Bf109F vs P-38F

[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)

There is an incredible disparity between the turn rates of the 38F and 109 in your plot - particularly at 1000m and 6500m where the velocities cross over.

Are you using the Clmax for the NACA 23016 airfoil 'bare' or with manuevering flaps? With manuevering flaps the USAAF had the P-38F turning with the P-51 at Eglin Field (between 12000 and 15000+ feet!

Your plots show the 51D to be approx 0ne degree per sec slower than the 109 on the deck but you show 5+ degrees difference between the 109 and the 38F on the deck and 4 1/2 degrees at 12,000 where the 38F had parity with a 51A.

Which Clmax are you using for the 38F and what value are you using for AoA at CLmax? What Cd0 are you using for the 38 and what values for trim drag (with or without maneuvering flaps)?

Where is the math?

[mkloby]

Hi Mkloby,

If you increase the force of the power strokes, you'll increase the torque of the engine, and there is usually some kind of torque limit not close off the 30 min operating conditions. (Even worse and more complicated, bad things can happen in the combustion chamber. I'm not familiar with all the nasty details of that either, but "detonation" is a keyword there.)

Alternatively, you can increase the frequency of power strokes, which will keep you clear of the torque limits as the power is developed through an increase of engine speed at the same internal forces as before. That was historically the main route to emergency power for piston engines.

Below a diagram showing the operating conditions of the B-29's R-3350 engine. Note that there is a narrow band for each manifold pressure at which operation of the engine is both possible and sensible. You can always increase rpm without danger, that will needlessly increase fuel consumption. If you decrease rpm however, that will increase "engine pressures", internal forces or torque, which are more or less three different ways of looking at the same problem.

(While on the US B-29, it was the task of the flight engineer to keep the engine in the best operating range, many German aircraft were equipped with single-lever control systems that selected the optimum combination of rpm and boost and a couple of other variables such as ignition timing automatically, based on information from perhaps a half dozen of sensors. I'm not sure if the DB 601E in the Me 109F-4 was manually or automatically controlled, but the concept of staying in the small safe and sensible operating area as outlined in the B-29 graph was the same regardless.)

Regards,

Henning (HoHun)

HoHun,
Interesting - it just isn't make sense to me why increasing engine RPM would necessitate increasing prop RPM. On every aircraft I have flown with a constant speed prop, the blade angle is managed in order to maintain a specified RPM. If power is increased, blade angle then increases to maintain the same N2, if power decreases, it reduces blade angle.

I have read that the 109F had an electric operated constant speed prop. I am not sure how this one worked. I have read that it was automatic with a manual override option as well.

[CharlesBronson]

P-38, better firepower and faster, with the correct tactic the messer is toasted. I think the both types meet each other over Tunisia in late 1942...right ? Many Me-109 in that teather of operation were the G type already.
By the way 635 mk/h sound a very good figure for the F-4 considering that is the same speed quoted for the G-2 variant wich had a little more powerful engine ( 1350 compared with 1475 hp).

[HoHun]

Hi Mkloby,

>Interesting - it just isn't make sense to me why increasing engine RPM would necessitate increasing prop RPM. On every aircraft I have flown with a constant speed prop, the blade angle is managed in order to maintain a specified RPM. If power is increased, blade angle then increases to maintain the same N2, if power decreases, it reduces blade angle.

It works more or less like that on the Messerschmitt, too. If you set rpm to 2700 rpm to begin with, you could hypothetically control power through boost pressure alone, though that would not be the most efficient way to operate the engine.

Regards,

Henning (HoHun)

[mkloby]

Hi Mkloby,

>Interesting - it just isn't make sense to me why increasing engine RPM would necessitate increasing prop RPM. On every aircraft I have flown with a constant speed prop, the blade angle is managed in order to maintain a specified RPM. If power is increased, blade angle then increases to maintain the same N2, if power decreases, it reduces blade angle.

It works more or less like that on the Messerschmitt, too. If you set rpm to 2700 rpm to begin with, you could hypothetically control power through boost pressure alone, though that would not be the most efficient way to operate the engine.

Regards,

Henning (HoHun)

You seem to be referring to engine RPM. 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.

[HoHun]

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 :-)

>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.

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)

[HoHun]

Hi Charles,

>By the way 635 mk/h sound a very good figure for the F-4 considering that is the same speed quoted for the G-2 variant wich had a little more powerful engine ( 1350 compared with 1475 hp).

I don't know where you have the 635 km/h for the Me 109G-2 from, but the wartime summary report on the Me 109G-6 credits the Me 109G "Grundausführung" ('basic variant') with 630 km/h at 1.30 ata/2600 rpm. The 1475 HP you list is for the full 1.42 ata/2800 rpm emergency power setting.

Kurfrst - Leistungzusammenstellung Me 109 G.

As background: The 'basic variant' is essentially a G-2 with rigid tail wheel and all the little bumps of a G-6, but without the MG 131 blisters. It's a hypothetical plane serving as baseline for establishing the performance of G-6 series production aircraft with all the variations they were built with, but of course its performance figures were based on flight tests of multiple Gustav aircraft in different configurations.

The real G-2 was a bit cleaner still, and accordingly a bit faster as well.

Regards,

Henning (HoHun)

[CharlesBronson]

I don't know where you have the 635 km/h for the Me 109G-2 from, but the wartime summary report on the Me 109G-6 credits the Me 109G "Grundausführung" ('basic variant') with 630 km/h at 1.30 ata/2600 rpm. The 1475 HP you list is for the full 1.42 ata/2800 rpm emergency power setting.

I saw that figure in the well know Squadron Signal and the Osprey collection ...I know, I know those are not technical editions.

[Vincenzo]

saw your figure and explication, now i think that 670 km/h for full power 109 F-4 isn't correct for compressibility effect, (like the 660km/h for climb/combat power setting, that coming 635 km/h corrected)

[Soren]

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.

[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