Area Ruling Questions

[Jane-DoH]

Okay, for a long time I understood the area-rule concept as basically "where the wings get thicker and bigger, the fuselage gets thinner", eventually as I actually read more about the concept relating to cross-sectional area the concept I used was basically to think of the airplane like a sliced loaf of bread with each section getting progressively bigger until the middle then narrowing back down and the idea of area ruling is to produce a cross-sectional configuration that produces the minimum wave-drag -- thus with the fuselage cross-section thinning down as the wing's cross-section increasing as it's span and thickness increased then decreased, the ideal cross-sectional shape is maintained.

More recently, I read the best explanation yet: As the airflow goes over the wings, like usual, it accelerates over the top; at transonic speeds, the airflow goes supersonic then dams up into a shockwave -- the faster you go, the more area over the top of the wing is supersonic, and the shockwave traverses further and further back; the fuselage is also curved as well and as the airflow goes over convex shaped sections, you get an acceleration over those areas too, and supersonic zones as well with shockwaves terminating at the end of them; being that the thickest point of the fuselage and wings are often right near each other, the fastest airflow over the wing and fuselage effectively amplify the effects of each other producing an unusually powerful shockwave compared to the effects of just one of them by themselves. This explanation seems to explain why the XF-91 Thunderceptor originally was conceptualized with a V-tail -- less interference effects if you only have two airfoils joining the tail rather than three.

Now the questions I have involve the following

1.) The Germans first grasped the concept of Area-Ruling sometime around 1943 by a guy named Otto Frenzl, and by late 1943 wrote a description of this: After the war was over, why did we not end up with this knowledge then? We took all kinds of stuff from the Germans as we progressively occupied them towards the end of the war, and we have it now. The only thing I could think of is if the Russians got it, then after the Cold War we got the information.

2.) If the XF-91 Thunderceptor was originally conceived around a V-tail to avoid transonic interference effects where the tail joined the fuselage, then how is it that it wasn't understood that where the wings of the aircraft joined the fuselage of the aircraft you would get similar results?

3.) How come the F-102 and F-106 required area ruling and the XF-92 did not? The XF-92 had a smaller fineness ratio and thicker wings than the F-102 (all of which to my knowledge aggravate transonic interference effects).

4.) Do air-intakes count as cross-sectional area? Thinking of area ruling like the sliced-loaf of bread it seems to make sense as you get a very low-cross sectional area for the diameter (as there's a hole where the intakes are). I'm not sure where the engines get factored in here, but being that when they're on they produce more thrust than drag, I assume there's no factor; regardless if you think of area ruling not just as cross sectional area but the interference effect of multiple sets of airflows over curved surfaces interacting with each other and amplifying each other's effects, it doesn't seem to be valid (though without a traditional nose the curvature would start at the intake lip and that might yield less fuselage curvature)

[FlightPathOBN]

1. The Germans and the Americans developed the area rule interdependently, and the concepts merged after WW2.

2. The XF-91/92, predate Whitcombs supersonic research. The XF91 max speed was mach 1, so it was not likely an issue.

3. The F102/106 did not originally incorporate the area rule and had difficulties at the sound barrier. The YF-102/106 did and speed through the barrier, the 106 being roughly 2 times as fast at Mach 1.6.

4. Yes the area of the intakes count, as a function of the nose break. You have to factor in the nose section.

[Jane-DoH]

FlightPathOBN

1. The Germans and the Americans developed the area rule interdependently, and the concepts merged after WW2.

Then how come we weren't aware of that 1943 research paper post WW2? It would seem that we weren't fully aware of area-ruling until 1952 with Richard Whitcomb's work.

The XF91 max speed was mach 1, so it was not likely an issue.

Actually, the XP-92/XP-92A and XF-91 were both designed to have supersonic performance. The XF-91 had an afterburner, four rocket-engines, and was capable of Mach 1.71 with the rockets and everything running. It was most certainly supersonic.

3. The F102/106 did not originally incorporate the area rule and had difficulties at the sound barrier.

The YF-102 had no area-rule, the YF-102A was area-ruled as was the production F-102A; the F-106 was area-ruled from the get-go and was originally called the F-102B

4. Yes the area of the intakes count, as a function of the nose break. You have to factor in the nose section.

But if you don't have a nose-section, just an intake lip?

[FlightPathOBN]

A bit combative with someone answering your questions.

The area rule was a concept, but there was no way to actually test it out because supersonic wind tunnels were not available until 1951. The XF-91 developed in 1946, so it would not have had the advantage of the area rule design validations.

