DB-60X manifold pressure handling

"Maybe somebody found directions to the pilots how to handle the MP in these conditions?

I see only one way to get full performance: switch the prop to manual pitch control, fully advance engine lever and set the desired rpm again using manual rpm control."

"You are right and wrote exactly what I mean (except the fact that at 2300 rpm and 5500 m the supercharger can give exactly 1.15 ata - it must be calculated if it's so). As the main throttle is not fully open there is only one hint allowing to get full supercharger pressure as MP - switch to the manual pitch control, then fully advance the engine lever and set desired rpm manually controlling prop pitch."

that doesn't appear to be what Yo-Yo was saying.

I think the key word here is 'full performance' I imagine with a lot skill and flight time a highly skilled pilot could get the aircraft to reach higher limits than the automatic system.

Remember these automatic systems are essentially the precursor to the modern flight envelope computers of course there would be inadequacies with the automatic system but when you are in a dogfight would you really prefer to be keeping an eye on everything or just let the automatic system do the job and halve your work load.

That said I have heard when the system was brought to the 109 some of the more experienced pilots realized they could do the job better than the automatic system and indeed didn't use it.

That is sort of what I figured. Although having to operate the engine manually to obtain full performance would be a pain in the ass. Anyhow I that is all I wanted to know.

You do not get better MP on the 109 by switching back to AUTO due to the how the system works (already described). It just might be possible to squeeze out an extra shaft hp or two from the engine by reducing rpm slightly with manual rpm control, but the whole thing just doesn't make sense on a combat aircraft. Or any aircraft for that matter, as the aim would be unrealistic - to nullify common losses in the system itself.

For special, very low power range/endurance maximizing cruise conditions, fiddling with manual rpm could be advantageous and was prescribed (ie. manually set given rpm for given ata pressure). However these are special, static state cruising conditions where it isn't really a problem.

Otherwise "full" power is obtained by fully slamming the throttle forward, manual or automatic...

 

That said I have heard when the system was brought to the 109 some of the more experienced pilots realized they could do the job better than the automatic system and indeed didn't use it.

Any sources? I've read pretty much all top german (and finnish) 109 aces books available and never read anyone would have done that.

iirc in spitfire on my tail steinhilper describes that some pilots refused to use the auto-prop system in the E4s...of course thats early war but still, i cant give exact sources now, but im pretty sure, that ive read it several times in several books,articles and the like...

Ok, thanks. I should read his book too. Let me know if you find anyone who refused to use it in F-K series...

At settings below Kampfleistung you could disable automatic prop pitch, and maintain rpm while increasing boost by moving the power lever forward. This is just like any other aircraft. However, many other aircraft had the throttle gradually open up fully at high altitude, so there'd be the optimum full throttle altitude also at lower boost settings. The DB did not, so at high altitude, at low power settings, disabling automatic pitch could give you higher boost at the same rpm. On the other hand, if you needed more power at high altitude, you could leave automatic pitch and increase rpm along with boost for an overall much bigger effect - on the bottom line, manual pitch would only allow you to fly maximum boost at reduced rpm.

The DB did not, so at high altitude, at low power settings, disabling automatic pitch could give you higher boost at the same rpm.

No, no, no.... read the pages I posted. For high altitudes, there is an override switch for the (1st) Reglerklappe, which opens it fully. In addition, the s/c always delivers ca. 0,05 ata extra pressure.

The "could" part is only possible if the unified throttle setup was somehow incorrectly linking boosts and rpm at lower settings, but i strongly doubt those engineers would be that amateurish..

You can maybe decrease rpm a bit at manual for the same boost, so as to use all that "extra" 0,05 ata that is wasted.. and maybe gain.. well about 20 PS perhaps, and say 10 liter saving in fuel.

The Reglerklappe is not the problem, it is fully open at high altitude without any overrides. But if you reduce boost to below 1.30 ata (DB605A), the Leistungsklappe is not fully open and will not be adjusted. If you set the engine to 1.15 ata, it will reduce boost from 1.30 to 1.15 or ~proportionally at higher altitude.

Yes it is not possible to separately adjust MAP and RPM w/o disabling automatic control first.. I probably misunderstood your post, however I think the only practical application would be special (reduced) settings for max endurance and perhaps, range.

However if you reduce rpm, supercharger capacity will suffer as well.

Yes, at high altitude on manual, on the bottom line you'll be able to reduce resistance in the manifold a little bit and it will have a small, positive impact on endurance / range. I doubt it will even be a two digit percentage. Under the same conditions you'll get more performance by increasing rpm along with boost and for that can leave everything on automatic.

