they goofed on JN-4's? - RC Groups
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Oct 25, 2017, 02:12 AM
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they goofed on JN-4's?


Enjoying the F-15 thread . In the same vein, give this a think, won't ya?

I'm a long time student of JN-4's. There is the shared Curtiss JN-3 origin for both Canadian Aeroplanes LTD's JN-4 ,commonly known as the "Canuck", and a separate evolution of Curtiss' JN-4 series, culminating in the best known American variant, commonly known as the JN-4D "Jenny". Major components, struts, and fitting will interchange between the two and there was considerable mixing of parts on some production batches . Some 200 Canadian wing sets fitted to American fuselages, etc. AS far I can tell, dimensions, weights, and moments are identical, AS are the airfoils, radiators, engines, etc.. What is not generally appreciated is that the two types are rigged quite differently. American JN-4D has greater stagger and 5 deg. of engine down thrust, while Canuck has 7" less stagger and no down thrust. What was/is going on???

If one were to build two otherwise identical RC model airframes, one finished as a Canuck and the other a JN-4D, which one would require trim ballast? and were would it go? I see the American version as a mass of conflicting practices. Upper wing moved forward, on an existing airframe noted for being tail heavy AND then added down thrust?????? Lower wing area of JN-4D is slightly less than the Canuck.

I may have original weight and balance data for Canuck but nothing on JN-4D. I have worked on example s of both full size aircraft. IMHO, the Canuck is a more obvious improvement of the Curtiss JN-3. It is certainly better appointed in fittings, finish, and strength. It is also lighter overall and has dual ailerons.

Amelia Earhart received her first flight instruction from Neta Snook, 1922, at Kinner Field, CA. It would appear her Canuck was fitted with American JN-4H wings and rigged in the Canadian fashion.
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Oct 25, 2017, 04:36 AM
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would the stagger be an attempt to change the CoP ? to accommodate different munitions etc ?? or bigger pilots and or ??

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Oct 25, 2017, 11:43 AM
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Quote:
Originally Posted by packardpursuit
What is not generally appreciated is that the two types are rigged quite differently. American JN-4D has greater stagger and 5 deg. of engine down thrust, while Canuck has 7" less stagger and no down thrust. What was/is going on???
If one were to build two otherwise identical RC model airframes, one finished as a Canuck and the other a JN-4D, which one would require trim ballast? and were would it go? I see the American version as a mass of conflicting practices. Upper wing moved forward, on an existing airframe noted for being tail heavy AND then added down thrust?????? Lower wing area of JN-4D is slightly less than the Canuck.
Moving the top wing forward would move the aircraft aerodynamic center forward, not by the same amount but approximately according to the ratio of the wing areas. So the CG would need to move forward IF the same static margin was maintained. But maybe the Canuck already had more than enough static margin?

If stability was still adequate with the new wing position and no ballast, the JN-4D would be trimmed to fly slower than the Canuck. This would aggravate any tendency of the nose to rise with power application. The down thrust might have been to alleviate this without adding ballast.
Oct 25, 2017, 01:42 PM
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Quote:
Originally Posted by packardpursuit
AS far I can tell, dimensions, weights, and moments are identical, AS are the airfoils, radiators, engines, etc..
These sources mention additional differences:

Quote:
JN-4 (Canadian) Canuck — Canadian-built version, 1,260 built by Canadian Aeroplanes Ltd. for the RFC in Canada/RAF in Canada and USAAC: Independently derived from the JN-3, it had a lighter airframe, ailerons on both wings, a bigger and more rounded rudder, and differently shaped wings, stabilizer, and elevators. Its use by the USAAC was curtailed as the lighter structure was claimed to cause more accidents than the US-built aircraft, although no air fatalities were attributed to the structural integrity of the type.
https://en.wikipedia.org/wiki/Curtiss_JN-4

Quote:
During the First World War, the Royal Flying Corps set flying schools in Canada, beginning in 1917. The Royal Flying Corps selected the Curtiss JN‑3 “Jenny” two-seater biplane as the training aircraft of choice. The type was then manufactured in Canada under license by Canadian Aeroplanes Limited, and the Canadian version was given the designation JN‑4 “Canuck”. The JN-4 incorporated several design changes requested by the Royal Flying Corps, including the substitution of a joy stick for the control wheel and constructing tail units principally of metal instead of wood.
http://www.rcaf-arc.forces.gc.ca/en/...rtiss-jn4.page
Oct 25, 2017, 10:42 PM
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Thanks EVERYONE for joining in You've giving me some things to think about.

Early on and certainly by the time of JN-4D, Curtiss had fully abandoned the "Double Dep" wheel control, in favor ofjoy stick.

I fail to see why lighter structure would possibly "cause more accidents". I suppose they meant that it might not standup to rough handling, etc. Gotta say, it sounds like somebody was just making things up, again. Metal tail feathers on Canuck is only partially true. Still quite a bit of wood within the outlines, especially the horizontal stab. BTW metal tube framing of rudder and elevators was a real step forward and would become standar practice in 1920's.

I always thought the down thrust was added to help relieve pilot strain a t keeping the nose down.

At the end of the day it's hard to see the JN-4D as a real improvement over the
JN-3. While Canuck is, most definitely.


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