Leading edge shape on German fighter aircraft?

[spicmart]

The leading edge of the wings of German fighter aircraft seem to be rounder/blunter than those of many other nation's planes (of course with exceptions). What advantages and disadvantages does it have?
Also their nose, i. e. the spinners seem not as pointed. does anybody know more?

 

[tomo pauk]

We can take a look at time the planes were designed.
The Bf-109 was a contemporary of Hurricane, ie. being designed in the era when monoplanes were to replace biplanes in most of the air forces. The blunt LE points us into a thick wing, such a a wing offering the increased structural strength, along with better lift coefficient. The drag coefficient is also greater; the drag of wings was not that great because the wings themselves being comparatively small.
The later designs, be it Allied or Axis, would (some of them should) feature the sharper leading edges. Not many of the fighters were featuring sharp leading edges, to my eyes it was the MC.20x series with sharpest LEs. Spitfire comes close, too. The Fw-190 was using, should we say, a more advanced wing profile (NACA 230 series, same as Grumman Bearcat, for example), not a blunt LE there?

As for the spinners: some AFs were not using them in their radial-engined fighters, mostly because of engine cooling. If we take a look at Bf-109, the outlines of the spinner smoothly blends into engine cowling, that would be impossible to achieve with sharp spinner.

 

[spicmart]

We can take a look at time the planes were designed.
The Bf-109 was a contemporary of Hurricane, ie. being designed in the era when monoplanes were to replace biplanes in most of the air forces. The blunt LE points us into a thick wing, such a a wing offering the increased structural strength, along with better lift coefficient. The drag coefficient is also greater; the drag of wings was not that great because the wings themselves being comparatively small.
The later designs, be it Allied or Axis, would (some of them should) feature the sharper leading edges. Not many of the fighters were featuring sharp leading edges, to my eyes it was the MC.20x series with sharpest LEs. Spitfire comes close, too. The Fw-190 was using, should we say, a more advanced wing profile (NACA 230 series, same as Grumman Bearcat, for example), not a blunt LE there?

As for the spinners: some AFs were not using them in their radial-engined fighters, mostly because of engine cooling. If we take a look at Bf-109, the outlines of the spinner smoothly blends into engine cowling, that would be impossible to achieve with sharp spinner.

There are some planes that held the same profile to the end (same NACA airfoil), for example the 190, Corsair and the Grumman family of fighters. They did have blunt LEss in comparison.
Because if you take a closer look the majority of fighters had sharper LEs than german fighters:
Lavochkins, Yaks, the japanese from the Zero onwards (Tojo, Frank, Ki-100, George), Spitfire of course, even the P-47.
Laminar flow wings are excluded from this.
Just take no laminar airfoils
Why do you consider NACA 230 advanced?

 

[tomo pauk]

I don't consider it advanced, it was advanced in late 1930s

You can note that the planes you've mentioned were all designed after the Bf-109 was, their engineers able to use the ever better aerodynamic theory, along with air tunnel data.
Once the wing was designed production started, it was a major undertaking to change it while the big war was going on.

 

[spicmart]

Of course in the late thirties .
It is maybe right with the 109 but not the spitfire regazding the time they have been created.
And what about the Fw 190 and the Grumman fighters? They were later and too late aircraft yet with an (outdated) airfoil?

 

[Shortround6]

All airfoils are a compromise. Many sharp edged, low drag air foils have poor stall characteristics and or poor lift drag ratios at low speeds. Field performance may be more important than a few mph of top speed, especially to a carrier plane. You can have the fastest fighter plane in the world, if it can't get off a carrier deck it is useless to the navy.

 

[tomo pauk]

Of course in the late thirties .
It is maybe right with the 109 but not the spitfire regazding the time they have been created.
And what about the Fw 190 and the Grumman fighters? They were later and too late aircraft yet with an (outdated) airfoil?

