Hand Pumps and Oil Pressure... How to Fly a WWI Plane?

stephen · 24 October 2006, 01:27 PM

The German planes had a switch to control the air pressure inside the fuel tank (labeled "druck" on the instrument panel), and another switch to control oil pressure ("oldruck"). Any information on precisely how these controls were operated would be appreciated.

- Was the air pressure inside the fuel tank operated by a hand pump, and was the hand pump the primary means of pressurizing the fuel tank or was it a backup system for a mechanical pump?

- What does "auf" and "zu" mean in German... "off" and "on?"

- What does "druck" and "oldruck" mean in German... "pressure" and "backpressure?"

- If so, why would anyone want to turn the air pressure and oil pressure off? Both seem rather critical to powered flight.

I'm trying to understand exactly what the DRUCK and OLDRUCK switches did and how they operated. Thanks for your thoughts.

Romani · 24 October 2006, 03:40 PM

Quote:

Originally Posted by stephen

T
- If so, why would anyone want to turn the air pressure and oil pressure off? Both seem rather critical to powered flight.

It seems to me that for whatever reason (like fire or risk of fire due to battle damage or breakdown) you want to cut the fuel feed to the engine, it would be a standard safety measure to drop the air pressure in the fuel tank as well.

Maxim08 · 24 October 2006, 04:47 PM

To partially answer your title, handpumps for air pressure in the fuel system were used to build pressure in the fuel prior to the engine or wind driven pump being operative. Many engines used pressurised fuel systems to push the fuel to the engine as opposed to fuel being sucked out via a fuel pump.
Pressure from the handpump would be disengaged / switched off, after the fuel sytem was up to pressure.
The Smithsonian book on the Albatross restoration has a very complete description of starting and running a Mercedes inline engine. All of the valving etc is explained there. Can't find a copy right now, perhaps someone will scan it for you??
Regards,
John

bshatzer · 24 October 2006, 09:34 PM

"Ol" (with an umlaut over the "o") is oil.

I would assume "oldruck" is just "oil pressure".

rammjaeger · 25 October 2006, 12:15 AM

Stephen,

auf = on (open)

zu = off (closed)

Druck = pressure

Öldruck = oil pressure

Romani and Maxim08 made already points concerning the explanation.
I leave a more comprehensive explanation to the "Flugtechniker" on the Forum because my English technological vocabulary is not comprehensive enough.

VBR
Rammjaeger

stephen · 25 October 2006, 05:58 AM

Okay, let's see if I'm getting warm here...

German aircraft used release valves to maintain the correct air pressure inside the fuel tank and to regulate oil pressure. Prior to starting the engine, the pilot used a hand pump to pressurize the fuel tank. Once in flight, a wind-driven or mechanical fuel pump became operative and maintained fuel tank pressure that was regulated by a release valve. The oil pump relied on a similar valve for pressure control. Switches manipulating these valves were located on the pilot’s instrument panel. The switch for fuel tank air pressure valve had a steel placard labeling it “Druck” (German for pressure) while the oil pressure valve placard read “Öldruck” (oil pressure) and each had a setting for “open” or “closed” (auf and zu).

How am I doing so far?

Then, if the air pressure inside the fuel tank or oil system was too great, it would be manually released by opening the proper valve for a few moments?

R Pope · 25 October 2006, 06:44 AM

I would think the shutoff valves were on the lines leading to the system, so the pressure was shut off from the pump. That way, no back pressure could reach the hand pump in the cockpit.
Also, when the engine was shut off, the pressure in the gas tank would be relieved to prevent possible flooding of the carb.
This is not from any specific knowledge of WWI engines, just general stuff from years of playing with antique machinery.

Greybeard · 25 October 2006, 06:54 AM

There's an important thing to specify: inline or rotary?

Indeed, only a rotary should require oil under pressure, an inline doesn't make sense: just a scavenging pump that sucks oil from carter and pumps it to camshaft should be required, all in a closed circuit, since dry carters I think still weren't used.

On the contrary, rotary engine need pressurized oil to be injected into hollow crankshaft, as well as fuel.

I heard also of pressurized fuel tanks ALWAYS kept pressurized by pilot-driven hand pump (no mechanical or wind-driven pumps), feeding gravity tanks into upper wing.

About valves, I think they could be closed only after landing, to shut-off engine, prior to switch-off magnetos.

Ransom E. Olds · 25 October 2006, 10:12 AM

The oil pressure gage is only a gage, not a means of adjusting oil pressure. If there were a means whereby the operator could actually adjust the pressure of a running engine I'm sure J. C. Whitney would have offered one, or several, in his estimable catalog. Ransom

stephen · 25 October 2006, 03:12 PM

Quote:

Originally Posted by Ransom E. Olds

The oil pressure gage is only a gage, not a means of adjusting oil pressure. If there were a means whereby the operator could actually adjust the pressure of a running engine I'm sure J. C. Whitney would have offered one, or several, in his estimable catalog. Ransom

I agree but then why does my OLDRUCK (oil pressure) gauge placard have a position for "on" and "off?"

Make'um no sense'um.