Cabin altitude regulations in the propliner era?

[braselc5048]

I'm looking at getting A2A's b377 up to really high altitudes (32,000 ft), but with a full simulation of the pressurization system, and a 6.5 PSI pressure differential limit, that would require a cabin altitude of perhaps 10-11,000 feet, maybe 500 ft more. Today the limit is 8000 ft cabin altitude, but what was, or was there even, a limit back in the propliner days? (Other then what captain and flight engineer thought proper.)

[Tom/CalClassic]

Hi,

The limit imposed by the authorities that affected flights had to do with oxygen supplies, not pressurization. If there was no oxygen available to each passenger (and no propliner had that), the flights with passengers aboard were limited to 25,000 ft. Freight flights could go higher, if the plane had a higher certification ceiling (FSAviator says the B377 certification ceiling was 25,000 ft). But almost all propliners were designed for maximum efficiency between 18,000 and 23,000 ft - you normally had to be very light to go any higher.

Hope this helps,

[braselc5048]

Ok then. When was the limit imposed? It might not have existed yet, since the b377 was flying as early as the late 40's.

The certification ceiling being from lack of cabin oxygen makes more sense than what I've heard from somewhere about not being able to maintain pressurization if a turbo fails, since every single flight I've done above that altitude ended with the outboard engines reduced in power enough to make their turbos useless for cabin pressure anyway, and you can maintain pressure at 31,000 ft (highest so far) and have the cabin descend with only two turbos providing pressure. Strange why the certification ceiling is that low, my initial cruising altitude is 26,000 ft westbound, and I haven't had any problems up there. Perhaps Boeing simply didn't bother, since it wasn't really useful as a freighter anyway.

[Dennis the menace]

31,000 feet?

Why on earth would you want to fly a piston engine airliner in such an incorrect and unhistorical way?  At 31,000 feet you're up at an altitude that the first commercial jets flew at when going into service in 1958 and 1959. Even THEY didn't fly much above 31,000 or 32,000 when making the fist trans-Atlantic and trans-Pacific runs - the engines and payload limits didn't permit an economically feasible flight at a higher altitude.

NO piston engine airliner is economically efficient above 25,000 feet.  Your IAS should tell you that. And that would have to be very light, at the end of its run, with a light passenger payload and with approximately 25% fuel remaining. So this was somewhat rare - even for a L-1649 or a DC-7. Practically unheard of for a B-377 except for scientific testing or some experimental purposes. Even the giant Tu-114 flew at just 19,000 to 21,000 feet on its runs to Cuba. Props need density to "bite" into, and as you climb, the air becomes less dense with less to "bite" into, and less oxygen to feed into the engines.  Multi-speed superchargers and variable pitch propellers can only do so much and no more.

Most trans-continental flights were 19,000 feet, with a few of the larger, more powerful aircraft at 21,000 feet.  Trans-oceanic flights were "stair-stepped" up to 21,000, with 22,000 or 23,000 only for the last leg of the journey.

A Boeing 377 is a slug and certainly was not cruising much above 19,000 feet if even that.  It was lucky just to reach its destination with all four engines turning.  Many B-377 flights from the west coast of the USA to Hawaii that began at just 8,000 feet and only a few hundred miles from Honolulu the plane had finally made it up to 15,000 or 16,000 feet.  This is because it was NOT economical to fly the beast less than fully loaded, and fully loaded this is its limit, unless you want to stress the airframe and engines and enjoy paddling around somewhere in the mid-Pacific waiting for some tuna boat to hopefully fish you out of the water.

I would recommend the excellent tutorial available on this website: www.calclassic.com/tutorials.htm

You might want to read this. Here is an accident investigation report of a Pan Am Stratocruiser flight 944 on the first leg of its around the world service. The flight was from San Francisco to Honolulu. It departed with 36 passengers and a crew of 8. Its assigned cruising altitude was 10,000 feet at an airspeed of 226 knots. Gross weight at departure was 147,000 pounds - the maximum allowable - and this included the fuel need for approximately 13 hours. That's the reality of how they flew in real life.    rbogash.com/Stories/AAR%20PAA%207%2011_8_1957.pdf

[Tom/CalClassic]

And that tutorial is called the Propliner Tutorial 2008.

