Which aircraft had laminar flow wings?

[spicmart]

There are many planes known to have laminar flow wings like the Mustang, Sea Fury, Hornet, Raiden etc.. Yet there are some I've never heard to have them but if you look at pictures one could think that they feature them.
E.g. the Mosquito, the B-26 Marauder, some russian and japanese fighters.
Their wing leading edge is sharper and not as round as those of planes like the 109, 190 Corsair etc.. Also the maximum wing thickness seems to be further aft. Might this be an indication if laminar flow wings?

 

[Shortround6]

Not really. Most "conventional" wing profiles had the max thickness at around 30% of the cord. it could vary a bit but that left an awful lot of "room" for variations in thickness of wing for the profiles. Like one wing could be very near max thickness at 20% cord and another with the same max thickness in actual numbers at 30% (the same location) but use more taper getting there so at 20% it is thinner. It could very well look different but it is not a laminar flow wing.
Now before we get bogged down in what is laminar flow and what is not and NO wing outside a laboratory maintained laminar flow over the whole wing.
In General a laminar flow wing kept the airflow over the wing from going turbulent for another 5-15% of the cord than the normal airfoils. perhaps even as high as 20%. Many airfoils could keep the airflow smooth (laminar) for the first 5-15% of the cord.

a few extreme examples

Please note that airfoil #3 was quite common on WW I biplanes. WHile it gave high lift at low speeds and was thin as measured in percent it was not only high drag but often had a bad stall.

 

[Balljoint]

Agree with what's been said. However, a wing is "more laminar" if the thickness portion is further back on the wing, i.e. so that the airstream has positive contact with the wing. Also, once the wing starts to fall away from the direction of the airstream, the Coanda effect can be enhanced by tripping the air flow to set up a turbulent boundary layer.

As long as the airstream is "attached" to the wing, i.e. flying rather than stalling, it would seem that the flow is more or less laminar, i.e. organized and parallel. Perhaps someone with some actual knowledge can comment on this.

 

[pbehn]

Laminar Flow Airfoil

Some interesting stuff on the above link.

N.A. designed the mustang to be low drag the wings may have been designed to be laminar flow but from what I have read this was not achieved it requires surface cleanliness and smoothness not achievable on a combat aircraft in service. The whole aircraft was designed for low drag especially the close to zero cooling drag radiator, the whole plane was built to very fine tolerances to cut down drag at joints etc even the engine could be termed low drag as it had a lower profile than the early Merlins.

from the above link (which surprised me)
The Consolidated B-24 Liberator "Davis" airfoil was also a laminar flow airfoil, which predates the Mustang's. However, the designers of the B-24 only knew that their airfoil had very low drag in the wind tunnel. They did not realize that it was a laminar flow airfoil.

Also the Tempest was supposed to have laminar flow wings to overcome problems of the Typhoons thick wings.

 

[tomo pauk]

Not just that Tempest have had a more modern wing profile, the wing itself was much thinner in and of somewhat greater area. A real improvement over the Typhoon's wings.

 

[Zipper730]

from the above link (which surprised me)
The Consolidated B-24 Liberator "Davis" airfoil was also a laminar flow airfoil, which predates the Mustang's. However, the designers of the B-24 only knew that their airfoil had very low drag in the wind tunnel. They did not realize that it was a laminar flow airfoil.

Did David R. Davis realize that this low drag extended to high speed?

 

[Shortround6]

I could be wrong but in the case of the Davis airfoil it didn't.

I would note that the extent of the laminar flow rarely (if ever) reached the figures shown in actual service aircraft.
Some older airfoils

 

[pbehn]

SR the laminar flow discussion seems to be more like an abstract philosophical debate at time.

"A favorable pressure gradient is required to maintain laminar flow. Laminar flow airfoils are designed to have long favorable pressure gradients. All airfoils must have adverse pressure gradients on their aft end. The usual definition of a laminar flow airfoil is that the favorable pressure gradient ends somewhere between 30% and 75% of chord."

To my mind something that has only 30% of something is way short but that is what is said. Certainly 30% is better than nothing, the Davis profile as lower drag than others. it may or may not have 100% laminar flow but none did.

 

[Zipper730]

Just to be clear a pressure gradient means the range of pressure along the foil? As for adverse pressure gradients, you mean something that produces a "suction" to basically hold the airflow onto the surface?

 

[KiwiBiggles]

The "pressure gradient" refers to the change of pressure along the chord or the aerofoil. Intuitively, fluids flow readily from a higher pressure to a lower pressure. On the leading part of the aerofoil, the pressure is dropping along the chord, from ambient (or thereabouts) at the leading edge until the lowest pressure is reached; within this section of the chord we say that there is a favourable pressure gradient, and the flow stays largely attached to the surface. From the point of lowest pressure on, the pressure is increasing to once again reach ambient at the trailing edge; in this section the flow is 'fighting against' the unfavourable pressure gradient, and so has a tendency to detach from the surface and become turbulent.

