Last night, I watched the William Shatner “There’s somethin on the wing!” episode of The Twilight Zone for the first time (yeah, I’m a late bloomer – what can I say?). The episode “Nightmare at 20,000 Feet” was first aired in 1963 (and in the process of looking that up and seeing the episode title, part of my question has already been answered, but I’ll carry on).
The thing that got my attention right away is that the prop plane in the episode is flying through the middle of a storm, and in all my flying experience, passenger jets tend to fly well above cloud level…I guess about 35,000 feet is typical from what I know.
So my questions are as follows:
Was it normal to fly at much lower altitudes 45 years ago?
If so, was the biggest (or sole) limiting factor the prop engine vs. later jet engines, or were there other technology advances that made it more practical and preferable to fly higher as years went on?
If a newer and better type of engine came about today that made it possible to fly passenger aircraft even higher (say, 60,000 - 80,000 feet), would there be advantages to that?
I assume prop engines can only get a plane going so fast. How long would it have taken to fly from LA to NY in 1963? Could that even be done non-stop?
Pardon the extended ignorance in these questions, please. I’m looking to be educated.
All engines that rely on combustion lose efficacy, or require technological improvements such as turbocharging, as they gain altitude. It’s because there are fewer and fewer oxygen molecules to mix with fuel molecules. You either need to
Scale down the number of fuel molecules mixing with fewer oxygen molecules, which is what itty-bitty prop planes do. This improves fuel efficiency, but doesn’t give you any more power
Compress big blobs of air, which have more oxygen molecules, into smaller blobs of air and then stuff them into the engine and mix with fuel. This is what turbochargers and other sorts of compressors do.
Even the best jet engines in the world will lose power with altitude. Most commercial jets have service ceilings in the low to mid 40’s-foot range.
Most thunderstorms in the U.S. top out in the 30k range, with some occasional monsters in the 40’s and even low 50’s. T-storms in Africa and the tropics can get into the 50’s. Even commercial jets need to divert to avoid those.
There are planes that can fly that high (U-2, Blackbird…God rest it’s soul) but really the primary variable driving that service ceiling isn’t engine power. It’s WEIGHT. And to a lesser degree, airfoil design.
This is why the Russians fell behind us in aircraft development in the 50’s and 60’s, and couldn’t get something up high enough to stop the U-2 until Powers got shot down. Their preferred method of gaining altitude was to keep trying to slap on a bigger and bigger engine to the same plane. There are rapidly diminishing returns with that approach, at least as far as gaining altitude as your objective function.
An as you can observe from Burt Rutan’s X-Prize winner, a major difference between his craft and the extremely-high-flying craft of the late 1950’s and early 1960’s is use of composite materials. If commercial travel is going to get up to the 60-80k range, it will be from breakthroughs in material design that reduce weight. Not engine technology.
A typical turboprop passenger plane from the ‘old days’ was the Convair series.
Cruise speeds for these were in the mid-200 knot range. That’s 10 hours of flight time from L.A. to New York. But they couldn’t do it in one go, without refueling.
My guess is they probably stopped at least twice on the trip, making it an all day ordeal or even a 2-day job.
Performance specs are at the bottom. Service ceilings were in low-20s, putting them squarely in T-storm range. And also, I might add, not much clearance on a windy day over the Rockies. With strong winds and a stable atmosphere you can get some head-against-the-ceiling knocks from leeward turbulence near a mountain range, even if you’re 4000-5000 feet above the ridge.
Possibly the peak of U.S. made turboprops was the Lockeheed Electra, introduced in 1958. It had a service celing of 28,400 feet (of course the operating height was usually much lower) and a top speed of 405 mph (which meant a usual cruising speed in the 350 mph area).
The last major pure piston aircraft developed was the Douglas DC-7 with a cruise speed of 350 mph and a service ceiling of 25,000 feet.
Wiki notes two Electra crashes which directly relate to the OP
So yes, they flew through, rather than above, thunderstorms, and yes, unfortunate incidents sometimes happened.
IIRC about the longest route an Electra would fly non-stop was New York/Chicago. A DC-7 could fly transcontinental routes. American Airlines advertised 8-hour non-stop service between Los Angeles and New York.
I’m told (by an old AA pilot) that they rarely could get a DC-7 the full distance at that speed. In order to claim to still be competitive with the new jets, they had to run the entire time at max-continuous power. The plane had enough *fuel *to get that far at that setting, but it would often have to stop at Phoenix to add oil.
