Bf-109 drag values
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GregP
Major
So would I!
Good discussion on 109 performance, including some views/assumptions on drag (read the whole thing) over on Butch2k's board:
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drgondog
Major
I had Hoerner's Fluid Dynamics Drag in one of my undergrad aero courses. He did a complete analysis on the 109G in Chapter XIV-Complete Aircraft.
Drag is an interesting subject. Are you looking for Cd0 or trying to calculate drag for all flight regimes in steady, level flight?
Drag is an interesting subject. Are you looking for Cd0 or trying to calculate drag for all flight regimes in steady, level flight?
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Hoerner states the Cd of Bf-109G (with wing bulges, fixed tailwheel, no gondolas, at 380 mph) to be as high as 0,036 - rather high figure, and the lowest figure I'm aware for 109 is as low as 0,023. Since I'm not good at the subject: maybe the analysis made prior arriving at the final result was different? The bulges and tail wheels can influence the result, but not as much as 50%?
The P-51 and Spitfire are at some 0,021-0,022, so I'm looking to arrive at the correct value, for the comparison
The P-51 and Spitfire are at some 0,021-0,022, so I'm looking to arrive at the correct value, for the comparison
drgondog
Major
Hoerner states the Cd of Bf-109G (with wing bulges, fixed tailwheel, no gondolas, at 380 mph) to be as high as 0,036 - rather high figure, and the lowest figure I'm aware for 109 is as low as 0,023. Since I'm not good at the subject: maybe the analysis made prior arriving at the final result was different? The bulges and tail wheels can influence the result, but not as much as 50%?
The P-51 and Spitfire are at some 0,021-0,022, so I'm looking to arrive at the correct value, for the comparison
The 51 value for CDo is ~ .017, Spit IX/FW 190 about .022, P-38 about .025, 109G about .028-.031. The value you looked at in Hoerner is Total Drag = CDo+CDi+CDp.
When you start talking about a/c like the P-51B-1 at 440mph TAS at 29000 (or 109K-4, etc) you will also have a Cdm for mach related compressible drag.
When you start talking about drag in other regimes other than level flight you need to be conscious that as CL approaches CLmax, the drag related to lift OTHER than CDi, due to angel of attack, also start to become very significant.. this would be form/profile drag as airflow separates, trim drag due to control surface deflections, upwash/downwash inside the stream tube behind the prop.
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Thanks for setting my numbers straight, Bill
If I gather the values right, both those stated here and at LEMB, the following could be said about the Cd0 values of Bf-109:
-Emil: 0.025
-Friedrich, early Gustavs: 0.023 (better value, mainly due to the streamlining of front part of the plane, radiators, retractable tail wheel, deletion of tail strut)
-late Gustavs: ranging between 0.028-0.031 (worse values that F/early G because of fixed tailwheel, HMG bumps openings, whether the gondola weapons are carried or not, bigger wheels(?) )
Any corrections are welcome.
If I gather the values right, both those stated here and at LEMB, the following could be said about the Cd0 values of Bf-109:
-Emil: 0.025
-Friedrich, early Gustavs: 0.023 (better value, mainly due to the streamlining of front part of the plane, radiators, retractable tail wheel, deletion of tail strut)
-late Gustavs: ranging between 0.028-0.031 (worse values that F/early G because of fixed tailwheel, HMG bumps openings, whether the gondola weapons are carried or not, bigger wheels(?) )
Any corrections are welcome.
Maybe the late means G-5 and G-6. On the other hand the higher tail and deeper oil cooler increased drag in the later Gs and in K-4.
Juha
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I have no problems to accept corrected values, based on some research, of course. I'd like to make it clear that NONE of the values is fruit of my research (the subject is above my league), but from our own drgondog (Bill) and people from LEMB (Bill posts there, too).
Good catch, thanks
drgondog
Major
Riacrato - the only thing I see draggy on the Bf 109 E in comparison to G is the horizontal stabilizer strut. OTOH the G has bulge after bulge, etc, etc.
