Multi-engined aircraft

BrokenYugo wrote:

HappyAndy wrote: A spare main engine sounds positively Soviet

Soviet deign philosophy would be to add a spare engine's worth of weight to the main engines to improve their reliability.

Actually, Soviet design philosophy would be to make the engine so that it and the airframe only lasted one flight and then was replaced as cheap as possible. Look at their WWII tanks. They had intentionally built-in obsolescence. The average lifespan of a tank was 7 days out of combat and 16 hours in combat, so they engineered all the components to last just that long. After all, what's the point of an engine that will hold up for 200,000 hours, when it's going to get blown to E36 M3 in 72 hours?

I don't complain about my neighbors' meth labs. They don't complain about my noise.

Steam passenger trains had (have, I guess if you could still find one) an APU that was a steam turbine running about a 10KW generator to run the cars.

MIG I-250 had a prop engine for take off flying around and a 'jet' for high speed intercept which had a short duration. Gas turbines were new technology and the Russians were't confident in them. It was a sort of hybrid with drive for the turbone coming off the piston engine then fuel being injected after. I guess it was a sort of afterburner in some respects. I'm not sure if it went into service before the end of the war or not.

Yes the side view drawing and the pics have some differences. Go do your own Googling.

My father and grandfather once crossed the Atlantic (the short way up Newfoundland to Greenland) in a Piper Comanche (pretty standard single-engine, 4-seat airplane). Talking with the traffic controllers, a pilot from British Airways had a bit of conversation with them. (You must read his words in the most stereotypical "Jolly good chap!" British officer voice.)

Dad: [talks to control] ...Comanche 4-8-Papa.
Brit: Comanche 4-8-Papa, this is British Airways [number].
Dad: This is 4-8-Papa.
Brit: Aha! Twin Comanche. Bloody good airplane.
Dad: Negative British Airways [number]. 4-8-Papa is a PA-24 single Comanche.
Brit: PA-24? You've only got one engine! I've got four.
Dad: Just means we're less likely to lose it.
Brit: Haha! Roger that. I've lost one already.

NickD wrote: Actually, Soviet design philosophy would be to make the engine so that it and the airframe only lasted one flight and then was replaced as cheap as possible....

This is actually pretty close. From what I read, the standard Soviet philosophy (at least it used to be) was to design their planes (e.g. Mig 21) to be easy to maintain and to just replace the engines at a standard interval. More optimizing for quantity rather then quality (materials etc.) As noted, the T34 is a great example of this. TOTAL crap, build and quality wise compared to a Panther, but when you can make 5 of them for the effort of one Panther, it works out..

NickD wrote: Well, the old Convair B-36 Peacemaker had pods designed to go on the underside of the wing that would have carried spare engines because the R-4360s were so prone to failure (due to being mounted in a pusher configuration) and catching fire. There's no records of those pods ever being used, but the problem was common enough that the slogan "six burning, four turning", referring to the six jet engines and 4 prop engines, became two turning, two burning, two smoking, two choking, and two more unaccounted for."

Your quote is funny but not accurate. It's "Six turning and four burning" The B-36 had 6 radials and then they added the 4 jet engines to assist climbing performance and "dash" speed when approaching a bombing target.

aircooled wrote:

NickD wrote: Actually, Soviet design philosophy would be to make the engine so that it and the airframe only lasted one flight and then was replaced as cheap as possible....

This is actually pretty close. From what I read, the standard Soviet philosophy (at least it used to be) was to design their planes (e.g. Mig 21) to be easy to maintain and to just replace the engines at a standard interval. More optimizing for quantity rather then quality (materials etc.) As noted, the T34 is a great example of this. TOTAL crap, build and quality wise compared to a Panther, but when you can make 5 of them for the effort of one Panther, it works out..

