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Switch on the circuit breaker of the mechanical-electrical VDM-automatic system (on the right cockpit sidepanel next to the rudder pedal) and the circuit breaker for the entire adjustment system (on the main distribution panel). Switch (below the throttle lever) on "Manual". Move middle thumb switch (on throttle lever) back and forth and then leave at 12 o'clock. Switch at "Automatic system ON", the screw must now run at 1 o'clock (valid only for DB 601 N). If the screw runs further, then the accumulator voltage is too low. If the accumulator cannot be replaced, then use the automatic system only in the air (at RPM over 1900).
Screw adjustment system (operation)
a) Generally, "automatic system ON".
At the start of a power dive by "pressing" and with quickly throttling up, impermissable overrevving of the engine is to be expected. Careful!
When idle-gliding with an indication of less than 200 kph the automatic system should be switched off (switch on the throttle lever) or take care not to exceed the final limit.
b) Economy flight (max. reach, barrier) by precisely keeping the RPM and boost pressure according to the range table through manual control.
Before diving, switch to "automatic system ON"
For feathering and with failure of the automatic system also set the screw manually.
c) When flying on manual adjustment with functioning automatic system, then the folding interlock must not be flipped up. With a malfunctioning automatic system, the interlock should be folded away.
d) If a dive is started with a switched-off automatic system, it is not allowed to switch to 'automatic' by giving full throttle at high speed, otherwise the engine will overrev.
e) When flying with manual adjustment, take care that the air screw is not set over 12 o'clock and further, for the limit is only at 1 o'clock. (For DB 601 N)
Here's another question, also about the automatic system overshooting. This is the section describing the use of the manual and automatic systems in flight:
View attachment 680664
Screw adjustment system (operation)
a) Generally, "automatic system ON".
At the start of a power dive by "pressing" and with quickly throttling up, impermissable overrevving of the engine is to be expected. Careful!
When idle-gliding with an indication of less than 200 kph the automatic system should be switched off (switch on the throttle lever) or take care not to exceed the final limit.
b) Economy flight (max. reach, barrier) by precisely keeping the RPM and boost pressure according to the range table through manual control.
Before diving, switch to "automatic system ON"
For feathering and with failure of the automatic system also set the screw manually.
c) When flying on manual adjustment with functioning automatic system, then the folding interlock must not be flipped up. With a malfunctioning automatic system, the interlock should be folded away.
d) If a dive is started with a switched-off automatic system, it is not allowed to switch to 'automatic' by giving full throttle at high speed, otherwise the engine will overrev.
e) When flying with manual adjustment, take care that the air screw is not set over 12 o'clock and further, for the limit is only at 1 o'clock. (For DB 601 N)
Once again, it seems as if the automatic system is capable of exceeding the limits of the propeller. It makes sense that with engine power at idle and at low airspeed, the automatic system is trying to maintain a minimum rpm, and thus reducing the blade angle as much as it can, but is there really no safeguard in the system to have it stop reducing blade angle automatically when the limit is reached? How far is the automatic system capable of reducing the blade angle beyond the limit? Is it also possible to exceed the limit in manual mode?
Lastly, a few related questions:
The manual consistently gives the clock limit for blade angle as 1 o'clock, but apparently only for the DB 601N. Do you know the limit for the 601E, or 601A?
What is the minimum rpm the automatic system will try to maintain? I know at max boost, it will maintain max rpm, and lesser rpm corresponding to lesser boost, but it seems there would have to be a point where a minimum rpm have to be maintained at boost settings lower than a certain limit.
Similarly, what input is the automatic system referencing when determining the correct rpm to maintain? I don't think it can reference boost pressure directly, since above full throttle height, boost pressure decreases even with the throttle lever full forward, and if the automatic system started reducing rpm in response, boost pressure would drop further, causing the system to further reduce rpm, and so on. Obviously that won't work. So is it referencing the physical position of the throttle lever or linkages somehow?
Assuming a high speed dive with a low power setting in automatic mode, the automatic system with be increasing blade angle to maintain the correct rpm. Is there a max angle the system will move the blades to, which upon reaching, will no longer be able to prevent rpm from rising?
How fast does the motor change blade angle?
Thanks for any insight you can give!
Thanks Snautzer.Thanks Eng. Enjoying your replies on this.
