Prandtl's Tripped Science vs Boeing Max

Prandtl making tripped experiments

Danger of tripping 

Ludwig Prandtl is viewed as the Father of Modern Fluid Mechanics because he offered a resolution of the pressing problems of fluid mechanics in the beginning of the 20th century including d'Alembert's paradox through his discovery of the laminar and turbulent boundary layer in wall bounded fluid flow.

The legacy of Prandtl is described in Prandtl-Essentials of Fluid Mechanics edited by Herbert Oertel, Springer 2004, with the following introduction

• The development of modern fluid mechanics is closely connected to the name of its founder, Ludwig Prandtl. 
• In 1904 it was his famous article on fluid motion with very small friction that introduced boundary-layer theory. 
• His article on airfoil theory, published the following decade, formed the basis for the calculation of friction drag, heat transfer, and flow separation.
• Prandtl was particularly successful in bringing together theory and experiment, with the experiments serving to verify his theoretical ideas. 
• It was this that gave Prandtl’s experiments their importance and precision. His famous experiment with the tripwire, through which he discovered the turbulent boundary layer and the effect of turbulence on flow separation, is one example. 
• The tripwire was not merely inspiration, but rather was the result of consideration of discrepancies in Eiffel’s drag measurements on spheres. 
• Two experiments with different tripwire positions were enough to establish the generation of turbulence and its effect on the flow separation. For his experiments Prandtl developed wind tunnels and measuring apparatus, such as the Göttingen wind tunnel and the Prandtl stagnation tube. 
• His scientific results often seem to be intuitive, with the mathematical derivation present only to provide service to the physical understanding, although it then does indeed deliver the decisive result and the simplified physical model. 
• According to a comment by Werner Heisenberg, Prandtl was able to “see” the solutions of differential equations without calculating them.

To give the highlighted parts perspective recall that when I was awarded the Prandtl Medal in 2014 by ECCOMAS, I stated that I would receive the medal under the condition that it would be expressed that the New Theory/Computation of Flight developed together with Johan Hoffman and Johan Jansson showed that Prandtl had misled modern fluid mechanics into a fruitless search for the origin lift and drag of an airplane wing in a boundary layer so thin that it could never be resolved in computation. This was not allowed to be expressed and the result was that I did not accept to receive the medal. The story can be read here.

The New Theory of Flight supported by refined computations since 2014 shows that contrary to Prandtl wall bounded slightly viscous flow can be modeled by a slip boundary condition without any boundary layer, which makes the flow computable as time variable turbulent flow. There is thus now massive evidence that Prandtl was wrong, seriously wrong. 

Signs that there is something fishy with Prandtl's boundary layers as the origin of drag and lift can be seen in the above highlights: 

1. Prandtl use a tripwire to change the flow to fit what he could "see" without mathematics and computation. 
2. His results were intuitive.     

The effect of artificially tripping the flow in experiments has led to the misconception that skin friction drag is a major part of total drag with form/pressure drag a minor part, viewed to be relevant  also for an airplane wing without tripping device. The New Theory gives hard evidence that this is seriously misleading by computing drag and lift with slip in close accordance to observations.

The lesson is that if you rely on intuition rather than correct mathematics and are ready to trip experiments to fit, then you can end up with something with little connection to reality. Evidently Prandtl did so. The consequences are severe with the Boeing Max debacle a result of misconceived engineering computation following Prandtl.

PS The following question/answer appears on FAQ at Secret ion Flight:

Q30: Why is the flow tripped by a wire, strip or ribbon in wind tunnel measurements of drag of wing, when a real wing does not have any tripping device and the tripping thus appears to be artficial?

A30: The rationale presented is that the tripping will force the development of a turbulent boundary layer with substantial skin friction,  which according to Prandtl should be present. The tripping is thus done to artificially fit reality to theory, which is opposite to the basic principle of science to fit theory to reality. In the New Theory, which fits with untripped experiments, the flow of air meets the wing with a slip boundary condition modeling vanishing skin friction.

Boeing 737 Max: Perspective and Questions

The BNP of Sweden is about 500 billion USD, and that of the US 18 000 billion USD, about 40 times as big reflecting a population of 10 million in Sweden and 300 million in the US.

Today nearly 1000 Boeing Max are grounded each one selling for 100 million USD with a total of 100 billion USD grounded, about 20% of the BNP in Sweden and 0.5% of the BNP of the US.

The yearly revenue of Boeing is about 100 billion and the total stock value 200 billion USD.

Questions:

• Will the Max ever fly again? What happens with Boeing if not? If half of the total value is lost? 
• Why did the Boeing engineers design an airplane which showed to have a tendency to stall? 
• Was it because they used standard CFD (computational fluid dynamics) software which could not predict stall?
• What new CFD software will be required to get the Max in the air?

PS Boeing 797/NMA Is Going Back To The Drawing Boards:

• Boeing has shelved all of its plans for the ‘797 NMA’ and has been asked to return to the drawing board by its new CEO.

Will the 737 Max also be returned to the drawing board?  Compare with this post.

Boeing Flight Simulator?

The Guardian reports:

• Boeing now recommends 737 Max flight simulator training for pilots.
• Decision is a reversal of company’s long-held position that computer-based training alone was adequate.

