Supercritical airfoil

[jim]

Tatsuo Hasegawa was a desigher that was involved in the development of Ki-94-II . A very late japanese prototype of high altitude , single engined interceptor. A unique characteristique was that Hasegawa designed an airfoil that he named "TH airfoil" . It was very similar to the supercritical airfoil that the americans developed in the 60s . Unfortunately Ki-94-II was not ready to fly before the end of war
My question is: What advantages would have the use of such airfoil in a piston engined fighter? Could be decisive?

 

[drgondog]

Delays transonic drag rise and diminishes the wave drag - so faster in a dive with more control is one example.

 

[jim]

Delays transonic drag rise and diminishes the wave drag - so faster in a dive with more control is one example.

Since it has effect on transonic area - above M 0,7- that means for axis piston engine fighters would be useful only during dives .Correct?
Wikipedia suggests that such wings have also good landing behavior. True?
Such wings require heavier structures and control surfaces?

 

[tomo pauk]

This web page seem wort a look:

Tatsuo Hasegawa, Ki-94

One of the pictures linked there shows the flap system that looks like the version of Fowler flaps, that should allow for good low speed behavior.

 

[jim]

This web page seem wort a look:

Tatsuo Hasegawa, Ki-94

One of the pictures linked there shows the flap system that looks like the version of Fowler flaps, that should allow for good low speed behavior.

Nice site Mr tomo pauk
But i got confused. It calls the TH airfoil , laminar flow
From what i have read ,that means that it was not supercritical airfoil.
all late war japanese fighters used fowler flaps as combat flaps . I wonder why germans did not use them as well
The combination of laminar flow wing with combat flaps looks interesting to me

 

[tomo pauk]

Nice site Mr tomo pauk
But i got confused. It calls the TH airfoil , laminar flow
From what i have read ,that means that it was not supercritical airfoil.

Here is the article about the supercritical airfoil, the TH airfoil seems not to be in that category.

all late war japanese fighters used fowler flaps as combat flaps .

Yep, their variation on theme were called 'butterfly flaps', mostly automatically operated IIRC?

I wonder why germans did not use them as well
The combination of laminar flow wing with combat flaps looks interesting to me

Japanese were putting great emphasis on maneuverability, much more than another belligerents. The combination you find interesting should allow the 'Sea Mustang' to be a viable choice?

 

[wuzak]

And here I was expecting a discussion about wings whose feedback to pilots would "is that all you've got", "you can do better" or "your grandma could fly better than you".

 

[zjtins]

The Ki-94 page showing that airfoil and the Whitcomb airfoil are not the same.
The Ki-94 wing and airfoil resemble the P-51, which make sense as in it works use it.

 

[jim]

Here is the article about the supercritical airfoil, the TH airfoil seems not to be in that category.



Yep, their variation on theme were called 'butterfly flaps', mostly automatically operated IIRC?



Japanese were putting great emphasis on maneuverability, much more than another belligerents. The combination you find interesting should allow the 'Sea Mustang' to be a viable choice?

i find it interesting because ,perhaps, could be a way for the germans to offset the results of lack of evolution of their aeroengines in mid war years. The laminar flow wing could allow greater speeds for the needs of the western front ,while the combat flaps could offer greater agility and lower landing speeds for the needs of the eastern front. At least on paper

 

[zjtins]

Laminar flow reduced drag at zero incidence but also reduce lift at high incidence. There are always tradeoffs.

 

[nincomp]

The Ki-94 page showing that airfoil and the Whitcomb airfoil are not the same.
The Ki-94 wing and airfoil resemble the P-51, which make sense as in it works use it.

I agree. I do want to point out, however, that the "laminar airfoils" used in WWII did not produce extensive laminar flow in practice (laminar flow turned out to be extremely sensitive to small variations in profile and smoothness - even flush rivets would cause turbulent airflow). They did, however increase the speed of the aircraft by delaying compressibility issues.

The forum member "Glider" may have some more input, since gliders (sailplanes) have been the primary type of aircraft to successfully utilize laminar flow.

The supercritical airfoils were often touted as generating good lift at low speeds, but they did not catch on with slower aircraft. I recall that there was a flurry of attempts to use supercritical airfoils on some lower speed General Aviation and homebuilt aircraft in the 1970's and 1980's, but interest soon waned. As I recall, the airfoils required a disconcertingly large angle of attack at takeoff and landing as well as generating a large nose-down moment. There were likely other unfavorable characteristics of which I am not aware.