SR6 covers this - judging from the planes the NACA 230 series were used (Fw-190, Bearcat, A-20), it was a very balanced profile, with good low and 'useful' high speed characteristics. The Fw-190 was able to take off with a torpedo, not shabby for the small wing area, though engine take-off power was commendable. The Fw-190Gs were undertaking operations with 2 x 300L (= 132 imp gals, 950 lbs) drop tanks and a 500 kg (~2200 lb) bomb. So I wouldn't say it was outdated. The high speed was not it's forte, when compared with really thin wings, or the laminar flow ones. The high speed of the Fw-190 was achieved partly because the wing was of modest area for power installed. Eg. wing profile drag coefficient, on a lift coefficient of 0,2, was 0,0089 for the Fw-190, compared with 0,0072 for P-51 (Von Karman report, via Vee's for victory). Bf-109B was at 0,0101, same source.

Spitfire was a later design, vs. Bf-109. It was using NACA 2200 series profile, also the hot stuff in mid-1930s as I can gather. It was a very low drag profile (Spitfire's wing have had the thickness of only 13,2 % at wing root, Hurricane was 19% IIRC), enabling the Spitfire to be both fast (despite the considerable wing area) and with low wing loading (because of considerable wing area) - meaning good handling maneuverability. The weight-lifting was not it's forte, the heaviest external payload being the 170 gal slipper fuel tank (170 imp gals x 7,2 = 1224 lbs, plus the empty tank weight), the slipper fuel tank capacity reduced to 144 gals if the rear fuel tanks are installed full. Applicable for Spit IX, according to Morgan Shackledy, pg. 314 (yep, finally got that one ).

 

[spicmart]

Eg. wing profile drag coefficient, on a lift coefficient of 0,2, was 0,0089 for the Fw-190, compared with 0,0072 for P-51 (Von Karman report, via Vee's for victory). Bf-109B was at 0,0101, same source.


Can you explain what this means?

 

[tomo pauk]

We can put the lift coefficient aside for a moment.
The wing profile drag coefficient (Cd of wing) is higher for the Fw-190 some 25% (compared with P-51), the Bf-109B has the Cd of wing even greater, some 40%, when compared with P-51. That means that wing drag (or, equivalent flat plate, basically, the Cd multiplied with wing area) will be, for same wing area, 25% greater in Fw-190, and 40% greater in Bf-109B.

The wing area of P-51D was 21,83 m^2, that of Fw-190A was 18,30, of Bf-109B was 16 m^2. Multiplied with respective Cd of wings, we arrive at 0,157, 0,163 and 0,1616 m^2 of equivalent flat plate; the greater that, the more engine HP need to be used to overcome the drag generated. Of course, for plane's total drag, the drag of other parts of the plane need to be calculated in.

 

[davebender]

Did all Fw-190s use the same type wing? Did all P-51s use the same type wing?

 

[tomo pauk]

Fw-190 - yes, once it was decided, in prototype stage, to go with a 'big' wing, the 'small wing' being used on 1st prototypes. The V5 1st received 'big wing' (ie. the same size used until the end)
P-51 - IIRC the -H was using all-new wing.

 

[nuuumannn]

Can you explain what this means?

In layman's terms, the co-efficient of lift is a figure that is based on varying factors that determine how much lift a particular wing profile might create. The opposite is with drag co-efficient. Lift/Drag ratio is the efficiency of an aerofoil section taking these two factors into account. In Tomo's post it means the P-51D had a more efficient wing than the Fw 190A and the Bf 109B. Lee Atwood was said to be a keen fisherman and modelled the profile of the P-51's wing on the body of a trout.

 

[tomo pauk]

Lee Atwood was said to be a keen fisherman and modelled the profile of the P-51's wing on the body of a trout.

That's a good one Schmued was the designer.

 

[riacrato]

Fw-190 - yes, once it was decided, in prototype stage, to go with a 'big' wing, the 'small wing' being used on 1st prototypes. The V5 1st received 'big wing' (ie. the same size used until the end)
P-51 - IIRC the -H was using all-new wing.

IIRC P-51 wing changed from B/C to D adding the bend at wing root, thus slightly increasing wing area. Profile stayed the same though I assume.

 

[Shortround6]

I believe the wing stayed the same (with kink to clear main wheels) from the Mustang I (P-51/P-51A) through the "D". Not sure about the "F, "G" and "J". "H" had the kink removed.

 

[nuuumannn]

Schmued was the designer.

Attwood researched the aerodynamic considerations that went into the Mustang, including the wing profile and the radiator location and the use of the Meredith effect. Ray Rice was also a major influence on the design, too. It was a joint effort, just like Mitchell was not solely responsible for the Spitfire.