So, firstly to comment upon the description of the pitch indication "running too far " with low battery voltage. This description is thought to be a problem with interpretation or the technical writers understanding. As you probably know, the electrical pitch motor (EVG, 14501) is a reversible 24v electric motor with range of operation electrical contacts that cut the operation at a minimum (fine) setting and at a maximum (coarse) setting. Each end position disconnects the contacts for operation in that direction but leaves the contacts for operation in the opposite direction still available, if the selection the other way is made. This is to prevent the motor stopping forever at one end of travel! So, the electrical path is broken at the end of travel and the motor stops, in this case "1.00 O'clock". With low battery charge, the motor may not run all the way to the end stop before stalling and the electrical contacts may still be applying the low voltage/current although the motor is stalled. This is the condition that is described. Additionally, the switching of the power is done by relays and, they may fail to maintain good contact at low voltage. Also, some pitch indicators are electrical operation, that might have been an issue with indication at very low battery. In use, the system has no problem of "running past the limits" or "overunning at low battery".
Next point soon!
Eng
Here, we must comment upon language. These instructions often translate with quite blunt warnings about "limits" etc. I think that the general style is a little stern. Also, the descriptive terms used are often strange.
To note, this propeller control system in "AUTOMATIK" uses a simple cam controlled speeder-cup regulator for engine RPM. The regulator cam profile is designed to give a bias on the spring force in the regulator that gives a specific RPM versus the throttle position. There is no sensed link to Manifold Air Pressure MAP.
At low throttle position, the controlled RPM will be low and the combination of fast throttle movement with very steep dive could cause the engine to overrev.
The usual caution is given for flight where the propeller control system may be at or near its range of travel. This seems overstated, and they would rather that the pilot switch off the system "HAND" for low throttle, low airspeed descents. Also, there are cautions to avoid "limits", which in this case is probably the fine position cut-off.
Manual prop control was used for long-range flying with precise engine RPM/MAP. The caution to switch back to AUTO "before diving" is again curious, as it applies to all forms of flight after completing the range flying.
Item C. Again strange words, the word MUST is strange, especially as item D says you can't just use the interlock to select AUTO. They are mixing incomplete descriptions of how to manage the system with partial orders that do not cover all scenario's.
Item E basically does the same old caution of not setting too fine a blade pitch as you can easily overrev.. but it doesn't say that!
Your last two questions about "limits" should now be answered. The Automatik and Hand operations have the same theoretical range of blade pitch but, the function of the Automatic control is simply a product of the throttle lever position and actual engine speed.
Eng
Hi again,
The blade angle pitch limits are given for different aircraft, engines and propeller types. These are really the design range of movement. However, the figures given do have some tolerance and, there is a "fudge" factor for engines and propellers that perform slightly differently at the "12 o'clock" pitch setting for Take-Off, as a repaired or shortened prop will do. I am not sure what you need the figures for, but the Bf 109 fine pitch cut-off for the 601A/N would be about 1.00 o'clock, the E about 12.45. The actual setting figures are about 15min less but, that is the difference between the setting and what you get with a running system.
The minimum rpm speed in AUTO is about 1700, but the generator drops off line about 1900 rpm and the battery was small.
The rpm in AUTO is selected by throttle position and the throttle linkage to that cam on the regulator.
The max blade angle is very coarse, in fact it is feathered on the Bf 109 F-2, about 85 degrees at the 0.75 radius setting position.
The basic pitch change rate is 1.5 deg/sec
Cheers
Eng
So, does 1700 rpm correspond to the idle setting of the throttle lever, or does everything less than some higher position of the lever yield a target rpm of 1700, and above that point a linear increase to max rpm at full throttle? Is 1700 rpm the standard minimum setting across all the DB variants, or is there some variation between different models?
How does governor mechanism compare to the hydraulically operated CSP systems on allied aircraft in terms of sensitivity and responsiveness? Will it hold RPM as precisely, with constant tiny adjustments, or will it wander a bit more? Assuming a responsibly fast throttle movement, is it more or less prone to overshoot the target rpm and yo-yo back and forth?
Is the 1.5 deg/sec speed the only speed that will be used, or will lesser voltage be supplied for a slower rate of change for smaller adjustments?
My purpose for all of this is building a computer simulation of the operation of the engine in various variants, starting with the DB 601N and E on the Bf 109F. I'm trying to get all the details right. Currently I'm working through the propeller, but the coolant, boost control, oil, supercharger, etc, etc are all on the list as the project progresses.
Once again, thanks for you help!
Dan