The design of early laminar flow aerofoils pushed the point of maximum thickness rearwards, to try to delay the onset of turbulence. Of course by moving the point of lower pressure further aft, the adverse pressure gradient becomes much steeper and more likely to become turbulent, so there is a delicate balance between keeping attached non-turbulent flow over as much as the chord as possible, and causing too much turbulence and detached flow towards the trailing edge.

 

[spicmart]

I would say the Yak-3 wing looks quite laminar-flow-profile-like.
What do you think?

 

[pbehn]

View attachment 550163
View attachment 550165


I would say the Yak-3 wing looks quite laminar-flow-profile-like.
What do you think?

If it was as easy as just how a profile looks then huge resources wouldn't have been spent on wind tunnels. A Spitfires wing looks very aerodynamic and is thinner than a P-51s so to a layman like me it would seem to be lower drag. The physics of laminar flow are complicated and in some ways counter intuitive, "laminar flow" wings were in any case just slightly better not actually true laminar flow and achieving better laminar low did compromise other areas of performance slightly.

 

[Wurger]

Yak-3 like other flighters of the Yak series had the Clark YH ( modified Clark Y ) airfoil for the wing used. The max thickess for the profile is at 30% chord. So it is not the laminar airfoil because such ones have the max thickness at 35-70% chord. For sure the Polish bomber PZL 37 Łoś had the laminar airfoil IAW-743.

 

[drgondog]

Without going too deep in the weeds, NAA crafted the 45-100 airfoil based on the planned/design pressure distribution to achieve Low Drag while still achieving:
1.) CL, CD and CMac values
2.) Stall characteristics
3.) Minimum CDo for a broad range of angle of attack 'alpha'
4.) Wing Thickness T/C 'large enough' to maintain Low Frag but also reduce structural weight of primary spars.

Beginning with a pressure distribution close to the NACA 125 Laminar Flow Airfoil, the Horkey team cranked Friden Calculators for two weeks to perform complex space conformal mapping - combining Laplace, Theodorsen and Kutta-Joukowski methods. The first cut on the Pressure distribution was one that would generate desired Lift, Drag and Moment characteristics (without knowing yet what the airfoil shape must be) as described by Millikan's principles of selecting a wing, then map the associated surface velocities to achieve the pressure distribution about a rotating cylinder in a Complex Space. The conformal mapping process begins by distributing the velocity data along a rotating Circle in Complex Space, then by transformation, map the circle to an airfoil shape with similar but not yet final desired velocity distribution in Real Space.

The primary goal for a 'Laminar' flow airfoil/wing was to develop a smooth aerodynamic shape and surface which enabled more attached flow before boundary layer separation (BL separation is the trigger to cause a 'profile increase' to the free stream, which causes increasing pressure drag losses). This was achieved to a greater degree in wind tunnel tests of the NACA-125 Laminar Flow airfoil. The NACA-125 airfoil was too thick for High Speed application. It was unique in that it gradually achieved maximum thickness at approximately 50% of chord length instead of the conventional ~25%. Another objective for laminar flow airfoils was to extend the region of peak pressure distribution across a greater percentage of the airfoil chord, to regions past the maximum thickness of the airfoil. Accompanying such shape, for same thickness to chord ratio, is a lower velocity gradient (rate of change of airflow velocity) from airfoil nose to point of maximum thickness, than the corresponding conventional airfoil which had a maximum thickness closer to 25% of the chord. The shape of the wing was also more wedge like than conventional bulbous shape.

FWIIW, the NAA/NACA 45-100 airfoil max T/C was 16.1% at the root and at ~ 37.5 % of the Chord.[edit] The later XP-51F/G/J and H with NACA 65 and 66 series airfoils were close to 60%.

Horkey stated that there was in fact a small but definable laminar flow on the 45-100 but the primary purpose was Low Drag, which it achieved better than any US fighter. (I hesitate to state 'all' including other nations) save the series 66 on the P-63. Like the series 66 on the P-51H, both had slightly lower drag than 45-100 but the 66.2x-116 airfoil on the P-63 was a beast for low speed/stall range.

The Primary aerodynamic value for the NAA/NACA 45-100 was that the lower velocity gradient combined with the 'sharper' LE combined to delay both BL growth and Mach transition to a region further aft along the chord. Took 'longer' to reach critical mach, and when the shockwave originated further aft - the effect on the pitching moment was lower than say the P-38 or P-47 (or Bf 109 and Fw 190). The BL build up as a function of chord position was also lower - hence another reason for low drag.