In August 1952, the first YF-102 was NOT able to achieve Mach 1 (0.98) in the tunnel and Whitcomb redesigned it using the area rule, and in October 1953, the YF-102A hit supersonic.
In January 1954, the flight test on the original was done by the Air Force and in level flight was only able to achieve 0.98 Mach, confirming the wind tunnel tests.

These are from Hansen, Engineer in Charge, and "Nasa's Contributions to Engineering"

[Brian Abraham]

The Sears–Haack body is the aerodynamic body shape with the lowest theoretical wave drag. Aircraft designed to operate at high subsonic or supersonic speeds have their cross-sectional areas designed to match as closely as possible the proportions of Sears-Haack body.

By Whitcomb's area rule, the derivative of cross-sectional area gives wave drag. Thus, the Sears–Haack body is pointed at two ends and grows to a maximum and then decreases toward the second point.

Under the area rule, shapes with the same cross-sectional area at each point along their length as this shape have the minimal amount of wave drag, and the overall shape of many aircraft designed with transonic flight considerations have cross-sectional areas that approach this form (despite appearances).

The area rule was discovered by Otto Frenzl when comparing a swept wing with a w-wing with extreme high wave drag working on a transonic wind tunnel at Junkers works in Germany between 1943 and 1945. He wrote a description on 17 December 1943, with the title “Arrangement of Displacement Bodies in High-Speed Flight”; this was used in a patent filed in 1944. The results of this research were presented to a wide circle in March 1944 by Theodor Zobel at the “Deutsche Akademie der Luftfahrtforschung” (German Academy of Aeronautics Research) in the lecture “Fundamentally new ways to increase performance of high speed aircraft.”

Subsequent German wartime aircraft design took account of the discovery, evident in the slim mid-fuselage of aircraft such as the Messerschmitt Me P.1112, P.1106, and the indisputably wasp-waisted Focke-Wulf Fw 1000x3 type A long range bomber, but also apparent in delta wing designs like the Henschel Hs 135. Several other researchers came close to developing a similar theory, notably Dietrich Küchemann who designed a tapered fighter that was dubbed the “Küchemann Coke Bottle” when it was discovered by U.S. forces in 1946. In this case Küchemann arrived at the solution by studying airflow, notably spanwise flow, over a swept wing. The swept wing is already an indirect application of the area rule.

The derivation and shape were published independently by two separate researchers: Wolfgang Haack in 1941 and later by William Sears in 1947.

Wallace D. Hayes, a pioneer of supersonic flight, developed the supersonic area rule in publications beginning in 1947 with his Ph.D. thesis at the California Institute of Technology.

Richard T. Whitcomb, after whom the rule is named, independently discovered this rule in 1952, while working at the NACA. While using the new Eight-Foot High-Speed Tunnel, a wind tunnel with performance up to Mach 0.95 at NACA's Langley Research Center, he was surprised by the increase in drag due to shock wave formation. The shocks could be seen using Schlieren photography, but the reason they were being created at speeds far below the speed of sound, sometimes as low as Mach 0.70, remained a mystery.

In late 1951, the lab hosted a talk by Adolf Busemann, a famous German aerodynamicist who had moved to Langley after World War II. He talked about the difference in the behavior of airflow at speeds approaching supersonic, where it no longer behaved as an incompressible fluid. Whereas engineers were used to thinking of air flowing smoothly around the body of the aircraft, at high speeds it simply did not have time to "get out of the way", and instead started to flow as if it were rigid pipes of flow, a concept Busemann referred to as "streampipes", as opposed to streamlines, and jokingly suggested that engineers had to consider themselves "pipefitters".

Several days later Whitcomb had a "Eureka" moment. The reason for the high drag was that the "pipes" of air were interfering with each other in three dimensions. One could not simply consider the air flowing over a 2D cross-section of the aircraft as others could in the past; now they also had to consider the air to the "sides" of the aircraft which would also interact with these streampipes. Whitcomb realized that the Sears-Haack shaping had to apply to the aircraft as a whole, rather than just to the fuselage. That meant that the extra cross-sectional area of the wings and tail had to be accounted for in the overall shaping, and that the fuselage should actually be narrowed where they meet to more closely match the ideal.

[Jane-DoH]

FlightPathOBN

A bit combative with someone answering your questions.

My apologies -- I didn't intend to be combative. I don't mind constructive criticism when I'm imparting knowledge to other people, so I didn't see it as being a major problem.

The area rule was a concept, but there was no way to actually test it out because supersonic wind tunnels were not available until 1951.