The thing to be conscious of in regards to Cd, Cdo figures is that they related to the frontal area of the aircraft. Some aircraft simply compensated by being smaller as the Me 109 did or used higher efficiency wings.
The gun bulges, the wing bulges from larger wider tires and the loss of retractiable tail wheel all added drag to the Me 109. Both the gun bulges and loss of retractabillity were completely avoidable. Noither of these problems exhibited in say the P-51 or P-47, both of which had a retractable tail wheel.
The P-51 did loose some of its advantageous low drag due to the fact that the wings could not maintain their low drag laminarity due to surface contamination.
A big factor was surface smootheness, higher construction quality on the Me 109 airframe would have achieved as much speed gain as removing the gun bulges and re-incoraprating the retractable tail wheel alone.
The gun bulges, the wing bulges from larger wider tires and the loss of retractiable tail wheel all added drag to the Me 109. Both the gun bulges and loss of retractabillity were completely avoidable. Noither of these problems exhibited in say the P-51 or P-47, both of which had a retractable tail wheel.
The P-51 did loose some of its advantageous low drag due to the fact that the wings could not maintain their low drag laminarity due to surface contamination.
A big factor was surface smootheness, higher construction quality on the Me 109 airframe would have achieved as much speed gain as removing the gun bulges and re-incoraprating the retractable tail wheel alone.
drgondog
Major
You should take a look at Hoerner's analysis to get an idea of the contributions and relative effects.
If total drag was high on 109, why was it so fast? Power does not explain, as the 109 did not have particular great power. It seems self contradiction so I think its incorrect. This German report shows Spitfire and 109 on same engine, so power is same. http://www.wwiiaircraftperformance.org/me109/db109g.pdf 109 is faster by about 20 kph. So drag is less obvious.
Also please show me button head rivts in 109.. it was all flush rivet as I know.
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Hi drgondog,
E-4/7 has:
- a less streamlined cowling (with plenty of bulges and small openings, too)
- wing bulges for MG-FF
- tailplane-struts
- older style and I assume more "draggy" radiatiors
later Gs have:
- wing bulges for larger main wheels
- fixed tailwheel
- bulges on cowling
- larger oil cooler
I guess I'd have to look at the composition of those drag values (but can't
), from first impression I had expected them to be about even.
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Tante Ju. The Bf 109 had much less induced drag than the Spitfire (at the cost of high wing loading), that's where the better total drag comes from.
Parasitic drag is that drag caused by the aircraft and wing moving through the air. It does not produce any lift.
Induced drag is that drag caused as a byproduct of producing lift. It can be calculated from the L/D ratio of the wing cross section for a given angle of attack (given in tables) with corrections for aspect ratio, planform and wing twist. Since L/D is often around 50:1 in level flight it is a small component of drag. However when pulling G it becomes more significant.
The Me 109 wing likely had less parasitic drag since it was smaller. At very high speed, near transonic, the Spitfire wing may have had less parasitic drag since the thickness/chord ratio was less. and so less shockwave drag was created.
In terms of induced drag the Me 109 was almost certainly worse even though the wing had less parasitic drag.
This is because as the wings angle of attack is increased its lift increases rougly linearly with angle of attack however the drag tends to increase with the square of the angle of attack.
The smaller wing of the Me 109 must pull higher angles of attack to generate the same lift (though remember they have different wing sections). Because the Me 109 had slats that might have allowed about 40% extra angle of attack and roughly 40% extra lift the aircraft can certain generate a great deal of lift from its smaller wings. However to generate that high lift from small wing means more induced drag is created; this will slow the aircraft down and cause it to loose height. In other words at some point in turning flight the advantage that the Me 190 had in having less parasitic drag from the wing will be overcome by greater induced drag in turning flight.
The drag on a wing has two components: a parasitic and a induced component, though in charts and tables they are usually combined into one they can be seperated out in some of the equatuons which give lift and drag in terms of a polynomial.
Having sufficient power was absolutely critical for Me 109 which is probably why in late 1944 when Me 109G10, Me 109K4 and likely Me 109G14ASM were reasonably common that some P-51 pilots reported being outmanouvered at altitude.
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