Typical cruising altitudes for turbocharged piston airliners were in the 20-25,000 foot range, where there was a lot more weather that could not be avoided than with jets, and less thorough and reliable forecasting that would let them get around it.
Back to one of my earlier questions: if one could develop a commercial plane capable of cruising at 60,000 feet or higher, would it be advantageous to do so? What would be the optimal cruising altitude for avoiding turbulence without having to break free of the atmosphere altogether?
If it costs less in fuel to run a plane at that altitude, then it will succeed. All other concerns (speed, smooth ride, less diversions) will pale in comparison. The higher you go the less air resistance which should mean less fuel, also you have to travel slightly further.
A big issue at high altitude is induced drag. That is, the drag created in the process of lift. At low airspeeds, a wing will generally operate at a higher angle of attack, and create more drag to remain aloft. Wing design is an important variable here - at high altitude, you want very long, very narrow wings (high aspect ratio). Look at a U2 spy plane, and you’ll see what I mean.
Airliners actually do have quite long and thin wings, compared to low altitude piston planes. But there’s a limit you reach both structurally and in regards to loss of manoeverability both on the ground and in the air.
In addition, the engines are designed to most efficient at certain altitudes. When you combine engine design with airframe design, you come up with some optimal altitudes for the plane to fly at. You can move the optimal point a few thousand feet in one direction or another, but current airliner designs are pretty good and represent the best tradeoff we can manage today.
One other factor is safety. When you get into the really rarified heights, a depressurization of the cabin is a much bigger deal. The jets that do fly up in the 50K range have different certification requirements and operational requirements for the crew.
For those who are interested (and who are still reading this thread) I would highly recommend “Skunk Works” as a bit of light holiday reading. You can probably get it in paperback form for less than $10.
One of my Top 10 all-time favorite books. A nice mix of management theory, engineering breakthroughs and Cold War history wrapped into one. Starring Kelly Johnson as the patriarch.
I can’t remember if the following fact is in the book, but as Sam referenced above, the wings on the U2 were something to behold. The original test pilots were afraid to get into the plane because they were so long and thin they flapped like birds’ wings in the wind. Someone leaned up against the fuselage when it was sitting on the test ramp and put a dent in the skin, since it was so thin to conserve weight. And the Blackbird, of course, was the ultimate coup-de-grace.
Amazing that all of that stuff was accomplished nearly 50 years ago.
Thermodynamic considerations dictate that jet engines tend to be most efficient where the temperature is lowest. At the tropopause (typically high 30,000’s to low 40,000’s of feet) temperature ceases to drop with increasing altitude, so that’s a good place to fly. It’s also above nearly all weather, which is a big plus.
To fly efficiently at 60,000’ would require bigger wings, which involve extra cost and weight (which itself hurts). So you’re not likely to see aircraft interested in efficiency at that sort of altitude.
In 1964 my wife and I flew, on what was supposed to have been a jet, but turned out to be a stretched DC6 prop, from NY to London non-stop. Of course, we were flying in the direction of the prevailing winds. On the return flight, they weighed us all (passengers and carry-on and surely the checked bags as well and then they flew from London to Glasgow, refueled and then to NY. I don’t think the London-Glasgow distance is more than a couple hundred miles, so they were obviously right on the edge. I think the flight over took about 12 hours. We actually spent several hours in Glasgow (why?) and I have no memory of how long we flew on the return.
I flew a Pan Am 707 (MATS contract) bird across the Pacific Westbound in 1963.
Last DC-6 (seats all facing backwards, C-118? MATS) I flew was From Japan to California with fuel stops at Wake an Hawaii … We were not allowed off the plane. Total Time Enroute = 33½ hours.
Oh, in 1988 or 89, as a test I took an Cessna C-310Q turbo (1970 model) to 31,000 in the winter. We flew an IFR route from Tulsa to Eastern Colorado and back to Tulsa. It was not a workable altitude for what we were biding on. We had some falling snow and ice crystals in the cockpit, above 26,000 feet, the cabin heater would not stay lit. “Janitrol” The right engine quit after about 20 minutes at 31,000. The right prop hub was so cold the engine could not be feathered and we could not get it to restart until 8,000 feet on the decent back to Tulsa. Flying it at that altitude was like balancing on the head of a pin.