FW-190 Design Analysis

Here is a WWII vintage design analysis of the FW-190.

Happy Thanksgiving!

The electrical systems on the Fw 190 for undercarriage, flaps and all trimming tail are a fascinating aspect of this aircraft. In the 19030s/40s the Luftwaffe was heading in the direction of all-electric systems. It seems to have caused many developmental problems for Focke Wulf on the Fw 191 bomber, even Kurt Tank, himself originally an electrical engineer, was very opposed to it. It worked well on the Fw 190 though at some point they reverted to hydraulic systems on some of the later models due to raw material issues. Electrical systems don't bleed oil and faults can easily be isolated by circuit breakers.

Plus electrics are lighter than hydraulics in some cases.

Simplicate and add lightness...

Cheers,
Biff

BiffF15 said:

Plus electrics are lighter than hydraulics in some cases.

Simplicate and add lightness...

Cheers,
Biff

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It's quite surprising how slow the industry has been to adopt electrical systems when complete widebody airframes have been lost to simultaneous bleed out of multiple hydraulic systems. American engineers developed the ability to point guns electrically with high precision and I would have that that this would be the basis.

Douglass tried electrically boosted controls on its Skyshark, I read they lagged a little in response to pilots inputs, don't know if that was resolved. The aircraft coupled gearbox issue and the loss of a test pilot tend to dominate the narratives, if it had of succeeded it may have started a trend.

Work was done in the 90's on electric actuator systems that were supposed to be an upgrade for the Space Shuttle. They were not ever installed in the Shuttle but found other applications. The earliest users actually were video games that featured motion like a flight simulator. Maintenance was a lot easier for malls and other establishments that did not want hydraulic oil all over the floor.

By the way the F-106 used high pressure pneumatics for flight control and weapons bay functions. Pneumatics are F A S T but can be rather hazardous. On the F-106 they had to put spacers on the door actuator rods to keep accidental actuations from cutting the ground crew people in half.

It's quite surprising how slow the industry has been to adopt electrical systems when complete widebody airframes have been lost to simultaneous bleed out of multiple hydraulic systems.

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There's quite a big difference between a single seat fighter and a 250+ seat airliner. You need real power to move big flaps, big multi wheel undercarriages etc. Hydraulics has more grunt. Also, most airliners these days do have electrical systems that drive control surfaces, but coupled with hydraulics. If hydraulics wasn't needed, they'd not use it in modern airliners - as Biff pointed out, saves weight (electronic systems introduce their own degrees of complexity). ATRs for example have electric flaps, but rely on hydraulics for their undercarriage.

Besides, very few aircraft have been lost to multiple hydraulic system failure, normally, one system might fail, but extremely rarely both; I am aware of one such failure, in a 737, but considering the number of them in service use, that's a rare case. Normally hydraulic system failures are driven by some other consequence, like engine failure or such like - hydraulic pumps are driven by engines, but there are back-up electrical systems that drive stand-by hydraulic pumps, which prevent total system failure. cases where lines and components have failed do happen, but this doesn't always necessarily result in the loss of the aircraft. Considering the number of aircraft lost due to hydraulic system failure as a cause, i.e. very few, the use of hydraulics won't go away yet. Damn, more skydrol in the eyes...

Just a note on the Fw 190, it was a very clever design and its electric systems (as well as other devices, such as the Kommandgerat engine management system) were quite advanced. It wasn't the first to so equipped. The Avro Manchester (and consequently the Lancaster) had multiple electrical systems, which took quite a bit of effort to get right.

nuuumannn said:

There's quite a big difference between a single seat fighter and a 250+ seat airliner. You need real power to move big flaps, big multi wheel undercarriages etc. Hydraulics has more grunt. Also, most airliners these days do have electrical systems that drive control surfaces, but coupled with hydraulics. If hydraulics wasn't needed, they'd not use it in modern airliners - as Biff pointed out, saves weight (electronic systems introduce their own degrees of complexity). ATRs for example have electric flaps, but rely on hydraulics for their undercarriage.

Besides, very few aircraft have been lost to multiple hydraulic system failure, normally, one system might fail, but extremely rarely both; I am aware of one such failure, in a 737, but considering the number of them in service use, that's a rare case. Normally hydraulic system failures are driven by some other consequence, like engine failure or such like - hydraulic pumps are driven by engines, but there are back-up electrical systems that drive stand-by hydraulic pumps, which prevent total system failure. cases where lines and components have failed do happen, but this doesn't always necessarily result in the loss of the aircraft. Considering the number of aircraft lost due to hydraulic system failure as a cause, i.e. very few, the use of hydraulics won't go away yet. Damn, more skydrol in the eyes...