I thought the first supersonic tunnel was available in November 1945, I'd almost swear I read about this when I was reading about the development of the USN's Bumblebee project, which would ultimately evolve into the RIM-8 Talos.

I don't know much about the specifics of the wind-tunnel though, if it was suitable for testing a model aircraft and if NACA even knew about it.

The XF-91 developed in 1946, so it would not have had the advantage of the area rule design validations.

True, but they still seemed understood about the basic principle to some extent -- after all they did intend to use a V-tail as to reduce the interference effects of where the tail surfaces joined the fuselage.

In August 1952, the first YF-102 was NOT able to achieve Mach 1 (0.98) in the tunnel and Whitcomb redesigned it using the area rule, and in October 1953, the YF-102A hit supersonic.
In January 1954, the flight test on the original was done by the Air Force and in level flight was only able to achieve 0.98 Mach, confirming the wind tunnel tests.

Fascinating, I remember reading in several locations that the plane could do 812 to 870 mph (I've heard claims this was in a dive or level flight -- it would make sense if that was in a level flight) -- if this figure was based on a dive-speed, then these figures seem entirely possible.

The area ruling made a hell of a difference as the F-102A was way more than twice as fast. It was probably twice as fast as a YF-102 in a dive in level flight :}


Brian Abraham

The Sears–Haack body is the aerodynamic body shape with the lowest theoretical wave drag. Aircraft designed to operate at high subsonic or supersonic speeds have their cross-sectional areas designed to match as closely as possible the proportions of Sears-Haack body.

Understood

The area rule was discovered by Otto Frenzl when comparing a swept wing with a w-wing with extreme high wave drag working on a transonic wind tunnel at Junkers works in Germany between 1943 and 1945. He wrote a description on 17 December 1943, with the title “Arrangement of Displacement Bodies in High-Speed Flight”; this was used in a patent filed in 1944. The results of this research were presented to a wide circle in March 1944 by Theodor Zobel at the “Deutsche Akademie der Luftfahrtforschung” (German Academy of Aeronautics Research) in the lecture “Fundamentally new ways to increase performance of high speed aircraft.”

What happened to that research post-war? We have the knowledge now, what happened between 1945 and now?

Wallace D. Hayes, a pioneer of supersonic flight, developed the supersonic area rule in publications beginning in 1947 with his Ph.D. thesis at the California Institute of Technology.

If his discovery was made in 1947, why wasn't it applied right away rather than years later in 1952? Was it due to the inability to validate it in the tunnel, or some other reason?


R.C.
"That being said, I'd like to remind everybody in a manner reminiscent of the SNL bit on Julian Assange, that no matter how I die: It was murder (even if there was a suicide note or a video of me peacefully dying in my sleep), and should I be arrested or framed for a criminal offense, or disappear entirely -- I think we all know who to blame for it"

[Jane-DoH]

I just found something very interesting regarding area-ruling. I was reading this book called "U.S. Naval Air Superiority: Development of Shipborne Jet Fighters 1943-1962" by Tommy H. Thomason

There is a section on page 211 (Figure 13-1) which discusses the fact that Grumman actually seems to have figured out the benefit of Area-Ruling before Richard Whitcomb did. Did they derive this data on their own, or using Wallace D. Hayes' data?

[FlightPathOBN]

See if you can locate details of the Volta Conference 1935. There appears to be some ref to the area rule presented by Adolf Busemann. In 1944, Dietrich Kuchmann appears to have presented data about a 'coca cola shaped' fuselage, with Robert Jones developing the same concept at the same time. (1945)


Things really do go better with Coke...

[Jane-DoH]

FlightPathOBN

See if you can locate details of the Volta Conference 1935.

Area ruling was discussed as early as 1935?

There appears to be some ref to the area rule presented by Adolf Busemann.

At what point did Busemann discover the area rule?

Robert Jones developing the same concept at the same time. (1945)

I knew Robert T. Jones did a lot of research on swept wings which if I recall were based on data reduced from the Gluhareff Delta. I didn't know he was doing research on Area Ruling.

[FlightPathOBN]

Volta Conf in 1935 subject was "High Speeds in Aviation"

Recalling the Vth Volta Congress: High Speeds in Aviation - Annual Review of Fluid Mechanics, 28(1):1 (http://www.annualreviews.org/doi/abs/10.1146/annurev.fl.28.010196.000245?journalCode=fluid)

I found the reference to the above post in the book, Nasa's Contributions to Aeronautics", Case 2..Richard Whitcomb abd the Quest for Aerodynamic Efficiency"

[CliveL]

Area ruling was discussed as early as 1935?

