Bf 109F-4 performance research page

[HoHun]

Hi Wotan,

>He amended or actually added a new page 8 showing the what he believes was the official clearance of the emergence power (1.42 ata) for the DB 601 E.

Oh, thanks, I hadn't seen that yet.

I can confirm that the page states quite clearly that 2700 rpm/1.42 ata are considered take-off/emergency power. There is no time limit given, but take-off/emergency usually was cleared for at least 3 - 5 min. (1 min power, which was rare, was called "increased short-duration power".)

Regards,

Henning (HoHun)

[JB73]

i don't know all the "technical" aspects of all of this, but something just dawned on me.

if that rating of 1.42 or whatever was only allowed for 1 minute, what impact would that have on overall speed for such a short duration?

in AH when flying level at 25k, hitting the WEP for 1 minute does not do a whole ton. yes some, but not 40-50mph difference.

IF wep gives that mush of an overall speed boost, it take ALOT longer than 1 minute to reach that speed i have found.

so how is that anyway?

thanks

[GRUNHERZ]

1.42ata 2700rpm is Start and Emergency power, so it's clearly our WEP and not some super limited type.

[HoHun]

Hi JB73,

>if that rating of 1.42 or whatever was only allowed for 1 minute, what impact would that have on overall speed for such a short duration?

Due to the exact wording of the manual reproduced by Irmur, that's not very likely.

However, as you point out, 1 min of peak power does not allow the aircraft to reach its top speed. In fact, even 5 min of peak power might not be enough to reach top speed - the F-1/F-2 Kennblatt specifically points that out.

(Strictly speaking, the aircraft never reaches its top speed by accelerating in level flight, but it can get very, very close to it so that acceleration becomes imperceptible :-)

Of course, stabilized top speed can still be reached by approaching it from a dive.

High-altitude top speed can be very difficult to measure accurately due to the poor excess power and the limited possibilities for a dive. The GM-1 boosted Luftwaffe aircraft sometimes had 10 min of WEP or more, and yet ran out of WEP before reaching stabilized top speed!

So you're making an excellent point, even if in our special case, we can rule out the 1 min assumption with considerable confidence :-) But it was definitely an possibility that had to be checked!

Regards,

Henning (HoHun)

[Wotan]

Just some perspective...

If 1.42 ata / 2700 (Start- und Notleistung; Take off and Emergency power)  was available from Feb '42 it would provide a max speed of 660-670 km/h (410-415 mph)

In AH2 @ 20000ft the Bf 109F-4 does just 394 mph (635 kmh) at 1.42 ata / 2700 rpm.

If you look at Hohun's graph based on Ireg's data max speed at 1.30 ata / 2500rpm is 403 mph (648km/h) @ 6000m (19685 ft).

At 1.30 ata / 2500 rpm the AH2 F4 only does 382 mph (614 km./h)

The Spit Vb in AH2 runs at 16lbs boost and ws cleared in Aug '42.

If we believe this data then the AH2 Bf 109F-4 is 21 mph to slow at 1.30 ata / 2500 rpm @ 20k

and 16 to 20 mph to slow at 1.42 ata / 2700rpm @ 20k.

The 1.42 ata (AH WEP) on the F4 should be limited to 3 to 5 min. But even so the F4 would be 21 mph faster at what AH considers 'military power'...

[JB73]

what is 1.42 ata anyway LOL

im guessing some way to measure manifold pressure or something.

and if it is, how is it masured in game ie what guage and such.

[Wotan]

ATA = Atmosphäre Absolutdruck

1.42 (ATA) * 28.96 = 41.12 inHG (manifold pressure)

Check this thread over my squad forum:

PS and ATA conversion equations

note AH conversions are off and Pyro is aware. He hasn't gotten around to fixing it.

in AH 42.2mp  = 1.42 ata

[JB73]

ty

[Angus]

So why is that single 109 so much faster?
I mean, it's faster than a 190, and faster than early 109G's.

So no reason to upgrade ?!?!?!

[Crumpp]

So why is that single 109 so much faster?

It's faster than the FW-190 in this test because the FW-190 is using the BMW 801C motor.

The BMW 801 motor was still experiencing teething troubles at this point as well.

Crumpp

[Naudet]

So why is that single 109 so much faster?

The question should not be why is this single 109F so much faster, but why is the single 109F tested by the RAE so much slower?

Speed tests at Rechlin and DB were done with different planes, JG26 had several 109F fielded during the tactical trials and the top speeds all those 109Fs reached were around 660-670km/h@2700rpm@1.42ata.

[Kweassa]

If that's true, then it's quite hard to understand the speed differences of the Friederich and Gustav...

 If the F-4 could do 416mph, that's faster than the speeds listed for the G-2 and the G-6. So if the F-4 does 416mph, does that mean the G-2 and the G-6 should also be much faster than it is?

[Angus]

What about climb rates then?
The Gustav outclimbs the Friedrich, but yet only the latest Gustavs are faster.
Ah, well, of course maybe faster at other alt bands though.

Well, the Friedrich is cleaner (much prettier) and lighter, it was the favourite model of most of the pilots for agility.
So, climb comparison?

BTW, our AH 109G2 outclimbs the AH Spit XIV to 20K

[Crumpp]

The question should not be why is this single 109F so much faster, but why is the single 109F tested by the RAE so much slower?

Horsepower development?  I know the loss of power the RAF experienced in BMW 801's was gasoline related.  Could the DB601E have had a similar problem?  

Anyone know the details of the how the RAE came into possesion of that 109?  Was it a recovered crash and how versed were they on the technical details of the design?

Crumpp

[Wmaker]

Originally posted by Kweassa
If that's true, then it's quite hard to understand the speed differences of the Friederich and Gustav...

 If the F-4 could do 416mph, that's faster than the speeds listed for the G-2 and the G-6. So if the F-4 does 416mph, does that mean the G-2 and the G-6 should also be much faster than it is?

In Finnish Air Force tests G-2 did 395mph at 19500ft with 1.3ata. This plane was taken out from standard squadron service. I was a fairly new plane though when the tests were done. It had a fixed-down tail wheel. So at with 1.42ata and reractable tail-wheel it would have been clearly faster.

Here's the much debated speed gained by the soviets for G-2. I remember a comment which was supposedly written in a flight test report regarding a captured 109G. It was something like "109 can achieve suprisingly fast speeds for short times". This comment referred to 109s radiators' cooling gills which can be fully shut for short times. Like I said I don't have the source for this line right now so take it as I wrote it...

The difference in speed was circa 30mph between the fully open and fully closed positions. This speed different of course reduces with alt. So my long shot theory is that maybe The Abbeville boys were also playing with the radiators like their russian 'buddies'.

Disclaimer: Once again, just an idea to keep me entertained.