109 prop pitch (rpm) and the supercharger

[Crumpp]

I reckon Crumpp is not aware of the fact that by coarseing the pitch in the 109 the rpm drops accordingly.

Not if you are using it right.

Rpm will drop as the speed increases and the propeller begins to drive the engine. Coarsen pitch as the rpm begins to drop to maintain it.

[kohmelo]

Originally Posted by Crumpp

Is that hard to understand or something? It must be as we have multiple pages on this simple concept.

Originally Posted by Robo.

...I reckon Crumpp is not aware of the fact that by coarseing the pitch in the 109 the rpm drops accordingly.
Crumpp wake up!

I really start to believe we are losing something in translations or then I am only one. (Honestly I needed to take dictionary on my hand)

You must maintain that rpm setting at a constant rate.
- You must pursue that (efficient) rpm setting at a continuous rate (by manual pitch)

Its like Bouy rocking after a wave.
Wave hits Buoy -> it must maintain its stability at a constant rate

I really believe that most of us are speaking of the same thing but everybody have their eyes fixed on one single point of this issue

[ACE-OF-ACES]

Originally Posted by kohmelo

I really start to believe we are losing something in translations or then I am only one.

Not really, Only thing that makes it hard to read is Crumpp's atempt at trying to redefine the word 'maintain'.. Clinton would be proud!

[NZtyphoon]

Originally Posted by Crumpp

At high altitudes, the airplane is essentially in slow flight for most of the envelope. That makes cooling harder and overboost conditions will heat the motor up faster.

If they wanted to use a limited overboost condition, they would be constantly changing rpm between maximum continious and higher limited overboost to cool the motor.

Interesting how this only now becomes a measure to cool the hydraulic supercharger, according to our resident aviation expert; still it is correct that the hydraulic coupling of the DB supercharger led to problems with overheating that the pilots needed to control by constantly altering rpm - not maintaining it.

Originally Posted by Crumpp

A complete sidetrack as to how they are using the propeller and rpm to gain speed.

Wrong; the pilots were needing to adjust rpm and pitch constantly to periodically rest the supercharger - any gain in speed was a by-product, not a tactic.

[macro]

Originally Posted by Crumpp

Not if you are using it right.

Rpm will drop as the speed increases and the propeller begins to drive the engine. Coarsen pitch as the rpm begins to drop to maintain it.

eh?

rpm will increase as speed increases not drop, until you adjust pitch, at least my 109 does anyway lol

[Crumpp]

rpm will increase as speed increases not drop, until you adjust pitch, at least my 109 does anyway lol

OOPs, yes it should increase and you coarsen the pitch to keep rpm constant.

You must maintain that rpm setting at a constant rate.
- You must pursue that (efficient) rpm setting at a continuous rate (by manual pitch)

Correct.

They are changing rpm to an overboost condition, adjusting pitch to maintain the overboost rpm setting, and then reducing it let things cool down.

When they reduce rpm, they also adjust the pitch to maintain the new rpm setting as the aircrafts speed changes.

[Crumpp]

NZtyphoon

Maybe it is time for your stability and control documents.

You know, the ones with the picture of the Spitfire and the general comments that have nothing to do with the Spitfire?

[NZtyphoon]

Originally Posted by ACE-OF-ACES

Not really, Only thing that makes it hard to read is Crumpp's atempt at trying to redefine the word 'maintain'.. Clinton would be proud!

Perhaps this might help



is different to



but, rather than keeping things



Crumpp likes to change context and words to maintain whatever argument he thinks he has.

[ACE-OF-ACES]

Originally Posted by NZtyphoon

Crumpp likes to change context and words to maintain whatever argument he thinks he has.

Bingo!

[Kurfürst]

Originally Posted by NZtyphoon

still it is correct that the hydraulic coupling of the DB supercharger led to problems with overheating that the pilots needed to control by constantly altering rpm - not maintaining it.

Nope, it's incorrect. Hydraulic couplings generate more heat to the oil during slip (friction generating heat), but it doesn't mean the oil was overheating, because

a) the fact that increased oil cooling requirements could be and were compensated by increasing oil cooling capacity (note the rather sizeable oil radiator on the 109)

b) the fact that at and above FTH the hydraulic coupling has minimum slip (in the order of about 3%) and therefore, the heat load is only marginally different from a fixed ratio mechanically geared supercharger. If there's no extra friction, there is no extra heat, simple as that.

This is evident from DB heat charts, i.e. the DB 605A lubricant heat transfer was 65 000 kcal/hour at sea level, when the hyd. supercharger was operating at maximum slip, but only 43 000 kcal, or roughly 2/3s at FTH, where the hyd. supercharger was operating at minimum slip.

Wrong; the pilots were needing to adjust rpm and pitch constantly to periodically rest the supercharger - any gain in speed was a by-product, not a tactic.

Bull on all accounts.. the supercharger itself does not "overheat", its just a piece of magnesium alloy and does not operate at extreme temperatures, neither does it have any sort of forced cooling.

Secondly, increasing revs by about 200 rpm _was_ a sanctioned tactic that increased the supercharger capacity and altitude output of the engine, as noted in the November 1940 LWHQ notice that has been already posted, and led to some noteworthy speed increase above rated altitude, as noted by the 109F manual. And if the speed increases, the pitch angle does need to be changed of course, just as at any rpm and at any altitude, when the speed increases.

All they did was manipulating the pitch to let rpm increase, and then - by when the rpm has increased - manipulating pitch to compensate for increase airspeed AND maintain increased rpm.