High lift is not required for high speed cruising, but it is required for the high-G maneuvers needed by fighter aircraft. The higher speed aircraft that use supercritical airfoils of which I am aware also utilize high-lift devices (leading-edge slats and slotted fowler flaps) for low speeds.

The distinguishing traits of the supercritical airfoils that I have seen are relatively large diameter leading edges, almost flat upper surfaces, and very noticeable downward cusps (curve) near the trailing edges. This was certainly not an intuitive design, especially at a time when very little was known about compressibility and the effect of shock waves. Indeed, the Whitcombe airfoil was not developed until the 1960's

Not-the-same Jim.

P.S. Wuzak, "is that all you've got", "you can do better" or "your grandma could fly better than you". I hope that you are happy now.

 

[jim]

Laminar flow reduced drag at zero incidence but also reduce lift at high incidence. There are always tradeoffs.

Not in P 51 s case. It could out run and out manouver , out dive and out climb ,at the same time ,any of its opponents. At least that is the claim of many people. no tradeoffs for P51.

 

[jim]

I agree. I do want to point out, however, that the "laminar airfoils" used in WWII did not produce extensive laminar flow in practice (laminar flow turned out to be extremely sensitive to small variations in profile and smoothness - even flush rivets would cause turbulent airflow). They did, however increase the speed of the aircraft by delaying compressibility issues.

The forum member "Glider" may have some more input, since gliders (sailplanes) have been the primary type of aircraft to successfully utilize laminar flow.

The supercritical airfoils were often touted as generating good lift at low speeds, but they did not catch on with slower aircraft. I recall that there was a flurry of attempts to use supercritical airfoils on some lower speed General Aviation and homebuilt aircraft in the 1970's and 1980's, but interest soon waned. As I recall, the airfoils required a disconcertingly large angle of attack at takeoff and landing as well as generating a large nose-down moment. There were likely other unfavorable characteristics of which I am not aware.

High lift is not required for high speed cruising, but it is required for the high-G maneuvers needed by fighter aircraft. The higher speed aircraft that use supercritical airfoils of which I am aware also utilize high-lift devices (leading-edge slats and slotted fowler flaps) for low speeds.

The distinguishing traits of the supercritical airfoils that I have seen are relatively large diameter leading edges, almost flat upper surfaces, and very noticeable downward cusps (curve) near the trailing edges. This was certainly not an intuitive design, especially at a time when very little was known about compressibility and the effect of shock waves. Indeed, the Whitcombe airfoil was not developed until the 1960's

Not-the-same Jim.

P.S. Wuzak, "is that all you've got", "you can do better" or "your grandma could fly better than you". I hope that you are happy now.

Mr nincomp
Very informative post. Excellent
What would be your proposition, for the wing of an ideal WW2 fighter? A wing that would achieve the controvertial goals of high speed, low consuption at cruising speed ( goals that require low drag) and high manouverability and rate of climb (goals that require high lift).

 

[drgondog]

There was no real application for a supercrit wing during WWII. It delayed transonic wave formation - true - but because of the necessity for the cusp at the trailing edge to provide lift, the center of lift was moved aft with attendat growth of CMac - which created more sever problems (pitch down) when the shock wave formed. Additionally the CL of that type wing is lower for Scrit wing than conventional/comparable t/c ratio.

 

[tomo pauk]

It would be, indeed, hard to beat the laminar flow wing combined with Fowler flaps, and maybe also slats?

For P-51: statements about the plane's ability to out-climb and outmaneuver opponents should 1st take into account the height, position, speed and loading state of both.

 

[nincomp]

Mr nincomp
Very informative post. Excellent
What would be your proposition, for the wing of an ideal WW2 fighter?

Well I am fairly certain tht @ a}f)oil 0f gibb3r ugh fl33mzfoil would be best!
And that is my opinion. Gee, is my keyboard acting up? Too bad, because that was a brilliant answer.
[I could not claim that my cellphone was losing your signal, so I did the best I could... I blamed the keyboard]

I honestly do not know. There are some on this forum with more knowledge than I. I do know that no one wing design would be the best at everything, so there is not a one-shape-fits-all answer. A high altitude fighter may not make the best low level fighter or fighter-bomber. To make the decision more difficult, second question would be "how much complication do you want?" The P-38 had fowler flaps. The Me-109 had retractable leading edge slats. Are the control surfaces to be boosted or not?

