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Full-Scale 1903 Wright Flyer failed the test Thrust = Drag in a NASA wind tunnel

I have found a presentation about an extensive set of tests done in 1999 on a full scale replica of Flyer I 1903. The plane did not behave well and was not able to produce enough thrust to overcome the drag.

"In the wind tunnel, the reproduced propeller fell short of T=D @ 28 mph test condition when operating at the maximum permitted speed of 340 RPM. These data are being analyzed" $C_L=C_L(C_D)$

$C_L=C_L(C_D)$ Flyer I replica

Source: Full-Scale 1903 Wright Flyer Wind Tunnel Test Results From the NASA Ames Research Center

Unfortunately, the presentation, also quite explicit, does not give the values of the Thrust, Drag or Drag - Thrust at 28 mph. I calculated the Drag from $C_L=C_L(C_D)$, Lift = Weight (the mass of the airplane is known) and and the surface of the wings. Using a simulator I also evaluated the thrust delivered by some modern propellers, having the same diameter as the ones the Wright Brothers said they had used in 1903, and they deliver enough thrust at 28 mph and 340 RPM.

There should be other more detailed articles, which I can not find, about the same set of tests because they planned the experiments for years and it is expected a lot of data was obtained.

I would be really interested to know either the exact geometry of the propellers to calculate their thrust with a simulator or find somewhere the diagram $Thrust = Thrust_{340\:RPM}(v_{air})$ corresponding to the tested replica. If you can find such a document please tell me about it.

Anyway at 6 hp / propeller (12 hp in total) I calculated that only propellers with an efficiency well below 50% (miserable even for the standard of 1903) could have failed to produce enough thrust for the Flyer I replica at 28 mph.

Update 1

A Mathcad demonstration which shows that the efficiency of the propellers used by the Flyer I replica should be below 31.2% to fail the test T = D.

A Mathcad demonstration which shows that the efficiency of the propellers used by the Flyer I replica should be below 31.2% to fail the test T = D

Update 2

Another wind tunnel set of tests was done in 2003 on a different Flyer I replica (see: Flying Qualities of the Wright 1903 Flyer: From Simulation to Flight Test). Also the lift drag diagram for the case "props off" was about the same as the one obtained in 1999, the thrust generated by the propellers at 340 RPM and Q = 2 psf which translates in a 28 mph plane speed, the same as in the 1999 tests, was 80 lbf (36.28 kgf) more than double than the Drag = 17.44 kgf calculated for the 1999 replica. Unless quite different propellers had been used in 1999 and 2003 the 1999 propellers should not have failed the test T = D at 28 mph. It appears that various investigation teams have used propellers with different geometries.

Flyer I 2003 replica - Drag Coefficient, On Rail

Flyer I 2003 replica - Drag Coefficient, On Rail - Propellers off Flyer I 2003 - Thrust

Flyer I 2003 replica - Static and dynamic thrust of the propellers two dynamic pressures, $Q = 0.5\rho V^2$. 1) $Q = 1\:lbf/ft^2$ ($V=19.98\:mph$) 2) $Q = 2\:lbf/ft^2$ ($V=28.26\:mph$). $\rho=1.2\:kg/m^3$

Source: "Flying Qualities of the Wright 1903 Flyer: From Simulation to Flight Test" (AIAA-2004-0105)

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    $\begingroup$ I do not understand. what is the question here? $\endgroup$ – Federico Jan 15 '16 at 8:35
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    $\begingroup$ The question is to find a more detailed article than "Full-Scale 1903 Wright Flyer Wind Tunnel Test Results" that will explain why the Flyer I replica failed the test T = D because as I already mentioned it could not have failed such a test unless the efficiency of the propellers had been well below 50% !! while the Wright Brothers maintained the efficiency was 66%. $\endgroup$ – Robert Werner Jan 15 '16 at 8:41
  • $\begingroup$ they maintained a 66% efficiency where? in this other question is reported an extract from a letter where they write 23% aviation.stackexchange.com/q/21821/1467 also, I am not sure a "find this document for me" is a good question for this site. $\endgroup$ – Federico Jan 15 '16 at 8:49
  • $\begingroup$ 1) Maybe you are more experienced than me in finding such documents. This is the reason I posted the topic on this site. 2) You gave me a link referring to something else. Somebody there mentioned 23% as being the efficiency of the gasoline engine used by the Wright Brothers not the efficiency of the propellers. 23% for a 1903 motor is quite good. That 66% is mentioned in a lot of places, example: wrightstories.com/… $\endgroup$ – Robert Werner Jan 15 '16 at 8:59
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    $\begingroup$ To clarify: Are you suspecting Nasa tests to have taken place on a replica which didn't conform to the original? $\endgroup$ – mins Jan 15 '16 at 19:48