Bf109F vs P-38F (2 Viewers)

[mkloby]

Hi Mkloby,

>You seem to be referring to engine RPM. I am referring to maintaining a specified prop RPM

Hm, unlike as with some turbine types, on most aircraft piston powerplants engine rpm and prop rpm are directly proportional to each other as they're connected through a fixed-ratio gearing (or directly, in lower powered types). If I mixed the two terms, that would be because they change in unison so that I didn't think of them as separate

I need to get an old aircraft manual to look at now, because that seems to defeat the whole point of a constant speed prop, ie changing pitch to maintain a set propeller RPM.

Hm, I don't think that we already touched this topic, but increased thrust (regardless how it's achieved) does in fact improve an aircraft's specific excess power, improving its capability for sustained turns.

Instantaneous turns will be unaffected, of course. I guess that's what you were thinking of?

(Just so that the idealized term "instantaneous" won't cause unnecessary confusion: non-stabilized turns of finite duration would actually be influenced by power available

Regards,

Henning (HoHun)

I confused you with that one, sorry about that - "turns" is a rotary wing slang for Nr (rotor rpm). I was referring to prop rpm there. I'll blame it on the V-22, since we still call it Nr.

 

[FLYBOYJ]

Hi Mkloby,

>You seem to be referring to engine RPM. I am referring to maintaining a specified prop RPM

Hm, unlike as with some turbine types, on most aircraft piston powerplants engine rpm and prop rpm are directly proportional to each other as they're connected through a fixed-ratio gearing (or directly, in lower powered types). If I mixed the two terms, that would be because they change in unison so that I didn't think of them as separate

I need to get an old aircraft manual to look at now, because that seems to defeat the whole point of a constant speed prop, ie changing pitch to maintain a set propeller RPM.

A few things to look at here folks.

Although you have have a recip aircraft with a constant speed prop attached to the engine either directly or through an RGB, RPM will be controlled by the Prop - power by the engine and we measure that "power" though manifold pressure. To take it a bit further we cold also measure torque so we don't put too much power or rpms on the RGB depending on power and prop settings. This is more commonly found on turbine engines because they could put out a lot more torque a lot quicker than recips, especially in engines like a PT6.

The constant speed prop will build up or reduce speed based on engine RPM delivered to the prop governor which will allow pitch changes depending if we're in a dive or climb. As Henning stated earlier, there are some aircraft that have this happen automatically (I actually think the Fw.190 was the first aircraft to have this - Mooney copied the set up in the late 1960s I believe.)

Also consider that there always needs to be a way to prevent the propeller from driving the engine. In many turbine engines this is done automatically but I believe in recips the pilot or FE will have to prevent this.

 

[HoHun]

Hi Mkloby,

>I need to get an old aircraft manual to look at now, because that seems to defeat the whole point of a constant speed prop, ie changing pitch to maintain a set propeller RPM.

Thanks to Micdrow's and Roy's efforts, we have a great collection of them in the technical forum section

>I confused you with that one, sorry about that - "turns" is a rotary wing slang for Nr (rotor rpm). I was referring to prop rpm there. I'll blame it on the V-22, since we still call it Nr.

Ah, I see! But even then I still don't understand your original comment, I have to admit:

"I am referring to maintaining a specified prop RPM - there is no reason I can see that should cause prop RPM to increase turns, regardless of an increase in engine power at higher engine RPM."

Regards,

Henning (HoHun)

 

[HoHun]

Hi Flyboyj,

>As Henning stated earlier, there are some aircraft that have this happen automatically (I actually think the Fw.190 was the first aircraft to have this - Mooney copied the set up in the late 1960s I believe.)

I think it was actually Bramo who developed the single-lever control before merging with BMW, who applied the technology to the BMW 801 then.

I think the Focke-Wulf Fw 200 was already equipped with single-lever control before the Fw 190, but I'm not entirely certain of that.

Regards,

Henning (HoHun)

 

[Vincenzo]

670 km/h doesn't seem illogical if GM-1 was used, but if the propeller couldn't transfer the extra power then I guess its a moot point.

for true info for GM-1 gave also highest velocity, but nobody was talking with GM-1 used

 

[drgondog]

Hi Vincenzo,

>saw the comparison with P-38-F so encounter only in late '42, i think notleistung was available or not?

Hm, it seems "Zeugmeister" has found some new documents since I last checked this topic ... it looks like Notleistung was cleared with the February 1942 manual: Beim-Zeugmeister: Seite 8 - Flugzeughandbuch der Bf 109 F-4

Attached a comparison based on Notleistung.