The P-51 was impressive with its "laminar flow" wing, but the the Me-109, Me262 and F8F Bearcat (which was a little bit late for the war) each did very well with non-laminar flow designs.

In addition, I know that at least one highly modified P-51-based race plane used different airfoils, but I can't find the info at the moment. I also don't know how well the performance at the Reno Air Races correlates to better fighter performance.

Maybe GregP or someone else can help here?

ps. I started this response several hours ago before my Wife and Kids got home. I stopped to have some family time.
Drgondog is more knowledgeable than I am, so I am glad that he has responded since I began this post.

 

[OldSkeptic]

Not in P 51 s case. It could out run and out manouver , out dive and out climb ,at the same time ,any of its opponents. At least that is the claim of many people. no tradeoffs for P51.

Oh there were. Its climb was only average for the time (that was as much a weight issue though) and as for out turning, depends on the flight regime.

I was just re-reading a Mustang pilot's account where he and another pilot got into a turning contest with a 190 at lower altitudes. He was in the rear and could just slowly out turn the 190 (he was very experienced), which was holding the leading Mustang in its turn (and both Mustangs had cranked on a bit of flap to aid their turn too).
At a higher speed and altitude then the Mustang would have almost certainly turned far faster than the 190.
But the margins in various flight regimes were narrower than most people realise.

But one big price it paid was its nasty stall characteristics (which have little warning), which catches out people even today with their warbirds (a Mustang went down a couple of years ago, with a classic stall).

Pilots were warned not snap roll, (ever) as you would go straight into a spin. High G turns could easily go straight into an accelerated stall and spin, not too bad if you had enough altitude to recover, but if you didn't life could get interesting. Plus, before the strakes were introduced, you risked losing the rear upper tailplane.

So it was very good across a wide range of flight envelopes, but it wasn't perfect, but then again nothing was (or even is today).

 

[nincomp]

OldSkeptic,
I am glad that you brought up the vices of the Mustang's laminar-flow wing. I tend to tread lightly when discussing any of its potential shortcomings since, for some, the P-51 is a religion, not an airplane. I was certainly raised to believe this. You are a braver man than I, OldSkeptic.

If I had wanted to give a simple, short, and not quite accurate answer to Jim's question of the ideal airfoil, I would have said a laminar flow type with gentler stall characteristics. The landing speed of such a wing, without additional high-lift devices would still be pretty high. I don't think that I would be comfortable landing at over 100 knots on a bumpy, soggy grass field.

I recently saw a documentary (on Youtube) about the Tempest. One pilot commented on the higher landing speed caused by the "low-lift high-speed wing." This supports zjtin's comment about the lower maximum lift of laminar flow designs.

Did the laminar-flow-winged Tempests have the same kind of unpleasant stall characteristics as the Mustang?

Thanks
Jim (but not the same Jim as the OP - unless I have developed some type of split personality)

 

[zjtins]

I looked up the ME109 E airfoil and P51D airfoil. The P51 drops CL drops rapidly above 10 degree AoA, the ME109 continues with a greater CL until around 20 degrees AoA. What saves the P51 is as long as they kept speed up then 6-8 degrees AoA is all the plane can do in a continuous banking turn. Once below ~275 MPH the ME109 has the advantage.

 

[nincomp]

To piggyback on zjtins' and my previous comments, the question of the "best airfoil" depends largely what you want it to do.

An interesting example of a potentially useful requirement would be the ability to perform a maneuver that several pilots have stated they used in order to turn the tables on a pursuing fighter. The lead plane would pull up suddenly into a high-speed stall. This would allow the plane to move up, over, and behind the attacker (the stall would quickly reduce airspeed). In order to do this maneuver, the aircraft must have gentle power-on stall characteristics and not tend to snap into a spin.

To paraphrase several expert pilots, it is important to know the capabilities of both your plane and of the enemy's plane, then force the enemy into a flight regime where your plane has the advantage.