Area ruling to reduce wave drag has been around for a lot longer than that in yacht design!

[FlightPathOBN]

Area rule comes into play with supersonic speeds, so I am not sure if that would ever be useful to a yacht.

I understand that the keel for the Kiwi was designed using the area rule...just not sure how that was justified...
http://operationsbasednavigation.com/wordpress/wp-content/uploads/2011/07/KiwiKeel.jpg

[CliveL]

One reason is that the maximum speed is limited by wave drag and that depends on the shape of the waterline when the boat is heeled. Making sure that this is a good 'wave drag reducer' depends on having a good area distribution oo the waterline . This is just area ruling.

[FlightPathOBN]

Well, I have long stated that many aeronautical issues have already been solved in nautical design, and that we need to look at cross discipline research...after all...air is just thin water...

[Jane-DoH]

FlightPathOBN

Volta Conf in 1935 subject was "High Speeds in Aviation"

Recalling the Vth Volta Congress: High Speeds in Aviation - Annual Review of Fluid Mechanics, 28(1):1 (http://www.annualreviews.org/doi/abs/10.1146/annurev.fl.28.010196.000245?journalCode=fluid)

I found the reference to the above post in the book, Nasa's Contributions to Aeronautics", Case 2..Richard Whitcomb abd the Quest for Aerodynamic Efficiency"

The article only has one page shown and doesn't mention anything about area-ruling. Regardless I'm surprised that people were talking about area-ruling this far back in time. It makes it even more surprising that the YF-102 had to be redesigned with area-ruling.

Why wasn't this commonly known in the United States until the 1950's?

[bearfoil]

Brian Abraham

As an aside, it is rumored that at Bell, a decision was made to design the X-1 in the shape of a .45 caliber bullet, as this projectile was supersonic.

Do you think that the success Bell had with their rocket created temporary obstacles to the aha of area rule?

I was unaware the 102 ever went super. For years, in the '50's, everything popular had "Coke Bottle Shapes".

[galaxy flyer]

Brian

The Deuce didn't go supersonic as originally designed, but was about 1.3 when the fuselage was area ruled to account for the cross section of the delta wing. The F-106 was designed area ruled on the design board.

What is more interesting was how long it took to use area ruling in subsonic planes. Most business jets (mine, for example and the Citation X. "Mine" in the I fly it sense) now have area ruled tail cones, as did my namesake's tail.

[barit1]

Ditto the 747, especially the SP.

[Jane-DoH]

bearfoil

As an aside, it is rumored that at Bell, a decision was made to design the X-1 in the shape of a .45 caliber bullet, as this projectile was supersonic.

IIRC it was a .50 calibur bullet they based the shape on. You're correct though in that they selected that shape because they knew it could fly supersonic.

Do you think that the success Bell had with their rocket created temporary obstacles to the aha of area rule?

That's something I'm interested in hearing too...


galaxy flyer

The Deuce didn't go supersonic as originally designed, but was about 1.3 when the fuselage was area ruled to account for the cross section of the delta wing.

It was stated to be more than twice as fast when area ruled. The top speed was 0.98 when level and non-area ruled so it's top speed would have to be over 1.96

The F-106 was designed area ruled on the design board.

That's correct, it also had a number of improved design features. The inlets were variable-geometry which improved efficiency at both subsonic and supersonic speeds (larger area when subsonic, smaller area when supersonic) and allowed a shorter inlet duct, which in turn allowed the forward fuselage to be cleaned-up (the aft fuselage was cleaned up too -- it didn't have those blister fairings); it had an idle-thrust reducer which helped reduce the tendency for the exhaust to blow around unsecured objects when taxiing (I don't think it had any significant effect on thrust at high power or on burner); it also had a multi-stage afterburner and more fuel capacity. I don't know if it had conically cambered wings from the get-go, but early models did have the wing-fences, and later models had a fixed-slot in lieu of them (I'm amazed they didn't have compressibility problems with an open slot at supersonic speeds, but evidently it didn't).

[bearfoil]

If the 102 went double, I'll grind one up and eat it, fluids and all.

The sweetest looking a/c that features a/r is the T-38. That pinchee waist is sexy. Transonic only, but the world's best trainer. I think the Thunderbirds looked at their best in the little sweetie. Thanks to the fuel shortage, every silver lining has a cloud.

[barit1]

The HondaJet (http://world.honda.com/HondaJet/) is a good example.

[galaxy flyer]

Jane

Just had a beer with a friend who flew Deuces--M 1.2 was about it, says he. I am not sure he would eat one, though. Cost me two Guinnesses