I assume you have also read the B377 MiniTutorial, included in my download. If not, it is in the FSAviator Archive forum (FSAviator created all of my flight dynamics).

calclassic.proboards.com/thread/3156/377-mini-tutorial

The relevant section:

"OPERATIONAL CEILING (OC).

The 'Boys Big Book of Wonderplanes' loves to tell us the easy to research and invariant 'service ceiling' of aeroplanes, but the information is of no practical use unless the aeroplane is an interceptor. Other types of aeroplane cannot retain autorich mixture using AVGAS as the primary engine coolant during prolonged cruise. They must reduce to a MAP and RPM which allow use of autolean mixture, (or weaker).

The only ceiling that matters in real life is the one associated with the limited power we intend to use to cruise today!

Our Operational Ceiling also depends on our current weight and the current weather. Of course we can use climb or METO power to climb a heavy airliner to much higher levels we cannot possibly sustain using only cruise power, but what is the point of that! If we are not flying an interceptor during an interception we must always reject climb power long before it is insufficient to continue climb. We need to locate our (cruise power) operational ceiling at our current weight in the current weather *while we are still employing far higher climb power* because operating any aeroplane at its cruise power OC allows it to achieve the maximum velocity (KTAS) available from cruise power.

In real life we could inform our captaincy decision with forecasts of cloud and QNH and OAT and ice ahead. We would make a 'predictive' decision. In MSFS we must make a 'reactive' captaincy decision instead. Sooner or later our reactive decision will always be proven wrong by today's weather, but inside MSFS we have no other 'informed choice'.

Once we are *at or above the level specified by the real ATC departure*, (versus 'obstacles' of all kinds ahead), and climb power will not sustain 166 KIAS at 500 VSI we must reject climb on reaching the next semi circular level, in expectation that it will be our OC for the time being.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
MONITOR IAS decay at 500 VSI
When IAS = 165 KIAS REJECT CLIMB
Continue to next semi circular level
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

The more the weather around us deviates from average (ISA conditions) the more flawed this necessarily reactive captaincy decision will prove to be, but in MSFS we have no other informed choice. When IAS falls below 166 KIAS at 500 VSI we reject climb and test whether we are below our OC, at our current weight, in the current weather, using normal cruise power."

Hope this helps,

[dave mcqueen]

The flight engineer on the ill fated Clipper 944 (Romance of the Skies) lived down the street from my parents house. In addition to his job at PAA Dad used to have a side business repairing radios/TVs/stereos/tape recorders etc. That flight engineer had dropped off a tape recorder to have fixed, which Dad did. Needless to say it was never retrieved.

I have a map from 1959 that Dad gave me that was saved from a B377 flight from Hickham to Travis showing the rhumbline route of flight with notations of the reported positions, altitude, times and reported winds at each reporting point. The Stratocruiser started at 9,000 feet and eventually step-climbed up to 13,000 feet by the time it reached the West Coast. So although the absolute service ceiling may have been in the neighborhood of 31,000 feet, operationally they ordinarily flew, as Dennis stated, way lower.

[Dennis the menace]

The link below is very good reading on Pan Am flight 944. 

Pan Am was issued an airworthiness directive to replace a defective oil transfer tube that was factory brazed in place with a stronger bolted in place unit and failed to do so.  Pan Am elected not to carry out safety modifications because they planned on retiring the B-377 fleet in favor of jets in the next year or so.  When the poorly brazed oil transfer tube breaks off, it creates oil starvation in the propeller hub dome and that can lead to a runaway prop, which in turn can lead to the destruction of the aircraft.  Pan Am instead choose to focus on a "lone, crazed purser" as the cause of the accident and not its failure to comply with airworthiness safety directives.

Boeing’s 377s had a history of problems with propellers. The airline had initially adopted seven-foot-long Hamilton-Standard Hydromatic propellers with hollow-core steel blades. But centrifugal force tended to push the neoprene in the cores (the blades weren’t truly hollow) toward the tips of the blades, creating an imbalance and, in at least a few instances, causing pieces of blades to fly off. When the wreckage of a Pan Am Stratocruiser that disappeared over the Brazilian jungle in 1952 was finally found, investigators discovered that the airplane had literally shaken itself to pieces after losing first a propeller and then an engine.

