Late 1941 - late 42: Bf-109 vs. Fw-190

[69TA]

The Rechling tested 649km/h as max speed for G-1 with 1.3 ata, 700km/h is clearly too much for the power increase achieved by increasing boost to 1.42 ata. GM-1 might explain at least partly so big increase in speed. At what height the speed was achieved according to Voigt?

Juha

I believe the Rechlin test you mentioned was actually 650km/h and the plane had a fixed tail wheel reducing the speed some 12km/h. So the 662km/h at 1.3ata seems accurate.

Well unfortunately, the GM-1 nitrous system cannot be part of the explanation of the speed increase. Reason is, the GM-1 system was not designed to be used at the altitude were the plane had its top speed. The GM-1 was used to increase the power (and speed of course) at higher altitudes, for the DB605 it was above 10 000m.
Vogt claims 700km/h at volldruckhöhe (VH) which is the largest reached flight altitude without power loss for the engine. According to the Augsburg data sheet for the G-1 the VH for 1.3ata boost was 7000m.

 

[Juha]

I believe the Rechlin test you mentioned was actually 650km/h and the plane had a fixed tail wheel reducing the speed some 12km/h. So the 662km/h at 1.3ata seems accurate.

Well unfortunately, the GM-1 nitrous system cannot be part of the explanation of the speed increase. Reason is, the GM-1 system was not designed to be used at the altitude were the plane had its top speed. The GM-1 was used to increase the power (and speed of course) at higher altitudes, for the DB605 it was above 10 000m.
Vogt claims 700km/h at volldruckhöhe (VH) which is the largest reached flight altitude without power loss for the engine. According to the Augsburg data sheet for the G-1 the VH for 1.3ata boost was 7000m.

When 1.42ata was finally allowed in autumn 43, it had also been allowed a short time in July 43, my quess is that those G-1s, if any, still around had fixed tailwheel. IIRC according to Kurfürst, one G-1 clocked with GM-1 680km/h and see Delcyros' post above. IMHO it is inmaterial whether the engine was 1.3ata or 1,42ata with GM-1 because its use was paractical only above FTH, so supercharger couldn't deliver even 1.3ata anymore.

Juha

 

[Tante Ju]

This may be interest for thread. German compilation of flight tests, 190A - 109G.

http://www.wwiiaircraftperformance.org/me109/frm1l43-190-109.pdf

It is clear that up to about 6 km, Fw 190A was faster airplane, above 6 km Gustav was better airplane. Gustav climbs much better at any altitude.

 

[Juha]

Hello Delcyros
thanks for the link.

Juha

 

[tomo pauk]

Thanks for the links, delcyros Tante Ju. Too bad we don't know more about the plane's conditions on the performance comparisons. The G-1 fares well, speed-wise, also between 2,5 and 4 km, vs. the 190 running at same setting (Steig Kampfleistung).

 

[delcyros]

Vogt claims 700km/h at volldruckhöhe (VH) which is the largest reached flight altitude without power loss for the engine. According to the Augsburg data sheet for the G-1 the VH for 1.3ata boost was 7000m.

This claim is a bit dubious from my perspective. The -109G1´s DB-605A had a full pressure height (VDH) of 5,700m static. Even if we grant dynamic pressure gain, it´s 6,500m (tested on -G1) and not 7,000. Thus, it´s not logical to assume Vogt´s statement -which I haven´t read, I admit- is representative for a DB-605A driven Bf-109G1.
Kurfürst once had the idea that the 700 km/h figure is not a tested one but a calculated performance estimate for 1.42 ata, basing on the 670km/h figure of the Bf-109F4 (1.42ata), which likely was not corrected for compressibility. If You are willing to accept this working theory, it explains for the differences seen in the data.

IMHO it is inmaterial whether the engine was 1.3ata or 1,42ata with GM-1 because its use was paractical only above FTH, so supercharger couldn't deliver even 1.3ata anymore.

I guess this is true for british boost pressure systems. In the german powerplants, the ata setting and it´s rpm made a difference at all altitudes, including altitudes above full pressure height. Though, in the latter case, the difference reduces markedly with altitude:



[speculation on my part]
The first stage GM-1 adds 300 bhp at 8000m to the output, increasing power from 950 to 1250bhp. At this altitude, normal speed of the -G1 according to the graph proposed by Neil above would be ~642 to 644 km/h. With 300hp extra provided by GM-1 kicking in, and assuming that the sqrt^3 rule applies too (ignoring compressibility issues and ram effect), the top speed expected is 704 km/h / 437mph at 2600 rpm. 2800 rpm -which has been suggested as possible with GM-1 at 9,500m -altough I haven´t seen any sources to confirm this- may restore 1250 bhp when the engine would only develop 815bhp at 1.42 ata / 2,800 rpm. The speed at this altitude at 1.30 ata / 2600 rpm / 790 bhp is given by Neil with 635 km/h. If that is to be found to be true, the max. estimate would be 739 km/h / 459mph.
The true airspeed speed likely would have been a bit lower due to reduced prop efficiency at this altitude or higher, due to ram and exhoust jet effects, depending on how that precisely works out (I don´t know that).
[end speculation]

 

[silence]

May I ask, what is this "sqrt^3 rule"?