Regards,

Henning (HoHun)

The P-38F-15 and all suceeding versions have the inboard NACA 23016 airfoil with manuever flap inboard of the engines, and a NACA 4412 outboard of the engines. I am chasing an obscure reference to determine whether all P-38F's were retrofitted with the manuever flap but for sure the -15 had them

Lockheed P-38F Lightning

As near as I can determine 121 F-15s were produced before 9/42when the G series superceeded the F. Which version are you using for your comparisons? The Mike Williams data for the USAAF March 8, 1943 report are F-1's

Which P-38F did you model and what math approach did you use for Clmax calculations in turn performance to account for the different stall characteristics?

 

[Vincenzo]

why a planes build in '42 have a '43 serial number?

 

[FLYBOYJ]

why a planes build in '42 have a '43 serial number?

The serial number year represents when the contract was issued.

 

[Vincenzo]

The serial number year represents when the contract was issued.

so it's more strange planes build before of contract??

 

[FLYBOYJ]

so it's more strange planes build before of contract??

Because that' the way the contract is let out, especially when large numbers are involved. It actually represents a purchase for the indicated "fiscal year." Although being built in 1942, the aircraft in question was purchased with 43' "money." This will happen with multi-year funding or military equipment.

 

[Vincenzo]

i found that US fiscal year start at october so planes ordered last 3 months of '42 are in '43 fiscal

 

[FLYBOYJ]

i found that US fiscal year start at october so planes ordered last 3 months of '42 are in '43 fiscal

Yes, the contract could have been awarded in that manner.

 

[mkloby]

Hi Mkloby,

>I need to get an old aircraft manual to look at now, because that seems to defeat the whole point of a constant speed prop, ie changing pitch to maintain a set propeller RPM.

Thanks to Micdrow's and Roy's efforts, we have a great collection of them in the technical forum section

I'm sifting through various manuals and trying to dig up info...

>I confused you with that one, sorry about that - "turns" is a rotary wing slang for Nr (rotor rpm). I was referring to prop rpm there. I'll blame it on the V-22, since we still call it Nr.

Ah, I see! But even then I still don't understand your original comment, I have to admit:

"I am referring to maintaining a specified prop RPM - there is no reason I can see that should cause prop RPM to increase turns, regardless of an increase in engine power at higher engine RPM."

Regards,

Henning (HoHun)

Apparently it is difficult to find good detailed info on the actual operation of the VDM 109 prop. My basic point being is that even if engine rpm and power are increased, blade pitch should be able to be increased as well maintaining an "ideal" propeller rpm regardless of engine rpm.

From what I understand the 109F had an AUTOMATIC setting, which would adjust blade pitch without manual inputs (although it could be overridden manually).

Seems like there is something I am missing here.

 

[drgondog]

Yes, the contract could have been awarded in that manner.

Joe - there are some strange practices all over the map -

P-51D prototypes USAAF #AC-30479 awarded in 2-27-43 were USAAF serial number 42-106539 and 6740 (THESE TWO were 'plucked' from the P-51B-10NA Block below)

P-51D-5NA, USAAF #AC-40064, dated 4-13-43 were USAAF serial numbers 44-13253 through 44-14052. This is the first block after the two prototypes.

P-51C-10NT, USAAF #AC-40063 (contract no. PRECEEDING the above P-51D-5NA) was dated 5-3-43 (dated AFTER the above P-51D-5NA).. go figure.

P-51B-10NA, AC-30479, dated 10-20-42 were USAAF serial numbers 43-7113 thru 7202, then 42-106429 to 42-106538 (see two ships above that became D prototypes - same contract), then 42-106541 through 106738.

 

[HoHun]

Hi Mkloby,

>Apparently it is difficult to find good detailed info on the actual operation of the VDM 109 prop. My basic point being is that even if engine rpm and power are increased, blade pitch should be able to be increased as well maintaining an "ideal" propeller rpm regardless of engine rpm.

The propeller could do that, but the engine, geared to the propeller at a fixed ratio, would not run at the optimum speed for the power output selected that way.

The DB 601E data sheet attached below shows the use of different engine speeds for different power outputs. It's perfectly typical for the period in this regard, and you'll find the same progression of engine speeds with increasing power in US Specific Engine Flight Charts.

>From what I understand the 109F had an AUTOMATIC setting, which would adjust blade pitch without manual inputs (although it could be overridden manually).

I believe that the automatic setting was meant single lever operation with the desired speed set by the propeller lever. Upon flipping a small electrical switch mounted below the throttle quadrant (very hard to make out in cockpit shots of the Me 109), the propeller went to variable pitch operation, with the pilot using two pushbuttons on the throttle grip to adjust propeller pitch. Unlike Allied aircraft, most German aircraft featured a propeller pitch indicator with two hands, calibrated just like a clock, and the standard operation pitch values were actually given in the manner "for take-off, set pitch to a 'quarter to twelve'" and so on.

