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NA 50/68 (P 64) - the true shapes questions (reliable drawing needed)


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Hi,

I am considering conversion of SH Harvard into NA 50 or NA 68, depending on the efforts. I found some drawings for both, but there are questions in my mind about what I have found.

First important question is about the wing shape. 

There are two kinds of drawings, showing straight trailing edge or not straight. Here, on one picture two possible variants are show for P64 (NA 68)

184650-30ae27716df738b7c4a0b03435c15baf.

Basically they all (P 64)  should be of the same construction ordered in small number by Thailand and never delivered. 

IpcSKcjKs3Ei23a1oP5IcYZe6HmGQjl5pH71VONG

Here are drawings for NA 68 

http://www.airwar.ru/image/idop/fww2/p64/p64-1.gif

 

And the 1:48 model of NA 50 

08_CMKPLT238_L.JPG

 

Please have a look here on the shadow - suggests straight line (on first the sunlight come almost vertical)

images?q=tbn:ANd9GcQARqIlFhj7eSBLT4yxEFA

images?q=tbn:ANd9GcSNoPSJ3FSl0fqGYQ_hK9o

 

But here no difference in wing between NA 50 and NA 68

na-50-p-64-jpg.575046

 

I am a bit puzzled... I will be grateful for enlightening me. 

Regards

J-W

 

 

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Posted (edited)

Doesn't look like the NA68 had a straight trailing edge- see the linked photos and drawings. BTW, IIRC, Xotic-72 did an all resin P-64 in 1/72 scale that was fairly accurate, but good luck finding one, and at a price that isn't obscene. You can find a kit review and build article on the internet.

Mike

 

https://en.wikipedia.org/wiki/North_American_P-64#/media/File:USAAC_P-64.jpg

 

https://www.aerialvisuals.ca/Airframe/Gallery/0/93/0000093726.jpg

 

http://www.airwar.ru/image/idop/fww2/p64/p64-1.gif

 

http://www.airwar.ru/image/idop/fww2/p64/

Edited by 72modeler
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I've studied what is said in Hagedorn's book in the Warbird Tech series, and it is difficult to be definitive on this point.  The machines fall well inside the range of designs in which some show the major set of changes to improve the aircraft's handling, and some do not.   That they are modified aircraft in other ways does not help.  The presence of the Harvard 1 rudder would hint at a (modified) early wing, but this was also seen on the slightly later SNJ-2.  To me, it would seem to be most likely that the NA-50 was very early to be fitted with the revised outer wing panels (i.e straight trailing edge) as these did not appear on production US trainers until the NA-54/BC-2 and NA-55/BC-1A.  To have sorted it and redesigned it for a new fighter seems too long, but as NA used Contract Numbers rather than some development-based system, who can be certain of this?  Aircraft were still being produced to later contracts with the earlier wing, for example the French trainers NA-57 and NA-64 although the latter did have the longer rear fuselage, a slightly modified wingtip and the "T-6" triangular tail.  Many of the aircraft in this range of contract numbers appear to be "hybrids".  There is at least one photo of an NA production line showing such apparent inconsistencies on parallel assembly lines.

 

However the NA-50A would have been built when the new outer wings were firmly in production, and they were not just simple reruns of the NA-50 so a change to a modified form of the new wing panel is certainly possible.  However, this is far from certain because it would have been cheaper for NA to have simply used the jigs for the NA-50 wings than create a new set, or subset, of the new ones.   On the other hand, if these new wings were expected to improve the handling of the aircraft in the same way as the full-span ones on the trainer and attack aircraft, why not?

 

It is a shame that the Boomerang can offer no hint: because this was required to be built alongside Wirraways the early wing planform was followed, even had Wackett known about the new shape in any detail.  The equivalent Chinese fighter is simply not known about in sufficient detail.

 

Were I chopping an NA-16 variant to produce an NA-50, the earlier wing would be the most tempting.  Not least because NA were known to be considering a wide range of variants for their original NA-16 design, and this included single-engined fighters.  Given South American interest, this project would have been dusted off rather than designed from scratch with anything "cutting edge".  For the NA-50A, I'm not so sure.