The Reglerklappe is not the problem, it is fully open at high altitude without any overrides. But if you reduce boost to below 1.30 ata (DB605A), the Leistungsklappe is not fully open and will not be adjusted. If you set the engine to 1.15 ata, it will reduce boost from 1.30 to 1.15 or ~proportionally at higher altitude.

Not sure I'm following this. Your post and previous ones seem to be saying that the blower has a staged output which I don't think is the case, it's continuously variable. Thus in the case you raise, my conception of operation is that setting the power lever to 1.15 ata the blower provides circa 1.20 ata and will continue to do so at whatever height (increasing output in response to changes in barometric pressure) until the blower is physically unable to do so.

The two feed lines between the throttles react to the the pressure changes which occur when the throttle is moved and one of these controls fuel metering for the injection system. (This why the throttle valve cannot be opened fully?).

I read the diagram as a mechanical feedback system where the engine is given "optimum" air/fuel mixture at whatever throttle setting or height until the blower runs out of breath. You appear to be suggesting something else or do I have the wrong end of the stick?

As for manual prop pitch, I know of only one use of it in later 109's and that is as K has suggested for long steady cross country flight. (Even then this use of manual prop pitch is implied. It's from the English translation of the G6 pilot notes. It also gives a use of it when doing a forced landing where the prop (presumably not turning) is set to 6 o'clock. I don't think it's realistic to think anyone would have bothered with it TBH.

I was talking about high altitude, where the blower no longer is physically able to provide the boost. As a sidenote, the blower does not provide constant ata over altitude, as can for instance be seen in the chart Kurfürst provided in post #16. The 1.30 ata setting delivered up to about 1.8 ata, in which case the Reglerklappe cuts off anything above 1.30 ata. At sea level, 1.30 ata are still being exceeded even at the 2100 rpm setting and the Reglerklappe need to regulate.

At what height does the Reglerklappe fully open and stay open?

When pressure between the two throttles drops below 1.30 ata. This depends on a few things, like engine rpm and speed, but taking the chart in post #16 as an example - Kampfleistung at 2600 rpm in level flight - it happens at 6100 m.

Thanks for the reply. I am still digging for info about how the db605 operates.

I have discovered that the system seems to work in the way I imagined it did, in that the primary control is the cockpit power lever which gives a blower output for a given setting, ie 1.3ata. The Reglerklappe appears to work and act only as a limiter if blower output is exceeds 1.3ata when the throttle is set to 1.3ata. The "Reglar" kind of gives the game away.

It appears the overblowing by the blower from the ground up to 2.2km is due to the oil pump running at fixed output (max?) that provides the oil to the hydraulic clutch that drives the blower fan. I.e. the blower speed is fixed up to 2.2km (in this diagram we are discussing, the k4's engine's first power peak is at circa 1km.)

There is a second oil pump that also feeds the hydraulic clutch but in relation to barometric pressure changes, speeding up the blower as pressure drops off. In K's diagram we see a more or less continuous and steady blower output at 1.3ata from 2.2km up as a result of the action of the second oil pump.

From the diagram it would appear. that the Reglerklappe is fully open at 2.2km and stays open from this point up unless pressure exceeds 1.3ata, whereupon it would regulate by closing somewhat and as you say be wide open at FTH. I stiil don't fully understand the why of first power peak that all DB engines have. Still digging.

Simply put, it is the full throttle altitude of the first charger gear. As you say, below that altitude there is a constant volume of oil pumped into the supercharger coupling, which costs power, more in the denser air down low, just as if it was a fixed coupling as on any other aircraft engine at the time. It's wasted power to excessively compress and then throttle air (sea level) instead of compressing it to the required level, without any throttle (2.1 km). Also supercharged air temperature drops up to the 2.1 km mark (DB605A), resulting in more power there then at sea level.

Yes, I was wondering about the round about way they handled the blower up to 2.1km. My best guess was that it was somekind of safety measure in there was a need of instant boost to climb over some obstacle that popped up soon after take off.

Thanks for the temp clue, but does not temperature continue to fall up to 30 000ft? (Thinking here that blower fan and fan drive gear raise temp a bit above 2.1km? and thus small drop in power?)

The temperature of the supercharged air increased up to 5-6 km, depending on rpm, where the supercharger reached maximum rpm with the coupling fully filled with oil. Above that, air temperature dropped down again. As an example, the curve in the DB605A manual for 2600 rpm gives 70°C at sea level, 58°C at 2100m, rising to 98°C at about 5.5 km and down to 70°C at 11km, because outside air gets cooler and compression remains constant above full throttle altitude.