The army with the cheapest weapon usually wins. The Panther and late Tigers were worth 2 or 3 Shermans or T-34s in a fight. But it also cost Germany something like 20x the money of a Sherman to build a single tank and it was a month long procedure, as they were not done on an assembly line and running changes were made constantly and they were way overbuilt, designed to hold up for amounts of time that just weren't going to happen in an ongoing major war.

aircooled wrote: This is actually pretty close. From what I read, the standard Soviet philosophy (at least it used to be) was to design their planes (e.g. Mig 21) to be easy to maintain and to just replace the engines at a standard interval. More optimizing for quantity rather then quality (materials etc.) As noted, the T34 is a great example of this. TOTAL crap, build and quality wise compared to a Panther, but when you can make 5 of them for the effort of one Panther, it works out..

Okay, another family airplane story. My dad had a Nanchang CJ-6a. It was a military primary trainer, basically the Chinese equivalent of the Yak-18. These airplanes used some absurdly crude and kinda funny systems. Like: starter, flaps, gear operation, and brakes were all pneumatic. (Air doesn't freeze in the Siberian winter). They also had redundant wing spars. The smaller back-up wingspar was rated for +4/-1 G's (basically full acro). A fellow Yak/CJ owner summed it up nicely:

[Russian accent] Russian engineering: Strong, like bull. Smart, like tractor. [/Russian accent]

jimbbski wrote:

NickD wrote: Well, the old Convair B-36 Peacemaker had pods designed to go on the underside of the wing that would have carried spare engines because the R-4360s were so prone to failure (due to being mounted in a pusher configuration) and catching fire. There's no records of those pods ever being used, but the problem was common enough that the slogan "six burning, four turning", referring to the six jet engines and 4 prop engines, became two turning, two burning, two smoking, two choking, and two more unaccounted for."

Your quote is funny but not accurate. It's "Six turning and four burning" The B-36 had 6 radials and then they added the 4 jet engines to assist climbing performance and "dash" speed when approaching a bombing target.

Not nessesarilly. The 36 would often return with one or two broken engines. Radials don't like being buried in tight spaces.

Lockhead P2 Neptune used jet motors for take off

Also, I've heard that the BAC 146 used 4 motors vs 2 for noise abatement. 2 larger engines would've made more noise that 4 smaller...

It might just be lore, but when I got in to third party maintenance all the old guys were going gaga over a batch of Northwest DC-10s we pulled out of the desert for refurbishing as ATA troop transports.

(picture of DC-10)

So as they were talking I overheard that the Douglas company wanted to make a 2-engined plane but engine technology at the time wasn't powerful enough for the weight of the aircraft (by a slim margin) so they put one in the vertical stab (see it there in the tail). The idea was that once engine technology caught up with the plane they would redesign the vertical stab to look more like a traditional fin.

There was also mention of ETOPS certification (Extended Twin Engine Operations, or as we mechanics say "Engines Turn or People Swim") I'm not sure how an aircraft gets ETOPS certified, but the idea is that the ETOPS certified plane would be flying long distances over water so it needed to be "extra reliable".

Anyhoo, the old guys also said that the third engine was there as a compromise for that certification and that the DC-10 was basically an ETOPS workhorse (whatever that means). I always took it to mean that they thought the DC-10 was responsible for establishing the certification, since it had "third engine insurance", so other planes could now operate over oceans with only two engines.

I think this might come close to "having an 'extra' engine"

Appleseed wrote:

jimbbski wrote:

NickD wrote: Well, the old Convair B-36 Peacemaker had pods designed to go on the underside of the wing that would have carried spare engines because the R-4360s were so prone to failure (due to being mounted in a pusher configuration) and catching fire. There's no records of those pods ever being used, but the problem was common enough that the slogan "six burning, four turning", referring to the six jet engines and 4 prop engines, became two turning, two burning, two smoking, two choking, and two more unaccounted for."

Your quote is funny but not accurate. It's "Six turning and four burning" The B-36 had 6 radials and then they added the 4 jet engines to assist climbing performance and "dash" speed when approaching a bombing target.

Not nessesarilly. The 36 would often return with one or two broken engines. Radials don't like being buried in tight spaces.

Yeah, I did get that backwards, whoops. But the problem with the radial engines wasn't being in close proximity, Appleseed. It was that they were mounted backwards of how they were designed to be operated. Instead of warm air flowing back across the carburetors, they now had cold air being drawn over them, which would ice up the carburetor air inlets and gradually richen up the fuel mixture until the unburnt fuel in the exhaust lit off and caught fire.