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Posted (edited)

I just remembered I have a copy of North American Aircraft, 1934-1998, Volume 1, p46-48, by Norm Avery, and there are photos, 3-view drawings of the NA68, and description of both the NA50 and NA68 variants. I'm not sure if the information will be helpful or not, but I have paraphrased it below. Hope you will find this useful.

 

NA50: 'Seven fighters for Peru; factory serials 50-948/954. 840 hp P&W R-1820-77 Cyclones. Based on the BC-1 airframe; wingspan shortened to 37' 4", sweep back reduced and wingtips squared. Fuselage structure strengthened and a 3-blade prop fitted. Armament fitted was 2 .30 cal cowling guns and 2 .30 cal wing guns, with provision for under wing bomb  racks. Peruvian pilots ferried the first three to South America, and the remaining four were crated for shipment by boat.'

NA68: ' Six fighters for Thailand; factory serials 68-3058/3063. NA68- 840 hp P&W R-1820-77 Cyclones, based on the BC-1 airframe.  Fitted with a more streamlined cowling with the .30 cal guns enclosed in streamlined fairings, the lower cowling  was faired into the lower wells for the retractable landing gear, which had larger fairing doors that completely enclosed the landing gear when retracted. Two 20 mm cannon could be fitted under the wings, and the fuselage was lengthened slightly by the addition of the triangular rudder of the AT-6. All were built, accepted, flight tested, and paid for, but while awaiting shipment, wartime conditions caused the U.S. Government to revoke their export license. All six NA68's were taken over by the USAAC and given new serials: 41-19082/19087 and used at Luke Field, AZ as advanced fighter trainers with the designation P-64.'

Mike 

Edited by 72modeler
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Humph, I've got that and never thought to look in it.  So I dug it out now, and its drawing of the NA-50A/NA-68/P-64 shows it with a wing that has very little sweep on the leading edge (c5degs) and considerable forward sweep on the trailing edge (c.10 degs), so not exactly based on either standard wing planform.  However, likely to have been the same for both variants.  Changing to this planform makes sense because of the heavier engine.

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Might be worth a look here - lots of images of the P-64 flown by the late Paul Poberezny, founder of the Experimental Aircraft Association:

https://www.google.com/search?q=paul+poberezny+P-64&client=firefox-b-d&ei=A6y2YLiTPIrbtQb_pIXwDg&oq=paul+poberezny+P-64&gs_lcp=Cgdnd3Mtd2l6EAMyBQghEKABOgkIABCwAxAHEB46BQguELADOgUIABCwAzoHCAAQsAMQHjoCCAA6BggAEBYQHlDxMFipRmClSmgBcAB4AIABaIgB7gOSAQM1LjGYAQCgAQGqAQdnd3Mtd2l6yAEGwAEB&sclient=gws-wiz&ved=0ahUKEwj4oP_RtffwAhWKbc0KHX9SAe4Q4dUDCBA&uact=5

 

As a kid, I too had the urge to convert a Harvard to a P-64; I wrote Mr Poberezny a letter and he very graciously sent me photos of his aircraft.

 

John

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Sorry Jure, but that's a modified Warbird, and cannot be taken as at all representative of a true NA-50/68.

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Posted (edited)

Many thanks for so far discussion. Let me try to conclude where we are. ...

The photos of machine of Mr. P. Poberezny shows exactly what Graham told - the small slope of leading edge and larger forward of trailing  (this is NA 68/P64):

50120017198_35e88b10a9.jpg 

Interesting are also fairings behind wheels bays.  They are absent in Harvard

North-American-T-6-Texan-Courtesy-of-Lon

 

The obvious reason must be the weight of engine,

On 6/1/2021 at 11:03 PM, Graham Boak said:

Changing to this planform makes sense because of the heavier engine.

as Graham mentioned.  However,  the NA 50 looks like has rather  regular Harvard style wing (as the Boomerang does also, of course shortened). Thera are two photos:

https://s3.eu-west-2.amazonaws.com/abpic-media-eu-production/pictures/full_size_0173/1260540-large.jpg 

Ke0LTLGGV60Jqqvtn7zqn05zI_-eE4Jp28sxMj8S

On the first,  color photo (link only) of the machine standing as monument it looks that small angle forward exists, on above BW photo it looks more like straight line. 