 

[Peter Gunn]

Without going too deep in the weeds, NAA crafted the 45-100 airfoil based on the planned/design pressure distribution to achieve Low Drag while still achieving:
1.) CL, CD and CMac values
2.) Stall characteristics
3.) Minimum CDo for a broad range of angle of attack 'alpha'
4.) Wing Thickness T/C 'large enough' to maintain Low Frag but also reduce structural weight of primary spars.

Beginning with a pressure distribution close to the NACA 125 Laminar Flow Airfoil, the Horkey team cranked Friden Calculators for two weeks to perform complex space conformal mapping - combining Laplace, Theodorsen and Kutta-Joukowski methods. The first cut on the Pressure distribution was one that would generate desired Lift, Drag and Moment characteristics (without knowing yet what the airfoil shape must be) as described by Millikan's principles of selecting a wing, then map the associated surface velocities to achieve the pressure distribution about a rotating cylinder in a Complex Space. The conformal mapping process begins by distributing the velocity data along a rotating Circle in Complex Space, then by transformation, map the circle to an airfoil shape with similar but not yet final desired velocity distribution in Real Space.

The primary goal for a 'Laminar' flow airfoil/wing was to develop a smooth aerodynamic shape and surface which enabled more attached flow before boundary layer separation (BL separation is the trigger to cause a 'profile increase' to the free stream, which causes increasing pressure drag losses). This was achieved to a greater degree in wind tunnel tests of the NACA-125 Laminar Flow airfoil. The NACA-125 airfoil was too thick for High Speed application. It was unique in that it gradually achieved maximum thickness at approximately 50% of chord length instead of the conventional ~25%. Another objective for laminar flow airfoils was to extend the region of peak pressure distribution across a greater percentage of the airfoil chord, to regions past the maximum thickness of the airfoil. Accompanying such shape, for same thickness to chord ratio, is a lower velocity gradient (rate of change of airflow velocity) from airfoil nose to point of maximum thickness, than the corresponding conventional airfoil which had a maximum thickness closer to 25% of the chord. The shape of the wing was also more wedge like than conventional bulbous shape.

FWIIW, the NAA/NACA 45-100 airfoil max T/C was ~ 37.5 %. The later XP-51F/G/J and H with NACA 65 and 66 series airfoils were close to 60%.

Horkey stated that there was in fact a small but definable laminar flow on the 45-100 but the primary purpose was Low Drag, which it achieved better than any US fighter. (I hesitate to state 'all' including other nations) save the series 66 on the P-63. Like the series 66 on the P-51H, both had slightly lower drag than 45-100 but the 66.2x-116 airfoil on the P-63 was a beast for low speed/stall range.

The Primary aerodynamic value for the NAA/NACA 45-100 was that the lower velocity gradient combined with the 'sharper' LE combined to delay both BL growth and Mach transition to a region further aft along the chord. Took 'longer' to reach critical mach, and when the shockwave originated further aft - the effect on the pitching moment was lower than say the P-38 or P-47 (or Bf 109 and Fw 190). The BL build up as a function of chord position was also lower - hence another reason for low drag.

I read this three (3) times... now my head hurts.

I did glean two (2) things from this, well, three (3) actually:

1. Mustang -> FAST
2. Bill -> SMART
3. Me -> Feel like knuckle dragger...

 

[spicmart]

Spontaneously I would say the Yakovlev's wings are less draggy than those of Me 109 and Fw 190....

 

[Simon Thomas]

FWIIW, the NAA/NACA 45-100 airfoil max T/C was ~ 37.5 %. The later XP-51F/G/J and H with NACA 65 and 66 series airfoils were close to 60%.

I take it you meant that the location of the max T/C was at those points. An airfoil with a T/C of 60% would be rather thick.

Edit: Some great information in your post. Do you know the dates of when they started & finished design work on the airfoil?

 

[AlfaKiloSierra]

In fact, the term "laminar flow" wing is misleading, as the surface is not smooth enough to prevent turbulent flow. There was a Royal Air Establishment study that used a P-63 with polished filler paint, and that specific airplane attained laminar flow on the wing up to 60% of the chord behind the leading edge; however, the measured waviness of the surface was found to be less than 0.005 inches, unattainable in the field.

 

[Niceoldguy58]

The B-32 also used the so-called "Davis Wing". I'm not sure about the B-36, but it may have as well.

I'm not entirely sure about the B-29, but I believe the Boeing wing used on that beast probably had laminar characteristics, too

AlanG

 

[pbehn]

View attachment 550255
View attachment 550256

Spontaneously I would say the Yakovlev's wings are less draggy than those of Me 109 and Fw 190....

Black crosses were known to disrupt airflow.