Also, keep in mind that these engines had an appetite for oil, with each engine requiring a dedicated 100 gallon tank of lubricating oil. And there were also 56 sparkplugs on each engine, and they were prone to fouling due to the lead in aviation fuel of the time, requiring replacing 336 spark plugs at each service. And because they were so big, they didn't fit in any hangars azt the time and all service had to be done outside, in the elements.

P-3 Orions have 4 turboprop engines and frequently cruise around with one or two not running and the props feathered. This is to save fuel to give them a longer time randomly flying around not being able to find submarines that are watching them fly by and wondering why all the props aren't turning.

During the early '80s, when I was flying out of Kinston, NC, they were using the airport as a base to fight forest fires in Eastern NC. In addition to the C-130s, DC-4s, and a PB4Y, they had 3 C-119 Flying Boxcars with a jet engine mounted in a pod on top of the fuselage, in the center of the wing. They'd go lumbering down the 6005' runway and barely get the wheels off the ground in time to clear the fence at the other end. Obligatory hotlink:

The AJ Savage was another plane with an auxiliary jet engine.

Many 3 and 4 engine transport category aircraft are certified for a intentional one engine inoperative takeoff. These flights are ferry flights and as such the only people allowed aboard are the necessary crew. I came across the following procedure for a two engine takeoff on a Boeing 727.

http://www.airliners.net/forum/viewtopic.php?f=3&t=601473&p=9504231&hilit=3+engine+ferry+on+4+engine+airliners#p9504231

Quoting UA735WL (Reply 31): I remember seeing a post on an earlier thread by a 727 pilot (maxpower1954?) that debunked the idea that the 727 had extended range on 2 engines- something to the tune of that MCT was required to maintain altitude and the extra fuel consumption of maintaining that thrust negated the lack of a 3rd engine AND actually made the aircraft burn more fuel (per ground unit traveled) due to the slower attainable speeds of 2 engine flight.

I concur. If it worked it would have been SOP by operators to do this. 2 engine cruise didn't help fuel savings at all.

Quoting highflier92660 (Reply 30): Can any Boeing 727 pilots on anet tell us the two-engine takeoff procedures? I assume it's bleed-off/ packs-off and what T/O flap setting were normally used? Quoting BravoOne (Reply 32): I think you have it right regarding the packs & bleeds. I would have to imagine flaps 5 would be the best choice but not having done it I remain clueless. I really doubt that World ever ferried a 727 across the CEP on two engines FWIW.

Just ran a quick runway analysis on my old 727 program, yeah, it's quite limiting to do a 2 engineferry. Must be VFR, avoid icing enroute.

Oakland rwy 30, 24 degrees C, 727-200 with -15 engines. Flaps 5 you are limited by climb gradient to 136,700

Basically with a BOW weight of around 95k, you have about 2.5-3 hours of fuel.

Books says.... BEFORE TAKEOFF Use flaps 5° for takeoff unless runway performance is limiting. Turn galley power off. Reduce nonessential electrical loads. Turn cabin pressurization bleeds off for takeoff.

TAKEOFF The procedure described for Takeoff in the Normal Procedures section is equally applicable to two engine ferry takeoffs, except that 400 ft will be used as a level off height for flap retraction (unless higher is required for obstacle clearance). When a pod engine is inoperative, considerable rudder pedal steering will be required at the start of the takeoff roll. This procedure is suitable for ferry takeoff from dry runways for all B-727 aircraft. Takeoff will be made with increased VR and V2 speeds, based on the Runway Limit or Climb Limit Two-EngineFerry Maximum Gross Takeoff Weight, whichever is lower. This will produce the maximum second segment climb rate. All takeoffs will be performed from the Captain's seat. All thrust levers will be advanced for takeoff, to ensure proper activation of all takeoff warnings. If the takeoff is aborted because of to directional controllability, DO NOT ATTEMPT ANOTHER TAKEOFF. Do not operate gear and flaps simultaneously.

PS in