But here http://warbirdinformationexchange.org/phpBB3/viewtopic.php?f=3&t=14358 I have found that indeed, P 64 has a new design outer parts of wings, so maybe this is the main difference between NA 50 and  NA 68 (besides the different engine and tail from other variants of Harvards)

 

Regards

J-W

 

 

 

 

Edited by JWM
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8 hours ago, JWM said:

Interesting are also fairings behind wheels bays.  They are absent in Harvard

They are not evident in any of the wartime photos I have seen of NA68 P-64's, nor are they present on several photo of  Poberezny's  airplane, but appear to have been added at some point. I am just guessing here, but there might be two reasons for their installation (1) T-6's/Harvards  were often raced in a special class dedicated to the type, and thus might have been fitted to smooth the airflow around the wheels, which IIRC, do protrude very slightly above the wing surface, or (2) Poberezny might have fitted fatter tires, which would have protruded further into the airflow, thus the use of fairings to lessen drag. As actor Gordon Jackson (MacDonald) said in the movie The Great Escape, "That's as far as my thinking takes me!" :giggle:

Mike

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If you compare the proportion of aileron span to complete outer panel of wing there is a big difference between those numbers for Na 50 and Na 68 and even Na 68 prototype

"regular" NA 68 (P64) 

4562157340_cb8f6f8352_z.jpg

 

Prototype of NA 68 

http://www.airwar.ru/image/idop/fww2/p64/p64-1.jpg

"regular" NA 50

http://www.airwar.ru/image/idop/fww2/p64/p64-11.jpg

 

Perhaps two last  of above has the same wing, changed then in prototype after initial trials into one with trailing edge going more forward with span?

 

Difference in aileron span is not noticed on any drawings I know!

REgards

J-W

 

 

 

 

 

 

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Nevertheless, the wingspan in all three discussed photos is the same, because the trailing edge length from the fuselage fairing to the outer end of the aileron is 247% of the wheel track. Only the flap to aileron ratio in the outer (dihedralled) wing partl changes. In the production NA-50 and the NA-68 prototype, the aileron occupies 7 inter-rib sections of the wing (56% of the trailing edge length), and in the production P-64 only 6 sections (48% of the span).

Probably a significant increase in MTOW (additional machine guns and cannons in nacelles) made enlarging the flap area a necessity.

Cheers

Michael

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It might be interesting to see if there was a similar change in the full-span trainer version of these wings.  If so, then the reason lies in something more subtle in the handling changes.  Did the fully-armed A-27 also have an increased flap area?  Perhaps, other than take-off, the weight change was less significant.

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The second parameter for consideration is maneuverability. In case of NA 50 it could be the motivation for keeping the same area of ailerons on shortened wings (the force is same though it acts on smaller arm due to smaller wingspan). However adding guns below wings in NA 68 the moment of inertia (regarding longitudinal axis) increased, so one could expect larger, not smaller ailerons... I think  this wing with moved forward trailing edges resulted in lower stability and thus NA 68 has higher maneuverability so there was no need to keep ailerons large.  But maybe it was just practical decision - there is an opinion, that shortened wing of NA 68 had the same number of ribs as long wing of Harvard, but ribs were more tightly packed. It must result is smaller span of aileron.

I do not know in fact what were the reasons and what were the consequences for flight properties. Only the photos show that ailerons were smaller in NA 68 compare to NA 50 and that is all. 

Regards

J-W

 

 

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It seems that the restoration in Peru has been completed...

 

https://www.scramble.nl/military-news/peruvian-torito-restored?fbclid=IwAR3dJ3cSHk2bFOvGAP8eSqBjovmFxYgJ3wiZohaGbzT6qsNDi9_Nyu28Noo

 

Interesting new wheels she is wearing, and the oleo struts appear to be pumped to an excessive extension. 

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9 hours ago, Derek_B said:

It seems that the restoration in Peru has been completed...

I am sure that they could be a good source of drawings! Only if they wish to publish...

J-W

 

 

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