Electric Vs Hydraulic?

IIRC the Stirling had electrically actuated u/c and it was terribly unreliable and having refurbished one of the gearboxes, unnecessarily heavy. lThe manual lowering of the u/c works in almost exactly the same way as the Herc in that a locking pawl is disengaged allowing a handle to be rotated. A job to be given to the lowliest member of the crew/erks (delete as applicable:diablo:)

Pneumatics had other problems too !!
Internal moisture and all its demons possibly the worst !!

cheers baz

Does anyone know if Dunlop were the first to introduce pneumatics onto an aircraft – brakes on an Avro Avian in 1932.?

Re 2hotwot’s comment about British industry championing pneumatics, Dunlop had a tussle with the Air Ministry in 1939 when AM decreed that all future “large” military aircraft were to have hydraulic brakes. Privately organised trials on a Halifax showed pneumatics to be superior over the low-pressure hydraulics. The later high pressure hydraulics were better. (Info from “We Re-invented The Wheel” by Ron Vice)

Roger Smith.

Does anything modern still use pneumatics?
I know that the British aircraft industry championed it but I have also heard pilots swearing at it for unreliable brakes in particular.
Also noted how Spitfire legs sometimes don’t retract quickly when someone pulls G during the retract cycle.

Not that I’m aware of, apart from de-iceing boots, although I remember reading recently about potentially using engine bleed air and air motors to replace hydraulics.

Also, early variable pitch propellors used to be electric but since changed to hydraulics.

Does anything modern still use pneumatics?
I know that the British aircraft industry championed it but I have also heard pilots swearing at it for unreliable brakes in particular.
Also noted how Spitfire legs sometimes don’t retract quickly when someone pulls G during the retract cycle.

Lets not forget that other power source used on aircraft to power things – Pneumatics.
Aircraft like the Dove had pneumatics for flaps, undercarriage and brakes.
Air weighs less than hydraulic oil (and copper string for that matter) and if you have a leak you’re flying in the stuff you need to pump back in.

The C130 doesn’t really use electrics to operate it’s main undercarriage or flaps.
The selection is electric but the ballscrews are operated by hydraulic motors (via drive shafts and gearboxes).There’s a separate hyd motor for each side on the main undercarriage and a single, central one for the flaps.

All three hydraulic motors can be disengaged from the drive system to be hand cranked in the case of hyd failure. The undercarriage can also be disengaged so it free falls.The nose leg operates on a big ram and there are a few ways it can be operated if the main system fails.

The only electrically operated controls are the trim tabs (aileron, elevator and rudder). The air deflector doors and oil cooler flaps also have electric actuators.

Depends how it is spoken about, most hydraulics are electrically actuated. I thought thet Herc flaps were operated by electric screw jacks though?

The systems I’m familiar with have a pump that supplies fluid under pressure to a jack, that’s controlled by a mechanical connection to the pilot’s controls. Modern fly by wire stuff replaces the rods/cables etc. with electric string, the advantage with the former, in some cases, is that you retain a degree of control if you lose hydraulic pressure.
Not totally sure about Herc flaps, I’d imagine depending on the deployment time you could have an electric drive as the motor wouldn’t need to be as powerful if you could accept a pause between selecting a flap setting and getting it. Obviously with flight controls you can’t make that trade off. Mind you if you’re already developing hydraulic pressure at 3000psi, why not use it for the flaps!

Not a new idea even for the limited electric actuation in the C130…….the earlier Boeing B29 and Vickers Valiant were nearly all electric actuation (including control surfaces, hi lift & Landing Gears = Valiant – really big rotax jobs……. also Valiant brakes and Nose wheel steering remained hydraulic).

For big Actuators
Electric is heavy, no really heavy even with the latest motor technology (Don’t allways believe what the saleman tells you).
Electric is expensive, no really expensive, lots of Swiss watch type gears, overrun brakes, clutches, ball bearings, precision ground roller screws etc
Electric is inefficient, lots of friction losses at each gear/ bearing stage <75%
Electric has lots of nasty jamming type failures, plenty of nooks and crannies for stuff to jam in.

But in certain application electric is good;-
Smaller high power density hydrualic becomes less competative and electric system makes power distribution a dream

True Hydraulic can leak a bit but;-
Load for Load < half the mass of electric
its cheap – two tubes, a few seals and your away
its highly mechanically effeicent 90%+
and with just two tubes what can go wrong and spoil your day!

Depends how it is spoken about, most hydraulics are electrically actuated. I thought thet Herc flaps were operated by electric screw jacks though?

I think a lot of larger aircraft use hydraulics because it’s only recently been possible to get electric actuators man enough to do the job but light enough to be used in an aircraft. I’m certain the Hercules has hydraulic flight controls, actually having just googled it they do along with the flaps u/c etc. with two hydraulics systems. There may be some sort of electric reversion mode but I think that refers to a back up pump.
The other problem is generating the required levels of power.
Westlands have been trying to replace the hydraulic controls on a Merlin with electric actuators but they’ve been having reliability problems.

Youv’e also got electro hydraulic actuated U/C componants in aircraft.
Thought most flap mechanisms were electrically and mechanically operated