As to why they handled the low altitude supercharging the way they did, I can also just guess. I suppose they wanted to have higher boost at lower rpm, too, for instance when taking off with manual 12o'clock pitch, where the engine would start with low rpm and only catch up during the take off run, not supposed to exceed the rpm limit until after gear up. The way it is, 2300rpm will already give you the ~1.42 at sea level, certainly good to have, might be what DB had their eyes on.

As to why they handled the low altitude supercharging the way they did, I can also just guess. I suppose they wanted to have higher boost at lower rpm, too, for instance when taking off with manual 12o'clock pitch, where the engine would start with low rpm and only catch up during the take off run, not supposed to exceed the rpm limit until after gear up. The way it is, 2300rpm will already give you the ~1.42 at sea level, certainly good to have, might be what DB had their eyes on.

Another possible explanation is the camshaft profile used in the DB 605 allowed for 105º of valve overlap compared with, for example, the Merlin which had a 43º overlap. See also:

http://www.enginehistory.org/German/daimler-benz.shtml

DB 605 start and run

How on earth is valve overlap and supercharger control is related??

The actual boost in the engine is regulated by the performance valve anyway... and besides the fact that the DB 6xx supercharger control principle waaay predates the extended valve overlap (which appeared on the 601E).The generous valve overlap, if anything, is a benefit of the precise timing possible with direct fuel injection vs the more orthodox method.

Personally, I believe the fixed first speed on the DB series is simply because its much simpler and foolproof to do that this way, rather to overcomplicate things with a double barometric clutch control, for the benefit(?) of a mighty 50-70 PS extra at a rather useless low altitude range... especially with later, MW boosted engines, where the (barometrically controlled) second speed kicked in at ca 600 m altitude already. That being said, the fixed ratio might has to something with the early 601 series lower rpm and special take off ratings - presumably for bombers.

How on earth is valve overlap and supercharger control is related??

The timeline you mentioned disproves it, however you could reasonably think that they'd increase low RPM boost to compensate for a cam with more overlap, which doesn't produce as much power away from peak RPM.

The timeline you mentioned disproves it, however you could reasonably think that they'd increase low RPM boost to compensate for a cam with more overlap, which doesn't produce as much power away from peak RPM.

Does Kurfurst actually know when the "DB 6xx supercharger control principle" incorporating two throttles, was first set out? This patent for a Daimler-Benz hydraulic supercharger was filed in March 1938, but Kurfurst is forgetting that Daimler-Benz started building the Rekord (R series) of racing DB 601s at around this time; the RV in the record breaking He 100 V8, for instance, "ran so roughly" it could very well have had a "wild cam" with lots of valve overlap; also note that there were only two throttle settings available:

(From Heinkel He 100:Record Breaker Erwin Hood, page 52. )

Who's to say that with this experience in racing engines, that DB hadn't designed the supercharger to allow for future power increases, including the possibility of using more extreme valve timing overlap? The chances are excellent that the DB 601E and DB 605, and their superchargers, were designed with the benefit of experience drawn from the DB 601 R. series.

Friedrick. where to start...

Have a look at post 16in this thread, the 605a power graph. It clearly shows the power lever set to a setting of 1.3ata yet the blower on the ground is putting out 1.42ata, but the engine is only getting 1.3ata! This is because of the reglerklappe which prevents engine overboost as it's supposed to, ok? So why was this? Most likely is Kurfurst's pragmatic explanation of keep it simple stupid (KISS). This also made the engine very responsive, I imagine, when the lever was pushed rapidly forward.

As for,

"Who's to say that with this experience in racing engines, that DB hadn't designed the supercharger to allow for future power increases, including the possibility of using more extreme valve timing overlap? The chances are excellent that the DB 601E and DB 605, and their superchargers, were designed with the benefit of experience drawn from the DB 601 R. series. "

You're going to have to buy more books. With a FTH of only 6.5km the blower in 1942 was just about adequate. Set is relation to the knowledge in 1942 that Boeing were developing a bomber (B29) that would fly at 16km and be over Germany in 1943, can you imagine the panic in the German high command? Clue, they had no aircraft that could even fly that high and not even one on the drawing board at that stage.

That the Db605 and late 109's were as good as they were was something of a miracle, needed the bigger 603 blower and needed mw50 to stay competitive. Be under no illusions, the clock was ticking from the day the Japanese bombed Pearl Harbour. Chuck in Stalingrad and Diamler Benz were playing catch up to achieve height and speed in aero engines from then on.

Db also had "racing" experience with inverted V12's in Auto Union race cars in the early '30's.