Luftwaffe engines

TAS · Post by **TAS** » 24 May 2003 15:17

Does anyone know why the Luftwaffe intentionally desyncronised their engines? i've heard repeatedly how the Brits could tell the difference between the friendlies and non from the syncronization. i figure it was either decidedly intimitading, or more fuel effecient, but i also wonder if it increased wear on the frame of the aircraft. would that also affect accuracy of the weapon systems?

Matt L · Post by **Matt L** » 24 May 2003 21:32

Hi TAS,

I've read that Luftwaffe bomber pilots often changed the revs of their engines to confuse ground observers about their altitude- thus making it more difficult for AA gunners to engage them effectively.

Matt

gabriel pagliarani · Post by **gabriel pagliarani** » 25 May 2003 01:11

If "desynchronize" means to change the typical roar of an engine, it was easily done by cutting off fuel to some cylinders only for a while and just before breakings. It was easy to do on german liquid-cooled engines because feeding was obtained by mechanical injection directly in the cylinders. A sort of easy cut-off was reasonable at low power regimen by cutting the injection to a certain number of cylinders simply by closing a fuel-valve. Allied used only carburetors and the partial "cut off" of carburetors is very hard to obtain. But the change of roar was effective in the attempt to "inquinate" "acoustic Doppler effect" detection necessary to understand the ground speed of the bandit. During WW2 there were not Radar Doppler and the same effect was obtained by detecting the standard acoustic frequency of the bandit's engine: raisin frequencies = bandit coming, lowering freq.= bandits outgoing.

varjag · Post by **varjag** » 25 May 2003 12:16

Hey Gabriel - how do you mess with the fuel-injector pump - to starve some cylinders? It's mechanically operated by the engine itself and should distribute fuel equally to all cylinders or none..? This sounds fanciful - let me know?

gabriel pagliarani · Post by **gabriel pagliarani** » 25 May 2003 18:52

I have seen a MW-50 mounted on the german original DB605 over the MC205V reply now held in Vigna di Valle Air Museum. At least 20 years ago old AMI mechanics and veterans where evaluating the possibility to reproduce a MC205 starting with the second airframe they could build up with the spare parts of a MC202 previously rebuilt. The engine was pulled up by a fisherman just facing Anzio: the remains of the german pilot and the Bf109G were found and buried only 10 years later. Piece by piece was completely restored and I had the luck to be invited for a show. The direct injection system was very similar to a std. Diesel mechanical injection system. There was an alternate pump with 4 little pistons driven by an helycoidal gear probably rotated by one or more valve-shafts, a drain collector and a rotative distributor linked direcly to the main shaft. The big difference I noted was in the mixer-mechanical analogic computer, similar to a big watch. The main differences between an injecting system for Otto engines and the same for a Diesel are in timing (to be anticipate on Ottos) pressure and quantity of fuel. In a Diesel if you need more power simply open fuel valves and more the fuel more the power: in a Otto engine the same but with a "stechiometric" mix of fuel disperded in air as aerosol. This mix could vary from 1 Mol of gasoline in 16 Mol of air to 1:20. But the quantity of air is linked to the partial pressure of Oxygen (20% of total) and relative pressure of air, because a plane can be feed at 1 Atm at ground till 0.01 Atm at 10000 mt. Therefore the opening of fuel jettisons was mechanically linked to the variable "throat valves" of air (...or papillons) and to a double absolute Vacuum baromether adjusting the opening to the ext. pressure. every injector was controlled by more than a tiny mechanical shut off.valve: the adjustements were memorized on a half rotating disk working as a carillon built in the "negative" mode. The carillon has the memory on the active gear, in the while MW50 had it on the receiver gear. Another section supplied the overboosts: over a certain fuel openings and/or ext.pressure was lowered, a secondary injecton system was able to inject methanol or peroxide or both with a third "kit" not present there. Injectors were fed 3 x any position of the distributor, 1 position x stroke, 4 strokes, 12 cyls. It was easy to cut off 3 cyls each time, if this is your question. This is all that I know about that fuel system.
I am sorry, but I saw all these things half an hour 20 years ago...

Xavier · Post by **Xavier** » 25 May 2003 19:59

I love your posts Gabriel!!!

on cummins brand engines, the so called "engine brake" (jacobs brake or "jake" for the truckers) the engine stops (slows down) the truck by mechanichally keeping the injectors cancelled on 2-4 or the 6 cilynders and letting the chambers fill with air and not making combustion.... this is made on demand via micro switches (electrical) conected to electro-oleo-mechanichal plungers on top of injectors...

Xavier
the link scrounger

varjag · Post by **varjag** » 26 May 2003 03:29

Thank you very much Gabriel for that explanation. I (think) I get the point.

gabriel pagliarani · Post by **gabriel pagliarani** » 27 May 2003 09:15

Thank you, but it is too much for a thing so small.
I forgot the deicing procedure tested by Lindbergh: simply shutting off a magnet he caused some blasts in the exhaust pipes and vibrations consequently broke icy formations in the inlet duct of carburetor. But it was a dangerous manouvre. Someone during airshows does the same thing to simulate an engine failure or a shot-downing. The big risk is in an explosive back-flame. Probably modern sparking circuits applied on old 4 stroke engines avoid this kind of risk.