I think it was standard to go to manual operation of propeller pitch (and cowl flaps) for take-off and landing to avoid the lag times introduced by automatic gouvernors. A modern description of the procedures used with a restored Me 109G published recently in a German magazine shows that they adhere to this practice, too.

Regards,

Henning (HoHun)

 

[FLYBOYJ]

Joe - there are some strange practices all over the map -

P-51D prototypes USAAF #AC-30479 awarded in 2-27-43 were USAAF serial number 42-106539 and 6740 (THESE TWO were 'plucked' from the P-51B-10NA Block below)

"Plucked" Part of an original procurement and then re-manufacturerd, I seen either the original s/n used or anothwer one re assigned

P-51D-5NA, USAAF #AC-40064, dated 4-13-43 were USAAF serial numbers 44-13253 through 44-14052. This is the first block after the two prototypes.

I think paid with 1944 money

P-51C-10NT, USAAF #AC-40063 (contract no. PRECEEDING the above P-51D-5NA) was dated 5-3-43 (dated AFTER the above P-51D-5NA).. go figure.

Pot luck!!

P-51B-10NA, AC-30479, dated 10-20-42 were USAAF serial numbers 43-7113 thru 7202, then 42-106429 to 42-106538 (see two ships above that became D prototypes - same contract), then 42-106541 through 106738.

Again "plucking" or remanufacturing of the airframes is my guess.

Did you see the post about the A-37's in Vietnam? They too carried two set of S/Ns - my guess is they started out life as a T-37 and went through depo and was modded to an A-37.

I guess in the end its all about how Uncle Sam want to pay for something. Right now we're starting work that's on 2010 funding, so I'm told - some things never change!

 

[mkloby]

Hi Mkloby,

The propeller could do that, but the engine, geared to the propeller at a fixed ratio, would not run at the optimum speed for the power output selected that way.

Hey HoHun,
From what I have read (and what you have been trying to tell me!) the Bf 109, I believe from D on) had a Variable Pitch Prop. Some sources seem to indicate that the 109s had Constant Speed Prop, which is what confused me. We're good now. Thanks!

 

[HoHun]

Hi Mkloby,

>From what I have read (and what you have been trying to tell me!) the Bf 109, I believe from D on) had a Variable Pitch Prop. Some sources seem to indicate that the 109s had Constant Speed Prop, which is what confused me. We're good now. Thanks!

Hehe, welcome, but I don't think we've fully exploited the confusion yet

The Me 109 from some version on did in fact have a constant speed propeller.

The desired speed was normally set by a simple analogue computer to match the boost pressure selected by the pilot according to a pre-defined curve. (Maybe more inputs and outputs were involved, but that's the most important thing it did.)

However, if the pilot thought it made sense, he could also flip a switch and operate the constant speed propeller in "dumb" variable pitch mode.

Except that they didn't have a single-lever control but a conventional throttle lever/propeller speed lever combination, some US aircraft had similar capabilities for manual pitch control, for example the FM-2 Wildcat.

From NACA report WR-E-192, here a chart showing the basic relation between rpm and manifold pressure the BMW 801 engine computer would yield under normal conditions. The propeller was a constant-speed unit, but on which speed it attempted to stabilize was commanded by the engine computer depending to the power lever position that also governed rpm.

The DB 601E must have had a similar, if maybe somewhat simpler unit, too.

Regards,

Henning (HoHun)

 

[HoHun]

Hi again,

From the same NACA report WR-E-192, another chart showing the functional units of the BMW 801 engine computer. Note that it includes the constant-speed governor of the propeller (which can be overridden by the pilot in just the same way as that of the DB 601E).

Regards,

Henning (HoHun)

 

[mkloby]

Hehe, welcome, but I don't think we've fully exploited the confusion yet

The Me 109 from some version on did in fact have a constant speed propeller.

The desired speed was normally set by a simple analogue computer to match the boost pressure selected by the pilot according to a pre-defined curve. (Maybe more inputs and outputs were involved, but that's the most important thing it did.)

However, if the pilot thought it made sense, he could also flip a switch and operate the constant speed propeller in "dumb" variable pitch mode.)

If the aircraft had a constant speed prop, the prop gov would seek to maintain an "ideal" prop rpm speed. If the engine is geared to the propeller at a fixed ratio, as you earlier stated, I don't understand how this is possible.

I had read in AUTO mode the prop pitch would be set to a prescribed pitch setting based on boost, not that a prescribed prop rpm speed was tied to boost. Also, another document stated that the prop gov limited prop rpm in proportion to the throttle setting. It would not govern the rpm at a set rpm...