 

[tomo pauk]

Agreed that it was the joint effort.
The P-51 wing shape was base upon NACA 45 series, the NAA number of the wing design being 73-01001. The alternative design, based on NACA 230 series, have had the design number X73-01003. (per Vee's for Victory, pg. 109), that one was not built, of course.
There is also a reference in Mustang by Gruenhagen, pg. 40, where is stated that NAA was provided with unpublished NACA research material.

added: for the lightweight P-51s (-F, -G -H), the wing was of new design, thinner, with slightly different sweep back, washout, chord, while featuring the flaps ailerons of smaller area than wartime standard wing (P-51 through P-51K), per Gruenhagen

 

[nuuumannn]

where is stated that NAA was provided with unpublished NACA research material.

Yep, it was Attwood who went to NACA and who came across F.W. Meredith's paper on airflow cooling research. He approached the RAE at Farnborough as well.

 

[drgondog]

A lot to synthesize from the posts above. First Total Parasite Drag is the sum of individual drag components which vary with RN (i.e. Wing, Empennage, Cockpit enclosure, Fuselage, Carb/radiator scoop, exhaust stack) plus miscellaneous items which are not a function of RN such as (pitot tube. bomb racks, radio masts, machine gun ports or exposed barrels, surface roughness and 'leaks' from control surface and door/hatch/wheel enclosures).

For Zero CL, other wise referred to as Zero Lift Drag Coefficient, ALL the above Parasite Drag components are summed - then multiplied by the Correction for Compressibility.

When Lift is greater than Zero, an additional Parasite Drag component, namely Drag due to angle of attack is also added to the Parasite Drag block. For conventional engine a/c these components are the original Empennage, Cockpit Enclosure, Fuselage, etc but only that portion of the wing immersed in the propwash/slipstream. That summation is multiplied by the point on the "increment of Parasite Drag Coefficient vs Lift Coefficient plot derived from Wind Tunnel testing. This Delta is also a function of Reynolds Number. For a P-51, the wing parasite drag base = ~ 38% of the CL=0 Wing Parasite Drag.

The Wing/Empennage, Fuselage and Radiator Scoop dominate Parasite Drag.

To get total Drag, you then add to the Mach corrected Parasite drag above to Induced Drag.

The L/D ratio is calculated on the ratio of Total Lift/Total Drag at the point where Induced Drag = Parasite Drag. Cruise speeds and optimal range estimations start in this velocity range and vary, naturally, with altitude

For those that remember my frustration in explaining the major differences between CDo in zero lift level flight versus banked/high G/high CL flight to frame assumptions regarding modeling turn performance above and beyond W/L and CL discussions, the above explanation is central to my arguments.

Combine Drag factors above which is only 'testable' for level or non-eccentric angle of attack flight in a wind tunnel and move to the real world
- take the next leap of complexity to derive the Free Body diagram of a banked, asymmetrically loaded lift (and drag) distribution, add trim drag, calculate non-optimal propeller efficiencies at mid velocity/constant RPM/Max Power settings with sideslip considerations - and just try to calculate the corner speed and actual CL.

 

[drgondog]

As to P-51H. Some interesting differences from the preceding Mustang designs.
1. Wing was newer 66 series low drag airfoil. 66-(1.8) 15.5 section at root, 66-(1.8) 12 section at tip.
2. Wing span slightly larger, area 235 sq ft vs 233.2. Mean Aerodynamic Chord = 80.17 in vs 79.6 in.
3. Wetted area greater, fuselage length greater, empennage area greater.
4. Parasite drag lower at any given RN, Induced Drag Lower for any given Velocity
5. Empty weight of P-51H was 6535 pounds, P-51B was 7043 w/85 gallon tank (empty), P-51D was 7260 w/85 gallon tank (empty).
6. W/L for empty condition for P-51H was 27.8, for P-51B was 30.2, for P-51D was 31.1

It is easy to see why the P-51H with the same engine as the B/D will always have for same load out a better turn, climb and level speed than the B/D. It took more than a year for Packard to iron out the 1650-9 post, VE Day, and by that time 150 octane fuel as well as requirement for WI/90" boost was no longer important.