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I have had skydrol in the eyes. Most unpleasant. A result from an ops check gone awry. The hydraulic mechanic cross threaded a B nut on a hydro pump R&R. When 3000 psi hit that nut, it exploded sending skydrol in every direction. Me standing 15 feet away got the brunt.
Most unpleasant to say the least.

If I recall correctly, it was a DC-10 in the late '80's that had a tail engine go out and as the fan section shrapneled, it took out the hydraulic lines which led to the crash. The design was changed to prevent this from happening again, but the bad reputation for DC-10's was cemented.

(ETA, edited for correct timeline)

soulezoo said:

If I recall correctly, it was a DC-10 in the late '80's that had a tail engine go out and as the fan section shrapneled, it took out the hydraulic lines which led to the crash. The design was changed to prevent this from happening again, but the bad reputation for DC-10's was cemented.

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Left engine being replaced with a forklift, which subsequently cracked the attach fittings. When the engine broke free on rotation, it took the hydraulic lines and fluid with it, and down she came.

Two different accidents Clayton. soulezoo is talking about UA Flight 232.

Using electrics to open and close the baggage compartment doors on DC-10's rather than hydraulics led to disaster. The airlines wanted electrics so they could open and close the cargo doors without running an engine or using a hydraulic ground unit. But if an electrically driven door latch does not engage you never know it. If a hydraulically driven door latch does not engage the unit starts screaming. The result was that if the door did not latch they found out when it blew off at altitude.

They had designed the DC-10 fuselage so that the controls all ran under the cabin floor. During testing the Genera Dynamics designed DC-10 fuselage failed when subjected to a simulated decompression. GD said they had to redesign it. MDAC said no, the DC-10 had to beat the Lockheed L-1011 out the door and there was no time. So when the baggage compartment door blew off the floor collapsed and took out the flight controls.

Clayton Magnet said:

Left engine being replaced with a forklift, which subsequently cracked the attach fittings. When the engine broke free on rotation, it took the hydraulic lines and fluid with it, and down she came.

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we had a safety class when I was in the maintenance dept and that case ( among others ) was sited. they tried to use an expedient method of hanging the engine back on but it overstressed either the mount or one of the bolts fracturing it. several accidents could have been averted has someone on the ground done something different...which was the point of the class.

Clayton Magnet said:

Left engine being replaced with a forklift, which subsequently cracked the attach fittings. When the engine broke free on rotation, it took the hydraulic lines and fluid with it, and down she came.

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Different accident. The one you are referring to happened at Chicago O'Hare.

DerAdlerIstGelandet said:

Different accident. The one you are referring to happened at Chicago O'Hare.

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United airlines flight 232, a DC10 that lost all hydraulics and flight controls due to engine fragments bleeding out all systems. Japan airlines 123 same situation with a 747 but caused by explosive decompression on a faulty repair.

Tragic on another level as USMC traffic controllers stationed in Japan had been listening on the unfolding events and had readied sea stallions with medics crews to repail down ropes. The offer was refused which meant survivors died overnight as Japanese rescuers hiked into the valley.

I recall a DHL hit by a MANPADS in Iraq. A incomplete list here.

Flight with disabled controls - Wikipedia.

"modern" systems just don't have enough segregation. The industry is just not as advanced as it thinks it is. The systems that boosts the tail should have complete segregation from one of the systems that run the ailerons and spoilers. No routing through the same point.

Prior to the most recent generation of airliners aircraft such as the 727 could revert to spring tab control.

A modern fly by wire airliner which have no manual backup, ie no cables or spring tabs should be able to convert it's ailerons into elevons if it lost its elevator for pitch/roll and spoilers for yaw.

You can distribute thermal batteries at each actuator and even use the aircraft WiFi to get to severed controls. Fancifull but entirely possible.

nuuumannn said:

Just a note on the Fw 190, it was a very clever design and its electric systems (as well as other devices, such as the Kommandgerat engine management system) were quite advanced. It wasn't the first to so equipped. The Avro Manchester (and consequently the Lancaster) had multiple electrical systems, which took quite a bit of effort to get right.

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I recall reading of Lancaster (I think) crew who were able to use electrical trim tabs to fly the aircraft despite loosing all control cables.

As an electrical engineer, there are a number of ways to lose all electronics, just as there are a number of ways to lose all hydraulics. As one who worked at a manufacturer of aircraft actuators (hydraulic, electric, electro-hydraulic, and electro-mechanical), I can say that all actuator types are electrically controlled already, even hydraulic ones (with a servo valve spool).