In order for a flight simulator to correctly prepare pilots to handle real flight, the simulator must represent reality, which requires CFD (computational fluid dynamics) software capable of predicting the real reaction of the airplane upon control input from the pilot, including the critical phenomenon of stall which must be avoided. Standard CFD does not have this capability since it is based on prescriptive modeling.

Without CFD the action of an airplane, beyond simply guessing, will have to be discovered from extensive experience in real flight, where extreme situations such as stall are hazardous to test and thus must be avoided.     

DFS Direct Finite Element Simulation is new CFD software based on first principle physics without prescriptive modeling, which has shown to be truly predictive of complex flight dynamics including stall, beyond the capability of standard CFD.    

The design debacle behind the two 737 Max crashes can be connected to the use of standard CFD without stall prediction.

The question is now if Boeing is going to use DFS to design the intended upgrade of the automatic stall prevention system MCAS and the flight simulator preparing pilots to handle 737 Max with MCAS. Or if Boeing will continue to rely on standard software without stall prediction.

See also: Boeing employees’ frightening internal messages released in 737 Max investigation:

• Would you put your family on a Max simulator trained aircraft? I wouldn’t.
• This airplane is designed by clowns who in turn are supervised by monkeys.

Can FAA Authorise an Airliner for Passenger Transportation with Negative Longitudinal Stability?

The new Boeing 737 Max came out from a hastened design process, where an existing airframe dating back to 1967 was equipped with larger more fuel efficient engines mounted further forward and higher on the wings to satisfy requirements on ground clearance. The Max showed a tendency to stall in climb and turn as an effect of the new engines apparently giving extra lift thus moving the centre of lift CL ahead of the center of gravity CG into possibly negative longitudinal stability. To compensate the software MCAS was installed with the objective to automatically pitch the nose down upon input from an angle of attack sensor. For details, see Boeing 737 Max Groundings.

It appears that the idea was to hide the MCAS to not distract the pilot, but with a malfunctioning sensor that led to the fatal crashes.

But a civil airplane for passenger transportation is required to have positive longitudinal stability (see also FAA 1962 4b.150) with then CL behind CG, which pitches the nose down on increasing angle of attack and thus, without software or pilot control, maintains stable flight without stall.

Apparently, Boeing did not have the capacity to predict the tendency to stall of the new design using Computational Fluid Dynamics CFD, and so make a redesign into airplane with better stall characteristics. DFS is CFD software with the unique capability of predicting stall.

How could then FAA authorise the Max, when it was clear from the presence of MCAS that the Max design did not fully meet a requirement of longitudinal stability?  Or was the MCAS hidden also to FAA? And how will it be possible for FAA to reauthorise the Max if the basic design is kept and only the software is updated? Is it possible to guarantee that the MCAS will always work as intended, if the flight characteristics cannot be fully explored in real life testing and neither in CFD simulation? The new DFS Flight Simulator under construction can answer this question.

The Swedish military jet fighter JAS-Gripen was designed to have negative longitudinal stability to allow quick turns, which required stabilising software. After two crashes the software was modified into slower turns, which was ok since the plane was not used for combat.

First crash:

Second crash (2.23):

Boeing Halts Production of 737 Max vs DFS

Boeing will halt production of troubled 737 Max airplane. It’s unclear how long the suspension will last.

Compare with CFD State-of-the-Art/NASA 2030 Vision vs DFS recalling that Boeing and its competitors are very conservative companies and penetration of CFD is gradual.

Yes, Boeing indeed took a very conservative approach when launching the new 737 Max by equipping a design from 1967 by new larger supposedly more fuel efficient engines, which had to mounted farther forward and higher to clear ground. 

The result showed to be an airplane with a tendency to stall in low-speed climb and turn, which must have come as a surprise, because the standard software for CFD Computational Fluid Dynamics used by Boeing does not have the capability to predict the complex flow dynamics of stall. 

But the design was kept by Boeing, in line with its conservative company strategy, and to fix the instability the MCAS software was installed with the objective to automatically pitch the nose down on input from an angle of attack sensor. But the system malfunctioned with catastrophic consequences. 

The idea has then, since the the 737 Max fleet was grounded in March 2019, been to improve the software to make it safe, but reauthorisation by FAA is dragging and may never come. So now the production is halted and may never be resumed. 

DFS Direct Finite Element Simulation from Icarus Digital Math  is new software for CFD with the capability if predicting full flight characteristics of an airplane including stability and tendency to stall, as a realisation already today of NASA CFD Vision 2030.  DFS comes with new mathematical theory explaining for the first time The Secret of Flight.             

DFS as new computation/theory is now being presented to Boeing towards evaluation of the new predictive capabilities of DFS and possible incorporate into the designs process. Big values are at stake.

The catch for Boeing is that if the Max requires stabilising software, then it will be very hard to demonstrate that the software always will operate as intended and thus for FAA to re-authorise. The other possibility is that in fact the software is not needed, but that requires predictive computational simulation capability at Boeing trusted by FAA, since real flight testing of extreme situations is hazardous. In both cases, both Boeing and FAA have a problem, for which the only real solution may well be to put an end to the whole story of 737 Max.

How long time would it take for Boeing to make a whole new design (for the new engine or better) meeting todays expectations, using a tool like DFS and then start production?  Two years?