Pan Am and Hamilton-Standard sought to solve the problem by nickel-plating the blades. But when another Stratocruiser—with newly plated blades—was forced to ditch off the Oregon coast in 1955 because of a runaway propeller, the airline realized that hollow-core props weren’t the 377’s only problem.

A runaway, or “over-speeding,” propeller was a nightmare for any flight crew. If the variable-pitch propeller could not be feathered—its blade pitch changed to point the leading edges in the direction of flight—centrifugal force wrenched the blades to the lowest pitch stop. The resulting drag was equivalent to that produced by a solid disk the diameter of the propeller in front of the wing. At that pitch, even if the prop simply windmilled, there was a danger that it would fly apart and pieces would penetrate the fuselage.

Equally terrifying was the fact that a runaway could occur virtually without warning, and left the pilots only seconds to react. Often the first indication of a problem was a sudden change in propeller noise, from the normal dull throbbing to a rapidly ascending, blood-curdling whine. One Pan Am pilot likened the sound to “the cry of a thousand banshees.”

www.airspacemag.com/history-of-flight/the-mystery-of-the-lost-clipper-5467157/?page=1

[braselc5048]

Ok everybody, calm down, I've read the tutorial and I'm actually following it., You're supposed to climb to the highest altitude you can while maintaining climb power and airspeed, and 500 FPM as well if flying under CONUS regulations, which I'm usually not (I've had exactly 2 of my 10+ flights cross US airspace at any point - vintage phase everywhere else), and can maintain in cruise power. At climb power of 2650 BHP (per engine), that altitude is 24,000 feet. (I'm using real world charts, and apparently a2a's managed to get the b377 to follow them, although I extrapolated the charts past the end of the power/speed lines to 30,000 ft (although the lines stop at 25,000 feet, the scale and graph goes to 30,000 ft).) And she flies perfectly fine up there. And of course, if you're anywhere else in the world in the 50's, the 500 FPM requirement doesn't (I think?) apply. I step climb, according to a (weight based) flight plan, although there's more power reductions then climbs. A typical eastbound flight at MTOW is something like this:

start 147,000 lb
1000 lb ground fuel
4500 lb climb

141,500 lb, 25,000 ft, 2000 BHP

135,000 lb, 25,000 ft, 1900 BHP

130,000 lb, 25,000 ft, 1800 BHP

125,000 lb - more options from this point. For this example, 27,000 ft, 1800 BHP

120,000 lb - possibly 27,000 ft, 1700 BHP, or perhaps 29,000 ft, 1700 or 1800 BHP.

115,000 lb - option to climb to 31,000 ft or reduce power to 1600 BHP, but it's usually not worth it, since each step in the flight plan is 400-something miles, it takes much of that to descend at the maximum rate of 300 FPM (the only way to descend faster wile maintaining cabin pressure is to lower the landing gear!), and we're only allowed to plan to use 40,000 lb of fuel anyway, leaving a 15%, 6000 lb headwind reserve. Usually I just continue the previous altitude and power for 100-odd miles until top of descent.

Indicated airspeed is in the 170-198 knot range, at the lower end of the range at lower power settings and higher altitudes. IAS, TAS and distance travelled is in the flight plan as well.

I only ever got to 31,000 ft once, and that was at the end of a very long flight that took off at a relatively low weight.

And that really is the most efficient way to fly it, according to both the FSAviator propliner tutorial and the chart's I'm using. You fly faster and burn less fuel per mile at the same engine power, according to the charts. Step climbs and power reductions as usual, just several thousand feet higher. If using the 25,000 foot limit, then you'll spend the entire flight at either 25,000 ft or 24,000 ft.

I don't like using power less then 1600 BHP, since the cruise control chart doesn't have any marks for power settings less then that, so I've got nothing to plan a flight on.