There are advantages and disadvantages to all types, but the vast majority are electro-hydraulic.

The plant where I worked had actuators on all US fighter and bomber types, most of the world's airliners, and many other aircraft, including foreign. We had actuators on the F-35, F-22, F-18, F-15, F-14, F-4, F-100, F-101, F-102, F-104, F-105, A-1, A-4, A-6 ... you get the picture, back into pre-WWII times. The actuator type is universally picked by the aircraft design entity, not by the actuator manufacturer. In the case of the USA, the government agency overseeing the design of an aircraft picks the actuator type. The actuator manufacturer offers options and suggestions, and even new development suggestions.

We designed one for a development exercise that could withstand a direct hit from a certain size popular ground defense cannon and still remain functional. The government funded it and the prototype still worked after the demonstration.

Yes, there HAVE been some complete failures. The frequency of these has been so low as to be almost non-existent. The number of flights per day of actuator-controlled aircraft is staggering, and the statistical possibility of complete actuator failure is lower than most would believe. In 2014, there were 37.4 million commercial flights scheduled. That does not include actuator-controlled business flights, private flights, military flights, or any other types of flights. So, even if the chances of failure are 1 in 40 million, it might happen in one year somewhere due to the sheer number of flights operated worldwide.

There are no completely failure-proof actuators anywhere in the universe to be had as an alternative, and the reliability of the existing actuators defies reasonable belief. We have actuators still operating on planes delivered in the 1940's and earlier, with nothing more than normal recommended maintenance and overhaul when due. Before I left the company, we overhauled one of ours that was delivered in 1935! It passed testing and went back into service (on a private aircraft).

nuuumannn said:

Besides, very few aircraft have been lost to multiple hydraulic system failure, normally, one system might fail, but extremely rarely both; I am aware of one such failure, in a 737, but considering the number of them in service use, that's a rare case.

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The statistical culprit here is the DC10, which was designed without adequate redundancy and fault tolerance in it's hydraulic and some other systems in the race to beat the L1011 to the marketplace. It won the race, but impacted air safety in a bad way. The L1011 was the better machine, but lost the race, and then suffered a sensational (flight crew error) accident right after entering service. The media coverage of this accident condemned the TriStar in the court of public opinion as it constantly referred to the recent notorious teething problems of the C5A. All these years later, the non aviation public who remember that crash mostly don't remember that it was crew error. Just another Lockheed failure. This was one of the first in the series of accidents that eventually led to Cockpit Resource Management.
Cheers,
Wes

The public doesn't seem to distinguish between machine-caused fatalities and man-caused fatalities. It has always interested me that the public thinks guns kill people instead of people killing people, but they ignore the same logic when it comes to the automobile or cigarettes or anything else they perceive they really need, even though it kills a lot of people.

That somehow should be addressed. If a man-machine fatality is caused by human error, the machine is NOT to blame.

The DC-10, incidentally, has a good safety record after design flaws were rectified, comparable to similar second-generation passenger jets.

GregP said:

The DC-10, incidentally, has a good safety record after design flaws were rectified, comparable to similar second-generation passenger jets.

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Some of the design flaws were never rectified, just worked around. And only after several ineffective modifications that didn't address the real problems. By the time that happened the damage had been done. The cabin was never properly vented to the baggage compartment with the vulnerable baggage door. They finally fixed the baggage door latch(after four tries), but the cabin floor would still collapse if another baggage door latch failed. And the hydraulic lines still run in the wing leading edge where they're vulnerable to impact. And they still run to the rudder right around the tail engine turbine case where an engine disintigration or a bird strike can take out the rudder circuit. Al Haines' Sioux City landing could still happen again. Except there are hardly any DC10s left in domestic sevice. The Ten's PR record has way outshined its safety record.
Cheers,
Wes

Actually, the Sioux City crash couldn't happen again because of the hydraulic fuses that were added to the hydraulic systems after that event. The fuses probably should have been added after Chicago but the fix for that was procedures. (I'm a United mechanic and primarily worked heavy maintenance on DC-10s - and then 747s - while we had them.) What was fatal to the Sioux City plane was the extensive damage done to the two hydraulic lines (different systems) coming outboard along the aft stabilizer spar to the R/H elevator actuators and one small bit of damage that severed the third system's line coming outboard along the forward stab spar and through the stab box to the same actuators. Dumb, but thorough, luck.

The B787 has replaced the bleed air systems and, of all things, the brakes with (massive) electrics. The engineers really like the electric brakes but we're experiencing some reliability issues with them (we've got the Goodriches). The three hydraulic systems are 5000psi. woohoo