them in service, it’s because these old propeller-driven jalopies can out-pace and out drag a modern fighter flight vectoring to intercept them!
Yeah, so like, everyone knows that turboprops are just slow and really crappy, right?
Tupolev Tu-95 ‘Bear’
Maximum speed: 920 km/h (510 knots, 575 mph)
Service ceiling: 13,716 m (45,000 ft)
Range: 15,000 km (8,100 nmi, 9,400 mi) unrefueled
Empty weight: 90,000 kg (198,000 lb)
Max. takeoff weight: 188,000 kg (414,500 lb)
If that doesn’t make you double take on your ideas of efficiency and technical advancement and that maybe jets per-sec are not the economic and practical efficiency solution then maybe this will, it’s the European’s answer to the US C-17A, the A400M.
https://en.wikipedia.org/wiki/Airbus_A400M_Atlas
Airbus A400M
Empty weight: 76,500 kg (168,654 lb) ; operating weight[98]
Max takeoff weight: 141,000 kg (310,852 lb)
Cruising speed: 780 km/h (485 mph; 421 kn) (Mach 0.68–0.72)
Initial cruise altitude: at MTOW: 9,000 m (29,000 ft)
Range: 3,298 km (2,049 mi; 1,781 nmi) at max payload (long range cruise speed; reserves as per MIL-C-5011A)
Range at 30-tonne payload: 4,540 km (2,450 nmi)
Range at 20-tonne payload: 6,390 km (3,450 nmi)
Ferry range: 8,710 km (5,412 mi; 4,703 nmi)
Service ceiling: 11,300 m (37,073 ft)
And then there’s this current example of innovation, a small 400 kt turboprop with a 41,000 ft ceiling:
http://en.wikipedia.org/wiki/Piaggio_P.180_Avanti
So very old and very new turboprop aircraft have directly comparable the speeds of jets. They also have similar high ceilings and reliability levels and the exact same safety systems, plus routinely provide efficient narrow and/or wide-body haulage of enormous payloads, to long range destinations in ‘hot ‘n high’ density-altitude conditions.
So the basic air transport problem is not the design potential, nor the hardware and propulsion and materials options that can be mobilized to build with far greater efficiency, to do the same job, just as well. The real problem is that the flying public simply distrust propeller-driven aircraft and perceive them to be less safe, even though we actually know they’re every bit as safe as a jet, far safer in fact is some phases of flight, such as the approach to land.
As a result, airline fleet buyers do not create a demand for and do not request to buy the vastly more efficient high performance turboprops as a viable and worthwhile solution. Props are simply considered passe!
Plus airline manufacturers and operators have to meet stringent regulatory safety requirements that many alternative novel designs simply can’t efficiently attain when it comes time to perform the super expensive certification trials. If they fail they have to go back into development, then re-test again, which is extremely expensive. So conservativeness of design and using what is known to definitely work and meet the required standard, and also what the flying public will agree to sit in and fly on, is what matters the most to manufacturers and airline operators.
Radical efficiency through change is not a good thing for either. The public simply do not trust radical changes in airliner design. For instance, a recent over-reaction to new innovation within a fairly conventional twin jet aircraft design, an example in August 2014 from the NY Post:
http://nypost.com/2014/08/08/terror-filled-flight-as-planes-engine-fails-over-atlantic/
So if we’re going to go into efficiency of aviation designs, and slow pace of innovation, there’s a whole lot more to it than just comparing photos of then and now, and suggesting that not much has changed.
(btw, your photo of that 1950s 707 cockpit has a late 1990s era GPS RNAV moving-map display system sitting atop its glare shield … things like satellite constellations allowing precise global area-navigation have in fact changed quite a lot)
Tupelov Bear doing 510 kt at 45,000 ft. Oh, yes, and pigs may fly. You don’t believe the Russians, do you? Dear me, I presume you also believe that MH -17 was brought down by a ground-attack aircraft that cannot fly at more than 25,000 ft.
So let’s look at that claim. Doing 510 kts at 45,000 ft is mach .89. Do you know how fast that is? The B747 is the fastest major commercial aircraft, and it only does .83. Do you realise that a turboprop at .89 would have supersonic prop blades? Do you understand the problems?
If the Tu-95 does have a high speed, it will be at low level, say 20,000 ft, where mach is not so muchof a problem. Remember that mach is proportional to temperature, so the lower you go the faster you go.
Why did Boeing and Airbus not use turboprops? Pass on that, it may simply be fashion. It is well-known that a small jet would be much more efficient as a turboprop – but usually turboprops are limited to about 350 kt, otherwise they become inefficient. That is 100 kt slower than a 737 at altitude.