 

[Juha]

May I ask, what is this "sqrt^3 rule"?

IIRC something like that while the drag is increased by the square of the speed increase, but the engine output (hp) is equal to the thrust (force) from the propeller multiplied by the speed of the aeroplane. This means the speed will only be increased by the cubic root of the horse power increase.

Juha

 

[drgondog]

The question has to be adressed and answered by the source I gave (Vogt). His book is almost brand new so it is fair to assume that he had access to all of the other sources that has been mentioned in this thread.

By the way, I do not consider wikipedia as a reliable source but I must point out that the same figure, 700km/h for the G-1 is stated there FWIW...

With due respect to Vogt - why is it fair to assume that 'access=impeccable scholarship' ?? or that 'new=better'?

Part of the debate you are in is a result of lack of credibility for the conclusions you present. It is fair to challenge Kurfurst or Norwarra or Vogt as you will, but if Vogt results fly in the face of the others, then maybe best to look to Vogt's published Source and see what that is?

 

[Juha]

...I guess this is true for british boost pressure systems. In the german powerplants, the ata setting and it´s rpm made a difference at all altitudes, including altitudes above full pressure height. Though, in the latter case, the difference reduces markedly with altitude:
...

Thanks for that, I should have remembered the graphs which showed 109G speed with 1.3 ata and 1.42ata in which the speed is higher for the latter case all the way from SL to 12km altitude.

Juha

 

[69TA]

With due respect to Vogt - why is it fair to assume that 'access=impeccable scholarship' ?? or that 'new=better'?

That is your words and your insinuations not mine

It is fair to challenge Kurfurst or Norwarra or Vogt as you will, but if Vogt results fly in the face of the others, then maybe best to look to Vogt's published Source and see aht that is?

Agreed. And that is what i said.

 

[drgondog]

Agreed. And that is what i said.

Yo 69TA - These (below) are your words, what YOU said - not mine. I made no insinuations.

"The question has to be adressed and answered by the source I gave (Vogt). His book is almost brand new so it is fair to assume that he had access to all of the other sources that has been mentioned in this thread."

OH?? why is it 'fair to assume' anything just because his book is new - and who (other than you) says 'the question has to be addressed and answered by the source 'you' gave? Are you a well known researcher with credentials in any subject?

 

[tomo pauk]

This claim is a bit dubious from my perspective. The -109G1´s DB-605A had a full pressure height (VDH) of 5,700m static. Even if we grant dynamic pressure gain, it´s 6,500m (tested on -G1) and not 7,000. Thus, it´s not logical to assume Vogt´s statement -which I haven´t read, I admit- is representative for a DB-605A driven Bf-109G1.
Kurfürst once had the idea that the 700 km/h figure is not a tested one but a calculated performance estimate for 1.42 ata, basing on the 670km/h figure of the Bf-109F4 (1.42ata), which likely was not corrected for compressibility. If You are willing to accept this working theory, it explains for the differences seen in the data.

+1

I guess this is true for british boost pressure systems. In the german powerplants, the ata setting and it´s rpm made a difference at all altitudes, including altitudes above full pressure height. Though, in the latter case, the difference reduces markedly with altitude:

Juha is right here, the highest altitude the DB-605A was able to provide 1,42 ata was 5,7km (no ram), above that altitude the boost was decreasing.

 

[drgondog]

69TA - to recapitulate our discussion:
"With due respect to Vogt - why is it fair to assume that 'access=impeccable scholarship' ?? or that 'new=better'?

To which you responded:
That is your words and your insinuations not mine

I said further:

"It is fair to challenge Kurfurst or Norwarra or Vogt as you will, but if Vogt results fly in the face of the others, then maybe best to look to Vogt's published Source and see what that is?"

and you said:
Agreed. And that is what i said.

I hope we can have useful dialogue but I am fine with churlish behavior.

You will never have to worry about me 'implying' or 'insinuating'. If you act like a pompous ass I will call you a pompous ass. There will be no question in your mind, no sublty, noy coy or sly remarks.

If you attempt to bully acknowledged friends and great contributors on this site with unsubstantiated bovine fecal matter - then refer to rule number one above will apply. You have a long path back to generate credibility with some pretty knowledgable experts on this forum - why not relax and treat other (opposing) points of view with respect, even if you are sure of your facts?

 

[69TA]

I am not here to seek "credibility" as you seem to think. I see no reason for You to lecture me on anything. YOU should stick to the topic in thread and try to contribute in positive way instead. Then you will have my respect. You want to continiue this crap, do it in a private message to me.

 

[drgondog]

P O M P O U S A S S.. clear enough?

 

[69TA]

talkin bout yourself I see...

 

[drgondog]

As an occasional practioner of the 'art' I know the symptoms and can spot the PA's from afar.

 

[Njaco]

ENOUGH!!!!

If you act like a pompous ass I will call you a pompous ass.

Sorry Bill,not on this forum.

To everyone, one more word that is off-topic of the thread and attacking another member and vacations will be given.

 

[silence]

deleted