Our Operational Ceiling also depends on our current weight and the current weather. Of course we can use climb or METO power to climb a heavy airliner to much higher levels we cannot possibly sustain using only cruise power, but what is the point of that! If we are not flying an interceptor during an interception we must always reject climb power long before it is insufficient to continue climb. We need to locate our (cruise power) operational ceiling at our current weight in the current weather *while we are still employing far higher climb power* because operating any aeroplane at its cruise power OC allows it to achieve the maximum velocity (KTAS) available from cruise power.

I can't imagine a situation in the strat where it's possible to climb to an altitude you can't sustain using cruise power without rate of climb decreasing to absurdly low levels. I also can't imagine any reason to fly below 15,000 feet other then strong headwinds or pressurization problems. And I was only hoping to get to 32,000 ft for a brief time at the end of a transatlantic flight.

Also, BOAC's 50-passenger "Monarch" config, with 50 passengers with 2 bags each, and 3 stewardesses with 1 bag each, only comes out to 142,000 lb with a full fuel load. Was it common to take on extra cargo for those flights to increase to MTOW?

Finally, I've learned to take FSAviator tutorials with a grain of salt. For example, the reason the b377 was a commercial flop wasn't misreading the market and providing too much luxury, that was only the british (accommodations were comparable to connies in terms of luxury, and b377's seated more too), it was because it was a maintenance nightmare with too-high operating costs.

[Dennis the menace]

Any commercial aircraft has what's generally known as a "load factor". That is the seats that are necessary to be sold for the aircraft to break even. Every seat under that number that is unsold results in the flight producing a financial negative balance for that flight. The greater the number of unsold seats, the higher the financial loss. To mitigate this, airlines fill up the holds with freight and mail.

I used to have a chart that showed approximately the number of seats required to be sold in order for the flight to break even financially. The chart was from the mid 1970s I recall. With maximum freight and mail in the holds, a B-707 needed 60% of the seats sold at that time to break even. A DC-8 was a bit more, at around 65%. DC-10s and L-1011s needed just under 50% of the seats sold to break even. What got my attention, and why I grabbed the chart off the wall when I worked at Stewart Davis Aviation was that the Convair 880 need 94% of it's seats sold, and the Convair 990 needed 98% sold. That explains why the Convairs went out of service so quickly once cheap fuel went away.

A flight attendant on a Southwest flight told me that after they load in all the freight and mail, Southwest only needed to sell just 26 seats for that particular flight to break even. Not sure what 737 it was, but it was a newer one.

So the answer is yes, if they can, the airlines will fill the holds on ever flight with anything legal that can make them money. Not only will they fill them to the max, they have been known to over fill them and then doctor up the loading manifests to hide that the aircraft is overweight. Even leaking, non compliant oxygen generators might be loaded so long as it will make them a buck. Just ask the 110 persons aboard Value Jet flight 592.

[Defender]

Braselc, Hi.

Just curious. Have you read the various Flight Global articles on the Stratocruiser. In particular there's a very good 3 parter from 1949 on the delivery flights. A lot of information on the flight profiles/performance and the various limitations.

Also do the charts you're using show the minimum permitted cruise IAS at high weights and altitudes?  On the Starliner for example, real world charts limit MTOW lean mixture initial cruise altitude to about 13,000' and you have to be around 140,000 lbs to get to 20,000' or about 6 hours into the flight. I understand the main reason was that the IAS achievable wasn't high enough to allow adequate engine cooling. Yes, you might go a bit higher on auto rich but at punitive fuel consumption if range was important. And CHT gauges in FS9 are not always realistic.

Bill  

[braselc5048]

Apr 23, 2014 12:06:11 GMT -5 Defender said:

Braselc, Hi.

Just curious. Have you read the various Flight Global articles on the Stratocruiser. In particular there's a very good 3 parter from 1949 on the delivery flights. A lot of information on the flight profiles/performance and the various limitations.

Also do the charts you're using show the minimum permitted cruise IAS at high weights and altitudes?  On the Starliner for example, real world charts limit MTOW lean mixture initial cruise altitude to about 13,000' and you have to be around 140,000 lbs to get to 20,000' or about 6 hours into the flight. I understand the main reason was that the IAS achievable wasn't high enough to allow adequate engine cooling. Yes, you might go a bit higher on auto rich but at punitive fuel consumption if range was important. And CHT gauges in FS9 are not always realistic.