Try getting a link to the max mach number for the Tu-95, if you really think it will go that fast.
Ralph
Silver ralph
Mach numbers are specifically and ONLY related to the speed of sound in the density of air at the altitude and temperature of the air at point where the aircraft was traveling.
Air density changes dramatically with altitude, speed of sound changes dramatically with altitude, temperature changes dramatically with altitude. However, the speed of the aircraft OVER GROUND DOES NOT CHANGE with altitude. The double-prop, contra-rotating Tu prop’s are a remarkable invention that have been successful and far more efficient that the early jets, the early turbo-props, and most engines built since then. The original Tu-85 straight wing and its fundamental air frame and ultra-smooth riveted assembly were copied from (liberally speaking) the US B-29 aircraft captured in Russia in WWII, the later Tu-95 added the turbo-prop engines and swept wing to increased performance. Engine, supercharger, piston-ring/engine pressure and propeller design has continued since the 50’s – records attempted with high-camber/high-speed propellers and low flight weights are NOT going to reflect “normal best-economy/best-altitude/best-performance” propellers.
ground speed records are claimed based on wind speed and wind direction as well: The upper air wind speeds (northern hemisphere from west to east) make ground speed records easier (faster) when travel from west-to-east. The 510 knots ground speed is easily possible even without substantial jet stream assistance.
Look again at the details of your charges about Mach number, and only use ground speeds to compare performance. NEVER Mach numbers.
>>NEVER Mach numbers.
Utter rubbish. You are obviously a wannabe, who has never flown a jet in his life.
No aircraft flies on TAS above 28,000 ft. It is mach and mach alone, that determines high level airspeeds of aircraft – which nullifies your compariton with a 747 and modern jets. And the fact that the TU-95 is quoting TAS clearly implies that this 500kt claim is a speed determined at low level.
And using wind to determine groundspeed? Eh? What an infantile claim. I have has a 190 kt tail wind, before now, does that mean I have been supersonic while only doing .70 ?? Absurd nonsense.
Ralph
I mean ‘to determine a groundspeed as the performance speed of an aircraft’.
Clearly, the perfomance of an aircraft is determined by the relative airflow over the aircraft, as measuerd in TAS or Mach. Adding windspeed to form a bogus ‘performance groundspeed’ is a suggestion worthy of a kindergarten.
R
@ur momisugly Silver ralph:
“Tupelov Bear doing 510 kt at 45,000 ft. Oh, yes, and pigs may fly. You don’t believe the Russians, do you?”
—
Nowhere did I say that a Bear does 510 kt at 45,000 ft, that was an assumption that you made. What I said was this:
“… The Russian ‘Bear’ maritime patrol turbo-PROP aircraft has a max cruise speed of 510 knots(!!) with contra-rotating props. …”
And then I referenced its purported basic specs, one of which was “Service ceiling: 13,716 m (45,000 ft)”.
Get it now?
I did not have to “believe the Russians” when I provided that, I simply referenced a Wiki page which you’re free to edit and backup with evidence, if you feel so confident to correct it, given you know the truth of such things.
By the way a propeller is not a helicopter blade, the prop is not leading into the airstream and accelerating against the airstream, it is simply rotating perpendicular to it. i.e. the tip speed is a function of RPMs and prop blade length. Do you also know the RPM of the props too then? Your comment about transonic issues (namely shock cavitation detachment of the airflow) was inapplicable blah-blah.
If you have actual evidence that a Bear can not achieve 510 kts (and remember, this speed can be measured whilst empty with an aircrew and low fuel flight, the weight and altitude were not given) then do so, otherwise your objection is blah-blah.
However, I do agree with you that ground speed has nothing to do with that speed claim, it is indeed a Mach measurement of airflow via pressure measurement with respect to the airframe’s passage in it.
Btw, 747s were certified for to max cruise at ~492 knots which at FL330 (the typical max speed altitude for most jets) is Mach 0.845, not Mach 0.83. Yes, I’m fully aware that a jet or turboprop does not achieve its max cruise speed at its certified altitude ceiling. That speed usually occurs at about 2/3 to 3/4 of its altitude ceiling.
But the actual general point made by me, which I note that you completely ignored, was not about nit-picking over specs, it was to show that turboprops are neither definitively slower than jets, nor as expensive to operate and that they’re equally capable of flying enormous payloads for very long distances comparatively cheaply and fuel-efficiently, and likewise that they too can operate and remain stable above almost all tropospheric WX, in the same way that jets do, and to achieve similar range boosting effects at such altitudes.
Jets don’t have almost any clear advantage.
And I provided two other examples of precisely that, the A400M, and the Avanti-II, which you also ignored. So what did your remarks clarify or alter, what point did you make that changes what I’ve pointed out?
Next time write an actual counter-point if you want to be taken seriously when calling into question airliner design and efficiency and the options available. It isn’t a pi**ing contest, it’s just a discussion.
By the way a propeller is not a helicopter blade, the prop is not leading into the airstream and accelerating against the airstream, it is simply rotating perpendicular to it.
________________________________________
Again not true, which again shows you are a wannabe, who has never flown a large cargo turbu-prop.
At zero speed the blades are fine. As speed increaces the blades coarsen into the airflow, to maintain the required angle of attack/incidence. So at high airspeed, the blades receive a rotational airflow vector determined by engine rpm, and also an airspeed airflow vector determined by aircraft airspeed. So for any given rpm, the blades will indeed experience a greater airflow speed, when the aircraft flies faster, and therefore may go supersonic as speed increases.
The Wiki page says the prop-blades do indeed go supersonic. But I would doubt that, as designers stay away from supersonic blades, as they are inefficient. I imagine the blades CAN go supersonic, in certain flight regimes, but normally operate subsonic.
And if the Tu-95 is achieving its high speed at low level (and I still doubt such a high TAS figure), your comparison with a 747 is nonsense – the 747 will also do 510 knots at low level. But most pilots and passengers appreciate being up above the weather – so why sit down in the CBs and icing, when you can be up above it all? And jets are more efficient at high level.
It may be true that Boeing could make a more efficient low-level turboprop-powered 747. But efficiency is not the only consideration, when designing an aircraft. And a wannnabe would not begin to understand what those considerations are.
Ralph
Prop driven aircraft can and did exceed the speed of sound in WWII though none survived to tell the tale…getting a prop tip through the sound barrier is no different from getting a wing through the sound barrier, and that is that.
The real point is it actually the most efficient way to do stuff? Generally its not worth going supersonic for passenger and freight as the cost jumps dramatically. Commercial aircraft are flown on the plateau representing the most return on investment in fuel and airframe per year. In reality that represents most planes not in a headwind or late, cruising at not much over 400mph. Which a turboprop can easily reach.
It is rare to exceed 500mph, though both jets and props can.
Arguably a modern turbofan is halfway to a turboprop anyway. The actual physics show that for a given cruising speed the optimal power unit will have a large mass of air accelerated to just beyond the cruising speed to provide the thrust. That means large diameter intakes and exhausts (or propellors) and subsonic exhausts too. Small high velocity exhausts – pure jets – do not make for efficient use of fuel, until the airframe speed starts to match the exhaust velocity.
The A400M shows a design which has (probably) been compromised on fuel efficiency, but not by much, as it has a pretty good range – to optimise STOL capability especially on rough landing fields.
In short, all options are open, and there are no absolute limits on what type or layout of aircraft would be needed to compensate for hotter thinner air, the problem is essentially trivial to non-existent, and the fuss made about it out of all proportion to the problem.
Even if there is a problem, which one doubts.
“””””…..
Leo Smith
November 29, 2014 at 4:01 am
Prop driven aircraft can and did exceed the speed of sound in WWII though none survived to tell the tale…getting a prop tip through the sound barrier is no different from getting a wing through the sound barrier, and that is that….”””
Can you provide a reference to ANY documented case of ANY WW-II aircraft (1939-1945) ever exceeding Mach 1.0 even in a vertical full power on dive.
I’m not aware of any.
I am aware of a very deliberate case of a power dive from high altitude, circa 45,000 feet, by a pilot trying to escape from a cracked canopy risk of depressurization. With a two stage supercharged RR-Griffon engine (needed to reach that altitude), he never got close to Mach one at any altitude and speed.
The dive was monitored by radar, as well as the pilot’s reports. He did get into that whole control reversal mode, but never went Mach one. The flight was studied by the chief test pilot for that aircraft, who stated that it was impossible to reach Mach 1 in that aircraft. And it was not even the fastest prop plane of WW-II by a long shot. It was an aerial reconnaissance type designed for high altitude. (Mark XIX Spitfire I think; maybe a Mark XXI)
If I’m not mistaken, that recon flight was the very last official RAF mission by ANY Spitfire, and took place somewhere in Asia; probably Malaysia. Post WW-II of course.
Faster types, like the Hawker Tempest, also never went supersonic. Even ME 262s couldn’t.
Chuck Yeager really WAS the first. The rest is fairy tales.
As a rule I NEVER rely on specifications produced by a manufacturer’s *marketing* department.
Nor do I, I check the AFM because it is a regulated certification document specified for use within the formal certification approval, and it’s legally required to be accurate presented measured data. However, that accurate manual does in fact come from the manufacturer, just not from the marketing/promotions/sales dept.