Bill  

Um, I'm using A2A's payware b377 in FSX, with accu-sim. Not the b377 from this website. Minimum climb airspeed is 170 knots, and I've never cruised slower then that, although come to think of it, I might have been at 165 knots once. On a side note, I was pouring through the real-world charts I have, and I noticed that one place in them Boeing said there's no reason it can't spend the entire flight at 24,000 or 25,000 feet under CAA regulations.

[Tom/CalClassic]

Ah, that's the answer. You are using a plane with a less accurate flight model.

[Dennis the menace]

Payware is oftentimes "flop ware" compared to the models available at this site.

I flew the DH-104 Dove before it had the modified flight dynamics available here. It used to fly unrealistically high and fast, and seemed far too easy to maneuver. After using the flight dynamic modifications, it flew like a totally different aircraft entirely. It felt underpowered, sluggish, heavy and maneuvered like a truck - in other words, perfect!

[braselc5048]

Frankly, I think A2A did a pretty good job, with very in-depth systems (including engines) modeling. And I've been using real-world charts that somebody posted on (their) forum, since A2A somehow neglected to provide them. And it matches pretty closely. Direct quote from said charts:

The service ceiling at cruising power and cowl flap deflection exceed 25,000 feet at all weights up to 135,000 lbs. The 3 engine ceiling defined by CAR 04.1231(b) exceeds 5000 feet at all weights up to 135,000 lbs.

It appears that takeoff at 135,000 lbs may be immediately followed by climb to and cruising at altitudes up to 25,000 feet.

I think that these charts might be for the earlier, Curtiss propeller version, since they list MTOW as around 142,000 lb. It does sound about right, since if using an initial cruising altitude of 26,000 feet at (by this point) around 142,000 ish llbs, rate of climb drops below 500 FPM at climb power and maintaining climb airspeed around 24-25,000 feet.

It was, after all, not so much a pure civilian airliner design as an airliner version of the KC-97 stratotanker and C-97 stratofreighter, which along with the b377 were themselves were derivatives (including the entire wing and engine installation) of the B-50 bomber, which was designed for high-altitude flights to avoid interception (it worked until the soviets used jets). Considering it shares the wing and power plant (and lower fuselage and tail) with a bomber designed for operation at 30,000 feet plus, 25,000 to 30,000 (or a little more) feet as a cruising altitude actually makes sense. The only reason in couldn't normally cruise at those altitudes were CAA regulations limiting it to 25,000 feet.

For what it's worth, the service ceiling is 34,000 feet, which appears to be a closer figure to what the airplane was actually capable of. And going to 34,000 ft would be a stupid idea. So, I'm wondering what the British regulations were, and weather those or CAA (today FAA) regulations would apply to a BOAC plane flying from New York to Liverpool, once out of US airspace.

[herkpilot]

The basic rules of safety for pressurized flight as developed and followed by the US military and later civilian authorities has been not to exceed FL250 in a pressurized acft unless supplemental oxygen is available to every person on board. In the piston days (DC 6/7 and Connie) that lack of passenger oxygen limited flight to FL250 and below. The pilots had to have oxygen available but not the pax.

One of the design issues in early passenger jets was how to provide readily available oxygen to each passenger. That briefing about putting your own mask on first is very serious, as a sudden loss of pressure at altitude may leave you with only 20-30 seconds of alertness. A few trips through the altitude chamber during our annual physiological training really reinforced how quickly one could pass out.

However with no pax on board and one pilot breathing oxygen and the other crew members with oxygen readily available there was no upper limit as long as the cabin pressure remained below 10,000 ft. Been there, done that, once nursing a tired old E model Hercules up to FL330. The problem with climbing to jet altitudes in a prop plane is that you become a moving roadblock to faster traffic.

I suspect that the most nations adopted their aviation rules from ICAO in the post war years which generally followed US standards for safety. So fill the plane with cargo and have at it.

Hy